Pinniped High levels of organic chemicals accumulate in these animals since they are near the top of food chains and have large reserves of blubber. Lactating mothers can pass the toxins on to their young. These pollutants can cause gastrointestinal cancers, decreased reproductivity and greater vulnerability to infectious diseases. Other man-made threats include habitat destruction by oil and gas exploitation, encroachment by boats, and underwater noise. Pinniped Pinnipeds, commonly known as seals, are a widely distributed and diverse clade of carnivorous, fin-footed, semiaquatic marine mammals. They comprise the extant families Odobenidae (whose only living member is the walrus), Otariidae (the eared
Mammal classification and the new McKenna/Bell classifications of mammals. Extinct groups are represented by †. Several important fossil mammal discoveries have been made that have led researchers to question many of the relationships proposed by McKenna and Bell (1997). Additionally, researchers are subjecting taxonomic hypotheses to more rigorous cladistic analyses of early mammal fossils. Luo et al. (2002) summarized existing ideas and proposed new ideas of relationships among mammals at the most basal level. They argued that the term mammal should be defined based on characters (especially the dentary-squamosal jaw articulation) instead of a crown-based definition (the group that contains most recent