Fossils: Early ancestor of diplodocus ran on its back legs and used its forelimbs to grasp FOOD

A 205 million year old ancestor of the famous, slow-moving, long-necked dinosaur diplodocus, ran on two hind legs. It used its forelimbs and grasped food with its forelimbs.

University of Bristol scientists have reached this conclusion after reconstructing the limb muscles of Thecodontosaurus (a small dinosaur that lived in Thecodontosaurus in the Triassic).

The team believes that the findings help to explain how giant, quadripedal sauropods such as the diplodocus, which measures 100 feet in length, evolved from Thecodontosaurus, a wolf-sized animal.

One of the earliest ancestors of the famous, long-necked dinosaur diplodocus ran up its back and used its forelimbs in order to grab food around 205 million years ago. Illustration of Thecodontosaurus showing its leg muscles.

The University of Bristol scientists concluded that the muscles of Thecodontosaurus’ left limbs were intact. The dinosaur was known to have lived in the UK during the Triassic. Pictured: Fossils of Thecodontosaurus’ left ilium (top and bottom left) and left ischium (right) bones

The team stated that the findings help to explain how huge, quadripedal sauropods such as the diplodocus, which measures 100 feet in length, evolved from Thecodontosaurus, a wolf-sized animal.

Antonio Ballell (palaeobiologist) and his colleagues at the University of Bristol School of Earth Sciences conducted this research. 

‘The University of Bristol houses a huge collection of beautifully preserved Thecodontosaurus fossils that were discovered around Bristol,’ said Mr Ballell.

“The remarkable thing about these fossilized bones, is that most preserve the scars or rugosities left by the limb muscle with which it was attached.

These features — when well enough preserved — can be used in tandem with an understanding of the musculature of closely-related, living species to infer the shape and direction of the limb muscles, the team explained. 

‘For the study of dinosaurs, it is necessary to examine modern crocodilians as well as birds. These forms a group which we call archosaurs. It means “ruling reptiles”. Dinosaurs are extinct members of this lineage,’ added Mr Ballell.

“Due evolutionary resemblance we can compare muscle anatomy in birds and crocodiles, and then study the scars left by the bones. This allows us to reconstruct and identify the positions of the muscles in dinosaurs.

Emily Rayfield, palaeontologist as well as co-author of this paper said: “These types of muscle reconstructions are fundamental for understanding functional aspects of the extinct organisms’ lives.”

“We can use these information to simulate the movements and running of these animals using computational tools.”

 ‘The University of Bristol houses a huge collection of beautifully preserved Thecodontosaurus fossils that were discovered around Bristol,’ said palaeobiologist Antonio Ballell. Pictured: an artist’s impression of Thecodontosaurus, with a human silhouette for scale

“The incredible thing about fossilised bones [pictured] is that many preserve the scars and rugosities that the limb musculature left on them with its attachment,’ Mr Ballell added

These features — when well enough preserved — can be used in tandem with an understanding of the musculature of closely-related, living species to infer the shape and direction of the limb muscles, the team explained. Pictured: sketches of Thecodontosaurus’ limb bones, showing muscle attachment sites (origin sites in red, insertion in blue)

From the inferred orientation and size of Thecodontosaurus’ limb muscles, the researchers have proposed that the dinosaur was quite agile.

In addition, based on its well-developed elbow flexors and extensors and the limited range-of-motion available at the shoulder, the little dinosaur likely used its forelimbs not to walk on but instead to grasp at objects.

This is quite different to Thecodontosaurus’ giant sauropod relatives, who are thought to have been able to reach such colossal sizes by shifting to a quadrupedal posture that used all four limbs for walking.

But, it was noted by the team that the muscles of the small dinosaur had many similarities to its bigger relatives. 

This included a reduction of the brevis fossa and shelf on the upper part of the hip bone, and a possible reversal of the M. iliofemoralis — a hip abductor muscle — which could have helped to enabled the switch to quadrupedalism.

‘From an evolutionary perspective, our study adds more pieces to the puzzle of how locomotion and posture changed during the evolution of dinosaurs and in the line to the giant sauropods,’ said paper author and palaeontologist Mike Benton.

“How did limb muscles change in evolution from small bipeds to multi-ton quadriplegics?” he questioned.

“Reconstruction of Thecodontosaurus’s limb muscles gives us fresh information about the beginning stages of this important evolutionary transition.”

Royal Society Open Science has published all of the findings.

SAUROPODS LONG-NECKED, SMALL-BRAINED DINOSAURS

Sauropods was the first group of herbivorous dinosaurs to succeed. The Sauropods ruled most terrestrial ecosystems for over 140,000,000 years. 

Their necks were long and their tails were short. They also had small skulls.

The elephants could reach 130ft (40m) in length and were up to 80 tons (80,000kg), which is 14 times as heavy as an African elephant.

Sauropods was the first group of herbivorous dinosaurs to succeed. The Sauropods ruled most terrestrial ecosystems for over 140,000,000 years.

They were common – they are found on every continent except Antarctica.  

Their nostrils were located higher than other terrestrial vertebrates’, high above their skulls. 

A few fossils show that the nostril openings of these skulls extended so far that they are very near the eye openings. 

Sauropods like the Diplodocus started to diversify around 180 million years ago in the Middle Jurassic. 

Source: University of California Museum of Paleontology