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Samrukia: the mysterious pterosaur phoenix

November 30, 2011

Samrukia jaw. Back when it was considered a bird, I've always wondered if it had a massive bill, given the wideness of the mandibula. Now, it puzzles me as a pterosaur too.

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?

Azhdarchoid premaxillae collection (A, Tupuxuara; B, Thalassodromeus; C, Zhejiangopterus; D, Quetzalcoatlus; E, Shenzhoupterus; F, Jidapterus; G, Chaoyangopterus; H, TMM 43489-2).

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?

Tupuxuara by Raúl Martín, doing what David Peters hates to admit to be true.

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.

5 Comments leave one →
  1. December 1, 2011 5:45 pm

    Samrukia is not a thalassodromid 🙂 I’m withholding comments on Samrukia for now but, don’t worry, will get round to it eventually. I am, and of course always have been, extremely familiar with Eric Buffetaut’s argument.

    • December 1, 2011 7:33 pm

      Many, many thanks for acknowledgement!

      And indeed, this is just an idea; I admit that the thalassodromedid idea is something of a stretch.

  2. Eric Buffetaut permalink
    December 22, 2011 9:25 pm

    My impression is that you overlook the fact that the whole anterior part of the holotype of Samrukia nessovi, as shown on the photo above, is purely fictitious. The only genuine parts are the posterior parts of the mandibular rami (as Naish et al. clearly mentioned, although apparently they did not wish to, or could not, physically remove the “invented” anterior part).There is absolutely no serious reason to suppose that the anterior part was as short as on this reconstruction. It cannot even be demonstrated that it was toothless, although that seems likely enough for a Late Cretaceous pterosaur. In all likelihood, that pterosaur simply had a “normal” pterosaur lower jaw, with a long, narrow mandibular symphysis.
    In any cas, by all means don’t take that reconstruction of the anterior part of the jaw at face value ! It was reconstructed that way because it was first thought to belong to an oviraptorosaur (the person who reconstructed it told me so).

    • December 22, 2011 10:25 pm

      Many thanks for the clarification! Indeed, it clarifies a lot of doubts I had.

      Are you familiar with the suggestion that it was an ornithocheirid?

      • Eric Buffetaut permalink
        December 23, 2011 8:30 am

        It may be an ornithocheirid, but frankly I find it difficult to identify a pterosaur accurately on just the posterior part of the mandibular ramus. There is no way to decide whether it had teeth, for instance, and that doesn’t help.
        That being said, with a lot of detailed anatomical comparison, it may be possible to pinpoint what it is more clearly. The trouble is that that part of the jaw has often received little attention and is not that well known in many pterosaurs. There seems to be some variation among pterosaur groups in the morphology of that area (notably in the structure of the articular region), as I mentioned in my paper.
        At the moment, my guess would be azhdarchid or perhaps pteranodontid, but it is just a guess.
        To be frank, my main concern was to show that it is not a bird, and exactly what kind of pterosaur it is does not bother me much. It seems pretty run-of-the-mill to me.

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