#poposauroids

[dinosaur-discourse]

Crocodylo-Month, Day 9: Family Shuvosauridae

Looking at Shuvosaurus, you would probably never assume that it was a relative of crocodilians.  Indeed, upon its discovery in 1993, paleontologists initially assumed it was an ornithomimosaur, based on its long neck, toothless beak, and bipedal stance.

It wasn’t until 2006, when the related species Effigia (pictured above) was described, that Shuvosaurus was revealed to have been a member of Pseudosuchia.  Specifically, it belonged to Poposauroidea, along with previously covered animals Qianosuchus, Arizonasaurus, and Lotosaurus.  It formed  its own unique family (Shuvosauridae) with Effigia.

The shuvosaurids were astonishingly similar to the ornithomimosaurs, and probably had similar lifestyles.  They were adapted for fast running, and were probably omnivores or herbivores.  They both lived in the southwestern U.S. during the Late Triassic - a time and place that was apparently a hotbed of crocodilian diversity.

Given the dinosaur-like proportions of the shuvosaurids, as well as the presence of deactivated feather-forming genes in modern crocodilians, it’s possible that these animals (along with some of their contemporaries) were feathered.  If that were the case, they would have been nearly indistinguishable from certain coelurosaurian theropods.

(Images by Nobu Tamura.)

[dinosaur-discourse]

Crocodylo-Month, Day 4: Lotosaurus

(Image by Nobu Tamura.)

Lotosaurus is another poposauroid, belonging to a more derived family than the previously covered poposauroids, Qianosuchus and Arizonasaurus.  (Although its dorsal ridge is quite similar to Arizonasaurus’s, the two animals are not closely related; the “sail back” is believed to have evolved independently on two different occasions among the poposauroids.)

Lotosaurus is one of the most completely known poposauroids, thanks to a bonebed of ten individuals (indicating that it may have lived in large herds) found in a Middle Triassic fossil formation of central China.  Its toothless beak suggests that it was a large herbivore, unlike any of its known relatives.

[dinosaur-discourse]

Crocodylo-Month, Day 3: Arizonasaurus

(Image by Nobu Tamura.)

Arizonasaurus was a poposauroid belonging to the family Ctenosauriscidae, a family distinguished by their “sail backs”.  It’s unclear what purpose these structures served; theories include thermoregulation, visual communication and display, and “shock absorption” to alleviate the stresses of bipedal locomotion (although the last one is probably not true, as all of these animals were likely quadrupedal).

Arizonasaurus lived in Arizona (of course) about 243 million years ago, making it one of the oldest known archosaurs (along with its other poposauroid relatives).  At ten feet long, Arizonasaurus was one of the largest carnivores in its native ecosystem, and was probably an apex predator.  It likely preyed on many of its smaller relatives.

[dinosaur-discourse]

The Carolina Butcher

Last year, a new species of crocodilian relative was discovered from Late Triassic North Carolina.  Dubbed Carnufex carolinensis - “the Carolina butcher” - this animal grew up to nine feet long, and was capable of walking on its hind legs.

Carnufex is interesting for being a basal crocodylomorph - a member of the clade that includes modern crocodilians.  This proves that crocodylomorphs were vying for apex-predator positions during the Late Triassic, along with early theropods, as well as several other groups of pseudosuchians known as rauisuchids and poposauroids.  

This extreme diversity of predators proved unsustainable, and many of these animals - including Carnufex - died out by the time the Triassic period was over.  Theropod dinosaurs became the top predators for hundreds of millions of years afterward, while Carnufex’s surviving relatives were relegated to less dominant positions.