SVP 7 – Montanazhdarcho, not an azhdarchid

Carroll 2015 reports
on the North American Late Cretaceous pterosaur, Montanazhdarcho.

From the abstract:
“The latest Cretaceous fossil record of pterosaurs is dominated by azhdarchids, despite various reports of non azhdarchid material from the Late Campanian and Maastrichtian. However, the only indisputable non-azhdarchid pterosaur material from the latest Cretaceous has been the single nyctosaurid humerus from the Gramame Formation of Brazil*. This study presents evidence that Montanazhdarcho minor is a nonazhdarchid member of the Azhdarchoidea**. M. minor was assigned to the Azhdarchidae based on diagnostic features of the humerus, shoulder girdle, and the partial cervical vertebra of the holotype MOR 691. The initial description focused mainly on the diminutive size (2.5 m wingspan). Subsequent discoveries of postcranial material from thallasadromines, tapejarines, and azhdarchids have revealed that the postcranial features initially used to assign M. minor to the Azhdarchidae are synapomorphies for the more inclusive Azhdarchoidea clade. Phylogenetic analysis reveals that Montanazhdarcho possesses multiple characters that are shared by the Tapejarinae and Thallasadrominae: (1) a broad and well-developed tubercle at the ventroposterior margin of the coracoid; (2) a massive, distinct ulnar crest with a developed proximal ridge; (3) a strong boot-like ventral margin of the humeral head; (4) an ulna/radius as long or longer than metacarpal IV; an (5) a phalanx IV-1 that is as long or longer than metacarpal IV. The results of this study show that the Late Cretaceous pterosaur fauna was not entirely dominated by azhdarchids and recognizes important post-cranial characters that better define Azhdarchoidea. The reappraisal of M. minor as a non-azhdarchid member of theAzhdarchoidea also recognizes M. minor as the first known pterosaur of that clade found in North America, as well as one of the latest occurrences of the group.”

*Actually there is a large rostrum that belongs to another tupuxuarid from the Latest Cretaceous of southern Texas (Fig. 1), so it is not surprising to find tapejarid material then and there.

TMM 42489-2, the tall crested Latest Cretaceous large rostrum and mandible. It's a close match to that of Tupuxuara, otherwise known only from Early Cretaceous South American strata.

Figure 1. TMM 42489-2, the tall crested Latest Cretaceous large rostrum and mandible. It’s a close match to that of Tupuxuara, otherwise known only from Early Cretaceous South American strata.

** Azhdarchoidea improperly includes tapejarids. In the large pterosaur tree the azhdarchids are derived from dorygnathids while the tapejarids are derived from germanodactylids.

References
Carroll N 2015.
Reassignment of Montanazhdarcho minor as a nonazhdarchid member of the Azhdarchoidea. Journal of Vertebrate Paleontology abstracts.
Padian, K., Horner, J.R., and de Ricqlès, A.J 1993. A new azhdarchid pterosaur from the Two Medicine Formation (Late Cretaceous, Campanian) of Montana, identified on the basis of bone histology. Journal of Vertebrate Paleontology 13: 52A.
Padian K, de Ricqlès AJ and Horner JR 1995. Bone histology determines identification of a new fossil taxon of pterosaur (Reptilia: Archosauria)”, Comptes Rendus de l’Academie des Science Serie II (320): 77-84.
McGowen MR, Padian K, de Sosa MA and Harmon RJ 2002. Description ofMontanazhdarcho minor an azhdarchid pterosaur from the Two Medicine Formation (Campanian) of Montana. PaleoBios 22(1): 1–9.

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