Tremarctinae

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Tremarctinae
Temporal range: late Miocene–present
Tremarctinae.png
Spectacled bear, Arctodus simus and Arctotherium bonariense
Scientific classification OOjs UI icon edit-ltr.svg
Domain: Eukaryota
Kingdom: Animalia
Phylum: Chordata
Class: Mammalia
Order: Carnivora
Family: Ursidae
Subfamily: Tremarctinae
Merriam & Stock, 1925
Genera

† Plionarctos
† Arctodus
† Arctotherium
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. [1] 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.

Contents

Evolution

Skeletal reconstruction of Arctodus simus. DSC09100 - Extinct Bear (37221999825).jpg
Skeletal reconstruction of Arctodus simus.

Tremarctinae originate with their common ancestor, Plionarctos, in the Middle Hemphillian (earliest Late Miocene, ~10Ma) of North America; Plionarctos is last recorded in the early Blancan (Early Pliocene, ~3.3Ma). Around the Miocene-Pliocene boundary (~5 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. [1] Correspondingly, a 2016 study suggested that the mean divergence dates for Arctotherium, Arctodus and Tremarctos were 4.8 Ma, and between Arctotherium and Tremarctos at 4.1 Ma. [2] A further study calculated the divergence date between Arctodus and Tremarctos at 5.5 Ma. [3] All three genera are first recorded from the Blancan (Pliocene/Pleistocene boundary) of North America. [4]

An indeterminate Arctotherium is first recorded from the late Pliocene of El Salvador. [5] In the Early Pleistocene, short-faced bears began to establish themselves more thoroughly in both North and South America. [6] 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. [7] 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. [6] 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, [8] and to reinvade Central America. [9]

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. [5] Around this time, Tremarctos ornatus , otherwise known as the spectacled bear, starts appearing in the South American fossil record. [10] 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. [11] [12]

Anatomy

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 a deeper but not a shorter face than most living bears. [13] Osteological differences between tremarctine and ursine bears include an extra lateral cusp between the trigonid and talonid on the m1 molar, a premasseteric fossa on the mandible, and often an entepicondylar foramen on the humerus of tremarctine bears. [14] Additionally, tremarctine bears' skulls are deeper and more brachycephalic, their zygomatic arches and glenoid fossas are well developed, and they have larger molars in comparison with ursines. Moreover, tremarctine bears' orbits are also bigger, more rounded and lateralized. [13]

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. [15] [16] Additionally, the much more gracile form of Arctodus , in contrast with the robust Arctotherium angustidens , has puzzled researchers. [17] [18] 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 . [4]

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. [19]

Systematics

Tremarctinae within Ursidae

†Hemicyoninae

†Ursavinae

†Agriotheriinae

Ailuropodinae Recherches pour servir a l'histoire naturelle des mammiferes (Pl. 50) (white background).jpg

Ursinae Ursus arctos - 1700-1880 - Print - Iconographia Zoologica - Special Collections University of Amsterdam - (white background).jpg

Tremarctinae (short‑faced bears)

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 . [12] [18] 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. [2]

Tremarctines are occasionally referred to as arctodonts or arctotheres in older scientific literature, [20] although this has fallen out of fashion.

Taxonomy

The following taxonomy of the tremarctine bears follow by Mitchell et al. (2016): [2]

See also

Related Research Articles

<span class="mw-page-title-main">Bear</span> Family of carnivoran mammals

Bears are carnivoran mammals of the family Ursidae. They are classified as caniforms, or doglike carnivorans. Although only eight species of bears are extant, they are widespread, appearing in a wide variety of habitats throughout most of the Northern Hemisphere and partially in the Southern Hemisphere. Bears are found on the continents of North America, South America, and Eurasia. Common characteristics of modern bears include large bodies with stocky legs, long snouts, small rounded ears, shaggy hair, plantigrade paws with five nonretractile claws, and short tails.

<span class="mw-page-title-main">Nearctic realm</span> Biogeographic realm encompassing temperate North America

The Nearctic realm is one of the eight biogeographic realms constituting the Earth's land surface.

