Beringian wolf

Shrinking of the Bering land bridge

The Beringian wolf was a hypercarnivorous ecomorph of gray wolf which inhabited eastern Beringia (modern day Alaska) and northern Wyoming during the Late Pleistocene and early Holocene. It was similar in size to other Pleistocene gray wolves and modern Alaskan wolves, but had a shorter, broader palate, with large carnassials relative to its overall skull size. This adaptation allowed it to predate and scavenge on Pleistocene megafauna. Such an adaption is an example of phenotypic plasticity.

Lineage

In 1975, a study was made of ancient canid remains dated to the Late Pleistocene and early Holocene that had been uncovered by miners decades earlier around Fairbanks, Alaska. These were identified as Canis lupus and described as "short-faced wolves".

Haplogroup

In 2010, a study compared the mDNA haplotypes of 947 modern gray wolves from across Europe with the published sequences of 24 ancient wolves from western Europe dated between 1,200-44,000 years BP. The study found that phylogenetically the haplotypes represented two haplogroups and referred to these as haplogroup 1 and 2. The 947 European wolves revealed 27 different haplotypes with haplogroup 1 forming a monophyletic clade, and all other haplotypes forming haplogroup 2. Comparison with gray wolves from other regions revealed that haplogroups 1 and 2 could be found spread across Eurasia but only haplogroup 1 could be found in North America. The ancient wolf samples from western Europe all belonged to haplogroup 2, which suggested a long-term predominance in this region. A comparison of current and past frequencies indicated that in Europe haplogroup 2 became outnumbered by haplogroup 1 but in North America haplogroup 2 became extinct and was replaced by haplogroup 1 after the LGM. Access into North America was available between 20,000-11,000 years ago, after the Wisconsin glaciation had retreated but before the Bering land bridge became inundated by the sea. Therefore, haplogroup 1 was able to enter into North America during this period.

Analysis of stable isotopes, which offer conclusions about the diet and therefore the ecology of the extinct wolf populations suggest that the Pleistocene wolves from haplogroup 2 mainly preyed on Pleistocene megafaunal species, which became rare at the beginning of the Holocene 12,000 years ago. "Thus, Pleistocene wolves across Northern Eurasia and America may actually have represented a continuous and almost panmictic population that was genetically and probably also ecologically distinct from the wolves living in this area today." "The Pleistocene Eurasian wolves are morphologically and genetically comparable to the Pleistocene eastern-Beringian wolves." The specialized Pleistocene wolves, thus, did not contribute to the genetic diversity of modern wolves. Rather, modern wolf populations across the Holarctic are likely be the descendants of wolves from populations that came from more southern refuges as suggested previously for the North American wolves.

These 2 haplogroups exclude the older-lineage Himalayan wolf and the Indian gray wolf.

Haplotypes

A study on the skeletal material from 56 Late Pleistocene eastern-Beringian wolves based on uncalibrated radio carbon dating showed a continuous population from 45,500 years BP to 12,500 years BP, and one single wolf dated at 7,600 BP. This indicates that their population was in decline after 12,500 BP, although megafauna was still available in this region until 10,500 BP. The latter specimen is supported by the discovery of a remaining pocket of residual megafauna that still inhabited interior Alaska around that time.

An mtDNA analysis of 20 of these wolf samples yielded 16 haplotypes and were compared to those of 436 modern wolves. None of these haplotype was shared with the modern wolves but similar haplotypes were found in Late Pleistocene Eurasian wolves. Six eastern-Beringian wolves had the same sequence found in two wolves from Ukraine dated 30,000 years BP and 28,000 years BP, and from Altai dated 33,000 years BP. Two eastern-Beringian wolves matched another haplotype with a wolf from the Czech Republic dated at 44,000 years BP. The phylogeny indicates that, aside from the older-lineage Himalayan wolf and the Indian gray wolf, the Beringian wolf's unique haplotypes are basal to other gray wolves. Its genetic diversity was higher than that of its modern counterparts, implying that the wolf population of the Late Pleistocene was larger than at present. Modern North American wolves are not their descendents, however ancient North American wolves are associated with a distinct group of 4 modern European haplotypes (but these are not their direct descendents), and this supports the existence of a separate origin for ancient and extant North American wolves. Two of these 4 haplotypes includes w22 only found in Italy and w14 from Rumania.

