Leaping Lagerpetids, and other updates

 

Preserved elements of Venetoraptor gassenae, from Müller et al. (2023).

I've long considered the Triassic to be the most fascinating period in Earth's history (aside from, perhaps, our own). As well as being a crucial period in understanding the history of Earth's ecosystems and recovery from extinction events, the Triassic has always had an allure and mystery to me, owed in part to its enigmatic, almost alien animals. Researchers have likewise been confounded by many mysteries relating to the Triassic over the years, including the origin of ornithischian dinosaurs. The origins of another group at roughly the same time have proved equally enigmatic: the pterosaurs, yet again.

Pterosaurs, of course, were flying archosaurs that were diverse through most of the Mesozoic, and happen to have been dinosaurs' closest cousins. In my last post, I examined the final extremity of the pterosaurs' existence, at the end of the Cretaceous. In this one I'll be touching (albeit lightly) on the other extremity, namely their beginnings.

And the occasion for this topic? Why, it's Venetoraptor gassenae, an animal described in Nature by Rodrigo T. Müller and colleagues last week. Although neither a dinosaur nor a pterosaur, it is a part of the group containing both, Ornithodira. Like the majority of early ornithodirans thus far, it's from the southern continents, specifically Rio Grande do Sul, Brazil, and is named after the nearby locality of Vale Vêneto (not Venice, as I'd assumed at first glance).

Venetoraptor is a lagerpetid, a group of archosaurs known of since the 1970s, but all species but one were only discovered in the 21st Century. (Or possibly two, should one consider the Scottish Scleromochlus a lagerpetid, as Müller et. al do. Scleromochlus was named in 1907.) Lagerpetids are relevant to our story because, they appear to be pterosaurs' closest relatives. Pterosaurs are such odd animals, highly specialized for flight; even the earliest ones we have are already highly derived. It's prompted many researchers to wonder what the intermediate stages might have looked like, but "proto-pterosaurs" have thus far proved frustratingly difficult to find.

Lagerpetids are, so far, the closest thing we've got, and they look outwardly rather like primitive dinosaurs, not too much like pterosaurs at a first glance. In fact, they were considered dinosauromorphs for decades, and it's only since more or less the start of the current decade that they've consistently been found as pterosauromorphs instead, largely on account of an improving fossil record. Lagerpetids are so-named because of their slender, rather elongated legs; the animal which gave the family its name, Lagerpeton, means "hare reptile". They're known from South America, Madgascar, the southwestern United States, and possibly the UK, and appear to have died out well before the end of the Triassic.

Although I humbly submit that all lagerpetids are pretty interesting animals, Venetoraptor is particularly neat because it's so far the first lagerpetid to actually have decently preserved skull and hand elements.For most other lagerpetids, these leg and hip bones tend to be all we have, with occasional bits of something else to liven things up. The preservation of these comparatively rare elements in Venetoraptor broadens our understanding of the anatomy of these animals considerably.

Venetoraptor's skull features an edentulous (toothless) premaxilla, which appears to have sported some sort of beak. The paper describes this beak as raptorial, like that of a modern bird of prey, though they stop short of saying what the animal's diet might have been. It's worth noting that other archosauriforms which aren't predators, such as parrots for just one example, sport a similarly hooked beak, so this doesn't necessarily indicate that Venetoraptor was an active predator. I personally consider it likely that it was hunting small vertebrates and insects like many of its relatives, but it could always have been doing something entirely different. Since the premaxilla doesn't seem to be preserved in any other known lagerpetids, it remains possible that others in the family also shared this feature.

The hands are also a point of interest, and understandably Müller et al. pay quite a bit of attention to these. There has been some contention in the past over whether lagerpetids were strictly bipedal or not, but based on their comparatively long and slender hind limbs I think this argument was always sort of moot. Venetoraptor has rather large hands that would not be well-suited for walking upon, and most likely were put to other purposes, such as grasping or climbing, though it's hard to say what. The paper also makes a lot out of the particular elongation of digit IV, the longest of the four digits on Venetoraptor's hand, drawing a comparison to the extremely elongated digit IV which makes up the primary support for the pterosaur wing. It's an interesting connection, though not a slam dunk, as other archosaurs, including primitive dinosaurs like Herrerasaurus, have a similarly elongated final digit. Either way, I hope to see more in future studies, as the evolution of the pterosaur wing must be one of the most fascinating stories in vertebrate biology.

We may never find weird, gliding half-pterosaurs like various authors have envisioned, but lagerpetids can still give us an intriguing look at the split between the earliest dinosaurs and pterosaurs, and provide us with hints about how pterosaurs evolved so rapidly to become the first flying vertebrates. I'm excited to find out more about this group as time passes and reveals even more surprises for us.

There's been a lot of other interesting finds I've missed out on recently, such as the oldest known diplodocoid sauropod and an absolutely massive phytosaur, but nevertheless, I persevere. I've had a rather chaotic year but I'm determined to keep Archosaurophilia rolling no matter what.

More to come soon - I promise!

Sources:

• Müller, Rodrigo T., Martín D. Ezcurra, Mauricio S. Garcia, Federico L. Agnolín, Michelle R. Stocker, Fernando E. Novas, Marina B. Soares, Alexander W. A. Kellner, and Sterling J. Nesbitt. (2023) "New reptile shows dinosaurs and pterosaurs evolved among diverse precursors." Nature 620: 589-594. DOI: 10.1038/s41586-023-06359-z