Over eight decades ago, while pondering the heavily-armored dinosaur Scolosaurus, the eccentric paleontologist Franz Nopcsa proposed what is probably one of the oddest ideas in the annals of paleobiological speculation. Scolosaurus was a low-slung quadruped that shuffled around what were then thought to be parched sand dunes. Even though its close ankylosaurian relatives had been interpreted as herbivores from the very start, the Cretaceous desert may have been nearly devoid of low-lying vegetation. But there was another source of food. Perhaps Scolosaurus was an insectivore, Nopcsa suggested, nabbing little arthropods as if the dinosaur were an overgrown horned toad.
Nopcsa’s proposal didn’t catch on. The little leaf-shaped teeth in ankylosaurian mouths accorded better with an herbivorous diet, and a rare find of ankylosaur gut contents confirmed that some of these dinosaurs ate seeds, fruit, leaves, and other low-growing plants. But new evidence has led paleontologist Robert Hill and colleagues to tentatively revive Nopcsa’s idea for a different armored dinosaur. The chief line of evidence is a bone that’s never been seen in a non-avian dinosaur until now.
Most dinosaurs go undiscovered. Of those we find, most are in pieces. Fewer still are represented by elements that came apart but remained in close proximity (or are in association). An even smaller number are articulated, preserving the moment of burial. But even then, even in seemingly the most complete and beautifully-articulated specimens, certain parts are often missing. Among them are delicate little throat bones that dinosaurian tongues attached to.
While carefully cleaning up a skull and series of neck vertebrae from the 80-75 million year old ankylosaur Pinacosaurus, preparators Virginia Heisey and Joe Groenke started to uncover thin, triangular bones in the dinosaur’s throat. These were the paraglossalia – elements that had only previously seen in birds.
In our living dinosaurs, paraglossalia are relatively small and flat. They make up the forward-most part of a set of elements called the hyobranchial apparatus. This set of rods, derived from the gill arches of the four-limbed fish that were also our ancestors, provides an attachment site for the tongue muscles at the front and embeds into the pharynx at the back.
There’s a variety of reasons why no one has recognized paraglossalia in non-avian dinosaurs until now. The most obvious is that these elements are usually made of cartilage and probably decay before fossilization. And even when these elements turn to bone, Hill and coauthors point out, they are very thin. The front part of the paraglossalia in Pinacosaurus are so thin that they’re translucent. Even then, these parts might remain embedded in rock that stabilizes the skull, confused for unimportant bone shards and prepared away, or simply set aside as unknown bones. In fact, paleontologists already had at least one example of paraglossalia in collections prior to this discovery. When Hill and colleagues had another look at the armored dinosaur Edmontonia, they found another instance of these elements.
Other dinosaurs resting in museum collections probably have paraglossalia, too. That’s because the presence of these elements in both birds and ankylosaurs – distant cousins in the dinosaur family tree – indicates that this apparatus went back to the last common ancestor of all dinosaurs, at the very least. Field workers, preparators, and paleontologists should keep a sharp eye out for these bones that may have otherwise been set aside as mystery pieces.
This is about more than simply adding more bones to the dinosaurian skeleton, though. In the case of Pinacosaurus, Hill and co-authors report that the paraglossalia are much larger and more robust than what’s seen in birds. This dinosaur must have had a powerful tongue. Rather than chomping at vegetation with its jaws, it may have plucked and scooped green food with a muscular tongue.
But here’s where Nopsca comes in. Pinacosaurus lived in a relatively arid environment of rolling sand dunes. Plants may have been rare, and insect fossils are commonly found in the same rocks. While it’s a speculative stretch, Hill and colleagues entertain the idea that Pinacosaurus could have slurped up social insects and millipedes as a large part of its diet. As anteater, pangolins, armadillos, and even salamanders show us today, a powerful tongue can be quite useful in snaffling ants and other invertebrates. Instead of being bumpy vegetarians, some ankylosaurs might have been highly-armored anteaters.
Hill, R., D’Emic, M., Bever, G., Norell, M. 2015. A complex hyobranchial apparatus in a Cretaceous dinosaur and the antiquity of avian paraglossalia. Zoological Journal of the Linnean Society. doi: 10.1111/zoj.12293