''Rhizosmilodon'' is an

extinct Extinction is the termination of an organism by the death of its Endling, last member. A taxon may become Functional extinction, functionally extinct before the death of its last member if it loses the capacity to Reproduction, reproduce and ...

genus Genus (; : genera ) is a taxonomic rank above species and below family (taxonomy), family as used in the biological classification of extant taxon, living and fossil organisms as well as Virus classification#ICTV classification, viruses. In bino ...

of saber-tooth cat of the

subfamily In biological classification, a subfamily (Latin: ', plural ') is an auxiliary (intermediate) taxonomic rank, next below family but more inclusive than genus. Standard nomenclature rules end botanical subfamily names with "-oideae", and zo ...

Machairodontinae Machairodontinae (from Ancient Greek μάχαιρα ''Makhaira, machaira,'' a type of Ancient Greek sword and ὀδόντος ''odontos'' meaning tooth) is an extinct subfamily of carnivoran mammals of the cat family Felidae, representing the ...

that lived during the

Early Pliocene Early may refer to: Places in the United States * Early, Iowa, a city * Early, Texas, a city * Early Branch, a stream in Missouri * Early County, Georgia * Fort Early, Georgia, an early 19th century fort Music * Early B, stage name of Jamaican d ...

and was discovered in the U.S. state of

Florida Florida ( ; ) is a U.S. state, state in the Southeastern United States, Southeastern region of the United States. It borders the Gulf of Mexico to the west, Alabama to the northwest, Georgia (U.S. state), Georgia to the north, the Atlantic ...

History and Naming

The first fossils of ''Rhizosmilodon'' were discovered in fossil beds of central Florida by Steven C. Wallace and Richard C. Hulbert Jr and described in 2013. The holotype specimen, UF 124634, consists of a single right mandible. Many bones of ''Rhizosmilodon'' have been discovered including; Teeth; mandibles; foot bones; leg bones; and a single skull. All specimens of ''Rhizosmilodon'' have only been found in Florida. The locality of ''Rhizosmilodon'' suggests a North American origin of the Dirk-Toothed cats. Specimens of ''Rhizosmilodon'' were originally referred under '' Megantereon hesperus''. The Etymology of the genus name was given by Wallace & Hubert to mean "root of Smilodon", with "rhizo" meaning "root" because of the apparent ancestral relation to '' Smilodon''. The species name "fiteae" was named in honor of Barbara Fite, who donated the paratype specimen, UF 135626, to the Florida Museum of Natural History.

Description

Comparable in size to a medium-sized modern jaguar at about 165 lb, some estimates ranging between 55.7 to 58.3 kg (122.9 to 128.5 lbs) and 76.6 to 85.0 kg (168.9 to 187.4 lbs). Fossils of ''Rhizosmilodon'' are known only from Florida. The best specimens for this species are its lower jaw, a single skull, and teeth, which carry intermediate characteristics between advanced forms such as ''Smilodon'' and primitive forms such as ''Paramachairodus''. Based on the mandible alone, ''Rhizosmilodon'' has the primitive traits traits: a large lower canine and a small but evident jaw flange. The derived traits include various measurements of the incisors, p3, p4, and m1 teeth, with the lower canine being laterally compressed. Serrations only on the canine teeth support the placement of ''Rhizosmilodon'' within the tribe Smilodontini rather than the scimitar-toothed Homotherini. The severity of the serrations place ''Rhizosmilodon'' as a more ancestral genus than ''Megantereon'' and ''Smilodon''. It was likely an ambush predator, preying on animals such as deer, tapirs and horses. Its size and robustness would have allowed it to climb into trees.

Phylogeny

Phylogenetic relationships of ''Rhizosmilodon'' with other Machairodonts based on analysis of 37 cranio-mandibular characters.

References

{{Taxonbar, from1=Q12278450, from2=Q111033701 Smilodontini Extinct mammals of North America Fossil taxa described in 2013 Monotypic prehistoric carnivoran genera