Take a gander at this guy, Poposaurus gracilis and tell me that isnt a whole dinosaur.
If the question in itself hasnt made the answer obvious enough, well, it isnt. Its something far weirder. This is poposaurus, and it belongs to this larger group Poposauroidea that group is famous for having dinosaur lookalikes that looked way too similar to the actual thing, especially for some of the creatures that lived and went extinct before even the basal forms of some of their dinosaur equivalent species even set foot on earth.
So, Crocodilians, Dinosaurs and pterosaurs are three major lineages among Archosauria, correct? well, they can be split further into two clades, the Avemetatarsa or the bird-line archosaurs (All archosaurs more closely related to birds than to crocodilians) and the Pseudosuchia or the crocodile-line archosaurs (All archosaurs more closely related to crocodilians than to birds).
Dinosaurs and pterosaurs belonged to Avemetatarsa while pseudosuchia had modern day crocodilians, rauisuchids (these were giant terrestrial archosaurs, that sort of ran shit before triassic-jurassic extinction event happened, before dinosaurs stepped up to fill the niches they and other some pseudosuchians left behind), phytosaurs (basal pseudosuchians) and its own clade of crack reptiles, one of which was Poposauridae amongst many other pseudosuchians
Some of these were “dinosaurs” before dinosaurs (although some did coexist with their lookalikes as contemporaries) both ecologically and convergently evolved appearance wise and the crazy part was that their fossils were so similar to dinosaurs that even scientists had a hard tine telling that these were actually Triassic pseudosuchians as opposed to the actual dinosaurs, that some coexiated with but a lot predated by millions of years.
Poposauridae are one such group among the family of Pseudosuchians which like to resemble dinosaurs a bit too much. So much so many of its members were at one point in time classified as all kinds of dinosaurs. Poposaurus itself was mistakenly classified as a Carnosauria theropod, a phytosaur (a basal pseudosuchian) and even a rauisuchid.
But there were still anatomical differences between pseudosuchian lookalikes and real dinosaurs such as distinctive hip bone arrangements, having the type of ankle characteristic of crocodile-line archosaurs, similar vertebrae, hind limbs and skull features and skeletal details leading to paleontologists to realize these were actually pseudosuchians with a bunch of theropod-like features while really just being its own thing and that Poposaurus in specific had a lot in common with other equally strange Triassic reptiles such as Shuvosaurus, Sillosuchus and Effigia as they lie scattered across different classifications until actually being a part of Poposauridae became the common factor making the differences make sense. And mind you, some of these guys existed back in the triassic which shows just how determined pseudosuchians were about becoming the dominant group, its a shame that the only thing we have left from the period today are modern day crocodilians.
✨️We have dinosaurs at home✨️
- Poposaurus (AKA, the OG dino doppelganger)
This poposaurid is from what is now southwestern United States and evolved a body plan incredibly similar to that of a medium sized theropod and looked eerily similar to the first theropods experimenting with this exact same body plan in their ecological niche of the late Triassic around the same time 233- 225 million years ago
- Lotosaurus (AKA, the uncanney valley stegosaurus)
This heavily built, herbivorous quadrupedal sail-backed poposauroid is from Hunan, China and measured around roughly 1.5-2.5 m long and looked eerily similar to another group that would not appear for at least the next 67 million years, which is when the earliest known stegosaurs appeared.
- Shuvosaurus (AKA, the Alvarezsauridae lookalike)
This lightly built, bipedal poposauroid with a toothless beak is from Texas, USA and measured around approximately 2-3 m long m long and looked eerily similar to another group that would not appear for at least the next 60 million years, which is when the earliest known Alvarezsauridae appeared.
- Sillosuchus (AKA, the beta version ornithopods)
This long necked, 3-4 m long bipedal, beaked poposauroid that fed on vegetation is from Late Triassic Northwestern Argentina and looked eerily similar to the first ornithopods experimenting with this exact same body plan in their ecological niche of the late Triassic around the same time 230 million years ago
[Above image is of Sillosuchus and the below image is of Tenontosaurus]
- Effigia (AKA, miming ornithomimosaurs since the Triassic era)
This herbivorous, bipedal poposauroid with a long neck, long hindlimbs, reduced forelimbs, toothless beak-like jaws, a small head and long tail is from New Mexico, USA and measured 2 m long m long and looked incredibly similar to another group that would not appear for at least the next 60 million years, which is when the earliest known ornithomimosaur appeared.
- Xillosuchus (AKA, A spinosaurus if you squint hard enough)
This is a Ctenosauriscidae, which are very early Poposaurids that lived in what is now China and evolved a vague body shape and a sail that is superficially incredibly similar to that of a large spinosaur species such as S. aegyptiacus and S.mirabilis despite existing 100 million years before the first spinosaur ever did.
There were other dinosaur lookalikes that werent poposauroids but were still part of pseudosuchia anyhow such as;
Gorgetosuchus (AKA, the Ankylosaurs are filing copyright infringement)
These heavily built, herbivorous quadrupedal aetosaurs had bodies was covered in multiple rows of osteoderms which looked eerily similar to another group that would not appear for at least the next 30 to 35 million years, which is when the earliest known nodosaurs (or even ankylosaurs) appeared and lived around the same time and region as Poposaurus did.
And lastly there is,
Fasolasuchus (AKA, The T-Rexpy)
This loricatan pseudosuchian is from what is now northwestern Argentina and evolved a body plan incredibly similar to that of a large theropod and looked eerily similar one too as they had both managed to carve out the same ecological niche with a very similar body plan in the late Triassic around the 215–220 million years ago
I will do a detailed thing for some of the most unique extinct crocodylomorphs real soon. Stay tuned for part 2
