A reassessment of the late Eocene - early Oligocene crocodylids Crocodylus megarhinus Andrews 1905 and Crocodylus articeps Andrews 1905 from the Fayúm Province, Egypt

• Main Author: Adams, Amanda Jane
• Other Authors: Brochu, Christopher A. (Christopher Andrew), 1967-
• Format: Others
• Language: English
• Published: University of Iowa 2016
• Subjects: publicabstract; Crocodile; Description; Egypt; Fayum; Megarhinus; Phylogenetics; Geology
• Online Access: https://ir.uiowa.edu/etd/3033; https://ir.uiowa.edu/cgi/viewcontent.cgi?article=6378&context=etd

The Fayúm Province of Egypt covers an almost continuous time span from the middle Eocene through the early Oligocene and has produced a number of vertebrate fossils important to evolutionary history. This area includes early crocodylids inaccurately assigned to crown-group Crocodylus, which has been shown through molecular and morphological phylogenetic analyses to have diverged during the Miocene. We reviewed two taxa from the early Oligocene Gebel Qatrani Formation, Crocodylus megarhinus Andrews 1905 and Crocodylus articeps Andrews 1905, which had previously been synonymized, with C. articeps thought to be based on a juvenile specimen of C. megarhinus. Crocodylus megarhinus outwardly resembles most living species of Crocodylus, however it is a basal crocodylid lacking diagnostic features for the crown genus. The holotype of C. articeps is now lost, but based on a cast and published images of the original material, it was a slender-snouted form that can be distinguished from smaller specimens of C. megarhinus. Although not synonymous with C. megarhinus, C. articeps cannot be diagnosed or scored for existing character matrices sufficiently to allow precise phylogenetic placement. Previous analyses of C. megarhinus included information from C. articeps; recoding C. megarhinus based only on material referable to that species does not change its phylogenetic position, but it forces a reconsideration of the polarity of character states in clades leading to the origin of crown-genus Crocodylus which, in turn, may inform efforts to resolve the relationships among living crocodylid lineages. Based on its confirmed phylogenetic position as a basal crocodylid, C. megarhinus provides insight into the ancestral conditions of all crocodylids and supports an African origin for Crocodylidae.