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A reconstruction of the Edmontosaurus skull LACM 23502, with a beak based on a natural mold. From Morris, 1970.

I’ve never liked the term “duck-billed dinosaur.” I know it’s part of the accepted dinosaur lexicon, just like “raptor” is, but every time I hear the phrase I think of a sluggish, swamp-bound Edmontosaurus dabbling in the water for soft water plants and algae. Paleontologists tossed out this imagery decades ago—hadrosaurs were terrestrial creatures with jaws specially adapted to grinding down tough vegetation.

I admit that the skull of Edmontosaurus looks superficially duck-like. Much like a mallard’s, the Late Cretaceous hadrosaur’s mouth is long, low and generally bill-shaped. The resemblance between these very, very distant relatives helped inspire images of wading hadrosaurs. But most Edmontosaurus skulls you see in museums present only the bony framework of the skull. The tough keratinous beak that tipped the skull typically decayed during the fossilization process, but in 1970, paleontologist William Morris described a rare Edmontosaurus skull with a beak trace.

You can see the specimen on display at the Natural History Museum of Los Angeles today. Designated LACM 23502, this Edmontosaurus skull was collected by Harley Garbani near Montana’s Ft. Peck Reservoir. Other Edmontosaurus have been found here, but this fossil included a natural mold of the dinosaur’s beak. (While the beak itself was not preserved, the mold showed what the internal surface looked like. In life, the actual beak sat on top of the fossilized mold.) The structure was not shaped just like a duck’s bill. On the bottom jaw, the beak surface curved slightly upward, and the upper half of the beak created a vertical, fluted surface that hung over the tip of the lower jaw. Maybe the term isn’t the most apt—and I’m open to suggestions—but Edmontosaurus seemed to be a shovel-beaked dinosaur rather than a duck-billed one.

At the time Morris described the skull, though, hadrosaurs were still thought to be semi-aquatic dinosaurs. Morris believed that the bill traces he described supported this idea and imagined that ridges on the interior part of the mold helped the dinosaurs strain plants and small invertebrates from the water. “A filtering device would be very important in assuring that these large animals could ingest large amounts of concentrated food relatively free of water in a manner similar to that of the dabbler ducks,” Morris wrote, which made the term “duck-bill” seem all the more apt for these dinosaurs.

Despite Morris’ insistence that hadrosaurs nourished themselves by slurping plant-heavy Cretaceous soup, though, we now know that Edmontosaurus and kin were terrestrial animals capable of breaking down tougher plant materials. Exactly how the beak of Edmontosaurus contributed to feeding is not entirely clear—perhaps the beak cropped vegetation that was broken down by the rows of small teeth lining the jaws. One thing is for sure, though. The duck-bills weren’t really so duck-like after all.

Reference:

Morris, William J. (1970). “Hadrosaurian dinosaur bills — morphology and function“. Contributions in Science (Los Angeles County Museum of Natural History) 193: 1–14.