228 Million B.C.T. - The Norian Age Began

The Norian is a division of the Triassic geological period.  It has the rank of an age (geochronology) or stage (chronostratigraphy). The Norian lasted from ~228 to ~208.5 million years ago. It was preceded by the Carnian and succeeded by the Rhaetian. 

230 Million B.C.T. - Dinosaurs Diverged

Around 230 million years ago, dinosaurs diverged from the archosaur ancestors.

Dinosaurs diverged from their archosaur ancestors approximately 230 million years ago during the Middle to Late Triassic period, roughly 20 million years after the Permian-Triassic extinction event wiped out an estimated 95% of all life on Earth. Radiometric dating of the rock formation that contained fossils from the early dinosaur genus Eoraptor establishes its presence in the fossil record at this time. Paleontologists think that Eoraptor resembles the common ancestor of all dinosaurs. If this is true, its traits suggest that the first dinosaurs were small, bipedal predators.

When dinosaurs appeared, terrestrial habitats were occupied by various types of archosaurs and therapsids, such as aetosaurs, cynodonts, dicynodonts, ornithosuchids, rauisuchians, and rhynchosaurs. Most of these other animals became extinct in the Triassic, in one of two events. First, at about the boundary between the Carnian and Norian faunal stages (about 215 million years ago), dicynodonts and a variety of basal archosauromorphs, including the prolacertiforms and rhynchosaurs, became extinct. This was followed by the Triassic-Jurassic extinction event (about 200 million years ago), that saw the end of most of the other groups of early archosaurs, like aetosaurs, ornithosuchids, phytosaurs, and rauisuchians. These losses left behind a land fauna of crocodylomorphs, dinosaurs, mammals, pterosaurians, and turtles.  The first few lines of early dinosaurs diversified through the Carnian and Norian stages of the Triassic, most likely by occupying the niches of the groups that became extinct.

230 Million B.C.T. - The Carnian Pluvial Event Occurred

The Carnian Pluvial Event (CPE) is a major global climate change and biotic turnover occurred during the Carnian stage, during the Late Triassic Period around 230 million years ago.

The base of the CPE is marked by a ~ 4% negative shift in carbon stable isotopes of fossil molecules from higher plants and total organic carbon. A ~ 1.5‰ negative shift in oxygen stable isotopes of conodont apatite suggests a global warming. Major changes in organisms responsible for calcium carbonate production occurred during the CPE. A halt of carbonate sedimentation is observed in deep water settings of Southern Italy that was probably caused by the rise of the Carbonate Compensation Depth.  High extinction rates occurred among ammonoids, conodonts, bryozoa and crinoids. Major evolutionary innovations followed the CPE, as the first occurrence of dinosaurs, calcareous nannofossils and scleractinian corals. 

235 Million B.C.T. - The Carnian Stage Began

Around 235 million years ago, the Carnian stage began.

The Carnian (less commonly, Karnian) is the lowermost stage of the Upper Triassic series (or earliest age of the Late Triassic epoch). It lasted from about ~235 until ~228 million years ago. The Carnian is preceded by the Ladinian and is followed by the Norian. Its boundaries are not characterized by major extinctions or biotic turnovers, but a climatic event (known as the Carnian Pluvial Event) occurred during the Carnian and seems to be associated with important extinctions or biotic radiations.

242 Million B.C.T. - The Ladinian Age Began

Around 242 million years ago, the Ladinian age began.

The Ladinian is a stage and age in the Middle Triassic series or epoch. It spans the time between ~242 and ~235 million years ago. The Ladinian was preceded by the Anisian and succeeded by the Carnian (part of the Upper or Late Triassic).

247 Million B.C.T. - The Anisian Age Began

Around 247 million years ago, the Anisian Age began.

In the geologic timescale, the Anisian is the lower stage or earliest age of the Middle Triassic series or epoch and lasted from 247.2 million years ago until 242 million years ago. The Anisian age succeeds the Olenekian age (part of the Lower Triassic epoch) and precedes the Ladinian age.

251 Million B.C.T. - The Olenekian Age Began

Around 251 million years ago, the Olenekian Age began.

In the geologic timescale, the Olenekian is an age in the Early Triassic epoch or a stage in the Lower Triassic series. It spans the time between 251.2 and 247.2 million years ago. The Olenekian follows the Induan and is followed by the Anisian. 

Archosaurs - a group encompassing crocodiles, pterosaurs, dinosaurs, and ultimately birds - are diapsid reptiles that first evolved from Archosauriform ancestors during the Olenekian.

252 Million B.C.T. - The Induan Age Began

Around 252 million years ago, the Induan Age began.

The Induan is, in the geologic timescale, the first age of the Early Triassic epoch or the lowest stage of the Lower Triassic series. It spans the time between 252.2 and 251.2 million years ago.

The Induan age followed the mass extinction event at the end of the Permian period. Both global biodiversity and community-level (alpha) diversity remained low through much of this stage of the Triassic. Much of the world remained almost lifeless, deserted, hot, and dry. The lystrosaurids and the proterosuchids were the only groups of land animals to dominate during the Induan stage. Other animals, such as the ammonites, fishes, insects, and the tetrapods (cynodonts, amphibians, reptiles, etc.) remained rare and terrestrial ecosystems did not recover for 30 million years. Both the seas and much of the freshwater during the Induan were anoxic.

252 Million B.C.T. - A Mysterious Coal Gap Appears

At the beginning of the Triassic period around 252 million years ago, a mysterious coal gap appeared.

At the start of the Triassic period coal is noticeable by geologists today as being absent throughout the world. This is known as the "coal gap" and can be seen as part of the Permian–Triassic extinction event. Sharp drops in sea level across the Permo Triassic boundary may be the proper explanation for the coal gap. However, theories are still speculative as to why it is missing. During the preceding Permian period the arid desert conditions contributed to the evaporation of many inland seas and the inundation of these seas, perhaps by a number of tsunami events that may have been responsible for the drop in sea level. This due to the finding of large salt basins in the southwest United States and a very large basin in central Canada.

Immediately above the boundary the glossopteris flora was suddenly largely displaced by an Australia wide coniferous flora containing few species and containing a lycopod herbaceous under story. Conifers also became common in Eurasia. These groups of conifers arose from endemic species because of the ocean barriers that prevented seed crossing for over one hundred million years. For instance, Podocarpis was located south and Pines, Junipers, and Sequoias were located north. The dividing line ran through the Amazon Valley, across the Sahara, and north of Arabia, India, Thailand, and Australia. It has been suggested that there was a climate barrier for the conifers.  Although water barriers are more plausible. If so, something that can cross at least short water barriers must have been involved in producing the coal hiatus. Hot climate could have been an important auxiliary factor across Antarctica or the Bering Strait, however. There was a spike of fern and lycopod spores immediately after the close of the Permian. In addition there was also a spike of fungal spores immediately after the Permian-Triassic boundary. This spike may have lasted 50,000 years in Italy and 200,000 years in China and must have contributed to the climate warmth.

An event excluding a catastrophe must have been involved to cause the coal hiatus due to the fact that fungi would have removed all dead vegetation and coal forming detritus in a few decades in most tropical places. In addition, fungal spores rose gradually and declined similarly along with a prevalence of woody debris. Each phenomenon would hint at widespread vegetative death. Whatever the cause of the coal hiatus must have started in North America approximately 25 million years sooner.

252 Million B.C.T. - The Triassic Period Began

Around 252 Million B.C.T., the Triassic Period began.

The Triassic is a geologic period and system that extends from about 252.2 ± 0.5 to 201.3 ± 0.2 million years ago. It is the first period of the Mesozoic Era, and lies between the Permian and Jurassic periods. Both the start and end of the period are marked by major extinction events. The Triassic was named in 1834 by Friedrich von Alberti, after the three distinct rock layers (tri meaning "three") that are found throughout Germany and northwestern Europe — red beds, capped by chalk, followed by black shales — called the "Trias."

The Triassic began in the wake of the Permian–Triassic extinction event, which left the Earth's biosphere impoverished.  It would take well into the middle of the period for life to recover its former diversity. Therapsids and archosaurs were the chief terrestrial vertebrates during this time. A specialized subgroup of archosaurs, dinosaurs, first appeared in the Late Triassic but did not become dominant until the succeeding Jurassic. The first true mammals, themselves a specialized subgroup of Therapsids also evolved during this period, as well as the first flying vertebrates, the pterosaurs, who like the dinosaurs were a specialized subgroup of archosaurs. The vast supercontinent of Pangaea existed until the mid-Triassic, after which it began to gradually rift into two separate landmasses, Laurasia to the north and Gondwana to the south. The global climate during the Triassic was mostly hot and dry, with deserts spanning much of Pangaea's interior. However, the climate shifted and became more humid as Pangaea began to drift apart. The end of the period was marked by yet another major mass extinction, wiping out many groups and allowing dinosaurs to assume dominance in the Jurassic.

252 Million B.C.T. - The Insects Were Exterminated

During the Great Dying (the Permian-Triassic Extinction Event) of 252 million years ago, the only mass extinction (mass extermination) of insects occurred.

At the end of the Permian, the biggest mass extinction in history took place, collectively called the Permian–Triassic extinction event.  In this extinction event, it is estimated that thirty percent (30%) of all insect species became extinct making the Permian-Triassic extinction event the only mass extinction of insects in Earth's history until today.

The Permian had great diversity in insect and other invertebrate species, including the largest insects ever to have existed. The end-Permian is the only known mass extinction of insects, with eight or nine insect orders becoming extinct and ten more greatly reduced in diversity. Palaeodictyopteroids (insects with piercing and sucking mouthparts) began to decline during the mid-Permian; these extinctions have been linked to a change in flora. The greatest decline occurred in the Late Permian and was probably not directly caused by weather-related floral transitions.

Most fossil insect groups found after the Permian–Triassic boundary differ significantly from those that lived prior to the Permian-Triassic extinction. With the exception of the Glosselytrodea, Miomoptera, and Protorthoptera, Paleozoic insect groups have not been discovered in deposits dating to after the Permian–Triassic boundary. The caloneurodeans, monurans, paleodictyopteroids, protelytropterans, and protodonates became extinct by the end of the Permian. In well-documented Late Triassic deposits, fossils overwhelmingly consist of modern fossil insect groups.

