''Chiromyoides'' is a small

plesiadapid Plesiadapidae is a family of plesiadapiform mammals related to primates known from the Paleocene and Eocene of North America, Europe, and Asia. Plesiadapids were abundant in the late Paleocene, and their fossils are often used to establish the ...

primatomorph The Primatomorpha are a proposed mirorder of mammals containing the flying lemurs (order Dermoptera or colugos) and lemurs (Strepsirrhini, adapiformes and lemuriformes). However, notably, the haplorhini are sister to the lemurs, together for ...

that is known for its unusually robust upper and lower

incisor Incisors (from Latin ''incidere'', "to cut") are the front teeth present in most mammals. They are located in the premaxilla above and on the mandible below. Humans have a total of eight (two on each side, top and bottom). Opossums have 18, w ...

s, deep

dentary In anatomy, the mandible, lower jaw or jawbone is the largest, strongest and lowest bone in the human facial skeleton. It forms the lower jaw and holds the lower teeth in place. The mandible sits beneath the maxilla. It is the only movable bone ...

, and comparatively small cheek teeth. Species of ''Chiromyoides'' are known from the middle

Tiffanian The Tiffanian 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 60,200,000 to 56,800,000 years BP lasting . It is usually co ...

through late

Clarkforkian The Clarkforkian 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 56,800,000 to 55,400,000 years BP lasting . Considered ...

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 re ...

(NALMA) of western North America, and from late

Paleocene The Paleocene, ( ) or Palaeocene, is a geological epoch that lasted from about 66 to 56 million years ago (mya). It is the first epoch of the Paleogene Period in the modern Cenozoic Era. The name is a combination of the Ancient Greek ''pal ...

deposits in the

Paris Basin The Paris Basin is one of the major geological regions of France. It developed since the Triassic over remnant uplands of the Variscan orogeny (Hercynian orogeny). The sedimentary basin, no longer a single drainage basin, is a large sag in the ...

France France (), officially the French Republic ( ), is a country primarily located in Western Europe. It also comprises of overseas regions and territories in the Americas and the Atlantic, Pacific and Indian Oceans. Its metropolitan ar ...

. The unique dental

morphology Morphology, from the Greek and meaning "study of shape", may refer to: Disciplines *Morphology (archaeology), study of the shapes or forms of artifacts *Morphology (astronomy), study of the shape of astronomical objects such as nebulae, galaxies, ...

of ''Chiromyoides'' has led several authors to propose a specialized

ecological Ecology () is the study of the relationships between living organisms, including humans, and their biophysical environment, physical environment. Ecology considers organisms at the individual, population, community (ecology), community, ecosy ...

role for the genus.

Gingerich Gingerich is a surname of German origin. Other forms of the name are Gingrich, Gingerick and Gingery and its original form Güngerich, also written Guengerich. In Bern, Switzerland it was record as early as 1389 and in 1692 it was first recorded ...

(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 A beard is the hair that grows on the jaw, chin, upper lip, lower lip, cheeks, and neck of humans and some non-human animals. In humans, usually pubescent or adult males are able to grow beards. Throughout the course of history, societal a ...

et al. (2020) suggested that it may have consumed wood-boring insects in a manner similar to the

aye-aye The aye-aye (''Daubentonia madagascariensis'') is a long-fingered lemur, a strepsirrhine primate native to Madagascar with rodent-like teeth that perpetually grow and a special thin middle finger. It is the world's largest nocturnal primate. ...

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 :''Berrú leads here. For Max Berrú Carrión (1942-2018), the Ecuadorian and Chilean musician, see Max Berrú'' Berru () is a commune in the Marne department in northeastern France. Berru, along with the neighboring commune of Cernay-lès-Rei ...

. Gingerich (1973) described the first North American species, ''Chiromyoides caesor'', from two upper incisors found in northern

Wyoming Wyoming () is a state in the Mountain West subregion of the Western United States. It is bordered by Montana to the north and northwest, South Dakota and Nebraska to the east, Idaho to the west, Utah to the southwest, and Colorado to the sou ...

