Santanadactylus brasiliensis is one of the many Romualdo Formation pterosaurs, named by P.H. de Buisonje (1980). The holotype is University of Amsterdam M 4894, an associated humerus and scapulocoracoid. The humerus looks pretty standard for Anhangueria, and it likely belongs to this clade (in fact I would not be surprised if it is within Anhanguera sensu lato, but that’s a problem for another day).
de Buisonje referred another specimen, University of Amsterdam M 4895, as the paratype. This specimen consists of two flattened, elongate cervical vertebrae. Although not associated with the holotype, they were found in the same chalk nodules. Since the original publication, the assignment of these cervicals to the same taxon as the holotype has been questioned (e.g. Bennett 1989, Kellner 1995, Leal et al. 2018), with the latter two publications considering the specimen an azhdarchoid.
To test the affinities of the paratype (hereafter the Amsterdam specimen), I coded it into my azhdarchoid phylogenetic analysis. I also added the holotype of Santanadactylus brasilensis, although the fragmentary nature of the specimen and the dataset’s non-focus on anhanguerians makes it difficult to place.
The Amsterdam specimen ended up as the outgroup to the Chaoyangopteridae + Azhdarchidae clade (I refuse to call it Neopterodactyloidea). Could this represent an azhdarchoid outside any of the four major groups? The specimen shows an interesting mix of features present in both tapejarids (e.g. lateral pneumatic foraminae) and chaoyangopterids (e.g. sunken neural arch, low neural spine). It may be a transitional form between the plesiomorphic state and the derived “elongate” form epitomized in azhdarchids.
Of course, it is not implausible that the Amsterdam specimen is an aberrant member of another clade. Forcing it into Chaoyangopteridae takes 3.999 to 7.208 extra steps (depending on wheteher Cretornis or Microtuban are included), where it ends up as the outgroup to everything else. It only takes 2.206 extra steps to force it into Tapejaridae, although it ends up within Sinopterus, which I’m confident is artifactual due to there being no clear synapomorphies. So although other alternatives are not far off, a position outside the chaoyangopterid-azhdarchid clade seems to be the best-supported preliminarily.
Overall, the pterosaur fauna of the Crato and Romualdo Formations are fairly similar, with thalassodromids, tapejarines, and anhanguerians present in both. Definite chaoyangopterids are only present in the Crato Formation (represented by Lacusovagus and the cervical series UFC 721), while the Amsterdam specimen hails from the overlying Romualdo. If the Amsterdam specimen is indeed its own lineage, this implies the presence of a ghost lineage – a fifth major azhdarchoid lineage – since it postdates the chaoyangopterid-azhdarchid split. But more material and study is needed before we can say anything definite.
While we’re on the topic of Santanadactylus, historically it has been a mess. Many other remains have been referred to Santanadactylus, but in light of Romualdo’s pterosaur diversity, little of it has any right to be so. S. spixii, based on a partial wing, is generally agreed to not be related to Santanadactylus now (my analysis tentatively recovers it as a dsungaripterid, but support is not high, and I haven’t been able to access the full description so the codings are incomplete). Although other material has been referred to Santanadactylus brasiliensis, due to lack of association, overlap, or diagnosability, the taxon should be restricted to the holotype (Kellner and Tomida 2000), and the relationships between it, S. pricei, and the other Romualdo anhanguerians is still murky. But that’s another issue for another day.
Kudos to Dean Schnabel for bringing this specimen to my attention.
Bennett, S.C. (1989). “A pteranodontid pterosaur from the Early Cretaceous of Peru, with comments on the relationships of Cretaceous pterosaurs”. Journal of Paleontology 63: 669-77.
de Buisonje, P.H. (1980). “Santanadactylus brasilensis nov. gen., nov. sp., a long-necked, large pterosaurier from the Aptian of Brasil”. Proceedings of the Koninklijke Nederlandse Akademie van Wetenschappen B 83(2): 145-72.
Kellner, A.W.A. (1995). “The relationships of the Tapejaridae (Pterodactyloidea) with comments on pterosaur phylogeny”. In: Sun, A.; Wang, Y. (eds). Sixth Symposium on Mesozoic Terrestrial Ecosystems and Biota, Short Papers. China Ocean Press, Beijing: 73-7.
Kellner, A.W.A.; Tomida, Y. (2000). “Description of a new species of Anhangueridae (Pterodactylidea) with comments on the pterosaur fauna from the Santana Formation (Aptian-Albian), northeastern BRazil”. National Science Museum Monographs 17.
Leal, M.E.C.; Pegas, R.V.; Bonde, N.; Kellner, A.W.A. (2018). “Cervical vertebrae of an enigmatic pterosaur from the Crato Formation (Lower Cretaceous, Araripe Basin, NE Brazil). From Hone, D.W.E.; Witton, M.P.; Martill, D.M. (eds). New Perspectives on Pterosaur Palaeobiology. Geological Society, London, Special Publications, 455: 195-208.