Curated timeline

Dinosaur Evolution

60 Milestones of the Mesozoic: The definitive chronological guide to the evolution, diversification, and extinction of the non-avian dinosaurs.

• Permian-Triassic Mass Extinction (about 252 Million Years Ago)

  The 'Great Dying' wipes out 90% of Earth's species, clearing ecological niches for the ancestors of dinosaurs to emerge.

• Divergence of Avemetatarsalia (about 245 Million Years Ago)

  The archosaur lineage splits, separating the ancestors of crocodiles from the bird-line archosaurs that would become dinosaurs.

• Appearance of Nyasasaurus (about 243 Million Years Ago)

  Fossils from Tanzania suggest Nyasasaurus may be the earliest known dinosaur or its closest relative.

• The Carnian Pluvial Episode (about 232 Million Years Ago)

  A million-year period of increased rainfall triggers a major shift in flora, allowing early dinosaurs to expand rapidly.

• Evolution of Eoraptor (about 231 Million Years Ago)

  One of the earliest definitive dinosaurs, Eoraptor was a small, bipedal omnivore found in South America.

• Saurischia and Ornithischia Split (about 230 Million Years Ago)

  Dinosaurs divide into two main groups based on hip structure: the 'lizard-hipped' Saurischians and 'bird-hipped' Ornithischians.

• Rise of the Herrerasaurids (about 230 Million Years Ago)

  Among the first large predatory dinosaurs, Herrerasaurus showcases early specialized hunting traits.

• Pisanosaurus: Early Ornithischian (about 228 Million Years Ago)

  One of the earliest known bird-hipped dinosaurs appears in South America, representing the root of the herbivore lineage.

• Diversification of Prosauropods (about 221 Million Years Ago)

  Early long-necked herbivores like Plateosaurus appear, marking the start of the sauropod lineage.

• Coelophysis: Early Theropod Success (about 210 Million Years Ago)

  Highly successful, slender pack-hunters like Coelophysis dominate North America, showing early social behaviors.

• Triassic-Jurassic Extinction (about 201 Million Years Ago)

  A mass extinction eliminates many competing reptiles, allowing dinosaurs to become the dominant land animals.

• Evolution of Heterodontosaurids (about 200 Million Years Ago)

  Small ornithischians evolve specialized teeth, including canine-like tusks, for a more varied diet.

• Dilophosaurus: Early Jurassic Apex (about 193 Million Years Ago)

  Characterized by double head crests, Dilophosaurus was one of the first large predatory dinosaurs of the Jurassic.

• Cryolophosaurus: The 'Elvis' Dinosaur (about 190 Million Years Ago)

  A large theropod found in Antarctica, proving dinosaurs lived in high-latitude, cooler environments.

• The Dawn of Giants (Sauropoda) (about 190 Million Years Ago)

  True sauropods begin to reach massive sizes, evolving specialized vertebrae for their long necks.

• First Armored Dinosaurs (about 185 Million Years Ago)

  Scelidosaurus appears as an early ancestor to later armored giants like Stegosaurus and Ankylosaurus.

• Megalosaurus and the Middle Jurassic (about 166 Million Years Ago)

  Large apex predators like Megalosaurus rule Europe. It would later become the first dinosaur ever scientifically described.

• Rise of the Mamenchisaurids (about 160 Million Years Ago)

  Sauropods in East Asia evolve extraordinarily long necks, some exceeding 15 meters in length alone.

• Yi qi: The Bat-Winged Dinosaur (about 160 Million Years Ago)

  A bizarre theropod from China that evolved membrane wings similar to bats, showing experimental flight paths.

• Mammals in the Dinosaur Era (about 160 Million Years Ago)

  Early eutherian mammals like Juramaia evolve alongside dinosaurs, mostly remaining small and nocturnal.

• The Golden Age of Sauropods (about 155 Million Years Ago)

  Giant dinosaurs like Diplodocus and Apatosaurus dominate the landscape of the Late Jurassic Morrison Formation.

• Appearance of Brachiosaurids (about 154 Million Years Ago)

  Sauropods with longer front legs than back legs appear, allowing them to graze on the highest tree canopies.

• Ceratosaurus: The Horned Predator (about 153 Million Years Ago)

  A unique Jurassic carnivore with a prominent nose horn and blade-like teeth, coexisting with Allosaurus.

• Evolution of Stegosaurids (about 150 Million Years Ago)

  Iconic plated dinosaurs like Stegosaurus thrive, featuring defensive spikes and dorsal plates.

• Compsognathus: The Mini Predator (about 150 Million Years Ago)

  One of the smallest known dinosaurs of its time, this agile theropod hunted lizards and insects in Europe.

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