Fossils of an arm bone and pieces of bone from the back and hips, unpacked from the drawers of London's Natural History Museum, could belong to the earliest dinosaur ever found, scientists report in the journal Biology Letters today.
Fossil of the right humerus (arm bone) of Nyasasaurus parringtoni. The prominent crest (deltopectoral crest), unique to dinosaurs, can be seen on the left.
Named Nyasasaurus parringtoni, the ancient animal was the size of a Labrador dog with a tail more than a metre long. It lived about 245 million years ago, which is 10 to 15 million years before any previously known dinosaur or dinosaur-like creature. This means that dinosaurs evolved much earlier than previously thought, in the Middle rather than Late Triassic.
The fossils were unearthed in the 1930s by Cambridge University’s Rex Parrington, from the Manda Beds near Lake Nyasa (now Lake Malawi), Tanzania, hence the species name. They were studied by former curator Alan Charig in the 1950s during his PhD, and then donated to the Museum. Although he intended to publish this work, he passed away before finishing it.
An international team, including Museum dinosaur expert Dr Paul Barrett, decided to take another look at the fossils. They found dinosaur features in the bones, as Barrett explains. 'Although the material is limited, it is very distinctive and completely unlike that of other contemporary reptiles.'
'In particular, a prominent crest, found on the upper arm bone, is a feature found only in Nyasasaurus and other dinosaurs. This crest would have supported large muscles, associated with strong grasping forelimbs.'
Cross-section of humerus, showing large spaces for blood vessels.
The microscopic structure of the bone tissue also shows a woven texture and large spaces for blood vessels, which indicates that the animal grew quickly, typical of dinosaurs.
The team also studied a second fossil from Iziko South African Museum, Cape Town, South Africa. It contained several bones from the neck of another Nyasasaurus individual that also shows many dinosaur-like features. It was originally described by South African palaeontologist Sidney Haughton in the 1930s, but had been largely overlooked until now.
Because the remains of Nyasasaurus are incomplete, there is still room for debate over its exact relationship with other Triassic reptiles.
The team's analysis suggests that is it is most likely a very early dinosaur, as it shares most features with this group. Barrett adds, 'It is not clear if it belongs to any particular dinosaur subgroup such as the meat-eating theropods or plant-eating sauropodomorphs.'
It is possible that instead of being a true dinosaur, Nyasasaurus might have been a very close relative, lying just outside the dinosaur group. ‘If the newly named Nyasasaurus parringtoni is not the earliest dinosaur, then it is the closest relative found so far,' says Lead author Dr Sterling Nesbitt from the University of Washington.
Section through Nyasasaurus fossil bone showing woven texture.
'The distinction between dinosaurs and some other contemporary reptile groups is getting smaller the more animals we find that are close to this reptile-dinosaur transition,' says Barrett.
'Although we only know Nyasasaurus from fossil fragments, the anatomy of its upper arm bone and hip vertebrae have features that are unique to dinosaurs, making us confident that we’re dealing with an animal very close to dinosaur origin'.
'Dinosaurs started as just one of a number of evolutionary experiments in reptile evolution that were occurring during the Middle Triassic Period.
'They only really took off as a group due to a certain amount of luck, slipping through a major extinction late in the Triassic that took out most of their competitors.'
Whether Nyasasaurus was the oldest dinosaur or oldest dinosaur relative, its discovery has pushed back the timing of when dinosaurs began to evolve.
Nyasasaurus parringtoni may have looked like this early dinosaur, Eoraptor, from Argentina. © De Agostini UK Ltd / Natural History Museum, London
The previous oldest dinosaurs were uncovered from rocks in Argentina that are dated to around 228 million years old. An example is the early dinosaur Eoraptor, which Nyasasaurus may have looked like.
The new research also supports the theory that dinosaurs evolved in southern Pangaea, known as Gondwana, the supercontinent that existed during the Triassic (252 to 201 million years ago). Nyasasaurus was found in Africa which was part of Gondwana along with what is now South America, Madagascar, Antarctica, Australia and India.
The Museum looks after thousands of dinosaur specimens, but as this research shows, there could be even more waiting to be uncovered. Barrett concludes, 'Nyasasaurus highlights the important role of museums in housing specimens whose scientific importance might be overlooked unless studied and restudied in detail. Many of the more important discoveries in palaeontology are made in the lab, or museum storerooms, as well as in the field.'