252 Million B.C.T. - Marine Life Was Decimated

During the Permian-Triassic extinction event that began around 252 million years ago, it is estimated that as much as 96 percent of all marine species were exterminated.

Marine invertebrates suffered the greatest losses during the Permian-Triassic extinction. In the intensively-sampled south China sections at the Permian-Triassic boundary, for instance, 286 out of 329 marine invertebrate genera disappear within the final 2 sedimentary zones containing conodonts (eel-like creatures) from the Permian.

Statistical analysis of marine losses at the end of the Permian suggests that the decrease in diversity was caused by a sharp increase in extinctions instead of a decrease in speciation. The extinction primarily affected organisms with calcium carbonate skeletons, especially those reliant on ambient CO₂ levels to produce their skeletons.


Among benthic organisms, the extinction event multiplied background extinction rates, and therefore caused most damage to taxa that had a high background extinction rate (by implication, taxa with a high turnover). The extinction rate of marine organisms was catastrophic.


Surviving marine invertebrate groups include: articulate brachiopods (those with a hinge), which have suffered a slow decline in numbers since the Permian-Triassic extinction.  The Ceratitida order of ammonites; and crinoids ("sea lilies"), which very nearly became extinct but later became abundant and diverse.

The groups with the highest survival rates generally had active control of circulation, elaborate gas exchange mechanisms, and light calcification; more heavily calcified organisms with simpler breathing apparatus were the worst hit.  In the case of the brachiopods at least, surviving taxa were generally small, rare members of a diverse community.


The ammonoids, which had been in a long-term decline for the 30 million years since the Roadian (middle Permian), suffered a selective end-Guadalupian extinction pulse. This extinction greatly reduced disparity, and suggests that environmental factors were responsible for this extinction. Diversity and disparity fell further until the Permian-Triassic boundary.  The extinction here was non-selective, consistent with a catastrophic initiator. During the Triassic, diversity rose rapidly, but disparity remained low.

252 Million B.C.T. - The Great Dying Occurred

Around 252 Million B.C.T., the Permian-Triassic extinctinon event -- the most severe extinction event in the history of the Earth -- occurred. 

The Permian–Triassic (P–Tr) extinction event, informally known as the Great Dying, was an extinction event that occurred 252.28 million years ago, forming the boundary between the Permian and Triassic geologic periods, as well as the Paleozoic and Mesozoic eras. It is the Earth's most severe known extinction event, with up to 96% of all marine species and 70% of terrestrial vertebrate species becoming extinct. It is the only known mass extinction of insects.  Some 57% of all families and 83% of all genera became extinct. Because so much biodiversity was lost, the recovery of life on Earth took significantly longer than after any other extinction event, possibly up to 10 million years.

Researchers have variously suggested that there were from one to three distinct pulses, or phases, of extinction. There are several proposed mechanisms for the extinctions; the earlier phase was likely due to gradual environmental change, while the latter phase has been argued to be due to a catastrophic event. Suggested mechanisms for the latter include large or multiple bolide impact events, increased volcanism, coal/gas fires and explosions from the Siberian Traps, and sudden release of methane clathrate from the sea floor; gradual changes include sea-level change, anoxia, increasing aridity, and a shift in ocean circulation driven by climate change.

Pin-pointing the exact cause (or causes) of the Permian–Triassic extinction event is a difficult undertaking, mostly because the catastrophe occurred over 250 million years ago, and much of the evidence that would have pointed to the cause has either been destroyed by now or is concealed deep within the Earth under many layers of rock. The sea floor is also completely recycled every 200 million years by the ongoing process of plate tectonics and seafloor spreading, thereby leaving no useful indications beneath the ocean. With the fairly significant evidence that scientists have managed to accumulate, several mechanisms have been proposed for the extinction event, including both catastrophic and gradualistic processes (similar to those theorized for the Cretaceous–Paleogene extinction event). The former include large or multiple bolide impact events, increased volcanism, or sudden release of methane hydrates from the sea floor. The latter include sealevel change, anoxia, and increasing aridity. Any hypothesis about the cause must explain the selectivity of the event, which primarily affected organisms with calcium carbonate skeletons, the long (4– to 6-million-year) period before recovery started, and the minimal extent of biological mineralization (despite inorganic carbonates being deposited) once the recovery began.

Evidence that an impact event may have caused the Cretaceous–Paleogene extinction event has led to speculation that similar impacts may have been the cause of other extinction events, including the P–Tr extinction, and therefore to a search for evidence of impacts at the times of other extinctions and for large impact craters of the appropriate age.

Reported evidence for an impact event from the P–Tr boundary level includes rare grains of shocked quartz in Australia and Antarctica; fullerenes trapping extraterrestrial noble gases; meteorite fragments in Antarctica; and grains rich in iron, nickel and silicon, which may have been created by an impact.  However, the accuracy of most of these claims has been challenged. Quartz from Graphite Peak in Antarctica, for example, once considered "shocked", has been re-examined by optical and transmission electron microscopy. The observed features were concluded to be not due to shock, but rather to plastic deformation, consistent with formation in a tectonic environment such as volcanism.

Several possible impact craters have been proposed as possible causes of the P–Tr extinction, including the Bedout structure off the northwest coast of Australia and the hypothesized Wilkes Land crater of East Antarctica. In each of these cases, the idea that an impact was responsible has not been proven, and has been widely criticized. In the case of Wilkes Land, the age of this sub-ice geophysical feature is very uncertain – it may be later than the Permian–Triassic extinction.
If impact is a major cause of the P–Tr extinction, the crater likely would no longer exist. As 70% of the Earth's surface is sea, an asteroid or comet fragment is more than twice as likely to hit ocean as it is to hit land. However, Earth has no ocean-floor crust more than 200 million years old, because the "conveyor belt" process of seafloor spreading and subduction destroys it within that time. Craters produced by very large impacts may be masked by extensive flood basalting from below after the crust is punctured or weakened. Subduction should not, however, be entirely accepted as an explanation of why no firm evidence can be found: as with the K-T event, an ejecta blanket stratum rich in siderophilic elements (e.g., iridium) would be expected to be seen in formations from the time.
One attraction of large impact theories is that theoretically they could trigger other cause-considered extinction-paralleling phenomena, such as the Siberian Traps eruptions (see below) as being either an impact site or the antipode of an impact site. The abruptness of an impact also explains why species did not rapidly evolve in adaptation to more slowly manifesting and/or less than global-in-scope phenomena.

270 Million B.C.T. - Olson's Extinction Occurred

Around 270 Million B.C.T., Olson's extinction occurred.

Olson's Extinction was a mass extinction that occurred 270 million years ago in the Early Guadalupian of the Permian period and which predated the Permian–Triassic extinction event. Everett Olson noted that there was a hiatus and a sudden change in between the Early Permian and Middle/Late Permian faunas. Since then this event has been realized across many groups, including plants, marine invertebrates, and tetrapods.

The first evidence of extinction came when Everett C. Olson noted a hiatus between Early Permian faunas dominated by pelycosaurs and therapsid dominated faunas of the Middle and Late Permian. First considered to be a preservational gap in the fossil record, the event was originally dubbed 'Olson's Gap'. To compound the difficulty in identifying the cause of the 'gap', researchers were having difficulty in resolving the uncertainty which exists regarding the duration of the overall extinction and about the timing and duration of various groups' extinctions within the greater process. Theories emerged which suggested the extinction was prolonged, spread out over several million years or that multiple extinction pulses preceded the Permian–Triassic extinction event. The impact of Olson's Extinction amplified the effects of the Permian–Triassic extinction event and the final extinction killed off only about 80% of species alive at that time while the other losses occurred during the first pulse or the interval between pulses.

During the 1990s and 2000s researchers gathered evidence on the biodiversity of plants, marine organism and tetrapods that indicated an extinction pulse preceding the Permian–Triassic extinction event had a profound impact on life on land. On land, even discounting the sparse fossil assemblages from the extinction period, the event can be confirmed by the stages of time bracketing the event since well preserved sections of the fossil record from both before and after the event have been found. The 'Gap' was finally closed in 2012 when it was confirmed that the terrestrial fossil record of the Middle Permian is well represented by fossil localities in the American southwest and European Russia and that the gap is not an artifact of a poor rock record since there is no correlation between geological and biological records of the Middle Permian.

There is no widely accepted theory for the cause of Olson's Extinction. Recent research has indicated that climate change may be a possible cause. Extreme environments were observed from the Permian of Kansas which resulted from a combination of hot climate and acidic waters particularly coincident with Olson’s Extinction . Whether this climate change was a result of Earth's natural processes or exacerbated by another event is unknown.

Fauna did not recover fully from Olson's Extinction before the impact of the Permian-Triassic extinction event. Estimates of recovery time vary, where some authors indicated recovery was prolonged, lasting 30 million years into the Triassic.

Several important events took place during Olson's Extinction, most notably the origin of therapsids, a group that includes the evolutionary ancestors of mammals.

A future extinction event, specifically due to anthropogenic changes, has been hypothesized by a number of scientific and environmental groups. Various possible causes include climate change, pollution, and habitat destruction. This is of great concern, due to the loss of biomes, the resources within them, and possible extinction of animal species. A better understanding of the process of extinction in the past may help determine the best course of action to preserve similar ecosystems today. Examining the conditions that led to the Olson's Extinction and the Permo-Triassic Extinction and the recovery of ecosystem from these events, may help contribute suitable solutions to resolving the current climate crisis.

Around 270 Million B.C.T., beetles evolved.

Coleoptera is an order of insects commonly called beetles. The word "coleoptera" is from the Greek koleos, meaning "sheath"; and pteron, meaning "wing", thus "sheathed wing". The reason for the name is that most beetles have two pairs of wings, the front pair, the "elytra", being hardened and thickened into a sheath-like, or shell-like, protection for the rear pair, and for the rear part of the beetle's body. The superficial consistency of most beetles' morphology, in particular their possession of elytra, has long suggested that the Coleoptera are monophyletic, but there is growing evidence that this is unjustified, there being arguments for example, in favor of allocating the current suborder Adephaga their own order, or very likely even more than one.

