''Chiromyoides'' is a small plesiadapid primatomorph that is known for its unusually robust upper and lower incisors, deep dentary, and comparatively small cheek teeth. Species of ''Chiromyoides'' are known from the middle Tiffanian through late Clarkforkian

North American Land Mammal Ages The North American land mammal ages (NALMA) establishes a geologic timescale for North American fauna beginning during the Late Cretaceous and continuing through to the present. These periods are referred to as ages or intervals (or stages when ref ...

(NALMA) of western

North America North America is a continent in the Northern Hemisphere and almost entirely within the Western Hemisphere. It is bordered to the north by the Arctic Ocean, to the east by the Atlantic Ocean, to the southeast by South America and the Car ...

, and from late Paleocene deposits in the Paris Basin, France. The unique dental morphology of ''Chiromyoides'' has led several authors to propose a specialized ecological role for the genus. Gingerich (1976)

hypothesized A hypothesis (plural hypotheses) is a proposed explanation for a phenomenon. For a hypothesis to be a scientific hypothesis, the scientific method requires that one can test it. Scientists generally base scientific hypotheses on previous obser ...

that ''Chiromyoides'' was a specialist on seeds, while Szalay and Delson (1979) and Beard et al. (2020) suggested that it may have consumed wood-boring insects in a manner similar to the aye-aye.

Origins and discovery

The type species of ''Chiromyoides'', ''Chiromyoides campanicus'', was originally described in 1916 from fragmentary craniodental material discovered in Cernay, France, with additional material also later found at Berru. Gingerich (1973) described the first North American species, ''Chiromyoides caesor'', from two upper incisors found in northern Wyoming. Several years later, he described three additional North American species, ''Chiromyoides major'', ''Chiromyoides minor'', and ''Chiromyoides potior'', from isolated upper incisors found in northern Wyoming, southern Wyoming, and southern Colorado, respectively. Secord (2008) named ''Chiromyoides gingerichi'' from material found in northern Wyoming and southern Montana, Burger and Honey (2008) named ''Chiromyoides gigas'' from several incisors found in northern Colorado, and Beard et al. (2020) named ''Chiromyoides kesiwah'' from material found at several localities in southwestern Wyoming. A second European species, ''Chiromyoides mauberti'', was named by De Bast et al. (2018) from isolated teeth and several mandibular fragments found near Rivecourt, France.

Evolutionary relationships

''Chiromyoides'' is known only from isolated teeth, mandibular fragments, and maxillary fragments, and its relationships to other plesiadapiforms are not well understood. ''Chiromyoides'' is generally acknowledged to be a member of the family Plesiadapidae, along with '' Plesiadapis'', '' Platychoerops'', '' Nannodectes'', and '' Pronothodectes''. Recent phylogenetic analyses suggest that ''Chiromyoides'' is descended from ''Plesiadapis'', perhaps most closely related to '' Plesiadapis walbeckensis'' or '' Plesiadapis tricuspidens''. Beard et al. (2020) found that species of ''Chiromyoides'' separated into two distinct clades: a more southern clade consisting of ''Chiromyoides gigas'', '' C. minor'', and ''Chiromyoides kesiwah'' from southern Wyoming and Colorado, and a northern clade including ''Chiromyoides major'', ''Chiromyoides gingerichi'', ''Chiromyoides campanicus'', and ''Chiromyoides mauberti''. ''Chiromyoides caesor'' formed a polytomy with the two main clades. ''Chiromyoides potior'' was not included in their analysis. The nesting of the European species ''C. campanicus'' and ''C. mauberti'' in the northern clade suggests that ''Chiromyoides'' dispersed into Europe from North America.

Age and biogeography

The oldest specimens of ''Chiromyoides'' are ''C. minor'' from the Chappo Type Locality in Lincoln County, Wyoming, and an edentulous mandible from the Black Peaks region of southwest Texas that has been referred to either ''C. minor'' or an indeterminate species of ''Chiromyoides''. Both the Chappo locality and the Ray's Bonebed locality of southwest Texas where the edentulous mandible was found are arguably middle Tiffanian (Ti3) in age. ''Chiromyoides caesor'' and ''C. kesiwah'' come from slightly younger Tiffanian (Ti4) beds in the Bighorn Basin and Washakie Basin, respectively, while ''C. potior'', ''C. gigas'', ''C. gingerichi'', and ''C. major'' come from even younger Tiffanian and Clarkforkian deposits in Colorado, Wyoming, and Montana. ''Chiromyoides campanicus'' comes from localities in the Paris Basin that appear to correlate with the late Tiffanian of North America, while ''C. mauberti'' occurs in somewhat younger strata that correlates with the North American Clarkforkian NALMA.

References

{{Taxonbar, from=Q85752148 Plesiadapiformes Prehistoric primate genera Eocene primates Thanetian life Ypresian life Clarkforkian Wasatchian Eocene mammals of Europe Paleogene England Fossils of England Paleogene France Fossils of France Eocene mammals of North America Paleocene mammals of North America Fossils of the United States Paleontology in Colorado Paleontology in Montana Paleontology in Texas Paleontology in Wyoming Fossil taxa described in 1916