Megafaunal wolf

Location of a dog's carnassials; the inside of the 4th upper premolar aligns with the outside of the 1st lower molar, working like scissor blades

The megafaunal wolf was a Late Pleistocene – early Holocene hypercarnivore similar in size to a large extant gray wolf (Canis lupus). It had a shorter, broader palate with large carnassial teeth 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.

Name

In 2007, the words "megafaunal" and "wolf" appeared separated in the title of a study.^[1] In 2013, one of the study co-authors first used the term "megafaunal wolf" in a media release.^[2]

Haplogroup

Polychrome cave painting of a wolf-like canid, Font-de-Gaume, France.

In 2010, a study compared the mDNA haplotypes of 947 modern gray wolves from across Europe with the published sequences of 24 Pleistocene wolves from western Europe dated between 1,200-44,000 years BP. The study found that phylogenetically the haplotypes represented two haplogroups that were separated by 5 mutational steps 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 Pleistocene 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 Last Glacial Maximum.^[3] 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.^[4] 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 found in Beringia and Belgium preyed mainly on Pleistocene megafauna,^[1][5][3] which became rare at the beginning of the Holocene 12,000 years ago.^[6][3] The Pleistocene Eurasian wolves have been found to be morphologically and genetically comparable to the Pleistocene eastern-Beringian wolves,^[7] with some of the ancient European and Beringian wolves sharing a common haplotype (a17).^[1][3] It has been proposed that Pleistocene wolves across northern Eurasia and northern North America represented a continuous and almost panmictic population that was genetically and probably also ecologically distinct from the wolves living in this area today.^[8][3] 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.^[8] Haplogroup 2 did not go extinct in Europe, and if before the Last Glacial Maximum haplogroup 2 was exclusively associated with the wolf ecomorph specialized in preying on megafauna, it would mean that in Europe it was capable of adapting to changing prey.^[3]

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

Morphology

Pleistocene wolf skulls and jaws from Hutton and Banwell Cave (Somerset) and Oreston Cave (Plymouth)

Megafaunal wolves were similar in physical size to other Pleistocene-era wolves and large extant gray wolves, but with stronger jaws and teeth. They tended to have short, broad palates with large carnassials relative to their overall skull size. These features suggest a 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 megafaunal wolves were more specialized than modern gray wolves in killing and consuming relatively large prey and scavenging.^[1]:1147

In comparison to other gray wolves, megafaunal wolf samples include many more individuals with moderately to heavily worn teeth and a significantly greater numbers of broken teeth. The distribution of fractures across the tooth row differs as well, with these wolves having a 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.^[1]:1148

In 2014, a study of the morphology of wolf (Canis lupus) remains from Europe dating from the Middle-Late Pleistocene and Holocene indicated that the size of the lower carnassial teeth did not fluctuate directly with changes in climate but possibly with the spread of cold mega-fauna and therefore in the dietary regime. The lower-carnassial length can be used to estimate carnivore body size.^[9]

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 that was also a megafaunal hypercarnivore . 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.^[10]

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 Pleistocene and extant gray wolves, the megafaunal wolf was hypercarnivorous, with a craniodental morphology more capable of capturing, dismembering, and consuming the bones of very large mega-herbivores. When their prey disappeared, this wolf did as well, resulting in a significant loss of phenotypic and genetic diversity within the species.^[1]:1148

Habitat

Based on the morphological and genetic evidence, the megafaunal wolf's distribution was across the northern Holarctic.

Paleoecology

Ukok Plateau, one of the last remnants of the mammoth steppe^[11]

The last glacial period, commonly referred to as the 'Ice Age', spanned 125,000^[12] to 14,500^[13] years ago and was the most recent glacial period within the current ice age which occurred during the last years of the Pleistocene era.^[12] 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.^[13]

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.^[14] During the last glacial maximum, the continent of Europe was much colder and drier than it is today, with polar desert in the north and the remainder steppe or tundra. Forest and woodland was almost non-existent, except for isolated pockets in the mountain ranges of southern Europe.^[15]

