Question

What features of the Placentalia differentiate them from Therians of the late Cretaceous?

Answer 1

The fundamental difference between the late creatceous therians and placentalians lies is the presence of the placenta, the organ which is imvolved in transferring oxygen and nutrients to the embryo attached to the mother by the placenta in the placentalia group. The late cretaceous therians do not have a placenta externally.

There is a difference in the teeth distribution. Placentals have four premolars and three molars lining both the upper and lower jaws whereas the marsupials have three premolars and four molars in the same rergion and another difference is that the Placentalians have two sets of teeth one in the younger stage and the other in the adult stage or late juvenile stage. whereas late cretaceous therians have only one set and only few among them gets replaced.

The late cretaceous therians mostly have an external pouch for the young but the placentalians do not

The male late cretaceous therians and placentalians are similar in reproductive system but in female late cretaceous therians there are two sets of reproductive organs whereas the placentalian females have only one set excet the fallopian tubes which are two in number.

The late cretaceous therians develop after birth in the pouch wheres the placentalians develops majorly inside the mother before birthing and is born with physical and mental capabilities caomparitve to the adult.