Paleontologists have described a completely unexpected new species of reptile that lived 230 million years ago (Triassic period).
Dr. Stocker and co-authors describe Triopticus primus, a bizarre Late Triassic animal, whose skull structure is converged on by distantly related dome-headed pachycephalosaurs. The unique body plans observed in Triopticus primus and other archosaurs at the ‘dawn of the age of dinosaurs’ re-evolved in dinosaurs and crocodylians after the end-Triassic mass extinction. Image credit: Michelle R. Stocker et al.
The ancient reptile has been given the official name Triopticus primus, which means ‘the first of three eyes.’
“From the Latin ‘tri’ (three) and ‘optic’ (vision) for the large opening in the skull roof, resembling a third eye socket. The specific name is from the Latin ‘primus’ (first),” the paleontologists explained.
Triopticus primus belonged to a group of reptiles called archosauriformes.
Complete details of what this creature looked like and how big it was are not yet known, though it was likely no bigger than an alligator.
For now, paleontologists only have a fragment of skull. The remainder of the face and jaw, the vertebrae, and the rest of the skeleton is missing, either long lost to natural elements.
The fossil was found at the Otis Chalk Quarry 3 in Howard County, Texas.
Triopticus primus had a thickened skull roof, just like the dome-headed pachycephalosaur dinosaurs that lived more than 100 million years later.
And even more unexpected, many of the other extinct animals found with this creature resemble later dinosaurs as well.
“Triopticus primus 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,” said Dr. Michelle Stocker, of Virginia Polytechnic Institute and State University and the University of Texas at Austin.
“What we thought were unique body shapes in many dinosaurs actually evolved millions of years before in the Triassic period, about 225 million years ago.”
Convergence – where distantly related animals evolve to look very similar to each other – 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 primus in the Otis Chalk fauna display structures that are easily recognized in later dinosaurs as well, such as the long snouts of Spinosaurus, the toothless beaks of ornithomimids, and the armor plates of ankylosaurs.
“It is extremely rare to have so many diverse species in a single ancient community be converged upon over a broad swath of later geologic time,” the scientists said.
“The Otis Chalk fauna is an amazing single snapshot of geologic time where you have this extraordinary range of animal body plans all present at the same time living together,” said Dr. Stocker, lead author of a report published this week on Triopticus primus in the journal Current Biology.
“Among the animals preserved in the Otis Chalk fauna, Triopticus primus exemplifies this phenomenon of body-shape convergence because its skull shape was repeated by very distantly-related dome-headed dinosaurs more than 100 million years later.”
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 on Earth, 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,” said Dr. Sterling Nesbitt, also from Virginia Polytechnic Institute and State University and the University of Texas at Austin.
“These early body shapes were later mimicked by dinosaurs.”
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Michelle R. Stocker et al. 2016. A Dome-Headed Stem Archosaur Exemplifies Convergence among Dinosaurs and Their Distant Relatives. Current Biology 26: 1-7; doi: 10.1016/j.cub.2016.07.066
