<P> The North American wolves became larger, with tooth specimens indicating that C. priscolatrans diverged into the large wolf C. ambrusteri . during the Middle Pleistocene in North America . Robert A. Martin disagreed, and believed that C. ambrusteri was C. lupus . Nowak disagreed with Martin and proposed that C. ambrusteri was not related to C. lupus but C. priscolatrans, which then gave rise to C. dirus . Tedford proposed that the South American C. gezi and C. nehringi share dental and cranial similarities developed for hypercarnivory, suggesting C. ambrusteri was the common ancestor of C. gezi, C. nehringi and C. dirus . </P> <P> In 1908 the paleontologist John Campbell Merriam began retrieving numerous fossilized bone fragments of a large wolf from the Rancho La Brea tar pits . By 1912 he had found a skeleton sufficiently complete to be able to formally recognize these and the previously found specimens under the name C. dirus (Leidy 1858). </P> <P> Canis dirus lived in the late Pleistocene to early Holocene in North and South America and was the largest of all Canis species . In 1987, new hypothesis proposed that a mammal population could give rise to a larger form called a hypermorph during times when food was abundant, but when food later became scarce the hypermorph would either adapt to a smaller form or go extinct . This hypothesis might explain the large body sizes found in many Late Pleistocene mammals compared to their modern counterparts . Both extinction and speciation - a new species splitting from an older one - could occur together during periods of climatic extremes . Gloria D. Goulet agreed with Martin and further proposed that this hypothesis might explain the sudden appearance of C. dirus in North America, and that because of the similarities in their skull shapes that C. lupus gave rise to the C. dirus hypermorph due to abundant game, a stable environment, and large competitors . Nowak, Kurten and Berta disagreed with Goulet and proposed that C. dirus was not derived from C. lupus . The three noted paleontologists Xiaoming Wang, R.H. Tedford and R.M. Nowak have all proposed that C. dirus had evolved from C. ambrusteri, with Nowak stating that there were specimens from Cumberland Cave, Maryland that indicated C. ambrusteri diverging into C. dirus . The two taxa share a number of characteristics (synapomorphy), which suggests an origin of C. dirus in the late Irvingtonian in the open terrain in the midcontinent, and then later expanding eastward and displacing its ancestor C. ambrusteri . </P> <P> Merriam named 3 unusual species based on specimens recovered from the Rancho La Brea tar pits . They were regarded by Nowak as taxonomic synonyms for Canis lupus . </P>

How a population of wolves may have undergone speciation to form the first population of dogs
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