Duvenoy

I caught that one. Jack Horner makes a damned good case for T. rex being a sort of giant land vulture. I was especally impressed with the leg measurements -- the thigh being as long or longer than the shin. Clearly not much of a runner, but an animal that could walk tremendous distances with great effentcy. I don't recall if it was mentioned, but the energy burned by an animal the size and weight of T rex would be huge if it were to do any serious running.

I'm just about convinced that Horner is right.

doov

Strawberry

The first mammals were all egg-laying, and were nearly wiped out when marsupials evolved, because marsupial incubation was more reproductively successful. Marsupials, for the same reason, were almost wiped out when placental mammals (like humans) evolved. Australia was isolated from the rest of the world before placental mammals evolved, so they were only ever exposed to marsupials and egg-laying mammals (other than Aborigines, and, more recently, Westerners and the placental livestock introduced from other parts of the world). So the egg-laying mammals had a better chance of surviving in Australia, since they didn't have to compete with placental mammals as well as marsupials.

I learned all this in my evolution course this year, don't have sources, but I could try to find them if you want them.

Kosmo

Just curious, why would a huge olfactory system preclude the idea that T-rex was a hunter rather than a scavenger?

Viti

There was quite a bit of additional evidence (the legs as Doov mentioned, the usless forearms, etc), but they looked at the olfactory part of the brain compared to the rest of the brain and compared it with known predatory dinosaurs, living predators, and living scavengers. The ratio most closely matched scavengers (Turkey Vultures to be precise, whose olfactory systems are much much larger than those found in non-scavenger birds) which need to be able to find already dead animals from long distances in order to feed.

Duvenoy

Yes indeed. It ties together so well. This amazing creature could simply 'follow it's nose' to carrion miles away. There were a lot of really huge animals in the Cretateous. Why not a really huge scavenger? T. rex was very well equiped for it, with it's great, serated teeth and heavily muscled jaws that could easily open a carcass.

There are parallels found today. In South America, black and turkey vultures will often wait to feed at a carcass until the powerful king vulture arrives to tear it open. It is easy to imagine various, smaller scavengers waiting on the ultimate arrival of T rex to tear through the thick hide of another, dead dino.

That T. rex might (probably) have been a scavenger takes away not at all from it's majesty.

doov

beastmaster

I suspect the T Rex was an opportunist -- a scavenger at times and a predator at times, kind of like a hyena. The T Rex needs a lot of meat. Living or dead or rotting -- no sense snubbing an available calorie.

Just a guess tho.

Viti

Of course that's the other possibility...but Horner's view is why call it a predator unless there is evidence for it? He demonstrated that any kind of running or hunting on the part of T.Rex would have caused it to fall and not be able to get itself back up (something about it's posture, size, center of gravity and useless little forelimbs). Of course injured, weak, or infant animals could have been picked off as with todays scavengers....but I don't now if that's considered predatory or a type of scavenging.

edited to add: I am not any kind of T.Rex nerd or anything...the guy's (Horner I guess his name is) approach sorta glued me to the show. His science was so pure...he wanted to follow where the evidence led instead of trying to fit the evidence into the preconceived notions about T.Rex being some sort of super predator. I know this is what scientists try to get us laymen and the anti-science crowd to understand and his enthusiasm for the process and keeping it pure just sucked me in.

Duvenoy

Indeed. Show me a large preditor that won't scavenge, and I'll show you one that's starving to death.

The same way, a dedicated scavenger will certainly take the opportunity to snap up the weak and crippled. A couple of years ago, I re-habed a black vulture that some moron had shot and a game warden had brought me. I found it to be a very interesting animal. The wound wasn't terribly serious -- my long-suffering vet fixed it up nicely -- and the biggest problem I had with it was keeping it from developing a feeding response to my presense. I noticed that whenever my fat, lazy cat came near it's cage, it became very interested.

Black vultures are a major preditor of neonate turtles, snakes, and anything else they can overpower.

I was sorry to see 'Buzz the Buzzard', as my grand kids called it, go. It was a most rewarding animal, and gave me a whole, new perspective on vultures.

doov

The Lone Ranger

My impression is that Horner goes a bit too far in his "T. rex was a big walking vulture" hypothesis.

For instance, he has argued that the reason tyrannosaurids had such well-developed binocular vision (useful for an active predator, but not especially important to a scavenger) is because they simply inherited it from their predatory ancestors. The problem is that tyrannosaurids' snouts were narrowed in such a way as to facilitate binocular vision; similarly, their eye sockets appear to have been rotated forward somewhat, compared to older theropod lineages. This strongly implies that binocular vision in tyrannosaurids was, rather than an evolutionary leftover like the human appendix, something that had been strongly selected for.

Biomechanical studies indicate that Tyrannosaurus rex almost certainly wasn't capable of high-speed running for any length of time. So, it probably wasn't running down prey like wolves do. On the other hand, tyrannosaurs were extremely powerfully-built animals. Their teeth were interestingly-shaped, as well. The forward teeth were somewhat "D" shaped, whereas those in the sides of the mouth were more bladelike. Given the size of a Tyrannosaurus rex's mouth and the shape of its teeth, it's been estimated that a fully-grown animal could have taken up to 500 pounds of flesh from a victim with a single bite. This would likely have been a fatal wound even to a 3-ton Triceratops.

Some "duckbill" dinosaurs have been found with partially-healed injuries in their tails which appear to have been inflicted by tyrannosaurs. This strongly suggests that tyrannosaurs did attack live prey, at least on occasion.

***

As has been pointed out, few predators will turn up an opportunity to scavenge, so I don't doubt that tyrannosaurs would have scavenged whenever the opportunity arose. I suspect that they did hunt for prey too, though.

Perhaps they hunted in a manner analogous to modern rattlesnakes. Rattlesnakes strike their prey and inject venom, then immediately withdraw. Since they don't try to subdue their victims, they don't have to risk being injured by prey animals' struggles. After a suitable time has passed, the rattlesnake uses it chemoreceptive tongue to trail its victim to where it collapsed, and eats it.

So, maybe tyrannosaurs, when carrion wasn't available, were ambush hunters. If a tyrannosaur could get close enough to a potential victim, it could rush in, deliver a mortal wound with one bite, then withdraw. Eventually, the victim would almost surely succumb to blood loss or infection. The tyrannosaur could simply use its well-developed sense of smell to follow at a safe distance, waiting for the victim to collapse.

Cheers,

Michael

lpetrich

Much like the present-day Komodo Dragon, which hunts by making a big bite, and then tracking down would-be escaping prey.