Giant marine reptiles gave live birth in open ocean

With Aaron LeBlanc, a doctoral candidate at the University of Toronto at Mississauga, Field demonstrated the jaw and teeth features present in the fossils are only found in mosasaurs. The fossils were also deposited in the deep ocean.

When you’re dealing with reptiles it’s generally a safe bet to assume the adults lay eggs in what is described as “oviparous” birth. But some modern reptiles, notably some lizards and snakes, exhibit viviparous birth, or birth completely without an egg. Still others exhibit ovoviviparous birth where there is still an egg but the young remain inside the mother’s body until they hatch.

So which form of birth did mosasaurs employ? They could have come ashore to lay eggs but no egg-laying sites had ever been discovered. Because these baby mosasaur fossils were found in the open ocean where egg-laying is not possible, the circumstances suggest that mosasaurs may have been viviparous. Along with pregnancy discoveries in other marine reptile groups like plesiosaurs, this also suggests that viviparity evolved in reptiles earlier than expected, or even independently multiple times.

Unfortunately for us, and for mosasaurs, they went extinct some 66 millions years ago in the mass extinction event that also killed the dinosaurs.

Reference:

Field, D. J., LeBlanc, A., Gau, A., Behlke, A. D. (2015), Pelagic neonatal fossils support viviparity and precocial life history of Cretaceous mosasaurs. Palaeontology, 58: 401–407. doi: 10.1111/pala.12165

Nick
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