A more detailed analysis of the genetic material from three specimens were dated at 28,000 years BP, 21,000 years BP, and 20,800 years BP respectively (with the samples deposited in GenBank with accession numbers KF661088, KF661089 and KF661090) and classified as Canis lupus.

Skull and dentition

Wolf mandible diagram showing the names and positions of the teeth.

Ecological factors including habitat type, climate, prey specialization and predatory competition will greatly influence gray wolf genetic population structure and cranio-dental plasticity. Therefore, within the Pleistocene gray wolf population the variations between local environments would have encouraged a range of wolf ecotypes that were genetically, morphologically and ecologically distinct from one another.

Beringian wolves were similar in physical size to Pleistocene wolves found in Rancho La Brea (California) and modern Alaskan wolves, but with stronger jaws and teeth. Beringian wolves tended to have short, broad palates with large carnassials relative to their overall skull size. The row length of their premolars was longer, the P4 wider, and the M1 and M2 longer than other wolves. These features suggest a gray wolf adapted for producing relatively large bite forces. The short, broad rostrum increased the mechanical advantage of a bite made with the canine teeth and strengthened the skull against torsional stresses caused by struggling prey. Relatively deep jaws are characteristic of habitual bone crackers, such as spotted hyenas, as well as canids that take prey as large as or larger than themselves. Overall these features indicate that eastern-Beringian wolves were more specialized than modern gray wolves in killing and consuming relatively large prey and scavenging.

In comparison to other gray wolf populations, Beringian wolf samples include many more individuals with moderately to heavily worn teeth. In addition, eastern-Beringian wolves exhibit heavier wear and significantly greater numbers of broken teeth. Overall fracture frequencies ranged from a low of 2% in Canis lupus irremotus (Canada, Idaho) to a high of 11% in the eastern-Beringian wolves. The distribution of fractures across the tooth row differs as well, with eastern-Beringian wolves having much higher fracture frequencies of incisors, carnassials, and molars. A similar pattern was observed in spotted hyenas, suggesting that increased incisor and carnassial fracture reflects habitual bone consumption, because bones are gnawed with incisors and subsequently cracked with the cheek teeth.

In 2015, a study looked at specimens of all of the carnivore species from Rancho La Brea, California, including remains of the large wolf Canis dirus guildayi that was also a megafaunal hypercarnivore and exhibited a high incidence of tooth breakage. The evidence suggests that these carnivores were not food-stressed just before extinction and that carcass utilization was less than among large carnivores today. The high incidence of tooth breakage likely resulted from the acquisition and consumption of larger prey.

Ecology

Paleoecology

The last glacial period, commonly referred to as the 'Ice Age', spanned 125,000 to 14,500 years ago and was the most recent glacial period within the current ice age which occurred during the last years of the Pleistocene era. The Ice Age reached its peak during the last glacial maximum, when ice sheets commenced advancing from 33,000 years BP and reached their maximum positions 26,500 years BP. Deglaciation commenced in the Northern Hemisphere approximately 19,000 years BP, and in Antarctica approximately 14,500 years BP which is consistent with evidence that this was the primary source for an abrupt rise in the sea level 14,500 years ago. A vast Mammoth steppe stretched from Spain across Eurasia and over the Bering land bridge into Alaska and the Yukon where it was stopped by the Wisconsin glaciation. This land bridge existed because more of the planet's water was locked up in glaciation than now and therefore the sea-levels were lower. When the sea levels began to rise this bridge was inundated around 11,000 years BP. The fossil evidence from many continents points to the extinction mainly of large animals at or near the end of the last glaciation. These animals have been termed Pleistocene megafauna.

