Spectacled bear


The spectacled bear, also known as the Andean bear, 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. 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.

Etymology

Tremarctos ornatus is commonly referred to in English as the "spectacled bear", a reference to the light colouring on its chest, neck and face, which may resemble spectacles in some individuals, or the "Andean bear" for its distribution along the Andes. The root trem- comes from a Greek word meaning "hole"; arctos is the Greek word for "bear". Tremarctos is a reference to an unusual hole on the animal's humerus. Ornatus, Latin for "decorated", is a reference to the markings that give the bear its common English name. T. ornatus is locally known as jukumari, ukumari or ukuku ; translating to "hole bear", the tan facial markings usually appear on the face except around the bear's eyes, making it look like the bear has holes for eyes

Taxonomy

The spectacled bear is last surviving member of the subfamily Tremarctinae, which also includes its extinct sister species Tremarctos floridanus from North America, and the fellow short-faced bears Arctodus, and Arctotherium, which became extinct at the end of the Pleistocene around 12,000 years ago.

Diagnostics

Unlike almost all other extant bears, tremarctine bears like T. ornatus appear to have disproportionately shorter snouts, 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; Tremarctine bears have shorter and taller skulls, but not a shorter face than most living bears.
In addition to being brachycephalic, tremarctine bears' skulls possess well developed zygomatic arches and glenoid mandibular fossas, a premasseteric fossa on the mandible and often an entepicondylar foramen on the humerus. Moreover, tremarctine bears' orbits are also bigger, more rounded and lateralized than ursine bears. Unlike tremarctine bears, ursine bears have only one masseteric fossa on their mandible and more slender and elongated skulls, with generally narrower molars. Cranial differences between tremarctine and ursine bears also include an extra lateral cusp between the trigonid and talonid on the m1 molar, with tremarctines possessing larger molars in comparison with ursines. Additionally, there are differences with the number of chromosomes, with Ursus possessing 74 and Tremarctos possessing 52. Within the Tremarctinae subfamily, Tremarctos is noteworthy for its relatively smaller teeth, the presence of anterior premolars, well-defined masseteric fossae, and a W-shaped cusp pattern on the lower m1 molar.

''Tremarctos''

T. floridanus and T. ornatus are morphologically very similar, and are considered sister species. However, T. floridanus was around twice as big as T. ornatus, being around the size of a larger American black bear. Though both species have short rostrums in comparison with ursine bears, the rostrum of T. ornatus is relatively broader compared with T. floridanus. T. floridanus also possessed a signature "glabella" on the frontal bone of the cranium. Both species share practically identical dentitions, though the dentition of T. ornatus was smaller, often with an increased number of premolars and relatively shorter molars. Tremarctos ''ornatus has mandibular condyles in line with the plane of the teeth while T. floridanus has raised mandibular condyles, suggesting T. ornatus potentially possesses a larger gape. The lower jaws of T. ornatus are smaller; while the ramus of the mandible is taller in T. floridanus, the relative height of the mandible's coronoid process is the same in both species. The canalis semicircularis lateral suggests that T. floridanus had a head posture of 38°, which is more oblique than its sister species T. ornatus ; as T. ornatus inhabits densely vegetated areas, the more oblique head posture in T. floridanus could infer a greater capacity for long distance vision.
Both species also differ slightly in their post-cranial proportions. T. floridanus has been described as a relatively long-limbed species compared to T. ornatus, with the humerus, femur and neck being notably longer compared to body length. While the forelimbs of T. ornatus are longer than their hindlimbs, the hindlimbs of T. floridanus are the same length as their forelimbs. Additionally, T. ornatus has also been described as possessing much more gracile limb bones. However, the paws of T. floridanus are proportionally shorter and smaller than T. ornatus. Kurtén compared the differences between the Tremarctos'' species as the differences between brown bears and Eurasian cave bears.

