First Therapsids
Therapsids mark the point where the mammal-side branch became more active, more specialized, and more clearly aimed toward the later mammal body plan.
Evolution
Last Non-Mammaliaform Cynodonts
Tritylodontids were not mammals, but they were late-surviving mammal-side cousins that carried many mammal-like traits without crossing into the mammaliaform line.
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Last Non-Cynodont Therapsids
Dicynodonts were late-surviving non-cynodont therapsids: mammal-side animals, but not on the direct road to mammals.
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Last Non-Mammal Mammaliaforms
Not every mammaliaform became a mammal; some were late-surviving side branches near the mammal line.
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First Cynodonts
Cynodonts were a more advanced branch of therapsids where the mammal-like jaw, teeth, palate, and breathing package began to come together.
First Crown Mammals
Crown mammals are the branch that includes the common ancestor of all mammals alive today and every descendant of that ancestor.
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Last Non-Therapsid Synapsids
Late caseids represent the fading old-line synapsids: still mammal-side animals, but not yet therapsids.
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First Synapsids
Early synapsids looked reptile-like, but they were not on the reptile line. They were the first recognizable step on the long road toward mammals.
Diatoms Emerge
Diatoms began as tiny glass-shelled “silica” algae, with round centric forms appearing first and elongated pennate forms later adding direction, symmetry, and movement to the microscopic world.
Triassic–Jurassic Extinction: Volcanoes Open the Age of Dinosaurs
The Triassic–Jurassic extinction cleared ecological space for dinosaurs to become the dominant land animals of the Jurassic.
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Oceans Lose Their Breath
The Devonian extinction shows that evolution can be reshaped not by one sudden blow, but by a long collapse in ocean health.
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Ordovician–Silurian Extinction: Ice Strikes the Seas
The Ordovician–Silurian extinction shows how climate change can reshape evolution by collapsing old ecosystems and opening space for new life.
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Snowball Earth: When Ice Reached the Equator
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.
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Bilaterian Split: The Origin of Agency
The animal evolution of the bilaterian body plan is directionality, which gave us agency.
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The K-Pg Extinction
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 P-T Extinction
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.
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The Synapsid World of the Late Permian
About 255 million years ago, during the late Permian, our mammalian ancestory, the synapsids ruled the land.
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Cenozoic Era: Age of Mammals & Birds
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.
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Mesozoic Era: Age of Dinosaurs
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.
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Paleozoic Era: The Age of Synapsids
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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