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Bakonydraco was a tapejarid like azhdarchid… or an actual tapejarid

January 9, 2014
Bakonydraco galaczi by Sergei Krasovskiy, in conflict with the ceratopsian Ajkaceratops.

Bakonydraco galaczi by Sergei Krasovskiy, in conflict with the ceratopsian Ajkaceratops.

Bakonydraco galaczi is a very odd pterosaur. Known primarily from a single, yet extraordinarily well preserved mandible from the Santonian-aged Csehbánya Formation of Hungary’s Bakony Mountains (as well as associated forelimb bones and neck vertebrae that most likely belong to it), Bakonydraco is part of a strange insular assemblage of animals that also include several types of dwarf ornithischian dinosaurs (including Ajkaceratops, the first european ceratopsian to be discovered) and abelisaurs, the undetermined paravian Pneumatoraptor and the freshwater mosasaur Pannoniasaurus, as well as a variety of terrestrial and alligatoroid crocodylomorphs, albanerpetontids, fish, turtles, enantiornithes and varanoid lizards. With azhdarchid pterosaurs also known from the formation, and living in a time period where the only other significantly represented clade of toothless pterosaurs were the marine pteranodontians, Bakonydraco‘s subsequent classification as an azhdarchid was rather predictable, but since day one that this animal was considered very odd by the standards of it’s clade.

The holotype, MTM Gyn/3

The holotype, MTM Gyn/3

Bakonydraco<'s most distinctive characteristic is it's mandibular symphysis, which is quite aptly described as "spear-like". Vertically tall at the base both on the upper surface and on the underside, forming a sharp "cone", bearing a posterodorsal curvature and notoriously made distinct from the rest of the jaw by a transverse ridge – which could implicate the end of the lower jaw rhamphotheca in the live animal -, it seems like the logical extreme of the "short rostrum" azhdarchid jaw model, trading the longer stork-like beak for a shorter pecking weapon; other azhdarchids with short rostrums include the Javelina Formation azhdarchid and Hatzegopteryx, though no other azhdarchid shows such extreme changes in the mandible symphysis morphology.

The original paper describing the specimen compared this mandible morphology to that of tapejarid pterosaurs, specifically Tapejara proper and Sinopterus, which also possess similar short, dystally deep lower jaw symphysis. In particular, the jaw is most similar to Tapejara‘s, only differing significantly in that the depth in the symphysis’ base has evolved into a full blown ventral crest in Tapejara, and that the shared posterodorsal ridge at the anterior dorsal surface of the symphysis is blunt in Bakonydraco but not in Tapejara. Sinopterus lacks the transverse ridge and the posterodorsal curvature common to both animals; if the three composed a clade of closely related species, one could argue that Sinopterus would be the most conservative member and Tapejara the most specialised, with Bakonydraco somewhere in the middle.

Indeed, this comparision between tapejarids and Bakonydraco went as far as the initial lifestyle proposition: Atilla Ösi et al. proposed that Bakonydraco was a frugivorous animal in the same vein as often theorised for tapejarids, citing the theoretical gap of the closed jaws as ideal for grabbing fruits and leaves, though it notes that the animal’s size would have limited quadrupedal climbing and arboreal motion, forcing the animal to either forage on forests with spaceous branches, or walk around in the ground and browse from shrubs and low trees. While the paper does argue in favour of piscivory due to then accepted notions of all pterosaurs being mutant seagulls, the fact that azhdarchids are now known to have been terrestrial foragers makes Ösi’s hypothesis of an okapi-like Bakonydraco grabbing fruits and leaves from shrubs as it walks past them the more likely explanation, an exceptionally accurate prediction that Witton 2008 was dutiful to notice. Most importantly, tapejarids have also been understood to be terrestrial foragers as well, their tree climbing capacities being only marginally better than those of other azhdarchoids (as adults, at least), so frugivory in these animals would also have been obtained via browsing.

Thus, it is fairly reasonable to consider Bakonydraco a particularly strong case of convergent evolution, an azhdarchid occupying or evolving towards occupying a similar ecological niche to that of the earlier tapejarid pterosaurs, presumably filling vacant niches. The idea that Late Cretaceous azhdarchids moved into ecological niches previously occupied by other pterosaurs, is nothing new, as with the case of the rather thalassodromedid like Javelina azhdarchid – and perhaps even the gigantic Hatzegopteryx, whose adaptations for macropredation seem very similar to those of Thalassodromeus itself -, and indeed the Late Cretaceous predominance of these pterosaurs may represent a systematic radiation in response to the absence of other azhdarchoids. Since the examples offered are “short snouted” azhdarchids, it should perhaps be of interest to examine the diversity of these azhdarchids before the post-Turonian Late Cretaceous.

