Tremarctinae

{{Short description|Subfamily of bears}} {{Automatic taxobox | fossil_range = {{Fossil range|7|0|prefix=Late Miocene{{snd}}Holocene,}}{{Period fossil range|Neogene-Quaternary|7|0}} | image = Tremarctinae.png | image_caption = Spectacled bear, ''Arctodus simus'' and ''Arctotherium bonariense'' | taxon = Tremarctinae | authority = Merriam & Stock, 1925 | subdivision_ranks = Genera | subdivision = †''Arctodus'' †''Arctotherium'' †''Plionarctos'' ''Tremarctos'' }}

The '''Tremarctinae''' or '''short-faced bears''' is a subfamily of Ursidae that contains one living representative, the spectacled bear (''Tremarctos ornatus'') of South America, and several extinct species from four genera: the Florida spectacled bear (''Tremarctos floridanus''), the North American giant short-faced bears ''Arctodus'' (''A. pristinus'' and ''A. simus''), the South American giant short-faced bear ''Arctotherium'' (including ''A. angustidens'', ''A. vetustum'', ''A. bonariense'', ''A. wingei'', and ''A. tarijense)'' as well as ''Plionarctos'' ''(P. edensis and P. harroldorum),'' which is thought to be ancestral to the other three genera.<ref name="krause">{{Cite journal | last = Krause | first = J. |author2=Unger, T. |author3=Noçon, A. |author4=Malaspinas, A. |author5=Kolokotronis, S. |author6=Stiller, M. |author7=Soibelzon, L. |author8=Spriggs, H. |author9=Dear, P. H. |author10=Briggs, A. W. |author11=Bray, S. C. E. |author12=O'Brien, S. J. |author13=Rabeder, G. |author14=Matheus, P. |author15=Cooper, A. |author16=Slatkin, M. |author17=Pääbo, S. |author18=Hofreiter, M. | title = Mitochondrial genomes reveal an explosive radiation of extinct and extant bears near the Miocene-Pliocene boundary | journal = BMC Evolutionary Biology | volume = 8 | page = 220 | date = 2008-07-28| issue = 1 | doi = 10.1186/1471-2148-8-220 | pmid=18662376 | pmc=2518930 | doi-access = free | bibcode = 2008BMCEE...8..220K }}</ref> Of these, the '''giant short-faced bears''' (''Arctodus simus'' and ''Arctotherium angustidens'') may have been the largest ever carnivorans in the Americas. The group is thought to have originated in eastern North America, and then invaded South America as part of the Great American Interchange. Most short-faced bears became extinct at the end of the Pleistocene.

