Dire Wolf

The real dire wolf went extinct thousands of years ago. Along with its extinct counterpart Smilodon, it is one of the most well-known prehistoric wolf or carnivores in North America. During the Late Pleistocene and Early Holocene epochs (125,000–9,500 years ago), the black dire wolf roamed the Americas and eastern Asia. The species was named four years after the first specimen was discovered, in 1858. Aenocyon dirus guildayi and Aenocyon dirus dirus are the two subspecies that have been identified. The Rancho La Brea Tar Pits in Los Angeles have produced the biggest collection of its fossils.

Dire wolf remains have been discovered in a variety of habitats, including North America's plains, grasslands, and some forested mountain ranges, South America's arid savanna, and eastern Asia's steppes. The elevation of the sites varies from sea level to 2,255 metres (7,400 ft). Only five unsubstantiated claims of dire wolf fossils have been discovered north of 42°N latitude. Temperature, prey, or habitat limits imposed by closeness to the Laurentide and Cordilleran ice sheets that existed at the time are suggested to be the cause of this range restriction. However, dire wolf fossils discovered in northeast China in 2020 suggest that dire wolves traversed Beringia during its existence.

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Direwolf Scientific Classification

Kingdom: Animalia

Phylum: Chordata

Class: Mammalia

Order: Carnivora

Family: Canidae

Subfamily: Caninae

Tribe: Canini

Subtribe: Canina

Genus: †Aenocyon

Species: †A. dirus

Direwolf History and Evolution

The fossil bones of extinct giant wolves began to be discovered in the United States in the 1850s, and it wasn't immediately evident that they all belonged to the same species. The first specimen of what would subsequently be known as Aenocyon dirus was discovered in the Ohio River bed near Evansville, Indiana, in mid-1854. The geologist Joseph Granville Norwood obtained the fossilized jawbone with cheek teeth from Francis A. Linck, an Evansville collector. Palaeontologist Joseph Leidy found that the specimen belonged to an extinct wolf species and gave it the name Canis primaevus. Norwood's letters to Leidy are kept in the Academy of Natural Sciences of Philadelphia, along with the type specimen (the first of a species with a documented description). While investigating the Niobrara River valley in Nebraska in 1857, Leidy discovered the vertebrae of an extinct Canis species, which he named C. dirus the following year. When Leidy discovered that the term C. primaevus (Leidy 1854) had already been used by the British naturalist Brian Houghton Hodgson for the dhole, he renamed it Canis indianensis.

John Campbell Merriam, a palaeontologist, began recovering numerous fossilized bone fragments of a huge wolf from the Rancho La Brea tar pits in 1908. By 1912, he had discovered a full skeleton, allowing him to properly designate these and other previously discovered individuals as C. dirus. 

Björn Kurtén recognized geographic variation within dire wolf populations in 1984 and proposed two subspecies: Canis dirus guildayi (named by Kurtén in honour of palaeontologist John E. Guilday) for specimens from California and Mexico with shorter limbs and longer teeth, and Canis dirus dirus for specimens east of the North American Continental Divide with shorter limbs and longer teeth. Kurtén named the nominate subspecies C. d. dirus after a maxilla found in Hermit's Cave, New Mexico.

When compared to existing wolf-like canines, a DNA analysis published in 2021 indicated the dire wolf to have a very divergent lineage, which is compatible with Merriam's suggested taxonomic classification of the dire wolf as genus Aenocyon.

The canid family first appeared in North America 40 million years ago, with the canine subfamily Caninae appearing 32 million years ago. The ancestors of the fox-like Vulpini and the dog-like Canini descended from the Caninae 9 million years ago. Eucyon, particularly the coyote-like Eucyon davisi, was the first to represent this group, which was widely distributed over North America. The Cerdocyonina, which includes today's South American canids, evolved from the Canini 6–5 million years ago. Its sister, the wolf-like Canina, appeared 5 million years ago, but they are thought to have evolved as early as 9 million years ago. Canines migrated into Eurasia and Africa some 7 million years ago, with Eucyon giving rise to the first of the species Canis in Europe. C. chihliensis, the first wolf-sized member of Canis, originated in China around 4-3 million years ago and spread across Eurasia and Africa, giving rise to other wolf-like relatives. Canis genus members would later spread across North America.

