Is Tyrannosaurus overrated?

Mar 2017
873
Colorado
Hm, groups of hunting adults.
And another possibility ...

Paleontologists usually restrict dinosaur behavior to things they can observe in modern reptiles. Besides the fact they weren't exactly the kind of reptiles we have available at present, I subscribe to the 800-lb gorilla philosophy: once you get really big, you can pretty much have whatever behavior you like.

In spite of that, I dug up this little tidbit on reptile behavior that might explain multiple adults:
"The Chuckawalla, Sauromalus obesus (Berry, 1971) is the only lizard known to have harems. In this species, large tyrant males defend large territories within which good-sized but subordinate males are restricted by the tyrant's action to mini-territories about rock piles and basking sites. Females have feeding and basking site territories generally larger in area than those of the subordinate males. Tyrants patrol their territories daily, restricting the activities of subordinate males and visiting the females within their territory. Patrolling occurs before, during, and after the breeding season. Only the tyrant mates with the females, but most mating is initiated by the female (Berry, 1971)."
https://watermark.silverchair.com/14-1-35.pdf?token=AQECAHi208BE49Ooan9kkhW_Ercy7Dm3ZL_9Cf3qfKAc485ysgAAAaEwggGdBgkqhkiG9w0BBwagggGOMIIBigIBADCCAYMGCSqGSIb3DQEHATAeBglghkgBZQMEAS4wEQQMwya2-UzfL-2DK5cvAgEQgIIBVBWDGAjvEIA3NS8wYuExOfSHeLMUfr9KipKcuoY5QPYDd5Vd5GQiuDo0NGlRuX_WqFZ2y0P1QNjl4qgENvKKfjtjtkZbcrwAZGrOhevFLVmYuGehICIXXKSVZ_OaVzoALqyc5nF7R3-9l9aw5kNZaDXYl4lOFrdvZ-nHbV6ieTMta-4d6mjIx2pbzmGe6iTjKX3niAArvLpZ3uRibFKZh7gU-AodaTIjwkH-aOqg10D6Wy1kQJczq63a_HNJUXLZDAYEq1JiygQSWBSLmdO7QWEwk-05rAC0t3yXqltMWhZQDKrcSrsx6RrKrXtRDTvmj61gkHT1t2wK9SqWDuTrX0zc5dnEeYUJcsM0vqY0Y5UAb7fk3UdIyET40Fk9evmL7dg0BNRy0VtvOJvrOhXjs-7qJ2zS1oBCQEtC_BfjKdpdecYF1yZ4ce8Z7CYtL7LKhlH-aVM
-- apropos of this particular discussion, I like the use of the word "tyrant"




While I was poking around, I stumbled into a Nat'l Geographic website that claimed the top T.rex speed was 12 MPH.
"Which you could outrun..."

12MPH is a 5min mile. Can *YOU* run that fast?

https://www.quora.com/What-is-the-average-running-speed-of-a-human
Average jogging 8MPH
Average marathon running 8.8MPH
Average running (peak condition) 10-15MPH (as long as the adrenalin lasts)
 
Last edited:

Corvidius

Ad Honorem
Jul 2017
3,047
Crows nest
That is of course a possibility for group behaviour and is not dissimilar to lions, with one or two adult males with a pride, and younger, or now displaced males, living on the periphery of the pride. It would be handy to be able to discern which elements of bird behaviour are ancestral dinosaur behaviours, and which parts are specific to birds, other than flying of course. We look at a flock of birds and generally see them as the same as a herd of mammals, but they are not. While you can see a flock of hundreds of thousands, or even a million or more starlings, you are not seeing a community in the same way a herd of wildebeest are a community. The starlings are a collective of pairs and immature individuals. We see large flocks of rooks roosting at dusk, yet for all of the day they are in a pair and only join the roost at dusk. I would say this is a consequence of the mobility given them by flight, but we cannot be sure that 66 million and more years ago there was not also a variation of this behaviour, with mated pairs, let's say of ornithomimosaurs, coming together to form collectives of nuclear families and not the harem system seen in herding mammals and some reptiles. Penguins are a good example of flightless dinosaurs living as pairs within a wider group for protection, sociability and the finding of a mate, but not with a harem system.

However, Tyranosaurs being large apex hunters were rare in the environment, so their social lives will be on a reduced scale, to say the least, and I think lions might provide a possible model, though I do think that the bird pair bonding is ancestral to at least theropods, though I think it also applied to ornithischians, particularly ornithopods. We know Maiasaura lived in groups and nested, and it is the nesting behaviour that indicates potential bird pair bonding. With birds tied to their helpless young in a nest, one adult will remain with them, hence the need for pair bonding. Young herding mammals are born able to run within minutes of them being born, so only the mother is needed to care for it. Parasaurolophus all seem to have a crest and there is, to my knowledge no sign of sexual dimorphism, likewise with Tyranosaurs. This is more birdlike than anything else as, apart from birds like Mallards and Peacocks, it is difficult to impossible to tell the sexes apart, and this uniformity of looks may contribute to why birds are incessantly noisy and they need to shout out who and where they are as they all, within a species, look the same, vide penguins and corvids. Hadrosaurs may have been just as noisy as a huddle of penguins by necessity, whether they were a crested species or not. I do think that the Mesozoic was very noisy, and probably very colourfull, far more so than in a fairly drap and silent mammal dominated world. Take away the birds and you will notice how quite it all is. But I digress. So I think that it is more probable that non avian dinosaurs acted more like birds in their social behaviour than mammals or living reptiles.