== Taxonomy == Tremarctinae was erected by John Merriam and Chester Stock in 1925.<ref name=":8">{{Cite book |last=Merriam |first=John C. |url=https://catalog.hathitrust.org/Record/002038394 |title=Papers concerning the palaeontology of the Pleistocene of California and the Pliocene of Oregon. |last2=Moody |first2=Clarence Lemuel |last3=Stock |first3=Chester |date=1925 |publisher=The Carnegie institution of Washington |series=Contributions to palaeontology from the Carnegie institution of Washington |location=Washington}}</ref> Traditionally, analyses of the phylogenetic inner relationships of tremarctines had ''Plionarctos'' and ''Tremarctos'' as basal groups with respect to a short-faced bear clade of ''Arctodus'' and ''Arctotherium''.<ref name=":1" /><ref name=":2">{{cite journal |last1=Soibelzon |first1=Leopoldo H. |last2=Schubert |first2=Blaine W. |year=2011 |title=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=Journal of Paleontology |volume=85 |issue=1 |pages=69–75 |doi=10.1666/10-037.1 |hdl=11336/104215 |s2cid=129585554 |hdl-access=free}}</ref> A study of the affinities of bears belonging to ''Arctotherium'' indicates that they were more closely related to the spectacled bear than to ''Arctodus'', implying convergent evolution of large size in the two lineages.<ref name=":3">{{Cite journal |last1=Mitchell |first1=Kieren J. |last2=Bray |first2=Sarah C. |last3=Bover |first3=Pere |last4=Soibelzon |first4=Leopoldo |last5=Schubert |first5=Blaine W. |last6=Prevosti |first6=Francisco |last7=Prieto |first7=Alfredo |last8=Martin |first8=Fabiana |last9=Austin |first9=Jeremy J. |last10=Cooper |first10=Alan |date=2016-04-30 |title=Ancient mitochondrial DNA reveals convergent evolution of giant short-faced bears (Tremarctinae) in North and South America |journal=Biology Letters |volume=12 |issue=4 |article-number=20160062 |doi=10.1098/rsbl.2016.0062 |pmc=4881349 |pmid=27095265}}</ref> Tremarctines are occasionally referred to as ''arctodonts'' and/or ''arctotheres'',<ref name=":8" /><ref name=":6">{{Cite book |last1=Janis |first1=Christine M. |url=https://books.google.com/books?id=I-RgojcDyWYC&q=tremarctos |title=Evolution of Tertiary Mammals of North America: Volume 1, Terrestrial Carnivores, Ungulates, and Ungulate Like Mammals |last2=Scott |first2=Kathleen M. |last3=Jacobs |first3=Louis L. |date=1998-05-28 |publisher=Cambridge University Press |isbn=978-0-521-35519-3 |language=en}}</ref><ref name=":26">{{Cite web |last1=Packard |first1=E.L. |last2=Allison |first2=I.S. |last3=Cressman |first3=L.S. |title=Mammalian Tracks in the Late Pliocene or Early Pleistocene Beds of Lake County Oregon |url=https://www.oregon.gov/dogami/milo/archive/MiningDistricts/LakeCounty/UnclassifiedDistrict/LakeCountyFossilLocalities/LakeCountyFossilLocalitiesReports.pdf |access-date=June 11, 2017 |website=Oregon Geology}}</ref> or ''tremarctotheres'' in older scientific literature.<ref>{{Cite web |title=Rancho La Brea: a record of Pleistocene life in California |url=https://authors.library.caltech.edu/records/05rtr-69j43 |access-date=2025-07-07 |website=authors.library.caltech.edu}}</ref>

