Aardonyx celestae – The Start of Something Big (Sauropoda)

Scientists have published a report into a recently discovered set of fossilised dinosaur bones that provide clues regarding the evolution of the largest land animals ever to walk the Earth.

A paper written by a joint team of South African and U. S. based scientists on a new dinosaur species, believed to be the ancestor of the Sauropods has been published in the online scientific journal Proceedings of the Royal Society of Biology.  This new species of dinosaur has been classified as a basal Sauropod, a member of the Sauropodomorpha, a group of primitive herbivores from which the huge giants such as Apatosaurus, Diplodocus and  Brachiosaurus evolved.  This new dinosaur has been named Aardonyx celestae, the name is a combination of Afrikaans and Greek which means “Earth Claw”.

The fossils were found in the Northern Free State of South Africa, near the small town of Senekal, in the Bethlehem region.  The fossils represent at least two individuals, both believed not to be fully grown when they died.  The largest specimen is estimated to have measured approximately 7 metres in length.

The fossils reveal a number of characteristics that indicate that this species may have been a transitional species. Elements of the anatomy are characteristic of the larger, later Sauropods.

Matthew Bonnan, a vertebrate palaeontologist at Western Illinois University, one of the authors of the research paper states that this relatively small dinosaur was a Sauropod ancestor with features foreshadowing those of its more famous descendants such as Apatosaurus.

The fossils have been dated to the very early Jurassic, approximately 195 million years ago (Sinemurian faunal stage).  The Sauropodomorphs were the first plant-eating dinosaurs, the earliest forms evolved in the mid Triassic but the fossil record for Triassic Sauropodomorphs is extremely poor.  One of the oldest known Sauropodomorphs was Saturnalia, fossils of which have been found in Brazil.  During the Triassic and early Jurassic the continents we know today as South America, Antarctica, Australia and Africa were joined together to form one single land mass – Gondwanaland.  Theoretically, a primitive dinosaur called have walked from South America to South Africa, perhaps the Sauropodomorphs evolved in the southern hemisphere.

An Illustration of Aardonyx celestae

Picture Credit: Adam Yates

The bones shaded in white indicate those elements of the skeletons that have been recovered from the dig site.  The discovery of most of the skull has helped scientists to understand the taxonomic relationship between this early Jurassic dinosaur and its descendants.

When Matthew and his colleagues studied the length of the rib bones and compared these to the length of the forelimbs, they concluded that the front legs of this dinosaur were capable of bearing considerable weight but for the majority of the time this dinosaur may have adopted a bipedal approach.  In essence, Aardonyx may have been a facultative biped, an animal that walked around on its hind legs, but would adopt a quadrupedal stance (all fours) as and when required.

In biology, the ability to undertake an activity by desire rather than obligation is referred to as facultative.  In this case, the bipedal A, celestae could walk on all fours if it chose to do so.  The later much heavier Sauropods were so large they rarely if changed their quadrupedal stance.

The large number of small pits along the creature’s jawbone suggests that Aardonyx lacked a fleshy cheek that would have constrained how far the creature could open its mouth.  Its wide gape, Bonnan and his colleagues suggest, enabled this dinosaur to grab large mouthfuls of foliage with each bite.  Also, a strip of bone that ran along the base of the peg-like teeth braced them against side-to-side forces produced when the dinosaur stripped foliage from trees.

Commenting on these characteristics, Adam Yates, a palaeontologist at the University of the Wiwatersrand in Johannesburg and lead author in this study stated:

“These features are the first steps on the road to the specialised, bulk-browsing herbivory seen in Sauropods.”

An Illustration of the Skull of A. celestae

Fossil material illustrated

Picture Credit: Matthew Bonnan

The shaded parts of the diagram indicate those parts of the skull that have been discovered to date.  Scientists hope that these South African fossils will shed more light on the evolution of the Sauropods.

It is hoped that more information on the Sauropodomorphs will be revealed when the fossilised remains of Thecodontosaurus are prepared and properly studied.  The best specimen of this English Sauropodomorph that dates from the mid to late Triassic has not been removed from its rock matrix.  However, a recently awarded Heritage Lottery Fund (HLF) grant will enable a complete preparation process to take place.

To read more about the work on Thecodontosaurus: Bristol’s Dinosaur Thecodontosaurus to Rise Again Thanks to Grant

The size and shape of muscle attachments on this dinosaur’s femur indicates that the leg muscles were powerful but that the creature was, for the most part, rather slow-moving, a characteristic certainly shared with its extremely large descendants.  For instance, estimates of the top speed of a dinosaur as big as a Brachiosaur have been as low as 7 kmh, that is slower than most people walk.  However, if you are the size of a three-story house running away is not the best defensive option, not many meat-eaters would be bold enough to tackle a gigantic herbivore such as a Brachiosaur.

Matthew Bonnan stated:

“This dinosaur wasn’t running a lot.  The overall shape of Aardonyx and particular aspects of its limbs, teeth and jawbone are anatomical hints of things to come in later Sauropods.”

Commenting on the discovery, Paul Upchurch, a vertebrate palaeontologist at University College, London said:

“This is a very interesting animal.  The large number of bones recovered from various parts of the skeleton provide a good idea of what the creature might have looked like.”

He went on to add:

“Many of the features expected in a Sauropod ancestor are present in Aardonyx, but they’re combined in an unusual mosaic.  For instance, although the creature had a wide gape that would have allowed it to grab large mouthfuls of vegetation, it had a narrow snout, unlike the broad U-shaped snout seen in most true Sauropods.  This animal is expected, but in an unexpected sort of way.” 

Scientists have predicted that more primitive Sauropodomorphs will be found, hopefully these new South African discoveries will help shed light on the evolution of the Sauropoda and may help palaeontologists to understand the evolution of the Ornithischian dinosaurs as well as the Saurischian dinosaurs.   The most primitive of all dinosaurs, the ancestor of all that was to follow; was probably a small, gracile, bipedal, meat-eater.  Fossils of primitive members of the Sauropodomorpha will help scientists to learn more about the evolution of different types of dinosaur and the radiation of different forms that occurred during the Triassic/Jurassic periods.

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