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Fossil Species of Florida

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Mammalia, Carnivora, Feliformia, Felidae, Machairodontinae, Smilodontini

RHIZOSMILODON FITEAE
WALLACE & HULBERT, 2013

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Common Name: Fite’s saber-tooth cat


Alternate Species Names: Megantereon hesperus sensu Berta and Galiano (1983)


Source of Species Name: named for Barbara Fite of Lutz, Florida, who donated the paratype specimen to the Florida Museum of Natural History.


Age Range: early Pliocene (late Hemphillian Land Mammal Age), about 4.5 to 5 million years ago.


Florida Fossil Occurrences:

Florida map with occurrences indicated

Figure 1. Map of Florida, with black circles indicating counties where fossils of Rhizosmilodon fiteae have been found (the circles do not indicate a specific location within the county where the fossils were found, and some counties may have two or more different locations producing this species).


Florida Fossil Sites with Rhizosmilodon fiteae:
Hardee County—Fort Green Mine South
Hillsborough County—Four Corners Mine East
Polk County—District Grade Mine; Fort Green Mine; Fort Meade Mine (Gardinier); Palmetto Mine; Phosphoria Mine; Rockland Mine (US Steel); TRO Quarry, Payne Creek Mine; Whidden Creek Site, Fort Meade Mine (Gardinier)

Overall Geographic Range: Rhizosmilodon fiteae is known only from the Central Florida Phosphate Mining Distict, Polk and adjacent counties, Florida. Type locality is the Whidden Creek Site in the Fort Meade Mine of Gardinier, Inc., Polk County, Florida.

Comments: The first published record of a small-sized, saber-toothed cat from the Central Florida Phosphate Mining District (Bone Valley) was by Berta and Galiano (1983). They referred a single partial mandible to Megantereon hesperus, a species otherwise known only from the Blancan Land Mammal Age in North America. Because the age of the Florida specimen was then the oldest record of the genus Megantereon, Berta and Galiano (1983) inferred that the genus had evolved in North America and subsequently dispursed throughout the Old World. Several later studies called the identification of Berta and Galiano (1983) into question (Turner, 1985; Palqvist et al., 2007; Webb et al., 2008; Hodnett, 2010).

After the publication of Berta and Galiano (1983), about two dozen additional specimens of a small-sized, saber-toothed cat were collected in the phosphate mines of central Florida. These demonstrated that their age was definitely late Hemphillian (earliest Pliocene), and that they were definitely not Megantereon (Webb et al., 2008). Wallace and Hulbert (2013) conducted an analysis of their evolutionary relationships, and showed that they did belong in the tribe Smilodontini, and were the sister taxon to Megantereon and Smilodon (Fig. 2). So, Wallace and Hulbert (2013) formally named this cat Rhizosmilodon fitae. It is not known to occur in other areas, but most species of felids have large geographic ranges, so it would not be surprising to find its fossils in other areas of North America. It is the oldest known member of the tribe Smilodontini.

Skull of Olsen's alligator

Figure 2. Evolutionary relationships of some of the sabertooth cats, subfamily Machairodontinae. The genera Rhizosmilodon, Megantereon and Smilodon make up the tribe Smilodontini. After Wallace and Hulbert (2013).


Based on the size its humerus and tibia, Rhizosmilodon fitae weighed about 75 kg or 165 lbs., the same as a medium-sized, modern jaguar, Panthera onca, or a slightly larger than average modern cougar, Puma concolor. This is much smaller than Xenosmilus hodsonae or Smilodon fatalis, which are about the size of a modern tiger, and instead more similar in size to Smilodon gracilis and Megantereon hesperus. Although not directly associated with any cranial specimens, postcranial bones from the Central Florida phosphate mines can be confidently referred to Rhizosmilodon fitae, because no other felid of similar size is present in the fauna, and they show features which differentiate the limb bones of machairodontine felids from pantherine felids. For example, the entepicondylar foramen on the distal end of the humerus is closed by a relatively thin, narrow wall of bone (Fig. 3; Wallace and Hulbert, 2013). Like Smilodon, the humerus of Rhizosmilodon is relatively robust, suggesting powerful forelimbs for its size. It was most likely primarily an ambush predator, with a preferred prey size in the general range of 50-100 kg, such as deer, peccaries, small tapirs, and small horses which are all known from the same fossil sites.

