Evolution of the wolf
This dental arrangement has been modified by adaptation over the past 60 million years for diets composed of meat, for crushing vegetation, or for the loss of the carnassial function altogether as in seals, sea lions, and walruses.
The first members of the dog family Canidae appeared 40 million years ago,[20] of which only its subfamily the Caninae survives today in the form of the wolf-like and fox-like canines.
[27]: p240 A number of researchers believed that the lines of C. priscolatrans, C. etruscus, C. rufus, C. lycaon, and C. lupus were components involved in some way that lead to the modern wolf and coyote.
[27]: p241 Johnson noted that some specimens found in Cita Canyon, Texas, had larger, broader skulls,[40] and along with other fragments Nowak suggested that these were evolving into wolves.
[27]: p241 [28] Tedford disagreed with previous authors and found that its cranio-dental morphology lacked some characteristics that are shared by C. lupus and C. latrans, and therefore there was not a close relationship but it did suggest C. lepophagus was the ancestor of both wolves and coyotes.
[11]: 148 In 1908 the paleontologist John Campbell Merriam began retrieving numerous fossilized bone fragments of a large wolf from the Rancho La Brea tar pits.
[27]: p243 [50] The two taxa share a number of characteristics (synapomorphy), which suggests an origin of A. dirus in the late Irvingtonian in the open terrain in the midcontinent, and then later expanding eastward and displacing its ancestor C.
[11]: 181 However, in 2021, a study indicated the dire wolf to be a highly divergent lineage which last shared a most recent common ancestor with the wolf-like canines 5.7 million years ago.
Coyotes, dholes, gray wolves, and the extinct Xenocyon evolved in Eurasia and expanded into North America relatively recently during the Late Pleistocene, therefore there was no admixture with the dire wolf.
Wang and Tedford proposed that the genus Canis was the descendant of the coyote-like Eucyon davisi, and its remains first appeared in the Miocene (6 million YBP) in south-western USA and Mexico.
[65][17] In Italy, the earliest Canis lupus specimens were found at La Polledrara di Cecanibbio, 20 km north-west of Rome in strata dated 340,000–320,000 YBP.
[71] In 2002, a study was undertaken into the fossil skulls of two large canids that had been found buried within meters of the doorway of what was once a mammoth-bone hut at the Eliseevichi-I Upper Paleolithic site in the Bryansk Region on the Russian Plain, and using an accepted morphologically based definition of domestication declared them to be "Ice Age dogs".
"[76] The domestic dog compared to the modern wolf shows the greatest variation in the size and shape of the skull (Evans 1979) that range from 7 to 28 cm in length (McGreevy 2004).
[74] Wayne (1986) concluded that the dog is closer in skull morphology to C. latrans, C. aureus, C. adustus, C. mesomelas, Cuon alpinus and Lycaon pictus than to the wolf.
[78] The ventral edge of the dog's horizontal ramus of the mandible has a convex curve that does not exist in the wolf (Olsen 1985; Clutton-Brock 1995), and no discussion of this difference could be found in the literature.
However, Biknevicius and Van Valkenburgh (1997) noticed that the horizontal ramus of bone-processing predators is thicker dorso-ventrally at the point caudal to the site of bone processing.
[89][91][92] The mitochondrial protein-coding genes evolve much faster and are powerful markers for inferring evolution history at category levels such as families, genera, and species.
The techniques used to extract, locate and compare genetic sequences can be applied using advances in technology, which allows researchers to observe longer lengths of base pairs that provide more data to give better phylogenetic resolution.
The explanation proposed for this mito-nuclear discord is that mitochondrial DNA introgression occurred from an ancient ancestor of genus Canis into the lineage that led to the black-backed jackal around 6.2–5.2 million years ago.
However, studies show that one or more of these ancient populations is more directly ancestral to dogs than are modern wolves, and conceivably these were more prone to domestication by the first humans to invade Eurasia.
[131] As of 2020, the oldest known intact wolf remains belongs to a mummified pup dated 56,000 YBP that was recovered from the permafrost along a small tributary of Last Chance Creek near Dawson City, Yukon, Canada.
An mDNA study of 34 wolf remains from North America dated between 1856 and 1915 found their genetic diversity to be twice that of modern wolves in these regions, and two thirds of the haplotypes identified were unique.
[47] In 2016, a whole-genome DNA study proposed, based on the assumptions made, that all of the North American wolves and coyotes diverged from a common ancestor less than 6,000–117,000 years ago.
[13] The study suggested that previous datings based on the divergence between wolves and coyotes of one million years ago using fossils of what appeared to be coyote-like specimens may not reflect the ancestry of the modern forms.
[161][162] In 2015, a study looked at the mitochondrial control region sequences of 13 ancient canid remains and one modern wolf from five sites across Arctic north-east Siberia.
[163][164] In 2015, a study looked at the paleoecology of large carnivores across the Mammoth steppe during the Late Pleistocene by using stable isotope analysis of their fossil collagen to reconstruct their diets.
Grey wolves have a wide, natural distribution across the Holarctic that includes many different habitats, which can vary from the high arctic to dense forests, open steppe and deserts.
One of these studies found that the variation in 11 key genes affected wolf vision, sense of smell, hearing, coat color, metabolism, and immunity.
The study identified 1,040 genes that are potentially under selection due to habitat variation, and therefore that there was evidence of local adaption of the wolf ecotypes at a molecular level.
[5] Ecological factors including habitat type, climate, prey specialization and predatory competition will greatly influence grey wolf genetic population structure and cranio-dental plasticity.