The oldest known insect that resembles species of Coleoptera date back to the Lower Permian (270 million years ago), although they instead have 13-segmented antennae, elytra with more fully developed venation and more irregular longitudinal ribbing, and an abdomen and ovipositor extending beyond the apex of the elytra. Today's true beetles have features that include 11-segmented antennae, regular longitudinal ribbing on the elytra, and genitalia that are internal.  At the end of the Permian, the biggest mass extinction in history took place, collectively called the Permian–Triassic extinction event: 30% of all insect species became extinct.  However, it is the only mass extinction of insects in Earth's history until today.

299 Million B.C.T. - Pangaea and Panthalassa

Around 299 Million B.C.T., the Earth was dominated by the supercontinent Pangaea and by the superocean Panthalassa.

Sea levels in the Permian period were generally low, and near-shore environments were limited by the collection of almost all major landmasses into a single continent -- Pangaea. This could have in part caused the widespread extinctions of marine species at the end of the period by severely reducing shallow coastal areas preferred by many marine organisms.

During the Permian, all the Earth's major land masses were collected into a single supercontinent known as Pangaea. Pangaea straddled the equator and extended toward the poles, with a corresponding effect on ocean currents in the single great ocean ("Panthalassa", the "universal sea"), and the Paleo-Tethys Ocean, a large ocean that was between Asia and Gondwana. The Cimmeria continent rifted away from Gondwana and drifted north to Laurasia, causing the Paleo-Tethys to shrink. A new ocean was growing on its southern end, the Tethys Ocean, an ocean that would dominate much of the Mesozoic Era. Large continental landmasses create climates with extreme variations of heat and cold ("continental climate") and monsoon conditions with highly seasonal rainfall patterns. Deserts seem to have been widespread on Pangaea. Such dry conditions favored gymnosperms, plants with seeds enclosed in a protective cover, over plants such as ferns that disperse spores. The first modern trees (conifers, ginkgos and cycads) appeared in the Permian.

299 Million B.C.T. - The Permian Period Began

Around 299 million years ago, the Permian Period began.

The Permian is a geologic period and system which extends from 298.9 ± 0.2 to 252.2 ± 0.5 million years ago. It is the last period of the Paleozoic Era, following the Carboniferous Period and preceding the Triassic Period of the Mesozoic Era. It was first introduced in 1841 by geologist Roderick Murchison, and is named after the ancient kingdom of Permia.

The Permian witnessed the diversification of the early amniotes into the ancestral groups of the mammals, turtles, lepidosaurs and archosaurs. The world at the time was dominated by a single supercontinent known as Pangaea, surrounded by a global ocean called Panthalassa. The extensive rainforests of the Carboniferous had disappeared, leaving behind vast regions of arid desert within the continental interior. Reptiles, who could better cope with these dryer conditions, rose to dominance in lieu of their amphibian ancestors. The Permian Period (along with the Paleozoic Era) ended with the largest mass extinction in Earth's history, in which nearly 90% of marine species and 70% of terrestrial species died out. It would take well into the Triassic for life to recover from this catastrophe.

305 Million B.C.T. - The Carboniferous Rainforest Collapse

Around 305 million years ago, the rainforests that marked the Carboniferous Period collapsed.

The Carboniferous Rainforest Collapse (CRC) was an extinction event that occurred around 305 million years ago in the Carboniferous period. Vast coal forests (so called because the compacted remains of the dense vegetation formed coal seams) covered the equatorial region of Euramerica (Europe and America). Climate change devastated tropical rainforests, fragmenting the forests into isolated 'islands' and causing the extinction of many plant and animal species. The change was abrupt, happening during the Moscovian (315 to 307 Million B.C.T.) and Kasimovian (307 to 303 Million B.C.T.) stages of the Pennsylvanian subperiod.

In the Carboniferous, the great tropical rainforests of Euramerica supported towering lycopsids, a heterogeneous mix of vegetation, as well as a great diversity of animal life: giant dragonflies, millipedes, cockroaches, amphibians, and the first reptiles.

The rise of rainforests in the Carboniferous greatly altered the landscapes by creating low-energy, organic-rich anastomosing (merging) river systems with multiple channels and stable alluvial islands. The continuing evolution of tree-like plants increased floodplain stability by the density of floodplain forests, the production of woody debris, and an increase in complexity and diversity of root assemblages.

Collapse occurred through a series of step changes. First there was a gradual rise in the frequency of opportunistic ferns in late Moscovian times. This was followed in the earliest Kasimovian by a major, abrupt extinction of the dominant lycopsids and a change to treefern dominated ecosystems. This is confirmed by a recent study showing that the presence of braided, meandering, and branching rivers, occurrences of large woody debris, and records of log jams decrease significantly at the Moscovian-Kasimovian boundary. Rainforests were fragmented forming shrinking islands further and further apart and in latest Kasimovian time, rainforests vanished from the fossil record.

Before the collapse, terrestrial invertebrates were diverse and included annelids, molluscs, and arthropods, including giant arthropleurids. Most were detritivorous, eating 'litter' off of the forest floor.  However, some had evolved herbivorous and predatory forms.

Before the extinction event, terrestrial vertebrates were predominantly amphibians and a few basal amniotes (‘reptiles’). Amphibians were tied to waterside habitats and were primarily piscivores ("fish eaters"), though a few had evolved to become insectivores.

Before the collapse, animal species distribution was very cosmopolitan: the same species existed everywhere across tropical Pangaea, but after the collapse each surviving rainforest island developed its own unique mix of species. Many amphibian species became extinct while reptiles diversified into more species after the initial crisis. These patterns are explained by the theory of island biogeography, a concept that explains how evolution progresses when populations are restricted into isolated pockets. This theory was originally developed for oceanic islands but can be applied equally to any other ecosystem that is fragmented, only existing in small patches, surrounded by another habitat. According to this theory, the initial impact of habitat fragmentation is devastating, with most life dying out quickly from lack of resources. Then, as surviving plants and animals re-establish themselves, they adapt to their restricted environment to take advantage of the new allotment of resources and diversify. After the Carboniferous Rainforest Collapse, each pocket of life evolved in its own way, resulting in a unique species mix which ecologists term endemism.

The Carboniferous Rainforest Collapse affected several large groups, labyrinthodont amphibians were particularly devastated, while the first reptiles fared better, being ecologically adapted to the drier conditions that followed. Amphibians must return to water to lay eggs; in contrast, reptiles - whose amniote eggs have a membrane ensuring gas exchange out of water and can therefore be laid on land - were better adapted to the new conditions. Reptiles acquired new niches at a faster rate than before the collapse and at a much faster rate than amphibians. They acquired new feeding strategies including herbivory and carnivory, previously only having been insectivores and piscivores.
The depletion of the plant life also contributed to the deteriorating levels of oxygen in the atmosphere, which facilitated the enormous arthropods of the time. Due to the decreasing oxygen, these sizes could no longer be accommodated, and thus between this and the loss of habitat, the giant arthropods were wiped out in this event, most notably the giant dragonflies and millipedes (Meganeura and Arthropleura).

The extinction event caused by the Carboniferous Rainforest Collapse had longterm implications for the evolution of amphibians. Under prolonged cold conditions, amphibians can survive by decreasing metabolic rates and resorting to overwintering strategies (i.e. spending most of the year inactive in burrows or under logs). However, this is only a short term strategy and not an effective way of dealing with longterm unfavorable conditions, especially desiccation. Since amphibians had a limited capacity to adapt to the drier conditions that dominated Permian environments, many amphibian families failed to occupy new ecological niches and went extinct.


There are several hypotheses about the nature and cause of the Carboniferous Rainforest Collapse, some of which include climate change. Specifically, at this time, the climate became cooler and drier. This is reflected in the rock record as the Earth entered into a short, intense ice age. Sea levels dropped by a hundred meters (300 hundred feet) and glacial ice covered most of the southern continent of Gondwana.

The cooler, drier climate conditions were not favorable to the growth of rainforests and much of the biodiversity within them. Rainforests shrank into isolated patches, these islands of rainforest were mostly confined to wet valleys further and further apart. Little of the original lycopsid rainforest biome survived this initial climate crisis, only to survive in isolated refuges.

Then a succeeding period of global warming reversed the climatic trend; the remaining rainforests, unable to survive the rapidly changing conditions, were finally wiped out. As the climate aridified through the later Paleozoic, the rainforests were eventually replaced by seasonally-dry biomes. Though the exact speed and nature of the collapse is not clear, it is thought to have occurred relatively quickly in geologic terms, only a few thousand years at most.

Major meteoroid events near the time of the CRC included the formation of the Weaubleau-Osceola structure, a serial impact which has been dated to 330-335 million years ago and would have affected the Euramerican continent.

Additionally, increased volcanism may have contributed to the CRC.  After restoring the center of the Skagerrak-Centered Large Igneous Province (SCLIP)using a new reference frame, it has been shown that the Skagerrak plume rose from the core–mantle boundary (CMB) to its ~300 Ma position. The major eruption interval took place in very narrow time interval, of 297 Ma ± 4 Ma. This rift formation coincides with the Moskovian/Kasimovian boundary and the Carboniferous Rainforest Collapse.

In recent years, scientists have put forth the idea that many of Earth's largest extinction events were due to multiple causes that coincided in time. Proponents of this view suggest multiples causes because they either do not see a single cause as sufficient in strength to cause the mass extinctions or believe that a single cause is likely to produce the taxonomic pattern of the extinction. Two of Earth's largest extinction events have been hypothesized to be multi-causal in nature:
The cause of the Permo-Triassic extinction (252.28 million years ago) is unclear and some authors have indicated that it may be best explained by a "Murder on the Orient Express Scenario" where multiple causes contributed to a devastating impact on life. Possible causes supported by strong evidence include the large scale volcanism at the Siberian Traps, the releases of noxious gases, global warming, and anoxia.
Additionally, a scenario combining three major causes to the K-T (Cretaceous-Tertiary) extinction (66-65 million years ago): volcanism, marine regression, and extraterrestrial impact, together wiping out the non-avian dinosaurs 65 million years ago.


