Canis lupus hominis

Posted in Extinct | Tagged Tyrannosaurus rex | 26 Comments

26 Responses

1. on August 28, 2011 at 12:36 pm Suhail

   Present day Hyenas can both scavenge and hunt as the situation demands.

   
   
2. on August 28, 2011 at 4:45 pm Peggy Richter

   Almost all predators will scavenge if the opportunity arises. Lions chase hyenas off their kills, Leopards chase off cheetahs, bears will chase off wolves. “Pure scavengers” actually seem to be pretty rare (vultures). I’ve always felt that the Horner theory of Trex as a scavenger was more for publicity than actual science. He’s a good scientist, but he’s not above making flashy statements to get attention and funding. I’m sure T rex didn’t overlook the free meals (animals dead from non predatory causes) and certainly wasn’t above chasing off any smaller predators for a meal, but that’s not the same thing as asserting that this was all it could do.

   
   
3. on August 28, 2011 at 5:24 pm Suhail

   I doubt T-Rex as a hunter, because all three manners of hunting in present day carnivores would fail on him. He was not as fast as a Cheetah for sure, did not hunt in packs, and would have made a terrible stealth hunter like a leopard, Jaguar, or polar bear.

   The only present day carnivores that come to mind that T-Rex could have hunted like are Grizzly and Tigers (with the exception of Amur Tigers). Grizzlies do hunt, but it is a combination of stealth and run only against calves (of moose and caribou) and sick animals. Tigers, otoh, kill faster prey routinely. However, they do not and cannot hunt elephants. A T-Rex on his own could not have taken on a herd of Triceratops just like a tiger on his own does not take on a group of elephants. Also, it could not have hunted Hadrosaurs for they have been found to be grazers, and T-Rex could not have outrun them or ambushed them in the open grazing lands.

   
   
   • on August 28, 2011 at 7:39 pm Jess

     There were no other large predators in T. rex’s ecosystem. That means that the only animals predating on the ceratopsians and hadrosaurs would have been Dromeosaurus and Troodon. Both small. I don’t think so. Rexy was a big, big animal. No modern exclusive scavenger is so big, because large ass animals are not just dropping dead all over the place. Big animals require large amounts of food. We are talking about an animal that was equal to, or larger than, all of the prey species in it’s environment. You don’t evolve that kind of size if you’re a scavenger. You also don’t evolve a big head with very thick teeth that are mostly useful for making large holes in things if you’re mostly biting stuff that’s already dead. Binocular vision isn’t necessary, either.

     There is plenty of evidence that rex was biting live animals, which then escaped and continued to live. You don’t run around biting live, large animals unless you are hunting them. There is also plenty of evidence that rex and his relatives lived in groups. This doesn’t prove that he would have hunted in packs, but it doesn’t disprove it, either.

     Depending on who you ask, rex was plenty fast enough to chase down a hadrosaur or a ceratopsian. A distance runner he was probably not.

     Sue, the very famous rex sold at auction, had a broken lower leg, and the Wankel rex had broken femur. Stan had a broken NECK. Most rex specimens show these kinds of serious injuries, healed. Kind of hard to do the large amounts of moving around around such a large ‘scavenger’ would have needed to do, with a broken leg or a broken neck. Probably these animals had family members that were bringing food to them. Lucky, isn’t it, that these scavengers were able to find not only enough food to feed themselves, but also their injured compatriots? Sue and the Wankel rex’s broken legs are beautifully healed, by the way. Not crooked or deformed at all.

     Tigers do kill elephants and even rhinos, on occasion. Most predators are opportunistic.

     The Tyrannosaurus page on Wikipedia is actually pretty informative, you should check it out.

     http://en.wikipedia.org/wiki/Tyrannosaurus

     
     
     • on August 29, 2011 at 1:00 pm pennypup

       I’m with you on this one Jess. I’m sure Rex was oppertunistic as any carnivore is. But I have no doubt he was hunting prey just as often as scavaging.

       
       
       • on August 29, 2011 at 7:08 pm Dave

         Large predators don’t really scavenge. There are a bunch of them who thrive on kleptoparasitism though. Bears are really bad for this, and there are cultures who lead this life solely by chasing wolves away.