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. The most common definition of megafauna is an animal with an adult body weight of over 44 kg. Across Eurasia, the Straight-tusked elephant became extinct between 100,000–50,000 years BP. The hippopotamus, interglacial rhinoceros (Stephanorhinus), cave bear (Ursus spelaeus), and heavy-bodied Asian antelope (Spirocerus) died out between 50,000-16,000 years BP. The spotted hyena, woolly rhinoceros and mammoths died out between 16,000-11,500 years BP. The musk ox died out after 11,500 BP, as did the giant deer (Megaloceros) with the last pocket having survived until about 7,700 years BP in western Siberia.^[16] A pocket of mammoths survived on Wrangel Island until 4,500 years BP.^[17] As some species became extinct, so too did their predators. Among the top predators, the sabre-toothed cat (Homotherium) died out 28,000 years BP,^[18] the Eurasian cave lion 11,900 years BP,^[19] and the leopard in Europe died out 27,000 years BP.^[20] The Late Pleistocene was characterized by a series of severe and rapid climate oscillations with regional temperature changes of up to 16 °C, which has been correlated with megafaunal extinctions. There is no evidence of megafaunal extinctions at the height of the LGM, indicating that increasing cold and glaciation were not factors. Multiple events appear to also involve the rapid replacement of one species by one within the same genus, or one population by another within the same species, across a broad area.^[21]

Modern human's ancestors first appeared in East Africa 195,000 years ago.^[22] Some migrated out of Africa 60,000 years ago with one group reaching Central Asia 50,000 years ago.^[23] From there they reached Europe, with human remains dated 43,000-45,000 years BP discovered in Italy,^[24] Britain,^[25] and in the European Russian Arctic 40,000 years ago.^[26][27] Remains of mammoth that had been hunted by humans 45,000 YBP have been found at Yenisei Bay in the central Siberian Arctic.^[28] Another group left Central Asia and reached the Yana River, Siberia, well above the Arctic circle 27,000 years ago.^[29] Modern humans then made their way across the Bering land bridge and into North America between 20,000-11,000 years ago, after the Wisconsin glaciation had retreated but before the Bering land bridge became inundated by the sea.^[4] These people then populated the Americas. In the Fertile crescent the first agriculture was developing 11,500 years ago.^[30]

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

Beringia

Shrinking of the Bering land bridge

Beringia is a loosely defined region surrounding the Bering Strait, the Chukchi Sea, and the Bering Sea. It includes parts of Chukotka and Kamchatka in Russia as well as Alaska in the United States. In historical contexts it also includes the Bering land bridge, an ancient land bridge roughly 1,000 miles (1,600 km) wide (north to south) at its greatest extent, which connected Asia with North America at various times — all lying atop the existing North American plate, and east of the Siberian Chersky Range — during the Pleistocene ice ages. During ice ages more water was stored as ice, the sea levels fell, and a land bridge was exposed.

East Beringia

In 2007, a study was undertaken on the skeletal material from 56 Pleistocene-period East Beringian wolves from permafrost deposits in Alaska. 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.^[1] Megafauna was still available in this region until 10,500 BP, with the age of the more recent wolf specimen supported by the discovery of a remaining pocket of residual megafauna that still inhabited interior Alaska between 7,500–10,500 BP.^[31]

The East Beringian wolf was identified as an ecomorph of the gray wolf (Canis lupis) with a skull morphology that was adapted for hunting and scavenging megafauna. None of the 16 mtDNA haplotypes recovered from a sample of 20 of the wolves was shared with any modern gray wolf, but similar haplotypes were found in Late Pleistocene Eurasian gray 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. Its 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 present. Modern North American wolves are not their descendents, and this supports the existence of a separate origin for ancient and extant North American wolves.^[1]

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 identified as Canis lupus.^[32]

West Beringia

In 2009, a study was made on the skull fragment and right mandible of a wolf (Canis lupus) found near Lake Taimyr in the Taimyr Peninsula, Arctic Siberia, Russian Federation (the Lake Taimyr wolf). It is one of the most northern-most records of Pleistocene carnivora in Eurasia. The skull was aged by radio carbon dating to 16,220 BP.^[33]

The adult skull was small and assumed to be a female as it did not differ in size to an extant female wolf skull from northern Siberia.^[33] Another study of the Lake Taimyr wolf found that its comparatively small size and characters of the cheekteeth and skull raised the possibility that it might have been a domesticated or semi-domesticated animal.^[34]

The increased skull width in comparison to extant wolves indicated pronounced development of the temporalis muscles. The specimens were compared to a wolf (Canis lupus spelaeus) fossil found near Burnberg, Germany and near the Paleolithic site of Kostenki 1 on the Don River near Voronezh, Russia. Both of the European fossil skulls demonstrated the same dentition as the fossil wolf from Taimyr. The skull and teeth arrangement suggest a considerable portion of carrion and bones in the diet. In the severe environmental conditions of the Late Pleistocene arctic zone of Eurasia, carrion had been one of the principal food sources for these animals. "Notably, the Pleistocene C. lupus from eastern Beringia, by the skull shape, tooth wear and isotopic data, is also reconstructed as a specialized hunter and scavenger of extinct North American megafauna."^[33]

