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 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 »
Styracosaurus was a striking horned ancient cousin of Triceratops, showing that ceratopsids branched into different styles long before the dinosaurs came to an end.
Wuerhosaurus shows that the stegosaur branch survived longer than many people realize, but not all the way to the end of the dinosaurs.
The Last Stegosaurus: Wuerhosaurus Read More »
Even near the end, ornithischians remained a diverse and successful branch of plant-eating dinosaurs.
The Last Ornithischians 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 »
Triceratops, one of the last great horned dinosaurs, roamed western North America at the very end of the Age of Dinosaurs with its three horns, broad frill, and heavy four-legged build.
A smaller, earlier horned dinosaur that helps show the transition toward the larger, more elaborate ceratopsids. It did not yet have the full giant frill-and-horn look of Triceratops, but it sits close to that later line in the broader horned-dinosaur story. Lived from about 90 to 89 million years ago.
Bashanosaurus primitivus is one of the earliest known stegosaurs and a strong candidate for representing an early form close to the ancestry of later plated dinosaurs like Stegosaurus.
Bashanosaurus primitivus Read More »
Stegosaurus is the classic plated dinosaur most people picture: large back plates, a small head, and a spiked tail used for defense. It lived late in the Jurassic.
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 »
Ornithodirans were the early branch that later gave rise to both pterosaurs and dinosaurs, including birds.
Ornithischians Diverge Within Dinosauria “Bird Hipped” Read More »
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 »
Before dinosauromorphs like Asilisaurus, the evolutionary lineage would include earlier archosaurs. One such early archosaur is Marasuchus lilloensis, which lived around 240 million years ago. Marasuchus exhibits several primitive features that are on the evolutionary path towards dinosaurs. Kingdom: Animalia > Phylum: Chordata > Class: Reptilia > Order: Dinosauriformes 30 to 40 cm (12 to
Marasuchus lilloensis Read More »
