14 Jan 2021
The dire wolves, North American ice age predators, were not related to common wolves. Analysis of ancient proteins and genetic material has shown that the dire wolf line split from the rest of the canines about 5.7 million years ago and developed in isolation in North America. As noted in an article for the journal Nature, from an evolutionary point of view, dire wolves are farther from the living large canines than African jackals, and their resemblance to common wolves is just a result of convergence.
In the Pleistocene and Early Holocene, North and South America was home to numerous herbivores, from horses and camels to mammoths and giant sloths. This abundance of prey sustained large predators, the most famous of which were the dire wolves (Canis dirus), the inspiration for the direwolves in Game of Thrones. These representatives of the canine family, who lived from two hundred and fifty to thirteen thousand years ago, weighed about seventy kilograms and specialized in big game.
The remains of dire wolves are quite common in North American sediments: for example, the bones of four thousand individuals were found in the bituminous pits on the La Brea ranch alone. Yet paleontologists know little about the origin and evolutionary relationships of this species. It is generally assumed that the dire wolf was a close relative of the common wolf (Canis lupus) or even a subspecies of it, which adapted to hunting giant herbivores.
To understand this issue, a team of researchers led by Angela Perri (Angela Perri) from the University of Durham decided to use genetic analysis. After examining the remains of forty-six dire wolves, experts have found five specimens with preserved ancient DNA. They were found in the American states of Wyoming, Tennessee, Idaho and Ohio, and their age ranged from thirteen to more than fifty thousand years. The authors were able to extract from these specimens samples of mitochondrial and nuclear DNA. They also included data on a type I collagen protein that was found in one of the dire wolves from the La Brea ranch.
After studying the composition of dire wolf collagen, Perry and her colleagues concluded that this species is not a close relative of the common wolf. Moreover, these predators were found to be unrelated to the entire evolutionary lineage, including wolves, domestic dogs, coyotes (Canis latrans) and African golden wolves (Canis lupaster).
In the next step, the authors compared the nuclear genomes of dire wolves and ten other canine species: common, African golden and Ethiopian (Canis simensis) wolves, coyote, red wolf (Cuon alpinus), hyena dog (Lycaon pictus), black-backed dog (Canis mesomelas) and striped (Canis adustus) jackals, as well as Andean (Lycalopex culpaeus) and gray foxes (Urocyon cinereoargenteus). The analysis identified three distinct evolutionary lines: the first included wolves from the genus Canis, as well as red wolves and hyena dogs, the second included African jackals, and the third included dire wolves (the foxes included in the study were removed from all three lines). The branch of dire wolves split from the rest of the canines about 5.7 million years ago, while African jackals and large canines diverged about 5.1 million years ago. According to the authors, on this basis, African jackals should be distinguished into a separate genus Lupulella, and dire wolves into the genus Aenocyon.
Modern canid species often interbreed with each other, so Perry and her colleagues decided to check if there was a gene exchange between dire wolves and common wolves and coyotes, which were adjacent to each other in North America. To do this, scientists analyzed a sample that included the genetic data of dire wolves, as well as twenty-two modern wolves and coyotes, three ancient dogs and one Pleistocene wolf. It turned out that dire wolves did not interbreed with other North American canines.
According to the authors, the evolution of dire wolves and their relatives (such as the « wolf » Canis armbrusteri and the Pliocene « coyote » Canis edwardii) has been in isolation in North America since the late Miocene, while the ancestors of modern large canids appeared in the Old Light and colonized America relatively recently, in the late Pleistocene. Thus, the resemblance of dire wolves to ordinary wolves is just a result of convergence.
Unlike dire wolves, common wolves and coyotes survived the extinction of the North American megafauna at the Pleistocene-Holocene boundary. Perhaps this is due to the fact that the behavior of these dogs is more flexible – in particular, they can switch to different types of food. In addition, wolves and coyotes have the ability to interbreed with each other and with dogs, due to which they can acquire adaptations that are useful for survival (for example, genes for resistance to infectious diseases).
Four years ago, a perfectly preserved mummy of a wolf cub was found in the Canadian permafrost. After carefully studying it, paleontologists came to the conclusion that it belonged to a female who died at the age of six to seven weeks due to the collapse of a burrow more than fifty thousand years ago. Judging by the mitochondrial genome, the cub belonged to an evolutionary branch that includes ancient wolves from Beringia and Siberia and is basal in relation to all living wolves (except for the high-mountain populations from Asia).
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