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When dinosaurs bite

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Matt Walker Matt Walker | 15:05 UK time, Tuesday, 26 July 2011

Drawing of theropods dinosaurs (image:Mark Hallet Paleoart / SPL)

How did carnivorous dinosaurs get their meat? (image:Mark Hallet Paleoart / SPL)

Tyrannosaurus rex’s name means “tyrant lizard”: its moniker reflecting the carnage supposedly wrecked by this famous ancient reptile’s huge jaws and rows of impressive teeth.

In the now classic film Jurassic Park, another big-jawed, two-legged theropod dinosaur, Velociraptor, was depicted as a salivating, fleet-of-foot hunter of more sluggish species.

But the truth is that we still know little about the meat eating habits of dinosaurs.

Now some of that may change with the discovery of a fossilised sauropod bone.

Because on this bone are scoured a series of bite marks made by carnivorous dinosaurs, including the longest and deepest bite marks made by a dinosaur yet documented.

Even more intriguingly perhaps, the bone appears to have been bitten or chewed on by a series of different carnivores, revealing something about how groups of dinosaur scavenged carcasses just as big cats, hyenas and vultures might scavenge a kill in modern Africa.

When it comes to the diets of dinosaurs, scientists can make a number of educated assumptions.

Species tend to have mouth parts adapted to their particular diet, and the huge jaws, and rows of long conical teeth of T. rex, for example, suggest it was a top carnivore, one of the largest of all time on land.

Tooth-marks in sauropod bone (image: Prof In Sung Paik)

The longest and deepest tooth-marks made by a dinosaur yet documented, gouged into a sauropod tail bone (image: Prof In Sung Paik)

Velociraptor is known to be much smaller than depicted in Jurassic Park, but it too was thought to be an able carnivore, due to its serrated teeth and sickle-shaped claw on its limbs. One well known fossil, called “Fighting dinosaurs”, contains the petrified remains of Velociraptor mongoliensis and the plant-eating Protoceratops andrewsi in combat, providing direct evidence of predatory behavior.

Another fossil, which I reported last year, shows another predatory Velociraptor caught in the act of eating another large-horned Protoceratops.

However, palaeontologists uncovered fossil fragments of this Velociraptor’s teeth alongside scarred bones of the herbivore. The teeth of the predator matched marks on the herbivore's bones, suggesting Velociraptor scavenged its carcass.

So we still cannot be sure whether many carnivorous dinosaurs, including even T. rex, were primarily scavengers or predators.

But the discovery of the sauropod bone provides yet more evidence that scavenging did indeed take place, and on a wide scale.

The bone is a caudal vertebra, or tail bone, of an adult medium-sized sauropod called Pukyongosaurus millenniumi.

It was initially discovered in December 2008, among a bed of bones exposed on a small island within a modern tidal flat in South Korea, in what is known today as the Cretaceous Hasandong Formation.

Velociraptor depicted scavenging the large horned herbivore Protoceratops (Image: Brett Booth)

Velociraptor depicted scavenging the large horned herbivore Protoceratops (image: Brett Booth)

Until being uncovered by its discoverers, Professor In Sung Paik of Pukyong National University and colleagues, the tail bone lay preserved under a thick block of sandstone.

“We took it to the laboratory and cleaned it. I observed some grooves and scars on the clean surface of the bone, and recognised that they are tooth-marks,” Prof Paik tells me.

Further analysis revealed much more.

The tail bone is scarred by a number of teeth-marks, of differing lengths and depths.

One tooth-mark is 17cm-long and 1.5cm-deep, making it the longest and deepest tooth-mark made by a dinosaur yet documented.

The size and shape of this and other large marks suggest they could have been made by a tyrannosaurid theropod – the group to which T. rex belonged.

Other smaller marks criss-crossing the bone were made by other species of smaller theropod dinosaur, say the researchers. They were able to rule out crocodiles or their relatives as having made the marks.

The characteristics of these teeth-marks help reveal how they were formed; whether it be during hunting, predation, scavenging or gnawing on or chewing the bone after all its flesh had been removed.

The tyrannosauridae were huge carnivores (image: Mark Hallett Paleoart / SPL)

The tyrannosauridae were huge carnivores (image: Mark Hallett Paleoart / SPL)

For example, the longest tooth-marks on top of the bone, and a corresponding set underneath, were likely made during the same bite, with the upper teeth of the carnivorous tyrannosaurid making the 17-cm long gouge.

The multiple parallel grooves of these bite marks show they were made by nipping and scraping.

The palaeontologists could also ascertain that the tooth-marks on the bone were not generated during hunting, or an attack when the prey was alive.

In part, that is because the marks are too long and deep to have been inflicted during a surprise attack, and are not unbroken, as also would be expected during a hunt.

No other P. millenniumi bones found at the site showed evidence of predatory attack, again pointing to scavengers feeding on this single part of the animal.

The little physical damage around these tooth marks also indicates they were made when the bone was still wet and covered with some flesh, report the scientists in the journal Palaeogeography, Palaeoclimatology, Palaeoecology.

A series of smaller tooth marks reveals that the sauropod’s body was scavenged by a succession of different theropods of different sizes and types, with diverse feeding strategies.

