Scientists uncovered secrets of the breeding habits of gigantic marine lizards that lived during the time of the dinosaurs.

The research team looked at young specimens collected more than 100 years ago, Wiley reported. These fossils were once believed to represent ancient birds, but an analysis of the jaws and teeth suggest they actually belonged to the ancient lizards, called mosasaurs.

"Their success as apex predators has been attributed to their rapid acquisition of aquatic adaptations, which allowed them to become fully pelagic. However, little is known about the breeding biology of derived, flipper-bearing mosasaurs, as the record of neonatal mosasaur fossils is extremely sparse," the researchers stated in their study abstract.

The samples looked at in the study included fragmentary cranial remains from the Niobrara Formation. These specimens are some of the smallest ever discovered.

"Coming across these tiny mosasaur specimens was really serendipitous. It's not every day that you're able to shed new light on the biology of animals that went extinct 65 million years ago," said lead author Daniel Field.

An analysis of the newborn mosasaur fossils suggests they were born and lived in the open ocean, as opposed to having land births.

"Contrary to classic suggestions, these findings suggest that mosasaurs did not lay eggs on beaches, and that newborn mosasaurs likely did not live in sheltered nearshore nurseries," said co-author Aaron LeBlanc.

The findings were published in a recent edition of the journal Paleontology.