=== Diagnostics ===

==== Skull ==== Tremarctinae appear to have a disproportionately shorter snouts compared with most modern bears, giving them the name "short-faced." This apparent shortness is an illusion caused by the deep snouts and short nasal bones of tremarctine bears compared with ursine bears; Tremarctinae had shorter and taller skulls, but not a shorter face than most living bears.<ref name=":4">{{Cite journal |last1=Figueirido |first1=Borja |last2=Soibelzon |first2=Leopoldo H. |date=2010 |title=Inferring palaeoecology in extinct tremarctine bears (Carnivora, Ursidae) using geometric morphometrics |url=https://onlinelibrary.wiley.com/doi/abs/10.1111/j.1502-3931.2009.00184.x |journal=Lethaia |language=en |volume=43 |issue=2 |pages=209–222 |bibcode=2010Letha..43..209F |doi=10.1111/j.1502-3931.2009.00184.x |issn=1502-3931|url-access=subscription }}</ref> In addition to being brachycephalic, tremarctine bears' skulls possessed well developed zygomatic arches and glenoid mandibular fossas,<ref name=":4" /> a premasseteric fossa on the mandible (except for ''Plionarctos''),<ref name=":6" /> and often an entepicondylar foramen on the humerus of tremarctine bears.<ref name=":7">{{Cite journal |last1=Steffen |first1=Martina L. |last2=Fulton |first2=Tara L. |date=February 2018 |title=On the association of giant short-faced bear ( Arctodus simus ) and brown bear ( Ursus arctos ) in late Pleistocene North America |url=https://linkinghub.elsevier.com/retrieve/pii/S0016699517300384 |journal=Geobios |language=en |volume=51 |issue=1 |pages=61–74 |bibcode=2018Geobi..51...61S |doi=10.1016/j.geobios.2017.12.001 |url-access=subscription}}</ref> Moreover, tremarctine bears' orbits are also bigger, more rounded and lateralized than ursine bears.<ref name=":4" /> The premassateric fossa is used to detect maturity in tremarctine bears, with only adults possessing fully developed fossa.<ref name="Emslie-1995">{{cite journal |last1=Emslie |first1=Steven D. |year=1995 |title=The fossil record of Arctodus pristinus (Ursidae: Tremarctinae) in Florida |url=https://www.floridamuseum.ufl.edu/wp-content/uploads/sites/35/2017/03/Vol-37-No-15.pdf |journal=Bulletin of the Florida Museum of Natural History |volume=37 |issue=15 |pages=501–514 |doi=10.58782/flmnh.hduf9651 |s2cid=168164209}}</ref> The features of tremarctine bear's individual morphology, such as dentition, can be quite variable (particularly the M2 molar).<ref name="Emslie-19952">{{cite journal |last1=Emslie |first1=Steven D. |year=1995 |title=The fossil record of Arctodus pristinus (Ursidae: Tremarctinae) in Florida |url=https://www.floridamuseum.ufl.edu/wp-content/uploads/sites/35/2017/03/Vol-37-No-15.pdf |journal=Bulletin of the Florida Museum of Natural History |volume=37 |issue=15 |pages=501–514 |doi=10.58782/flmnh.hduf9651 |s2cid=168164209}}</ref> Unlike tremarctine bears, ursine bears have only one masseteric fossa on their mandible and more slender and elongated skulls, with generally narrower molars (with the exception of polar bears).<ref name=":4" /><ref name=":18">{{cite book |last1=Kurtén |first1=B. |title=Pleistocene Mammals of North America |last2=Anderson |first2=E. |publisher=Columbia University Press |isbn=0-230-61399-3}}</ref><ref>{{Cite journal |last=Figueirido |first=Borja |last2=Soibelzon |first2=Leopoldo H. |date=2009 |title=Inferring palaeoecology in extinct tremarctine bears (Carnivora, Ursidae) using geometric morphometrics |url=https://www.scup.com/doi/10.1111/j.1502-3931.2009.00184.x |journal=Lethaia |language=en |volume=43 |issue=2 |pages=209–222 |doi=10.1111/j.1502-3931.2009.00184.x |issn=0024-1164|url-access=subscription }}</ref> Osteological differences between tremarctine and ursine bears also include an extra lateral cusp between the trigonid and talonid on the m1 molar.<ref name=":7" />

==== Postcranial ==== The ichnotaxon ''Ursichnus sudamericanus'' is referred to ''Arctotherium tarijense''; unlike the footprints of ursine bears, the heel impression is absent in the manus, and the digit III imprint is longer than the remaining digits.<ref>{{Cite journal |last1=Aramayo |first1=Silvia A. |last2=Manera de Bianco |first2=Teresa |last3=Bastianelli |first3=Nerea V. |last4=Melchor |first4=Ricardo N. |date=2015-12-01 |title=Pehuen Co: Updated taxonomic review of a late Pleistocene ichnological site in Argentina |url=https://www.sciencedirect.com/science/article/pii/S0031018215003661 |journal=Palaeogeography, Palaeoclimatology, Palaeoecology |series=Contributions of ichnology to palaeoecology, palaeogeography and sedimentology |volume=439 |pages=144–165 |bibcode=2015PPP...439..144A |doi=10.1016/j.palaeo.2015.07.006 |hdl=11336/125572 |issn=0031-0182 |hdl-access=free}}</ref> Being very similar to extant spectacled bears, ''Ursichnus sudamericanus'' suggests all tremarctines had long claws and five digits whose tips arrayed in a shallow arc.<ref>{{Cite journal |last=Weems |first=Robert E. |date=2018 |title=An Early Pleistocene (Early Irvingtonian) Footprint Fauna from the Bacons Castle Formation, Westmoreland County, Virginia |url=https://www.researchgate.net/publication/348579743 |journal=New Mexico Museum of Natural History and Science |volume=Bulletin 79 |page=740 |via=ResearchGate}}</ref> While all are plantigrade, Tremarctinaes can be distinguished between short-footed (''Tremarctos'') and long-footed forms (''Arctodus'').<ref name=":6" />

