Viviparous mammals are in the subclass Theria; those living today are in the marsupial and placental infraclasses. A marsupial has 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 marsupium, located in the front of the mother's abdomen. This is the plesyomorphic condition among viviparous mammals; the presence of epipubic bones in all non-placental mammals prevents the expansion of the torso needed for full pregnancy. Even non-placental eutherians probably reproduced this way.
Viviparous mammals are in the subclass Theria ; those living today are in the marsupial and placental infraclasses . A marsupial has 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 marsupium , located in the front of the mother 's abdomen . This is the plesyomorphic condition among viviparous mammals ; the presence of epipubic bones in all non - placental mammals prevents the expansion of the torso needed for full pregnancy . Even non - placental eutherians probably reproduced this way .
Which sub class are most viviparous mammals in?
Which sub class are most viviparous mammals in ?
Theria
Theria