         
         
         • on August 29, 2011 at 7:35 pm Jess

           Lions are notorious for stealing Hyena kills.

           
           
     • on August 29, 2011 at 7:13 pm Dave

       I never got where Horner got the idea Tyrannosaurus are scavengers. Yeah, so what? They got “useless” arms?

       You don’t evolve that kind of skull for no reason. There is no reason to evolve such a head NOT to predate.

       
       
       • on August 29, 2011 at 7:38 pm Jess

         I always found it amusing that there was no question that an animal like Carnotaurus, which has the weirdest little stumpy useless armlettes imaginable and a lightly built jaw to boot, was a predator, while rex couldn’t possibly be one. Same with Giganotosaurus, which also has reduced arms as well.

         People are strange.

         
         
       • on August 29, 2011 at 7:39 pm Jess

         Forgot to add: Horner is a hadrosaur guy, and rex as predator would have been eating the tasty, tasty hadrosaurs. Naughty rex! No prey for you!

         
         
       • on August 29, 2011 at 9:11 pm Suhail

         ‘Useless arms’ is just one argument. The major argument is built around the fact that T-Rex populations was almost as high as all of its ‘prey’ put together, which is unlike lions, Cheetahs and leopards and much more like Hyena population. Hyena population is higher because they can live on much greater variety of meat source available through scavenging / opportunistic feeding. Cheetahs, otoh, hunt gazelles and won’t stoop to hunt frogs.

         
         
         • on August 30, 2011 at 12:45 am Jess

           “T-Rex populations was almost as high as all of its ‘prey’ put together, which is unlike lions, Cheetahs and leopards and much more like Hyena population.”

           Citation, please. Studies show that the large predator to prey ratio at the time rex lived was similar to modern populations, few predators to lots of prey.

           
           
           • on August 30, 2011 at 9:41 pm Suhail

             http://abcnews.go.com/Technology/rex-ferocious-killer-opportunistic-scavenger/story?id=12974461

             
             
             • on September 1, 2011 at 3:43 pm Jess

               Did you read the paper? Because I went and found it and read it.

               From the ABC article:

               “”The census data would suggest that it’s like a hyena, just an opportunist. It would be just as likely to eat something dead as it would eat something alive,” said John “Jack” Horner, one of the study’s researchers and curator of paleontology at the Museum of the Rockies in Bozeman, Mont.”

               Almost every predator on the planet does this. Relatively few eat ONLY food they’ve just killed. Relatively few scavengers ONLY scavenge.

               “In general, he said, prey outnumber predators by a 10 to one ratio. But in the Hell Creek Formation of Montana, which includes fossils from 65 million to 95 million years ago, researchers found 72 total triceratops, 44 Tyrannosaurus rex and 36 duck bill dinosaurs, he said.

               “The fact that we have so many of them does suggest that the T. rex is doing something different [from predators],” Horner said.”

               Um, no. No, it doesn’t. I am really curious as to whether he understands how foolish this sounds. Almost every predator will scavenge. It’s less energy intensive and dangerous than hunting.

               And if you actually read the study, you can see how Horner is playing up the ‘scavenger’ issue in order to get some press time. From the study:

               [regarding numbers of rexes] “A similar comparison can be made with mammal census numbers from the Serengeti plains where the hyena population is twice that of the combined population of lion, leopard and cheetah [38,39]”

               “The relatively high abundance of Tyrannosaurus contradicts earlier suggestions that it was a very rare taxon in the Hell Creek Formation [21]. This census suggests that Tyrannosaurus was not strictly a predator, but instead more of an opportunistic feeder, possibly selecting similar food choices under circumstances comparable to that of hyenas in extant ecosystems, a trend unrecognized in earlier census studies.”

