''Pelycodus'' (from Ancient Greek πέλυξ (pélux), “bowl” + ὀδούς (odoús), “tooth”) is an extinct

genus Genus (; : genera ) is a taxonomic rank above species and below family (taxonomy), family as used in the biological classification of extant taxon, living and fossil organisms as well as Virus classification#ICTV classification, viruses. In bino ...

of adapiform primate that lived during the early Eocene (

Wasatchian The Wasatchian North American Stage on the geologic timescale is the North American faunal stage according to the North American Land Mammal Ages chronology (NALMA), typically set from 55,400,000 to 50,300,000 years Before Present, BP lasting . I ...

) period in Europe and North America, particularly 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 The Uintan North American Stage is the North American faunal stage, typically set from 46,200,000 to 42,000,000 years before present lasting 4.2 million years. The Uintan Stage is a key part of the North American land mammal age, North American Lan ...

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

frugivore A frugivore ( ) is an animal that thrives mostly on raw fruits or succulent fruit-like produce of plants such as roots, shoots, nuts and seeds. Approximately 20% of mammalian herbivores eat fruit. Frugivores are highly dependent on the abundance ...

s with an arboreal, quadrupedal locomotion.

History

''Pelycodus'' was first identified as ''Prototomus jarrovii'' by Cope in 1874, who pronounced it a rare inhabitant of both

Wyoming Wyoming ( ) is a landlocked U.S. state, state in the Mountain states, Mountain West subregion of the Western United States, Western United States. It borders Montana to the north and northwest, South Dakota and Nebraska to the east, Idaho t ...

and

New Mexico New Mexico is a state in the Southwestern United States, Southwestern region of the United States. It is one of the Mountain States of the southern Rocky Mountains, sharing the Four Corners region with Utah, Colorado, and Arizona. It also ...

. 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 Philip D. 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.Mikko's Phylogeny Archive

Morphology

''Pelycodus'' is placed within adapiforms because of its annular

ectotympanic The ectotympanic, or tympanicum, is a bony structure found in all mammals, located on the tympanic part of the temporal bone, which holds the tympanic membrane (eardrum) in place. In catarrhine primates (including humans), it takes a tube-shape. ...

, small eyes, non-elongated tarsus and numerous

premolar The premolars, also called premolar Tooth (human), teeth, or bicuspids, are transitional teeth located between the Canine tooth, canine and Molar (tooth), molar teeth. In humans, there are two premolars per dental terminology#Quadrant, quadrant in ...

and molar crests and within

Notharctinae Notharctinae is an extinct subfamily of primates that were common in North America during the early and middle Eocene (55-34 million years ago). The six genera that make up the group ('' Cantius'', '' Pelycodus'', '' Copelemur'', '' Hesperolemur ...

because of its four premolars, unfused

mandible In jawed vertebrates, the mandible (from the Latin ''mandibula'', 'for chewing'), lower jaw, or jawbone is a bone that makes up the lowerand typically more mobilecomponent of the mouth (the upper jaw being known as the maxilla). The jawbone i ...

, a

hypocone A cusp is a pointed, projecting, or elevated feature. In animals, it is usually used to refer to raised points on the crowns of teeth. The concept is also used with regard to the leaflets of the four heart valves. The mitral valve, which has ...

derived from the postprotocingulum and a

lacrimal bone The lacrimal bones are two small and fragile bones of the facial skeleton; they are roughly the size of the little fingernail and situated at the front part of the medial wall of the orbit. They each have two surfaces and four borders. Several bon ...

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 In biology, a clade (), also known as a Monophyly, monophyletic group or natural group, is a group of organisms that is composed of a common ancestor and all of its descendants. Clades are the fundamental unit of cladistics, a modern approach t ...

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 The Eocene ( ) is a geological epoch (geology), epoch that lasted from about 56 to 33.9 million years ago (Ma). It is the second epoch of the Paleogene Period (geology), Period in the modern Cenozoic Era (geology), Era. The name ''Eocene'' comes ...

, and is supporting evidence for

gradualism Gradualism, from the Latin ("step"), is a hypothesis, a theory or a tenet assuming that change comes about gradually or that variation is gradual in nature and happens over time as opposed to in large steps. Uniformitarianism, incrementalism, and ...

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

Literature cited

* {{Taxonbar, from=Q7161815 Notharctinae Eocene primates Prehistoric primate genera Fossil taxa described in 1875 Eocene mammals of North America Taxa named by Edward Drinker Cope Eocene mammals of Europe