The specific cause of the CRC is not known, but certainly a multiple cause scenario is a possibility.

The plant material that was lost during CRC extinction event was transported by water to low lying areas in bogs, marshes, lakes and inland seas. It decayed and as more material covered it, it was compressed, heated and eventually became coal, a fossil fuel in the form of a combustible black or brownish-black rock. Coal is the largest source of energy for the generation of electricity worldwide, as well as one of the largest worldwide anthropogenic sources of carbon dioxide releases. Gross carbon dioxide emissions from coal usage are slightly more than those from petroleum and about double the amount from natural gas.

The CRC has implications for the modern world.  The tropical and temperate rainforests of today have been subjected to heavy logging and agricultural clearance throughout the 20th century and the area covered by rainforests around the world is shrinking. A classic pattern of fragmentation is occurring in many rainforests including those of the Amazon, specifically a 'fishbone' pattern formed by the development of roads into the forest, and littoral rainforest growing along coastal areas of eastern Australia is now rare due to urban development.  It has been suggested that a combination of anthropogenic climate change and deforestation may lead to future rain forest collapse.

Modern rainforest collapse may result in massive loss of biodiversity.  This is of concern not only for the loss of a biome with many untapped resources but also because animal species extinction is known to correlate with habitat fragmentation. Biologists have estimated that large numbers of species are being driven to extinction.  Some estimates say that possibly more than 50,000 species are exterminated every year.  At that rate, a quarter or more of all species on Earth could be exterminated within 50 years due to the removal of habitat with destruction of the rainforests.

The application of palaeodata to the present conditions of this planet is still a science in its infancy, but presumably a better understanding of the process of habitat fragmentation and rainforest collapse in the past may help determine the best course of action to preserve similar ecosystems today. Specifically, examining the conditions that led to the Carboniferous Rainforest Collapse and the recovery of ecosystems after the extinction may help contribute suitable solutions to resolving the current crisis.

318 Million B.C.T. - The Permo-Carboniferous Glaciation

Beginning around 318 million years ago, a major glaciation occurred that led to a major marine extinction throughout the world.

A mid-Carboniferous drop in sea level precipitated a major marine extinction, one that hit crinoids and ammonites especially hard. This sea level drop and the associated unconformity in North America separate the Mississippian subperiod from the Pennsylvanian subperiod. This happened about 318 million years ago, at the onset of the Permo-Carboniferous Glaciation.

320 Million B.C.T. - Reptiles Emerged

Around 320 Million B.C.T., the first reptiles evolved.

Reptiles arose about 310-320 million years ago during the Carboniferous period. Reptiles, in the traditional sense of the term, are defined as animals that have scales or scutes, lay land-based hard-shelled eggs, and possess ectothermic (outside heat reliant) metabolisms. So defined, the group is paraphyletic, excluding endothermic (internal heat reliant) animals like birds and mammals that are descended from early reptiles. A definition in accordance with phylogenetic nomenclature, which rejects paraphyletic groups, includes birds while excluding mammals and their mammal-like reptile ancestors.

A group is said to be paraphyletic if it consists of all the descendants of the last common ancestor of the group's members minus a small number of monophyletic groups of descendants, typically just one or two such groups. For example, the group of reptiles, as traditionally defined, is paraphyletic: it contains the last common ancestor of the reptiles — including the extant reptiles as well as the extinct mammal-like reptiles — along with all descendants of that ancestor except for mammals and birds.

Though few reptiles today are apex predators, many examples of apex reptiles have existed in the past. Apex predators (also known as alpha, super, top- or top-level predators) are predators with no predators of their own, residing at the top of their food chain.  Reptiles have an extremely diverse evolutionary history that has led to biological successes such as dinosaurs, pterosaurs, plesiosaurs, mosasaurs, and ichthyosaurs.

Reptiles first arose from amphibians in the swamps of the late Carboniferous Period. Increasing evolutionary pressure and the vast untouched niches of the land powered the evolutionary changes in amphibians to gradually become more and more land based. Environmental selection propelled the development of certain traits, such as a stronger skeletal structure, muscles, and more protective coating (scales) became more favorable; and, thus, the basic foundation of reptiles were founded. The evolution of lungs and legs are the main transitional steps towards reptiles, but the development of hard-shelled external eggs replacing the amphibious water bound eggs is the defining feature of the class Reptilia and is what allowed these amphibians to fully leave water. Another major difference from amphibians is the increased brain size, more specifically, the enlarged cerebrum and cerebellum. Although their brain size is small when compared to birds and mammals, these enhancements prove vital in hunting strategies of reptiles. The increased size of these two regions of the brain allowed for improved motor skills and an increase in sensory development.

The origin of the reptiles lies about 320–310 million years ago, in the steaming swamps of the late Carboniferous period, when the first reptiles evolved from advanced reptiliomorph labyrinthodonts. The oldest known animal that may have been an amniote, a reptile rather than an amphibian, is Casineria (though it has also been argued to be an amphibian). A series of footprints from the fossil strata of Nova Scotia, dated to 315 million years, show typical reptilian toes and imprints of scales. The tracks are attributed to Hylonomus, the oldest unquestionable reptile known. It was a small, lizard-like animal, about 20 to 30 cm (8–12 in) long, with numerous sharp teeth indicating an insectivorous diet. Other examples include Westlothiana (for the moment considered a reptiliomorph amphibian rather than a true amniote) and Paleothyris, both of similar build and presumably similar habit. One of the best known early reptiles is Mesosaurus, a genus from the early Permian that had returned to water, feeding on fish. The earliest reptiles were largely overshadowed by bigger labyrinthodont amphibians, such as Cochleosaurus, and remained a small, inconspicuous part of the fauna until after the small ice age at the end of the Carboniferous.

323 Million B.C.T. - The Pennsylvanian Subperiod Began

Around 323 Million B.C.T., the Pennsylvanian subperiod began.

The Pennsylvanian is the younger of two subperiods (or upper of two subsystems) of the Carboniferous Period. It lasted from roughly 323.2 ± 1.3 to 298.9 ± 0.8 million years ago. As with most other geochronologic units, the rock beds that define the Pennsylvanian are well identified, but the exact date of the start and end are uncertain by a few million years. The Pennsylvanian is named after the American state of Pennsylvania, where the coal-productive beds of this age are widespread.

The division between the Pennsylvanian and Mississippian subperiods comes from North American stratigraphy. In North America, where the early Carboniferous beds are primarily marine limestones, the Pennsylvanian was in the past treated as a full fledged geologic period between the Mississippian and the Permian. In Europe, the Mississippian and Pennsylvanian are one more-or-less continuous sequence of lowland continental deposits and are grouped together as the Carboniferous Period. The current internationally used geologic timescale of the International Commission on Stratigraphy (ICS) gives the Mississippian and Pennsylvanian the rank of subperiods, -- subdivisions of the Carboniferous Period.

323 Million B.C.T. - The Mississippian Subperiod Ended

Around 323 Million B.C.T., the Mississippian subperiod came to an end.

The Mississippian is a subperiod in the geologic timescale or a subsystem of the geologic record. It is the earliest/lowermost of two subperiods of the Carboniferous period lasting from roughly 358.9 ± 0.4 to 323.2 ± 0.4 million years ago. As with most other geochronologic units, the rock beds that define the Mississippian are well identified, but the exact start and end dates are uncertain by a few million years. The Mississippian is so named because rocks with this age are exposed in the Mississippi River valley.

The Mississipian was a period of marine ingression in the Northern Hemisphere.  The ocean stood so high only the Fennoscandian Shield (Scandinavia) and the Laurentian Shield (Saint Lawrence and Great Lakes region) stood above sea level. The cratons (the geologic shields) were surrounded by extensive delta systems and lagoons, and carbonate sedimentation on the surrounding continental platforms, covered by shallow seas.

In North America, where the interval consists primarily of marine limestones, the Mississippian subperiod was in the past treated as a full-fledged geologic period between the Devonian and the Pennsylvanian. During the Mississippian subperiod an important phase of orogeny (mountain formation) occurred in the Appalachian Mountains.

In Europe, the Mississippian and Pennsylvanian are one more-or-less continuous sequence of lowland continental deposits and are grouped together as the Carboniferous system, and sometimes called the Upper Carboniferous and Lower Carboniferous instead.

340 Million B.C.T. - The Egg Evolved

Around 340 million years ago, the first egg bearing animals -- the first amniotes -- appeared on the Earth.

The amniotes are a group of tetrapods (four-limbed animals with backbones or spinal columns) that have an egg equipped with an amnios, an adaptation to lay eggs on land rather than in water as anamniotes do. They include synapsids (mammals along with their extinct kin) and sauropsids (reptiles and birds), as well as their fossil ancestors. Amniote embryos, whether laid as eggs or carried by the female, are protected and aided by several extensive membranes. In eutherian mammals (such as humans), these membranes include the amniotic sac that surrounds the fetus. These embryonic membranes, and the lack of a larval stage, distinguish amniotes from tetrapod amphibians.

The first amniotes (referred to as "basal amniotes"), such as Casineria, resembled small lizards and had evolved from the amphibian reptiliomorphs about 340 million years ago, in the Carboniferous geologic period. Their eggs could survive out of the water, allowing amniotes to branch out into drier environments. The eggs could also "breathe" and cope with wastes, allowing the eggs and the amniotes themselves to evolve into larger forms.

The amniotic egg represents a critical divergence within the vertebrates, one enabled to reproduce on dry land—free of the need to return to water for reproduction as required of the amphibians. From this point the amniotes spread across the globe, eventually to become the dominant land vertebrates.
Very early in the evolutionary history of amniotes, basal amniotes diverged into two main lines, the synapsids and the sauropsids, both of which persist into the modern era. The oldest known fossil synapsid is Protoclepsydrops from about 320 million years ago, while the oldest known sauropsid is probably Paleothyris, in the order Captorhinida, from the Middle Pennsylvanian epoch (ca. 306-312 million years ago).

