Marine Mammal Protection Act Indian manatee, sea otter, polar bear, and Pacific walrus. Species not present in U.S. waters include the West African and Amazonian manatee, dugong, Atlantic walrus, and marine otter. In efforts to conserve and manage marine mammal species, the Service has appointed field staff dedicated to working with partners to conduct population censuses, assess population health, develop and implement conservation plans, promulgate regulations, and create cooperative relationships internationally. Various Marine Mammal Management offices are located on either coast. The Service's Marine Mammal Management office in Anchorage, Alaska is responsible for the management and conservation of polar bears, Pacific walruses, and northern
Mammal determination system]] different from that of most other mammals. In particular, the [[sex chromosome]]s of a platypus are more like those of a chicken than those of a therian mammal. Viviparous mammals are in the subclass Theria; those living today are in the marsupial and placental infraclasses. Marsupials have a short [[gestation]] period, typically shorter than its [[estrous cycle]] and gives birth to an undeveloped newborn that then undergoes further development; in many species, this takes place within a pouch-like sac, the [[Pouch (marsupial)|marsupium]], located in the front of the mother's [[abdomen]]. This is the [[Symplesiomorphy|plesiomorphic]] condition among viviparous mammals;