Thalassodromids and more David Peters trolling
My latest dive into speculation has not been very successful. However, regardless of whereas Samrukia was an azhdarchid, a thalassodromedid, a bird or something else entirely, I’ve adquired an unhealthy obsession with Thalassodromidae after that post. Mark Witton fancies them a lot as well appearently, so at least I can confort myself in it being a normal obsession.
Composed of two genera (Thalassodromeus almost certainly with a single species, while the number of Tupuxuara may vary between one or three species depending on who you ask; there’s also the possibility that all these pterosaurs might be within the same genus, although most likely not the same species), Thalassodromidae is an unique product of the azhdarchoid radiation in the early Cretaceous, having been part of the pterosaur golden age. For the moment, they appear to have been exclusively south american; possible remains have occured in Texas, Morocco and Europe, but they might be assigned to other azhdarchoids. Alongside Pteranodontia, this would make thalassodromids the only other pterodactyloid clade with significant geographical restriction (in contrast with the usually cosmopolitian distribution of most pterodactyloid clades), which could had played a role in their demise, although in both cases there are probably simply taxa that lived elsewhere and weren’t preserved.
Thalassodromids have been in the center of an intense debate in regards to azhdarchoid phylogeny, focusing on whereas these animals were closer to tapejarids or to neoazhdarchs (azhdarchids and chaoyangopterids). Things got even more complicated as one study (Felipe Pinheiro, 2011) dragged chaoyangopterids into “Tapejaridae” as well, rendering Neoazhdarchia nonexistent. However, to my knowledge Neoazhdarchia has been recovered yet again, and frankly I’m leaning more to the Neoazhdarchia interpretation. Thalassodromids have only been included in “Tapejaridae” due to the shape of the crest base, which is frankly not very impressive. By contrast, they share with azhdarchids and chaoyangopterids large nasoanteorbital frenestrae that go significantly above their eyesockets (something unique among pterosaurs), straight jaws with shallow mandibles, long rostrums in front of the nasoanteorbital frenestrae, straight or conclave margins dorsally on the rostrum and a well developed notarium. Thalassodromids also appear to have their shoulders in the same position as in neoazhdarchs, unlike the “plane position” as in tapejarids, futher rendering them more likely to be neoazhdarchs.
What interests me most, however, is the palaeobiology of these pterosaurs. Originally thought to be skimmers, this notion is now considered pathetically inaccurate at best, given that these animals not only were too large, but lacked every single adaptation required for skimming. Other than that, however, not much has been done to examine what exactly they did. Being azhdarchoids, and neoazhdarchs at that, it is almost certain that they fed on the ground, hunting small animals on the foot like modern seriemas and secretary birds, and indeed their relatively short wings and well developed hindlimbs seem to suggest this. Notably, their necks are shorter and more flexible than those of chaoyangopterids and azhdarchids, and they are better flyers than tapejarids (whereas they shared their adaptations for climbing I don’t know), and so it has been suggested that they were rather generalistic predators/omnivores, feeding on whatever small animal or carcasse they found. This seems particularly true for Tupuxuara, but Thalassodromeus seems more specialised. It’s jaws are noted as being superficially scizzor like, not very efficient for grabbing prey, but perfect for slicing flesh. Combined with the short neck. this means that Thalassodromeus could had efficiently attacked large prey. While it’s too early to properly crown it as the “pterosaurian eagle”, I do think modern Haliaeetus offers a decent analogue, since they too are opportunistic predators/scavengers with a slight tendency for larger prey than the larid Charadriiformes they co-exist with.
An equally interesting part of thalassodromid palaeobiology is their growth. Studies regarding Tupuxuara show that the animal grew their crest along the upper jaw, and that only full grown animals had the iconic giant, flamboyant crest, proving that indeed pterosaur crests were just display devices, having no aerodynamic use. Appearently the fossils turned out to belong to Thalassodromeus rather than Tupuxuara if Mark Witton is to be believed, but the basic point remains. While not something that I believe had been explored in detail, it appears azhdarchoids had a slower growth rate than ornithocheiroids, or pteranodontians at least; while Pteranodon is notorious for the neornithe like growth rate, reaching adult size within an year, thalassodromids appear to have taken several years, much like in modern megapodes, thus following the iconic pterodactyloid model of occupying several ecological niches as they grew (hence why the previously mentioned idea that these animals might represent different growth stages of a single species – predictably, this works better with the three Tupuxuara species, with Thalassodromeus truly representing a different species). Unlike non-pterodactyloid pterosaurs and most sauropsids, which grow until they die, pterodactyloids had a clear finite growth, with the animal growing for many years but eventually ceasing to. Studies on Pterodaustro show that pterodactyloids reached sexual maturity before reaching their maximum size, much like in modern slow growing mammals. Yeah, much like us, pterodactyloids had puberty in their teenager years. Although at least they laid eggs.
