Terrestrial Killer Dsungaripterids
The more we learn about pterosaurs, the more we see an incredibly diverse clade of animals comparable functionally to modern mammals and the contemporary non-avian theropods in terms of behaviours and ecologies. It’s hard to imagine that six years ago the notion of pterosaurs being all seabird analogues was widely accepted.
There is, however, one group of pterosaurs which doesn’t seem to have benefitted from these discoveries. Dsungaripterids, the iconic “ugly pterosaurs”, are still considered for the most part to be specialised molluscivores, when evidence seems to be piling against such a lifestyle. While nearly all pterosaur clades benefitted from new literature about their ecological habits since the azhdarchid paper, dsungaripterids seem to be stuck where they have been for the past decades. This becomes both ironic and just plain depressing, given the history of research in these strange pterosaurs.
Historical research on dsungaripterid ecology
Dsungaripterids entered in the game more or less in the middle of the pterosaur discovery timeline: Dsungaripterus proper was found in 1964, and it’s relative Noripterus was described in 1973. Since very early on the bizarre cranial anatomy of these pterosaurs was noted, and unusual lifestyles were attributed to them, such as skimming and scavenging. Finally, around the late 70’s, it was more or less accepted that these animals were molluscivores, using their bizarre jaw tips to probe the mud and their molar-like teeth to smash the hard shells. Indeed, dsungaripterid cranial anatomy is uniquely suited for crushing: the nasoantorbitals are quite reduced when compared to those of other pterodactyloids, and the teeth, rather than increasing in size the further you go distally on the jaw, actually become smaller that way. The biggest teeth are precisely on the jaw base, where the bite force would have been strongest, exactly as you’d expect on an animal specialised to crush.
From a 20th century palaeontological view, it made sense. After all, if all pterosaurs were supposedly mutant seabirds, a mollusc eating one wouldn’t be especially weird, would it? Of course, even that was considered “too deviant”, and the same authors that assumed Thalassodromeus was a skimmer actually went as far as viciously suggesting a purely skimming lifestyle for dsungaripterids, stating that a molluscivorous diet was “a pathetic notion” (Kellner, 2006).
Eventually, however, some very odd things were noted in dsungaripterids.
So long as there are shellfish far away from the sea…
Since very early on, it was noted that dsungaripterids didn’t live in ecosystems apropriate for specialised molluscivores. Dsungaripterus itself, for instance, hails from the Junggar Basin, living somewhere in the Lower Cretaceous, and a few other fossil sites in Mongolia and Korea. All these localities are terrestrial ecosystems; the Lianmuqin formation actually has a system of lakes, but they seem woefully poor in aquatic fauna, and were likely seasonal. Instead, terrestrial animals, such as dinosaurs and protosuchids, are instead more common. The dsungaripterid Noripterus is noted as being more commonly found in deeper water sediments, but then again so are several flying animals unambiguously non-aquatic, such as the bat Archaeonycteris from the comparable Messel Pit, so it could be the result of simply a more volant lifestyle. At any rate, other dsungaripterids are noted as having distribution patterns identical to those of other terrestrial animals (Lü, J., Azuma, Y., Dong, Z., Barsbold, R., Kobayashi, Y., and Lee, Y.-N. (2009). Other dsungaripterids likewise don’t seem to be tied to particularly aquatic environments; Domeykodactylus, for instance, occurs in what appears to be an arid environment.
Besides the continental environments, dsungaripterids were among the first pterosaurs to have been found as being quite terrestrial. To quote Darren Naish, “the hindlimb and pelvic morphology of dsungaripterids indicates that they were well suited for terrestrial locomotion – perhaps more so than most other pterosaurs – with relatively robust limb bones well able to resist compression and buckling (Fastnacht 2005)”, and the animals’ skeletons were remarkably very robust. While other pterodactyloids had very thin bone walls, sometimes about a milimetre in thickness, dsungaripterids have very thick and flattened bones walls, some bones being entirely non-pneumatised. Likewise, their wings are proportionally rather short, rather unexpected for a gliding, seabird like animal. Instead, they offer a rounded profile, just like the wings of terrestrial birds, and it is very likely that, much like modern fowl, dsungaripterids usually engaged in relatively short flights, marked by powerful and rapid wingbeats and abrupt landings (hence the compression and buckling adapted hindlimbs).
In short, rather than soaring albatross like animals, Dsungaripterus and kin were rather robust, terrestrial creatures well adapted for running and galloping as well as quick quick, Galliforme-esque flights, though presumably more elegant and extensive, given the usual pterosaur differences like the forelimb launching (and thus the absence of huge hindlimb muscles and quicker take off) and the shape-changing wing membranes.
Nonetheless, for some reason, dsungaripterids still are largely reffered as molluscivores despiste the rarity of mussels in freshwater, the exclusively continental distribution, the lack of actual adaptations for swimming and wading (no proper studies have been made on dsungaripterid foot proportions, but nearly all reconstructions seem to depict rather average-sized feet) and the numerous adaptations for terrestrial locomotion, something a mollusc specialist shouldn’t need.
The radical proposition
Occam’s Razor therefore posits that, rather than to make up some bizarre excuse for all these traits in a supposed molluscivore, it’s more plausible that dsungaripterids simply had a less absurdly narrow diet.
Many of the adaptations present in dsungaripterids easily point towards more eclectic diets. The toothless, thin and frequently curved jaw tips could easily just serve to probe for general undergrowth morsels: worms, arthropods, snails, seeds, fungi and small vertebrates. Maybe they served to make manipulation and prey capturing easier, as with the surved beaks of several modern birds. Maybe they didn’t even evolved directly for foraging: they seem very apropriate for combat, either interspecific or against other animals, such as predatory theropods or possible ornithopod prey. Maybe they even were useful to rip off chunks of flesh; in most dsungaripterids, only the lower jaw is curved, which is consistent with a hook function.
The robust jaws and teeth are even less mysterious. Cracking hard food stuffs, may them be bones or nuts would certainly be a logical function. With hooked lower jaws and crushing teeth, a carnivorous diet isn’t at all unfeasiable, though such adaptations evolving for nut cracking would be delightfully adorable.
My personal opinion is that dsungaripterids were mostly opportunistic omnivores, not unlike modern bears and boars, with maybe some specialisation towards scavenging and/or general carnivory. Their robust bones are especially suspicious in that regard; unlike other terrestrial pterosaurs, which presumably preffered to evade predators by running or quick launching, the bulky dsungaripterids were more apt to stay and fight, defending their kills/found carcasses with their sheer power. In just a scenario, the powerful jaws would be a weapon to be reckoned with, all the more apropriate to deal with theropod threats.
All in all, this would paint a rather extraordinary picture of pterosaur radiations. Not only did several pterosaurs competed directly with theropods, such as the antelopine tapejarids and the phorusrhacid-like Thalassodromeus, at least one lineage blatantly paralleled large omnivorous mammals, and the presence of such pterosaurs could actually help explaining the relatively small size of most Mesozoic mammals even in areas where their more direct competitors, the terrestrial crocodyllians, were absent*. It certainly depicts the Mesozoic as it really was: not a bizarre “dragon age”, but basically a parallel Cenozoic, it’s dominant denizens being bizarre “furry” critters as wonderful as our mammals and birds.
* It is generally now agreed the main competitors of mammals in the Mesozoic were crocodyllians rather than dinosaurs. Indeed, some Mesozoic mammals grew to rather unexpected large sizes; for some time now, for instance, chinese fossils assigned to a Repenomamus relative were twice the size of the more well known mammal. To put in perspective, Repenomamus itself would give a wolverine a run for it’s money.