Wednesday, December 20, 2006

Sauropods: No Gastic Mills

No gastric mill in sauropod dinosaurs: new evidence from analysis of gastrolith mass and function in ostriches. 2006. O. Wings and P. M. Sander. Proceedings of the Royal Society B: Biological Sciences, early on-line publication.
Sauropods did not have a 'gastric mill.' How they processed their food without molars remains unclear.
From the press release:

Giant dinosaurs had a problem. Many of them had narrow, pointed teeth, which were more suited to tearing off plants rather than chewing them. But how did they then grind their food? Until recently many researchers have assumed that they were helped by stones which they swallowed. In their muscular stomach these then acted as a kind of 'gastric mill'. But this assumption does not seem to be correct, as scientists have now shown that some dinosaurs did not have gastric mills such as some living birds have.

For their investigations, the scientists therefore offered stones such as limestone, rose quartz and granite as food to ostriches on a German ostrich farm. After the ostriches had been slaughtered, the scientists investigated the gastric stones. It became clear that they wore out quickly in the muscular stomach and were not polished. On the contrary, the surface of the stones, which had been partly smooth, became rough in the stomachs during the experiments.

'Whereas occasionally stones were found together with sauropod skeletons, we don't think they are remains of a gastric mill such as occurs in birds,' Dr. Sander comments. In that kind of gastric mill the stones would have been very worn and would not have a smoothly polished surface. Apart from that, gastric stones are not discovered regularly at sauropod sites. When present, their mass is, in relation to the body size, much less than with birds.

Yet what else were the dinosaurs' gastric stones used for? The researchers presume that they were accidentally eaten with their food or could have been swallowed on purpose to improve the intake of minerals.

There is another group of dinosaurs, however, whose remains of gastric stones can be linked up with a birdlike gastric mill. From these theropods today's birds developed. The gastric mill could therefore have developed in the ancestral line of birds.