               Bit of a different spin that what he told the press, eh? Which do you think he really believes? And which do you think the press is actually going to jump on? Bigass rex with the sexy name and the giant teeth wasn’t a hunter? Or Bigass rex with the sexy name and the giant teeth did what most other predators do, which is hunt and eat dead stuff when they find it? If you’d like a good summary of the so-called controversy of rex as a predator, check out this link:

               http://blogs.smithsonianmag.com/dinosaur/2011/03/tyrannosaurus-hyena-of-the-cretaceous/

               I take it, Suhail, that you are not a dinosaur geek. Well, I have been married to one for seventeen years. My husband is not only a major dinosaur geek, but a paleoartist and has had illustrations published in a few scientific papers. One of his illos accompanied the press announcement of a feathered dinosaur last year. (Full disclosure: he has an illustration in the evolution book written by the author of the link above.)

               (Yes, I’m pulling a bit of ‘argument from authority.’ So sue me.)

               You don’t sit in a seething stew of dinosaur geekness for seventeen years without soaking some of it up. I’ve been watching Horner make a fool of himself with this predator/scavenger nonsense for a long, long time. The problem is that Horner *looks* like what the public thinks a paleontologist should look like, he’s a good storyteller, and he gives good screen. Plus he has this supposed ‘controversy’ about rex. The press loooooves arguments. Same with Robert Bakker, though his controversy, from the Dinosaur Heresies (active warm-blooded dinos), actually was a controversy at the time, and has since become widely accepted. Horner’s rex ‘controversy’ has never become accepted in the paleontological community, and it’s not even a controversy except to the mainstream press. To the people who matter, it’s not an issue. To the paleontological community, rex was like the vast majority of predators, hunted but wouldn’t pass up a free meal.

               
               
               • on September 2, 2011 at 8:43 pm Suhail

                 Hi Jess,

                 This is a great post. Sorry, I was and am unable to respond to it because I am busy with office and personal (building backyard for my dogs) work. I had posted the link earlier above and I am aware of it.

                 I will lock horns again on Saturday :-) In the meantime, please do read my response to Peggy.

                 
                 
     • on August 29, 2011 at 8:58 pm Suhail

       Jess, you wrote, “There were no other large predators in T. rex’s ecosystem. That means that the only animals predating on the ceratopsians and hadrosaurs would have been Dromeosaurus and Troodon. Both small. I don’t think so.”

       Makes some sense, but then in Grizzly bear ecosystem, the real hunters (Wolves and cougars) are much smaller than the bad brown bear. Grizzly mostly steals, hunts calves, and even scavenges. T-Rex could have stolen catches of much smaller carnivores.

       You wrote, “Rexy was a big, big animal……. Binocular vision isn’t necessary, either.”

       You have not explained how would such a big animal hunt. Also, not that hyenas have developed big jaws and they scavenge, steal, as well as hunt. Scavengers also have big teethes to crush bones

       You wrote, “There is plenty of evidence that rex was biting live animals….. This doesn’t prove that he would have hunted in packs, but it doesn’t disprove it, either.”

       This does not prove that he was a hunter. This does prove however, that he came close enough to living animals and could have killed them, but the prey had better defense mechanism.

       You wrote, “Depending on who you ask, rex was plenty fast enough to chase down a hadrosaur or a ceratopsian. A distance runner he was probably not.”

       Again simulations have shown that Hadrosaurs and ceratops could have easily outpaced T-Rex due the shapes of their bodies.

       “Tigers do kill elephants and even rhinos, on occasion. Most predators are opportunistic.”

       What sub-species of tigers are you talking about? Surely, not Javan, Sumatran and Amur Tigers. Bengal Tigers? Lion prides have been reported and vidioized to have killed elephants. Bengal tigers killing Indian elephants? I am not sure about.

       Net net, you have not explained how could T-Rex have hunted the prey. The examples of T-Rex attack evidence you gave only show that he failed as a hunter.

       
       
       • on August 30, 2011 at 12:15 am Dave

         Until recently, it was thought that hyenas were scavengers. This is not the case. Actually, through field observations, it’s the lions who steal the kills– then the predator would have to return with the mafia to beat them off to reclaim the carcass. So, no, they are not true scavengers.

         Bears? Look at their skull: http://www.sculpturegallery.com/three/grizzly_bear_skull.jpg

         It’s nowhere the same as the T-Rex.

         Plus, their behaviour is not truly universal. Their diet varies from region to region.