In North America, the dire wolf evolved. However, there are two opposing ideas about the ancestral lineage that gave origin to it. The first idea is based on fossil morphology, which implies that the dire wolf resulted from an extension of the genus Canis from Eurasia.

Morphological Evidence

The dire wolf was created by an extension of the genus Canis from Eurasia, according to morphological evidence based on fossil remains.

Robert A. Martin proposed in 1974 that C. armbrusteri (Armbruster's wolf), a huge North American wolf, was actually C. lupus. C. dirus was not derived from C. lupus, according to Nowak, Kurtén, and Annalisa Berta. In 1987, a novel idea stated that when food was plentiful, a mammal population may produce a larger form known as a hypermorph, but when food got limited, the hypermorph would either adapt to a smaller form or become extinct. This theory could explain why many Late Pleistocene wolf or mammals had larger bodies than their modern counterparts. During periods of environmental extremes, both extinction and speciation - the process by which a new species splits from an older one – could occur simultaneously. Gloria D. Goulet agreed with Martin, suggesting that this explanation may explain C. dirus's abrupt emergence in North America and, based on their skull forms, that C. lupus had given rise to the C. dirus hypermorph due to an abundance of game, a stable environment, and large competition.

Xiaoming Wang, Richard H. Tedford, and Ronald M. Nowak, three palaeontologists, propose that C. dirus developed from Canis armbrusteri, claiming that both species arose in the Americas and that specimens discovered in Cumberland Cave, Maryland, appear to represent C. armbrusteri diverging into C. dirus. Canis edwardii, according to Nowak, was the first wolf to appear in North America, and it looks to be related to the lineage that produced C. armbrusteri and C. dirus. Tedford argues that Canis chihliensis, an early Chinese wolf, was the ancestor of both C. armbrusteri and C. lupus, the grey wolf. 

C. dirus existed throughout North and South America from the Late Pleistocene to the early Holocene (125,000–10,000 years before present or YBP). The majority of fossils from the eastern C. d. dirus have been dated to 125,000–75,000 YBP, but the western C. d. guildayi fossils are not only smaller but also more recent, leading to the hypothesis that C. d. guildayi is a descendant of C. d. dirus. However, there are contested C. dirus specimens dating from 250,000 years ago. Aenocyon dirus nebrascensis was named after fossil specimens of C. dirus unearthed at four sites in Sheridan County, Nebraska, although Frick did not publish a description of them.

Nowak later referred to this material as C. armbrusteri, and Tedford formally described the specimens in 2009, noting that they shared some physical characteristics with both C. armbrusteri and C. dirus, although he only referred to them as C. dirus.

DNA Evidence

The dire wolf descended from an original lineage that originated in the Americas and was distinct from the species Canis, according to DNA evidence.

A mitochondrial DNA sequence was extracted from the skeletal bones of A. d. guildayi in 1992 in order to compare its related to other Canis species. Because these remains had been recovered from the La Brea pits and tar could not be separated from the bone particles, the attempt was futile. An attempt to recover DNA from a Columbian mammoth from the tar pits failed in 2014, with the study concluding that organic chemicals from the asphalt pervade the bones of all ancient samples from the La Brea pits, preventing DNA extraction. Researchers analyzed DNA from five dire wolf skeletons that date from 13,000 to 50,000 years ago in 2021. The dire wolf appears to be a very divergent lineage that last shared a common ancestor with wolf-like canines 5.7 million years ago, according to the sequencing. The study also compared the morphologies of multiple dire and grey wolf bone samples, which revealed that their morphologies were strikingly similar, supporting the notion that the dire and grey wolves shared a close evolutionary relationship.

The morphological similarities between dire and grey wolves were determined to be the result of convergent evolution. Although members of the wolf-like canines have been known to hybridize, the study found no evidence of genetic mingling between the five dire wolf samples and present North American grey wolves and coyotes, nor their common ancestor. This discovery suggests that the wolf and coyote lineages diverged from the dire wolf lineage.

