CT scans Help Unlock Tyrannosaur Ancestry at Natural History Museum
When we are asked about the best place to find a new species of dinosaur, an answer we often give is to look more closely at fossils already in museum collections. Often, old finds, if subjected to new research techniques can reveal some surprises. This was exactly what happened when a beautifully preserved partial skull and jaws of a meat-eating dinosaur, originally excavated nearly 100 years ago; turned out to be a candidate for the earliest ancestor of the mighty Tyrannosaurus rex.
The fossilised remains, the oldest-known relative of the mighty tyrannosaurs discovered to date, were found in 1910, during the excavations for a new reservoir near the town of Minchinhampton in Gloucestershire. The skull was found in rocks which form part of the Great Oolite limestone formation of the area. These rocks were laid down in a marine environment and along with the Inferior Oolite limestone formation they make up a good proportion of the Cotswolds. The county of Gloucestershire in south-west England is one of the most geologically diverse of all the English counties with outcrops of Cambrian, Devonian, Permian, Triassic and Jurassic aged rocks represented.
Tyrannosaur Ancestry
One of our team members was able to visit a fossiliferous outcrop earlier this year, dating from the Jurassic, Cleeve Hill.
To read the article on fossil hunting at Cleeve Hill: Fossil Hunting at Cleeve Hill.
Fossil Hunting at Cleeve Hill
The “Hideaway” at Cleeve Hill. Picture credit: Everything Dinosaur.
Picture credit: Everything Dinosaur
The lower portions of the skull including teeth are all the remains that have been found of this animal, but other fossils ascribed to theropods have been associated with this area. Since this fossil was found in marine strata, it is very likely that either the animal or its carcase was washed out to sea, perhaps by a flash flood before sinking to the bottom and being quickly covered in fine sediment.
A number of terrestrial animals are known from fossils that have been discovered in marine deposits, recently the femur of a long-necked dinosaur from the Jurassic, a Cetiosauriscus was pieced together from remains found in a Gloucestershire quarry.
To read the article about the recent Cetiosauriscus find: Cetiosauriscus Leg Bone found in Gloucestershire Quarry.
Examining the Skull
The skull was believed to represent a new species of a megalosaur type dinosaur, it was named as Proceratosaurus bradleyi, shortly after its discovery. The fossil skull was presented to the Natural History Museum in 1942 and despite representing one of the best preserved early theropod skulls in the collection, it was not studied in more detail until early in 2009 when a joint German/British team gained permission to subject the skull to CT scans to help reveal more of its internal structure.
Pictures show the fully prepared skull (the original preparation of the specimen has been augmented with more of the matrix removed to help improve the research). The skull is placed facing to the right and the sharp, backward pointing teeth in the jaws have now been fully exposed. The upper portion of the fossil was destroyed by an irregular fissure in the rock, so no other portions of the skull relating to this specimen have been found.
In the original 20th century paper, the dinosaur was identified as a megalosaur, known as a taxonomic waste basket, due to the amount of miscellaneous theropod remains associated with it. The original paper commented on the crushed and flattened state of the fossilised bones, but remarked how fragile, light and delicate the skull was.
The skull seems full of holes, and to the casual observer this is seen as something of a surprise, since they imagine meat-eating dinosaurs to have huge, heavy powerful jaws and heads. Theropod skulls were filled with air sacs, this would have helped to make them lighter. The first hole, above the snout and completely cleared of matrix is the naris (nasal area). A small, triangular bony projection can be seen on the top. This is the bony core of a nose horn, this is what gave this dinosaur its name (Proceratosaurus means “first horned lizard”).
The next opening in the skull is the large antorbital fenestra, this is found behind the naris and in front of the eye socket or orbit. The hole towards the rear of the skull behind the eye is called the laterotemporal fenestra.
The skull measures less than 30 cm long, it probably belonged to an individual no more than 3 metres long, twelve times smaller than its great descendant T. rex.
The fossil was sent to Austin, Texas where it was scanned using CT technology (computed tomography), to create X-rays and then a 3-dimensional computer image to reveal the internal structure of the fossil. The scientists discovered that the teeth, jaws and braincase resembled those of Tyrannosaurus rex, indicating that this humble, Gloucestershire predator may be an ancestor of the giant meat-eaters that survived to the very end of the Cretaceous.
Commenting on the relationship between Proceratosaurus and T. rex, Dr Angela Milner of the Natural History Museum in London stated:
“It was quite a surprise when our analysis showed we had the oldest known relative of T. rex.”
She went on to add:
“We care for over nine million fossils here at the Museum and this discovery highlights the importance of museum collections in current and future research. Fossils collected a century ago can now be studied again with the benefit of much greater knowledge of dinosaurs from around the world.”
To aid the scanning process some of the surrounding matrix was removed. As a general rule, the less dense the fossil, the greater the detail that CT scanning can reveal.
Co-author of the study, which has just been published in the Zoological Journal of the Linnean Society, Dr Oliver Rauhut stated:
“This is still one of the best preserved dinosaur skulls found in Europe. It is really surprising that it has received so little attention since its original description”.
Dr Oliver Rauhut holds dual appointments in the Department of Geological and Environmental Sciences at the Ludwig-Maximilians-Universität (LMU) in Munich and the Bavarian State Collection for Palaeontology and Geology. He is regarded as a leading expert on the taxonomic relationships between theropods.
The use of modern techniques to study fossils found in the 19th and 20th centuries will probably lead to many more amazing discoveries, as Dr Rauhut explained:
“I’m sure that many more tyrannosaurs are still out there to be found. I think we have just scratched the tip of the iceberg so far.”
Perhaps such new research will help to produce a more accurate cladogram of the relationships between members of the Theropoda.
To view models of dinosaurs such as Proceratosaurus and other early theropods: CollectA Age of Dinosaurs Prehistoric Life Models.
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