T.rex speed. That's difficult with estimates ranging from about 12 mph to nearly 50. The 50 is way too fast and can be discounted, and the 12 is too slow and can be discounted. We know they could engage in a stern chase with a hadrosaur, lame or not, so how fast do they need to be to catch a hadrosaur ? Well, how about 35mph, which is a recent estimate based on a re-appraisal of the size and disposition of hadrosaur caudofemoralis muscles. Personally I think that if possible, then that is too fast for T.rex, and 20 - 25mph for T.rex is perhaps closer to reality. What we don't know from the evidence of the failed T.rex attacks is at what distance apart they were at the start of the chase, and it's likely that T.rex had charged out from cover and surprised an either stationary or strolling hadrosaur. There is an analogy with cheetahs here in that you need to get the prey quickly before you run out of steam.

Btw, the low estimates for T.rex speed were worked out on the basis of the proportions of the femur and tibia, but failed to take into account that T.rex is digitigrade and walks on it's toes so the length of the metatarsal needs to be factored in. T.rex, as all theropods, live up to their name and have big feet, ie metatarsals. They are bigger in proportion to those of hadrosaurs and ceratopsians, so on paper should be able to outrun them, but what's on paper does not always get reflected in reality.

A caveat on the speeds is that it is is always assumed to be adult speeds, yet I would think that the majority of tyranosaurs living at any one time would be juveniles, not adults, and who knows what speeds the juveniles were capable of, certainly more than the adults, and increasing the younger they are, though there will be a point were speed decreases due to lack of muscle compared to an older animal. A ten year old may well be the speediest T.rex and capable of significantly higher speeds than an eighteen year old, though not the height to bite down onto the tail of a fleeing hadrosaur. How fast ? maybe 30 - 35 mph, but they are not built for speed in the way an ornithomimosaur is.
 
Mar 2017
873
Colorado
However, Tyranosaurs being large apex hunters were rare in the environment
Is that by analysis or by occurrence in fossil record?

Kirk Johnson (now at Smithsonian) started as a plant fossil guy. He'd warn against using existence in the fossil record as an indication of distribution or numbers. One tree puts out millions of leaves in its lifetime, each one suitable for fossilization (only a tiny fraction actually DO fossilize). An animal provides a single opportunity. Pretty much, we're lucky to find ANYTHING. There are what? 9 T.rex skeletons? That doesn't necessarily indicate they were rare in their environment.

T.rex was a big apex predator (agreed). It also ate big things that we believe were plentiful. I'm not being snarky. Have you seen a study that calculates distribution? You've obviously looked into this more than I.

Mt lions are less then 200 lbs. Not a big predator. They prey on elk around 500-700 lbs (& deer around 200 lbs). I live in a small valley ... which, according to state wildlife surveys, supports 3-4 lions. My point is that it supports a lot more lions than could be reasonably suspected from the prey populations (which aren't really that big). The lions ("shadow cats") are all singleton ambush predators. They associate just enough for the local female to have cubs about every three years. I've never seen two adult tracks together, but I suppose infrequent mating would be another explanation for those three adult T.rex's (rather than a harem).
 
Last edited:

Corvidius

Ad Honorem
Jul 2017
3,047
Crows nest
By analysis carried out by Robert Bakker based on occurence in the fossil record and other factors. While the data is from 1986 and more fossil tyranosaurs have been discovered since, Sue, Stan and Jane notably, there are still not very many, only 50, yet thousands of hadrosaur fossils, mostly partial, have been found. And to that must be added all the other prey species, such as Triceratops, and plenty of those have also been found. Bakker shows that T.rex, and other large theropods, formed only about 3,5% of the dinosaur population by the end of the Cretaceous. This is about the same as for apex mammalian predators, notably lions, before their numbers fell like a stone. These low numbers are in sharp contrast to other types of predator, for instance crocodilians who are present, at least in rivers, in large numbers. This discrepancy formed part of Bakker's theory that dinosaurs were endotherms. They need a lot to eat to maintain their high metabolic rates, and so need a lot of prey per individual. This limits the number that can inhabit a range as otherwise if there are too many they exhaust the food supply. Ectothermic crocodiles with their very low metabolism need food only infrequently, with many months before needing to eat, a possible reason for them surviving the extinction and high metabolism dinosaurs mostly dying out.

