Prodiplocynodon

''Prodiplocynodon'' is an extinct genus of basal crocodyloid crocodylian. It is one of the only crocodyloids known from the Cretaceous and existed during the Maastrichtian stage. The only species of ''Prodiplocynodon'' is the type species ''P. langi'' from the Lance Formation of Wyoming, known only from a single holotype skull lacking the lower jaw.

The skull was collected by the American Museum Expedition of 1892 from exposures near the Cheyenne River in Niobrara County. It was described by Charles C. Mook of the American Museum of Natural History in 1941. The generic name means "before ''Diplocynodon''" because Mook saw close similarities between the holotype skull and that of the alligatoroid ''Diplocynodon'' from the Eocene of Europe.

Description

Most of the cranial sutures that outline individual bones of the skull are not visible in the holotype, and are often obscured by cracks. However, the overall shape of ''Prodiplocynodon'' is similar to that of basal alligatoroids. Many of the features seen in ''Prodiplocynodon'' are common among eusuchians. The skull is short and triangular, being around in length. The orbits, or eye sockets, are quite large and subtriangular. The teeth are short and somewhat sharp, and in comparison to modern crocodiles show little variation. The orbits face directly upwards, but this may have been the result of slight compression in the holotype skull. The external nasal aperture, the opening for the nostrils, is very large. There is a constriction at the point of contact between the premaxilla and maxilla which would have been an area of reception for a large mandibular tooth. In ''Prodiplocynodon'', the constriction is not deep, being intermediate between that of ''Alligator'' and '' Crocodylus''.

Classification

Mook suggested that ''Prodiplocynodon'' may be ancestral to alligatorids and crocodylids because it possessed features of both families. However, Mook also noted that some of the features observed in ''Prodiplocynodon'' that are also found in modern crocodylians may be the result of evolutionary convergence, and thus ''Prodiplocynodon'' was also proposed to be an alligatorine.

Phylogeny

''Prodiplocynodon'' was not included in a phylogenetic study until 1996. In that study, ''Prodiplocynodon'' was excluded from the Alligatorinae because it lacked all seven of the unequivocal synapomorphies that were proposed for the clade. According to the 1996 study, characters that exclude ''Prodiplocynodon'' from Alligatorinae include the presence of a distinct lateral constriction between the premaxilla and maxilla, a contact between the nasal and lacrimal, and the lack of posterior massive crushing teeth. The 1996 analysis considered ''Prodiplocynodon'' to be the sister taxon to the Alligatorinae rather than the Crocodylinae because in ''Prodiplocynodon'', the jugal-lacrimal suture is much shorter than the ventral border of the orbit. However, the authors of the study mentioned that this character is also seen in some derived crocodylines, and is lost in some ingroups of Alligatorinae.

Successive phylogenetic studies have placed ''Prodiplocynodon'' as a basal member of Crocodyloidea along with ''Asiatosuchus'', as shown in the cladogram below:

A 2018 tip dating study by Lee & Yates simultaneously using morphological, molecular ( DNA sequencing), and stratigraphic (fossil age) data established the inter-relationships within Crocodilia, which was expanded upon in 2021 by Hekkala ''et al.'' using paleogenomics by extracting DNA from the extinct ''Voay''.

The below cladogram shows the results of the latest studies, which placed ''Prodiplocynodon'' outside of Crocodyloidea, as more basal than Longirostres (the combined group of crocodiles and gavialids).

References

External links

''Prodiplocynodon''
in the Paleobiology Database

{{Taxonbar, from=Q7247624

Late Cretaceous crocodylomorphs of North America
Late Cretaceous reptiles of North America
Crocodilians
Prehistoric pseudosuchian genera