Navajovius

Navajovius; Temporal range: Paleocene, 66–56 Ma PreꞒ Ꞓ O S D C P T J K Pg N
Scientific classification
Kingdom:	Animalia
Phylum:	Chordata
Class:	Mammalia
Order:	Plesiadapiformes
Family:	†
Genus:	†Navajovius; Matthew & Granger, 1921

Navajovius is an extinct genus of plesiadapiforms that lived during the Paleocene epoch (66 to 56 million years ago). Plesiadapiforms were small, arboreal mammals that are theorized to be either closely related to primates (Bloch et al. 2007) or dermopterans (Beard 1990). Navajovius has only been documented from localities within North America (Gunnell 1989). This genus was officially named in 1921 by Walter Granger and William Matthew and the type specimen is housed at the American Museum of Natural History (Matthew and Granger 1921).

History of discovery[]

Navajovius was first found in 1916 at the Mason Pocket locality outside of Ignacio, Colorado (Matthew and Granger 1921). The type species of this genus is Navajovius kohlhaasae and the type specimen is AMNH 17390, a fragmentary maxilla and lower dentary (Matthew and Granger 1921).

Several more specimens of N. kohlhaasae have been found in the United States, all dating to the Paleocene. One fossil was recovered from the Evanston Formation, Twin Creeks, Wyoming and two more from the Black Peaks Formation, Big Bend National Park, Texas (Gunnell 1989).

Two other Navajovius specimens which have not been formally described, have also been found in the Circle and Olive localities in Montana. These consist of only fragmentary teeth and there is too little information to identify them to the species level (Gunnell 1989).

The phylogenetic placement of one species originally placed within Navajovius has been debated. Navajovius mckennai was originally described in 1969 by Fred Szalay. However, based on newly collected fossil material, Beard and Dawson (2009) erected a new genus, Choctawius, that includes the type species, Choctawius foxi, as well as Choctawius mckennai, formerly Navajovius mckennai.

Etymology[]

The genus Navajovius was named by Matthew and Granger in 1921 for the Navajo Mountains north of the San Juan River, close to the place of its discovery (Matthew and Granger 1921). The species name, N. kohlhaasae, is named in honor of the specimen preparator, Erna Kohlhasse, who cleaned many of the delicate specimens collected from the Mason Pocket Locality (Matthew and Granger 1921; Simpson 1935).

Taxonomy[]

Navajovius has had a complicated history of classification since its discovery. Granger and Matthew (1921) initially placed it within the family Tarsiidae and was subsequently reassigned into the family Anaptomorphidae (Simpson 1935) and the subfamily Omomyinae (Simpson 1940). Navajovius has also been placed in the subfamily Uintasoricinae within the family Microsyopidae (Bown and Rose 1976) and into the superfamily Paromomyoidea under the tribe Navajoviini in 1979 (Szalay and Delson 1979; McKenna and Bell 1997).

Today, Navajovius is most commonly ascribed to Microsyopidae, a family within the suborder Plesiadapiformes (Gunnell 1989). Of the microsyopids, Navajovius is considered to be more primitive (Hooker et al. 1999). Navajovius is also classified under the subfamily Navajoviinae which sometimes includes the genus Berruvius. Though the validity of this classification is disputed (Hooker et al. 1999). There is only one named species under this genus, Navajovius kohlhaasae.

Description[]

Very few fossils belonging to this genus have been found, limiting the descriptive material to lower jaws, maxillae, and fragmentary teeth (Gunnell 1989). From these remains we can tell that Navajovius was quite small, with an estimated body mass of four grams (Gunnell 1989).

The dental formula of Navajovius is greatly debated. The lower dental formula has been suggested to be 2-1-2-3 (Granger and Matthew 1921; Szalay and Delson 1979), 1-1-3-3 (Simpson 1935; Bown and Gingerich 1972; Gunnell 1989), 1-0-3-3 (Gazin 1958), and 1-0-4-3 (Szalay 1969). A gap between the anterior dentition and cheek teeth is considered to be a space for the canine by some and a diastema by others, accounting for some of this disagreement (Gunnell 1989).

There are a few dental morphologies that are agreed upon. The first incisor is somewhat enlarged, procumbent and lanceolate in shape (Matthew and Granger 1921; Gunnell 1989; Hooker et al. 1999). The third premolar has a double root and is relatively smaller than both the second and fourth premolar (Gunnell 1989; Ridder 2018). The fourth premolar lacks a metacone and the paraconid is weak (Gunnell 1989; Ridder 2018). The lower molars have distinct, reduced paraconids (Matthew and Granger 1921; Gunnell 1989; Hooker et al. 1999; Ridder 2018) and the third molar is reduced in size (Gunnell 1989; Hooker et al. 1999; Ridder 2018).

