Walruses
Published on Nov 22, 2015
No Description
MORE DECKS TO EXPLORE
PRESENTATION OUTLINE
Evolution
It is believed that walrus evolved during the Oligocene Era from bear or dog like ancestors of the North Pacific (Riedman 1990). In relative terms the walrus is new to the North Pacific region. The presence of these animals, in accordance with fossil record, date back to one hundred thousand years ago. It is believed that walrus first entered this region from the northwest via the northern coast of Eurasia (USDI 1982). The genus Odobenus constitutes a separate order Pinnipedia. However, it is customary to consider them as a suborder within the family Carnivora (Gittleman 1989). The origin of pinnipeds is not clear especially when referring to the walrus. The modern view, however, is that they are monophyletic. Biologists have been arguing over pinniped evolution for years. If it is true that pinnipeds are monophyletic it would mean that walrus would be more closely related to other pinnipeds than to its relative the otter. Studies do show that walrus are in fact monophyletic and that they are more closely related to other pinnipeds than to mammals (Riedman 1990). Perhaps this controversy about the origin and evolution of the walrus is largely due to the aggressive behavior of the walrus and that its’ instincts more closely resemble that of the family carnivora.
Photo by Mervi Eskelinen aka tasselflower
EVOLUTION
The Walrus has many adaptations for survival in the harsh climate of the north pole. They have a large layer of blubber that can be six inches thick to keep in body heat. The walrus has vibrissae to help them sense where burrowing animals, such as clams and other bivalves, are and thus making it easier for the walrus to eat them. The walrus are able to dive to depths of 100 meters and can stay under water for 30 minutes. The rear flippers are adapted for swimming in the water but can also rotate and help walk while on land. Large tusks also are key to the survival of the walrus. They are used for defense and to haul themselves out of the water.
Photo by south92
Taxonomy and evolution
The walrus is a mammal in the order Carnivora. It is the sole surviving member of the family Odobenidae, one of three lineages in the suborder Pinnipedia along with true seals (Phocidae) and eared seals (Otariidae). While there has been some debate as to whether all three lineages are monophyletic, i.e. descended from a single ancestor, or diphyletic, recent genetic evidence suggests all three descended from a caniform ancestor most closely related to modern bears. Recent multigene analysis indicates the odobenids and otariids diverged from the phocids about 20–26 million years ago, while the odobenids and the otariids separated 15–20 million years ago. Odobenidae was once a highly diverse and widespread family, including at least twenty species in the Imagotariinae, Dusignathinae and Odobeninae subfamilies. The key distinguishing feature was the development of a squirt/suction feeding mechanism; tusks are a later feature specific to Odobeninae, of which the modern walrus is the last remaining (relict) species.
Two subspecies of walrus are widely recognized: the Atlantic walrus, O. r. rosmarus (Linnaeus, 1758) and the Pacific walrus, O. r. divergens (Illiger, 1815). Fixed genetic differences between the Atlantic and Pacific subspecies indicate very restricted gene flow, but relatively recent separation, estimated at 500,000 and 785,000 years ago. These dates coincide with the hypothesis derived from fossils that the walrus evolved from a tropical or subtropical ancestor that became isolated in the Atlantic Ocean and gradually adapted to colder conditions in the Arctic. From there, it presumably recolonized the North Pacific Ocean during high glaciation periods in the Pleistocene via the Central American Seaway.
An isolated population in the Laptev Sea is considered by some authorities, including many Russian biologists and the canonical Mammal Species of the World,[3] to be a third subspecies, O. r. laptevi (Chapskii, 1940), and is managed as such in Russia. Where the subspecies separation is not accepted, whether to consider it a subpopulation of the Atlantic or Pacific subspecies remained under debate until 2009, when multiple lines of molecular evidence showed it to represent the westernmost population of the Pacific walrus.
Young male Pacific walruses on Cape Pierce in Alaska: Note the variation in the curvature and orientation of the tusks and the bumpy skin (bosses), typical of males.
Anatomy
Photo by chiptape
Relatives Walruses are a member of the pinniped family, carnivores that forage at sea but usually return to land or ice to mate, give birth, tend to their young or molt. Pinnipeds have four webbed flippers and sensory organs adapted to air and water. They also have large eyes, whiskers that allow them to feed in dimly lit water, and small tails and external ears to limit drag. All pinnipeds have fur and are mammals.
Photo by Mark_W
