Otter females are called bitches or sows, and their offspring are called pups. The collective nouns for otters are bevy, family, lodge, romp (being descriptive of their often playful nature) or, when in water, raft. The feces of otters are typically identified by their distinctive aroma, the smell of which has been described as ranging from freshly mown hay to putrefied fish; these are known as spraints. The gestation period in otters is about 60 to 86 days. The newborn pup is cared for by the bitch, dog and older offspring. Bitch otters reach sexual maturity at approximately two years of
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;