The first amniotes, such as Casineria kiddi, which lived about 340 million years ago, evolved from amphibian reptiliomorphs and resembled small lizards. Their eggs were small and covered with a leathery membrane, not a hard shell like those of birds or crocodiles. Although some modern amphibians lay eggs on land, with or without significant protection, they all lack advanced traits like an amnion. This kind of egg became possible only with internal fertilization. The outer membrane, a soft shell, evolved as a protection against the harsher environments on land, as species evolved to lay their eggs on land where they were safer than in the water. The ancestors of the amniotes probably laid their eggs in moist places, as such modest-sized animals would not have difficulty finding depressions under fallen logs or other suitable places in the ancient forests; and dry conditions were probably not the main reason the soft shell emerged. Indeed, many modern day amniotes are dependent on moisture to keep their eggs from desiccating.

Amniotes can be characterized in part by embryonic development that includes the formation of several extensive membranes, the amnion, chorion, and allantois. Amniotes develop directly into a (typically) terrestrial form with limbs and a thick stratified epithelium, rather than first entering a feeding larval tadpole stage followed by metamorphosis as in amphibians. In amniotes the transition from a two-layered periderm to cornified epithelium is triggered by thyroid hormone during embryonic development, rather than metamorphosis. The unique embryonic features of amniotes may reflect specializations of eggs to survive drier environments; or the massive size and yolk content of eggs may have evolved to allow direct development of the embryo to a larger size.

Features of amniotes evolved for survival on land include a sturdy but porous leathery or hard eggshell and an allantois evolved to facilitate respiration while providing a reservoir for disposal of wastes. Their kidneys and large intestines are also well-suited to water retention. Most mammals do not lay eggs, but corresponding structures may be found inside the placenta.

360 Million B.C.T. - The Great Fossil Mystery

From 360 Million B.C.T. to 345 Million B.C.T., a gap in the fossil record occurred. It is as though after destroying most of the Creation that occurred during the Devonian Period, God paused for 15 million years, before beginning the Creation of the Carboniferous Period.

Romer's Gap is an example of an apparent gap in the tetrapod fossil record used in the study of evolutionary biology. Such gaps represent periods from which excavators have not yet found relevant fossils. Romer's gap is named after paleontologist Dr. Alfred Romer, who first recognised it.

Romer's gap ran from approximately 360 to 345 million years ago, corresponding to the first 15 million years of the Carboniferous Period. The gap forms a discontinuity between the primitive forests and high diversity of fishes in the end Devonian and more modern aquatic and terrestrial assemblages of the early Carboniferous.

There has been long debate as to why there are so few fossils from this time period. Some have suggested the problem was of fossilization itself, suggesting that there may have been differences in the geochemistry of the time that did not favor fossil formation. Also, excavators simply may not have dug in the right places. However, the existence of a true low point in vertebrate diversity has been supported by independent lines of evidence.

While initial arthropod terrestriality was well under way before the gap, and some digited tetrapods might have come on land, there are remarkably few terrestrial or aquatic fossils that date from the gap itself^.  Recent work on Paleozoic geochemistry has confirmed the biological reality of Romer's gap in both terrestrial vertebrates and arthropods, and has correlated it with a period of unusually low atmospheric oxygen concentration, which was independently determined from the idiosyncratic geochemistry of rocks formed during Romer's gap.

Aquatic vertebrates, which include most tetrapods during the Carboniferous, were recovering from a Late Devonian extinction -- a major extinction event that preceded Romer's gap, one on par with that which killed the dinosaurs. In the Late Devonian extinction, most marine and freshwater groups went extinct or were reduced to a few lineages, although the precise mechanism of the extinction is unclear. Before the Late Devonian extinction, oceans and lakes were dominated by lobe-finned fishes and armored fishes called placoderms. After Romer's gap, modern ray finned fish, as well as sharks and their relatives were the dominant forms. The period also saw the demise of the Ichthyostegalia, the early fish-like amphibians with more than five digits.

The low diversity of marine fishes, particularly shell-crushing predators (durophages), at the beginning of Romer's gap is supported by the sudden abundance of hard-shelled crinoid echinoderms during the same period. The Tournaisian stage -- the first fifteen million years of the Carboniferous Period that corresponds to the period of the Romer's Gap -- has even been called the "Age of Crinoids". Once the number of shell-crushing ray-finned fishes and sharks increased later in the Carboniferous, coincident with the end of Romer's gap, the diversity of crinoids with Devonian-type armor plummeted, following the pattern of a classic predator-prey cycle.

The gap in the tetrapod record has been progressively closed with the discoveries of such early Carboniferous tetrapods as Pederpes and Crassigyrinus. There are a few sites where vertebrate fossils have been found to help fill in the gap, such as the East Kirkton Quarry, in Bathgate, Scotland, a long-known fossil site that was revisited by Stanley P. Wood in 1984 and has since been revealing a number of early tetrapods in the mid Carboniferous; "literally dozens of tetrapods came rolling out: Balanerpeton (a temnospondyl), Silvanerpeton and Eldeceeon (basal anthracosaurs), all in multiple copies, and one spectacular proto-amniote, Westlothiana", Paleos Project reports. However, tetrapod material in the earliest stage of the Carboniferous, the Tournaisian, is typically scarce relative to fishes in the same habitats, which can appear in large death assemblages, and is unknown until late in the stage. Fish faunas from Tournaisian sites around the world are very alike in composition, containing common and ecologically similar species of ray-finned fishes, rhizodont lobe-finned fishes, acanthodians, sharks, and holocephalans.

For many years after Romer's gap was first recognized, only two sites yielding Tournaisian-age tetrapod fossils were known: one in East Lothian, Scotland and another in Blue Beach, Nova Scotia. In 1841, William Logan, the first Director of the Geological Survey of Canada, found footprints from a tetrapod. Blue Beach maintains a fossil museum and displays hundreds of fossils from this period that continue to be found as the cliff continues to reveal new fossils as it continues to erode. In 2012, tetrapod remains from four new Tournaisian sites in Scotland were announced. These localities are the coast of Burnmouth, the banks of the Whiteadder Water near Chirnside, the River Tweed near Coldstream, and the rocks near Tantallon Castle alongside the Firth of Forth. Fossils of both aquatic and terrestrial tetrapods are known from these localities, providing an important record of the transition between life in water and life on land and filling some of the lacunae (missing fossil record) in Romer's gap. These new localities may represent a larger fauna, as all lie within a short distance of each other and share many fishes with the nearby and contemporary Foulden fish bed locality (which has not produced tetrapods thus far).

360 Million B.C.T. - The Carboniferous Period Began

Around 360 million years ago, the Carboniferous Period began.

The Carboniferous is a geologic period and system that extends from the end of the Devonian Period, about 359.2 ± 2.5 million years ago, to the beginning of the Permian Period, about 299.0 ± 0.8 million years ago. The name Carboniferous means "coal-bearing" and derives from the Latin words carbo (coal) and ferre (to carry), and was coined by geologists William Conybeare and William Phillips in 1822. Based on a study of the British rock succession, it was the first of the modern 'system' names to be employed, and reflects the fact that many coal beds were formed globally during this time. The Carboniferous is often treated in North America as two geological periods, the earlier Mississippian and the later Pennsylvanian.

Terrestrial life was well established by the Carboniferous period. Amphibians were the dominant land vertebrates, of which one branch would eventually evolve into reptiles, the first fully terrestrial vertebrates. Arthropods (insects, arachnids, and crustaceans) were also very common, and many (such as Meganeura), were much larger than those of today. Vast swaths of forest covered the land, which would eventually be laid down and become the coal beds characteristic of the Carboniferous system. A minor marine and terrestrial extinction event occurred in the middle of the period, caused by a change in climate. The latter half of the period experienced glaciations, low sea level, and mountain building as the continents collided to form Pangaea.

360 Million B.C.T. - The Devonian Period Ends

Around 360 million years ago, the Devonian Period came to an end.

Although it is clear that there was a massive loss of biodiversity towards the end of the Devonian Period, it is not clear over how long a period these extinctions took place, with estimates varying from 500 thousand to 15 million years.  Neither is it clear whether it was a single mass extinction or a series of several smaller ones one after the other.  Nevertheless, the balance of evidence suggests that the extinctions took place over a period of some three million years beginning about 374 million years ago. 

During the late Devonian extinction, as many as seventy percent of all species vanished.  Marine species were more severely affected than those in freshwater.  Brachiopods, ammonites, and many other invertebrates suffered heavily, as did agnathan and placoderm fish.  On land, where plants were diversifying and amphibians were beginning their evolution, there seem to have been far fewer losses.

The causes of the Devonian extinction are unclear.  The disproportionate losses amongst warm water species suggest that the Earth's climate changed -- most likely for the cooler.  The global cooling was an important factor and it has been suggested that this was associated with (or may have even caused) a drop in the oxygen levels of the shallower waters.

370 Million B.C.T. - Amphibians Appeared

Around 370 million years ago, amphibians evolved.

Amphibians are ectothermic (relies on outside heat sources), tetrapod (four-limbed) vertebrates of the class Amphibia. They inhabit a wide variety of habitats with most species living within terrestrial, fossorial (underground), arboreal or freshwater aquatic ecosystems. Amphibians typically start out as larva living in water, but some species have developed behavioral adaptations to bypass this. The young generally undergo metamorphosis from larva with gills to an adult air-breathing form with lungs. Amphibians use their skin as a secondary respiratory surface and some small terrestrial salamanders and frogs lack lungs and rely entirely upon skin. They are superficially similar to reptiles but, along with mammals and birds, reptiles are amniotes (egg layers) and do not require water bodies in which to breed. With their complex reproductive needs and permeable skins, amphibians are often ecological indicators and in recent decades there has been a dramatic decline in amphibian populations for many species around the globe.

