Comptonatus chasei, a new iguanodontian dinosaur from the Lower Cretaceous Wessex Formation of the Isle of Wight

Comptonatus chasei gen. et sp. nov. (IWCMS 2014.80). Life restoration. Original artwork by John Sibbick.
Comptonatus chasei gen. et sp. nov. (IWCMS 2014.80). Life restoration. Original artwork by John Sibbick.

One of the best-preserved dinosaurs ever found in the UK has been unearthed on the Isle of Wight.

Named Comptonatus chasei, the new species cements the island’s reputation as one of the world’s most important places to study dinosaurs.

The newest member of the Iguanodon family is offering new insights into the UK’s ancient past.

Found in the cliffs of Compton Bay on the Isle of Wight, Comptonatus chasei would have been part of a thriving ecosystem more than 120 million years ago. It’s the latest in a flurry of new dinosaurs named from the island, revealing that the area’s past was much more diverse than first suspected.

One of the driving forces behind the island’s dinosaur “renaissance” is Dr Jeremy Lockwood, a scientific associate at the Natural History Museum. He is the lead author of the new paper describing Comptonatus chasei published in the Journal of Systematic Palaeontology.

“The description of Comptonatus represents the culmination of years of work,” Jeremy says. “Almost 150 bones have been unearthed, making it almost certainly the most complete new dinosaur found in Britain for 100 years.”

“It leaves me with a mixture of excitement at having been able to deal with such a rare specimen and also a sense of relief. It’s also a great pleasure to name this species after the fossil hunter Nick Chase, who had a phenomenal ability to find dinosaurs.”

Back in the Early Cretaceous, Comptonatus chasei would have been an unmistakable presence on the Isle of Wight. Weighing around 900 kilogrammes, or about the same as an American bison, it’s likely these dinosaurs would have roamed in herds.

This behaviour is one of the reasons the Iguanodon family, or iguanodontians, are sometimes called ‘the cattle of the Cretaceous’. Fossils from a variety of species suggest these herbivores would have stuck together as a defence against carnivores.

These could have included ambush predators like Vectiraptor, which may have been large enough to take on young Comptonatus. Larger dinosaurs like Riparovenator milnerae and Ceratosuchops inferodios may also have been a threat.

Analysis of Comptonatus suggests that it was about six years old and almost fully grown at the time of its death. Its body ended up lying on the ground of an ancient floodplain, which used to cover much of what is now the Isle of Wight.

When rain rushed down steep hills to the north, it would have swept up the bones along with plants, rocks and other debris. These were rapidly buried, helping to explain why Comptonatus is so well-preserved.

Over time, what was once a flood plain eventually became part of a cliff, where the dinosaur would remain buried for over 120 million years.

After millions of years of erosion, Comptonatus finally came to light in 2013 when it was spotted by Nick Chase. Jeremy was among the team called out to excavate the dinosaur and take its bones to the Dinosaur Isle Museum.

“When we were digging this dinosaur out of the cliff, it was thought to be a specimen of Mantellisaurus atherfieldensis,” Jeremy recalls. “This isn’t unusual, as most iguanodontians found on the island have historically been assumed to represent either Mantellisaurus or Iguanodon.”

“However, I thought this specimen showed some differences. This spurred me on to undertake a PhD looking at the variation in the iguanodontian dinosaurs of the Isle of Wight.”

Jeremy couldn’t have picked a better time to do so. Recent discoveries in Spain and the USA have revealed that the dinosaurs of the Early Cretaceous were more diverse than previously thought, suggesting the Isle of Wight might be as well.

As the bodies of the Iguanodon family are all quite similar, their heads are the best way to tell them apart. Unfortunately, the skull bones of these dinosaurs are fragile, and often damaged or destroyed before being discovered. This makes it hard for palaeontologists to know whether something is a new species.

However, by poring over the collections of the Dinosaur Isle Museum and Natural History Museum, Jeremy has found fossils which have previously been overlooked. In 2021, Jeremy identified a new iguanodontian from the Isle of Wight, called Brighstoneus simmondsi, based on a large, bulbous nose that set it apart from its relatives.

While the differences in Comptonatus aren’t quite so obvious, its completeness means there are more characteristics to distinguish it. Its teeth have grooves extending across their tops, for instance, while its shoulders have a different structure to its relatives.

Together, these convinced the scientists that the dinosaur should be a species in its own right. This now means three similarly sized iguanodontians lived on the Isle of Wight in the Early Cretaceous, separated from each other by a few million years.

Unfortunately, the generally poor preservation of the iguanodontians means there’s not currently enough evidence to know exactly how these different species evolved, or how they were related. Finding more species and better preserved fossils could help to solve this mystery once and for all.

“Recent discoveries suggest that we have been overlooking the fact that the iguanodontians were relatively diverse,” Jeremy explains. “However, it’s unclear whether this is because they evolved faster than previously thought, or that many species existed side by side.”

“This is the next big question we need to try and answer to understand these dinosaurs.”

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