Meat-eating dinosaurs not so carnivorous after all

Meat-eating dinosaurs not so carnivorous after all
New research by Field Museum scientists finds widespread herbivory in bird-like theropod dinosaurs. Four of the 90-theropod species involved in the study shown with dietary interpretations. All four species derive from the famous feathered dinosaur beds of the Early Cretaceous Yixian Formation, P. R. China, leading the scientists to speculate that dietary diversity may have contributed to the large numbers of contemporaneous theropods in ecosystems like those of the Yixian. Credit: Dennis Finnin and Roderick Mickens, copyright American Museum of Natural History

Field Museum scientists used statistical analyses to determine the diet of 90 species of theropod dinosaurs. Their results challenge the conventional view that nearly all theropods hunted prey, especially those closest to the ancestors of birds.

Tyrannosaurus rex may have been a flesh-eating terror but many of his closest relatives were more content with vegetarian fare, a new analysis by Field Museum scientists has found.

The scientists, Lindsay Zanno and Peter Makovicky, who will publish their findings in the journal , used statistical analyses to determine the diet of 90 species of . Their results challenge the conventional view that nearly all theropods hunted prey, especially those closest to the of . Rather, Zanno and Makovicky show that among the most bird-like dinosaurs—known as coelurosaurs—plant eating was a common way of life. "Most theropods are clearly adapted to a predatory lifestyle, but somewhere on the line to birds, predatory dinosaurs went soft," Zanno says.

Theropods are a group of bipedal dinosaurs colloquially known as "predatory" dinosaurs. Among theropod dinosaurs, all modern birds and several groups of their closest extinct relatives belong to a subgroup known as Coelurosauria. Coelurosauria also includes the iconic hunters Tyrannosaurus and Velociraptor. Most coelurosaurs were feathered. The most intelligent dinosaurs and those with the smallest body sizes also belong to this group.

The study was funded in part by the National Science Foundation. Lead author Lindsay Zanno's research was supported by a John Caldwell-Meeker Fellowship and by a Bucksbaum Fellowship for young scientists.

Pinning the Diet on the Dinosaur

Deducing the diet of extinct animals isn't always straightforward. In all but the rarest cases, paleontologists have nothing but fossilized bones and teeth to work with. Sometimes figuring out what a dinosaur ate is fairly obvious. No one doubts, for example, that the bone-crunching teeth and jaws of were the tools of a megapredator or that the tooth batteries of Triceratops were used for shearing plant material. However, many coelurosaurian dinosaurs have more ambiguous adaptations such as peg-like teeth at the front of the mouth or no teeth at all so determining their diet has been a challenge. "These oddball dinosaurs have been the subject of much speculation" says Makovicky, "but until now, we have not had a reliable way to choose between competing theories as to what they ate."

Fortunately a small percentage of these species also preserve clear-cut evidence of diet with their skeletal remains. Fossilized dinosaur dung, stomach contents, tooth marks, the presence of stones within the stomach that serve as a gastric mill for digesting vegetation, and even two dinosaur species preserved locked in the throes of combat all provide a direct window on diet. After collecting dietary data for almost 100 coelurosaur species, Zanno and Makovicky used statistical analyses to test whether certain skeletal traits (such as the loss of teeth or a long neck) could be found to correlate with direct evidence of plant eating among coelurosaurian dinosaurs.

They found almost two dozen anatomical features statistically linked to direct evidence of herbivory including a toothless beak. "Once we linked certain adaptations with direct evidence of diet, we looked to see which other theropod species had the same traits," Zanno said, "then we could say who was likely a plant eater and who was not."

Applying their data on diet, the researchers found that 44 theropod species distributed across six major lineages were eating plants and that the ancestor to most feathered dinosaurs and modern birds had probably already lost its appetite for flesh alone. Because plant eating was found to be so widespread in Coelurosauria, the hypercarnivorous habits of T. rex and other meat eating coelurosaurs like Velociraptor should be viewed "more as the exception than the rule," Zanno says. "This new research firmly supports what we've have been speculating about for some time," she says. "Its time to start seeing these animals in a new evolutionary context." The researcher's findings also suggest that iconic predators such as the Velociraptor of Jurassic Park fame and their close relatives may have evolved from omnivorous ancestors—an idea Zanno proposed last year in 2009 based on the discovery of a new plant-eating coleurosaur, Nothronychus graffami.

How to Make a Plant Eating "Predator"

Besides identifying diet, the researchers analyzed whether different groups of coelurosaurs followed the same evolutionary pathways toward an herbivorous diet. They found that over time, species lost their flesh-rending teeth, developing strange tooth types such as peg-, wedge-, and leaf-shaped teeth, and ultimately, some lost most or all of their teeth altogether and replaced them with a bird-like beak. While the new research suggests that dinosaurs evolved beaks to aid their transition to plant eating, once that innovation was accomplished, beaks continued evolving into a myriad of forms and help support a high degree of dietary diversity in modern birds. "This is a clear-cut indication that the repeated evolution of a toothless beak in theropod dinosaurs is linked to plant eating," Zanno says. However, "once a beak appeared on the scene, it continued to evolve. Theropods would have used their beaks in a myriad of ways; they still do," she said.

