Fossil 'Suggests Plesiosaurs Did Not Lay Eggs'

thebchuckster writes "Scientists say they have found the first evidence that giant sea reptiles — which lived at the same time as dinosaurs — gave birth to live young rather than laying eggs. They say a 78 million-year-old fossil of a pregnant plesiosaur suggests they gave birth to single, large young."

Livebearers

[Oswald McWeany]

Shouldn't be too surprising- livebearing shows up in all sorts of families that typically lay eggs- especially aquatic animals. Everyone is familiar with the humble guppy. You buy one for your daughter despite your better judgement- one week later you're overrun with the gaudy ugly fish as the live young start popping out everywhere. Many species of snail give birth to live young. Or "nearly so". Malaysian Trumpet snails and Quilted Melania two "cloning" species can pop out up to 9 live babies at a time. Even sexually reproducing snails can give live birth- species of Tylomelania from Sulawesi lay a single egg at a time that disolves before your eyes (if you're lucky) to reveal a minature snail. That doesn't mean live-bearing fish or mollusks are common- and if this dino gave live-birth, it doesn't mean that it was common with dinosaurs either.

Ovoviviparous?

[SMoynihan]

Very interesting. I suppose it makes logical sense that sea living creature would find it difficult to safeguard eggs, and with its size these would be very noticeable (and nutritious!). I guess it is similar to whale sharks nowadays, which are ovoviviparous in their reproduction (wikipedia link as below): the "embryos develop inside eggs that are retained within the mother's body until they are ready to hatch. Ovoviviparous animals are similar to viviparous species in that there is internal fertilization and the young are born live, but differ in that there is no placental connection and the unborn young are nourished by egg yolk; the mother's body does provide gas exchange (respiration), but that is largely necessary for oviparous animals as well."

http://en.wikipedia.org/wiki/Whale_shark [wikipedia.org]
http://en.wikipedia.org/wiki/Ovoviviparity [wikipedia.org]

However, the comment about single young is even more interesting - as whale sharks are even bearing very many (live) young. Maybe different again? (no expert here, just curious!)

Re:No different from sharks.

[Anonymous Coward]

You're correct with regards to sharks, but so far all evidence suggests dinosaurs laid eggs (including modern ones as birds). The creature being discussed in this article is a large marine reptile from the time of the dinosaurs, but it isn't a dinosaur. There are many extinct and large reptilians besides dinosaurs, including plesiosaurs [wikipedia.org], mosasaurs [wikipedia.org], ichthyosaurs [wikipedia.org] (who also had live birth), and pterosaurs [wikipedia.org] (known to lay eggs), etc.