How dinosaurs chewed

Rev. Merry Bear Koehl, Elberton, GA. — Mon, 29 Jun 2009 22:37:04 GMT

Not trying to sound like a Vulcan, but... Fascinating!

How dinosaurs chewed

Tom Churchill — Tue, 30 Jun 2009 04:09:00 GMT

Why can't you use the rover arm to help lift the rover up while turning the wheels on the other side to free it up

How dinosaurs chewed

Marty, Auckland — Tue, 30 Jun 2009 11:53:46 GMT

I'd love to see a diagram of this "hinge between the upper jaws and the rest of the skull"...

How dinosaurs chewed

Big J — Tue, 30 Jun 2009 14:14:42 GMT

Why all the hoopla.They could have just asked Nancy Pelosi who was around when these big guys roamed the earth,

How dinosaurs chewed

Eric, Salinas, CA — Tue, 30 Jun 2009 18:41:36 GMT

Finally an article we can really sink out teeth into Alan! Really interesting how scientists figure out how dinosaurs lived, ate and did all the things they did. I have a feeling that Hadrosaurs searched high and low for food. If they didn't find good grazing around the ground they probably looked up and ate from the trees. Always fascinating to see what new knowledge the scientists can glean from such old fossils.

How dinosaurs chewed

Richard, East Northport, NY — Tue, 30 Jun 2009 20:06:09 GMT

Big J,
Didn't you know that Sarah Palin can see hadrosaurs from her house?

How dinosaurs chewed

C. O., Wisconsin — Tue, 30 Jun 2009 21:10:33 GMT

I hate to point this out, but...
There have been several hadrosaur skeletons that have been found with preserved stomach contents, from several different localities and geologic ages. The stomach contents almost always have needles of Metasequoia trees in them. To state that these animals would have solely eaten low vegetation is ignoring the facts that the dinosaurs themselves show us. Perhaps the next project for this group of scientists would be to examine the stomach contents from these specimens, and determine if there is another line of evidence that can support what they say. If these animals ate plants with lots of silica in them, remnants of those plants should still be preserved too.
Also, to say that the chewing mechanism was completely different than anything known today, then say that the wear patterns are consistent with a modern animal that eats grass doesn't really hold much water. If the mechanism is different (which I completely agree with), it doesn't necessarily hold that a modern mammalian analogue will be all that informative, or that a comparison between the two will be very constructive.
It would be wise for news outlets to take into account whether or not a story actually has merit before publishing it for everyone to see. Many articles about dinosaurs are based on weak science, and mislead people about how much we know, and how much we CAN know about these wonderful animals.

How dinosaurs chewed

Alan Boyle — Tue, 30 Jun 2009 23:55:50 GMT

The claims about grazing vs. browsing are certainly not conclusive, C.O., but I think they're worth reporting. I think I do point out that the evidence goes both ways. I'm not going to pass up this kind of research (published in PNAS) just because some of the claims are still subject to debate. I asked Purnell about the stomach contents issue, and he said one of the questions about the contents would be whether or not those contents represented the usual diet of the animal. I didn't spend any time on that issue, however, primarily because it probably gets too deeply into the debate. Better to say that the evidence isn't solid and leave it at that. (I don't think I said the dinosaurs "solely" grazed, just that the researchers' surmise is that they were more likely to graze.) Purnell also said the type of wear seen with browsing animals was more along the lines of pits rather than scratches - but again, that's coming from Purnell's perspective. The important thing, I suppose, is to say that the question is somewhat unsettled. This NPS Web site, for example, says that hadrosaurs "probably grazed on all fours, but ran (or fled) upright on their back two legs" ... which makes the question sound more settled than it really is.

http://www.nps.gov/akso/parkwise/Students/
ReferenceLibrary/Paleontology/Hadrosaurs.htm

How dinosaurs chewed

~ender, Black Rock City, Playa — Wed, 01 Jul 2009 04:25:22 GMT

Perhaps eating tree needles was a poisonous act, which is why those stomach contents are preserved in the corpses? Or maybe they were indiscriminate grazers, and hoovered up whatever was around? Or, perhaps needles were acidic (like pine needles) and killed off competing plant growth leading to delicious tender shoots of good stuff growing up between the needles? Perhaps the hypothetical acidity was needed to balance their pH, just like some dinosaurs needed to eat rocks in order to grind up vegetable matter? Lots of reasons you could have needles in your stomach.

How dinosaurs chewed

Tim Rommes, Washington, UT — Wed, 01 Jul 2009 05:36:19 GMT

Tom Churchill (6/30, 0009)
That issue has been addressed by several people on the page you were reading.

C.O., Wisconsin (6/30, 1710)
“Also, to say that the chewing mechanism was completely different than anything known today, then say that the wear patterns are consistent with a modern animal that eats grass doesn't really hold much water.”
I’m not sure what you’re talking about. They do seem to have chewed in a way completely different way than anything alive today. After reading the whole article my attention hovers on, “But the dinosaurs didn't have the complex jaw joint that mammals have, leaving scientists to puzzle over exactly how hadrosaurs did all that chewing.” So then I wonder at what those “wear patterns are consistent with a modern animal that eats grass.” That complex jaw enables grinding which doesn’t happen with a jaw that swings like a door. Modern animals with complex jaws are able to grind food between flat teeth on opposing jaws that slide horizontally to each other. The wear patterns from this type of jaw, I expect, would be quite similar to the wear pattern on a jaw where “the tooth surfaces slid sideways across each other, grinding and shredding food in the process." It seems to me that the argument is a water holding bucket.

How dinosaurs chewed

John Burkitt — Wed, 01 Jul 2009 12:10:11 GMT

Maybe they weren't obligate browsers or grazers but did a bit of each? Maybe it varied by population or season? Think, folks, do humans eat meat or do they eat potatoes?

How dinosaurs chewed

G NelsonAlbuquerque, NM — Wed, 01 Jul 2009 12:50:47 GMT

Big J: Perhaps someone can study the dentition of a still living dinosaur...Rush Limbaugh.

How dinosaurs chewed

C.O., Wisconsin — Thu, 02 Jul 2009 18:05:04 GMT

Great comments in reply, folks! This is cool!

Anyhow, to re-join the debate...
I do believe that these studies have merit. However, I would like to see multiple lines of evidence used to answer a question like this, rather than only one approach. To say there are scratches on their teeth is one thing, and people have been working on this for quite some time. To say there are tooth scratches that are associated with siliceous plant remains that were found in the same individual animal's stomach contents is quite a bit stronger statement. At that point, inferences can be made that are much easier to defend.

The reason that I said that the comparison between tooth wear patterns doesn't hold water is that duckbill dinosaur teeth slid past one another in a much more vertical plane than do modern mammal teeth. Most of the actual surface that would be considered a "grinding" surface in duckbill teeth was actually made of dentine, which is much easier to damage and wears much faster than enamel. Modern herbivorous mammal teeth have a thick enamel cap on the teeth, which is especially suited to eating silica-rich plants. Between a different chewing mechanism, and grinding surfaces that are essentially different in composition, the comparison between dinosaurs and mammals is a bit weak *in my opinion*. Whatever duckbills ate, their teeth sure did get worn out fairly quickly. Personally, I would say that the incisors in rodents are functionally more similar to duckbill teeth than are molars in large herbivores.
Thanks for commenting everyone!