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'Vegetarian Meat Eaters' by Albertonykus 'Vegetarian Meat Eaters' by Albertonykus
From left to right: Therizinosaurus cheloniformis, Limusaurus inextricabilis, Incisivosaurus gauthieri, and Ornithomimus velox; the one leaping into the air is Troodon formosus; the one perched on Therizinosaurus cheloniformis' head is Ophisthocomus hoatzin

Although commonly known as "meat-eating dinosaurs", theropods actually comprise a number of dinosaurs that eat plants, making these dinosaurs "vegetarian meat eaters".

The most cited of these "vegetarian meat eaters" are the therizinosaurs. Most therizinosaurs were almost doubtlessly plant eaters, even though they had giant claws, which were probably for warding off predators and pulling branches towards their mouths. This has led some to nickname them "sloth dinosaurs", as the recently extinct ground sloths seem to have had a similar lifestyle. Their legs were short and not good for running, their teeth were small and blunt, and they seem to have had long intestines to house micro-organisms and digest plant material.

Also well known for (possibly) eating plants are the ornithomimosaurs, or ostrich dinosaurs. It isn't easy to tell what these enigmatic theropods ate because they either have very small teeth or none. However, they are often compared to ostriches and may well have eaten similar foods: plants, and occasionally small animals. Some ornithomimosaurs have been found with stones in their gut, which indicate that they probably did eat at least some plants, because many plant-eating dinosaurs are known to have eaten stones to help grind vegetation.

Another group of theropods which may have been plant eaters are the oviraptorosaurs. The diet of the oviraptorosaurs are something of a mystery, because, like the ornithomimosaurs, many of them don't have teeth, and these show various adaptations for a predatory lifestyle. In fact, a lizard was found fossilized in the stomach of Oviraptor philoceratops. However, those oviraptorosaurs that did have teeth seem to have eaten mostly - or perhaps even only - plants. Incisivosaurus gauthieri for example had rodent-like incisor teeth that show wear patterns similar to those of plant-eating dinosaurs.

Troodonts were a group of small dinosaurs closely related to birds and dromaeosaurids (and, together with the latter, are popularly dubbed "raptor dinosaurs). They had features that hint at both plant- and meat-eating. They had long legs and excellent senses of sight and hearing for tracking down small prey, but they also had short wings that were little good for hunting and their teeth were generally not blade-like and serrated but leaf-shaped and bumpy.

Needless to say, many modern birds eat plants, though few exclusively so. One exclusively plant-eating bird is Ophisthocomus hoatzin, a medium-sized bird found in the swampy forests of South America. It eats mainly fruit, flowers, and leaves, and is unique in having a crop that serves as a rumen, a cavity that is filled with plant-digesting bacteria.

Among the strangest of the plant-eating theropods was Limusaurus inextricabilis. All the other theropods discussed above belong to the coelurosaurs, or fuzzy theropods. Limusaurus inextricabilis, however, was a ceratosaur, and not particularly closely related to the coelurosaurs. All other known ceratosaurs seem to have been meat eaters, but Limusaurus inextricabilis had a beak that was short, blunt, and weak - in other words, little use for eating meat.
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:iconspongebobfossilpants:
SpongeBobFossilPants Featured By Owner Jan 5, 2015
Although it might not be as informative, would you be interested in doing a piece on dinosaurs with highly specialized feeding adaptations (Nigersaurus, Phoenicopterus, etc.)?
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:iconalbertonykus:
Albertonykus Featured By Owner Jan 5, 2015
Not likely to be a top priority for me, but I won't discount it.
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:iconspongebobfossilpants:
For how many of these are stomach contents known? I remember Mickey Mortimer saying that some of the anatomical characteristics used to diagnose herbivorous theropods are also present in Haliaeetus.
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:iconalbertonykus:
Albertonykus Featured By Owner Nov 17, 2014
Excluding preservation of gastroliths, gut contents are known for ornithomimosaurs (fish in Deinocheirus), oviraptorosaurs (lizards in Oviraptor, seeds in Ningyuansaurus), troodonts (seeds in Jinfengopteryx), and avialans (great variety of diets found in extant species needless to say, and some fossil taxa known to have fed on fish, seeds, tree sap, etc.). Perhaps it's ironic that many of them include animal material, but plants don't appear as likely to preserve as gut contents and it doesn't surprise me that these groups are not the strictest of herbivores. The presence of numerous small gastroliths, which many maniraptoriforms also have, may be a good indicator of a substantial diet of vegetation. I don't believe there is much opposition towards the broad notion that most maniraptoriforms were less hypercarnivorous than other theropods from anybody involved in the field, Mortimer included.

