the average weight is around 157 g, with maximum growth rates increasing moving toward the northern parts of collared pika territories. They have constricted, flat skulls with no supraorbital processes, slender zygomatic arches, and 26 teeth. While some mammals have reduced clavicles for more range of motion, the collared pika has a well-developed clavicle supporting the scapula. They do not have a pubic symphysis therefore it does not have a pubic arch within its pelvic girdle. In addition, an interesting characteristic about the male collared pika is that it has no scrotum and the location of its testes is not visibly apparent. This indicates no sexual dimorphism; consequently, one must examine the pseudocloaca for evidence of specific genitalia to distinguish the sex of the collared pika. Distribution and habitat/ecology Geographic distributionO. collaris is distributed over a wide range of terrain that encompasses the west side of the Northwest Territories, almost all of the Yukon Territory, northern British Columbia, and the central and southern parts of Alaska. Around 60% of collared pikas are found in regions of Canada, with most of them being in Yukon. More specifically, in Alaska, they occur most frequently in ranges around the Yukon-Tanana uplands and Chigmit Mountains, to the head of Lynn Canal near Skagway; in Canada, they occur from Richardson Mountains, south into northwestern British Columbia and west close to the Mackenzie River of the Northwest Territories. Of the 30 existing species of pika, only two inhabit North America, O. collaris and O. princeps. In relation to the location of distribution of the American pika, O. collaris is located farther north of those regions and is separated by 800 km. This gap occurs in both British Columbia and Alberta, Canada. Fossil history In 1973, within the Pleistocene deposits in central Alaska, preserved specimens of collared pika were found along with some dung pellets; the Yukon territory also contained some early fossilized specimens. The studies of the size variation of the fossils showed that the morphology of Pleistocene pikas was flexible with the alteration of environments from early to middle Pleistocene in both Alaska and Yukon. During the isolation of the Wisconsin glaciation, O. collaris may have become its own species separate from O. princeps.Habitat and ecology Collared pika colonies are mainly found in the mountain regions and they typically inhabit rock slides near areas of vegetation and fields of meadows. Due to these talus sites,