It was the T. rex of the crocodile world. But even for a creature 9 metres long, chomping through the wet, slippery shells of giant sea turtles isn鈥檛 easy. Now it seems the Late Jurassic croc Machimosaurus hugii had teeth with a special feature for this purpose.
After scrutinising fossilised teeth found in Portugal and Switzerland, where M. hugii once prowled lagoons and coastlines, a team led by Mark Young of the University of Edinburgh, UK, noticed subtle, serrated structures running up the side of the teeth, never seen before in any marine crocodile species. Called 鈥減seudo-denticles鈥�, these serrations formed on top of enamel ridges that extend to the tip of each tooth.
These structures may have enabled the species to change its diet. 鈥淎s serrated teeth increase the efficiency of slicing into prey, our discovery may help us learn when this group of marine crocs shifted from feeding on small, fast-moving prey like small fish to large-bodied prey like turtles,鈥� says Young.
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Improved grip
Young likens the serrations to shoe treads. 鈥淭he greater surface area of shoe treads helps grip in wet conditions,鈥� he says. 鈥淎s we know, Machimosaurus was eating sea turtles, so a better grip on the shells would have greatly helped with biting down and breaking the shell.鈥�
Another possibility, he says, is that the serrations strengthen the enamel, helping the teeth withstand the forces needed to crack open the shells. 鈥淚t鈥檚 possible the denticles helped in both ways,鈥� says Young.
But Jon Mitchell, who researches the evolution of snake teeth at the University of Chicago, is not convinced. 鈥淭he analogy with tyre or shoe treads is probably stretched, as the features extend down off the apex of the tooth, but only the apex of each tooth is going to regularly contact turtle shells,鈥� says Mitchell. 鈥淚鈥檇 be surprised if such subtle features had any meaningful function.鈥�
The team鈥檚 next step will be to explore when the serrations evolved in marine crocodiles, to see if fossils reveal a progression from fish to turtle-eating.
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