Microsyops

Dental morphology Consistent with other North American members of Microsyopidae, Microsyops has a lower central incisor that is enlarged, procumbent, and lanceolate. The expansive flattened surface of the lower central incisor is oriented towards the front of the tooth. The upper canine of Microsyops is double-rooted. The upper fourth premolar has a distinct metacone and a weak parastyle. Upper molars exhibit clear conules, in particular a distinct metaconule, unlike the condition in the closely related Craseops. The most characteristic aspect of the cranial morphology of Microsyops is the presence of a postorbital process. This trait is unlike the condition found in early Paleogene primates, which possess a full postorbital bar. However, Microsyops also differs from other plesiadapiforms, which lack either a postorbital bar or process. The postorbital process of Microsyops has been described as being superficially similar to that of dermopterans. Due to limited available material, very little is known about the postcranial morphology of Microsyops, and Microsyopidae in general. ==Taxonomy==

Microsyops was first described by Joseph Leidy in 1872. He compared lower jaw fragments, found by Dr. J. V. Carter in the Bridger Basin of southwestern Wyoming, to the condylarth Hyopsodus gracilis, named by Professor O. C. Marsh of Yale University. At the time he believed the fragments to represent the same animal and proposed the new binomial combination of Microsyops gracilis. Leidy later compared his M. gracilis to Marsh's Limnotherium elegans, which was originally described as a diminutive mammal and later as a primate. He concluded they were the same but with L. elegans as a species of the genus Microsyops, and that his original Microsyops gracilis should be properly named Microsyops elegans. Recognized species of Microsyops includes M. elegans, M. annectens, M. scottianus, M. augustidens, M. kratos, M. latidens, M. cardiorestes, M. vicarius, and M. knightensis, with M. elegans being the type species. However, the overall relationship between plesiadiforms and other living and fossil members of Euarchontoglires has been disputed. In a cladistic analysis including postcranial, cranial, and dental characteristics by Bloch et al. (2007), microsyopids were found to be plesiadapiforms more distantly related to euprimates than plesiadapoids or paromomyoids, and without any special relationship to dermopterans. However, while analyses support a euarchontan grouping, specific relationships of microsyopids to other plesiadapiforms, euprimates, scandentia, and dermoptera remain unresolved. Microsyopids are generally thought to be euarchontans, and some researchers consider them to be stem primates. == Palaeobiology ==

Palaeoecology Dental topographic analysis is suggestive of Microsyops angustidens being insectivorous. Its dietary pattern remained stable over geologic time, in contrast to that of the closely related Arctodontomys wilsoni and Arctodontomys nuptus. Diet and body size Body size diversity of Microsyops spans from the 700-gram Microsyops cardiorestes to over 3000 grams for Microsyops kratos, estimated using the dimensions of the upper and lower last premolar and first molar. ==Paleoenvironment==

Microsyopidae lived from the late Paleocene to the middle Eocene in North America. ==Notable fossils==

A well-preserved skull of Microsyops annectens from Carter Mountain in northwestern Wyoming has been used to generate a virtual endocast via micro-CT. Cranial capacity has been estimated as 5.9 cm, yielding an encephalization quotient (EQ) of 0.26-0.52 depending on different body mass estimates and the choice of equation used to estimate EQ. Microsyops has larger EQ than Plesiadapis cookei, and falls in the lower range of estimates for early Paleogene primates. However, basicranial anatomy is remarkably primitive, because the auditory bulla was not ossified and there are only grooves, rather than bony tubes, for the intrabullar parts of the internal carotid artery and its dependencies. The basicranial anatomy of Microsyops appears to be little changed from that of primitive placental mammals. ==References==