         
         
       • on August 30, 2011 at 1:17 am Jess

         http://jackjacksonj.webs.com/tigerskillingrhinos.htm
         http://jackjacksonj.webs.com/tigerskillingelephants.htm

         There you go. Now you can find me citations for this assertion:

         “Again simulations have shown that Hadrosaurs and ceratops could have easily outpaced T-Rex due the shapes of their bodies.”

         “Grizzly mostly steals, hunts calves, and even scavenges. T-Rex could have stolen catches of much smaller carnivores.”

         Explain to me why bears can kill calves but a rex could not kill a juvenile hadrosaur or ceratopsian. Oh, that’s right, moose are shitty mothers. A hadro or ceratopsian would never let their young get killed by a rex, because rex is a scavenger who couldn’t do more than a slow walk and chewed bones with it’s teeth that looked like railroad spikes. I get it now.

         “Also, not that hyenas have developed big jaws and they scavenge, steal, as well as hunt. Scavengers also have big teethes to crush bones.”

         Hyenas have very large carnassial teeth to CHEW bones. Rex does not have teeth made for chewing. It does not have a jaw made for chewing. It has teeth made for poking big holes into things and tearing a lot of flesh off, they have serrations. A good bite or two on an animal and rex would just have to follow it, keep it moving, so it loses blood, slows down, and becomes lunch.

         “The examples of T-Rex attack evidence you gave only show that he failed as a hunter.”

         It shows that rex was biting live animals that escaped. Maybe you can explain to me why a pure scavenger would even bother expending the effort to get close enough to a large, dangerous animal to bite it, when there are sooooo many dead ones lying about, just waiting to be eaten. Hunting is bloody dangerous.

         Net, net, you have shown me nothing that supports your assertion that rex was a pure scavenger. The only pure scavengers in the modern ecosystem are stuff like fish, and vulture types. All very small animals.

         http://en.wikipedia.org/wiki/Tyrannosaurus#Locomotion

         Deer, caribou, and moose all can run faster than wolves. Therefore, by your logic, there is no way that wolves could kill a deer, caribou or moose.

         
         
4. on August 30, 2011 at 12:18 am Dave

   “Net net, you have not explained how could T-Rex have hunted the prey. The examples of T-Rex attack evidence you gave only show that he failed as a hunter.”

   If they WEREN’T hunting, then they wouldn’t have bothered PURSUING the prey in the first place.

   
   
   • on August 30, 2011 at 1:02 am Jess

     No, they wouldn’t have. Pursuing prey is a dangerous business, which is most carnivores will scavenge or steal prey from other carnivores. It’s less dangerous to scavenge or steal.

     Most rex fossils are really beaten up. Either they were beating the shit out of each other, or hunting something dangerous.

     
     
     • on August 30, 2011 at 10:01 pm Suhail

       At least this fossil tells that T Rex’s may be fighting among themselves:

       http://abcnews.go.com/Technology/DyeHard/teenage-rex-bones-fierce-fight/story?id=8986505

       
       
5. on August 30, 2011 at 10:35 am Peggy Richter

   actually there is some evidence that Trex may have hunted in family groups since they have been found in groups. Deer can “out pace” wolves and certainly most of their prey can outpace a lion. What they may not be able to do is outendure the wolf or spot the lion in the grass as it runs from the lion behind it. Lions have taken out elephants although this isn’t obviously their primary prey (but there are smilodons who apparently did hunt mammoth). Useless arms? big deal. Wolves don’t use their feet, nor do hyena. Rex could have been a night stalker (it certainly had the vision and hearing to make this plausable). It wasn’t faster than a cheetah but neither were any of the prey animals as fast as an antelope either. It only had to be “fast enough”. It’s hard to think of a multiton animal stalking, but elephants show that they can indeed “disappear” into the brush relatively easily. There was a serious study on rex as a predator/hunter — http://rspb.royalsocietypublishing.org/content/early/2011/01/20/rspb.2010.2497.short — Intra-guild competition and its implications for one of the biggest terrestrial predators, Tyrannosaurus rex — which concluded that rex could NOT have been an obligate scavenger but had to include predation in its behavior.