== Evolution == thumb|225x225px|Skeletal reconstruction of ''Arctodus simus''.|leftTremarctinae originate with their common ancestor, ''Plionarctos,'' in the Middle Hemphillian (Late Miocene, ~7Ma) of North America; ''Plionarctos'' is last recorded in the early Blancan (Pliocene, ~3Ma).<ref name=":6" /> Around the Miocene-Pliocene boundary (~5.3 Ma), tremarctines, along with other ursids, experienced an explosive radiation in diversity, as C4 vegetation (grasses) and open habitats dominated, the world experienced a major temperature drop and increased seasonality, and a faunal turnover which extinguished 60–70% of all Eurasian faunal genera, and 70–80% of North American genera.<ref name="krause" /> Correspondingly, genetic studies suggest that the mean divergence dates for ''Arctotherium'', ''Arctodus'' and ''Tremarctos'' were between 5.5Ma and 4.8Ma,<ref>{{Cite journal |last1=Pedersen |first1=Mikkel Winther |last2=De Sanctis |first2=Bianca |last3=Saremi |first3=Nedda F. |last4=Sikora |first4=Martin |last5=Puckett |first5=Emily E. |last6=Gu |first6=Zhenquan |last7=Moon |first7=Katherine L. |last8=Kapp |first8=Joshua D. |last9=Vinner |first9=Lasse |last10=Vardanyan |first10=Zaruhi |last11=Ardelean |first11=Ciprian F. |date=June 2021 |title=Environmental genomics of Late Pleistocene black bears and giant short-faced bears |journal=Current Biology |volume=31 |issue=12 |pages=2728–2736.e8 |doi=10.1016/j.cub.2021.04.027 |pmid=33878301 |issn=0960-9822|doi-access=free |pmc=7617452 |bibcode=2021CBio...31E2728P |hdl=10037/22808 |hdl-access=free }}</ref>'''<ref name="Mitchell-2016">{{Cite journal |last1=Mitchell |first1=Kieren J. |last2=Bray |first2=Sarah C. |last3=Bover |first3=Pere |last4=Soibelzon |first4=Leopoldo |last5=Schubert |first5=Blaine W. |last6=Prevosti |first6=Francisco |last7=Prieto |first7=Alfredo |last8=Martin |first8=Fabiana |last9=Austin |first9=Jeremy J. |last10=Cooper |first10=Alan |date=2016-04-30 |title=Ancient mitochondrial DNA reveals convergent evolution of giant short-faced bears (Tremarctinae) in North and South America |journal=Biology Letters |volume=12 |issue=4 |article-number=20160062 |doi=10.1098/rsbl.2016.0062 |pmc=4881349 |pmid=27095265}}</ref>''' and between ''Arctotherium'' and ''Tremarctos'' at 4.1 Ma.<ref name=":3" /> All three genera are first recorded from the Blancan (Pliocene/Pleistocene boundary) of North America.<ref name=":0">{{Cite journal|last1=Fowler|first1=Nicholas L.|last2=Spady|first2=Thomas J.|last3=Wang|first3=Guiming|last4=Leopold|first4=Bruce D.|last5=Belant|first5=Jerrold L.|date=2021|title=Denning, metabolic suppression, and the realisation of ecological opportunities in Ursidae|url=https://onlinelibrary.wiley.com/doi/abs/10.1111/mam.12246|journal=Mammal Review|language=en|volume=51|issue=4|pages=465–481|doi=10.1111/mam.12246|bibcode=2021MamRv..51..465F |s2cid=233847639|issn=1365-2907|url-access=subscription}}</ref>