The earliest amphibians evolved in the Devonian Period from sarcopterygian (lobe-finned) fish with lungs and bony-limbed fins, features that were helpful in adapting to dry land. They diversified and became dominant during the Carboniferous and Permian periods, but were later displaced by reptiles and other vertebrates. Over time, amphibians shrank in size and decreased in diversity, leaving only the modern subclass Lissamphibia. The three modern orders of amphibians are Anura (the frogs and toads), Caudata/Urodela (the salamanders), and Gymnophiona/Apoda (the caecilians [worm or snake like amphibians]). The total number of known amphibian species is approximately 7,000, of which nearly ninety percent (90%) are frogs. The smallest amphibian (and vertebrate) in the world is a frog from New Guinea (Paedophryne amauensis) with a length of just 7.7 mm (0.30 in). The largest living amphibian is the 1.8 m (5 ft 11 in) Chinese Giant Salamander (Andrias davidianus) but this is dwarfed by the extinct 9 m (30 ft) Prionosuchus from the middle Permian of Brazil. The study of amphibians is called batrachology, while the study of both reptiles and amphibians is called herpetology.

The first major groups of amphibians developed in the Devonian period, around 370 million years ago, from lobe-finned fish similar to the modern coelacanth and lungfish, which had evolved multi-jointed leg-like fins with digits that enabled them to crawl along the sea bottom. Some fish had developed primitive lungs to help them breathe air when the stagnant pools of the Devonian swamps were low in oxygen. They could also use their strong fins to hoist themselves out of the water and onto dry land if circumstances so required. Eventually, their bony fins would evolve into limbs and they would become the ancestors to all tetrapods, including modern amphibians, reptiles, birds, and mammals. Despite being able to crawl on land, many of these prehistoric tetrapodomorph fish still spent most of their time in the water. They had started to develop lungs, but still breathed predominantly with gills.

Ichthyostega was one of the first primitive amphibians, with nostrils and more efficient lungs. It had four sturdy limbs, a neck, a tail with fins and a skull very similar to that of the lobe-finned fish, Eusthenopteron. Amphibians evolved adaptations that allowed them to stay out of the water for longer periods. Their lungs improved and their skeletons became heavier and stronger, better able to cope with the increased gravitational effect of life on land. They developed "hands" and "feet" with five or more digits; the skin became more capable of retaining body fluids and resisting desiccation. The fish's hyomandibula (jaw) bone in the hyoid region behind the gills diminished in size and became the stapes (ear bone) of the amphibian ear, an adaptation necessary for hearing on dry land. An affinity between the amphibians and the teleost (ray finned) fish is the multi-folded structure of the teeth and the paired supra-occipital bones at the back of the head, neither of these features being found elsewhere in the animal kingdom.

At the end of the Devonian period (360 million years ago), the seas, rivers and lakes were teeming with life while the land was the realm of early plants and devoid of vertebrates, though some, such as Ichthyostega, may have sometimes hauled themselves out of the water. It is thought they may have propelled themselves with their forelimbs, dragging their hindquarters in a similar manner to that used by the elephant seal. In the early Carboniferous (360 to 345 million years ago), the climate became wet and warm. Extensive swamps developed with mosses, ferns, horsetails and calamites. Air-breathing arthropods evolved and invaded the land where they provided food for the carnivorous amphibians that began to adapt to the terrestrial environment. There were no other tetrapods on the land and the amphibians were at the top of the food chain, occupying the ecological position currently held by the crocodile. Though equipped with limbs and the ability to breathe air, most still had a long tapering body and strong tail. They were the top land predators, sometimes reaching several meters in length, preying on the large insects of the period and the many types of fish in the water. They still needed to return to water to lay their shell-less eggs, and even most modern amphibians have a fully aquatic larval stage with gills like their fish ancestors. It was the development of the amniotic egg, which prevents the developing embryo from drying out, that enabled the reptiles to reproduce on land and which led to their dominance in the period that followed.

During the Triassic Period (250 to 200 million years ago), the reptiles began to out-compete the amphibians, leading to a reduction in both the amphibians' size and their importance in the biosphere. According to the fossil record, Lissamphibia, which includes all modern amphibians and is the only surviving lineage, may have branched off from the extinct groups Temnospondyli and Lepospondyli at some period between the Late Carboniferous and the Early Triassic. The relative scarcity of fossil evidence precludes precise dating, but the most recent molecular study suggests a Late Carboniferous/Early Permian origin of extant amphibians.

The origins and evolutionary relationships between the three main groups of amphibians is a matter of debate. A 2005 molecular phylogeny, based on rDNA analysis, suggests that salamanders and caecilians are more closely related to each other than they are to frogs. It also appears that the divergence of the three groups took place in the Paleozoic or early Mesozoic (around 250 million years ago), before the breakup of the supercontinent Pangaea and soon after their divergence from the lobe-finned fish. The briefness of this period, and the swiftness with which radiation took place, would help account for the relative scarcity of primitive amphibian fossils. There are large gaps in the fossil record, but the discovery of a proto-frog from the Early Permian in Texas in 2008 provided a missing link with many of the characteristics of modern frogs. Molecular analysis suggests that the frog–salamander divergence took place considerably earlier than the palaeontological evidence indicates.

As they evolved from lunged fish, amphibians had to make certain adaptations for living on land including the need to develop new means of locomotion. In the water, the sideways thrusts of their tails had propelled them forward but on land, quite different mechanisms were required. Their vertebral columns, limbs, limb girdles and musculature needed to be strong enough to raise them off the ground for locomotion and feeding. Terrestrial adults discarded their lateral line systems and adapted their sensory systems to receive stimuli via the medium of air. They needed to develop new methods to regulate their body heat to cope with fluctuations in ambient temperature. They developed behaviors suitable for reproduction in a terrestrial environment. Their skins were exposed to harmful ultraviolet rays that had previously been absorbed by the water. The skin changed to become more protective and prevent excessive water loss.

374 Million B.C.T. - The Kellwasser Extinction Event Began

Around 374 million years ago, one of the five major extinction events in the history of the Earth began.

The Late Devonian extinction was one of five major extinction events in the history of the Earth's biota. A major extinction, the Kellwasser Event, occurred at the boundary that marks the beginning of the last phase of the Devonian period, the Famennian faunal stage, (the Frasnian-Famennian boundary), about 374 million years ago. Overall, nineteen percent (19%) of all families and fifty percent (50%) of all genera went extinct. A second, distinct mass extinction, the Hangenberg Event, closed the Devonian period.

Although it is clear that there was a massive loss of biodiversity in the Later Devonian, the extent of time during which these events took place is uncertain, with estimates ranging from 500,000 to 25 million years. Nor is it clear whether it concerned two sharp mass extinctions or a series of smaller extinctions, though the latest research suggests multiple causes and a series of distinct extinction pulses through an interval of some three million years. Some consider the extinction to be as many as seven distinct events, spread over about 25 million years.

By the late Devonian, the land had been colonized by plants and insects. In the oceans, there were massive reefs built by corals and stromatoporoids. Euramerica and Gondwana were beginning to converge into what would become Pangaea. The extinction seems to have only affected marine life. Hard-hit groups include brachiopods, trilobites, and reef-building organisms; the latter almost completely disappeared, with coral reefs only returning upon the evolution of modern corals during the Mesozoic. The causes of these extinctions are unclear. Leading theories include changes in sea level and ocean anoxia, possibly triggered by global cooling or oceanic volcanism. The impact of a comet or another extraterrestrial body has also been suggested. Some statistical analysis suggests that the decrease in diversity was caused more by a decrease in speciation than by an increase in extinctions. This might have been caused by invasions of cosmopolitan species, rather than any single event. Surprisingly, jawed vertebrates seem to have been unaffected by the loss of reefs or other aspects of the Kellwasser event, while agnathans (jawless fish) were in decline long before the end of the Devonian.

During the Late Devonian, the continents were arranged differently, with a supercontinent, Gondwana, covering much of the southern hemisphere. The continent of Siberia occupied the northern hemisphere, while an equatorial continent, Laurussia (formed by the collision of Baltica and Laurentia) was drifting towards Gondwana. The Caledonian mountains were also growing across what is now the Scottish highlands and Scandinavia, while the Appalachians rose over America; these mountain belts were the equivalent of the Himalaya today.

The biota was also very different. Plants, which had been on land in forms similar to mosses, liverworts, and lichens since the Ordovician, had just developed roots, seeds, and water transport systems that allowed them to survive away from places that were constantly wet—and consequently built huge forests on the highlands. Several different clades had developed a shrubby or tree-like habit by the Late Givetian, including the cladoxylalean ferns, lepidosigillarioid lycopsids, and aneurophyte and archaeopterid progymnosperms. Fish were also undergoing a huge radiation, and the first tetrapods were beginning to evolve leg-like structures.

The Kellwasser event is the term given to the extinction pulse that occurs near the Frasnian/Famennian boundary. Most references to the "Late Devonian extinction" are in fact referring to the Kellwasser, which was the first event to be detected based on marine invertebrate record. There may in fact have been two closely spaced events here as shown by the presence of two distinct anoxic shale layers.

The extinction events are accompanied by widespread oceanic anoxia; that is, a lack of oxygen, prohibiting decay and allowing the preservation of organic matter. This, combined with the ability of porous reef rocks to hold oil, has led to Devonian rocks being an important source of oil, especially in the USA.

The Kellwasser event and most other Later Devonian pulses primarily affected the marine community, and selectively affected shallow warm-water organisms over cool-water organisms. The most important group to be affected by the Kellwasser event were the reef-builders of the great Devonian reef-systems, including the stromatoporoids, and the rugose and tabulate corals. Reefs of the later Devonian were dominated by sponges and calcifying bacteria, producing structures such as oncolites and stromatolites; the reef system collapse was so stark that bigger reef-building (effected by new families of carbonate-excreting organisms, the modern scleractinian or "stony" corals) did not recover until the Mesozoic era.

Further taxa to be starkly affected include the brachiopods, trilobites, ammonites, conodonts, and acritarchs. The surviving taxa show morphological trends through the event. Trilobites evolve smaller eyes in the run up to the Kellwasser event, with eye size increasing again afterwards. This suggests that vision was less important around the event, perhaps due to increasing water depth or turbidity. The brims of trilobites (i.e. the rims of their heads) also expanded across this period. It is thought that the brims serve a respiratory purpose, and that the increasing anoxia of waters led to an increase in their brim area in response. The shape of conodonts' feeding apparatus varied the lack of oxygen and thus seawater temperature.  This may relate to them occupying different trophic levels as nutrient input changed. As with most extinction events, specialist taxa occupying small niches were harder hit than generalists.