Thalassodromids had a very short temporal existence. Unless the moroccan, texan and european fossils attributed to them aren’t something else, these animals are known only from the Santana Formation in Brazil, dating to the Cenomanian. With the presence of much earlier chaoyangopterids and azhdarchids, it is almost certain that the temporal range of these animals extends further back in time, and given how they are considered to be outside the Chaoyangopteridae+Azhdarchidae clade, they were probably a quite long lived ghost lineage, possibly dating back to the Jurassic/Cretaceous border. Living as recently as 92 million years ago, they are among the most recent known non-azhdarchid azhdarchoids, but they too appear to be absent in the post-Turonian Cretaceous (keep reading though), much like a good chunk of the known pterosaur taxa. The exact reasons for their disappearence are not well established; as I previously indicated, pterosaurs being replaced by birds is unlikely, and in fact not taken seriously anymore among pterosaur specialist circles. In the case of thalassodromids, though, I’m more willing to accept possible replacement by birds than in other pterosaurs because of their generalistic lifestyle, which would perhaps not been very different from that of countless enantiornithe and ornithurine taxa.
However, a more likely reason for their disappearence is probably competition with their relatives, the azhdarchids. A number of post-Turonian azhdarchids have rostrums remarkably similar to those of thalassodromids, Bakonydraco and TMM 42489-2 in particular having been historically mistaken for thalassodromids. Either these azhdarchids replaced thalassodromids directly, or merely filled vacant niches left from earlier extinctions.
Still, it is possible that thalassodromids did survive after the Turonian, although so far remains possibly identified as thalassodromids might represent more azhdarchids that converged upon them. I’m waiting for Mark Witton’s book for clarification.
Previously I’ve brought up the idea that Samrukia might be a thalassodromid, because it was the only pterosaur clade that I think that have similar enough jaws. Darren Naish told me such wasn’t the case. Atypically of him, he did not provide further explanations as to why it isn’t the case, and I am genuinely curious. I don’t submit myself to authorithy without evidence, as even widely respected biologists need to justify their stances, but for the moment I won’t force my ideas about Samrukia‘s identity, because I’m sincerily confused about the specimen. While the thalassodromid identity is attractive, it is just that, an idea, and there might be countless other options, including more basal azhdarchoids, merely a juvenile Aralazhdarcho or even something else altogether. Hell, I even think my previous statements about it not being a chaoyangopterid are bogus now.
Still, I’m not the only one attracted to the Samrukia mystery. David Peters, infamous for his lizard pterosaur fetish, has given a shot at trying to pin point what exactly Samrukia is, and his answer is basically this:
And before you question my sanity, you should question David Peters’, for he was the one who suggested this. Not that anyone is questioning his sanity after 2006 though; I believe it has become really obvious.
His basic idea is that Samrukia‘s ramus are closest in shape to those of Criorhynchus, an ornithocheirid pterosaur, possibly synonimous with Ornithocheirus itself (ornithocheirid nomenclature and phylogeny are essencially just one big bitch fight, which will never have any consensus). One would be questioning how much sense that would make considering that Samrukia‘s ramus are considered to be incomplete, rendering his comparasion flawed as the similarity in shape is accidental (to be fair, the rami of Criorhynchus are probably incomplete as well though). One would also question the fact that ornithocheiroids like Criorhynchus have an extension of the jaw where the teeth are located, while Samrukia‘s jaw doesn’t appear to have this extension and other than the ramus the jaw is noted to be complete, meaning that in life the animal had a toothless, wide lower jaw. But like we all know by now, David Peters is like The Crazy Nastyass Honey Badger when it comes to fossils.
Never the less, a Crazy Nastyass Samrukia/Criorhynchus/Ornithocheirus/whatever is very appealing, so for the moment I too won’t care or give a shit and just classify Samrukia as an ornithocheiroid until Darren posts about it.
Before I end the post, I would like to remind you that I did talk about DP’s questionable sanity earlier. While I offered a stream of insults for polluting Google, I don’t think that he is necessarily stupid, just that he is insane. According to anecdotal evidence, he appears to be quite intelligent, and I currently believe that he is, in fact, the most successful troll in paleontological circles.