The phylogenetic relationships of the Paleocene crocodylian Akanthosuchus langstoni are assessed using published data matrices and morphological data from the holotype and referred specimens. Cladistic analyses indicate that Akanthosuchus is unequivocally nested within Alligatoroidea. Weak support from a majority rule consensus tree indicates that Akanthosuchus may be more closely allied with alligatorines than with caimanines, but in the strict consensus tree these relationships remain ambiguous. There is no evidence from phylogenetic analyses to support the hypothesis that Akanthosuchus represents the postcrania of the Paleocene crocodylians Navajosuchus or Ceratosuchus. Growth marks observed in histological sections of osteoderms of the holotype of Akanthosuchus langstoni indicate that it was at least eight years old at the time of death. Although the individual may not have been fully mature at the time of death, lineage dwarfism cannot be ruled out as a possible reason for its relatively small size.

Key words: Crocodylia, Alligatoroidea, Akanthosuchus, osteoderms, dwarfism.

Robert V. Hill rhill01@nyit.edu Department of Anatomy, New York College of Osteopathic Medicine, New York Institute of Technology, Old Westbury, NY 11568, USA; Spencer G. Lucas spencer.lucas@state.nm.us New Mexico Museum of Natural History and Science, 1801 Mountain Road NW, Albuquerque, NM 87104, USA.