Washington: Scientists have unearthed fossils of a pregnant plesiosaur in the US which indicates that the giant marine reptiles gave birth to single babies and may have nurtured their offspring about 78 million years ago.
The fossilised plesiosaur, excavated from a site in Kansas, was found to be pregnant and carrying a large foetus-- the first expectant plesiosaur mom to be unearthed since
the species was discovered almost 200 years ago.
"This is the first known pregnant plesiosaur. It demonstrates that the plesiosaur gives live birth and did not crawl out on land [to lay eggs]. It puts this 200-year mystery to rest," said study researcher Frank O`Keefe of Marshall University in West Virginia.
"The really interesting thing is how big this bouncing baby is. It`s really large by reptilian standards, by human standards, by any standards you use," O`Keefe was quoted as saying by LiveScience.
The sheer size of the foetus and the fact that the mother was only carrying one offspring, indicate that these marine reptiles gave live birth and may have invested much more time
and energy into their offspring than other marine reptiles at the time, similar to how humans invest years raising kids.
The plesiosaur, which belongs to the species Polycotylus latippinus, was about 15.4 feet long and was carrying a 5-foot foetus, O`Keefe said.
"This animal is not ready to be born; it`s about two-thirds done. It would have been a couple meters [6.5 feet] long by the time it was born," he added.
According to the researchers, who detailed their findings in the journal Science, many parts of the foetal skeleton including its skull hadn`t fully turned into bone.
It suggests the foetus was not nearly done gestating; it also had disproportionally short flippers and a large head, another sign it wasn`t fully developed.
"That`s what really strikes you about this baby, how not ready for prime time it is. It wouldn`t have been able to protect itself or eat," O`Keefe added.
The finding suggests that this species at least gave birth to live young. Called viviparity, live birth has been observed in other marine reptiles from this period, but in past examples, multiple, smaller (less than 30 per cent of the size of the mother) offspring were birthed.
Birthing just one big baby is rare for this period, and it suggests this mother reptile would be investing lots of resources into caring for the "only child", the researchers added.
The fossil is currently on display at the Natural History Museum of Los Angeles County.