<i>Megatherium</i> Genus of ground sloth (extinct)

Megatherium is an extinct genus of ground sloths endemic to South America that lived from the Early Pliocene through the end of the Late Pleistocene. It is best known for the elephant-sized type species Megatherium americanum, primarily known from the Pampas, but ranging southwards to northernmost Patagonia and northwards to southern Bolivia during the late Middle Pleistocene and Late Pleistocene. Various other species belonging to the subgenus Pseudomegatherium ranging in size comparable to considerably smaller than M. americanum are known from the Andean region.

<span class="mw-page-title-main">Spectacled bear</span> Species of mammal

The spectacled bear, also known as the South American bear, Andean bear, Andean short-faced bear or mountain bear and locally as jukumari, ukumari (Quechua) or ukuku, is a species of bear native to the Andes Mountains in northern and western South America. It is the only living species of bear native to South America, and the last remaining short-faced bear. Its closest relatives are the extinct Tremarctos floridanus, and the giant short-faced bears, which became extinct at the end of the Pleistocene around 12,000 years ago. Unlike other omnivorous bears, the diet of the spectacled bear is mostly herbivorous. The species is classified as Vulnerable by the IUCN because of habitat loss.

<i>Tremarctos</i> Genus of bears

Tremarctos is a genus of the bear subfamily Tremarctinae, endemic to Americas from the Pliocene to recent. The northern species, the Florida short-faced bear, became extinct 11,000 years ago. The sole living Tremarctos species is the South American spectacled bear.

<span class="mw-page-title-main">Ailuropodinae</span> Subfamily of bears

Ailuropodinae is a subfamily of Ursidae that contains only one extant species, the giant panda of China. The fossil record of this group has shown that various species of pandas were more widespread across the Holarctic, with species found in places such as Europe, much of Asia, North America and even Africa. The earliest pandas were not unlike other modern bear species in that they had an omnivorous diet but by around 2.4 million years ago, pandas have evolved to be more herbivorous.

<i>Chapalmalania</i> Extinct genus of procyonid mammals from South America

Chapalmalania is an extinct genus of procyonid from the Late Miocene or Early Pliocene to Early Pleistocene of Argentina, Venezuela, and Colombia.

<i>Agriotherium</i> Extinct genus of bears

Agriotherium is an extinct genus of bears whose fossils are found in Miocene through Pleistocene-aged strata of North America, Eurasia, and Africa. This long-lived genus persisted from at least ~11.6–2.5 Mya. Materials from the late-surviving A. africanum in Africa have suggested that A. africanum died out during the early Gelasian.

<i>Tremarctos floridanus</i> Extinct species of bear

Tremarctos floridanus is an extinct species of bear in the family Ursidae, subfamily Tremarctinae. T. floridanus became extinct at the end of the last ice age, 11,000 years ago. It's fossils have been found throughout the Southeastern United States, in northeastern Mexico, and in Belize from the Rancholabrean epoch, and from earlier epochs at some sites in western North America.

Cyonasua is an extinct genus of procyonid from the Late Miocene to Middle Pleistocene of South America. Fossils of Cyonasua have been found in Argentina, Bolivia, Uruguay, and Venezuela. The oldest well-dated fossils of Cyonasua are approximately 7.3 million years old. Most fossils of Cyonasua are late Miocene to early late Pliocene in age, but a single early Pleistocene specimen indicates that members of this genus survived until at least 0.99 million years ago.

<i>Arctodus</i> Extinct genus of bears

Arctodus is an extinct genus of short-faced bear that inhabited North America during the Pleistocene. There are two recognized species: the lesser short-faced bear and the giant short-faced bear. Of these species, A. simus was larger, is known from more complete remains, and is considered one of the most charismatic of North America's megafauna. A. pristinus was largely restricted to the Early Pleistocene of the eastern United States, whereas A. simus had a broader range, with most finds being from the Late Pleistocene of the United States, Mexico and Canada. A. simus evolved from A. pristinus, but both species likely overlapped in the Middle Pleistocene. Both species are relatively rare in the fossil record.

Plionarctos is an extinct genus of bear endemic to North America from the Miocene to the Pliocene, ~10.3—3.3 Mya, existing for about 7 million years.

