Samrukia: the mysterious pterosaur phoenix
Found in the Bostobynskaya Formation in Kazakhastan in 2011, Samrukia is a puzzling creature. It was first described as a bird, possibly within Carinatae, an example of the existence of large terrestrial birds in the late Cretaceous. While some people have suggested it to be a large volant bird, I’ve never been very concerned about it, because it would most likely turn out to be a giant flightless bird. Flightless birds are already known from the Cretaceous, such as Patagopteryx and Gargantuavis, all of them not remote island dwellers, but having evolved in territories filled with non-avian dinosaurs, proving that flight is sufficiently expendable to be lost even in the presence of predators (see my previous post on elephant birds).
Most surprisingly, however, is that, it turns out, that Samrukia might not had been a bird, but a pterosaur instead. So far, only Eric Buffetaut’s analysis (already published in November) seems to claim his, but then again there are few published papers on Samrukia. So far, on the DinosaurMailingList, the main issue seems to be the usage of the name*, so maybe it is safe to say that the “phoenix” is in fact a dragon, so to speak.
* Samrukia is not an official genus name, because so far none of the papers about it classify under ICZN’s snobbish standards. For the moment, I’ll use the name, and I honestly hope that Samrukia is chosen as the official genus name, because having a bird or pterosaur named after a phoenix is nice.
If Samrukia is a pterosaur, then a whole new can of worms is opened. As a bird, it was unique for being big; as a pterosaur, it’s estimated 30 centimeter skull (the mandibula we have is 27.5 cm long; the rami are incomplete, and the skull is not just jaw alone anyway) is remarkably small for a pterosaur. Pterodactyloids, the dominant pterosaurs through all of the Cretaceous period, are iconic for their ridiculously gigantic heads, and in azhdarchids (the most common pterosaurs in the post-Turonian Cretaceous), the jaws are so big that the torso actually fits in the nasoanteorbital frenestra. To see a pterodactyloid (and it has to be a pterodactyloid; the only other option are anurognathids, whose presence in the late Cretaceous is ambiguous, and they have much shorter and wider jaws, which are also toothed, unlike Samrukia‘s) with such small jaws is jarring to say the least. Most likely, Samrukia represents a juvenile, but it probably might be a small pterosaur overall. Notably, Gwawinapterus appears to have had similar sized jaws.
What kind of pterosaur Samrukia is?
Samrukia lived during the Santonian/Campanian boundary, it’s temporal range probably larger forwards or backwards in time. In this time period, the dominant pterosaurs were azhdarchids and pteranodontians, with isitodactylids almost certainly present given the presence of Gwawinapterus in the late Campanian/Maastrichtian. Other pterosaurs probably were present, but only undescribed ornithocheiroids are known for sure. So, where did Samrukia fit in the pterosaur tree of life?
I can right away tell that it sure wasn’t a pteranodontian; not only defenite pteranodontians are only known from the Western Interior Seaway (although nyctosaurids might had occured elsewhere), but their long, stork like jaws don’t resemble the shorter, wider mandibula of Samrukia. For this reason, I will also provide the controversial statement that Samrukia was most likely not an azhdarchid either, as even forms with atypical mandibulae like Bakonydraco still had less wide jaws. The azhdarchid Aralazhdarcho co-existed with Samrukia; the two pterosaurs certainly had an unique niche partitioning, avoiding direct competition with each other.
So, if not a pteranodontian or an azhdarchid, what kind of pterosaur Samrukia was?
A non-azhdarchid azhdarchoid?
While azhdarchids already existed in the lower Cretaceous, they only became promenient after the Turonian. This is because a large variety of other azhdarchoid pterosaurs dominated terrestrial ecosystems, and only after they became extinct did azhdarchids expand. However, I would not be surprised if these animals did in fact survive longer, specially because their ecological niches as generalistic carnivores and omnivores would allow them to survive well through events like the Turonian extinctions.
Of these azhdarchoids, I think chaoyangopterids are the least likely candidates. They greatly resemble their azhdarchid cousins, and the mandibulae are not exceptions. Indeed, while I think it is possible that some chaoyangopterids made it through to the Maastrichtian, they almost certainly were outcompeted by azhdarchids at least in Laurasia. Tapejarids are also an unlikely option, given their tendency to have lower jaw crests.
However, I think thalassodromedids are a decent possibility. These pterosaurs have mandibulae that are fairly close in shape to that of Samrukia, and given their relative rarity in non-lagerstätten fossil sites I think they’d easily could had survived without being preserved. Thought to have been generalists, they could easily co-exist with azhdarchids, perhaps opting for wetter terrains while their more common cousins took drier habitats. Samrukia would likely have represented a stem-thalassodromedid, that survived well after it’s well known and larger South American relatives became extinct. Amusingly, Darren Naish did consider that thalassodromedids did survive into the Maastrichtian, but appearently Mark Witton talked him out of that. I’m waiting for the latter’s book; maybe he changed his mind.
If Samrukia is indeed a thalassodromedid, it, alongside Gwawinapterus, further indicates that late Cretaceous pterosaur diversity was higher than previously thought. The greatest irony is that the phoenix of Bostobynskaya, once a proof of a higher avifauna diversity in the latest Mesozoic, now indicates that pterosaurs kept the tight leash on large volant animal niches.