Mauisaurus and Prognathodon
The image shows a portion of a model made about 1970 by Mr R J Jacobs of Canterbury Museum. The model depicts the mosasaur Prognathodon waiparaensis attacking the elasmosaur Mauisaurus haasti in a scene that might have occurred in the waters off Zealandia between 70 and 65 million years ago.
Zealandia, the ancestral landmass of New Zealand, separated from eastern Gondwana (comprising Australia and Antarctica) about 83 million years ago and drifted away, creating the Tasman Sea. While dinosaurs roamed the land surface of Zealandia, the seas around the micro-continent were home to a number of large marine reptiles. One group included giant marine lizards, the mosasaurs, that were the top predators of their time, reaching 15 metres in length; another group were the plesiosaurs with barrel-like bodies and four paddle-like limbs. Among the plesiosaurs were those with exceedingly long necks and small heads – the elasmosaurs - that grew up to 12 metres long.
Prognathodon waiparaensis must have been a fearsome sight. Its jaws were about 1 metre long and lined with large conical teeth. It also had two rows of teeth on the roof of its mouth, all curved backwards. When it bit into a victim, the curved teeth would have prevented the prey from pulling away until a large a chunk of flesh had been torn free. This would have been swallowed whole, and a joint about halfway along the mosasaur’s lower jaw would have helped ram the food into its throat.
Mauisaurus haasti was also a predator but fed mostly on small fish and squid-like molluscs. There is debate among experts about the function of the very long neck, with at least 68 vertebrae in the case of Mauisaurus, but it is certain that it could not bend back on itself as shown in the model. We know from examining the vertebrae that the neck had limited flexibility, with most movement taking place just behind the head and at the shoulders. For this reason some experts believe elasmosaurs fed at the sea bed with the long necks keeping the paddles clear of the sediment so that they did not stir up clouds of mud and limit visibility.