An indeterminate ''Arctotherium'' is first recorded from the late Pliocene of El Salvador.<ref name=":5">{{Cite journal |last1=Soibelzon |first1=Leopoldo H. |last2=Romero |first2=M.R. Aguilar |date=2008-10-14 |title=A Blancan (Pliocene) short-faced bear from El Salvador and its implications for Tremarctines in South America |url=http://www.schweizerbart.de/papers/njgpa/detail/250/59574/A_Blancan_Pliocene_short_faced_bear_from_El_Salvad?af=crossref |journal=Neues Jahrbuch für Geologie und Paläontologie - Abhandlungen |language=en |volume=250 |issue=1 |pages=1–8 |doi=10.1127/0077-7749/2008/0250-0001 |bibcode=2008NJGPA.250....1S |issn=0077-7749}}</ref> In the Early Pleistocene, short-faced bears began to establish themselves more thoroughly in both North and South America.<ref name="Soibelzon2005">{{cite journal |last1=Soibelzon |first1=L.H. |last2=Tonni |first2=E.P. |last3=Bond |first3=M. |year=2005 |title=The fossil record of South American short-faced bears (Ursidae, Tremarctinae) |url=https://www.researchgate.net/publication/223390695 |journal=Journal of South American Earth Sciences |volume=20 |issue=1–2 |pages=105–113 |access-date=2019-02-21|doi= 10.1016/j.jsames.2005.07.005|bibcode=2005JSAES..20..105S }}</ref> The medium sized ''Arctodus pristinus'' inhabited a broad range in the North American continent, with ''Tremarctos floridanus'' endemic to the Gulf Coast. The first records of ''Arctotherium'' in South America come in the form of the gigantic ''Arctotherium angustidens'', possibly the largest carnivorous land mammal ever, in Argentina circa 1 Ma. What the evolutionary history of ''Arctotherium'' in the previous 1.5 million years, and their history in South America, is unclear. In the Middle Pleistocene, both ''Arctodus'' and ''Arctotherium'' gave way to new forms; ''Arctodus pristinus'' gave way to the huge ''Arctodus simus'', which inhabited a pan-continental range, from Alaska to Mexico.<ref>{{Cite web|title=FIGURE 1—Map showing locations of reported Arctodus simus localities...|url=https://www.researchgate.net/figure/Map-showing-locations-of-reported-Arctodus-simus-localities-with-arrow-pointing-to-the_fig1_250071137|access-date=2022-02-12|website=ResearchGate|language=en}}</ref> ''Arctotherium angustidens'', on the other hand, was replaced by a series of smaller, medium-sized species- ''Arctotherium vetustum'', then shortly thereafter by ''Arctotherium bonariense'', and ''Arctotherium tarijense''.<ref name="Soibelzon2005" /> Although the smaller ''Arctotherium wingei'' is only known from Late Pleistocene records, the species' more archaic position in the ''Arctotherium'' family tree also suggests an origin in the Middle Pleistocene. ''Arctotherium wingei'' was the only known species of ''Arctotherium'' to principally inhabit a range north of the Southern Cone,<ref>{{Cite web|title=Figura 5. Distribución inferida de algunos mamíferos grandes y...|url=https://www.researchgate.net/figure/Figura-5-Distribucion-inferida-de-algunos-mamiferos-grandes-y-megamamiferos-emparentados_fig4_230597899|access-date=2022-02-12|website=ResearchGate|language=en}}</ref> and to reinvade Central America.<ref>{{Cite journal|last1=Schubert|first1=Blaine W.|last2=Chatters|first2=James C.|last3=Arroyo-Cabrales|first3=Joaquin|last4=Samuels|first4=Joshua X.|last5=Soibelzon|first5=Leopoldo H.|last6=Prevosti|first6=Francisco J.|last7=Widga|first7=Christopher|last8=Nava|first8=Alberto|last9=Rissolo|first9=Dominique|last10=Erreguerena|first10=Pilar Luna|date=May 2019|title=Yucatán carnivorans shed light on the Great American Biotic Interchange|journal=Biology Letters|volume=15|issue=5|article-number=20190148|doi=10.1098/rsbl.2019.0148|issn=1744-9561|pmc=6548739|pmid=31039726}}</ref>

