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Journal of Paleontology

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OSTEOLOGY AND PHYLOGENETIC SIGNIFICANCE OF EOSUCHUS MINOR (MARSH, 1870) NEW COMBINATION, A LONGIROSTRINE CROCODYLIAN FROM THE LATE PALEOCENE OF NORTH AMERICA

¹ Department of Geoscience, University of Iowa, Iowa City 52242, <christopher-brochu{at}uiowa.edu>

Eosuchus minor (Marsh, 1870) is based on skeletal fragments from the Late Paleocene or Early Eocene of New Jersey, but more complete material from the Late Paleocene of New Jersey, Maryland, and Virginia permits a detailed description and systematic assessment. It is a slender-snouted form and can be distinguished from most other crocodylians on the basis of an enlarged quadrate foramen aereum; a distinct W-shaped rugosity along the ventral margin of the basioccipital tuber; a prominent crest on the lateral braincase wall encompassing portions of the quadrate, pterygoid, and basisphenoid, forming the lateral wall of the lateral eustachian canal at its ventralmost extent; and arrangement of dentary alveoli into couplets. Specimens of larger crocodylians from the same units may represent either the adult form of E. minor or a separate taxon. The enlarged quadrate foramen aereum, couplet arrangement of dentary alveoli, and basioccipital tuber shape are shared with Eosuchus lerichei from the Late Paleocene of Europe. Eosuchus lies within Gavialoidea crownward of the basal forms Thoracosaurus and Eothoracosaurus. The braincase of Eosuchus is intermediate between that of Thoracosaurus and that of Gavialis; the basisphenoid retains a short (but externally visible) descending lamina, but the basisphenoid is also anteroposteriorly expanded at the level of the median eustachian foramen.

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