These weren’t made by carnivores biting into the bone, but by random tooth strikes, made perhaps as the scavengers tried to puncture the bone to get nutrients within.

This single sauropod tail bone then, bears marks that allow scientists to reconstruct a unique picture of how dinosaurs scavenged carcasses.

Prof Paik’s team believe that a large tyrannosaurid theropod came across the carcass, and defleshed it, producing the record breaking teeth-marks.

It also tried to gouge the bone to get inside it.

Hyena (image: Chrishtophe Courteau / NPL)

A succession of scavengers often arrive at modern kills (image: Chrishtophe Courteau / NPL)

A series of smaller carnivorous theropods then happened across the leftovers and tried to puncture the bone to again get at the nutrients within.

This is a scenario familiar in the modern world. Hyenas may happen upon on a recently killed or deceased antelope, for example, and opportunistically take much of its flesh. Then smaller scavengers arrive at the carcass to pick over the bones taking what they can.

In the Cretaceous period, however, these scavengers may, like T. rex, have stood up to 4 metres tall and weighed 7 tonnes.

Comments

  • Comment number 1.

    I would have expected this. A feeding strategy that evolved over 100 million years ago, and was apparently sucessful then, would very likely still be in use in a place like the East African plains today. Why should something that was sucessful then be changed today? If it works, don't change it, ought to be evolution's rule.

  • Comment number 2.

    I guess it is true that most people still think of dionsaurs in isolation and forget every eco system has a food chain and a pecking order just as complicated as in our time. I bet one sauropod could of been striped down to the bone in just a few days. It is a no wonder they are so few bones remaining. Nothing goes to waste. Just look at the UK. I lived here all my life and never seen any evidence of boar,wolves or bears outside of a museum and yet they roam the land for years before man came along. It would be easy to believe they never existed, let alone know how they lived and hunted. Yay for science.

  • Comment number 3.

    Trying to say whether a particular dinosaur was a carnivore or a scavenger is pointless. All predators are opportunistic feeders. They hunt when they must and scavenge when they can. Look at lions and hyenas. They kill and then try and steal each others kills. Why expect theropods to be any different?

  • Comment number 4.

    Matt, I understand the burden and significance of the points you're making in your story, but with regard to T. Rex, this's one of those situations where lack of information, but lots of unquestioned assumptions may've allowed us to get entirely hold of the wrong end of the stick.

    Let me say outright my own working position's T. Rex's almost certainly some kind of meat eater, but I've always been struck by both the feebleness and lack of reach of its 'arms'.

    They suggest it's never needed to use them to either defend itself or claw at its prey, which'd be entirely consistent with a critter more towards the carrion consumption region of the food chain - but such a physical 'arrangement' would also be more explicable if it turned out T. Rex'd developed gut bacteria which allowed it to munch on, say, trees, a vegetarian lifestyle not inconsistent with the group nesting and nurturing of living young now thought to be part of its life cycle.

    It's like in two other stories of yours, Penguins Take to the Air, and Why Do People and Other Primates Share Food?

    The scientists seem filled with preconceptions only technical innovations in the world of photography seem capable of puncturing: in the case of the penguins, it never seems to occur to them that penguins might actually be recapitulating the route by which birds first gained flight; but they also seemed amazed penguins're able to control their feathers in such a way as to control the production of air bubbles in water, yet if they'd ever paid attention to birds like seagulls hovering over the Mersey, or even pigeons eating cast off chips or vomit in Liverpool city centre, they'd've observed all birds seem capable of tightly closing or loosely expanding their feathers - or rapidly alternating between the two at a moment's notice - for the express purpose of controlling air flow, either to warm themselves up or cool themselves down, or to maintain the position they're holding in the air, or buoy themselves up or down, if and when the breeze should suddenly pick up or drop down.

    Ditto scientists seem startled not only people but primates generally seem capable of sharing food, but if they've ever watched how urban centred birds behave, they'd've witnessed groups of titchy sparrows viciously warring amongst themselves to be the one which gets to attempt to haul off an outsized piece of food too big for it to so much as get off the ground, never mind into its belly; then they'd've seen starlings arrive and form a cordoned off perimeter 'round the disputed food, spending more of their time repelling all 'boarders' than actually eating; and finally they'd've seen pigeons drop into the midst of the sparrow-starling war, skittling aside all and sundry, but instead of individually trying to haul off the food, or collectively keeping it for themselves, the pigeons merely peck a chunk out of the food while simultaneously launching the remainder over their head; and not even to other pigeons, either, but in a random fashion that allows any species near to it the opportunity to either similarly take a peck and launch it randomly overhead, or simply to revert to selfish snatch or group cordoning games.

    Now some'd say the pigeons behaviour isn't altruistic, but compared to the sparrows and the starlings it not only looks to me at the very least proto-altruistic, but also highly successful, as strategies go, because not only does it trump the stressful strategies of the other two every time but look the size of the 'casual' life styled pigeons to the size of 'neurotically' engrossed others.

    I'm not even asserting any of this's so, merely suggesting many scientists seem to observe the world through the lense of text book dogma rather than through actual 'open minded' eyes.

 

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