The significant idea of the bilaterian body plan is directionality. By moving from a radial (circle) to a bilateral (line) symmetry, life transitioned from a passive state of “being” to an active state of “doing.”
Bilaterian Split: The Origin of Agency Read More »
Before, during, and after the K–Pg extinction: a thriving Late Cretaceous world of dinosaurs, pterosaurs, birds, and flowering plants gives way to the asteroid strike and global collapse that ended the age of non-avian dinosaurs.
The K-Pg Extinction Read More »
The Permian-Triassic extinction was not just the end of many species. It was a planetary reset that destroyed the old synapsid-dominated world and opened the door for the archosaur line that would later give rise to dinosaurs.
The P-T Extinction Read More »
The Cenozoic era starts with the K–Pg extinction 66 million years ago. That event marks the sudden end of the reign of dinosaurs and the rise of mammals and birds.
Cenozoic Era: Age of Mammals & Birds Read More »
The Mesozoic era starts with the end-Permian mass extinction 252 million years ago. Dinosaurs ruled over all, including us. It ends the reign of dinosaurs with the K–Pg extinction 66 million years ago.
Mesozoic Era: Age of Dinosaurs Read More »
The start of the Paleozoic era is marked by burrowing life 538.8 million years ago. The era includes the dominant rise of our ancestors. It ends 252 million years ago with the end-Permian mass extinction, a volcanic cascade global warming event.
Paleozoic Era: The Age of Synapsids Read More »
Before the famous branches split into predators, long-necks, horned giants, and birds, there was one early ancestral species. One population eventually led to all dinosaurs: Allosaurus, Styracosaurus, and Diplodocus.
Dinosauria Emerge: True Dinosaurs! Read More »
Early sample: Aurornis Although the exact early avialan boundary is famously messy, we do know birds evolved from theropos. In the “Great Divide” of dinosaur classification, birds are members of the Saurischia (“lizard-hipped”) branch, specifically the Theropods. These ornithischians, or “bird-hipped” dinosaurs, are dinosaurs like Triceratops and Stegosaurus. Evolution produced a similar hip structure here
Avialae: The Bird Line Diverges (Theropoda) Read More »
Pterosaurs were the first vertebrates to conquer the air, evolving a unique “finger-wing” anatomy that allowed them to dominate the skies for 160 million years.
Pterosaurs Diverge From Dinosaur Ancestors (within Ornithodira) Read More »
LCA of crocodiles and birds — the larger archosaur branch that later gave rise to crocodilians, pterosaurs, dinosaurs, and birds.
Archosauria Diverge Within Reptiles Read More »
Pterosaurs were the first vertebrates to achieve powered flight, but they were not dinosaurs.
In a testament to our understanding of evolution, archosaurs emerged around 255 million years ago, eventually giving rise to dinosaurs about 230 million years ago. Bridging this gap, the dinosauromorphs – a transitional group between archosaurs and dinosaurs – evolved approximately 245 million years ago. One notable early dinosauromorph is Asilisaurus kongwe, found in present-day
Bird-line Archosaurs: Asilisaurus kongwe (within Ornithodira) Read More »
One of the last bird-line archosaurs before true dinosaurs is the Nyasasaurus parringtoni, which lived during the Middle Triassic period, around 243 million years ago. Discovered in Tanzania, Nyasasaurus represents a key transitional form, showcasing features that are both dinosaurian and pre-dinosaurian, highlighting the evolutionary path leading to more well-known dinosaurs of the Late Triassic
Bird-line Archosaur: Nyasasaurus parringtoni Read More »
