Abydosaurus – Skull Material in mid Cretaceous Sauropoda

Sauropod skull material is a bit like London buses, you wait ages for one to turn up and then four come along at once.  Thanks to a discovery in Utah (United States), scientists at Brigham Young University have an embarrassment of riches of Sauropod skull material to work on at the moment and all the skull material belongs to a single, new dinosaur genus – Abydosaurus.

Skull material in long-necked dinosaurs (Sauropods) is exceptionally rare in the fossil record, less than 10% of all the articulated or associated long-necked dinosaur fossils ever discovered actually have some skull material present at the dig site.  The reason for this is quite simple, take an animal such as Diplodocus, this Diplodocid dinosaur could reach lengths in excess of 25 metres, but even in an immense adult; the head was no bigger than that of a horse’s head.  So the heads were relatively small and being on a long, thin neck, skulls were prone to fall off any carcase, becoming detached.  Femurs, and vertebrae being much heavier than the skull bones have a greater chance of remaining close to other bones and surviving the preservation process.  These heavy bones are much more common than the skull.  Some Sauropods, the early Cretaceous Nigersaurus from West Africa, for example, had an exceptionally light and delicate skull.  The thin struts of bone that make up part of the skull material would only very rarely have survived the fossilisation process.  Even famous mounted exhibits in Natural History museums do not necessarily have the right head posed on the rest of the Sauropod’s body.  For example, there  have been instances where both Apatosaurus and Diplodocus exhibits have had casts of Camarasaurus skulls (a Macronaria-type Sauropod) stuck onto them.  This in the past was down to ignorance, or in some cases deliberately done to finish off an exhibit even though scientists were actually unaware at the time of what Diplodocid dinosaur skulls looked like.

Rare Things Indeed – Sauropod Skull Material

Picture Credit: Illustration by Michael Skrepnick

But why all the fuss about skull material, surely with several tonnes of fossil bones to be getting on with in your average Sauropod skeleton, that’s enough to keep even the most grumpy palaeontologist happy.  True, but skulls can tell scientist a great deal about an animal.  If the jaws are present an insight into diet and feeding behaviour can be obtained.  Studies into the braincase can be carried out and very importantly skull material can help establish whether the fossils represent a new genus or species of a dinosaur in many cases.

A paper on the new Brachiosaurid dinosaur named Abydosaurus mcintoshi was published yesterday in the German science publication Naturwissenshaften.  The research paper was compiled by scientists at Brigham Young University and this new mid Cretaceous Brachiosaurid is significant not just for the skull material associated with it, but because Brachiosaur fossils are increasingly rare in younger Mesozoic strata.   The Brachiosaurs seemed to have had their hey day in the late Jurassic, but over the course of the Cretaceous, the main types of Sauropod, such as the Diplodocids and Brachiosaurids become increasingly rare in the fossil record.  The Sauropods were by no means finished, particularly in the southern hemisphere, as the Titanosaurs were about to come to the fore, but the food chains and ecosystems of the Cretaceous were becoming increasingly dominated by herbivorous Ornithischian dinosaurs.

The remains and the fossilised skulls of this new dinosaur, were found at the National Dinosaur Monument site in Utah (United States), not in the famous Morrison Formation, but in much younger, sandstone rocks dating from around 105 million years ago (Albian faunal stage) – the Cedar Mountain Formation.

Finding just one skull would be impressive, but four is beyond what any dinosaur hunter could hope for.  The skulls revealed jaws crammed with dozens of tiny, peg-like teeth.

Commenting on the skull material, Professor Brooks Britt, a geologist at Brigham Young University stated:

“It’s quite a fortuitous thing.  In many dinosaurs, the bones of the head do not fuse up, especially in Sauropods.  You have an array of components that are held together by soft tissue.  The only thing that stays together is the brain case.”

National Park Service employees first discovered an interesting cache of bones near the monument’s visitor’s centre in the late 1990s and enlisted Professor Britt’s help to prepare the specimens.  After the initial find, park staff delivered a two-tonne block to Brigham Young’s University Museum of Palaeontology.  Dinosaur bones, including pieces of a skull, were apparent on the surface, but as the researchers carefully prepared the sandstone block, a second almost complete skull was revealed.

An Artist’s Impression of Abydosaurus mcintoshi

Abydosaurus

Picture Credit: Michael Skrepnick

The skulls are on display at the Brigham Young University Museum, where visitors can watch students work on other Abydosaurus bones in the preparation laboratory.

Professor Britt made follow-up trips to the dig site and found a fourth skull in 2003.  All four specimens belonged to juveniles who may have died in the same event and were quickly buried before scavengers and bacteria could destroy the carcasses.   Although it is difficult to estimate the size of an adult Abydosaurus from the fossil remains found so far, the research team have estimated that these animals could have reached lengths in excess of 25 metres.

The teeth of Abydosaurus are most intriguing, in a statement Professor Britt said:

“They [the teeth] are small, small as a triple-A battery cut in half, a centimetre in diameter.  Why is that?  Perhaps the teeth reflect food sources and eating habits, but the small teeth fit a pattern seen over the course of dinosaur evolution from the Jurassic to the Cretaceous.

“There is a trend from large to small teeth, packing them in there close together, not just in Brachiosaurus, but all the Sauropods that survived into the Cretaceous.  In the Jurassic, they had an array of tooth sizes, but in the end everyone has these small pencil-like teeth.  We attribute it to a way to increase the enamel, so their teeth last longer.”

Researchers believe that Sauropod dentition evolved over time to offer a greater surface area of enamel.  This would make them more durable and more hard-wearing when being employed to strip foliage.  It could also be an adaptation that reflects the growing numbers of Angiosperms (flowering plants) that were evolving and beginning to make up an increasing proportion of the diet of these huge animals.

Professor Brooks Britt with one of the Abydosaurus Skulls

Banging heads together

Picture Credit: Mark A. Philbrick/ photo courtesy of BYU

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