By the terminal Pleistocene, ''Arctodus simus'', ''Tremarctos floridanus'', ''Arctotherium tarijense'' and ''Arctotherium wingei'' collectively occupied a range from Alaska to southernmost Patagonia. All of these forms were extinct by the end of the early Holocene.<ref name=":5" /> Around this time, ''Tremarctos ornatus'', otherwise known as the spectacled bear, starts appearing in the South American fossil record.<ref>{{Cite journal|title=Access Suspended|url=https://bioone.org/access-suspended|access-date=2022-02-12|website=bioone.org|doi=10.2192/08gr017r1.1|s2cid=86731722|url-access=subscription}}</ref> Scholars suggest that the spectacled bear migrated into Central and South America upon the extinction of ''Arctotherium wingei'', if Pleistocene records of Andean ''Arctotherium'' sp. aren't confirmed as the spectacled bear.<ref>{{Cite journal|last1=García-López|first1=Daniel|last2=Ortiz|first2=Pablo|last3=Madozzo Jaén|first3=M.|last4=Moyano|first4=M.|date=2008-12-12|title=First Record of Arctotherium (Ursidae, Tremarctinae) in Northwestern Argentina and its Paleobiogeographic Significance|url=https://www.researchgate.net/publication/249023497|journal=Journal of Vertebrate Paleontology |volume=28|issue=4|pages=1232–1237|doi=10.1671/0272-4634-28.4.1232|bibcode=2008JVPal..28.1232L |hdl=11336/79528 |s2cid=86213882|hdl-access=free}}</ref><ref name=":1">{{Cite journal|last1=Soibelzon|first1=Leopoldo H.|last2=Rincón|first2=Ascanio D.|date=2007-07-27|title=The fossil record of the short-faced bears (Ursidae, Tremarctinae) from Venezuela. Systematic, biogeographic, and paleoecological implications|url=http://www.schweizerbart.de/papers/njgpa/detail/244/59121/The_fossil_record_of_the_short_faced_bears_Ursidae?af=crossref|journal=Neues Jahrbuch für Geologie und Paläontologie - Abhandlungen|language=en|volume=244|issue=3|pages=287–298|doi=10.1127/0077-7749/2007/0244-0287|bibcode=2007NJGPA.244..287S |issn=0077-7749}}</ref>

== Paleobiology == Tremarctines inhabited a wide range of niches- from small and mostly herbivorous bears inhabiting more forested habitat, such as ''Arctotherium wingei'' and ''Tremarctos ornatus'', to the colossal ''Arctotherium angustidens'' and ''Arctodus simus;'' plains adapted omnivores with a penchant for large quantities of meat. Although the two giant species appear superficially similar, both species had key, significant differences. While ''Arctodus simus'' had a wide range across North America for 800,000 years, ''Arctotherium angustidens'' appears to be limited to the Southern Cone, in open plains habitat. Furthermore, whereas ''Arctodus simus'' varied its diet between quasi-carnivory in Alaska to classic omnivory, ''Arctotherium angustidens'' had similar rates of carnivory across specimens, according to isotope studies.<ref>{{Cite journal|last1=Soibelzon|first1=Leopoldo H.|last2=Grinspan|first2=Gustavo A.|last3=Bocherens|first3=Hervé|last4=Acosta|first4=Walter G.|last5=Jones|first5=Washington|last6=Blanco|first6=Ernesto R.|last7=Prevosti|first7=Francisco|date=November 2014|title=South American giant short-faced bear (Arctotherium angustidens) diet: evidence from pathology, morphology, stable isotopes, and biomechanics|url=https://www.cambridge.org/core/journals/journal-of-paleontology/article/abs/south-american-giant-shortfaced-bear-arctotherium-angustidens-diet-evidence-from-pathology-morphology-stable-isotopes-and-biomechanics/2616CEF2B348B1453C68EF26CF2858C9|journal=Journal of Paleontology|language=en|volume=88|issue=6|pages=1240–1250|doi=10.1666/13-143|bibcode=2014JPal...88.1240S |s2cid=54869873|issn=0022-3360|hdl=11336/34149|hdl-access=free}}</ref><ref>{{Cite journal|last1=Chichkoyan|first1=Karina|last2=Figueirido|first2=Borja|last3=Belinchón|first3=Margarita|last4=Lanata|first4=José|last5=Moigne|first5=Anne-Marie|last6=Martínez-Navarro|first6=Bienvenido|date=2017-05-09|title=Direct evidence of megamammal-carnivore interaction decoded from bone marks in historical fossil collections from the Pampean region|url=https://www.researchgate.net/publication/316944512|journal=PeerJ|volume=5|article-number=e3117|doi=10.7717/peerj.3117|pmid=28503369|pmc=5426367 |doi-access=free }}</ref> Additionally, the much more gracile form of ''Arctodus'', in contrast with the robust ''Arctotherium angustidens'', has puzzled researchers.<ref>{{Cite journal |last=Lynch |first=Eric |date=2012-08-15 |title=Cursorial Adaptations in the Forelimb of the Giant Short-Faced Bear, Arctodus simus, Revealed by Traditional and 3D Landmark Morphometrics |url=https://dc.etsu.edu/etd/1477 |journal=Electronic Theses and Dissertations}}</ref><ref name=":2" /> However, it has been posited that the Pliocene extinctions of scavenger-niche mega-carnivores, such as the procyonid ''Chapalmalania'' in South America, and both ''Borophagus'' and ''Agriotherium'' in North America, was a shared impetus for gigantism in ''Arctodus'' and ''Arctotherium''.<ref name=":0" />