Evolution

Tremarctine bears first appear as Plionarctos during the late Miocene epoch of North America. An investigation into the mitochondrial DNA of bear species indicates that the short-faced bears diverged from the Ursinae subfamily approximately 5.7 million years ago. Around the Miocene-Pliocene boundary, tremarctine bears, along with other ursids, experienced an explosive radiation in diversity, as C4 vegetation and open habitats dominated. The world experienced a major temperature drop and increased seasonality, and a faunal turnover which extinguished 70–80% of North American genera.
Correspondingly, the genetic divergence date for Arctodus is between 5.5 million and 4.8 million years ago, and between Arctotherium and Tremarctos at 4.1 million years ago. All three genera evolved from Plionarctos in the Blancan faunal stage of North America, and are first recorded as the medium-sized Arctodus pristinus, ''Tremarctos floridanus and Arctotherium sp. from the Late Blancan of North America circa 2.6 million years ago. These first appearances coincide with the start of the Quaternary Glaciation, the formation of the Panama Land Bridge, and the second phase of the Great American Biotic Interchange, with the first records of the main South American faunal wave into the United States. A Plionarctos harroldum specimen from Taunton appears evolutionarily intermediate between Plionarctos harroldum and Tremarctos floridanus, affirming that Plionarctos harroldum is the likely ancestor of Tremarctos.
Genetic research on the mitochondrial DNA of tremarctine bears indicates Tremarctos was more closely related to Arctotherium than Arctodus. However, a preliminary investigation of tremarctine bear's nuclear DNA suggests an extensive history of hybridization between Tremarctos and Arctodus in North America, although hybridization with Arctotherium in either Central America or South America is also possible. Evidence of gene flow between Tremarctos and an ursine bear was also uncovered, most likely due to the extensive overlap between Tremarctos'' and the ancestors of the American black bear in Pleistocene North America.

''Tremarctos'' genus

The spectacled bear does not appear in the South American fossil record until the Holocene, suggesting that the extant spectacled bear descends from an independent, later dispersal event from North America to that of Arctotherium, possibly after Arctotherium wingei became extinct in the Americas at the end of the Pleistocene. As T. floridanus is known from 2.7 million years ago until at least 23,000 years ago in North America, T. floridanus may have evolved into T. ornatus in South America, in either the Pleistocene or the Holocene. However, current scholarly analysis asserts that A. wingei may have restricted the range of T. floridanus outside of Central and South America until the extinction of A. wingei, where subsequently Tremarctos begins to be found in the South America. The modern spectacled bear's genetics suggest a possible history of hybridization with Arctotherium as the Tremarctos genus interacted with Arctotherium in either Central America throughout the Pleistocene, or as Tremarctos migrated into South America at the end of the Pleistocene.
However, should the spectacled bear have been present in South America during the late Pleistocene, the spectacled bear could have co-existed with Arctotherium. As the spectacled bear prefers highland forests and Arctotherium preferred lowlands, their ranges would have had minimal overlap.
File:Spectacled Bear 616md.jpg|thumb|Spectacled bear footprint from Chaquil Cave, Peru
The genetic history of T. ornatus from 1 Mya to today suggests a history of decreasing population size, with effective population peaking at 450 kya. Correspondingly, the suggested breeding population dipped from 30,000 to 25,000, before rising to 40,000. This was followed by an extended and drastic decrease to the Holocene, tied to the climatic fluctuations of the Middle Pleistocene, high temperatures during interglacials shrinking the size of forests in the Americas, and the Late Pleistocene extinctions.
Molecular evidence from Colombian, Ecuadorian and Venezuelan spectacled bear specimens suggests a population divergence occurred between 15,000 and 25,000 thousand years ago. The earliest known remains of the spectacled bear are from a male from Chaquil Cave, north central Peru, and have been dated to 6,790 years ago. The extreme wear of the teeth suggests a primarily carnivorous diet. Further finds are from archeological sites in Colombia and an archeological site in Peru dated to 1,500 BP.