On Caupedactylus and Tupuxuara deliradamus

In 1988, Alexander Kellner and Diogenes de Almedeia Campos described a new species of pterosaur, Tupuxuara longicristatus, known from an anterior section of skull, mostly the front part of the nasoantorbital fenestra. Six years later, it was joined by T. leonardii, which is also fragmentary but distinguishable by a less extensive palatal ridge. Later, a much more complete specimen, IMCF 1052, was referred to T. leonardii on the basis of the palatal ridge extent.

In 2009, Mark Witton described and named T. deliradamus, and assigned two specimens. The holotype is a posterior section of skull. The referred specimen, KPMNH DL 84, is more complete, and shares these traits.

In 2013, Kellner named another species of pterosaur, Caupedactylus ybaka. This differs from Tupuxuara in, among other things, the downturn of the rostrum, palatal morphology… the posterior border of the NAOF and the inclination of the quadrate. Also that year, Hebert Bruno Campos and Jaime Headden presented a poster that, among other things, argued the mandible of the referred T. deliradamus specimen probably didn’t belong to it, but pointed out additional diagnostic characters from this specimen’s palate.

tupuxuara
Clockwise from top left: T. longicristatus, holotype of T. leonardii, IMCF 1052, C. ybaka, referred specimen of T. deliradamus, holotype of T. deliradamus. After Witton 2009, Kellner 2013, and Campos and Headden 2013. Not to scale.

T. longicristatus and T. leonardii can (probably) be distinguished from each other (depending on whether the extent of the palatal ridge is diagnostic – see Martill and Naish 2006, but see also Vremir et al. 2015), and Caupedactylus can easily be distinguished from both, but what about T. deliradamus? The diagnosis of T. deliradamus after Witton 2009 is as follows – the additional diagnostic characters provided by Campos and Headden 2013 are only visible in the referred specimen and are not considered right here.

  1. The angle of the quadrate relative to the occlusal margin is 150 degrees
  2. Lacrimal forms an angle of 120 degrees relative to the dorsal border of the nasoantorbital fenestra
  3. Posterior border of the NAOF is straight
  4. Orbit lies below half the height of the NAOF

Caupedactylus ybaka has all of these features. So it seems tempting to sweep that taxon into deliradamus. But the referred specimen of deliradamus – which also falls into this species’ diagnosis – is probably a different species than C. ybaka. The Kanagawa specimen has a distinctive palate, which differs from C. ybaka in the (probable) lack of a postpalatal fenestra and the presence of more developed vomers (Campos and Headden 2013). This, combined with the relative shortness and texture of the crest and other minor skull details, likely distinguish it from C. ybaka at the species level.

This means the holotype of deliradamus is indistinguishable from two species. As well, the holotype of deliradamus doesn’t preserve the anterior snout, whereas T. longicristatus and T. leonardii are only known from the anterior snout. So there’s a chance, even if small, that it could also be either of those. So that’s two to four different species that the deliradamus holotype is indistinguishable from. This would make Tupuxuara deliradamus a nomen dubium.

What, then, is the referred specimen? It differs considerably from IMCF 1052. It differs from C. ybaka. There’s very little overlap with the type of T. longicristatus, but they are pretty similar where they do overlap – for one, the angle of the NAOF is near-identical. The biggest difference is that the crest in T. longicristatus is deeper relative to the maxillary ramus despite the specimen being smaller. It’s uncertain whether this is of systematic significance or if it’s due to individual variation or sexual dimorphism – although the lack of perceptible dimorphism in Caiuajara (Manzig et al. 2014) does go against the latter. The anterior extent of the palatal ridge cannot be ascertained in KPMNH DL 84. It’s fair to assume KPMNH DL 84 is probably its own species of Thalassodromid.

Another specimen may also fall into this fray. In 2015, Ross Elgin figured and described an unnumbered “Tupuxuara-like Azhdarchoid” in the SMNK collections. It’s got great postcrania, but only the posterior skull is preserved. It also has a wide quadrate angle, an angled posterior NAOF border, and a low orbit. Unlike Caupedactylus ybaka and the Kanagawa specimen, though, it has a greater quadrate angle (161 degrees) and a really long, spear-like mandible. Might it be a third species in this mire?

elgin specimen.png
The Karlsruhe Tupuxuara-like azhdarchoid. From Elgin 2015.

In the data matrix of Azhdarchoid pterosaurs I’m building, all putative specimens of Tupuxuara are coded separately. Where they overlap, the codings for the holotype of T. deliradamus are identical to those of both the referred specimen and Caupedactylus. When I run the analysis, Caupedactylus ybaka and the two specimens of deliradamus form a polytomy, with the Karlsruhe specimen as the outgroup to that. Interesting.

caupedactylus tree section.png
The state of things. A couple postcrania-only specimens (incl. the Crato “Azhdarchid” SMNK PAL 2342, which is a Thalassodromid) were excluded due to instability

Should we call all these specimens Caupedactylus? For now I will. Though there is an element of subjectivity to generic assignment, keeping the “T. deliradamus” specimens in Tupuxuara would make the genus polyphyletic with respect to Caupedactylus and Thalassodromeus.

tl:dr; T. deliradamus likely nomen dubium, maybe we should be calling it Caupedactylus.

References
Campos, H.B.N.; Headden, J.A. (2013). “A review of Tupuxuara deliradamus (Pterosauria, Azhdarchoidea, Thalassodromidae) from the Early Cretaceous Romualdo Formation of Brazil”. International Symposium on Pterosaurs – Rio Ptero 2013.
Elgin, R.A. (2015). “Paleobiology, Morphology and Flight Characteristics of Pterodactyloid Pterosaurs”. Dissertation, University of Heidelberg.
Kellner, A.W.A. (2013). “A new unusual tapejarid (Pterosauria, Pterodactyloidea) from the Early Cretaceous Romualdo Formation, Araripe Basin, Brazil”. Earth and Environmental Science Transactions of the Royal Society of Edinburgh 103(3-4): 409-421.
Manzig, P.C.; Kellner, A.W.A.; Weinschutz, L.C.; Fragoso, C.E.; Vega, C.S.; Guimaraes, G.B.; Godoy, L.C.; Liccardo, A.; Ricetti, J.H.Z.; de Moura, Camila C. (2014). “Discovery of a Rare Pterosaur Bone Bed in a Cretaceous Desert with Insights on Ontogeny and Behavior of Flying Reptiles”. PLoS ONE 9(8): e100005.
Martill, D.M.; Naish, D. (2006). “Cranial Crests Development in the Azhdarchoid Pterosaur Tupuxuara, With Review of the Genus and Tapejarid Monophyly”. Palaeontology 49(4): 925-941.
Vremir, M.; Witton, M.; Naish, D.; Dyke, G.; Brusatte, S.L.; Norell, M.; Totoianu, R. (2015). “A medium-sized robust-necked azhdarchid pterosaur (Pterodactyloidea: Azhdarchidae) from the Maastrichtian of Pui (Hateg Basin, Transylvania, Romania)”. American Museum Novitates 3827.
Witton, M.P. (2009). “A new species of Tupuxuara (Thalassodromidae, Azhdarchoidea) from the Lower Cretaceous Santana Formation of Brazil, with a note on the nomenclature of Thalassodromidae”. Cretaceous Research 30(5): 1293-1300.

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