It took time to really know this dinosaur

The first complete dinosaur skeleton ever found has been studied in detail more than 160 years after it was first discovered.

The project, described in four studies in the Zoological Journal of the Linnean Society of London, reconstructed what Scelidosaurus looked like in life and suggests that it was an early ancestor of ankylosaurs, the armour-plated “tanks” of the Late Cretaceous Period.

David Norman from the University of Cambridge, UK, spent three years finishing what Richard Owen – the man who invented the word “dinosaur” – briefly started back in the 1850s.

The skeleton of Scelidosaurus was found in 193-million-year-old fossilised rocks on west Dorset’s Jurassic Coast and sent to Owen at the British Museum.

He published two short papers on its anatomy, but many details were left unrecorded and, Norman suggests in a previous paper, his work “is shown to be curiously narrow‐minded and somewhat muddled”.

Norman has now completed a study of all known material attributable to Scelidosaurus and reports that this has revealed many firsts.

“Nobody knew that the skull had horns on its back edge,” he says. “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, Norman says. It had been regarded as an early member of the group that included the stegosaurs and ankylosaurs, but that was based on a poor understanding of its anatomy; he suggests it now seems that it is an ancestor of the ankylosaurs alone.

And there is more to the story. For more than a century, dinosaurs have been primarily classified according to the shape of their hip bones: either saurischians (lizard-hipped) or ornithischians (bird-hipped).

However, in 2017, Norman and colleagues Matthew Baron and Paul Barrett argued that these family groupings needed to be rearranged, re-defined and re-named.

In a study published in the journal Nature, which made headlines but was also contested, they suggested that bird-hipped and lizard-hipped dinosaurs evolved from a common ancestor, potentially overturning more than a century of theory about evolutionary history.

Norman says that work also showed that the earliest known ornithischians first appeared in the Early Jurassic Period. “Scelidosaurus is just such a dinosaur and represents a species that appeared at, or close to, the evolutionary ‘birth’ of the Ornithischia,” he says.

The original skeleton is stored in the Natural History Museum in London.