Pelycodus

Taxobox
name = "Pelycodus"
fossil_range = early Eocene
regnum = Animalia
phylum = Chordata
classis = Mammalia
ordo = Primates
familia = †Nothactidae
subfamilia = †Notharctinae
genus = †"Pelycodus"
genus_authority = Cope, 1875
subdivision_ranks = Species
subdivision = †"Pelycodus jarrovii"
†"Pelycodus danielsae"

"Pelycodus" is an extinct Adapiform primate that lived during the early Eocene (Wasatchian) period in North America, specifically Wyoming and New Mexico. It is very closely related to "Cantius" and may even be its subgenus. It may also have given rise to the Middle Eocene Uintan primate "Hesperolemur", although this is controversial. From mass estimates based on the first molar, the two species, "P. jarrovii" and "P. danielsae", weighed 4.5 kg and 6.3 kg respectively and were frugivores with an aboreal, quadrupedal locomotion.

History

"Pelycodus" was first identified as "Prototomus jarrovii" by Cope in 1874, who pronounced it a rare inhabitant of both Wyoming and New Mexico. Over the next hundred years, approximately a dozen species were added, most more primitive dentally than the now renamed "Pelycodus jarrovii". Fleagle, J. G. 1999. Primate Adaptation and Evolution. San Diego, Academic Press. ] In 1977, all but two species were moved into "Cantius" by Phillip Gingerich on the basis of differences in their molars. Gebo, DL. 2002. Adapiformes: phylogeny and adaptation. The Primate Fossil Record. Cambridge University Press ] There is some disagreement as to whether Pelycodus is distinct enough to be a separate genus. [http://www.fmnh.helsinki.fi/users/haaramo/Metazoa/Deuterostoma/Chordata/Synapsida/Eutheria/Plesiadapiformes/plesiadapiformes.htm Mikko's Phylogeny Archive] ]

Morphology

Pelycodus is placed within adapiforms because of its annular ectotympanic, small eyes, non-elongated tarsus and numerous premolar and molar crests and within Notharctinae because of its four premolars, unfused mandible, a hypocone derived from the postprotocingulum and a lacrimal bone within the orbit.There is, however, a great deal of individual variation in the dentition of "Pelycodus", which has made it hard to differentiate between "Pelycodus" and "Cantius" species. Distinguishing features of the "Cantius"/"Pelycodus" clade are the comparatively smaller hypocones and mesostyles. The distinguishing features of "Pelycodus" from "Cantius" are its anteroposteriorly compressed trigonid, its small paraconid on M₂ and lack of hypoconulid on M_1-2. It has a much better developed hypocone and mesostyle than many species of "Cantius", but not quite as developed as "Notharctus". Gingerich, PD and Simons, EL. Systematics, Phylogeny and Evolution of Early Eocene Adapidae in North America. 1977. ] The shape of the molars indicates that "Pelycodus", like "Cantius" and unlike later folivorous Notharctines such as "Notharctus" and "Smilodectes", was most likely a frugivore, though perhaps not as strictly as "Cantius". However, there is almost no difference between the tarsal bones of the earliest "Cantius" and latest "Pelycodus", indicating that their arboreal, quadrupedal locomotion was probably primitive. Only with later Notharctines was there a shift toward more lemur-like locomotion with longer hindlimbs, trunks and tails, perhaps related to the shift in diet. Martin, Robert D. 1993. Primate Origins: plugging the gaps. Nature, 363:223-234.]

Phylogeny

It is very well demonstrated that chronologically successive lineages of "Cantius" grew progressively larger mesostyles and hypocones, eventually gaining enough distinction dentally to be placed in the genus "Pelycodus". This is one of the best stratophenetic sequences in the Eocene, and is supporting evidence for gradualism in evolution. However, even though this well documented fossil sequence appears linear, it probably is an underestimation of the diversity of these genera. It is not certain which, if any, lineages "Pelycodus" gave rise to. Some authors have suggested that it is closely related to "Notharctus", while others have argued that its size already exceeded that of primitive "Notharctus" and therefore was not the most parsimonious phylogeny. ] Godinot, M. A Summary of Adapiform Systematics and Phylogeny. Folia Primatologica, 1998 ] These scientists either link Pelycodus with the poorly known "Hesperolemur" or place it as a terminating branch.

References