The study claims that the dire wolf lineage originated in the Americas and that their geographic isolation allowed them to acquire reproductive isolation since their split 5.7 million years ago. There was no mingling with the dire wolf because coyotes, dholes, grey wolves, and the extinct Xenocyon developed in Eurasia and only recently expanded into North America during the Late Pleistocene. The dire wolf's long isolation suggests that other American fossil taxa, such as C. armbrusteri and C. edwardii, may also be members of the dire wolf's lineage. The findings of the study are compatible with the dire wolf's previously proposed taxonomic categorization as genus Aenocyon.

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Direwolves Physical Description

The average dire wolf sizes were close to those of two extant North American wolves: the Yukon wolf (Canis lupus pambasileus) and the Northwestern wolf (Canis lupus niger) (Canis lupus occidentalis). The largest northern wolves today stand 38 in (97 cm) tall at the shoulders and have a body length of 69 in (180 cm). Some of the dire wolf specimens found at Rancho La Brea are smaller, while others are larger.

When compared to a northern wolf of the same body size, the dire wolf had smaller feet and a larger skull. When compared to the Yukon wolf, the skull length could reach 310 mm (12 in) or longer, with a wider palate, frontal region, and zygomatic arches. The skull is large because of these dimensions. It had a higher sagittal crest, with a notable backward extension of the inion and the back ends of the nasal bones extending relatively far into the skull. The tar permits the bones to fragment in numerous directions, making a linked skeleton of a dire wolf from Rancho La Brea impossible to find. The components of a vertebral column were put together and found to be similar to those of a modern wolf, with the same number of vertebrae.

Geographic differences in dire wolves were not discovered until 1984 when a study of skeletal remains revealed differences in a few craniodental features and limb proportions between specimens found west of the Continental Divide (A. d. guildayi) and those found east of the Continental Divide (A. d. guildayi) (A. d. dirus). The rear limbs of A. d. guildayi were 8% shorter than the Yukon wolf due to a notably shorter tibia and metatarsus, while the front limbs were also somewhat shorter due to their slightly shorter lower bones, according to limb size comparisons. A. d. guildayi was not as well adapted for running as timber wolves and coyotes, with its comparatively lighter and smaller limbs and a huge head.

The limbs of A. d. dirus were substantially longer than those of A. d. guildayi. Because of 10 % longer humeri, 15% longer radii, and 15% longer metacarpals, the forelimbs were 14 % longer than A. d. guildayi. The hind limbs were 10% longer than those of A. d. guildayi, thanks to 10% longer femora and tibiae and 15% longer metatarsals. In terms of limb length, A. d. dirus is equivalent to the Yukon wolf. The largest A. d. dirus femur, measuring 278 mm, was discovered at Carroll Cave, Missouri (10.9 in).

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Direwolf Adaptations

Grey wolf craniodental plasticity, which is an adaptation of the cranium and teeth due to environmental effects, has been demonstrated to be strongly influenced by ecological factors such as habitat type, climate, prey specialization, and predatory competition. The dire wolf was a hypercarnivore with a skull and dentition designed for hunting enormous, struggling prey; the shape of its skull and snout altered over time, and changes in the size of its body have been linked to climate swings.

Paleoecology

The latest glacial period, known as the "Ice Age," lasted 125,000–14,500 years ago and was the most recent glacial episode within the present ice age, occurring during the Pleistocene era's final years. During the Last Glacial Maximum, ice sheets began to advance from 33,000 years ago and reached their maximum limits at 26,500 years ago. Deglaciation began roughly 19,000 years ago in the Northern Hemisphere and 14,500 years ago in Antarctica, which is consistent with evidence that glacial meltwater was the principal driver of a dramatic rise in sea level 14,500 years ago. The Wisconsin glacial cut off access to northern North America. The extinction of big animals, known as Pleistocene megafauna, near the end of the last glaciation is suggested by fossil evidence from the Americas.

