from australia's gogo formation, laid down in the devonian period, 380 million years ago, was found with an embryo inside it connected by an umbilical cord to a yolk sac. the find confirmed the hypothesis that a sub-group of placoderms, called ptyctodontids, fertilized their eggs internally. some fishes that fertilize their eggs internally also give birth to live young, as seen here. this discovery moved our knowledge of live birth back 200 million years. the fossil of another genus was found with three embryos in the same position. placoderms are a sister group of the ancestor of all living jawed fishes (gnathostomata), including both chondrichthyans, the sharks & rays, and osteichthyes, the bony fishes. among lizards, the viviparous lizard zootoca vivipara, the jackson's chameleon, slow worms and many species of skink are viviparous, giving birth to live young. some are ovoviviparous but others such as members of the genera tiliqua and corucia, give birth to live young that develop internally, deriving their nourishment from a mammal-like placenta attached to the inside of the mother's uterus. in a recently described example, an african species, trachylepis ivensi, has developed a purely reptilian placenta directly comparable in structure and function to a mammalian placenta. vivipary is rare in snakes, but boas and vipers are viviparous, giving birth to live young. female aphid giving birth the majority of insects lay eggs but a very few give birth to offspring that are miniature versions of the adult. the aphid has a complex life cycle and during the summer months is able to multiply with great rapidity. its reproduction is typically parthenogenetic and viviparous and females produce unfertilized eggs which they retain within their bodies. the embryos develop within their mothers' ovarioles and the offspring are clones of their mothers. female nymphs are born which grow rapidly and soon produce more female offspring themselves. in some instances, the newborn nymphs already have developing embryos inside them.