Short-faced bear

subfamily of mammals

Short-faced bears belong to the Tremarctinae subfamily of bears. There is one living representative, the spectacled bear (Tremarctos ornatus) of South America. Extinct members include Arctodus, Arctotherium, Plionarctos and the Florida spectacled bear (Tremarctos floridanus). Of these, the giant short-faced bears (Arctodus simus and Arctotherium angustidens) may have been the largest ever predators in the Americas.

Short-faced bear
Temporal range: late Miocene–present
Spectacled bear, Arctodus simus and Arctotherium bonariense
Scientific classification Edit this classification
Domain: Eukaryota
Kingdom: Animalia
Phylum: Chordata
Class: Mammalia
Order: Carnivora
Family: Ursidae
Subfamily: Tremarctinae
Merriam & Stock, 1925


Evolution change

Skeletal reconstruction of Arctodus simus.

The group evolved in eastern North America from Plionarctos, and then spread across the Americas as part of the Great American Interchange. Most short-faced bears became extinct at the end of the Pleistocene.[1]

The medium sized Arctodus pristinus and Tremarctos floridanus inhabited much of North America in the Early Pleistocene.[2] While a fragmentary Arctotherium is first found from El Salvador,[3] the next fossils are of the gigantic Arctotherium angustidens in Argentina, from around 1 million years ago. Arctotherium angustidens was possibly the largest predatory land mammal ever.[4]

In the Middle Pleistocene, Arctodus pristinus evolved into Arctodus simus, which inhabited most of North America, from Alaska to Mexico.[5] Arctotherium angustidens was replaced by smaller, medium-sized species- first Arctotherium vetustum, then by Arctotherium bonariense and Arctotherium tarijense.[2] Arctotherium wingei was the only known species of Arctotherium to inhabit tropical South America and Central America.[6][7]

Biology change

Short-faced bears were either smaller and mostly herbivorous bears inhabiting forested habitats, such as Arctotherium wingei and Tremarctos ornatus, or omnivores adapted for more open habitats, such as Arctotherium angustidens and Arctodus simus.

Although the two giant species appear similar, both species had key differences. While Arctodus simus inhabited most of North America for over a million years, Arctotherium angustidens has only been found in the Southern Cone, from open plains habitat. Also, while Arctodus simus varied its diet between mostly eating meat in Alaska to omnivory elsewhere, Arctotherium angustidens had similar rates of eating meat across specimens, according to studies of its bone chemistry.[8][9]

Additionally, the much more slender bones of Arctodus, in contrast with the robust Arctotherium angustidens, have puzzled researchers.[10][11] However, the extinctions scavenger-niche mega-carnivores in their habitats could have been a shared reason for evolving gigantism in Arctodus and Arctotherium.[12]

Arctodus and Tremarctos share characteristics common to herbivorous bears. These were either ancestral traits of the group, or clues to their preferred diets.[13] Arctotherium was more closely related to the spectacled bear than to Arctodus, implying convergent evolution of large size in the two lineages.[14]

A skeleton of the Florida spectacled bear (Tremarctos floridanus).

Taxonomy change

The following taxonomy of the short-faced bears follow Mitchell et al. (2016):[14]

