A new dinosaur with a dramatic sail along its back and tail has been identified from fossils found on the Isle of Wight in England - and it may have evolved its eye-catching look to impress potential mates.
The new iguanodontian dinosaur was identified by Jeremy Lockwood, a retired GP, as part of his PhD studies at the University of Portsmouth and the Natural History Museum, London. He made the discovery by carefully re-examining dinosaur bones held in the collections at the Dinosaur Isle museum, Isle of Wight.
Until now, the fossil material, which is around 125 million years old, had been assumed to belong to one of the two known iguanodontian dinosaur species from the Isle of Wight. But Lockwood noticed something unusual.
"While the skeleton wasn't as complete as some of the others that have been found, no one had really taken a close look at these bones before", Lockwood said. "It was thought to be just another specimen of one of the existing species, but this one had particularly long neural spines, which was very unusual."
On closer inspection, Lockwood realised the animal would have probably possessed a pronounced sail-like structure along its back, helping to set it apart from other dinosaurs found on the island. His findings are described in a new paper published today in the scientific journal Papers in Palaeontology.
The animal's most striking feature is a series of extremely elongated spines along its back and tail, which probably supported a large, sail-like structure.
Evolution sometimes seems to favour the extravagant over the practical. While the exact purpose of such features has long been debated - with theories ranging from body heat regulation to fat storage - researchers believe that the most likely explanation in this case is visual signalling, possibly as part of a sexual display and this usually is because of sexual selection.
Jeremy Lockwood, PhD student, University of Portsmouth
Lockwood explained: "Evolution sometimes seems to favour the extravagant over the practical. While the exact purpose of such features has long been debated - with theories ranging from body heat regulation to fat storage - researchers believe that the most likely explanation in this case is visual signalling, possibly as part of a sexual display and this usually is because of sexual selection".
"In modern reptiles, sail structures often show up more prominently in males, suggesting that these attributes evolved to impress mates or intimidate rivals. We think Istiorachis may have been doing much the same."
To work out what the sail might have been for, researchers carried out a close examination of the fossilised bones. They then created a large database of similar dinosaur back bones from direct observations, photos, scientific illustrations and reconstructions, and used it to trace the evolutionary history of the heights of back bones on a new family tree of iguanodontian dinosaurs. This allowed them to spot broader trends in how these sails evolved.
Dr. Jeremy Lockwood with the spinal column of Istiorachis macarthurae.
"These methods let us move beyond simply describing the fossil and actually test hypotheses about its function", said Lockwood. "We showed that Istiorachis's spines weren't just tall - they were more exaggerated than is usual in Iguanodon-like dinosaurs, which is exactly the kind of trait you'd expect to evolve through sexual selection."
The team studying the fossils included the Natural History Museum's Prof. Susannah Maidment. Susannah commented: "Jeremy's careful study of fossils that have been in museum collections for several years has brought to life the iguandontian dinosaurs of the Isle of Wight. His work highlights the importance of collections like those at Dinosaur Isle, where fossil specimens are preserved in perpetuity and can be studied and revised in the light of new data and new ideas about evolution. Over the past five years, Jeremy has single-handedly quadrupled the known diversity of the smaller iguanodontians on the Isle of Wight, and Istiorachis demonstrates we still have much to learn about Early Cretaceous ecosystems in the UK.
The Isle of Wight has become a hotspot for dinosaur discoveries in recent years, producing a flurry of new species. Finds like Brighstoneus, Comptonatus, and the terrifying spinosaurids Riparovenator and Ceratosuchops are helping scientists build a picture of the island as a bustling, biodiversity-rich landscape during the Early Cretaceous.
Importantly, Istiorachis appears to highlight a broader evolutionary trend. Research shows that elongation of neural spines in iguanodontians began in the Late Jurassic, before becoming a relatively common feature during the Early Cretaceous. However, true hyper-elongation, where spines stretch to more than four times the height of the vertebral body, remains rare.
Jeremy's careful study of fossils that have been in museum collections for several years has brought to life the iguandontian dinosaurs of the Isle of Wight. His work highlights the importance of collections like those at Dinosaur Isle, where fossil specimens are preserved in perpetuity and can be studied and revised in the light of new data and new ideas about evolution.
Professor Susannah Maidment, Natural History Museum
Similar displays are seen in living reptiles today, including several species of lizard, where elaborate crests and sails typically signal health and strength to potential mates.
Lockwood said: "Istiorachis is a deep-time example of the same evolutionary pressures we see shaping display structures in modern animals."
Jeremy has named the new dinosaur Istiorachis macarthurae after a famous Isle of Wight resident.
The name Istiorachis means 'sail spine', while macarthurae honours Dame Ellen MacArthur, the English sailor who in 2005 set a world record for the fastest solo non-stop voyage around the world on her first attempt and who comes from the Isle of Wight.
The discovery highlights the Isle of Wight as a highly diverse ecosystem of Cretaceous life. The Wessex Formation alone represents one of the richest non-marine vertebrate fossil deposits from this period anywhere in the world, capturing a critical moment as iguanodontians blossomed from relatively obscure Jurassic herbivores into the dominant duck-billed dinosaurs of the later Cretaceous.
For palaeontologists, Istiorachis is another reminder that in evolution, sometimes it pays to show off.
