Thanks to remarkably well-preserved skeletons, Late Triassic animals known as aetosaurs, reptiles that coexisted with some of the earliest dinosaurs, are now coming into clearer view. The new fossils reveal that these unusual animals looked and behaved like a cow, crocodile and armadillo hybrid.
The findings, published in the latest issue of the Journal of Vertebrate Paleontology, particularly shed light on a reptile called Typothorax, which was one of the last large herbivores to evolve before dinosaurs would come to dominate the planet.
It's believed that dinosaurs 230 to 200 million years ago avoided the over 8-foot-long and 225-pound Typothorax, which was covered with heavy body armor and had sharp, protruding spikes.
"Most of the dinosaurs we know from this time, like the turkey-sized Coelophysis, were too scrawny to be much of a threat to an armor-plated adult Typothorax," co-author Matthew Celeskey told Discovery News.
Celeskey, an exhibit designer and illustrator at the New Mexico Museum of Natural History and Science, explained that by the Late Triassic, the now-extinct archosaur group had split into two main branches: dinosaurs and their relatives on one side, and the ancestors of crocodiles and their relatives on the other. Typothorax and other aetosaurs fell in the latter group.
The two new Typothorax specimens, found by volunteers Paul Sealey and Scott Sucher in the New Mexico Badlands, show that the bodies of these animals were completely encased from head to toe in bony armor. One surprise discovery was that sharp spikes surrounded the cloaca (the cavity into which the intestinal, genital and urinary tracts open).
Given the arrangement of these spikes, how then did these animals mate?
"Very carefully," said Celeskey. "Or maybe not. Perhaps the spikes were just what they needed to get things going. The truth is we don't know exactly how the cloacal spikes would have affected mating, although I'm confident that two consenting Typothorax would have been able to figure it out."
The new skeletons, for a species called Typothorax coccinarum, also reveal that the reptile had a short and stubby neck, a blunt-nosed head and small, leaf-shaped teeth. Its front limbs sprawled, while its hind limbs were much larger and upright.
Project leader Andy Heckert, a geology professor at Appalachian State University, told Discovery News that Typothorax's main predators were probably phytosaurs, semi-aquatic archosaurs that bore a close resemblance to modern crocodiles, and rauisuchians, toothy, armored archosaurs that looked like lizards on steroids.
Justin Spielmann, who also worked on the study and is Geoscience Collections Manager at the New Mexico Museum of Natural History and Science, added that Typothorax and these two main predators all died out at the end of the Triassic period.
The wave of extinctions at that time likely paved the way for dinosaurs, which "became the predominant terrestrial herbivores and predators for the next 135 million years," said Celeskey.
Nicholas Fraser, Keeper of Natural Sciences at National Museums Scotland, told Discovery News that he found the new study to be "compelling, and the fossils are truly remarkable for their completeness."
"You can almost see (Typothorax) snuffling along looking for tasty shoots or digging away the soil to get at a root," perplexing predators with its body armor and spikes, said Fraser, co-author of the book "Triassic Life on Land: The Great Transition."
"With the earliest dinosaurs, turtles and mammals alongside some weird extinct groups, the Triassic world is a wonderful mix of the ancient and bizarre," Fraser concluded.
"These animals tend to fall into the ancient and rather bizarre category."