EVERYDAY SCIENCE

Detailed explanation-1: -Primates, cats, dogs, bears, hoofed animals, rodents, bats, seals, dolphins, and whales are among the dominant placental mammal groups today. Nearly 94% of all mammal species now are placental mammals (5, 080 species out of 5, 416).

Detailed explanation-2: -Placental mammal, (infraclass Eutheria), any member of the mammalian group characterized by the presence of a placenta, which facilitates exchange of nutrients and wastes between the blood of the mother and that of the fetus. The placentals include all living mammals except marsupials and monotremes.

Detailed explanation-3: -The placentals include all living mammals except marsupials and monotremes. Although some authorities consider the marsupials (cohort Marsupialia) to be placental mammals, these animals have a less-developed, less-efficient type of placenta that limits the gestation period.

Detailed explanation-4: -From humans to whales to bats, the placental mammals-so named for the placenta that nourishes the fetus during development-are mind-bogglingly diverse. (The placental mammals are one of three major groups of mammals; the other two are the egg-laying monotremes and the pouched marsupials.)