The Romanian azhdarchid mandible: the “missing piece”?

Vremir et al. recently published a paper on a new partial mandible of a large (+8 m wingspan) Azhdarchoid pterosaur from Romania. This specimen was collected in 1984 and is… not particularly well-preserved, but it is informative enough to give us an idea of its relations. The authors tentatively proposed a position as a primitive Azhdarchid, due to a combination of characters present in both Azhdarchids and Tapejarids.

LPB R.2347, the giant Hateg mandible being discussed here. From Vremir et al. 2018.

This new specimen (hereafter the Hateg mandible) is a lot like Bakonydraco. The mandible gently downturns anteriorly and has a deep, wide keel, unlike the thin crests of Tapejarids or the narrow keels of Tupuxuara or other Azhdarchids. The posterior symphysis has raised margins and a noticeable sulcus, and what may be a sulcus on the ventral surface. It even has medullary-type bone in the mandible too!

https://upload.wikimedia.org/wikipedia/commons/a/aa/Bakonydraco.jpg
The holotype mandible of Bakonydraco galaczi. It also has all those traits. From Osi et al. 2005.

The Hateg mandible doesn’t overlap with any of the Hatzegopteryx material, and Vremir et al. take the conservative stance of not referring this bone to the taxon. I still suspect there’s a link between the two anyways. How? The bone interior. Vremir et al. note they both have comparable internal bone, with relatively thick bone walls (up to 4-5 mm) and a spongy internal texture. Relatively thick bone walls are also seen in fossils of Hatzegopteryx, including the referred cervical EME 315. It could be argued this is an artifact of size, but the vertebra of the giant Arambourgiania has thinner bone walls (2.6 mm) and different internal structure (Naish and Witton 2017). The interior bone texture, likewise, is only known in other giant Romanian Azhdarchids – namely, EME 315 and the type material of Hatzegopteryx. Barring further material, it seems the Hateg mandible has as much right to be Hatzegopteryx as the cervical does.

I updated the Azhdarchoid matrix, adding the Hateg mandible and updating the codings of Bakonydraco. Earlier, the codings had followed the precedent of Andres et al. 2014, and thus recovered Bakonydraco as a Tapejarid. In light of the Hateg mandible, however, I felt it prudent to recode this specimen, with a different interpretation of multiple characters (e.g. de-coding the ventral keel as homologous with Tapejarid crests). I should note that the Bakonydraco OTU as is includes the (clearly Azhdarchid) rostrum fragment referred to it by Osi et al. 2011. The unassociated Azhdarchid cervicals described by Osi et al. 2005 seem to come in two different morphotypes (which may or may not relate to position in the neck), so I didn’t add them to the OTU. In any case, in light of the most probably Azhdarchid nature of the Hateg mandible, it seems Bakonydraco might just be a very weird Azhdarchid after all – there is no other evidence for a non-Azhdarchid in Santonian Hungary.

I ran the analysis two times, one with the Hateg mandible and Hatzegopteryx constrained and one without, to little difference. Hatzegopteryx is part of a clade of “short-necked” Azhdarchids that also includes the short-necked Pui Azhdarchid and the Canadian TMP 92.83. The Hateg mandible is part of this clade even without constraints due to sharing bone wall thickness and internal bone texture with Hatzegopteryx, and it drags Bakonydraco into the clade as well. This could be a more reasonable result than it might appear at first – there are Azhdarchid cervicals from the Csehbanya Formation that resemble other members of this clade (MTM Gyn/450; Osi et al. 2005). Perhaps this morphotype belongs to Bakonydraco. It is perhaps also noteworthy that both Hatzegopteryx and Bakonydraco have very wide skulls at the jaw joint.

Short necked clade.png
Results of the analysis. Several OTUs outside the short-necked clade are not shown here so as to not give too much away.

tl:dr; the new Romanian mandible can probably be tentatively assumed to be Hatzegopteryx. Bakonydraco might be an Azhdarchid after all, and the two might be related.

Hatzegopteryx skull.png
Reconstruction of the skull of Hatzegopteryx. Scale bars 25 cm; top scaled to LPB R.2357, bottom scaled to the holotype occiput.

And to address the elephant in the room: I’m not sure if this mandible fragment was part of the giant Romanian Azhdarchid material being hyped up as “Dracula”, which is allegedly different from and bigger than Hatzegopteryx thambema. Until more material is published I would take this with a grain of salt.

References

Naish, D.; Witton, M.P. (2017). “Neck biomechanics indicate that giant Transylvanian azhdarchid pterosaurs were short-necked arch predators“. PeerJ 5: e2908.
Osi, A.; Weishampel, D.B.; Jianu, C.M. (2005). “First evidence of azhdarchid pterosaurs from the Late Cretaceous of Hungary“. Acta Palaoentoloigca Polonica 50(4): 777-787.
Osi, A.; Buffetaut, E.; Prondvai, E. (2011). “New pterosaurian remains from the Late Cretaceous (Santonian) of Hungary (Iharkut, Csehbayna Formation)“. Cretaceous Research 32(4): 456-463.
Vremir, M.; Dyke, G.; Csiki-Sava, Z.; Grigorescu, D.; Buffetaut, E. (2018). Partial mandible of a giant pterosaur from the uppermost Cretaceous (Maastrichtian) of the Haţeg Basin, Romania“. Lethaia

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