An image from a powerpoint I’m making, depicting what the relations of some animals commonly called “dinosaurs” actually are compared to actual dinosaurs. Red are the non-archosaurs, yellow are non-dinosaurian archosaurs, and green are the dinosaurs.

That rauisuchian looks wonky, I know.

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Two artists’ renderings of “Proavis”, a hypothetical bird ancestor. The lizard-limbed would-be creature is certainly a product of its time, as birds were once thought to be descendants of the clade Pseudosuchia (the name Crurotarsi is more commonly used today and generally includes the same taxa). Traditionally, Pseudosuchia was considered a suborder of the now-obsolete order Thecodontia.

image

Gerhard Heilmann laid out the hypothesis of a pseudosuchian ancestry of birds in his highly influential 1926 book The Origin of Birds, which was considered the last word on the subject of bird evolution for several decades after its publication. Heilmann acknowledged a close relationship between non-avian theropod dinosaurs and birds but rejected the notion that the former directly gave rise to the latter. One example of his reasoning was that birds have a furcula (wishbone), a feature which non-avian theropods did not appear to him to possess (though we now know otherwise), yet ancient reptilian fossils that predated dinosaurs did show clear evidence of a furcula-like structure. Though the evidence to which we now have access overwhelmingly supports the hypothesis that birds are indeed the descendants of dinosaurs rather than the crocodile-like “thecodonts”, much of the book’s research remains of interest.

(“Proavis” art sources: x x)

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Poposaurus

… is an extinct genus of pseudosuchian archosaur from the Late Triassic of the southwestern United States. It belongs to the clade Poposauroidea, an unusual group of Triassic pseudosuchians that includes sail-backed, beaked, and aquatic forms. Since it was first described, Poposaurus has been variously classified as a dinosaur, a phytosaur, and a “rauisuchian”.

Like theropod dinosaurs, Poposaurus was an obligate biped, meaning that it walked on two legs rather than four. However, as a pseudosuchian, it is more closely related to living crocodilians than to dinosaurs. Poposaurus is thought to have evolved this form of locomotion independently, possibly from early archosaurs’ ability to high walk

(read more: Wikipedia)                (illustrations by Smokeybjb)

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Erpetosuchus is an extinct genus of pseudosuchian archosaur from the Late Triassic. The relationship of Erpetosuchus to other archosaurs is uncertain. In 2000 and 2002, it was considered a close relative of the group Crocodylomorpha, which includes living crocodylians and many extinct relatives. However, this relationship was questioned in a 2012 analysis that found the phylogenetic placement of Erpetosuchus to be very uncertain…

(read more: Wikipedia)

(illustrations: T - Mojcaj; B - Nobu Tamura)

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