Due to that fact, the developing mammalian embryo at this stage is called a blastocyst, not a blastula, which is more generic term.
[2] The evolutionary reason for such a change likely was that the advanced and structurally complex brain, characteristic of mammals, requires more time to develop, but the maximum time spent in utero is limited by other factors, such as relative size of the final fetus to the mother (ability of the fetus to pass mother's genital tract to be born), limited resources for the mother to nourish herself and her fetus, etc.
Thus, to develop such a complex and advanced brain in the end, the mammalian embryo needed to start this process earlier and to perform it faster.
[3] Another difference is that during the development of embryonic genitourinary tract, in case of female embryo of placental and marsupial mammals, the uterus is formed, a structure that neither monotremata nor lower chordates have.
[5] The anatomy of the area surrounding an embryo or fetus is different in litter-bearing animals compared to humans: each unborn animal is surrounded by placental tissue and is lodged along one of two long uterine horns rather than in the center of the pear-shaped uterus found in a human female.