#triopticus primus

By Tyler Young/ @cry-olophosaurus​

Etymology: Three eyes

First Described By: Stocker et al. 2016

Classification: Biota, Archaea, Proteoarchaeota, Asgardarchaeota, Eukaryota, Neokaryota, Scotokaryota Opimoda, Podiata, Amorphea, Obazoa, Opisthokonta, Holozoa, Filozoa, Choanozoa, Animalia, Eumetazoa, Parahoxozoa, Bilateria, Nephrozoa, Deuterostomia, Chordata, Olfactores, Vertebrata, Craniata, Gnathostomata, Eugnathostomata, Osteichthyes, Sarcopterygii, Rhipidistia, Tetrapodomorpha, Eotetrapodiformes, Elpistostegalia, Stegocephalia, Tetrapoda, Reptiliomorpha, Amniota, Sauropsida, Eureptilia, Romeriida, Diapsida, Neodiapsida, Sauria, Archosauromorpha, Crocopoda, Archosauriformes incertae sedis

Referred Species: T. primus

Status: Extinct 

Time and Place: 227 to 226 million years ago, in the Norian of the Late Triassic

Triopticus is known only from the Otis Chalk in Texas, the United States

Physical Description: Triopticus is a very puzzling and frustratingly enigmatic reptile, primarily because it is only known from the back portion of its skull and nothing else, leaving the shape of its body and even the size and shape of its snout a complete and utter mystery. We can’t even rely on phylogenetic bracketing to give us a guide of how it may have looked because its relationships cannot be pinned down beyond Archosauriformes. Even its body size is unclear, but it wasn’t a very big animal at least—the back of its skull could fit in the palm of your hand, so maybe around a metre long.

Nonetheless, the piece of skull that is known is very odd indeed. The back of its skull is remarkably similar to those of pachycephalosaurid dinosaurs, in that Triopticus was also a “bone head” with a thick bony “dome” over its head—it even flares out over the back and sides of the head like in pachycephalosaurs. Unlike pachycephalosaurs, however, the “dome” of Triopticus was not a single smooth structure, but was actually made up of five fused bosses on the bones of the skull that have clumped together to form a single bony dome-like structure. But, of course, the dome of Triopticus is even stranger than that of the pachycephalosaurs’. Right in the centre of the dome, between the bosses, there is a hole that drops right down to the roof of the skull. Like a doughnut. Why? No one knows. The hole happens to sit over right where the pineal gland could have been, and so the hole may have opened for a “third eye” on the top of its head, like many modern lizards and the tuatara have (this is where it gets its name!). And yet, the opening for the third eye was lost in the ancestor of Archosauriformes, so we shouldn’t expect Triopticus to have one in the first place. For that matter, the texture of the bone inside the hole is exactly the same as it is on the inside, implying it was covered in hard, opaque keratin like the rest of the dome. So Triopticus probably really did just have a hole in its head, you have to wonder how it kept that thing clean, or stop it from collecting rainwater.

As for the rest of the body, as frustratingly unclear as its relationships are, we can at least make an educated guess based on other archosauriforms. It was probably quadrupedal, with not very long sprawled to semi-erect legs, a long tail, and maybe some osteoderms running down its back. Of course, considering how weird just the back of its head is, and how other Triassic Weirdos have surprised us, I wouldn’t be surprised if Triopticus turned out to be weird all over. Maybe it was a biped with tiny forelimbs to really take the mickey out of the pachycephalosaur-convergance, who knows. (As it happens, the shape of its inner ear might suggest it really was bipedal, but the evidence is tenuous.)

Diet: Without any jaws and teeth, the diet of Triopticus is a mystery. All other known non-archosaur archosauriforms were carnivores, so it’s quite possible Triopticus was too. But there’s a first time for everything, and maybe the rest of its skull was just as abberant as its dome.

Behavior: Any and all speculations on the behaviour of Triopticus has to revolve around its dome. Fortunately, domes are interesting structures in animals, so there’s a decent amount to say. The obvious interpretation is that the dome convergently evolved for the same purposes suggested for pachycephalosaurs: head-butting. The utility of pachycephalosaur domes has been hotly debated, and presumably the same arguments apply here. Alternatively, the dome could have been just used for display. Either case implies Triopticus were social animals, either using the dome for visual communication or in confrontations between them. Triopticus had particularly big eyes and optic nerves for an archosauriform, so good vision must have been important for whatever it was doing. As before, any other behaviours are a mystery, although as an archosauriform we can reasonably speculate that it laid eggs and probably cared for its young to an extent.

Ecosystem: In the Otis Chalk, Triopticus co-existed with various other stem-archosaurs, including the herbivorous allokotosaur Trilophosaurus, the heavily armoured and boxy Doswellia, the phytosaurs Parasuchus and Angistorhinus, and three species of aetosaur. It also coexisted with at least four dinosaurmorphs, including the lagerpetid Dromomeron, a silesaurid, and the predatory theropods Chindesaurus and Lepidus. There was also the large predator Poposaurus, and even an ornithomimid-like shuvosaurid here too. This ecosystem in some ways was almost like a premonition of the later Cretaceous ecosystems, with phytosaur-like crocodiles, aetosaur-like ankylosaurs, poposaurid-like theropods, shuvosaurid-like ornithomimids, and even the Triopticus-like pachycephalosaurs. Whether Triopticus filled a similar ecological role to the pachycephalosaurs, and not just visual, is up for debate, and its lifestyle remains unknowable.

Other: The discovery of Triopticus and its uncanny similarity to pachycephalosaurs prompted a statistical analysis comparing the body types of various Triassic archosaurs and stem-archosaurs to those of Cretaceous dinosaurs. What they found was substantial overlap, so the eerie similarity between certain Triassic reptiles and dinosaurs wasn’t just people seeing things. The fact simply seems to be that Triassic stem- and crown-archosaurs had already evolved many of the distinctive body-types first known in—and thought to be characteristic of—dinosaurs. Triopticus now adds pachycephalosaurs into the “Triassic did it” roster, which at the time of discovery left only the giant sauropodomorphs, maniraptorans, and ceratopsians as the only ones not represented in the Triassic. Then Shringasaurus rolled around...

~ By Scott Reid

Sources under the cut

Triopticus and Mushroom