Reconstructions of dinosaurs at theme parks and museums often show their tongues waving — a feature that is completely incorrect. According to new research, published in the journal PLoS ONE, dinosaur tongues were probably rooted to the bottoms of their mouths in a manner akin to extant alligators.
“Tongues are often overlooked. But, they offer key insights into the lifestyles of extinct animals,” said study lead author Dr. Zhiheng Li, a researcher at the Key Laboratory of Vertebrate Evolution and Human Origins, Chinese Academy of Sciences.
Dr. Li and colleagues made their discovery by comparing hyoid bones (the bones that support and ground the tongue) of extinct dinosaurs, pterosaurs and alligators to the hyoid bones and muscles of modern birds and alligator specimens.
Hyoid bones act as anchors for the tongue in most animals, but in birds these bones can extend to the tip.
Because extinct dinosaurs are related to crocodiles, pterosaurs and modern birds, comparing anatomy across these groups can help scientists understand the similarities and differences in tongue anatomy and how traits evolved through time and across different lineages.
The researchers took high-resolution images of hyoid muscles and bones from 15 modern specimens, including three alligators and 13 bird species as diverse as ostriches and ducks.
The fossil specimens, most from northeastern China, were scrutinized for preservation of the delicate tongue bones and included a Tyrannosaurus rex, small bird-like dinosaurs as well as pterosaurs.
The results indicate that the hyoid bones of most dinosaurs were like those of alligators and crocodiles — short, simple and connected to a tongue that was not very mobile.
“The findings mean that dramatic reconstructions that show dinosaurs with tongues stretching out from between their jaws are wrong. They’ve been reconstructed the wrong way for a long time,” said Professor Julia Clarke, a paleontologist at the University of Texas at Austin.
“In most extinct dinosaurs their tongue bones are very short. And in crocodilians with similarly short hyoid bones, the tongue is totally fixed to the floor of the mouth.”
In contrast to the short hyoid bones of crocodiles, the scientists found that pterosaurs, bird-like dinosaurs, and living birds have a great diversity in hyoid bone shapes.
“The range of shapes could be related to flight ability, or in the case of flightless birds such as ostriches and emus, evolved from an ancestor that could fly,” they said.
“Taking to the skies could have led to new ways of feeding that could be tied to diversity and mobility in tongues.”
“Birds, in general, elaborate their tongue structure in remarkable ways. They are shocking,” Professor Clarke said.
“That elaboration could be related to the loss of dexterity that accompanied the transformation of hands into wings,” Dr. Li added.
“If you can’t use a hand to manipulate prey, the tongue may become much more important to manipulate food. That is one of the hypotheses that we put forward.”
The team also noted one exception linking tongue diversity to flight.
Ornithischian dinosaurs — a group that includes Triceratops, ankylosaurs and other plant-eating dinosaurs that chewed their food — had hyoid bones that were highly complex and more mobile, though they were structurally different from those of flying dinosaurs and pterosaurs.
“Further research on other anatomical changes that occurred with shifts in tongue function could help improve our knowledge of the evolution of birds,” Professor Clarke said.
Z. Li et al. 2018. Convergent evolution of a mobile bony tongue in flighted dinosaurs and pterosaurs. PLoS ONE 13 (6): e0198078; doi: 10.1371/journal.pone.0198078