Pelycodus
Encyclopedia
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 frugivore
s with an aboreal, quadrupedal locomotion.
and New Mexico
. Over the next hundred years, approximately a dozen species were added, most more primitive dentally than the now renamed Pelycodus jarrovii. In 1977, all but two species were moved into Cantius
by Philip D. Gingerich
on the basis of differences in their molars. There is some disagreement as to whether Pelycodus is distinct enough to be a separate genus.
, 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 M1-2. It has a much better developed hypocone and mesostyle than many species of Cantius, but not quite as developed as Notharctus. 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.
, 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. These scientists either link Pelycodus with the poorly known Hesperolemur or place it as a terminating branch.
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 , typically set from 55,400,000 to 50,300,000 years BP lasting . It is usually considered to be within the Eocene, more specifically the...
) period in North America, specifically Wyoming and New Mexico. It is very closely related to Cantius
Cantius
Cantius was a genus of adapiformes primate that lived in the Eocene....
and may even be its subgenus. It may also have given rise to the Middle Eocene Uintan
Uintan
The Uintan North American Stage on the geologic timescale is the North American faunal stage according to the North American Land Mammal Ages chronology , typically set from 46,200,000 to 42,000,000 years BP lasting . It is usually considered to fall within the Eocene epoch...
primate Hesperolemur
Hesperolemur
Hesperolemur actius is an extinct primate that lived in the middle Eocene of southern California. It is an immigrant taxa which appears to be most closely related to the earlier European forms of Cantius...
, 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
Frugivore
A frugivore is a fruit eater. It can be any type of herbivore or omnivore where fruit is a preferred food type. Because approximately 20% of all mammalian herbivores also eat fruit, frugivory is considered to be common among mammals. Since frugivores eat a lot of fruit they are highly dependent...
s 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 WyomingWyoming
Wyoming is a state in the mountain region of the Western United States. The western two thirds of the state is covered mostly with the mountain ranges and rangelands in the foothills of the Eastern Rocky Mountains, while the eastern third of the state is high elevation prairie known as the High...
and New Mexico
New Mexico
New Mexico is a state located in the southwest and western regions of the United States. New Mexico is also usually considered one of the Mountain States. With a population density of 16 per square mile, New Mexico is the sixth-most sparsely inhabited U.S...
. Over the next hundred years, approximately a dozen species were added, most more primitive dentally than the now renamed Pelycodus jarrovii. In 1977, all but two species were moved into Cantius
Cantius
Cantius was a genus of adapiformes primate that lived in the Eocene....
by Philip D. Gingerich
Philip D. Gingerich
Philip D. Gingerich is a Professor of Paleontology, Professor of Geological Sciences, Professor of Biology, Professor of Anthropology and Director, Museum of Paleontology at the University of Michigan. His research focus is in vertebrate paleontology, especially the Paleocene-Eocene transition and...
on the basis of differences in their molars. There is some disagreement as to whether Pelycodus is distinct enough to be a separate genus.
Morphology
Pelycodus is placed within adapiforms because of its annular ectotympanicEctotympanic
The ectomtympanic is a bone that suspends the eardrum in mammals. It is homologus with the angular....
, small eyes, non-elongated tarsus
Tarsus (skeleton)
In tetrapods, the tarsus is a cluster of articulating bones in each foot situated between the lower end of tibia and fibula of the lower leg and the metatarsus. In the foot the tarsus articulates with the bones of the metatarsus, which in turn articulate with the bones of the individual toes...
and numerous premolar
Premolar
The premolar teeth or bicuspids are transitional teeth located between the canine and molar teeth. In humans, there are two premolars per quadrant, making eight premolars total in the mouth. They have at least two cusps. Premolars can be considered as a 'transitional tooth' during chewing, or...
and molar
Molar (tooth)
Molars are the rearmost and most complicated kind of tooth in most mammals. In many mammals they grind food; hence the Latin name mola, "millstone"....
crests and within Notharctinae
Notharctinae
Notharctinae is an extinct subfamily of primates that were common in North America during the early and middle Eocene...
because of its four premolars, unfused mandible
Mandible
The mandible pronunciation or inferior maxillary bone forms the lower jaw and holds the lower teeth in place...
, a hypocone
Hypocone
The hypocone is the name for a main cusp found on the molars of the upper dentition of hominids. It is found on the distal lingual side of the tooth. It fits into the grooves of the lower dentition and is an adaptation for the overall grinding and tearing of foods using the occlusal of the tooth...
derived from the postprotocingulum and a lacrimal bone
Lacrimal bone
The lacrimal bone, the smallest and most fragile bone of the face, is situated at the front part of the medial wall of the orbit. It has two surfaces and four borders.-Lateral or orbital surface:...
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
Clade
A clade is a group consisting of a species and all its descendants. In the terms of biological systematics, a clade is a single "branch" on the "tree of life". The idea that such a "natural group" of organisms should be grouped together and given a taxonomic name is central to biological...
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 M1-2. It has a much better developed hypocone and mesostyle than many species of Cantius, but not quite as developed as Notharctus. The shape of the molars indicates that Pelycodus, like Cantius and unlike later folivorous Notharctines such as Notharctus
Notharctus
Notharctus was an early primate that inhabited Europe and North America 50 million years ago. Modern lemurs evolved from primates similar to this genus....
and Smilodectes
Smilodectes
Smilodectes is an extinct genus of primate that lived in Wyoming. It possesses a post-orbital bar and grasping thumbs and toes. Smilodectes has a small cranium size and the foramen magnum was located at the back of the skull, on the occipatal bone....
, 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.
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 EoceneEocene
The Eocene Epoch, lasting from about 56 to 34 million years ago , is a major division of the geologic timescale and the second epoch of the Paleogene Period in the Cenozoic Era. The Eocene spans the time from the end of the Palaeocene Epoch to the beginning of the Oligocene Epoch. The start of the...
, and is supporting evidence for gradualism
Gradualism
Gradualism is the belief in or the policy of advancing toward a goal by gradual, often slow stages.-Politics and society:In politics, the concept of gradualism is used to describe the belief that change ought to be brought about in small, discrete increments rather than in abrupt strokes such as...
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. These scientists either link Pelycodus with the poorly known Hesperolemur or place it as a terminating branch.