Middle Triassic–Present, 245–0 Ma (possible Early Triassic record)
|Clockwise from top-left:
Tupuxuara leonardi (a pterosaur),
Alamosaurus sanjuanensis, (a sauropod),
Tsintaosaurus spinorhinus (an ornithopod),
Daspletosaurus torosus (a tyrannosaur),
Pentaceratops sternbergii (a ceratopsian),
and Grus grus (an extant avian).
Avemetatarsalia (meaning "bird toes") is a clade name established in 1999 for all crown group archosaurs that are closer to birds than to crocodiles. An alternate name is Panaves, or "all birds", meaning all animals, living or extinct, which are more closely related to birds than to crocodiles.
Members of this group are basically the dinosaurs (including birds), the pterosaurs, and some earlier animals which are a bit difficult to place. They are one wing of the Archosaurs, the other being the Crurotarsi.
Origin[change | change source]
Bird-line archosaurs appear in the fossil record early in the Middle Triassic about 245 million years ago (mya), with the dinosaur-like Asilisaurus. However, Lower Triassic fossil footprints reported in 2010 from Poland may belong to a still more primitive type. If so, the origin of avemetatarsalians would be pushed back to around 249 mya. The oldest Polish footprints were made by an unknown small quadrupedal animal, but slightly later footprints show that moderately large bipedal dinosauromorphs had appeared by 246 mya.
The Permian-Triassic extinction event is dated at about 250 mya. The Triassic–Jurassic junction is about 200 mya. The age of the footprints suggests that the rise of the dinosaurs was slow and drawn out across much of the Triassic.
- Crurotarsi: The crocodile line of crown-group Archosauria
References[change | change source]
- Benton, M.J. (1999). "Scleromochlus taylori and the origin of dinosaurs and pterosaurs". Philosophical Transactions of the Royal Society of London 354: 1423–1446.
- Brusatte, S.L.; Niedźwiedzki, G.; and Butler, R.J. (2010). "Footprints pull origin and diversification of dinosaur stem lineage deep into early Triassic". Proceedings of the Royal Society B 278. doi:10.1098/rspb.2010.1746. PMC 3049033. PMID 20926435.