Extensive fossilised remains of a dinosaur named Spicomellus have been discovered in the Atlas Mountains near the Moroccan town of Boulemane.
About four metres long and weighing up to two tonnes, Spicomellus is the oldest known member of a group of tank-like armoured dinosaurs called ankylosaurs.
“The armour of Spicomellus is jaw-droppingly weird, unlike that of any other dinosaur – or any other animal alive or dead – that we've ever discovered,” said vertebrate paleontologist Richard Butler of the University of Birmingham in England, co-leader of the research published in the journal Nature.
“Not only did it have a series of sharp, long spikes on each of its ribs – unknown elsewhere among animals – but it had spines the length of golf clubs sticking out in a collar around its neck,” Mr Butler added.
Metre-long spikes
The extravagant armour may have served dual roles – as defence against large, meat-eating dinosaurs and as a display to attract mates.
“The armour surely had some defensive function, but it's difficult to imagine how the metre-long spikes around the neck were used for defence.” Mr Butler said.
In living animals, structures that tend to have no obvious function – like a deer's antlers or a peacock's tail – are usually associated with mating, according to vertebrate paleontologist and study lead author Susannah Maidment of the Natural History Museum in London.
“They could be used in courtship or territorial displays, or to fight against members of the same species during competitions for mates. Spicomellus's armour is totally impractical, and would have been a bit annoying in dense vegetation, for example. So we think that it is possible the animal evolved such elaborate armour for some sort of display, perhaps to do with mating,” Ms Maidment said.
Distinctive fused tail vertebrae suggested that Spicomellus possessed a weapon at the end of its tail to fight off predators – perhaps a club or spikes of some sort – though one was not recovered among the remains.
Such fused tail vertebrae previously have been found only in ankylosaurs with tail weapons. This would indicate that tail weapons appeared in ankylosaurs about 30 million years earlier than previously known.
Jurassic period
Ankylosaurs were among the most successful herbivorous dinosaurs. They are closely related to another group of plant-eaters called stegosaurs that boasted bony plates on the back and a spiky tail weapon.
Both groups arose during the Jurassic period. But the ankylosaurs outlasted the stegosaurs, thriving until an asteroid struck Earth 66 million years ago at the end of the Cretaceous period, ending the age of dinosaurs. The best-known member of the group, Ankylosaurus, was larger than Spicomellus, at about eight metres long, and inhabited western North America during the twilight of the dinosaurs. Its armour, including a formidable tail club, protected against predators, including Tyrannosaurus.
Early members of dinosaur groups often have fairly plain body plans compared to later counterparts. Spicomellus shows that was not the case with ankylosaurs.
