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 the metatherian "Sinodelphys", both dated to 125 million years ago. [[Epipubic]] bones, a feature that strongly influenced the reproduction of most mammal clades, are first found in [[Tritylodontidae]], suggesting that it is a synapomorphy between them and [[mammaliformes]]. They are omnipresent in non-placental mammaliformes, though "[[Megazostrodon]]" and "[[Erythrotherium]]" appear to have lacked them. It has been suggested that the original function of [[lactation]] ([[milk]] production) was to keep eggs moist. Much of the argument is based on monotremes, the egg-laying mammals. Therian mammals took over the medium- to large-sized ecological niches in the [[Cenozoic]], after the [[Cretaceous–Paleogene extinction event]] approximately