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Tuesday, September 22, 2020

Wonky skull of Styracosaurus leads palaeontologists to question past identifications of species


Wonky skull of five-metre-long Styracosaurus named ‘Hannah’ with a fan of long horns leads scientists to question previous theory that all dinosaurs had symmetrical faces

  • The intact Styracosaurus skull has wonky horns and was discovered in Canada 
  • Asymmetrical face suggests more morphological variability than thought 
  • Scientists fear incomplete skulls have been mistakenly classed as new species

New analysis of the skull of a Styracosaurus has led scientists to question a previous theory that all dinosaurs had symmetrical faces.

The well-preserved skull was discovered in 2015 by Scott Persons – then a graduate student at the University of Alberta – during an expedition in the badlands northwest of Dinosaur Provincial Park in Canada. 

The skull is from a Styracosaurus – a horned dinosaur over five metres in length with a fan of long horns, which walked the Earth about 75 million years ago.

The specimen was nicknamed Hannah, after Persons’ dog.

Paleontologist Scott Persons, pictured alongside the partially-uncovered skull

Paleontologist Scott Persons, pictured alongside the partially-uncovered skull

Analysis of the skull by paleontologists at the University of Alberta has now revealed that the Styracosaurus’ horns were asymmetrical.

This has important implications for how paleontologists identify new species of dinosaurs.

‘When parts of one side of the skull were missing, paleontologists have assumed that the missing side was symmetrical to the one that was preserved,’ said Persons. 

‘Turns out, it isn’t necessarily. Today, deer often have left and right antlers that are different in terms of their branching patterns. 

‘Hannah shows dramatically that dinosaurs could be the same way.’

Hannah's asymmetrical skull seen from all sides. It is not known if the Styracosaurus was a female but was around five meters in length

Hannah’s asymmetrical skull seen from all sides. It is not known if the Styracosaurus was a female but was around five meters in length 

Nicknamed Hannah, the dinosaur was a Styracosaurus - a horned dinosaur over five metres in length with a fan of long horns

Nicknamed Hannah, the dinosaur was a Styracosaurus – a horned dinosaur over five metres in length with a fan of long horns 

The differences in the skull’s left and right halves are so extreme that, had the palaeontologists found only isolated halves, they might have concluded that they belonged to two different species. 

Hannah shows that the pattern of dinosaur horns could vary significantly, meaning some fossils that were once assumed to be unique species will have to be reevaluated. 

‘The skull shows how much morphological variability there was in the genus,’ said Robert Holmes, professor in the Department of Biological Sciences, who led the study.  

How many dinosaur species existed? 

There are currently around 700 valid dinosaur species that have been discovered and named – with about 300 genera.

Scientists predict that there were many more as the fossil record is incomplete.

Fossils are not available for all periods of history due to some ages of rock worn from the earth’s surface such as the Middle Jurassic age.

Many dinosaurs from the Late Cretaceous period have been discovered. 

Existing species are incredibly varied with some dinosaurs weighing eight tons while others weighed just eight pounds.

Source: American Museum of Natural History 

It is tradition for the finder to nickname the discovery, Mr Persons decided to name it after his dog Hannah.

‘She’s a good dog, and I knew she was home missing me while I was away on the expedition,’ he said.

It is not known whether the fossil is actually female. 

Researchers gathered more information from the fossil by partnering with researchers Ahmed Qureshi and graduate student Baltej Rupal in the Faculty of Engineering who performed a 3D laser scan of the scull.

Mr Persons said: ‘That let our publication to include a digital reconstruction, allowing scientists all over the world to download the 3D model and inspect it in detail.

‘This is the future of paleontological collections: digital dinosaurs.’ 

‘Morphological variation and asymmetrical development in the skull of Styracosaurus albertensis’, was published in the journal Cretaceous Research.

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