<span class="mw-page-title-main">Haile Quarry site</span>

The Haile Quarry or Haile sites are an Early Miocene and Pleistocene assemblage of vertebrate fossils located in the Haile quarries, Alachua County, northern Florida. The assemblage was discovered during phosphate mining, which began in the late 1940s. Haile sites are found in the Alachua Formation. Two sites within the Ocala Limestone yielded Upper Eocene Valvatida and mollusks.

<i>Arctotherium</i> Extinct genus of bears

Arctotherium is an extinct genus of the Pleistocene short-faced bears endemic to Central and South America. Arctotherium migrated from North America to South America during the Great American Interchange, following the formation of the Isthmus of Panama during the late Pliocene. The genus consists of one early giant form, A. angustidens, and several succeeding smaller species, which were within the size range of modern bears. Arctotherium was adapted to open and mixed habitat. They are genetically closer to the spectacled bear, than to Arctodus of North America, implying the two extinct forms evolved large size in a convergent manner.

The Cuscatlán Formation is a geologic formation in El Salvador. It preserves fossils dating back to the Pliocene to Middle Pleistocene period.

Ursus ingressus is an extinct species of the family Ursidae that lived in Central Europe during the Late Pleistocene. It is named after the Gamssulzen Cave in Austria, where the holotype of this species was found.

<i>Panthera balamoides</i> Extinct species of carnivore

Panthera balamoides is a possibly dubious species described as an extinct species of the big cat genus Panthera that is known from a single fossil found in a Late Pleistocene age cenote in the Yucatan Peninsula, Mexico. P. balamoides has only a single reported specimen, the distal end of a right humerus, that is notably of exceptional size for a felid. It was unearthed in 2012 from an underwater cave and described in 2019 by an international group of paleontologists from Mexico and Germany led by Sarah R. Stinnesbeck. However, several authors have since proposed the humerus represents that of a bear, possibly the extinct Arctotherium, and not a cat.

<i>Protarctos</i> Extinct genus of bear

Protarctos is an extinct genus of basal ursine bear that lived in North America and Eurasia during the Pliocene and into Early Pleistocene.

<i>Pampatherium</i> Extinct genus of mammal

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References

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  3. ↑ Pedersen, Mikkel Winther; De Sanctis, Bianca; Saremi, Nedda F.; Sikora, Martin; Puckett, Emily E.; Gu, Zhenquan; Moon, Katherine L.; Kapp, Joshua D.; Vinner, Lasse; Vardanyan, Zaruhi; Ardelean, Ciprian F. (June 2021). "Environmental genomics of Late Pleistocene black bears and giant short-faced bears". Current Biology. 31 (12): 2728–2736.e8. Bibcode:2021CBio...31E2728P. doi: 10.1016/j.cub.2021.04.027 . hdl: 10037/22808 . ISSN   0960-9822. PMID   33878301.
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  7. ↑ "FIGURE 1—Map showing locations of reported Arctodus simus localities..." ResearchGate. Retrieved 2022-02-12.
  8. ↑ "Figura 5. Distribución inferida de algunos mamíferos grandes y..." ResearchGate. Retrieved 2022-02-12.
  9. ↑ 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.
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  11. ↑ García-López, Daniel; Ortiz, Pablo; Madozzo Jaén, M.; Moyano, M. (2008-12-12). "First Record of Arctotherium (Ursidae, Tremarctinae) in Northwestern Argentina and its Paleobiogeographic Significance". Journal of Vertebrate Paleontology. 28 (4): 1232–1237. Bibcode:2008JVPal..28.1232L. doi:10.1671/0272-4634-28.4.1232. hdl: 11336/79528 . S2CID   86213882.
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  14. ↑ Steffen, Martina L.; Fulton, Tara L. (February 2018). "On the association of giant short-faced bear ( Arctodus simus ) and brown bear ( Ursus arctos ) in late Pleistocene North America". Geobios. 51 (1): 61–74. Bibcode:2018Geobi..51...61S. doi:10.1016/j.geobios.2017.12.001.
  15. ↑ 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.
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  17. ↑ 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.
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  19. ↑ 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.
  20. ↑ Packard, E.L.; Allison, I.S.; Cressman, L.S. "Mammalian Tracks in the Late Pliocene or Early Pleistocene Beds of Lake County Oregon" (PDF). Oregon Geology. Retrieved June 11, 2017.
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