The Avashishta bacharamensis is dated to about 72 to 66 million years ago. It is known from a single tooth from Late Cretaceous India, Avashishta may represent a late-surviving haramiyidan, a non-mammalian mammaliaform near the mammal line. Its classification is debated, so this is best marked as a tentative “possible last known” entry. For sure, […]
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The Brasilodon is an early mammal/mammaliaform threshold at 225 million years ago. The more conservative textbook marker is the Morganucodon at 205 million years ago. The Natural History Museum notes that Brasilodon dates to 225 million years ago and predates Morganucodon, which is usually considered the first mammal, by about 20 million years.
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Using Tritylodontidae again, same as last n0n-mammaliaform therapsid. They are the best public-facing “last non-mammal cynodont” marker: advanced, rodent-like, herbivorous cynodonts that persisted into the Early Cretaceous. Nature describes tritylodontids as nonmammaliaform herbivorous cynodonts that originated in the Late Triassic, diversified in the Jurassic, and survived into the Early Cretaceous.
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For the beginning of Cynodonts, use the Late Permian, around 260 MYA, with early forms such as Procynosuchus. This is the branch where the mammal-like jaw, teeth, palate, and breathing package really starts tightening toward mammals.
The clean marker here is Tritylodontidae. They were cynodont therapsids close to mammals but outside Mammaliaformes, and they survived into the Early Cretaceous. Britannica specifically notes that the last known tritylodontids died out about 125 MYA.
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Raranimus is a good first-known marker for Therapsida. It is usually described as the most basal known therapsid from the Middle Permian. Britannica gives therapsids as a synapsid subgroup that first appears in the Permian and later gives rise to mammals.
For the end of the older synapsid stage, I’d use late caseids as your marker. Caseids are basal/non-therapsid synapsids that persisted into the Middle Permian, with the last known forms around the Roadian–Wordian range, before disappearing as therapsids took over.
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Echinerpeton and Archaeothyris are among the oldest known synapsids. They mark the mammal-side branch of amniotes, recognized by the single temporal opening behind the eye. UCMP frames Synapsida as a 300-million-year-old group with mammals as one surviving branch, while Archaeothyris is commonly treated as one of the oldest undisputed synapsids.
The Triassic–Jurassic extinction cleared ecological space for dinosaurs to become the dominant land animals of the Jurassic.
Triassic–Jurassic Extinction: Volcanoes Open the Age of Dinosaurs Read More »
The Devonian extinction shows that evolution can be reshaped not by one sudden blow, but by a long collapse in ocean health.
Oceans Lose Their Breath Read More »
The Ordovician–Silurian extinction shows how climate change can reshape evolution by collapsing old ecosystems and opening space for new life.
Ordovician–Silurian Extinction: Ice Strikes the Seas Read More »
Snowball Earth was a time when our planet may have frozen nearly from pole to pole, testing life and setting the stage for later biological change.
Snowball Earth: When Ice Reached the Equator Read More »
The animal evolution of the bilaterian body plan is directionality, which gave us agency.
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.
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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 »
About 255 million years ago, during the late Permian, our mammalian ancestory, the synapsids ruled the land.
The Synapsid World of the Late Permian 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.
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This trilobite reminds us that early animal life was already complex, varied, and successful hundreds of millions of years before dinosaurs, birds, or mammals ever appeared.