   
   
   • on September 1, 2011 at 4:28 pm Suhail

     Peggy,

     This is the only argument, i.e. T – rex may have hunted in family groups, that changes the dynamics. Yes, if only they hunted in groups could they be successful hunters. A single T-rex would not endeavour to take on a Triceratops just like a lonely lion won’t take on an elephant or an African Cape Buffalo.

     If T-rex hunted in family packs then they would also not need highly sophisticated arms. Difficult to imagine a T-rex with that useless an arm trying to take on a Triceratop on its own. It would be like a lone wolf trying to bring a bison down.

     Prides of lions that hunt elephants or buffaloes are highly specialized prides that would dare to do so. An average pride hunting zebras and gnus will never try hunting an elephant or a buffalo.

     
     
     • on September 2, 2011 at 4:19 pm Jess

       Relatively few of the very large theropods had ‘highly sophisticated arms.’

       Allosaurus:
       

       If you have ever stood next to one, and I have, the size of the arms is striking.

       Ceratosaurus also had fairly good sized arms:
       

       So did Megaraptor:
       

       A number of the really large theropods have reduced the arms in favor of the head. Rex was simply farther along in the process.

       Gigantotosaurus:
       

       Acrocanthosaurus:
       

       Tyrannotitan:
       

       Torvosaurus:
       

       Spinosuarus and relatives are considered fish-eating dinosaurs and they had some good sized arms for grabbing with:
       
       
       
       

       Carnotaurus had even smaller more useless arms that rex:
       

       (BTW, nobody is on tv blathering about how Carnotaurus must’ve been a pure scavenger.)

       As did Majungasaurus:
       

       There are more Tyrannosaurs than just rex, and there is no question in the literature that these were considered predators:

       Eotyrannus was a very early Tyrannosaur, and you can see it still has quite big arms:
       

       Albertosaurus:
       

       Daspletosaurus:
       

       Gorgosaurus:
       

       Tarbosaurus:
       

       You’ll note that almost none of these animals have arms that could reach the ground if the animal was standing, and almost none have arms long enough to reach an object in front of them without hitting it with their heads, first. The ‘necessity’ of sophisticated arms in this particular ecological niche is debatable. The were mostly animals adapted to grab things with their mouths, not their hands. Theropods had wrists that did not rotate, anyways, so their arms would have been of limited usefulness in grabbing a moving animal.

       What you are also failing to note, is that rex was as big or bigger than any of the prey animals in it’s environment. If Lions were as big as an elephant, they would not need to hunt with other lions to kill one, though it would make it easier and less dangerous.

       You are also completely ignoring the fact that many predatory animals prefer juvenile prey. They *know* that the adults are big and dangerous, and selectively go after juveniles. All of these prey dinosaurs were producing good-sized numbers of babies, indicating a lot of survival pressure on the young (you don’t have lots of young unless most of them are likely to die before reaching adulthood.) As dinosaurs were slow-growing, we are talking a very long time period when the young were small enough for a single rex to kill.

       Keep digging.

       
       
       • on September 2, 2011 at 8:51 pm Suhail

         OK we have beaten ‘useless arms’ argument into buzzard’s meat.

         The real argument,which is also my argument, for T-Rex as not a hunter is not ‘useless arm’ but high population density that is similar to hyenas in the Serengeti rather than hunters like lions, leopards and cheetahs. Second argument is my questioning the hunting style of T-Rex (if it did not hunt in packs). They were not swift hunters like cheetahs, could not have been stealth hunters like leopards and polar bears, and were not a pack animal. The only hunting style with relative size advantage I can attribute it is of Great White Shark. But then GWs population compared to their prey is very very small.

         
         
6. on September 1, 2011 at 8:59 pm Peggy Richter

   well, eagles don’t use their wings much either. Yet they are hardly scavengers. Think of Rex as a giant non flying eagle. They are, after all, pretty closely related to the birds. http://www.gavinrymill.com/dinosaurs/Cladogram/SaurischiaTherapoda.jpg

   A fairly large number of the predatory dinosaurs have “itty bitty arms”. For that matter, Crocodiles and monitor lizards like the Komodo dragon don’t use their feet to snatch prey, either.

   
   

Comments are closed.