From 60,000 years ago to the end of the Last Glacial Maximum, coastal southern California was cooler and had a more balanced supply of moisture than it is today. The mean annual temperature dropped from 11 °C (52 °F) to 5 °C (41 °F) during the Last Glacial Maximum, while annual precipitation dropped from 100 cm (39 in) to 45 cm (18 in). This area was undisturbed by the Wisconsin glaciation's climatic effects and is thought to have served as an Ice Age refuge for animals and cold-sensitive vegetation.

Prey

Researchers have removed and investigated a variety of animal and plant species that became ensnared and were then preserved in tar pits so that they might learn more about the past. The Rancho La Brea tar pits, near Los Angeles in Southern California, are a cluster of pits with sticky asphalt deposits deposited between 40,000 and 12,000 years ago. Methane pressure has been moving trapped asphalt via fissures to the surface since 40,000 YBP, generating seeps that can encompass several square metres and be 9–11 m (30–36 ft) deep.

Because of the enormous number of its fossils discovered there, the dire wolf has become well-known. The tar pits have yielded about 200,000 specimens (mainly pieces), with remnants ranging from Smilodon to squirrels, insects, and plants. The Last Glacial Maximum, when global temperatures were 8°C (14°F) lower than today, the Pleistocene–Holocene transition (Blling–Allerd interval), the Oldest Dryas cooling, the Younger Dryas cooling from 12,800 to 11,500 YBP, and the American megafaunal extinction event, when 90 genera of mammals weighing over 44 kg (97 lb) became extinct, are all represented in the pits.

The dire wolf, Smilodon, and the American lion (Panthera atrox) competed for the same food, according to an isotopic analysis of bone collagen taken from La Brea fossils. "Yesterday's camel" (Camelops hesternus), Pleistocene bison (Bison antiquus), "dwarf" pronghorn (Capromeryx minor), western horse (Equus occidentalis), and "grazing" ground sloth (Paramylodon harlani) common to North American meadows were among its prey. The American mastodon (Mammut americanum) and the Columbian mammoth (Mammuthus columbi) were both scarce in La Brea. The horses remained mixed feeders and the pronghorns mixed browsers, while camels and bison were forced to rely more heavily on conifers during the Last Glacial Maximum and its related vegetation transition.

The horse was an important prey species at the period, according to isotope data from La Brea dire wolf remains dated 10,000 years ago, whereas sloth, mastodon, bison, and camel were less common in the dire wolf diet. This suggests that the dire wolf was not a prey specialization and that it was hunting or scavenging the most abundant herbivores towards the end of the Late Pleistocene before extinction.

Dentition and Bite Force

The dire wolf was considered the most evolutionary derived (advanced) wolf-like species in the Americas when compared to members of the genus Canis. The dire wolf could be identified separately from all other Canis species by its possession of: "P2 with a posterior cusplet; P3 with two posterior cusplets; M1 with a mestascylid, entocristed, entoconulid, and a transverse crest extending from the metaconid to the hyperconular shelf; M2 with entocristed and entoconulid."

The dire wolf's morphology was similar to that of its surviving cousins, and if it was a communal hunter, its high bite force in comparison to modern canids shows it preyed on relatively large animals. The bite force rating of the bone-eating spotted hyena defied popular belief that bone consumption necessitated a high bite force in the canines and carnassials.

In all but four of the 15 parameters compared to current grey wolves, a study of dire wolf cranial dimensions and jaw muscles found no significant differences. The upper dentition was the same, with the exception that the dire wolf's dimensions were greater, and the P4's blade was larger and more massive, enhancing slicing capabilities at the carnassial. The dire wolf's jaw possessed a wider and more massive temporalis muscle than the grey wolf's, allowing it to generate slightly more biting force.

The dire wolf has less temporalis leverage than the grey wolf at the lower carnassial (m1) and lowers p4 because of the jaw position, although the functional significance of this is unknown. The dire wolf m1 was substantially larger and had greater shearing ability than the grey wolf, with slightly larger lower premolars than the grey wolf. The canines of dire wolves were stronger than those of extant canids of comparable size and were comparable to those of hyenas and felids. All of these differences suggest that the dire wolf was able to deliver more powerful bites than the grey wolf and that the dire wolf's flexible and rounded canines were more suited to battling prey.

