It has been suggested that birds are phylogenetically constrained, as being derived from reptiles, and likely have not overcome this constraint or diverged far enough away to develop viviparity.
22.
Traditionally this variety was classified into three modes, oviparity ( embryos in eggs ), viviparity ( young born live ), and ovoviviparity ( intermediate between the first two ).
23.
Like other stingrays, the estuary stingray exhibits aplacental viviparity, with the developing embryos sustained initially by yolk and later by histotroph ( " uterine milk " ) produced by the mother.
24.
Recent research into physiological, morphological and genetic changes associated with fish reproduction provide evidence that incubation in some species is a highly specialized form of reproduction similar to other forms of viviparity.
25.
The absence of genomic imprinting in a placental reptile, the southern grass skink, is interesting as genomic imprinting was thought to be associated with the evolution of viviparity and placental nutrient transport.
26.
Unless they find a relatively benign ecology somewhere where they might slowly lose the necessity for land incubation and thick-shelled eggs, they can't really make the leap to viviparity.
27.
Despite strong similarities between viviparity in mammals, researchers have historically been reluctant to use the term " pregnancy " for non-mammals because of the highly developed form of viviparity in eutherians.
28.
Despite strong similarities between viviparity in mammals, researchers have historically been reluctant to use the term " pregnancy " for non-mammals because of the highly developed form of viviparity in eutherians.
29.
The earliest documented case of viviparity in reptiles is the Early Permian mesosaurs, although some individuals or taxa in that clade may also have been oviparous because a putative isolated egg has also been found.
30.
Variations on the theme in biology are enormous, ranging from trophic eggs to squamate reptiles in particular, there is a correlation between high altitudes or latitudes, colder climates and the frequency of viviparity.
