Elasmosaurs swam the seas for over 130 million years, feeding on the plentiful fish and shellfish. They used grit and gastroliths in their large stomachs to break down their seafood diet.
Gastroliths – round, polished stomach stones – have been found amid their bones. These stones would have been swallowed to help grind down their catch and lower their natural buoyancy. In their selection of these pebbles, elasmosaurs displayed, at times, a remarkable geological discernment.
The Puntledge elasmosaur from Courtenay, British Columbia, for example, had a yen for basalt. When the fossilized skeleton was excavated, the stones in its abdominal cavity were all basalt, an indication that this particular elasmosaur had somehow learned to discriminate between basalt stones and all others.
Basalt, as any geologist will tell you, is harder (and therefore longer lasting as a grinding material) than many other rocks. Yet over time, even basalt will erode, particularly when subjected to the digestive juices of such an enormous creature. From the elasmosaur’s long neck and bulky body, paleontologists have concluded that that their fishing technique was probably a sudden snake-like strike with the head, sweeping the meal into their cage-like mouth long before the tell-tail body loomed in sight through the depths.
Swimming beneath a school of fish, they would have been hidden by their dappled camouflage, allowing them to swing their toothy mouths up into the schools and capture hapless fish to be swallowed whole. Less stealth was probably required to hunt ammonites – free-swimming shellfish that jetted along like armoured squid. During the Jurassic, ammonites, distant relatives of the chambered nautilus, populated the seas.
The ammonites’ heavy protection would have meant that their backward-looking view of the world was no problem when dealing with most predators, but the marine reptiles of the day were a fatal exception to the rule. Ammonite fossils with clear teeth marks have been found, putting both elasmosaurs and mosasaurs at the scene of the crime and solving murder mysteries millions of years old.