Dinosaurs got munchies for grass

[Keevan_Colton]

A study of fossil dinosaur dung has for the first time confirmed that the ancient reptiles ate grass.

Grass was previously thought to have become common only after the dinosaurs died out 65 million years ago.

But grasses were probably not a very important part of dinosaur diets - the fossilised faeces show the big beasts ate many different types of plants.

However, the Science journal study suggests grass was possibly an important food for early mammals.

Caroline Strömberg from the Swedish Museum of Natural History and her colleagues studied phytoliths (mineral particles produced by grass and other plants) preserved in fossil dinosaur dung from central India.

Theory dumped

The 65-67 million-year-old dung fossils, or coprolites, are thought to have been made by so-called titanosaur sauropods; large, vegetarian dinosaurs.

Fossil phytolith
Fossil grass phytoliths were found in the dinosaur dung
"It's difficult to tell how widespread [grass grazing] was," Ms Strömberg told the BBC News website, "Dinosaurs seem to have been indiscriminate feeders."

The study also sheds new light on the evolution of grass. Grasses are thought to have undergone a major diversification and geographic proliferation during the so-called Cenozoic, after the dinosaurs had gone extinct.

But the researchers found at least five different types of grass in the droppings.

This suggests grasses had already undergone substantial diversification in the Late Cretaceous, when the giant beasts still walked the Earth.

Defence mechanism

Many grasses today contain high levels of silica, which makes them tough and hard to chew. One theory proposes that this is an evolutionary defence against being eaten by herbivores.

This defence is traditionally thought to have been a response to large-scale grazing by mammals in the Cenozoic. But, if the theory is correct, it raises the possibility that grasses first began developing this defence in response to grazing by dinosaurs.

However, small mammals living alongside the dinosaurs may also have been grass feeders.

An enigmatic group of extinct mammals known as sudamericid gondwanatherians, which lived during the Late Cretaceous, show possible signs of adaptation to a grassy diet.

Their teeth are ideally suited for handling abrasive materials like grass. But because of grass's patchy presence in the fossil record, these features were interpreted as an adaptation to a semi-aquatic, or burrowing, lifestyle like that of modern beavers.

link

[wolveraptor]

I don't think small mammals could consume grass as a regular part of their diet. Other herbivores that eat grass have huge digestive tracts that process the tough material. Small animals don't have that luxury.

[Gil Hamilton]

The image of an stegosaurus smoking a phatty and looking real melvin popped up in my mind when I read that title.

Anyway, that's neat.

[LadyTevar]

I don't think small mammals could consume grass as a regular part of their diet. Other herbivores that eat grass have huge digestive tracts that process the tough material. Small animals don't have that luxury.

Forgive me, but I thought that animals like prairedogs, groundhogs, and other small rodents were grass-eaters.

[wolveraptor]

You're right. 61% of a prarie dog's diet is made up of grass. That's a percentage significantly lower than cows, though.

[LadyTevar]

You're right. 61% of a prarie dog's diet is made up of grass. That's a percentage significantly lower than cows, though.

True, but there's a good chance it echoes the early mammal's diet, and 61% is high enough for some evolutionary change to develop to allow for easy digestion.

If you want to get technical, any mammal *can* eat grass; cats and dogs eat it to help stomach ailments, but only a few can digest it properly.

[Darth Raptor]

Titanosaurs are sauropods. Their teeth were simple pegs and they employed a "bite and swallow" method of ingestion. Gastroliths and symbiotic microbes did the bulk of their food processing. I suppose this really depends on whether they or their bacteria had the enzymes necessary to break down silica. Still, this is strange because I would have thought ornithischians, who have teeth for proper chewing, would have adapted to grass first.

Although, this doesn't necessarily mean titanosaurs got any nutritional value from the grass they ate. They probably just ate everything in sight, and the grass got plucked up with the ferns they were really after.

[wolveraptor]

Still, this is strange because I would have thought ornithischians, who have teeth for proper chewing, would have adapted to grass first.

They might have. We've only found titanosaurids that ate grass. That doesn't mean ornistchians didn't first. Commonly known species such as Iguanodon probably didn't have abundant grass growth in their area.

[Darth Raptor]

They might have. We've only found titanosaurids that ate grass. That doesn't mean ornistchians didn't first. Commonly known species such as Iguanodon probably didn't have abundant grass growth in their area.

Iguanodonts enjoyed a nearly worldwide distribution by the end of the Cretaceous, although Iguanodon itself was long extinct by this time. Of all the dinosaurs to become grass-grazers I would have put my money on hadrosaurs, with ceratopsians coming in a close second. The rows and rows of constantly growing and replaced teeth are already there. It doesn't take much of a stretch to go from waxy cycad fronds to tough grasses. They wouldn't need miles and miles of intestines like the sauropods had- and may have developed rumination later (if they didn't have it already).

[wolveraptor]

Yes, but corprolites we've obtained from hadrosaurs have never shown a diet full of grass. I was just assuming that was because we'd never found ones in the right places.

[Darth Raptor]

Yes, but corprolites we've obtained from hadrosaurs have never shown a diet full of grass. I was just assuming that was because we'd never found ones in the right places.

Another thing to consider is that they may have been much more discriminate feeders than sauropods- simply passing up the more rare and relatively useless grasses for the better herbs that were still abundant at the time.

[wolveraptor]

If so, then maybe ankylosaur corprolites would be more likely to contain grass. Surely their wide mouths and low statures would've made them candidates.

[Darth Raptor]

If so, then maybe ankylosaur corprolites would be more likely to contain grass. Surely their wide mouths and low statures would've made them candidates.

You run into the problem of them being able to extract nutrition from them- again. Ankylosaurs don't approach the dental sophistication of ceratopsians and hadrosaurs- or even iguanodonts really. If memory serves, ankylosaur mouths are just more flat and broad than that of stegosaurs. Not saying they didn't eat it- they probably did (where available) just that it's little more than ruffage for them. Same with the titanosaurs though, really.

Grass was simply too new- and too rare for it to be a large, deliberate part of any dinosaur's diet. Had the KT catastrophe not occured the story would be different, their would be an explosive proliferation of grass-grazing dinosaurs in the early Tertiary.

In fact, that reminds me of a book I read ages ago in which Dougal Dixon speculated on dinosaur evolution had they survived. He postulated that lithe, fleet-footed titanosaurs would have dominated South America, but most of the grazers elswhere were iguanodonts.