Zanno and Makovicky also found that a toothless beak only evolved in lineages known to have had a gastric mill for grinding plants. In lineages where a gastric mill is not yet known, such as the bizarre, sickle-clawed therizinosaurs, the species retain teeth at the back of the mouth for shredding plant material.

Besides losing teeth and evolving beaks, the researchers found that as several lineages of coelurosaur turned to plant eating, they also evolved longer necks, which may have helped the animals to expand their browsing range.

A Dietary Advantage?

Coelurosaurian theropods were an extremely successful group of dinosaurs throughout the Cretaceous Period (145-65 million years ago) and many different species of coelurosaurs inhabited the same ancient environments but scientists have yet to figure out why. One theory is that the break up of continents and origin of new habitat opened up new dietary niches for coelurosaurs to explore. Zanno and Makovicky speculate that dietary diversification also may have played a role in their success. "The ability to eat plant materials may have played a pivotal role in allowing coelurosaurian dinosaurs to achieve such remarkable species diversity," Zanno noted, "but more study is needed to understand what role dietary shifts may play in evolutionary processes."

Because ceolurosaurian include the closest extinct relatives of birds, understanding their biology is also extremely important to understanding how, why, and under what conditions birds evolved and first took flight.

"We don't know what drove the ancestors to birds to take flight," she says, "seeking food in the trees is just one of many possibilities."

Using statistical analysis to find correlations between physical traits and diet could offer a new window as to how evolution works, the researchers said, and these techniques could be used to provide new insight into the common practice of becoming an herbivore throughout vertebrate history. Makovicky summarizes, "Being able to establish in extinct animals with confidence will allow us to start tackling even broader questions, such as whether animals tend to increase in body and diversity when they evolve herbivory."

Explore further

Trivia time: Tom Turkey, T. rex related

Provided by Field Museum
Citation: Meat-eating dinosaurs not so carnivorous after all (2010, December 20) retrieved 20 June 2019 from
This document is subject to copyright. Apart from any fair dealing for the purpose of private study or research, no part may be reproduced without the written permission. The content is provided for information purposes only.

Feedback to editors

User comments

Dec 21, 2010
And to all the beasts of the earth and all the birds in the sky and all the creatures that move along the ground—everything that has the breath of life in it—I give every green plant for food.” And it was so.
This is what the creator said {Genesis 1}after making the living creatures.

The change in diet happened AFTER the flood when God gave people {and also animals} the right to eat flesh(Genesis 9}:
The fear and dread of you will fall on all the beasts of the earth, and on all the birds in the sky, on every creature that moves along the ground, and on all the fish in the sea; they are given into your hands. 3 Everything that lives and moves about will be food for you. Just as I gave you the green plants, I now give you everything.

Notice how animals and birds etc. became fearful of human beings AFTER the flood.

To the moderators - this is a distinct alternative to the statements made by the researchers and is of value to chew upon.

Dec 21, 2010
We dont know what drove the ancestors to birds to take flight, she says, seeking food in the trees is just one of many possibilities.

Great admission by Zanno.
The answer is of course that birds did NOT evolve from anything, they were created the way the are - fully capable of flight.
Just think how impossible it is for NEW INFORMATION to arise from random physical processes. New information to make new materials and from that to make new features [ feathers and wings and bone sacs ] and then new information to USE those new features.
It is simply impossible. No amount of time will make it happen because new functional information does not arise from random physical processes. Period.

Dec 21, 2010
kevinrtrs, if you believe in the whole god delusion crap, then why are you even on this website.
please go back to the cave where you came from

Dec 21, 2010
He's now just wantonly trolling.

Dec 21, 2010
Incredible how people can read the Bible and yet lack comprehension skills - notice several points that get omitted by most literal readings of "Genesis"

(a) AT no point does God command a diet for the sea creatures.
(b) God doesn't say the animals can or will eat meat after the Flood. So when did that happen?

Like so much else in the Bible it's easy to imagine an interpretation, but then that's reading one's own ideas into the text isn't it?

Dec 21, 2010
Is it true that the "conventional wisdom" is that most of these dinosaurs were carnivores? That seems absurd on its face. Clearly most animals in an ecosystem must be plant eaters.

Dec 21, 2010
perhaps they mean the stereotyped "conventional wisdom"

Dec 21, 2010
and Kev, asking nicely; please, we understand you are passionate in your non-scientific, religious beliefs, but this is science based site so....find a religious one and leave us doomed-to-eternal-hell people to our own devices. Now that would be a Christian thing to do.

