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Fossil Species of Florida

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Mammalia, Carnivora, Arctoidea, Amphicyonidae, Amphicyoninae


Common Name: White’s beardog

Alternate Scientific Name: Amphicyon intermedius

Source of Species Name: (longiramus is Latin for “long branch”) When Amphicyon longiramus was originally named by Dr. Theodore E. White of the Harvard Museum of Comparative Zoology, he believed that it coexisted along with another, smaller species of Amphicyon. The name was used to emphasize this species’ seemingly longer limbs and skull (many bony elements are generally referred to as a “ramus” in anatomy). The two species originally named by Dr. White have since been combined under the name Amphicyon longiramus, with more specimens making it clear that the initial variation he observed was within a single sexually dimorphic species (Olsen, 1960).

Age Range: early Miocene (Hemingfordian), from about 18 to 16 million years ago.

Florida Fossil Occurrences:

Florida map with occurrences indicated

Figure 1. Map of Florida, with black circles indicating counties where fossils of Amphicyon longiramus 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 Amphicyon longiramus:
Gilchrist County—Thomas Farm

Overall Geographic Range: Known primarily from the Thomas Farm Site in north-central Florida and several localities in southeastern Texas. Emry and Eshelman (1998) reported specimens of “Amphicyon intermedius” from the Pollack Farm Local Fauna of Delaware, which are similar to the same elements of Amphicyon longiramus from Florida. This occurrence indicates that Amphicyon longiramus may have been distributed throughout much of the eastern half of North America during the early Miocene.

Comments: Amphicyon longiramus was the top carnivore of Florida’s early Miocene (Hulbert, 2001), with the largest body size among predatory animals preserved at the Thomas Farm locality. Body mass estimation among amphicyonids is notoriously difficult (Figueirido et al., 2011), due in part to the disproportionately long skulls in this group—a feature that is exaggerated in Amphicyon longiramus (Olsen, 1958); yet Amphicyon longiramus clearly dominates in size over contemporaneous carnivores. This makes identification of skeletal elements relatively easy for researchers.

Amphicyon longiramus is one of the oldest members of the subfamily Amphicyoninae in Florida. Along with the smaller amphicyonine Cynelos caroniavorus, also found at Thomas Farm (Hulbert, 2001), Amphicyon longiramus is thought to have dispersed from Europe into North America about 18 million years ago (Hunt, 1998). While other beardog species were present in Florida from the late Oligocene to the late Miocene (Hulbert, 2001), most are known only from sparse material. Amphicyon longiramus is the only species for which there is ample fossil evidence, and it is therefore the only Florida amphicyonid that has been thoroughly described (Olsen, 1958, 1960). The holotype of the species, along with other specimens, is housed in the Harvard Museum of Comparative Zoology. The Florida Museum of Natural History has over 550 specimens in its collection, and has the only known mounted skeleton of the species on public display.

Skull of Amphicyon longiramus

Figure 2. UF 162723, skull of Amphicyon longiramus, with diagnostic auditory region highlighted, in left lateral, dorsal, and ventral views. This relatively small individual is most likely a female.

Amphicyonids encompass a wide variety of carnivorous mammal ecomorphologies that are today filled by canids and ursids (Figuerido et al., 2011). Like modern carnivores, many species of beardogs (including Amphicyon longiramus) were highly sexually dimorphic (Hunt, 1998; Figs. 2-3), and burrows indicating denning behavior in large amphicyonids have been located in Nebraska (Hunt et al., 1983).

canine teeth of Amphicyon

Figure 3. Right lower canine teeth of Amphicyon longiramus from Thomas Farm demonstrating sexual dimorphism in body size. A, UF 271019, male; B, UF 154301, female.

Interestingly, two locomotive types seem to have developed within the family Amphicyonidae, emphasizing two different feeding strategies. Some amphicyonids were digitigrade, long-limbed, and had narrow limb articulations, making them effective running predators. One example is Borocyon robustum, a well-known amphicyonid in western North America (Hunt, 1998, 2009). These beardogs emphasized a shearing dentition excellent for slicing meat, and were the ecological equivalents of wolves. In contrast, other species of beardogs such as Amphicyon longiramus had plantigrade feet and robust limbs with broad articulations (Figs. 3-4), giving them a stance much more similar to modern bears (Hunt, 1998). These heavy, slow-gaited amphicyonines tended to have broader molars, well-designed for bone crushing, such as the upper first molar (M1) of Amphicyon longiramus pictured in Figure 6. Its closest modern ecologic equivalent is the grizzly bear.