Most researchers agree that the second incisor is absent (Gunnell 1989), the second premolar is single rooted, and that the fourth premolar is molariform in shape (Ridder 2018). The presence of the upper and lower canine is also debated. While most researchers include the lower canine in the dental formula, some suggest that it is absent all together (Gazin 1958; Ridder 2018). The presence of a vestigial upper canine has been suggested to be present as well (Ridder 2018). Based on its morphology and age range, Navajovius is sometimes suggested to be one of the more primitive microsyopids (Hooker et al. 1999).

Paleobiology[]

Habitat and range[]

Fossils of Navajovius have been found in several places in the western United States. N. kohlhaasae has been found in Colorado, Texas, and Wyoming. If the two unnamed specimens are included, the range can be pushed further north into Montana. All of these localities are considered to be from the Tiffanian North American Land Mammal Age (NALMA) and date back to the late Paleocene Epoch, about 61.7 to 56.8 million years ago (Gunnell 1989). As plesiadapiforms are largely thought to be arboreal, it can be assumed that the western United States was covered in forests during this time. Notes on the collection found in the Mason Pocket locality in Colorado, where the holotype for N. kohlhaasae was found, indicates that the majority of the fauna found there were arboreal (Simpson 1935). As there are currently no postcranial remains from Navajovius, there can be no analysis of locomotor behavior for this taxon.

Diet[]

Based on dental morphology, Navajovius most likely had a generalized diet, eating a variety of foods possibly including insects, fruits, and tree sap (Szalay and Delson 1979; Ridder 2018). The shape of their incisors and other anterior teeth suggest that they functioned for slicing and shearing (Gunnell 1989).

References[]

Beard, K. Christopher. 1990. “Gliding Behaviour and Palaeoecology of the Alleged Primate Family Paromomyidae (Mammalia, Dermoptera).” Nature 345 (6273): 340–41.
Beard, K. Christopher, and Mary R. Dawson. “Early Wasatchian Mammals of the Red Hot Local Fauna, Uppermost Tuscahoma Formation, Lauderdale County, Mississippi,” Annals of Carnegie Museum 78, no. 3 (2009): 193–243.
Bloch, Jonathan I., Mary T. Silcox, Doug M. Boyer, and Eric J. Sargis. 2007. “New Paleocene Skeletons and the Relationship of Plesiadapiforms to * Crown-Clade Primates.” Proceedings of the National Academy of Sciences 104 (4): 1159–64.
Bown, Thomas M., and Kenneth D. Rose. “New Early Tertiary Primates and a Reappraisal of Some Plesiadapiformes.” Folia Primatologica 26, no. 2 (1976): 109–38.
Bown, Thomas M., and P. D. Gingerich. “The Paleocene Primate Plesiolestes and the Origin of Microsyopidae.” Folia Primatologica 19, no. 1 (1973): 1–8.
Gazin, Charles Lewis. “A Review of the Middle and Upper Eocene Primates of North America.” Smithsonian Miscellaneous Collections 136, no. 1 (1958): 1–112.
Gunnell, Gregg Frederick. “Evolutionary History of Microsyopoidea (Mammalia, Primates?) and the Relationship of Plesiadapiformes to Primates.” Dissertation, 1986.
Hooker, J. J., D. E. Russell, and A. Phélizon. “A New Family of Plesiadapiformes (Mammalia) from the Old World Lower Paleogene.” Palaeontology 42, no. 3 (1999): 377–407.
Matthew, William D., and Walter W. Granger. “New Genera of Paleocene Mammals.” American Museum Novitates 13 (1921): 1–7.
McKenna, Malcom C., and Susan K. Bell. Classification of Mammals Above the Species Level. New York, NY: Columbia University Press, 1997.
Ridder, Ryan. “Fossil Mammals of the Twelvemile Bonanza Local Fauna, Late Tiffanian of Southwestern Wyoming,” 2018.
Rose, Kenneth D., and Thomas M. Bown. “A New Plesiadapiform (Mammalia; Plesiadapiformes) from the Early Eocene of the Bighorn Basin.” Annals of Carnegie Museum 65 (1996): 305–21.
Rose, Kenneth D., and Thomas M. Bown. “New Plesiadapiform Primates from the Eocene of Wyoming and Montana.” Journal of Vertebrate Paleontology 2, no. 1 (1982): 63–69.
Simpson, George Gaylord. “The Tiffany Fauna, Upper Paleocene: 1. Multituberculata, Marsupialia, Insectivora and ?Chiroptera.” American Museum Novitates 795 (1935): 1–19.
Simpson, George Gaylord. “Studies on the Earliest Primates.” Bulletin of the American Museum of Natural History 77 (1940): 185–212.
Szalay, Frederick S. “Mixodectidae, Microsyopidae, and the Insectivore-Primate Transition.” Bulletin of the American Museum of Natural History 140, no. 4 (1969): 193–330.
Szalay, Frederick S., and Eric Delson. Evolutionary History of the Primates. New York, NY: Academic Press, 1979.

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