. 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 Colorado (, other variants) is a state in the Mountain states, Mountain West subregion of the Western United States. It encompasses most of the Southern Rocky Mountains, as well as the northeastern portion of the Colorado Plateau and the wes ...

, respectively. Secord (2008) named ''Chiromyoides gingerichi'' from material found in northern Wyoming and southern

Montana Montana () is a U.S. state, state in the Mountain states, Mountain West List of regions of the United States#Census Bureau-designated regions and divisions, division of the Western United States. It is bordered by Idaho to the west, North ...

, 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

Europe Europe is a large peninsula conventionally considered a continent in its own right because of its great physical size and the weight of its history and traditions. Europe is also considered a subcontinent of Eurasia and it is located enti ...

an species, ''Chiromyoides mauberti'', was named by De Bast et al. (2018) from isolated teeth and several

mandibular In anatomy, the mandible, lower jaw or jawbone is the largest, strongest and lowest bone in the human facial skeleton. It forms the lower jaw and holds the lower teeth in place. The mandible sits beneath the maxilla. It is the only movable bone ...

fragments found near

Rivecourt Rivecourt () is a commune in the Oise department Department may refer to: * Departmentalization, division of a larger organization into parts with specific responsibility Government and military *Department (administrative division), a geogr ...

, France.

Evolutionary relationships

''Chiromyoides'' is known only from isolated teeth, mandibular fragments, and

maxilla The maxilla (plural: ''maxillae'' ) in vertebrates is the upper fixed (not fixed in Neopterygii) bone of the jaw formed from the fusion of two maxillary bones. In humans, the upper jaw includes the hard palate in the front of the mouth. The ...

ry fragments, and its relationships to other

plesiadapiforms Plesiadapiformes ("Adapid-like" or "near Adapiformes") is a group of Primates, a sister of the Dermoptera. While none of the groups normally directly assigned to this group survived, the group appears actually not to be literally extinct (in th ...

are not well understood. ''Chiromyoides'' is generally acknowledged to be a member of the family

Plesiadapidae Plesiadapidae is a family of plesiadapiform mammals related to primates known from the Paleocene and Eocene of North America, Europe, and Asia. Plesiadapids were abundant in the late Paleocene, and their fossils are often used to establish th ...

, along with ''

Plesiadapis ''Plesiadapis'' is one of the oldest known primate-like mammal genera which existed about 58–55 million years ago in North America and Europe. ''Plesiadapis'' means "near-Adapis", which is a reference to the adapiform primate of the Eocene p ...

'', '' Platychoerops'', '' Nannodectes'', and '' Pronothodectes''. Recent

phylogenetic analyses In biology, phylogenetics (; from Greek φυλή/ φῦλον [] "tribe, clan, race", and wikt:γενετικός, γενετικός [] "origin, source, birth") is the study of the evolutionary history and relationships among or within groups o ...

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 clade (), also known as a monophyletic group or natural group, is a group of organisms that are monophyletic – that is, composed of a common ancestor and all its lineal descendants – on a phylogenetic tree. Rather than the English term ...

: 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 An internal node of a phylogenetic tree is described as a polytomy or multifurcation if (i) it is in a rooted tree and is linked to three or more child subtrees or (ii) it is in an unrooted tree and is attached to four or more branches. A tr ...

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 Texas (, ; Spanish language, Spanish: ''Texas'', ''Tejas'') is a state in the South Central United States, South Central region of the United States. At 268,596 square miles (695,662 km2), and with more than 29.1 million residents in 2 ...

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 The Bighorn Basin is a plateau region and intermontane basin, approximately 100 miles (160 km) wide, in north-central Wyoming in the United States. It is bounded by the Absaroka Range on the west, the Pryor Mountains on the north, the Bigh ...

and

Washakie Basin Washakie (1804/1810 – February 20, 1900) was a prominent leader of the Shoshone people during the mid-19th century. He was first mentioned in 1840 in the written record of the American fur trapper, Osborne Russell. In 1851, at the urging o ...

, 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