femur of Amphicyon

Figure 4. Right femur (UF 176191) of Amphicyon longiramus. A, Anterior view, with robust portions of the femur enclosed in white brackets; B, posterior view; C, lateral view; D, medial view with fovea capitis highlighted. The fovea capitis is positioned more posteriorly in amphicyonids adapted for running.

astragalus of Amphicyon

Figure 5. Right astragalus (UF/FGS 6336) of Amphicyon longiramus. A, Medial view; B, anterior view, with broad astragalar trochlea for articulation with the tibia enclosed in white brackets. The trochlea is much narrower in amphicyonids adapted for running; C, posterior view.

upper molar of Amphicyon

Figure 5. UF 165019, left upper M1 of Amphicyon longiramus from Thomas Farm. Above, lateral or buccal view; below, occlusal view.

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Scientific Publications and Other References Cited:

Emry, R. J., and R. E. Eshelman. 1998. The early Hemingfordian (early Miocene) Pollack Farm Local Fauna: First Tertiary land mammals described from Delaware. Pp. 153-174 in R. N. Benson, ed., Geology and Paleontology of the Lower Miocene Pollack Farm Fossil Site, Delaware. Delaware Geological Society, Special Publication 21. http://putnam.lib.udel.edu:8080/dspace/bitstream/handle/19716/3590/SP21.pdf?sequence=1#page=147

Figueirido, B., J. A. Pérez-Claros, R. M. Hunt, Jr., and P. Palmqvist. 2011. Body mass estimation in amphicyonid carnivoran mammals: A multiple regression approach from the skull and skeleton. Acta Palaeontologica Polonica 56(2):225-246. http://www.bioone.org/doi/full/10.4202/app.2010.0005

Hulbert, R. C., Jr. 2001. The Fossil Vertebrates of Florida. University Press of Florida: Gainesville, FL. Pp. 198-202. http://www.flmnh.ufl.edu/vertpaleo/book.htm

Hunt, R. M., Jr. 1998. Amphicyonidae. Pp. 196-227 in C.M. Janis, K. M. Scott, and L. L. Jacobs, eds., Evolution of Tertiary Mammals of North America, Volume 1: Terrestrial Carnivores, Ungulates, and Ungulatelike Mammals. Cambridge University Press: Cambridge, UK.

Hunt, R. M., Jr. 2009. Long-legged pursuit carnivorans (Amphicyonidae, Daphoeninae) from the early Miocene of North America. Bulletin of the American Museum of Natural History 318:1-95. http://digitallibrary.amnh.org/dspace/handle/2246/5948

Hunt, R. M., Jr., X. Xiang-Xu, and J. Kaufman. 1983. Miocene burrows of extinct bear dogs: Indication of early denning behavior of large mammalian carnivores. Science 221(4608):364-366.

Janis, C. M., J. A. Baskin, A. Berta, J. J. Flynn, G. F. Gunnell, R. M. Hunt, Jr., L. D. Martin, and K. Munthe. 1998. Carnivorous mammals. Pp. 73-90 in C.M. Janis, K. M. Scott, and L. L. Jacobs, eds., Evolution of Tertiary Mammals of North America, Volume 1: Terrestrial Carnivores, Ungulates, and Ungulatelike Mammals. Cambridge University Press: Cambridge, UK.

Olsen, S. J. 1958. The fossil carnivore Amphicyon intermedius from the Thomas Farm Miocene, Part I: Skull and dentition. Bulletin of the Museum of Comparative Zoology 118(4):155-172. http://www.biodiversitylibrary.org/item/21136#page/193/mode/1up

Olsen, S. J. 1960. The fossil carnivore Amphicyon longiramus from the Thomas Farm Miocene, Part II: Postcranial skeleton. Bulletin of the Museum of Comparative Zoology 123(1):1-46. http://www.biodiversitylibrary.org/item/21160#page/11/mode/1up

White, T. E. 1942. The lower Miocene mammal fauna of Florida. Bulletin of the Museum of Comparative Zoology 92(1):1-49. http://www.biodiversitylibrary.org/item/21220

Original Author(s): Paul E. Morse

Original Completion Date: October 5, 2012

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

Last Up-dated On: March 28, 2013

Funding to generate the content and images of this and other Fossil Species of Florida web pages partailly provided by the National Science Foundation, grant CSBR 1203222, Jonathan Bloch, Principal Investigator

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