The Dortokidae are a group of poorly known ancient pan-pleurodiran turtles, endemic to Europe with a range from the Early Cretaceous to the Paleogene. In a new paper in the journal Cretaceous Research, paleontologists report the oldest record of a pan-pleurodiran turtle in the United Kingdom, as well as the first and only occurrence of a dortokid in the UK.
An eastern snake-necked turtle (Chelodina longicollis) peering from its shell on the road to Carnarvon Gorge, Queensland, Australia. Image credit: Damien Naidoo / CC BY-SA 3.0.
The new specimen was found in the Early Cretaceous Wessex Formation of the Isle of Wight by fossil collector Steve Burbridge.
It comprises a relatively complete shell with post cranial elements within a calcite-filled shell vacuity.
The fossils are the earliest of a so-called side-necked pan-pleurodiran turtle, named as such because they fold their neck into their shell sideways when threatened.
“This is an amazing discovery because it’s the first time this type of turtle has been found in the UK,” said Dr. Megan Jacobs, a paleontologist at the University of Portsmouth.
“Even more exciting is that we used a new technique of radiometric dating to determine the age of the fossil beyond any doubt.”
“And to top it off, CT scanning revealed all the tiny bones inside. It’s really incredible for what looks like a rolled beach pebble!”
The 127-million-year-old partial skeleton of Eodortoka cf. morellana from the Wessex Formation, the Isle of Wight, the United Kingdom. Image credit: Jacobs et al., doi: 10.1016/j.cretres.2023.105590.
Dr. Megan and colleagues dissected minerals from inside the turtle shell and analyzed them for uranium and lead.
By measuring the ratio of lead to radioactive uranium, they established the turtle was from the Early Cretaceous epoch, around 127 million years ago.
They identified it as Eodortoka cf. morellana, a species of dortokid turtle previously known from Spain.
“We’ve nicknamed the turtle ‘Burby’ after Steve who very kindly donated the specimen to the Dinosaur Isle Museum at Sandown on the Isle of Wight,” Dr. Jacobs said.
The paleontologists also used cutting-edge micro CT scanning to discern various tiny bones.
This advanced imaging technique provided invaluable insight into the structure and composition of the turtle’s shell, without damaging it.
“It’s beyond my wildest dreams to have one of my finds published. I could never have guessed it was such an incredibly important fossil. It’s so wonderful to see all the tiny bones inside too,” Burbridge said.
“It is exciting that we have been able to use cutting edge radiometric dating techniques to provide absolute constraints for this important sequence for the first time,” said University of Portsmouth’s Dr. Catherine Mottram.
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Megan L. Jacobs et al. 2023. A well preserved pan-pleurodiran (Dortokidae) turtle from the English Lower Cretaceous and the first radiometric date for the Wessex Formation (Hauterivian–Barremian) of the Isle of Wight, United Kingdom. Cretaceous Research 150: 105590; doi: 10.1016/j.cretres.2023.105590
