In the time of dinosaurs, mosasaurs ruled the seas. They were air breathing reptiles, that could grow up to 50 feet long and according to new research, they gave birth at sea to live offspring.
Researchers from Yale University and the University of Toronto identified specimens of young mosasaurs at the Yale Peabody of Museum of Natural History.
The 100 year old fossils were originally misidentified as birds and their proper identification answers long held-questions about the legendary aquatic predators.
“Mosasaurs are among the best-studied groups of Mesozoic vertebrate animals, but evidence regarding how they were born and what baby mosasaur ecology was like has historically been elusive,” said Daniel Field in a statement.
Field is the lead author of a study published online April 10 in the journal Palaeontology and a doctoral candidate in the lab of Jacques Gauthier in Yale’s Department of Geology and Geophysics.
In the study, Field and his fellow researchers described the youngest mosasaur’s found to date.
“These specimens were collected over 100 years ago. They had previously been thought to belong to ancient marine birds,” said Field.
Field and University of Toronto at Mississauga doctoral candidate Aaron LeBlanc found a variety of tooth and jaw features in the remains that have only ever been found in mosasaurs. Additionally, all the fossils were found in ocean deposits.
“Really, the only bird-like feature of the specimens is their small size. Contrary to classic theories, these findings suggest that mosasaurs did not lay eggs on beaches and that newborn mosasaurs likely did not live in sheltered nearshore nurseries,” said LeBlanc.
It is rare that researchers get the opportunity to answer questions about things like birth in a long extinct aquatic species.
“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.
The findings suggest that the mosasaur was a truly unusual reptile.
“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.
Modern reptiles and fish both reproduce by laying eggs. Even sea turtles come ashore to lay eggs and only for that reason. Only aquatic mammals, such as dolphins and whales, are known to give birth to live offspring at sea.
High sea levels during the cretaceous period led many reptiles into the warm oceans. Mosasaurs appear to have adapted very successfully to the period. Mosasaur remains have been found in nearly every part of Europe, North America, South America, Australia, New Zealand and Antarctica.
The animals became extinct roughly 65 million years ago.
