As Chris Clarke told me, "They were big ducks!" Two newly discovered elasmosaurid plesiosaur specimens from the Cretaceous contained a surprise that told us a little more about their diet.

What was found were specimens with their stomach contents preserved, and what they contained were gastroliths, or gizzard stones (no surprise there; plesiosaur remains have long been associated with gastroliths) and gastropods and crinoids. The gastroliths in this case were identified to have come from a site over 300km away, so the plesiosaurs were certainly doing some traveling over their lifetimes.

(A) Close-up of a block containing stomach content from QMF33037. Inset: Interpretation of the block, showing gastroliths (yellow), molluscan shell (red), and parts of the elasmosaurid's ribs (blue). The field of view is 49.8 mm across.

Here's a new word for me, too: bromalite. You've probably heard of coprolites before, fossilized feces. A bromalite is basically fossilized colon contents, all the stuff that has worked its way through the gut but hasn't been excreted yet…so this poor beastie was killed before it could void its bowels one last time. Here's a picture of that terminal lump of intestinal blockage:

End-on view of the QMF33037 bromalite; intact bivalve shell is visible to the lower right of the image. Scale bar, 5 cm.

This changes our view of their feeding habits a bit—they were ducking their heads down under water to scoop up benthic (bottom dwelling organisms) like clams and gulping them down. I've always had this image of long-necked plesiosaurs darting after fish, but they may have used those necks more to reach down and snaffle up less mobile prey.

Reconstruction of a Queensland elasmosaurid feeding on the benthos.

McHenry CR, Cook AG, Wroe S (2005) Bottom-feeding plesiosaurs. Science 310(5745):75.