This week for Temnospondyl Tuesday, we're going from one my blurb last week on one of the most charismatic dissorophids, Platyhystrix, to one of the most confusing dissorophids, Aspidosaurus. If you compare the two, they're basically known from the same type of material - mostly neural spines - but Aspidosaurus has normal-sized spines, so it doesn't get the celebrity treatment... Nonetheless, it is, *if correctly interpreted,* the longest-lived genus of dissorophid, so it apparently did something right to stick around for so long.
A casualty of war
Aspidosaurus probably has the most interesting history for a dissorophid considering the first one ever described was blown to smithereens by the Royal Air Force. It's somewhat common knowledge that the holotype of Spinosaurus aegypticus, the famous sail-backed carnivorous dinosaur from Africa that makes an appearance in Jurassic Park III and that is often cited in the debate over "biggest meat-eating dinosaur ever," was destroyed during World War II in an Allied bombing of Munich. Of course, Spinosaurus wasn't the only fossil in the museum (The Bavarian State Collection of Palaeontology and Geology / Bayerische Staatssammlung für Paläontologie). There are two good articles for reading up on the history of the museum in general (Wellnhofer, 1980; Reich & Wörheide, 2018), which provide a more detailed synopsis of the previous holdings of the museum, which were quite diverse and the vast majority of which were lost in the bombing. Among these other losses was the holotype of the type species of Aspidosaurus, A. chiton, collected at the turn of the 20th century from Texas by German palaeontologist Ferdinand Broili, who also has his own genus of dissorophid, Broiliellus, named after him. The holotype is represented by a partial skull and associated postcrania, which probably doesn't sound all that remarkable, but consider that there is only three other specimens of Aspidosaurus that includes even a fragment of cranial material, and the holotype thus becomes a lot more important. The only surviving record of the holotype is Broili's (1904) publication, which has decent figures and a pretty good description (albeit in German), but the preservation was apparently too poor to identify sutures. The subsequent material of Aspidosaurus has not necessarily proven itself to be much better preserved, which has ended up to be a real problem for phylogenetic analyses.
The short histor-
There is no short history of Aspidosaurus. It's not possible. There's so many misidentifications, confusion with Zatrachys, confusion with other dissorophids, invalidated names, revalidated names, etc. I'm not even going to try.
You can also toss in this headless weirdo, Alegeinosaurus aphthitos, that I synonymized with Aspidosaurus last year (Gee, 2018). This is the only one that actually comes from the type locality of Aspidosaurus chiton, the first-described and now-lost species of the genus, but it was named as a distinct genus and species by Case (1911), who thought that it was closer to Cacops. You'll probably notice that it has more similar proportions to the first Aspidosaurus I showed up top from Richards Spur, and the ornamentation is pretty similar too.
Okay...so is it all Aspidosaurus?
In my opinion, almost certainly not. At the very least, it's a mess. If you like taxonomy, like me, then you like messes, because they're like puzzles 100+ years in the making. If you don't like taxonomy, well... Normally, this wouldn't be that hard - you would go to the holotype of the type species, compare what you had, and then make a decision. Well, now that the holotype of the type species has been reduced to cosmic dust (perhaps you contain some of it within you - what a privilege!), that's a bit more difficult. When I synonymized Alegeinosaurus with Aspidosaurus, I based it on Broili's (1904) drawings; of all the Aspidosaurus material that's out there, the osteoderms of Alegeinosaurus are basically indistinguishable from those of Aspidosaurus chiton in: (a) proportions; (b) presence of only one series (apparently, but see below); (3) ornamentation, slight and with a lot of circular pits; and (4) the way the osteoderms overlapped each other. Oh, and the two species are from the same site.
This ended up coming around again in my latest paper, where we reported what we proposed was Aspidosaurus from Richards Spur. The osteoderms are again very similar to those that Broili figured - with one major caveat. We scanned the specimen and were able to prove that it actually has two osteoderm series; one is just much smaller than the other and not visible in dorsal view. Aspidosaurus is only supposed to have one osteoderm series! So then we were really up a creek because it because a question of whether the original Aspidosaurus only appeared to have one; the smaller one in the Richards Spur Aspidosaurus is not very easy to ID, and a lot of the time, people don't look at the undersides or prepare it in fine detail. You'll almost never find any other figures of Aspidosaurus osteoderms from underneath. Coincidentally, Broili actually did figure the underside, but it's still not clear that it only had one osteoderm series, and since it's gone, we'll never know. Anyway, you can compare for yourself and see whether you think my work stacks up. Might not be the same species, but I feel okay saying they're the same genus.
Aspidosaurus chiton on the left; Richards Spur Aspidosaurus in the middle; Alegeinosaurus on the right.
Aspidosaurus is no Platyhystrix. The internet is not flooded with reconstructions of it. I did not just buy a shirt with a logo of it. We barely know what the animal looked like. But that doesn't mean it's not important - if anything, it's really important - and we need to sort the whole taxonomic mess out to figure out what's going on so that we can get a better idea of what it represents for dissorophid evolution. If Aspidosaurus really was around for more than 25 million years, that's really interesting! If it's not, then that suggests a hidden diversity that's being masked by a general conservation of a particular osteoderm morphology for a broad swath of dissorophid evolution and our taxonomic lumping of that morphotype.
About the blog
A blog on all things temnospondyl written by someone who spends too much time thinking about them. Covers all aspects of temnospondyl paleobiology and ongoing research (not just mine).