Comparison of extension of splenial on dentary

Figure 3. UF 133983, humerus of Rhizosmilodon fiteae.


Rhizosmilodon fitae is best known from its mandible and lower teeth (Figs. 4-6). They show a mixture of primitive features found in Miocene machairodontines from Eurasia, such as Paramachaerodus, and derived features found in Smilodon and Megantereon. Among its primitive traits are a relatively large lower canine and third premolar (p3) teeth, relatively small incisors that do not jut out beyond the lower canine, fourth premolar (p4) with small anterior and posterior accessory cusps, and very small mandibular flange. Among its derived traits are p3 and p4 with strong posterior lean; long axes of p4 and first molar (m1) offset, not aligned with each other; a short, robust m1; and lower canine laterally compressed.

Comparison of teeth

Figure 4. UF 124634, holotype right mandible of Rhizosmilodon fitae with canine and first molar, from the Whidden Creek Site, Polk Co., Florida. Above, lateral view; below, medial view.



Comparison of teeth

Figure 5. UF 272337, partial right mandible of Rhizosmilodon fitae with fourth premolar and first molar. Top row right, lateral view; top row left, medial view; bottom left, occlusal (dorsal) view. Note offset between alignment of p4 and m1.



Comparison of teeth

Figure 6. UF 22890, left mandible of Rhizosmilodon fitae with third and fourth premolars and partial first molar. This is the specimen first described by Berta and Galiano (1983).



Database of available images of this species: Sorry, not yet available!


Scientific Publications and Other References Cited:

Berta, A., and H. Galiano. 1983. Megantereon hesperus from the late Hemphillian of Florida with remarks on the phylogenetic relationships of machairodonts (Mammalia, Felidae, Machairodontinae). Journal of Paleontology 57:892-899. http://www.jstor.org/stable/1304759

Hodnett, J.-P. 2010. A machairodont felid (Mammalia: Carnivora; Felidae) from the latest Hemphillian (late Miocene/early Pliocene) Bidahochi Formation, northeastern Arizona. PaleoBios 29(3):76-91.

Palmqvist, P., V. Torregrosa, J. A. Pérez-Claros, B. Martínez-Navarro, and A. Turner. 2007. A re-evaluation of the diversity of Megantereon (Mammalia, Carnivora, Marchairdontinae) and the problem of species identification in extinct carnivores. Journal of Vertebrate Paleontology 27(1):160-175. http://www.jstor.org/stable/4524675

Turner, A. 1985. Megantereon cultridens (Cuvier) (Mammalia, Felidae, Machairodontinae) from Plio-Pleistocene deposits in Africa and Eurasia, with comments on dispersal and the possibility of a New World origin. Journal of Paleontology 61(6):1256-1268. http://www.jstor.org/stable/1305213

Wallace S. C., and R. C. Hulbert Jr. 2013. A new machairodont from the Palmetto Fauna (early Pliocene) of Florida, with comments on the origin of the Smilodontini (Mammalia, Carnivora, Felidae). PLoS ONE 8(3): e56173. doi:10.1371/journal.pone.0056173

Webb, S. D., R. C. Hulbert, G. S. Morgan, and H. F. Evans. 2008. Terrestrial mammals of the Palmetto Fauna (early Pliocene, latest Hemphillian) from the Central Florida Phosphate District. Pp. 293-312 in X. Wang and L. G. Barnes (eds.), Geology and Vertebrate Paleontology of Western and Southern North America. Natural History Museum of Los Angeles County Science Series, Number 41.




Original Author(s): Richard C. Hulbert Jr.

Original Completion Date: May 1, 2013

Editor(s) Name(s): Richard C. Hulbert Jr.

Last Up-dated On: May 7, 2013

This material is based upon work supported by the National Science Foundation under Grant Number CSBR 1203222, Jonathan Bloch, Principal Investigator. Any opinions, findings, and conclusions or recommendations expressed in this material are those of the author(s) and do not necessarily reflect the views of the National Science Foundation.
Copyright © 2013 by Florida Museum of Natural History, University of Florida