The species of †Phareodus (Teleostei: Osteoglossidae) from the Eocene of North America and their phylogenetic relationships

ABSTRACT

The osteoglossomorph genus †Phareodus was first named by Leidy in 1873 although the type species of the genus is based on material reported earlier by Cope (†Osteoglossum encaustwn Cope, 1871). In North America, five species have at one time or another been included in this genus, and the type and figured materials of those nominal species are all from the early to middle Eocene deposits of the Laney and Fossil Butte members of the Green River Formation, southwestern Wyoming, USA. A detailed examination of the †Phareodus collection in FMNH, UALVP, and AMNH, including more than 50 well-preserved new specimens, confirms that †Phareodus encaustus and †P. testis are the only two valid North American †Phareodus species. These two species show little difference in their caudal skeleton, but can be distinguished from each other by seven cranial skeletal features: (1) anterior portion of frontal much broader in †Phareodus encaustus than in †P- testis, (2) parietal longer in †Phareodus encaustus than in †P. testis, (3) horizontal arm of preopercle shorter in †Phareodus encaustus than in †P. testis, (4) posterior infraorbitals longer than deep in †Phareodus encaustus but deeper than long in †P. testis, (5) lower and upper jaws longer in †Phareodus encaustus than in †P. testis, (6) mouth corner more posteriorly located in †Phareodus encaustus than in †P. testis, and (7) hyomandibula with a more expanded triangular anterior wing in †Phareodus encaustus than in †P-testis.

A phylogenetic analysis suggests that the Australian species †Phareodus queenslandicus is most closely related to †Phareodus encaustus, and that the European species †Phareodus (=†Brychaetus) muelleri could be sister to †Phareodus encaustus and †Phareodus queenslandicus.