For years it had remained there, one of those pieces that pass from one drawer to another because no one knows quite what to do with it. Then someone really set their sights on us again, and that fossil skull of a dinosaur changed the history of the Triassic. Bringing him out of the shadows was Simba Srivastava, a senior geosciences student at Virginia Tech.
In the laboratory he showed it with an almost comical frankness, inviting those in front of him to stick a finger into the brain cavity of the dinosaur and defining it without wide turns as a disastrous specimen, so badly damaged as to be almost disturbing. Precisely for this reason the work required patience, stomach and a considerable amount of obstinacy. For two years Srivastava reconstructed the skull piece by piece and tried to figure out where to place it in the dinosaur evolutionary tree. The result ended up Papers in Palaeontology and adds a heavy piece to the story of how dinosaurs conquered the Jurassic.
A dinosaur that no one expected
The story of the find begins in 1982, in Ghost Ranch, New Mexico, a desert area in the southwestern United States well known to paleontologists for its Triassic fossiliferous levels. A team from the Carnegie Museum of Natural History found it. Then the skull disappeared from center stage. Over thirty years passed, until Sterling Nesbitt rediscovered it in a drawer and took it to Virginia Tech to study it better together with Michelle Stocker. Usually such work ends up in the hands of researchers with more expertise behind them. Here, however, they have involved Srivastava since his first university year. And he took over the entire project.
The key came from computed tomography. The scans allowed us to digitally separate the compressed bones, distinguish what looked like an indistinct mush in the block and reconstruct a three-dimensional version of the skull, even 3D printed. From there the animal’s identity emerged: a carnivorous dinosaur that lived in a very remote era, more than three times older than that of Tyrannosaurus rex.
We are towards the end of the Triassic, the period that goes from approximately 252 to 201 million years ago. At that point the dinosaurs did not yet have the role of absolute dominators that cinema has nailed down in everyone’s imagination. The terrestrial planet was crowded with other protagonists: ancient relatives of crocodiles, early relatives of mammals, evolutionary lines that competed for space and survival. The reversal came with the end-Triassic extinction, when much of the competition disappeared and dinosaurs found themselves occupying the main stage. Srivastava summed it up with a simple image: from supporting actors to stars of the show.
The problem is that fossils from that passage remain rare. Those preserved well even more so. This is why a skull in such bad shape is worth so much: it straddles a decisive phase and tells of a world that we know at times, in flashes, with many gaps still in the middle.
Wide cheekbones, short muzzle and the look of a killer puppet
The skull, although deformed, retained enough details to understand that this dinosaur was outside the canon. I had very developed cheekbonesa large braincase, and most likely a short, deep snout. In the first dinosaurs, characteristics like this had never arisen with this combination. The message, quite clear, is that those groups were experimenting with more varied and complex forms than previously thought.
At that point the name also arrived: Ptychotherates bucculentus. From Latin, more or less, it means “bent hunter with full cheeks”. A technical, even elegant name for an animal that according to a paleoartist had the appearance of a “murder muppet”, a kind of killer puppet with a face too strange to go unnoticed.
After years of analysis, the team placed the new dinosaur among the Herrerasauriaone of the oldest groups of carnivorous dinosaurs known. The really interesting thing lies in the time in which it lived: this animal seems to belong to the last survivors of its lineage. And it is here that the skull stops being a curious find and becomes a thorn planted in a narrative that already seemed quite settled.
The rocks where it was found Ptychotherates they could date back to very little before the end-Triassic extinction. After that point, members of the same group no longer appear. The reading proposed by the scholars opens up an important consequence: that extinction overwhelmed the rivals of the dinosaurs and also erased some lines of dinosaurs that had been present for a long time. A broader, harder, more selective snip than what is usually said when talking about the rise of the dinosaurs.
There is also another important detail. Herrerasaurs this late in the Triassic are not seen elsewhere. For this reason, scholars think that the area that today corresponds to the American southwest may have been their last refuge, a sort of edge of the world for a lineage that was about to end.
All this passes through a single skull. A. It’s in the hands of a student, yet it handles an enormous amount of absences. It is the only evidence that dinosaurs of this group arrived so far in time, at these latitudes, with this skull shape.
