New Study Suggests Saturnalia Had a Small Head

The South American sauropodomorph Saturnalia (S. tupiniquim) lived some 233 million years ago.  As dinosaurs go, this 1.4 metre long animal might not be regarded as a superstar of the Dinosauria, it is not likely to be offered a starring role in any new instalment of the Jurassic Park movie franchise, but for palaeontologists, Saturnalia is a very significant dinosaur indeed.  Described twenty years ago, the skeleton of this little dinosaur demonstrates both sauropod and theropod traits and as such, any additional information gleaned about it can cause quite considerable shock waves in palaeontological circles.

A Life Reconstruction of Saturnalia tupiniquim

A life reconstruction of Saturnalia.
New study on the skull Saturnalia suggests it had a disproportionately small head.

Picture credit: Rodolfo Nogueira

New Study Published in the Journal PLOS One

Scientists from the Universidade de São Paulo in collaboration with a colleague from the Universidade Federal de Santa Maria have published a new study of the skull shape and size of Saturnalia in the on-line academic journal PLOS One.  The research team conclude that Saturnalia had a skull less than 10 centimetres in length, quite small in relation to the size of the animal.  Because it had a long neck and a small, lightweight skull, Saturnalia may have been able to move its head very quickly, helping it to secure tiny, elusive prey.  This idea is also supported by a study of the teeth of this dinosaur and brain shape inferred from an analysis of the skull bones.

The Skull of Saturnalia

Analysing the skull of Saturnalia.
The skull of Saturnalia was examined using computerised tomography.  The picture shows the skull elements that were subjected to the CT scan and a line drawing shows a lateral view of the proposed skull of Saturnalia (known fossil elements in green).

Picture credit: Rodolfo Nogueira

Saturnalia with a Reduced Skull

Computerised microtomography was used to assess the shape and structure of the delicate skull fossils still entombed inside their rock matrix.  This non-destructive technique enabled the research team to reconstruct the skull of this dinosaur and to identify the reduced skull.

One of the authors of the scientific paper, Mario Bronzati, postdoctoral fellow at the Department of Biology at the Ribeirão Preto School of Philosophy, Sciences and Letters (Universidade de São Paulo, Brazil) commented:

“It was very difficult to remove the fossil from the sediment in which it was trapped.  Doing so in the traditional way by scraping the sediment could break these bones because they were so fragile.”

Although numerous papers on Saturnalia tupiniquim have been published, little was known about the morphology of the skull.  The three-dimensional images that were created as a result of this analysis provided the researchers with the opportunity to study the head of this dinosaur in detail and the reconstruct the skull of this Late Triassic dinosaur.

A Diagram Showing the Skull of Saturnalia

Saturnalia skull diagram.
A diagram of the skull of Saturnalia (lateral view and dorsal view).

Picture credit: PLOS One

Studying the Skull of Saturnalia

The skull is disproportionately small when compared to the size of the dinosaur’s body.  It is thought that Saturnalia was carnivorous, eating small prey items  such as lizards, mammals and insects, but the consumption of plants cannot be ruled out.  The reduced skull is a characteristic of the Sauropodomorpha lineage and demonstrated in later sauropods such as Diplodocus and Brachiosaurus.  The specialisation of the skull and neck of Saturnalia has implications for the evolution of these lizard-hipped dinosaurs as later forms became entirely herbivorous.

Skull reduction significantly reduced the biomechanical contraints for the development of long necks, in turn, longer necks permitted access to food resources that were unreachable for other plant-eating dinosaurs.  This would have helped to provide a competitive advantage and might explain why later sauropods grew to such large sizes.  Thus, the idea that skull reduction was first acquired in a likely predatory member of the sauropodomorph lineage (i.e. Saturnalia) implies a scenario where a trait related to one habit (faunivory) was crucial for the evolution of a completely different lifestyle (herbivory) in a subsequently different selection regime.

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