An intriguing fossil suggests ancient aquatic reptiles (plesiosaurs) were live bearers:
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.
Writing in Science, they say this also suggests a degree of parental care.
– “Fossil ‘suggests plesiosaurs did not lay eggs'” (BBC News , August 11, 2011)
The fossil, found two years ago, was only studied recently, at which point, the fetus was discovered. Just how plesiosaurs reproduced has been a mystery because they breathe air, but – given their size and shape – would have difficulty manoeuvring on land. Obviously, live birth, as in whales, for example, eliminates landfall.
So far, it’s really just a promising direction. Note that some modern reptiles that lay eggs do care for their young, and some that give live birth do not. Much depends on whether the offspring actually benefit in any way from parental input.
It’s worth noting that – if this holds – it blows up theories about how live birth is an “evolutionary advance” over egg laying. It increasingly appears that life forms converge on needed traits.
Here, a mother ‘gator defends her eggs from conservation collectors:
See also: Live birth developed earlier than thought in lizards.