Dinosaur discovery: First complete skeleton given place in ‘dino family tree’

The world’s first complete dinosaur skeleton has finally been studied and its position on the Jurassic family tree identified. University of Cambridge researchers spent the past three years preparing a detailed description and biological analysis of the skeleton of the Scelidosaurus.

This completes the work started by the British Museum’s Richard Owen – who invented the term ‘dinosaur’ – 160 years ago after being sent the skeleton.

The dinosaur fossil was discovered on west Dorset’s Jurassic Coast and the rocks in which it was fossilised are approximately 193 million years old.

The team, led by Dr David Norman, revealed the dinosaur was an ancestor of the ankylosaur – the armour-plated ‘tanks’ of the Late Cretaceous.

The dinosaur expert’s work also revealed the skull had horns on its back edge, several bones not seen in any other dinosaur and a skull covered in hardened horny turtle-like plates.

After Richard Owen was sent the full Scelidosaurus fossil in 1858 he published two short papers on its anatomy, however much detail was left unrecorded.

Dr Owen did not reconstruct the animal as it might have appeared in life and made no attempt to understand its relationship to other known dinosaurs of the time.

He is now known to have ’re-buried’ it in the literature of the time, where it has remained ever since – known, yet obscure and misunderstood, according to Dr Norman.

Over the past three years, he has been working to finish the work which Dr Owen began, preparing a detailed description and biological analysis.

The original skeleton is stored at London’s Natural History Museum, with other specimens at Bristol City Museum and Cambridge’s Sedgwick Museum.

The results of Dr Norman’s work not only reconstructs what Scelidosaurus looked like , but reveal that it was an early ancestor of ankylosaurs.

For more than a century, dinosaurs were classified according to hip bone shape – they were either saurischians (‘lizard-hipped’) or ornithischians (‘bird-hipped’).

But in 2017, Dr Norman’s colleagues argued these dinosaur family groupings needed to be re-defined and re-named.

The researchers suggested bird-hipped dinosaurs and lizard-hipped dinosaurs such as Tyrannosaurus evolved from a common ancestor, potentially revolutionising more than a century of theory about the evolutionary history of dinosaurs.

Another fact that emerged from their work on dinosaur relationships was the earliest known ornithischians first appeared in the Early Jurassic Period.

Dr Norman said: ”Scelidosaurus is just such a dinosaur and represents a species that appeared at, or close to, the evolutionary ‘birth’ of the Ornithischia.

“Given that context, what was actually known of Scelidosaurus? The answer is remarkably little.”

Dr Norman has now completed a study of all known material attributable to Scelidosaurus and his research has revealed many firsts.

He said: “Nobody knew that the skull had horns on its back edge.

“It had several bones that have never been recognised in any other dinosaur.

“It’s also clear from the rough texturing of the skull bones that it was, in life, covered by hardened horny scutes, a little bit like the scutes on the surface of the skulls of living turtles.

“In fact, its entire body was protected by skin that anchored an array of stud-like bony spikes and plates.”

Now that its anatomy is understood, it is possible to examine where Scelidosaurus sits in the dinosaur family tree.

The dinosaur had long been thought of as an early member of the group including the stegosaurs, including Stegosaurus with its huge bony plates along its spine and a spiky tail, and ankylosaurs, the armour-plated ‘tanks’ of the dinosaur era.

That was based on a poor understanding of the anatomy of Scelidosaurus.

Now it seems that Scelidosaurus is an ancestor of the ankylosaurs alone.

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