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that these plesiosaurs only ate fish, and they never thought of them as bottom feed-
ers.
Gastroliths in some plesiosaurs would have helped to grind down those hard-
shelledcritters, increasing thesurfaceareaofanycalcium-carbonate shellsforeasi-
er dissolution in stomach acids. So this evidence syncs well with the “scooping”
hypothesis, while also explaining how feeding behaviors might have gotten those
rocks into marine-reptile bellies in the first place. Other plesiosaurs, though, might
have just accidentally consumed rocks as part of their wholesale ingestion of sea-
floor sediment, and gut contents of some specimens suggest just this.
Thiswiderangeofpastandpresentanimalsthatusegastrolithsisbynomeans
completely known, and more surprising examples surely await our detection. For
instance, the recent discovery of gastroliths in pterosaurs—dinosaurs' flying cous-
ins—was an unexpected one, but welcomed by paleontologists. In 2013, Laura
Codorniúandseveralotherpaleontologistsreportedonanassortmentofcoarsesand
to fine gravel in the body cavities of two specimens of the petite Early Cretaceous
pterosaur
Pterodaustro guinazui
from Argentina. These pterosaurs were always as-
sumed to have used their specialized beaks to strain their food from water, much
like modern flamingos. Also similar to flamingos, they probably ate small crusta-
ceansaspartoftheirdiet.Thegastroliths,then,wouldhavehelpedthepterosaursto
mash the harder-shelled crustaceans. This gastrolith presence also prompted the pa-
leontologists to reconsider the front teeth of
Pterodaustro
, which they noticed were
more robust than the teeth toward the back of the mouth. Accordingly, they pro-
posedthat the frontteeth were adapted forgrabbing sandandrocks.Inother words,
paleontologists gained new insights on the feeding habits and evolutionary history
of this pterosaur because of the trace fossils they contained. Gastroliths: is there
nothing they can't do?
How to Recognize a Dinosaur Gastrolith
Armed with this comprehensive knowledge of gastroliths in modern animals and a
few ancient ones, it now should be a breeze to identify dinosaur-related ones, right?