In this environment came a gray wolf ecomorph, and as the environment changed it too became extinct.

See further:Paleoecology at this time

Range

Aassumed path of Beringian wolves from Alaska to the Natural Trap Cave (denoted with a black dot). Dog icons represent sites where Beringian wolves have previously been found and paw prints represent the hypothesized path through the ice sheets.

Conceivably, the robust ecomorph also was present in western Beringia (Russia) in the Late Pleistocene, but specimens were not available for this study. A plausible scenario for the presence of two distinct Pleistocene gray wolves in North America relies on an early arrival of the more gracile wolf from the Old World, and migration to areas below the Wisconsin ice sheet. This gray wolf established itself into a carnivore guild that already contained forms both larger (dire wolf) and smaller (coyote) than itself. The presence of these two relatively common species (especially the dire wolf) seems to have prevented gray wolves from reaching high densities until after the demise of the dire wolf, approximately 10,000 years BP. The appearance of a more robust form of the gray wolf in eastern Beringia in the Late Pleistocene might represent evolution in situ or a secondary invasion from the Old World. Its success was favored by the absence of dire wolves north of the ice sheet.

Specimens that have been identified by morphology to be Beringian wolves and radiocarbon dated between 25,800-14,300 YBP have been found in the Natural Trap Cave at the base of the Bighorn Mountains in Wyoming, USA. The location is directly south of what would at that time have been the division between the Laurentide Ice Sheet and the Cordilleran Ice Sheet. A temporary channel between the glaciers may have existed from 25,800 YBP until the advance of the ice sheets 16,000-13,000 YBP. The migration of the Beringian wolf may have been the result of pursuing prey species, as the cave also contained specimens of Steppe bison that had migrated from Beringia and would have been prey for wolves, and Muskox that is known to be an important prey species of the Beringian wolf. Dire wolves were absent north of 42°N latitude in the Late Pleistocene, therefore this region would have been available for Beringian wolves to expand south along the glacier line. There is yet no evidence of expansion beyond this region.

Diet

Isotopic bone collagen analysis of the specimens indicated that they ate horse, bison, woodland muskox and mammoth i.e. Pleistocene megafauna. This supports the conclusion that they were capable of killing and dismembering large prey.

Compared with extant gray wolves and Pleistocene gray wolves from Rancho La Brea, the eastern-Beringian ecomorph was hypercarnivorous, with a craniodental morphology more capable of capturing, dismembering, and consuming the bones of very large mega-herbivores, such as bison. When their prey disappeared, this wolf ecomorph did as well, resulting in a significant loss of phenotypic and genetic diversity within the species. The timing of the extinction of horses in North America and the minimum population size for North American bison coincide with the extinction an entire wolf haplogroup in North America, supporting the notion that the disappearance of their prey caused the extinction of this wolf ecomorph.

A more in-depth analysis based on fossil findings in the Fairbanks region of Alaska found that mammoth was rare in the diets of Beringian carnivores – the short-faced bears, lions, Beringian wolves, and the omnivorous brown bear. Half of the wolf specimens were found to be muskox and caribou specialists, and the other half were horse and bison specialists or generalists. Two full-glacial (23,000–18,000 years BP) wolves were found to be mammoth specialists but we cannot tell if this was due to scavenging or predation. The only survivor of this guild was the brown bear, an omnivore.

Competitors

The eastern-Beringian wolf was well positioned as the dominant large, pack-hunting canid within a predator guild that included large felids, ursids, and two smaller canids, the dhole and coyote. One study found that the coyote of 10,000 years ago was more canivorous, much larger, and with skulls and jaws significantly thicker and deeper than those of recent populations.

See also

• Megafaunal wolf