Is there any good math on a physiologic limit to a biped’s mass?

Also, for the length estimates of these dinosaurs have the soft tissue cushion of cartilage between vertebrae and other bones been factored in?

Having even 1 cm between each vertebra could add a whole meter or more on the longer dinosaurs, compared to how the fossils and casts tend to look, due to the bones being put flush with each other, unlike in life where they obviously would have had some cartilage there.

BTW Zhen, I watched your video on UCMP 118742, I liked it a lot, and thanks for putting up something that can be easily shown to people who think Giganotosaurus was grossly larger than T-Rex.

UCMP 137538 is definitely a T.rex. It’s been around for a very long time, but its stats were only recently revealed in the cannibalism in tyrannosaurus paper.

11 tons is not out of the question considering the recent research says Sue is AT LEAST 9 tons.

Wait a second, if a 40 foot Tyrannosaur is 7 tons, then wouldn’t that make a 47ft Tyrannosaur around 11 tons? (based on weight cubed root divided by lengtht, x new length cubed) That sounds a little too big doesn’t it?

Are we sure that UCMP 137538 bone is from a Rex?

If so that is sort of black Swan on the topped out at 14m theory.

http://i.imgur.com/mm1El.jpg

MOR 008, UCMP 118742, MOR 1126, and MOR 1152 are all bigger than Sue. There might be a few more in that range too, but I don’t have the complete stats.

One thing people tend to over look about Sue is that its not really big, but just really old. Growth slows to a crawl around 19 years old, but they still do continue to grow. Sue is 28 years old, and a few tyrannosaurs were around Sue size at 18/19 years old.

1. Yeah, 15m does sound a bit too big, but I could see 13 or 14m. Much bigger it would be so heavy that moving around would get too difficult? The idea is that all of the “biggest” may have had a similar top end weight, as there is a physiologic limit to how heavy a biped is going to get. Or in other words there may not have been that large of a difference in the heaviest T.Rex and heaviest Giganotosaurs, as both were bipeds, and would therefor have similar limit in mass.

2. You’re theory on it prefering the young, as they are easier targets; does that also include the injured adults? Would it make sense for T.Rex to attack an injured adult over the choice of a healthy young one?

In this hypothetical situation you have a Hungry T.Rex, and there are two possible targets. One if a younger animal, its horns are not fully developed, the other one is a fully grown adult, but it is limping badly with a broken front foot?

1. Yeah, I’m sure there were bigger ones than we know of, though how much bigger is another question. Assuming they did have inderterminate growth (and that’s no certain) it would have slowed enormously later in life. I’m sure there were bigger rexes than Sue say, but I doubt they got to 15 let alone 20 m.

2.You don’t need to be smart to attack juvies. And see my paper (and posts) on juvenile hunting. Personally I’m not a big fan of the ‘bite and wait’ model, it’s not a common way of doing things and arguably tyrannosaurs don’t actually have a great set-up to practice this.

3. Such family / social groups are very specialised and such a predation split of responsibilites has obvious ecological problems. And yeah, of course they were predators and scavengers, see, ohhh lots of papers, including those by me and a great review by Tom Holtz.

Some ideas I wanted to run past you, I’m sure others have thought of these before, but I’m not sure exactly who’s they all are.

One of them pertaining to the largest dinosaur carnivores in general, but more Tyrannosaur specific.

1) Concept of the largest theropods and T.Rex. So far as we know these guys kept growing most of their lives right? We have only limited remains, even for say T.Rex, what is there? Few dozen specimens, and very few relatively complete ones? I mean if I randomly picked humans out of one city of a population of say 100,000 people, while I would get a decent clue as to the average adult size, would I really know the absolute limit a human could grow to? Even discounting humans with growth disorders, there is still a lot of variation in absolute adult size in most modern animals, and the big mammals don’t even grow their entire lives as dinosaurs did (correct me if I’m wrong on that too). My suspicion is that some specimens of T.Rex, Ginganotosaurus etc… likely grew up to, or close to the physiological limit for a bipedal animal. These truly huge, absolute largest specimens were simply so rare that their chance of fossilization which is also rare, simply did not coincide.

2) Looking at T.Rex, my suspicion is that these were generalists who still did not like to endanger themselves. T.Rex was relatively smart for a dinosaur, and I cannot see a lone T.Rex attacking an adult bull triceratops. Now a Juvenile separated from the herd? That one is a great target. One that is injured and cannot keep up with the herd? Also a good choice. All a Rex has to do, in those cases would be one bite, and quickly get away. The resulting infection and blood loss would soon, perhaps a few hours, put the animal into a state of shock, or at least sick enough to the point it could not defend itself at all, and T.Rex comes back to feed, risk free. Its a cheap tactic, but it makes a lot more sense than a T.Rex going one on one into mortal combat with an adult healthy bull triceratops, which I think is silly, and I think T.Rex would not even consider.

3) The above theory, I call being the cheapest bastard in the forest, does not well to give a good reason for T.Rex’ massive size however. It would make more sense for a more agile horse sized theropod to deliver the quick in and out bite. Now if they lived in family groups, Mom and her kids at the least, and a decent size family with different year classes all living together, then we have a situation where more agile sub-adults can use speed to make an infectious bite, on an already easy target, and then the larger family members could lumber on in and enjoy the family meal and they would be able to discourage other predators from trying to take away the kill. The whole family gets to eat. This “bullying” tactic to take kills away from other predators, as well as keep other predators from taking your families dinner away, seems like a winning survival strategy as well as an evolutionary push toward larger and larger size. Speed may be lost as the animal grows larger and more powerful, but if you have smaller faster family members to do the killing you don’t have to be very fast. It also allows for a greater absolute size, as even if you have grown far to heavy and slow to chase anything down, you are still getting to eat.

Its all speculation, but for some reason they were able to grow quite large, which would obviously reduce top speed, and increase risks of moving fast at all. Yet they were still managing to get food to keep on growing despite being big and slow.

I don’t know why some people get so upset at the idea of T.Rex being a scavenger, or preferring weaker targets, like the young or the injured. Its a great way to make a living. It also does not mean that Rex was a wimp either, which I think is what people are really upset about on the scavenger/weakened prey idea. Far from it. I’d bet money Rex was no wimp, Even though it may have given up stealth hunting in exchange for large size and power, I surely would not want to get close to it. I bet other faster stealthier theropods stayed the heck away from it, and never would want to fight it. When those smaller ones theropods made kills I’d bet it was only a matter of time before the king came to collect his taxes.

Lions and Hyenas are kill stealers too. So will large bears take kills from wolves. Scavenging in this way is hardly the behavior of a weakling, in fact in this sense scavengers are more dangerous than purer predators. Cheetahs are a great pure predator, they have great speed and stealth for killing, but they don’t have the power to back it up if a Lion comes a long and want to take the kill away for itself. Cheetahs would have a hard time making it as a scavenger because they lack the brute force and power a land scavenger needs.