Zanno had an exchange with Mortimer over her comments starting here, which may be of interest.
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:iconspongebobfossilpants:
Is there a consensus on how much meat (if any) ornithomimosaurs ate?
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:iconalbertonykus:
Albertonykus Featured By Owner Jul 16, 2014
Not that I'm aware of.
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:iconspongebobfossilpants:
Any chance therizinosaurs were dinosaurian pandas (that is, that they ate plants to feed on small animals hiding in the foliage)?
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:iconalbertonykus:
Albertonykus Featured By Owner Nov 15, 2013
It's possible they ate small animals opportunistically, but I'd like a source for pandas primarily eating bamboo for the associated protein, because I haven't been able to find any such indication from a cursory literature search.
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:iconspongebobfossilpants:
I saw someone mention it on Stock Animal Diet on TV Tropes; I'll PM him to see if he has any references.
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:iconalbertonykus:
Albertonykus Featured By Owner Nov 15, 2013
I saw that as well. Would be very interesting if true, though I can't help but be skeptical for now.
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:iconacepredator:
acepredator Featured By Owner Jan 25, 2015
I believe I have seen a clip of a panda killing a nearly dead lamb....
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:iconalbertonykus:
Albertonykus Featured By Owner Jan 26, 2015
I'm aware they eat meat, but it doesn't follow that they eat bamboo for the sake of obtaining protein (which was the claim being disputed).
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:icondarthgojira:
DarthGojira Featured By Owner Jun 22, 2012
Am I the only one who wants to see a documentary featuring a Styracosaurus stalking and killing a Troodon?
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:iconrandomdinos:
randomdinos Featured By Owner Dec 10, 2013  Hobbyist Traditional Artist
Well, I wanted to see a Shantungosaurus do the exact same thing to a Achillobator, does it count?
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:iconspongebobfossilpants:
Oops, I meant "Idiots".
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:iconspongebobfossilpants:
"Some ornithomimosaurs have been found with stones in their gut, which indicate that they probably did eat at least some plants, because many plant-eating dinosaurs are known to have eaten stones to help grind vegetation."

Care to provide me with a link? I need to show this to the didiots at Braingle.com...
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:iconalbertonykus:
Albertonykus Featured By Owner Nov 12, 2011
Here you go: [link]
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:iconkiibie:
Kiibie Featured By Owner Aug 15, 2009  Student Digital Artist
Aww cute :love: good job! :D ...even if I didnt read your text sorry :hmm:
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:iconalbertonykus:
Albertonykus Featured By Owner Aug 15, 2009
Thank you! I tried to make them cute. (Especially the Troodon formosus.)

That's okay. I know I probably typed too much information for everyone to stomach in one go.
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:iconkiibie:
Kiibie Featured By Owner Aug 15, 2009  Student Digital Artist
Your welcome :D

Yeah probably, but hey it's better to write too much than not enough :D
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:iconalbertonykus:
Albertonykus Featured By Owner Aug 15, 2009
Good point. I had to write some explanation for the strange title for people that aren't so dino-savvy. XD
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:iconkiibie:
Kiibie Featured By Owner Aug 15, 2009  Student Digital Artist
Yeah you've done right. But it's not that strange you know :P Good job thought :D
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:iconalbertonykus:
Albertonykus Featured By Owner Aug 15, 2009
Again, thanks. I understand; some people may just find it contradictory.
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