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Featured News Lipless T-rex ancestor changes the face of history

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Fri, 31 Mar 2017

Lipless T-rex ancestor changes the face of history

Holotype skull of Daspletosaurus horneri (MOR 590) and life reconstruction of its integument, based on the distribution of texture on the facial bones.
Holotype skull of Daspletosaurus horneri (MOR 590) and life reconstruction of its integument, based on the distribution of texture on the facial bones. © Dino Pulerà.

A James Cook University scientist has helped in the discovery of a new species of dinosaur – a close ancestor of the fearsome predator Tyrannosaurus Rex.

Fossils of the nine-metre long tyrannosaur, with armour-like skin on the snout and the sides of the lower jaw, have been discovered in Montana’s Rocky Mountain range.

The new find has been named Daspletosauraus horneri, or ‘Horner’s Frightful Lizard’ in honour of renowned paleontologist Jack Horner.

JCU’s Associate Professor Eric Roberts helped determine the age of a fossil from the newly discovered T-Rex relative.

“It’s about 75 million-years-old, so this animal lived about 9 million years before the extinction of the non-avian dinosaurs,” said Dr Roberts.

He said in geological terms, the nine-metre long beast was the youngest of the Daspletosaurus clan.

The study, which was led by Dr Thomas Carr of Carthage College in the USA and published today in Nature Publishing Group’s Scientific Reports, found evidence for a rare type of evolution. The study also literally changes the face of tyrannosaurs.

“Their faces were covered by a ‘mask’ of large flat scales and extensive patches of armour-like skin. We think the scales extended almost to the teeth, we found no evidence of lips,” said Dr Carr.

Dr Carr said Daspletosaurus horneri was the youngest, and last, of its lineage that lived after its closest relative, Daspletosaurus torosus, which is found in Alberta, Canada.

“The close evolutionary relationship between the species taken with their geographic proximity and their sequential occurrence suggests that together they represent a single lineage that changed over geological time, where D. torosus has morphed into D. horneri,” he said.

Dr Roberts said advances in radioisotopic dating of sedimentary deposits was key to understanding the significance of the find.

“New age dates presented in this study are just the tip of the iceberg. Ongoing work in this field will provide unprecedented improvements in the dating of Late Cretaceous dinosaurs from western North America over the next few years,” he said.

Images: - Please credit artist Dino Pulera for marked graphics.


Name: Daspletosaurus horneri, “Horner’s frightful lizard”.

Where found: Montana, USA.

When: 75.1-74.4 million years ago, Late Campanian Age, Late Cretaceous Epoch.

Geological unit: Two Medicine Formation. Represents a series of river channel and overbank deposits splaying out from the Cretaceous Rocky Mountains, intermixed by volcanic ash deposits.

Known fossils: skull and skeleton of subadult, skull and skeleton of adult, partial lower jaw of subadult, isolated bones of subadults and juveniles.

Skull length: 947.0+ millimetres.

Body length: ~9 meters. ~3/4 as long as Tyrannosaurus rex.

Distinct features: Wide snout, small orbital horns (in front of the eyes), slit-like pneumatic opening on inside of lacrimal bone (just in front of the eye).

Prey: Horned dinosaurs (ceratopsians), crested duckbill dinosaurs (hadrosaurs), dome-headed dinosaurs (pachycephalosaurs), smaller carnivorous dinosaurs (theropods).

Important facts: Last species of Daspletosaurus to have evolved in the American west, provides evidence for the phenomenon of anagenesis among dinosaurs, model species for the types of skin covering on the face in tyrannosaurs, suggesting a crocodile-like pressure-sensing snout.


Associate Professor Eric Roberts


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