Toothy snout recasts Australia's famed Muttaburrasaurus as a picky eater

In a surprising new study, Australia's most famous plant-eating dinosaur has been described as a "picky eater with a nose for good food" when it roamed across the continent around 96 million years ago. After examining different parts of the skull from new bones of the large-bodied ornithopod Muttaburrasaurus langdoni, fossil experts from across Australia and the US have released several new insights in a journal article published in PeerJ.

Lead author Dr. Matthew Herne, from The University of New England, says that the discovery redefines several assumptions made about the bumpy-nosed species, which is the fossil emblem of Queensland.

The first astonishing discovery was that Muttaburrasaurus had teeth at the tip of its snout.

"This was unexpected, because the beak (front part of the snout) of Muttaburrasaurus was thought to be toothless like many other well-known plant-eating species such as Iguanodon from Europe and the 'duck-billed' Hadrosaurs, mostly found in the Northern Hemisphere.

"But ornithischian dinosaurs of this size normally have beak-like snouts without teeth, with a good example of this being Triceratops," says Dr. Herne.

Therefore, the beak of this Australian dinosaur wasn't toothless and most likely a pickier eater. With its narrow toothy beak, Muttaburrasaurus would have browsed for particular leaves and seeds and possibly even invertebrates for varieties in their diet.

This also means that Muttaburrasaurus evolved from an earlier offshoot of the ornithopod dinosaurs from Camptosaurus and Iguanodon, when the earlier forms of the small-bodied ornithischians all had toothed beaks.

This new finding can help place Muttaburrasaurus more accurately on the dinosaur tree of life.

The new bones, unearthed in the same historic site in central Queensland as the original skeleton named after the township of Muttaburra, also reveal some tantalizing clues about the behavior and life of the animals.

Co-author Professor Vera Weisbecker, from Flinders University, says the findings were made by extracting the brain imprint on the skull and the inner ears.

"We realized that its inner ear was more like dinosaurs that walked on two legs, like Tyrannosaurus rex, than others that spent more time on all fours," she says.

"So it's possible that Muttaburrasaurus was a large herbivore walking and running on its hind legs when needed and used its front arms for support to crop food closer to the ground."

The team also found that the characteristic 'bulbous' shape of Muttaburrasaurus' nose is comprised of entirely new bones that are not found in other dinosaurs.

Dr. Herne says finding the new bones was exciting because they revealed two large complex air chambers above the main inhaled airflow which would have slowed down air as it breathed in.

"So we suspect that they indicate a very acute sense of smell, perhaps to help the animal find food, detect predators or assist in directional navigation," explains UNE Adjunct Research Fellow in Vertebrate Paleontology Dr. Herne, who is also affiliated with Queensland Museum and Australian Age of Dinosaurs Museum of Natural History in Queensland.

He says this feature of the nose also matches their very large olfactory bulbs—"among the largest of any dinosaur"—which are the parts of the brain where smell is processed.

Another co-author Dr. Joseph Bevitt, from the Australian Nuclear Science and Technology Organisation (ANSTO), says the use of advanced CT scanning, neutron scattering and synchrotron technologies provided detailed 3D digital models of the jaws and teeth.

"These remarkable new insights into the skull of Muttaburrasaurus provided other intriguing findings, including:

The discovery that premaxillary bones in the Muttaburrasaurus muzzle evolved to exclude the nasal bones from bordering the nostrils. This feature was only previously known in the hollow crested lambeosaurine hadrosaurs from the Northern Hemisphere, indicating possible independent convergent evolution between northern and southern hemisphere dinosaurs.

Eye socket measurements and fleshed-out restoration of the head show that its vision was typical for a large herbivore, with a wide field of view to the sides but with little ability to see in front of itself. The wide panoramic vista experienced by Muttaburrasaurus could have helped it avoid predators or track its herd.

Geological evidence suggests that Muttaburrasaurus lived close to the inland Eromanga Sea that invaded much of central Australia from 140 million to 90 million years ago. The CT examination of nasal cavities suggest Muttaburrasaurus could have used specialized nasal salt glands to remove excess salt from coastal plants and possibly crustaceans it consumed at the end of the inland sea.

Rather than shear or cutting, the newly acquired CT imagery of cheek teeth show that Muttaburrasaurus would have ground its food, like other ornithopods and in a similar way to horses, cows and kangaroos.

Researchers add there is still not enough evidence to tell whether Muttaburrasaurus lived in herds like many other large ornithischians such as the hadrosaurs or Triceratops.