This is the time when mammalian viviparity
had begun and two different types of viviparous systems using chorioallantoic and choriovitelline (yolk sac) placentas were established in the eutherians and marsupials, respectively (Figs.
Overall the conclusion is that although viviparity
allowed lizards in the past to invade and adapt to live in cold environments, and was therefore a key trait for evolutionary success, it will now ultimately lead to multiple events of extinction.
in the yellowtail rockfish Sebastes flavidus.
Birth rings are formed as a response of the stress caused by changing placental viviparity
to free-living lifestyle.
first discusses the compromises that have been made in evolution: sexual reproduction, viviparity
, a hemochorial placenta, a long gestation period, and a reproductive strategy that includes high parental investment in very few offspring, as well as the factors of morphological adaptation for habitual bipedalism, increased brain size and elaboration, and secondary altriciality of the newborn.
Most freshwater bivalves, including families of the order Unionoida, and the two veneroid families Sphacriidae and Corbiculidae, exhibit ovoviviparity and viviparity
to various degrees.
Brooding in Corbicula madagascariensis (Bivalvia, Corbiculidae) and the repeated evolution of viviparity
Natural history of reptilian development: Constraints on the evolution of viviparity
The success of viviparity
(live birth) in mammals requires the creation and maintenance of a uterine environment that accommodates and supports fetal growth and development, a means by which the mother provides adequate amounts of the substances upon which the growth and development of the fetus depend, and a means to terminate pregnancy at a time when offspring can survive outside the womb.
Some of these ephemeroid grasses hardly ever produce any seeds and instead reproduce vegetatively or by viviparity
, forming bulbils within the inflorescences or in the leaf axils.
A new hypothesis for the evolution of viviparity
The recent evolution of viviparity
in these starfish suggests that the factors promoting such changes in modes of development might be discovered in field studies of contemporary populations.