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.