The Hangenberg event impacted both sea and freshwater communities. This mass extinction impacted ammonites and trilobites, as well as jawed vertebrates including our tetrapod ancestors. The Hangenberg is linked to the extinction of forty-four percent (44%) of high-level vertebrate clades, including all placoderms and most sarcopterygians, and the complete turnover of the vertebrate biota. This led to the establishment of the modern vertebrate fauna, consisting mostly of actinopterygians, chondrichthyans, and tetrapods, in the Carboniferous. Romer's Gap, a 15 million-year hiatus in the early Carboniferous tetrapod record, has been linked to this event. It is also likely that some of the losses attributed to the Kellwasser event actually occurred during the Hangenberg extinction, due to the poor Famennian record for marine invertebrates.

The late Devonian crash in biodiversity was more drastic than the familiar extinction event that closed the Cretaceous.  It is estimated that twenty-two percent (22%) of all the families of marine animals (largely invertebrates) were eliminated. The family is a great unit, and to lose so many signifies a deep loss of ecosystem diversity. On a smaller scale, fifty-seven percent (57%) of genera and at least seventy-five percent (75%) of species did not survive into the Carboniferous. These latter estimates need to be treated with a degree of caution, as the estimates of species loss depend on surveys of Devonian marine taxa that are perhaps not well enough known to assess their true rate of losses, so it is difficult to estimate the effects of differential preservation and sampling biases during the Devonian.

Since the Kellwasser-related "extinctions" occurred over such a long time, it is difficult to assign a single cause, and indeed to separate cause from effect. The sedimentological record shows that the late Devonian was a time of environmental change, which directly affected organisms and caused extinction. What caused these changes is somewhat more open to debate.

From the end of the Middle Devonian, into the Late Devonian, several environmental changes can be detected from the sedimentary record. There is evidence of widespread anoxia in oceanic bottom waters; the rate of carbon burial shot up, and benthic organisms were decimated, especially in the tropics, and especially reef communities. There is good evidence for high-frequency sea level changes around the Frasnian/Famennian Kellwasser event, with one sea level rise associated with the onset of anoxic deposits. The Hangenberg event has been associated with sea-level rise followed swiftly by glaciation-related sea-level fall.

There are many proposed reasons for the Kellwasser Extinction Event.  One prime proposed reason is an extraterrestrial (bolide) impact.  Bolide impacts can be dramatic triggers of mass extinctions. It has been posited that an asteroid impact was the prime cause of the Kellwasser faunal turnover, but no secure evidence of a specific extraterrestrial impact has been identified in this case. Impact craters, such as the Kellwasser-aged Alamo and the Hangenberg-aged Woodleigh, cannot generally be dated with sufficient precision to link them to the event. Other impacts dated precisely are not contemporaneous with the extinction  Although some minor features of meteoric impact have been observed in places (iridium anomalies and microspherules), these were probably caused by other factors.

During the Devonian, land plants underwent a hugely significant phase of evolution. Their maximum height went from 30 cm at the start of the Devonian, to 30 m at the end of the period. This increase in height was made possible by the evolution of advanced vascular systems, which permitted the growth of complex branching and rooting systems. In conjunction with this, the development of seeds permitted reproduction and dispersal in areas which were not waterlogged, allowing plants to colonise previously inhospitable inland and upland areas. The two factors combined to greatly magnify the role of plants on the global scale. In particular, Archaeopteris forests expanded rapidly during the closing stages of the Devonian.

The tall trees of the Devonian required deep rooting systems to acquire water and nutrients, and provide anchorage. These systems broke up the upper layers of bedrock and stabilized a deep layer of soil, which would have been on the order of meters thick. In contrast, early Devonian plants bore only rhizoids and rhizomes that could penetrate no more than a couple of centimeters. The mobilization of a large portion of soil had a huge effect.  Soil promotes weathering, the chemical breakdown of rocks, releasing ions which act as nutrients to plants and algae. The relatively sudden input of nutrients into river water may have caused eutrophication and subsequent anoxia. For example, during an algal bloom, organic material formed at the surface can sink at such a rate that decomposing organisms use up all available oxygen by decaying them, creating anoxic conditions and suffocating bottom-dwelling fish. The fossil reefs of the Frasnian were dominated by stromatolites and (to a lesser degree) corals—organisms which only thrive in low nutrient conditions. Therefore the postulated influx of high levels of nutrients may have caused an extinction, just as phosphate run-off from Australian farmers is causing unmeasurable damage to the great barrier reef today. Anoxic conditions correlate better with biotic crises than phases of cooling, suggesting that anoxia may have played the dominant role in extinction.

Another suggested reason for the extinctions is the decrease in carbon dioxide.  The "greening" of the continents occurred during Devonian time. The covering of the planet's continents with massive photosynthesizing land plants in the first forests may have reduced carbon dioxide levels in the atmosphere. Since carbon dioxide (CO₂) is a greenhouse gas, reduced levels might have helped produce a chillier climate. Evidence such as glacial deposits in northern Brazil (located near the Devonian south pole) suggest widespread glaciation at the end of the Devonian, as a broad continental mass covered the polar region. A cause of the extinctions may have been an episode of global cooling, following the mild climate of the Devonian period. The Hangenberg event has also been linked to glaciation in the tropics equivalent to that of the Pleistocene ice age.

The weathering of silicate rocks also draws down carbon dioxide from the atmosphere. This acted in concert with the burial of organic matter to decrease atmospheric carbon dioxide concentrations from ~15 to ~3 times present levels. Carbon in the form of plant matter would be produced on prodigious scales, and given the right conditions could be stored and buried, eventually producing vast coal measures (e.g. in China) which locked the carbon out of the atmosphere and into the lithosphere. This reduction in atmospheric CO₂ would have caused global cooling and resulted in at least one period of late Devonian glaciation (and subsequent sea level fall), probably fluctuating in intensity alongside the 40,000 year Milankovic cycle. The continued drawdown of organic carbon eventually pulled the Earth out of its Greenhouse Earth state into the Icehouse that continued throughout the Carboniferous and Permian.

Other mechanisms that have been put forward to explain the extinctions include tectonic driven climate change; sea level change; and oceanic overturning. These have all been discounted because they are unable to explain the duration, selectivity, and periodicity of the extinctions.

385 Million B.C.T. - The Earth's First Trees

Around 385 million years ago, the first trees took root on the land.

The first tree may have been Wattieza, fossils of which have been found in New York State in 2007 dating back to the Middle Devonian (about 385 million years ago). Prior to this discovery, Archaeopteris was the earliest known tree. Both of these reproduced by spores rather than seeds and are considered to be links between ferns and the gymnosperms which evolved in the Triassic period. The gymnosperms include conifers, cycads, gnetales and ginkgos and these may have appeared as a result of a whole genome duplication event which took place about 319 million years ago.  Ginkgophyta was once a widespread diverse group of which the only survivor is the maidenhair tree Ginkgo biloba. This is considered to be a living fossil because it is virtually unchanged from the fossilized specimens found in Triassic deposits.

During the Mesozoic (245 to 65 million years ago), the conifers flourished and became adapted to live in all the major terrestrial habitats. Subsequently the tree forms of flowering plants evolved during the Cretaceous period. These began to dominate the conifers during the Tertiary era (65 to 2 million years ago) when forests covered the globe. When the climate cooled 1.5 million years ago and the first of four ice ages occurred, the forests retreated as the ice advanced. In the interglacials, trees recolonized the land only to be driven back again at the start of the next ice age.

Early Devonian plants did not have roots or leaves like the plants most common today and many had no vascular tissue at all. They probably spread largely by vegetative growth, and did not grow much more than a few centimeters tall. By far the largest land organism was Prototaxites, the fruiting body of an enormous fungus that stood more than 8 meters tall, towering over the low, carpet-like vegetation. By Middle Devonian, shrub-like forests of primitive plants existed: lycophytes, horsetails, ferns, and progymnosperms had evolved. Most of these plants had true roots and leaves, and many were quite tall. The earliest known trees, from the genus Wattieza, appeared in the Late Devonian.  In the Late Devonian, the tree-like ancestral fern Archaeopteris and the giant cladoxylopsid trees grew with true wood. These are the oldest known trees of the world's first forests. By the end of the Devonian, the first seed-forming plants had appeared. This rapid appearance of so many plant groups and growth forms has been called the "Devonian Explosion".

The 'greening' of the continents acted as a carbon dioxide sink, and atmospheric levels of this greenhouse gas may have dropped. This may have cooled the climate and led to a massive extinction event.

400 Million B.C.T. - Gondwana Became the South Pole

Around 400 million years ago, Gondwana, the supercontinent, became the South Pole. 

While Gondwana was the South Pole, the land that today is Africa was covered with glaciers, its ice cap was as thick as Antarctica's is today.  Indeed, the region that is today known as the Sahara -- a region that is today one of the hottest places on Earth -- bears traces of the time when the desert was an iceland.

407 Million B.C.T. - Insects Proliferate

By 407 Million B.C.T., insects began to proliferate on the Earth.

The evolution of insects dates back to the Devonian period, with the oldest definitive insect fossil being the Rhyniognatha hirsti, estimated at 407 to 396 million years ago (although the first possible fossils of insects may have appeared around 416 million years ago).

Global climate conditions changed several times during the history of the Earth, along with it the diversity of insects. The Pterygotes underwent a major radiation in the Carboniferous while the Endopterygota species underwent another major radiation in the Permian. Survivors of the mass extinction at the PT (Permian-Triassic) boundary evolved in the Triassic to what are essentially the modern Insecta Orders that persist to modern times. Most modern insect families appeared in the Jurassic, and further diversity probably in genera occurred in the Cretaceous. It is believed that by the Tertiary, there existed many of what are still modern genera; hence, most insects in amber are, indeed, members of extant genera. What seems most fascinating is that insects diversified in a relatively brief 100 million years (give or take) into the modern forms that exist with minor change into modern times.

