Date of Degree
MS (Master of Science)
Christopher A. Brochu
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.
The Fayúm Province of Egypt occupies a depression just west of the Nile Valley. Heavily explored throughout the late 1800s and early 1900s the area is known for the variety of well-preserved fossils covering an almost continuous time span from the Middle Eocene through Early Oligocene. The area is best known for the discovery of early whale relatives and early primates and as such a majority of the work focuses on them.
Several crocodylians have been found in these deposits, yet very little work has been done to revisit these specimens. In this study, specimens of the Early Oligocene Crocodylus megarhinus Andrews 1905 and Crocodylus articeps Andrews 1905 are reexamined in order to determine validity of each species and provide insight into the relationships among early crocodylids.
Historically the name Crocodylus Laurenti 1768 was applied to any fossil crocodylian that fit the general form of a crocodile. Molecular and morphological analysis have placed the divergence of this group of animals during the Miocene. Many species referred to Crocodylus early on likely do not belong there. It is necessary to revisit many of the earlier crocodylians in order to establish where they belong and clarify the phylogenetic relationships within Crocodylia.
A phylogenetic analysis confirms the placement of C. megarhinus outside the crown-group Crocodylus and instead places it as a basal member of family Crocodylidae. This provides support to establish a new genus for C. megarhinus, while C. articeps is designated nomen dubium due to the loss of the original specimen.
publicabstract, Crocodile, Description, Egypt, Fayum, Megarhinus, Phylogenetics
vii, 104 pages
Includes bibliographical references (pages 100-104).
Copyright 2016 Amanda Jane Adams