Australia's Ankylosaur Dinosaur Was Slow To Evolve

Artist's impression of Kunbarrasaurus ieversi. © Australian Geographic, used with permission.

Australia's most complete dinosaur skeleton has been revealed as a new genus, one which evolved much more slowly than its relatives on other continents.

The 1989 discovery of a more than 90 percent intact fossil near Richmond, Queensland bolstered Australia's limited dinosaur record. The bones clearly belonged to an ankylosaur, which University of Queensland PhD student Lucy Leahey described in a statement as: “A group of four-legged, herbivorous dinosaurs, closely related to stegosaurs.”

Only one other Australian ankylosaur, a very incomplete specimen known as Minmi, has been studied. First examination of the new fossil placed it in the same genus as Minmi. However, in the journal Peer J, Leahey has completed a more thorough study of what she has dubbed Kunbarrasaurus ieversi and found something much more interesting.

“Our work has revealed that Kunbarrasaurus is more primitive than the majority of other well-known ankylosaurs from North America and Asia,” said Dr. Steve Salisbury, Leahey's supervisor. “It appears to represent an early, less heavily ‘armored’ member of the group, close to the point at which the ankylosaurs diverged from the other main lineage of armored dinosaurs, the stegosaurs.”

 

 

Leahey told IFLScience that Kunbarrasaurus was found in a 100 to 110 million-year-old deposit. By that time Northern Hemisphere ankylosaurs resembled steampunk tanks or elements from a Mad Max film, covered in staggering armor and carrying clubs on the ends of their tails. Kunbarrasaurus, while armored, resembles ancestral versions that had only recently incorporated bones into their skin for defensive purposes.

“The diversity of body armor in ankylosaurs may have been for sexual selection as well physical protection,” Leahey said to IFLScience. However, she adds that ankylosaurs in North America or Asia had to fight off more fearsome theropods than anything yet found in Australia. Kunbarrasauruses 2 meters (6.6 feet) long probably benefited from carrying less weight.

CT scans of other ankylosaurs have found distinctively looping airways. Leahey told IFLScience that Kunbarrasaurus's airway has a single loop, differing from other dinosaurs but far less elaborate than its northern relatives. This complexity has been attributed both to the need to keep cool when carrying so much armor, and for vocalisation. Leahey added that the dinosaur's smaller size may have removed the need for such an elaborate air-conditioning system, but Australia was also much cooler than North America at the time.

A distinctively Kunbarrasaurian quirk is an almost entirely spherical inner ear, something previously only seen in turtles and tuatara. Most species' inner ears are more elongated. Leahey told IFLScience that the common ancestry of turtles and ankylosaurs was too far back for this to likely be a common inheritance, but that it was not clear what purpose it served for either species.

Leahey described the specimen as being one of the few ankylosaurs where the skin bones had not fused to the skeleton, giving us an “unobstructed view of the skull.”

Kunbarra means shield in Mayi, the local indigenous language, while the species name refers to the fossil's finder Ian Levers.

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