Chiromyoides

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Chiromyoides
Temporal range: Thanetian-Ypresian (Clarkforkian-Wasatchian)
~56.8–48.6  Ma
Scientific classification OOjs UI icon edit-ltr.svg
Domain: Eukaryota
Kingdom: Animalia
Phylum: Chordata
Class: Mammalia
Order: Plesiadapiformes
Family: Plesiadapidae
Genus: Chiromyoides
Stehlin, 1916
Type species
Chiromyoides campanicus
Stehlin, 1916
Species

Chiromyoides caesorGingerich, 1973
Chiromyoides gigasBurger and Honey, 2008
Chiromyoides gingerichiSecord, 2008
Chiromyoides kesiwahBeard et al., 2020
Chiromyoides majorGingerich, 1975
Chiromyoides maubertiDe Bast et al., 2018
Chiromyoides minorGingerich, 1975
Chiromyoides potiorGingerich, 1975

Contents

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 (NALMA) of western North America, 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 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. [1] [2] [3]

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. [4] [5] Gingerich (1973) described the first North American species, Chiromyoides caesor, from two upper incisors found in northern Wyoming. [6] 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. [7] 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. [8] [9] [3] 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. [10]

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 [11] [12] or Plesiadapis tricuspidens . [3]

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. [3] 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. [1] [3] 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. [1] [13] Chiromyoides caesor and C. kesiwah come from slightly younger Tiffanian (Ti4) beds in the Bighorn Basin and Washakie Basin, respectively, [8] [3] while C. potior, C. gigas, C. gingerichi, and C. major come from even younger Tiffanian and Clarkforkian deposits in Colorado, Wyoming, and Montana. [8] [9]

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. [12] [14]

Related Research Articles

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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 period, Adapis. Plesiadapis tricuspidens, the type specimen, is named after the three cusps present on its upper incisors.

<i>Bisonalveus</i> Extinct family of mammals

Bisonalveus is an extinct genus of shrew-like mammals that were presumably ground-dwelling and fed on plants and insects. Bisonalveus fossils have been discovered in the upper Great Plains region of North America, including sites in modern-day Wyoming, North Dakota, Montana, and Alberta. The fossils have been dated to 60 million years ago, during the Tiffanian North American Stage of the Palaeocene epoch. Bisonalveus is the last known genus of the Pentacodontinae sub-family to have arisen, replacing the genus Coriphagus in the early Tiffanian. Bisonalveus itself appears to have gone extinct by the middle Tiffanian.

<i>Paroodectes</i> Extinct genus of carnivores

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<span class="mw-page-title-main">Plesiadapidae</span> Family of mammals

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<span class="mw-page-title-main">Viverravinae</span> Extinct subfamily of carnivores

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<span class="mw-page-title-main">Didymictinae</span> Extinct subfamily of carnivores

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References

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