Then again, maybe not….

Pterosaur phylogeny according to Pterosaur phylogeny according to Andres, B. & Myers, T.S. 2013 (the red oval is my creation)

Pterosaur phylogeny according to Pterosaur phylogeny according to Andres, B. & Myers, T.S. 2013 (the red oval is my creation)

More recently, Andres, B. & Myers, T.S. 2013 argued that the convergence between Bakonydraco and tapejarids was a tad too extreme to have aroused independently, and that Bakonydraco actually is a tapejarid, a fairly derived one that is non-surprisingly the sister taxa of the Tapejara + Tupandactylus clade, with “Huaxiapterus” being the closest relatives outside of this clade (“Huaxiapterus” in this cladogram is considered to be paraphyletic, with H. benxiensis being closer than H. corollatus). This analysis makes full use of the character list and matrix dictated in previous pterosaur phylogeny tests, thus accurately pin pointing the number of characteristics that exclude Bakonydraco as an azhdarchid and showcasing the higher number of traits it has in common with tapejarid pterosaurs.

If this accessment is correct, then it means that Bakonydraco is not yet another type of azhdarchid, but an actual Santonian representative of Tapejaridae and thus of non-Azhdarchidae Azhdarchoidea, thus being not only more evidence of Late Cretaceous pterosaur diversity outside of Azhdarchidae, but also that Late Cretaceous azhdarchid radiation was independent from the “decline” of other azhdarchoid pterosaurs (except maybe thalassodromedids), that Tapejaridae existed as a ghost lineage for at least 16 million years, and that tapejarids could reach grander sizes than previously thought (Bakonydraco is speculated to have had a wingspan of 4 meters [based on azhdarchid proportions; tapejarids had proportionally slightly longer wings], while the largest unambiguous tapejarids had wingspans of around 2.9 meters; it was certainly much taller and heavier as well, since these animals were largely terrestrial pterosaurs with proportionally short wings).

If Bakonydraco was a tapejarid, then it might be expected that these pterosaurs retained the cosmopolitian presence that they had in the Lower Cretaceous, and that their general absence in the Late Cretaceous is correlated to a poorer fossil reccord and the absence of konservat-lagerstattën dating to this epoch. However, it could also be that the clade did indeed systematically disappear from most of the world, and that insular forms like Bakonydraco would have been all that was left of Tapejaridae by the Santonian; given the presence of other “relictual species” on the Csehbánya Formation, such as Pannoniasaurus, this definitely has some precedence. With no remains known from anywhere else in Europe, Bakonydraco galaczi was almost certainly an endemic species to the island that is now Hungary, and given it’s massive size compared to those of it’s relatives it would have been a blatant case of insular gigantism, while the dinosaurs it co-existed with were island dwarfs. Based on the inferred body proportions, it would have been one of the island’s tallest browsers, competing only with the local species of Rhabdodon for the leaves and fruits of it’s forest habitat. Bakonydraco might had even been the flightless pterosaur many look after, Cretaceous’ non-avian Aepyornis, though the presence of abelisaurs and a possible tetanuran would probably make this unlikely, and I am doubtful if pterosaurian flightlessness would have ever evolved anyway.

Whereas a tapejarid or an azhdarchid strongly convergent on one, Bakonydraco was a very unusual pterosaur, certainly one of the strangest cases of Mesozoic insular megafauna.

REFS

Ösi, Attila; Weishampel, David B.; and Jianu, Coralia M. (2005). “First evidence of azhdarchid pterosaurs from the Late Cretaceous of Hungary” (PDF). Acta Palaeontologica Polonica 50 (4): 777–787. Retrieved 2009-07-28.

Andres, B.; Myers, T. S. (2013). “Lone Star Pterosaurs”. Earth and Environmental Science Transactions of the Royal Society of Edinburgh

Wilton, Mark P. (2013). Pterosaurs: Natural History, Evolution, Anatomy. Princeton University Press.

2 Comments leave one →
  1. Gray Stanback permalink
    April 29, 2014 4:52 pm

    I still think the idea of Bakonydraco as a flightless pterosaur is at least plausible and cannot be ruled out. Bear in mind that the elephant bird–to which you compare it–coexisted with crocodiles, giant fossas, and at least two species of large eagle. If Bakonydraco was an island giant, a relic tapejarid, and endemic to the area that is now Hungary, then it probably didn’t do much long distance flying.

    • April 30, 2014 12:15 am

      Indeed, though it depends on whereas pterosaurs could become conventionally flightless in the first place.

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