Chiromyoides

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.

Chiromyoides
Temporal range: Thanetian-Ypresian (Clarkforkian-Wasatchian)
~56.8–48.6 Ma
Scientific classification
Kingdom: Animalia
Phylum: Chordata
Class: Mammalia
Order: Primates
Family: †Plesiadapidae
Genus: †Chiromyoides
Stehlin, 1916
Type species
†Chiromyoides campanicus
Stehlin, 1916
Species

†Chiromyoides caesor Gingerich, 1973
†Chiromyoides gigas Burger and Honey, 2008
†Chiromyoides gingerichi Secord, 2008
†Chiromyoides kesiwah Beard et al., 2020
†Chiromyoides major Gingerich, 1975
†Chiromyoides mauberti De Bast et al., 2018
†Chiromyoides minor Gingerich, 1975
†Chiromyoides potior Gingerich, 1975

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, C. 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, C. major, C. minor, and C. potior, from isolated upper incisors found in northern Wyoming, southern Wyoming, and southern Colorado, respectively.[7] Secord (2008) named C. gingerichi from material found in northern Wyoming and southern Montana, Burger and Honey (2008) named C. gigas from several incisors found in northern Colorado, and Beard et al. (2020) named C. kesiwah from material found at several localities in southwestern Wyoming.[8][9][3] A second European species, C. 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 C. gigas, C. minor, and C. kesiwah from southern Wyoming and Colorado, and a northern clade including C. major, C. gingerichi, C. campanicus, and C. 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]

References
  1. Gingerich PD (1976). "Cranial Anatomy and Evolution of Early Tertiary Plesiadapidae (Mammalia, Primates)". hdl:2027.42/48615. Cite journal requires |journal= (help)
  2. Szalay FS (1979). Evolutionary history of the primates. Delson, Eric. New York: Academic Press. ISBN 0-12-680150-9. OCLC 5008038.
  3. Beard, K. Christopher; Jones, Matthew F.; Thurber, Nicholas A.; Sanisidro, Oscar (2020-04-27). "Systematics and paleobiology of Chiromyoides (Mammalia, Plesiadapidae) from the upper Paleocene of western North America and western Europe". Journal of Vertebrate Paleontology. 0 (6): e1730389. doi:10.1080/02724634.2019.1730389. ISSN 0272-4634. S2CID 219070956.
  4. Stehlin HG (1916). "Die Säugetiere des schweizerischen Eocaens". Abhandlungen der schweizerischen paläontologischen Gesellschaft. 38: 1165–1298.
  5. Russell DE (1964). "Les mammifères paléocènes d'Europe". Mémoires du Muséum National d'Histoire Naturelle, Série C. 13: 1–324.
  6. Gingerich PD (August 1973). "First record of the Palaeocene primate Chiromyoides from North America". Nature. 244 (5417): 517–8. Bibcode:1973Natur.244..517G. doi:10.1038/244517a0. PMID 4621129. S2CID 4275012.
  7. Gingerich PD (June 1975). "New North American Plesiadapidae (Mammalia, Primates) and a biostratigraphic zonation of the middle and upper Paleocene". University of Michigan Contributions from the Museum of Paleontology. 24 (13): 135–148.
  8. Secord R (2008). "The Tiffanian Land-Mammal Age (Middle and Late Paleocene) In The Northern Bighorn Basin, Wyoming". hdl:2027.42/61362. Cite journal requires |journal= (help)
  9. Burger BJ, Honey JG (2008-09-12). "Plesiadapidae (Mammalia, Primates) from the late Paleocene Fort Union Formation of the Piceance Creek Basin, Colorado". Journal of Vertebrate Paleontology. 28 (3): 816–825. doi:10.1671/0272-4634(2008)28[816:PMPFTL]2.0.CO;2.
  10. Bast ED, Gagnaison C, Smith T (2018-05-04). "Plesiadapid mammals from the latest Paleocene of France offer new insights on the evolution of Plesiadapis during the Paleocene-Eocene transition". Journal of Vertebrate Paleontology. 38 (3): e1460602. doi:10.1080/02724634.2018.1460602. S2CID 89847768.
  11. Boyer DM, Scott CS, Fox RC (April 2012). "New craniodental material of Pronothodectes gaoi Fox (Mammalia, "Plesiadapiformes") and relationships among members of Plesiadapidae". American Journal of Physical Anthropology. 147 (4): 511–50. doi:10.1002/ajpa.22003. PMID 22378315. S2CID 205333634.
  12. Jehle M, Godinot M, Delsate D, Phélizon A, Pellouin J (2019-06-01). "Evolution of plesiadapid mammals (Eutheria, Euarchonta, Plesiadapiformes) in Europe across the Paleocene/Eocene boundary: implications for phylogeny, biochronology and scenarios of dispersal". Palaeobiodiversity and Palaeoenvironments. 99 (2): 293–351. doi:10.1007/s12549-018-0331-6. ISSN 1867-1608. S2CID 135259959.
  13. Gunnell GF (1994-03-31). "Paleocene mammals and faunal analysis of the Chappo Type Locality (Tiffanian), Green River Basin, Wyoming". Journal of Vertebrate Paleontology. 14 (1): 81–104. doi:10.1080/02724634.1994.10011540. ISSN 0272-4634.
  14. Smith T, Quesnel F, De Plöeg G, De Franceschi D, Métais G, De Bast E, et al. (2014-01-29). Butler RJ (ed.). "First Clarkforkian equivalent Land Mammal Age in the latest Paleocene basal Sparnacian facies of Europe: fauna, flora, paleoenvironment and (bio)stratigraphy". PLOS ONE. 9 (1): e86229. Bibcode:2014PLoSO...986229S. doi:10.1371/journal.pone.0086229. PMC 3906055. PMID 24489703.
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