''Arctodus'' and ''Tremarctos'' share characteristics common to herbivorous bears. This includes cheek teeth with large surface areas, a deep mandible, and large mandibular muscle attachments. Because herbivorous carnivorans lack an efficient digestive tract for breaking down plant matter via microbial action, they must break down plant matter via extensive chewing or grinding, and thus possess features to create a high mechanical advantage of the jaw. This presents the possibility that these traits may be an ancestral condition of the group, if not an indication of their preferred dietary habits.<ref>{{Cite journal |last1=Donohue |first1=Shelly L. |last2=DeSantis |first2=Larisa R. G. |last3=Schubert |first3=Blaine W. |last4=Ungar |first4=Peter S. |date=2013-10-30 |title=Was the Giant Short-Faced Bear a Hyper-Scavenger? A New Approach to the Dietary Study of Ursids Using Dental Microwear Textures |journal=PLOS ONE |volume=8 |issue=10 |article-number=e77531 |doi=10.1371/journal.pone.0077531 |issn=1932-6203 |pmc=3813673 |pmid=24204860|bibcode=2013PLoSO...877531D |doi-access=free }}</ref>

==Systematics== {{Cladogram|{{clade| style=font-size:90%;line-height:90%; |1={{dagger}}Hemicyoninae |2={{Clade |1={{dagger}}Ursavinae |2={{Clade |1={{dagger}}Agriotheriinae |2={{Clade |1=Ailuropodinae 75px |2={{Clade |1=Ursinae 75px |2={{Clade |label1='''Tremarctinae''' (short-faced bears) |1={{Clade |1={{dagger}}''Plionarctos'' |2={{Clade |1={{dagger}}''Arctodus'' |2={{Clade |1=''Tremarctos'' 75px |2={{dagger}}''Arctotherium'' }} }} }} }} }} }} }} }} }}|align=right|title=Tremarctinae within Ursidae}} The following taxonomy of the tremarctine bears follow by Mitchell et al. (2016):<ref name=":3" /> * Subfamily Tremarctinae Merriam & Stock, 1925 ** †''Plionarctos'' Frick, 1926 *** †''Plionarctos edensis'' Frick, 1926 *** †''Plionarctos harroldorum'' Tedford & Martin, 2001 ** †''Arctodus'' Leidy, 1854 *** †''Arctodus pristinus'' Leidy, 1854 *** †''Arctodus simus'' Cope, 1879 ** †''Arctotherium'' Burmeister, 1879 *** †''Arctotherium angustidens'' Gervais & Ameghino, 1880 *** †''Arctotherium bonariense'' Gervais, 1852 *** †''Arctotherium tarijense'' Ameghino, 1902 *** †''Arctotherium vetustum'' Ameghino, 1885 *** †''Arctotherium wingei'' Ameghino, 1902 ** ''Tremarctos'' Gervais, 1855 *** †''Tremarctos floridanus'' (Gildey, 1928) *** ''Tremarctos ornatus'' (Cuvier, 1825) – spectacled bear

==References== {{Reflist}}

==External links== {{Wikispecies|Arctodus}} {{Wikispecies|Tremarctos}} *[https://web.archive.org/web/20140331005507/http://www.beringia.com/research/bear.html Yukon Beringia Interpretive Centre - North American Short-Faced Bear]

Category:Tremarctinae Category:Bears Category:Mammal subfamilies Category:Fossil taxa described in 1925