Prehistoric lizard babies were born in water

Aigialosaurus bucchichi, a basal mosasaur. (Credit: Michael B. H./Wikimedia Commons)

Gigantic marine lizards that lived more than 65 million years ago gave birth to their babies in the open ocean, not on or near shore.

The new findings answer long-held questions about the initial environment of an iconic predator that could grow to 50 feet long and lived during the time of the dinosaurs.

mosasaur illustration
“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,” says Daniel Field. (Credit: Julius T. Csotonyi)

“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,” says Daniel Field, a doctoral candidate in the lab of Jacques Gauthier in Yale University’s geology and geophysics department.

Jaws and teeth

In the study, published in the journal Palaeontology, researchers describe the youngest mosasaur specimens ever found. Field had come across the fossils in the Yale Peabody Museum’s collections. “These specimens were collected over 100 years ago,” Field says. “They had previously been thought to belong to ancient marine birds.”

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Field and Aaron LeBlanc, a doctoral candidate at the University of Toronto at Mississauga, concluded that the specimens, which were found in deposits in the open ocean, showed a variety of jaw and teeth features that are only found in mosasaurs.

“Really, the only bird-like feature of the specimens is their small size,” LeBlanc says. “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.”

The Smithsonian Institution and the Natural Sciences and Engineering Research Council of Canada supported the work.

Source: Yale University