Dec 21, 2010
The answer is of course that birds did NOT evolve from anything, they were created the way the are - fully capable of flight.
Show me a pre-cambrian bird.
Just think how impossible it is for NEW INFORMATION to arise from random physical processes.
Yeah, good thing those physical processes aren't random. Carbon doesn't randomly or arbitrarily form particular bonds, it is consistently congruent to the understood patterns within Chemistry.
New information to make new materials and from that to make new features [ feathers and wings and bone sacs ] and then new information to USE those new features.
Natural chemical affinity guided through structural processes driven by natural chemical affinity.
It is simply impossible.
No, quite possible, and quite probable.
No amount of time will make it happen because new functional information does not arise from random physical processes. Period.
Correct, but as I said, physical processes aren't random.

Dec 21, 2010
If the flood killed them all, then why do we have so many dinosaurs trapped in ash beds? I mean, even if the volcano's came first, with so little available time the flood would have washed the ash away with ease. Oh wait, how could i forget? any evidence contrary to the devine word of god and only true source of knowledge was planted here to test our faith.

You see, this life is nothing more then a test of our worthiness to enter the kingdom of god. Those who correctly identify truth get to spend eternity with god, and those who are tricked by all the deception in this world are condemned to an eternity of suffering.

Thank you, Kevinrtrs for pointing out this deception so that we might be saved.

Dec 21, 2010
Oh btw Kevenrtrs, god doesnt want you here either: "pride goes before destruction, a haughty spirit before a fall. Better to be lowly in spirit and among the oppressed than to share plunder with the proud." we are the proud, and it would be better for your soul if you should leave this place.

Dec 21, 2010
So long as we're digging around in the old testiment, I find this passage just wonderful. Leviticus Chapter 21, 18-23.

For whatsoever man he be that hath a blemish, he shall not approach: a blind man, or a lame, or he that hath a flat nose, or any thing superfluous, Or a man that is brokenfooted, or brokenhanded, Or crookbackt, or a dwarf, or that hath a blemish in his eye, or be scurvy, or scabbed, or hath his stones broken; No man that hath a blemish of the seed of Aaron the priest shall come nigh to offer the offerings of the LORD made by fire: he hath a blemish; he shall not come nigh to offer the bread of his God. He shall eat the bread of his God, both of the most holy, and of the holy. Only he shall not go in unto the vail, nor come nigh unto the altar, because he hath a blemish; that he profane not my sanctuaries: for I the LORD do sanctify them.

Dec 21, 2010
"new functional information does not arise from random physical processes." well that statement either demonstrates an intent to deceive, or naive ignorance. Random physical processes self assemble into ordered states all the time. You can even test this at home. all you need is two pieces of glass, some water, and a heat source. Put some water between the two panes of glass, apply heat, and watch hexagons form.

Dec 21, 2010
Another great test of self ordered states is to simply boil water, add sugar while stirring until no more sugar will dissolve. Then take the sugar water off the heat, put a stick into the water, and let it cool down. Do this at night, and in the morning you will have a nice sugary treat attached to your stick. If you add food coloring you can even sell them as candy. No need to sculpt those intricate angles with an exacto knife, they just happen.

Dec 21, 2010
Sometimes I just want to kick Kev in the balls. He says such stupid things I almost cannot tolerate such ignorance. Really? You're going to tell us that the diets of dinosaurs were dictated by the accounts of genesis? Implying in the same breath that genesis is not a load of crap AND that dinosaurs were present 10,000 years ago?

Dec 22, 2010
No one liked my Leviticus quote? Probably over the top troll bashing. But in the days where Palin will jump down your throat for dropping an R-bomb, its nice to see God telling people with flat noses that they are not allowed to worship him.

Got nothing against God, but seriously the first 5 books in the old testament are nothing but the laws and fairy tales of the ancient Jewish people.

Dec 22, 2010

To the moderators - this is a distinct alternative to the statements made by the researchers and is of value to chew upon.

if it is of so much value to this discussion, why wont you join us in discussing it?

Dec 29, 2010

I hope you realize crystalization, in and of itself, has nothing whatsoever to do with complex machinery of life. You're not going to get a life form from a crystal, nor anything remotely similar. You cannot be seriously claiming that crystalization is somehow evidence for abiogenesis or evolution. You're ridiculous.

You're claiming that complex molecular machinery arises totally by accident, and even SH calling it "probable" is absolutely lying BS.

Biological mechanisms are forward thinking design, whereby often we find one component of an organism would be completely meaningless and useless without another component.

Let's take speech. Without ears, it's meaningless.

And without a sufficient brain, both speech and ears are meaningless.

Then there's sexual reproduction, particularly in mammals, which is so irreducibly complex that you people look like a bunch of lunatics trying to claim that something like this could happen by chance.

Please sign in to add a comment. Registration is free, and takes less than a minute. Read more