New Fossil sheds light on the origins of Triceratops, Stegosaurus and Iguanodon

Dinosaurs are divided up into two main groups, these are called Saurischians (lizard-hipped) and Ornithischians (bird-hipped).   There are a number of different features that distinguish these two groups but put simply each group of dinosaurs had a different layout of their hip bones.  In bird-hipped dinosaurs such as Stegosaurus and Triceratops, two hip bones – the ischium and the pubis point backwards.  In lizard-hipped dinosaurs such as Allosaurus and Diplodocus these two bones point in different directions.

This classification of dinosaurs was made in the 19th Century, before scientists realised that birds are closely related to dinosaurs, it is the lizard-hipped dinos that gave rise to the birds, not the bird-hipped dinosaurs as you might suppose.  The classification of dinosaurs is full of complications such as this, mainly because it is a bit of a “moveable feast”.  Improvements in research and new techniques coupled with more fossils means that scientists are adding to their knowledge all the time and some of the old established science is now being re-thought and re-written.

Anyway, a number of radio, TV and newspapers covered the story yesterday of the discovery of a new dinosaur called Eocursor claiming that this animal was a breakthrough in our understanding of the evolution of the bird-hipped dinosaurs.

The fossil was unearthed in the Karoo basin region of South Africa in 1993.  The Karoo basin is a very important part of the world for palaeontologists, this large area has a thick sequence of sedimentary rocks laid down between 260 mya – 190 mya, representing time from the mid Permian right through to the early Jurassic.  Little is known about the origins of dinosaurs, the earliest fossils date back some 230 million years, this new fossil is around 210 million years old.  It is important because this single specimen (backbones, lower jaw, limb bones and most importantly of all – the pelvis) shows the backward pointing bones in the pelvic area of an Ornithischian.  This fossil will help shed some light on the early evolution of the Ornithischia.

Eocursor, or to give it its proper species name Eocursor parvus (little, early runner), was a small, agile, plant-eater.  It was about the size of a dog and had teeth suited to eating plants, relatively long arms and hands, perhaps indicating that it moved around on all fours, but the hands may have been useful for grasping foliage as it fed.  The long hind legs and the light skeleton suggest that it was a swift runner, getting up onto its back legs and using its speed to avoid the slower predators such as the mammal-like cynodonts or the primitive crocodile-like Archosaurs

Although the remains were first uncovered in 1993, the skeleton has only recently studied and its significance had not been realised.

 Eocursor parvus (Scott Harman www.skeletaldrawing.com)

Picture depicting what Eocursor may have looked like taken from BBC News (Artist Scott Hartmann).

In a comment made by Dr Paul Barrett of the Natural History Museum  he stated; “the earliest dinosaurs we know are about 228 million years old, so this one is only just a bit younger than this”.

“The fossil record for early meat-eating dinosaurs is slightly better; and for some of the other plant-eaters, we also have not-too-bad a record. But for the ornithischians, we have almost nothing; so in that sense, this is a major find.”

The assessment of the work carried out by Dr Richard Butler (Natural History Museum) and his co-researchers at the Iziko South African Museum in Cape Town and the University of the Cambridge (UK) is reported in Proceedings of the Royal Society B: Biological Sciences.

Little Eocursor parvus may help palaeontologists shed some light onto the evolution of the Ornithischians, the part of the dinosaur family tree that gave rise to the Stegosaurs, Triceratops and Iguanodon.

When Eocursor roamed the earth, during the Triassic period, all the continental plates were pushed together to form one super-sized land mass called Pangaea, but not a lot is known about the evolution of herbivorous dinosaurs, indeed perhaps the best known early Ornithischian dinosaur is Fabrosaurus which lived during the early Jurassic, a few million years after Eocursor.

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