Europe

Cave wolf
Scientific classification
Kingdom:	Animalia
Phylum:	Chordata
Class:	Mammalia
Order:	Carnivora
Family:	Canidae
Genus:	Canis
Species:	C. lupus
Subspecies:	C. l. spelaeus
Trinomial name
Canis lupus spelaeus Goldfuss, 1823[35]

The cave wolf (Canis lupus spelaeus) possibly belongs to a specialized Late Pleistocene wolf ecomorph. Its bone proportions are close to the Canadian arctic-boral mountain-adapted timber wolf and a little larger than the modern European wolf. It appears that in the early to middle Late Pleistocene this large wolf existed all over Europe, but was then replaced during the Last Glacial Maximum by a smaller wolf-type which then disappeared along with the reindeer fauna, finally replaced by the Holocene warm-period European wolf Canis lupus lupus. These wolves have been not well-studied and have not been well-defined by DNA.^[36]

Cave wolf populations are known from Sophie’s Cave and other caves in the same area – the Zoolithen and Große Teufels Caves. Their dens have also been identified, especially in the Zoolithen Cave which had a large population and has yielded more than 380 bones as well as several skulls (including a holotype). Some postcranial bones have been compared, having similarly large proportions to those from the Sophie’s and Große Teufels Caves where the bone sizes are closer to those of Scandinavian Arctic and Canadian Columbian wolf subspecies than to those of the smaller European wolves.^[36]

Sophie’s Cave has demonstrated the first “Early Late Pleistocene wolf den”, with intensive faecal places and the first European record of half-digested cave bear bones found within the faecal areas in the cave. It demonstrates that wolves seem to have used this cave not as a cub raising den, but they were cave dwellers that fed on cave bear carcasses, similar but less so than cave hyenas but more so than cave lions. The abundant faeces seem to play a role in the “orientation” for trail tracking similar to modern wolves, and less as den marking. The high abundance in a limited area of the Bear’s Passage of the cave might be the result of periodical short-term den use of smaller cave areas. Wolves were scavenging on the bears that hibernated and died there, and therefore a simultaneous use as both a wolf and a cave bear den cannot be expected. Remains of a skeleton of at least one high adult wolf also might have been the result of a battle within the cave with the bears, the same as in the lion taphonomic record.^[36]

The ecology of the early to middle Late Pleistocene wolves on the mammoth steppe and the boreal forests is not known, nor if they used caves as dens.^[36]

In 2009, a study of the fossil remains of Paleolithic dogs and Pleistocene wolves found that 5 wolf specimens from Trou Baileux, Belgium (reference: ULg Depaepe 1988), Trou des Nutons, Belgium, (RBINS 2559-1), Mezine, Ukraine (PM NASU 5469 and 5488) and Yakutia, Siberia (ZIN RAS 29699) had a greater snout width than recent wolves. A similar trend was discovered in North American fossil wolves from East Beringia.^[37]>

Relationship with the domestic dog

In 2013, a leading evolutionary biologist stated that:

We know also that there were distinct wolf populations existing ten of thousands of years ago. One such wolf, which we call the megafaunal wolf, preyed on large game such as horses, bison and perhaps very young mammoths. Isotope data show that they ate these species, and the dog may have been derived from a wolf similar to these ancient wolves in the late Pleistocene of Europe.^[2]

In 2015, a study looked at the mitogenome contol region sequences of 13 ancient canid remains and one modern wolf from five sites across Arctic north-east Siberia. The 14 canids revealed nine haplotypes, three of which were on record and the others unique. Four of the Siberian canids dated 28,000 years before present (YBP), and one Canis c.f. variabilis dated 360,000 YBP. The phylogenetic relationship of the extracted sequences showed that the haplotype from specimen S805 (28,000 YBP) was one step away from another haplotype S902 (8,000 YBP) that represents the domestic dog and modern wolf lineages. Several ancient haplotypes were oriented around S805, including Canis c.f. variabilis (360,000 YBP), Belgium (36,000 YBP - the "Goyet dog") and Belgium (30,000 YBP), and Konsteki, Russia (22,000 YBP). Given the position of the S805 haplotype, it may potentially represent a direct link from the putative progenitor (including Canis c.f. variabilis) to the domestic dog and modern wolf lineages.^[38]

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