''Glirodon'' is a

genus Genus ( plural genera ) is a taxonomic rank used in the biological classification of living and fossil organisms as well as viruses. In the hierarchy of biological classification, genus comes above species and below family. In binomial nom ...

of extinct mammal from the Upper

Jurassic The Jurassic ( ) is a geologic period and stratigraphic system that spanned from the end of the Triassic Period million years ago (Mya) to the beginning of the Cretaceous Period, approximately Mya. The Jurassic constitutes the middle period of ...

. It was a relatively early member of the also-extinct order of

Multituberculata Multituberculata (commonly known as multituberculates, named for the multiple tubercles of their teeth) is an extinct order of rodent-like mammals with a fossil record spanning over 130 million years. They first appeared in the Middle Jurassic, a ...

, suborder "

Plagiaulacida Plagiaulacida is a group of extinct multituberculate mammals. Multituberculates were among the most common mammals of the Mesozoic, "the age of the dinosaurs". Plagiaulacids are a paraphyletic grouping, containing all multituberculates that lie ...

". These mammals lived in North America during the Mesozoic, also known as the "age of the

dinosaur Dinosaurs are a diverse group of reptiles of the clade Dinosauria. They first appeared during the Triassic period, between 243 and 233.23 million years ago (mya), although the exact origin and timing of the evolution of dinosaurs is t ...

s". The genus ''Glirodon'' has been described by Engelmann G.F. and Callison G. (1999) from a 'gliriform tooth'. The

species In biology, a species is the basic unit of classification and a taxonomic rank of an organism, as well as a unit of biodiversity. A species is often defined as the largest group of organisms in which any two individuals of the appropriate s ...

''Glirodon grandis'', also described by Engelmann and Callison, has been found in the Upper Jurassic formations of Dinosaur National Monument in

Utah Utah ( , ) is a state in the Mountain West subregion of the Western United States. Utah is a landlocked U.S. state bordered to its east by Colorado, to its northeast by Wyoming, to its north by Idaho, to its south by Arizona, and to it ...

(United States). Other than being a large, early American Multituberculate, (see

), the nature of this beast is somewhat unclear. It is an "allodontid (two families and the genus ''Glirodon'')", (Kielan-Jaworowska and Hurum, 2001). It had gliriform

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, wher ...

s; incisors with the "enamel reduced to a stripe on the front side." Apparently, this condition evolved several times among Multituberculates. It is based on a portion of snout. "''Glirodon'' retains the plesiomorphic 'plagiaulacidan' ("

dental formula Dentition pertains to the development of teeth and their arrangement in the mouth. In particular, it is the characteristic arrangement, kind, and number of teeth in a given species at a given age. That is, the number, type, and morpho-physiolog ...

and shares with Allodontidae the structure of the upper premolars (Pl.1 fis 2-4). It differs from the Paulchoffatiidae and Plagiaulacidae in having a single-cusped I3," (Kielan-Jaworowska & Hurum, 2001, p. 401-402). I3 refers to an upper incisor and 'plesiomorphic' means 'basal'. Present in stratigraphic zones 4 and 6.Foster, J. (2007). "Appendix." ''Jurassic West: The Dinosaurs of the Morrison Formation and Their World''. Indiana University Press. pp. 327–329.

References

* Engelmann & Callison, (1999), Glirodon grandis, ''a new multituberculate mammal from the Upper Jurassic Morrison Formation''. Vertebrate Paleontology of Utah, pp. 161–178, in the Utah Geological Survey, (ed. Gillette DD), 8/99. * Kielan-Jaworowska Z & Hurum JH (2001), ''Phylogeny and Systematics of multituberculate mammals''. Paleontology 44, p. 389–429. * Most of this information has been derived fro

MESOZOIC MAMMALS; Basal Multituberculata, an Internet directory. Multituberculates Morrison mammals Fossil taxa described in 1999 Prehistoric mammal genera {{jurassic-mammal-stub