The Devonian was a relatively warm period, and probably lacked any glaciers.  Reconstruction of tropical sea surface temperature from conodont apatite implies an average value of 30 °C (86 °F) in the Early Devonian. Carbon dioxide (CO₂) levels dropped steeply throughout the Devonian period as the burial of the newly-evolved forests drew carbon out of the atmosphere into sediments. This may be reflected by a Mid-Devonian cooling of around 5 °C (9 °F). The Late Devonian warmed to levels equivalent to the Early Devonian. While there is no corresponding increase in CO₂ concentrations, continental weathering increases (as predicted by warmer temperatures). Further, a range of evidence, such as plant distribution, points to Late Devonian warming. The continent Euramerica (or Laurussia) was created in the early Devonian by the collision of Laurentia and Baltica, which rotated into the natural dry zone along the Tropic of Capricorn, which is formed as much in Paleozoic times as nowadays by the convergence of two great air-masses, the Hadley cell and the Ferrel cell.

The oldest definitive insect fossil is the Devonian Rhyniognatha hirsti, estimated at 407 to 396 million years ago. This species already possessed dicondylic mandibles, a feature associated with winged insects, suggesting that wings may already have evolved at this time. Thus, the first insects probably appeared earlier, in the Silurian period. Like other insects of its time, Rhyniognatha presumably fed on plant sporophylls - which occur at the tips of branches and bear sporangia, the spore-producing organs. The insect’s anatomy might also give clues as to what it ate. The creature had large mandibles which may or may not have been used for hunting.

Just as the early Paleozoic can be called the age of the trilobite, the following time could be called the age of the insect. The insect fossil record extends back some 400 million years to the lower Devonian, while the Pterygotes (winged insects) underwent a major radiation in the Carboniferous.

Insect evolution is characterized by rapid adaptation with selective pressures exerted by environment, with rapid adaptation being furthered by their high fecundity. It appears that rapid radiations and the appearance of new species, a process that continues to this day, result in insects filling all available environmental niches. Insect evolution is closely related to the evolution of flowering plants. Insect adaptations include feeding on flowers and related structures, with some 20% of extant insects depending on flowers, nectar or pollen for their food source. This symbiotic relationship is even more paramount in evolution considering that about two-thirds of flowering plants are insect pollinated. Insects are also vectors of many pathogens that may even have been responsible for the decimation or extinction of some mammalian species. Compared to other organisms, insects have not left a particularly robust fossil record. Other than in amber, most insects are terrestrial and only preserved under very special conditions such as at the edge of freshwater lakes. Yet in amber, age is limited since large resin production by trees developed later than the ancient insects.

419 Million B.C.T. - The Devonian Period Began

Around 419 million years ago, the Devonian Period began.

The Devonian is a geologic period and system of the Paleozoic Era spanning from the end of the Silurian Period, about 419.2 ± 3.2 million years ago, to the beginning of the Carboniferous Period, about 358.9 ± 0.4 million years ago. It is named after Devon, England, where rocks from this period were first studied.

The Devonian period experienced the first significant adaptive radiation of terrestrial life. Since large vertebrate terrestrial herbivores had not yet appeared, free-sporing vascular plants began to spread across dry land, forming extensive forests which covered the continents. By the middle of the Devonian, several groups of plants had evolved leaves and true roots, and by the end of the period the first seed-bearing plants appeared. Various terrestrial arthropods also became well-established.

Fish reached substantial diversity during this time, leading the Devonian to often be dubbed the "Age of Fish". The first ray-finned and lobe-finned bony fish appeared, while the placoderms began dominating almost every known aquatic environment.

The ancestors of all tetrapods began adapting to walking on land, their strong pectoral and pelvic fins gradually evolved into legs. In the oceans, primitive sharks became more numerous than in the Silurian and the late Ordovician. The first ammonite mollusks appeared. Trilobites, the mollusk-like brachiopods and the great coral reefs, were still common. The Late Devonian extinction severely affected marine life, killing off all placoderms, and all trilobites, save for a few species of the order Proetida.

The paleogeography was dominated by the supercontinent of Gondwana to the south, the continent of Siberia to the north, and the early formation of the small continent of Euramerica in between.

The Devonian was a relatively warm period, and probably lacked any glaciers. Reconstruction of tropical sea surface temperature from conodont apatite implies an average value of 30 °C (86 °F) in the Early Devonian. Carbon dioxide (CO₂) levels dropped steeply throughout the Devonian period as the burial of the newly-evolved forests drew carbon out of the atmosphere into sediments. This may be reflected by a Mid-Devonian cooling of around 5 °C (9 °F). The Late Devonian warmed to levels equivalent to the Early Devonian.  While there is no corresponding increase in CO₂ concentrations, continental weathering increased (as predicted by warmer temperatures).  Furthermore, a range of evidence, such as plant distribution, points to Late Devonian warming. The climate would have affected the dominant organisms in reefs. Microbes would have been the main reef-forming organisms in warm periods, with corals and stromatoporoid sponges taking the dominant role in cooler times. The warming at the end of the Devonian may even have contributed to the extinction of the stromatoporoids.

The Devonian period was a time of great tectonic activity, as Euramerica and Gondwana drew closer together. The continent Euramerica (or Laurussia) was created in the early Devonian by the collision of Laurentia and Baltica, which rotated into the natural dry zone along the Tropic of Capricorn, which is formed as much in Paleozoic times as nowadays by the convergence of two great air-masses, the Hadley cell and the Ferrel cell. In these near-deserts, the Old Red Sandstone sedimentary beds formed, made red by the oxidized iron (hematite) characteristic of drought conditions.
Near the equator, the plate of Euramerica and Gondwana were starting to meet, beginning the early stages of assembling Pangaea. This activity further raised the northern Appalachian Mountains and formed the Caledonian Mountains in Great Britain and Scandinavia.

The west coast of Devonian North America, by contrast, was a passive margin with deep silty embayments, river deltas and estuaries, in today's Idaho and Nevada; an approaching volcanic island arc reached the steep slope of the continental shelf in Late Devonian times and began to uplift deep water deposits, a collision that was the prelude to the mountain-building episode of Mississippian times called the Antler orogeny.

Sea levels were high worldwide, and much of the land lay under shallow seas, where tropical reef organisms lived. The deep, enormous Panthalassa (the "universal ocean") covered the rest of the planet. Other minor oceans were Paleo-Tethys, Proto-Tethys, Rheic Ocean, and Ural Ocean (which was closed during the collision with Siberia and Baltica).

Sea levels in the Devonian were generally high. Marine faunas continued to be dominated by bryozoa, diverse and abundant brachiopods, the enigmatic hederelloids, microconchids and corals. Lily-like crinoids were abundant, and trilobites were still fairly common. Among vertebrates, jaw-less armored fish (ostracoderms) declined in diversity, while the jawed fish (gnathostomes) simultaneously increased in both the sea and fresh water. Armored placoderms were numerous during the lower stages of the Devonian Period and became extinct in the Late Devonian, perhaps because of competition for food against the other fish species. Early cartilaginous (Chondrichthyes) and bony fishes (Osteichthyes) also become diverse and played a large role within the Devonian seas. The first abundant genus of shark, Cladoselache, appeared in the oceans during the Devonian Period. The great diversity of fish around at the time, have led to the Devonian being given the name "The Age of Fish" in popular culture.

The first ammonites also appeared during or slightly before the early Devonian Period around 400 B.C.T.

A now dry barrier reef, located in present day Kimberley Basin of northwest Australia, once extended a thousand kilometers, fringing a Devonian continent. Reefs in general are built by various carbonate-secreting organisms that have the ability to erect wave-resistant frameworks close to sea level. The main contributors of the Devonian reefs were unlike modern reefs, which are constructed mainly by corals and calcareous algae. They were composed of calcareous algae and coral-like stromatoporoids, and tabulate and rugose corals, in that order of importance.

By the Devonian Period, life was well underway in its colonization of the land. The moss forests and bacterial and algal mats of the Silurian were joined early in the period by primitive rooted plants that created the first stable soils and harbored arthropods like mites, scorpions and myriapods (although arthropods appeared on land much earlier than in the Early Devonian and the existence of fossils such as Climactichnites suggest that land arthropods may have appeared as early as the Cambrian period). Also the first possible fossils of insects appeared around 416 B.C.T. in the Early Devonian. The first tetrapods, evolving from lobe-finned fish, appeared in the coastal water no later than middle Devonian, and gave rise to the first Amphibians.


Early Devonian plants did not have roots or leaves like the plants most common today and many had no vascular tissue at all. They probably spread largely by vegetative growth, and did not grow much more than a few centimeters tall. By far the largest land organism was Prototaxites, the fruiting body of an enormous fungus that stood more than 8 meters tall, towering over the low, carpet-like vegetation. By Middle Devonian, shrub-like forests of primitive plants existed: lycophytes, horsetails, ferns, and progymnosperms had evolved. Most of these plants had true roots and leaves, and many were quite tall. The earliest known trees, from the genus Wattieza, appeared in the Late Devonian.  In the Late Devonian, the tree-like ancestral fern Archaeopteris and the giant cladoxylopsid trees grew with true wood. These are the oldest known trees of the world's first forests. By the end of the Devonian, the first seed-forming plants had appeared. This rapid appearance of so many plant groups and growth forms has been called the "Devonian Explosion".

The 'greening' of the continents acted as a carbon dioxide sink, and atmospheric levels of this greenhouse gas may have dropped. This may have cooled the climate and led to a massive extinction event.

Primitive arthropods co-evolved with this diversified terrestrial vegetation structure. The evolving co-dependence of insects and seed-plants that characterizes a recognizably modern world had its genesis in the Late Devonian period. The development of soils and plant root systems probably led to changes in the speed and pattern of erosion and sediment deposition. The rapid evolution of a terrestrial ecosystem containing copious animals opened the way for the first vertebrates to seek out a terrestrial living. By the end of the Devonian, arthropods were solidly established on the land.