The Triassic

Found out an interesting thing in a paleontology YouTube video the other day. Like many, I’ve had an increasing awareness of and interest in the Triassic and all of the stuff going on during that time period which has never really been treated much in popular literature, and therefore wasn’t well known to the general public. Honestly, it wasn’t well known to specialists either; much of what we’ve learned about the Triassic is pretty new stuff discovered in the last few years, or at most the last couple of decades or so. Popular literature for kids, when I was young, pretty much just had Coelophysis, Plateosaurus, a generic phytosaur (usually Rutiodon, although they usually didn’t identify him) and “Teratosaurus”. Not that Teratosaurus isn’t a real animal, but it was a chimerical combination of a Teratosaurus skull (which is rauisuchid) and Efraasia post-cranial skeletal material (which is prosauropod), and Teratosaurus was not, as advertised fur decades, the first large carnosaurian therapod. Often, popular literature said very little about any of these animals other than that they lived in the Triassic and oh, hey, here’s an illustration of them. For many years, all I knew about phytosaurs was that they were like crocodiles but not, and the illustration of them had their nostrils up close to their eyes instead of on the end of their snouts like a crocodile. For instance.

Slowly the onion has been peeled back. I became aware of what were considered proto-dinosaurs like Lagosuchus and Lewisuchus from Greg Paul’s Predatory Dinosaurs of the World; although now Lagosuchus is usually called Marasuchus (I may have mentioned this before, but I hate seeing great well-known names get memory-holed like this, and sometimes I refuse to go along and keep using the “outdated” names anyway.) The Dinosaurs, a PBS special introduced me to herrerasaurids (or at least Herrerasaurus specifically) and animals like Scaphonyx. I started becoming more acquainted with the cynodonts, the kannemeyeriids and other dicynodontids, and started to become acquainted with the vast array of psuedosuchians who truly ruled the Triassic for the most part. But even then, the specialists didn’t know that much about a lot of stuff and it’s been a very dynamic area with lots of changes coming fast.

One of them which probably isn’t new, but it was new to me was that the Ischigualasto formation, famous for having still the earliest known dinosaurs to date, including Herrerasaurus and Eoraptor, was quite a cool ecosystem, and not tropical at all. In fact, almost all of the dinosaurs were located at relatively cooler latitudes during most of the Triassic, and the hotter more tropical areas were instead dominated by mesothermic pseudosuchians; including many that mimicked famous dinosaur morphologies in many ways; Sillosuchus looking like a prosauropod, for instance, or the bipedal rauisuchians looking very similar to much later appearing therapods, or revueltosaurs being confused for ornithischians, or aetosaurs looking like much later appearing nodosaurs, etc. Some of these also coexisted in the same ecosystems as the early dinosaurs, but the early dinosaurs clearly thrived in the cooler environments, and only spread to the tropical latitudes after the psuedosuchians had the major post-Triassic extinction event; one of the so-called Big Five extinction events and the real reason that the Age of the Dinosaurs even happened. If it hadn’t, the Mesozoic might well have been the Age of the Crocodiles instead.

Another fascinating discovery was the silesaur line; a sister-group of the dinosaurs that were obligate plant-eaters, not too unlike what we’d have expected to see for very early ornithischians. These guys were really just discovered about twenty years or so ago, and the group filled out with more specimens and species, and then, perhaps unsurprisingly, in the last couple of years or so new cladograms are now recovering them as early ornithischians. This actually makes a lot of sense for many good reasons; including that there is a long ornithischian ghost lineage throughout the Triassic until they burst on the scene in the early Jurassic as fabrosaurs and early ornithopods, etc. If the silesaurs are actually the ghost lineage, no longer ghost, then that fills in a major hole in the fossil record, and expands dramatically the scope of dinosaurs, and their variety and diversity during the Triassic. This is an interpretation that is gaining ground, but there’s still some inertia for silesaurs as sister group to dinosaurs rather than early ornithischian dinosaurs, so it hasn’t been universally adopted. In addition, there are some competing models for the structure of the dinosaur family tree, including uniting sauropods and ornithischians as “Phytodinosauria” and even uniting therapods and ornithischians (but not sauropods or their lineage) as "Ornithoscelida". These last two studies have been recovered in a few studies, but not seen as statistically very likely. The silesaurs as early ornithischians is better supported and has been recovered in several phylogenetic studies, but it’s still not seen as sufficiently definitive to replace the null hypothesis from earlier studies that recovered silesaurs just outside of Dinosauria.

In any case, for much of pop science’s coverage of the Triassic, it was seen as merely the preface to the coming of the dinosaurs, and while there were some unusual creatures kicking around, (and I haven’t even touched on drepanosaurs, nothosaurs, tanystropheids, etc.) it was treated as merely the time when somewhat mysteriously, dinosaurs, pterosaurs and mammals all first appeared, but were just setting up the stage for the Jurassic, when things were actually interesting. This isn’t true at all; the Triassic is a fascinating period and the ecosystems that it had are, to me, now among the most interesting out there.