References change

  1. Krause, J.; Unger, T.; Noçon, A.; Malaspinas, A.; Kolokotronis, S.; Stiller, M.; Soibelzon, L.; Spriggs, H.; Dear, P. H.; Briggs, A. W.; Bray, S. C. E.; O'Brien, S. J.; Rabeder, G.; Matheus, P.; Cooper, A.; Slatkin, M.; Pääbo, S.; Hofreiter, M. (2008-07-28). "Mitochondrial genomes reveal an explosive radiation of extinct and extant bears near the Miocene-Pliocene boundary". BMC Evolutionary Biology. 8: 220. doi:10.1186/1471-2148-8-220. PMC 2518930. PMID 18662376.
  2. 2.0 2.1 Soibelzon, L.H.; Tonni, E.P.; Bond, M. (2005). "The fossil record of South American short-faced bears (Ursidae, Tremarctinae)". Journal of South American Earth Sciences. 20 (1–2): 105–113. Bibcode:2005JSAES..20..105S. doi:10.1016/j.jsames.2005.07.005. Retrieved 2019-02-21.
  3. Soibelzon, Leopoldo H.; Romero, M.R. Aguilar (2008-10-14). "A Blancan (Pliocene) short-faced bear from El Salvador and its implications for Tremarctines in South America". Neues Jahrbuch für Geologie und Paläontologie - Abhandlungen. 250 (1): 1–8. doi:10.1127/0077-7749/2008/0250-0001. ISSN 0077-7749.
  4. Soibelzon, Leopoldo H.; Schubert, Blaine W. (January 2011). "The largest known bear, Arctotherium angustidens, from the early Pleistocene Pampean region of Argentina: with a discussion of size and diet trends in bears". Journal of Paleontology. 85 (1): 69–75. doi:10.1666/10-037.1. hdl:11336/104215. ISSN 0022-3360. S2CID 129585554.
  5. "FIGURE 1—Map showing locations of reported Arctodus simus localities..." ResearchGate. Retrieved 2022-02-12.
  6. "Figura 5. Distribución inferida de algunos mamíferos grandes y..." ResearchGate. Retrieved 2022-02-12.
  7. Schubert, Blaine W.; Chatters, James C.; Arroyo-Cabrales, Joaquin; Samuels, Joshua X.; Soibelzon, Leopoldo H.; Prevosti, Francisco J.; Widga, Christopher; Nava, Alberto; Rissolo, Dominique; Erreguerena, Pilar Luna (May 2019). "Yucatán carnivorans shed light on the Great American Biotic Interchange". Biology Letters. 15 (5): 20190148. doi:10.1098/rsbl.2019.0148. ISSN 1744-9561. PMC 6548739. PMID 31039726.
  8. Soibelzon, Leopoldo H.; Grinspan, Gustavo A.; Bocherens, Hervé; Acosta, Walter G.; Jones, Washington; Blanco, Ernesto R.; Prevosti, Francisco (November 2014). "South American giant short-faced bear (Arctotherium angustidens) diet: evidence from pathology, morphology, stable isotopes, and biomechanics". Journal of Paleontology. 88 (6): 1240–1250. Bibcode:2014JPal...88.1240S. doi:10.1666/13-143. hdl:11336/34149. ISSN 0022-3360. S2CID 54869873.
  9. Chichkoyan, Karina; Figueirido, Borja; Belinchón, Margarita; Lanata, José; Moigne, Anne-Marie; Martínez-Navarro, Bienvenido (2017-05-09). "Direct evidence of megamammal-carnivore interaction decoded from bone marks in historical fossil collections from the Pampean region". PeerJ. 5: e3117. doi:10.7717/peerj.3117. PMC 5426367. PMID 28503369.
  10. Lynch, Eric (2012-08-15). "Cursorial Adaptations in the Forelimb of the Giant Short-Faced Bear, Arctodus simus, Revealed by Traditional and 3D Landmark Morphometrics". Electronic Theses and Dissertations.
  11. Soibelzon, Leopoldo H.; Schubert, Blaine W. (2011). "The largest known bear, Arctotherium angustidens, from the early Pleistocene pampean region of Argentina: with a discussion of size and diet trends in bears". Journal of Paleontology. 85 (1): 69–75. doi:10.1666/10-037.1. hdl:11336/104215. S2CID 129585554.
  12. Fowler, Nicholas L.; Spady, Thomas J.; Wang, Guiming; Leopold, Bruce D.; Belant, Jerrold L. (2021). "Denning, metabolic suppression, and the realisation of ecological opportunities in Ursidae". Mammal Review. 51 (4): 465–481. doi:10.1111/mam.12246. ISSN 1365-2907. S2CID 233847639.
  13. Donohue, Shelly L.; DeSantis, Larisa R. G.; Schubert, Blaine W.; Ungar, Peter S. (2013-10-30). "Was the Giant Short-Faced Bear a Hyper-Scavenger? A New Approach to the Dietary Study of Ursids Using Dental Microwear Textures". PLOS ONE. 8 (10): e77531. Bibcode:2013PLoSO...877531D. doi:10.1371/journal.pone.0077531. ISSN 1932-6203. PMC 3813673. PMID 24204860.
  14. 14.0 14.1 Mitchell, Kieren J.; Bray, Sarah C.; Bover, Pere; Soibelzon, Leopoldo; Schubert, Blaine W.; Prevosti, Francisco; Prieto, Alfredo; Martin, Fabiana; Austin, Jeremy J.; Cooper, Alan (2016-04-30). "Ancient mitochondrial DNA reveals convergent evolution of giant short-faced bears (Tremarctinae) in North and South America". Biology Letters. 12 (4): 20160062. doi:10.1098/rsbl.2016.0062. PMC 4881349. PMID 27095265.