Notharctus is a genus of adapiform primate that lived in North America during the early to middle Eocene. Known from many geologic formations, including the Bridger Basin and the Devil's Graveyard Formation, Notharctus was wide-ranging throughout North America. The genus contains at least 4 species. Notharctus is among the first known fossil primates from North America, with the first fossil being collected by Joseph Leidy from the Fort Bridger Basin in 1870. Notharctus has a long classification history involving frequent reassessment and assignment to various mammal groups, including the obsolete Pachydermata and the Mesodonta. Notharctus belonged to an extinct primate group known as Adapiformes. Adapiform primates were among the first primates to exhibit a set of adaptations for life in the trees, such as grasping hands, binocular vision, and flexible backs. In addition to this, small orbits in the genera indicate that they were diurnal. The diet of Notharctus was likely leaves, and the genus moved similarly to modern day lemurs in life. The fingers of the genus were elongated for clamping onto branches, including the development of a thumb. Its spine is flexible and Notharctus was about 40 centimetres (16 in) in length, excluding the long tail. Notharctus was relatively large for an early primate, with a maximum weight of 6.9 kg (15 lb) being estimated for one species. The genus exhibits sexual dimorphism of the canines and developments of the brain which indicates it relied less on smell than other earlier primates. Notharctines, including Notharcus, are thought to have gone extinct during the Uintan stage of the middle Eocene due to a cooling climate.
Taxonomy
Notharctus is currently grouped within the Notharctidae, though it has been historically considered an adapid. Within the Notharctidae, Notharctus is considered within the subfamily Notharctinae. Notharctus as a genus is sometimes considered the sister taxon of Cantius, though other researchers consider Cantius to be ancestral to all notharctines. The name of the genus is derived from the Latin "noth", meaning spurious, and the Greek "arctos", meaning bear.
History of research Notharctus was one of the first discovered fossil primates from North America. The type species, Notharctus tenebrosus, was discovered by Joseph Leidy in 1870 from the Fort Bridger Basin, who had difficulties assigning it to any specific group of mammals, noting similarities in its jaw anatomy to carnivorans and to "pachyderms". Leidy opted to refer Notharctus to the pachyderms, but remarked in his description of the genus that the jawbone was incredibly anatomically similar to modern platyrrhine monkeys. This similarity was also noted by Othniel Charles Marsh, who compared the jaw to Hyopsodus. Marsh assigned these remains to the genus Limnotherium, then later he found more remains which he described as Thinolestes. Marsh found limb bones in October of 1872, which shared similarities with lemurs, causing him to assign the genus to the Quadrumana (an obsolete classification including all non-human primates). In 1876, Edward Drinker Cope proposed Notharctus and Pelycodus belonged to a new order, the Mesodonta, due to the fact that Pelycodus had been associated historically with creodont claws. This order acted as an "intermediate" between creodonts and prosimians, according to Cope. Cope later in 1885 considered Notharctus a lemuroid, yet he still considered the lemuroids close to the obsolete Insectivora and Condylarthra. In 1895, Karl Alfred von Zittel continued this error, referring Notharctus alongside Pelycodus, Microsyops and Hyopsodus within the Pachylemuridae. Notharctus was then later grouped within Adapis by Jacob Wortman in 1904 and Schlosser in 1887, who presumed the mesodonts were a polyphyletic assemblage. Wortman referred this group to the Neopithecini, a group also including simians but not lemurs. Henry Fairfield Osborn agreed with the classification of Notharctus as a primate, grouping Notharctus closely to Pelycodus in 1902, yet he still retained usage of the suborder Mesodonta, which united the Hyopsidontidae, the Notharctidae and the Anaptomorphidae. The family Notharctus was assigned to was given 2 names, with Marsh proposing Limnotheridae in 1875 while Osborn proposed Notharctidae in 1902. With Walter W. Granger's discovery of a nearly complete skeleton, also in Wyoming, it was firmly established as a primate. William King Gregory, in 1915, proposed that Adapis was a direct descendant of Notharctus, an idea first proposed by Schlosser. In 1917, Granger and Gregory published a revision of the genus, and in 1920 Gregory published a monograph which outlined the classification history and anatomy of Notharctus. Gregory considered Notharctus a lemuriform, rather than an adapiform (a grouping which did not exist at the time).
Description Notharctus is one of the best represented adapiform primates, with the postcranial and cranial morphology being well known. Notharctus is distinguished from other fossil primates by its stout jaws, typically fused mandible, and quadrate molars with a pronounced hypocone (a type of cusp on the molar which assists with grinding) and mesostyle (an intermediate cusp on the molar). The different species of Notharctus have been estimated at different sizes, with N. robustior estimated to weigh 6.9 kg (15 lb) while N. tenebrosus has been estimated to weigh 4.2 kg (9.3 lb). The postcranial anatomy of Notharctus has been described as similar to modern day platyrrhines.
Crania
… excerpt ends here. Continue reading the full article.
