A newly-described species of extinct reptile that roamed Texas more than 200 million years ago had a strikingly dome-shaped head with a very thick skull. A large natural pit on top lent the appearance of an extra eye.
Researchers looked at the 230-million-year-old skull in the collection at the University of Texas at Austin’s Jackson School of Geosciences. The new species, dubbed Triopticus primus, meaning “the first with three eyes,” was also scanned in a CT lab to reconstruct the internal anatomy, which would not be visible without cutting the bones into pieces.
The findings reveal new clues about the evolutionary history of dinosaurs because the thickened skull roof is nearly identical to that of the distantly related pachycephalosaur dinosaurs that lived more than 100 million years later. Many of the other extinct animals found with Triopticus also resemble later dinosaurs.
“Triopticus is an extraordinary example of evolutionary convergence between the relatives of dinosaurs and crocodylians and later dinosaurs that is much more common than anyone ever expected,” says lead author and Virginia Tech research scientist Michelle Stocker. “What we thought were unique body shapes in many dinosaurs actually evolved millions of years before in the Triassic Period.”
Convergence—where distantly related animals evolve to look similar to one another—is a widely recognized phenomenon in evolutionary biology. A classic example of this is a bird wing and a bat wing—both animals use their wings for flight, but the inner details of those wings are different and evolved independently.
Many of the other Triassic reptiles buried with Triopticus display structures that are also easily recognized later in dinosaurs, such as the long snouts of Spinosaurus, the toothless beaks of ornithomimids, and the armor plates of ankylosaurs. It’s extremely rare to have so many diverse species in a single ancient community be converged upon over a broad swath of later geologic time, researchers say.
Dinosaurs, like these distant cousins from the Triassic Period, are all reptiles. Reptiles rapidly evolved in terms of numbers of species soon after the greatest mass extinction of all time, at the end of the Permian Period.
“After the enormous mass extinction 250 million years ago, reptiles exploded onto the scene and almost immediately diversified into many different sizes and shapes. These early body shapes were later mimicked by dinosaurs,” says Sterling Nesbitt, assistant professor of paleontology at Virginia Tech and coauthor of the study in the journal Current Biology.
Complete details of what Triopticus primus looked like and how big it was are not yet known, though it was probably no bigger than an alligator. For now, researchers only have a fragment of skull. The remainder is missing, either long lost to natural elements, still waiting to be found out in the field, or inside a plaster jacket not yet opened at a lab.
Though many fossils are uncovered during long stints of dusty fieldwork in far-off places, the team’s discovery of this specimen—originally collected near Big Spring, Texas, by the Work Projects Administration (WPA) in 1940—happened in the Jackson School’s Texas Vertebrate Paleontology Collections in 2010, where it had been lying in plain sight for 70 years.
It’s not uncommon for new species to be found in fossil collections around the world. During the Depression, workers on the WPA found so many fossils during a short time span that they didn’t have time to clean all of them.
Source: University of Texas at Austin