Dire Wolf Behaviour

Predatory Birds and mammals were drawn to the dead or dying herbivores that had become entrapped at La Brea, and these predators became imprisoned as well. Herbivore trapping was projected to occur once every fifty years, and for every herbivore remains recovered in the trenches, ten carnivores were anticipated to be present. The most common carnivoran found at La Brea is A. d. guildayi, followed by Smilodon. In the tar pits, dire wolf remains exceed grey wolf remains by a five-to-one ratio.

Coastal California, with a climate slightly cooler and wetter than today, is thought to have served as a refuge during the Last Glacial Maximum, and a comparison of the frequency of dire wolves and other predator remains at La Brea to other parts of California and North America indicates significantly greater abundances; thus, the higher dire wolf numbers in the La Brea region did not reflect the higher dire wolf numbers in other parts of California and North America. It's likely that large groups of dire wolves fed together on these instances, even if just a few of the carnivores that were feasting became caught.

Sexual dimorphism refers to the difference between male and female members of a species other than their sex organs, and there is little variation among canids in this sense. The skull length, canine tooth size, and lower molar length of dire wolf bones dated 15,360–14,310 YBP and recovered from one pit revealed no dimorphism, similar to that of grey wolves, showing that dire wolves lived in monogamous pairs. The dire wolf's huge size and carnivorous dentition support the theory that it was a predator that hunted large animals.

Since they cannot utilize their forelimbs to struggle with food, the African wild dog, the dhole, and the grey wolf rely on their teeth to kill ungulates larger than themselves, and they work together as a pack consisting of an alpha pair. It's safe to believe that dire wolves lived in family groups led by an alpha couple. Large and sociable carnivores would have been the most successful at guarding prey carcasses stuck in the tar pits from smaller solitary predators, and thus the most likely to become trapped themselves. The tar pits' abundance of A. d. guildayi and Smilodon remains implies that both were gregarious predators.

All social terrestrial mammalian predators prey primarily on terrestrial herbivorous animals with a body mass comparable to the social group's combined mass attacking the prey species. The dire wolf's huge size allows for estimated prey sizes of 300 to 600 kg (660 to 1,320 lb). Stable isotope research of dire wolf bones shows that they preferred to eat ruminants like bison over other herbivores, but that they switched to other species when food became short, and that they occasionally scavenged on beached whales along the Pacific coast when they were available.

Climate Impact

Changes in dire wolf size have been linked to climate change in previous research. Later research analyzed the craniodental morphology of dire wolves from four La Brea pits, each representing four different time periods. The findings show that dire wolf size, tooth wear and breakage, skull shape, and snout shape have all changed throughout time. Between the onset of the Last Glacial Maximum and the warm Allerd oscillation, the size of the dire wolf had shrunk. Smaller body size, skulls with a larger cranial base and shorter snout (shape neoteny and size neoteny), and increased tooth breakage are all signs of food stress (reduced nutritional intake due to scarcity).

Dire wolves from 17,900 years ago had all of these characteristics, indicating food stress. Dire wolves from 28,000 years ago shared many of these characteristics, but they were the largest wolves investigated, leading to the hypothesis that these wolves were also suffering from food stress and that wolves from previous times were considerably larger. Nutrient stress is expected to result in stronger bite forces that devour carcasses more thoroughly and break bones, as well as changes in skull form that boost mechanical advantage. During the glacial period, North American climate records reveal cyclic changes that included rapid warmth followed by slow cooling, known as Dansgaard–Oeschger episodes.

These cycles would have increased temperature and aridity, causing ecological stress and, as a result, food stress at La Brea. The grey wolf, which was once huge, strong, and probably convergent evolution with the dire wolf in the Santa Barbara basin, was replaced by more gracile forms by the start of the Holocene by more gracile forms.