On the overall numbers of T.rex fossils we have versus how many may have been alive at any one time, then yes, you're right that as fossilization is so rare then the vast majority are lost from the record for ever. But this also applies to the prey of T.rex, and they are found in far high numbers than T.rex, so the ratio between them is probably correct. I cannot think of any reason for there to be any preservational bias against T.rex and for it's prey when they share the same ecology, and so subject to the same fossilization processes, in fact I can find a reason for it's prey to be underrepresented, and that is that T.rex pretty much devoured the entire animal, unlike the non bone devouring big cats.

As not a single verifiable T.rex egg has ever been found, then it can only be conjecture as to it's frequency of breeding and how many eggs it layed. As with most of it's living relatives, and all other dinosaurs that we have some record of, I guess it is reasonable to assume that they bred once a year and layed many eggs, and seemingly the bigger the dinosaur the more egss it layed, though even oviraptors like Citipati layed about thirty. As to how long altricial young had parental care we cannot know, maybe until the next generation came along, maybe longer, and I think this will vary between herbivores and carnivores. But at the moment T.rex reproduction and parental care is pretty much a blank page. Some people, me included, may surmise that T.rex young, those that survived the first year, were with their parents for an indeterminate time, but there is no proof of anything, yet.
 
Last edited:
Mar 2017
873
Colorado
Bakker shows that T.rex, and other large theropods, formed only about 3,5% of the dinosaur population by the end of the Cretaceous. This is about the same as for apex mammalian predators
3.5% sounds pretty low ... I started looking for references ... then stopped and thought about it.

100 mix of deer/elk, 3.5 lions ... that actually sounds a bit high.

A Canadian study of mt. lions showed the average kill rate is .24-1.38 ungulates/day. So the low end is 1 animal every four days. So if lion percent was 1% of prey, in a year one lion would eat 91 animals ... leaving 9. The Canadian study did point out that they eat a lot more than anyone thought.
Ferocious appetites: Study finds mountain lions may be eating more than previously believed | Outdoors | billingsgazette.com

Anyway, I'm basically agreeing with you ... and speculating that the theropod number was even lower. Which, of course, makes those three adults wandering around together even more puzzling.

A Water Ouzel bird is a tiny thing ... 1/3 of a North American Robin maybe. They're loners that need 15 sq-miles of territory. They somehow find each other to keep a stable population.
 
Last edited:

Corvidius

Ad Honorem
Jul 2017
3,047
Crows nest
Ah, I should have explained that 3,5% was an average. The actual ratio varies, in different locations and in different time periods, between 1 and 5 percent. Bakker found that Allosaurs had a predator to prey ration of only 1,5%. The ratio for African lions, and falling, is 0,3%. The mammal ratio over big time is about the same as that for dinosaurs at 4.%. That the mammal ratio today is around 1% overall is due to us killing them in large numbers and destruction of their environment for cultivation. The ratio in the UK, barring very small predators like the native wild cat, is essentially zero because all the wolves and lynx were killed a very long time ago.

Now, three adult tyranosaurs together in an environment were they were as rare as lions does seem puzzling. Of course at least two had to meet at least once a year, or longer depending on breeding frequency, but there could be another reason why we find three, and that is because they may have been pack hunters.

An interesting fact from Currie about T.rex's cousin the Tarbosaur. 30 to 50% of all dinosaur finds in the Nemegt Basin in Mongolia are those of Tarbosaurus, which is far too high, impossibly high. Trackway evidence shows Tarbosaurus providing only about 5% of all footprints. This difference between the trackway evidence and the actual ratio of animals found is explained by the mechanism of Tarbosaurus, like T. rex, devouring the entire prey animal and so skewing the preservational bias. I would add that one hadrosaur or triceratops contains far more meat than a single T. rex or Tarbosaur can consume in one sitting. Of course just like big cats they may well have returned to the corpse over a period of several days. On the other hand, a pack of large predators could finish off a multi ton prey animal at one sitting.

Edit: The discrepancy in the Nemegt between the number of prey fossils found versus the number of Tarbosaurs, and then the inverse number of footprints, still seems odd. I wrote that the numbers of predator to prey fossils in the range of T. rex is about what should be expected, though it could have shown less prey due to T.rex eating everything. As this large discrepancy does not seem to show with T.rex, I'm not sure why it would show with Tarbosaurus. I find it difficult to believe that Tarbosaurs completely consumed up to 50% of their total prey population as that rate of predation would drive the prey species quickly to extinction, particularly if you factor in the activities of other predators and other causes of death for prey species, not everybody gets chomped, and not all of those chomped are killed by Tarbosaurs as there were also "raptors" in the environment.

At only one point in time can we say that there were an unbelievably large number of predators in relation to their prey, and that is in the last days during the extinction, when eventually there were no prey, only starving predators. However, the fossils in the Nemegt are from before the extinction, not during it.
 
Last edited:

starman

Ad Honorem
Jan 2014
4,106
Connecticut
An interesting fact from Currie about T.rex's cousin the Tarbosaur. 30 to 50% of all dinosaur finds in the Nemegt Basin in Mongolia are those of Tarbosaurus, which is far too high, impossibly high. Trackway evidence shows Tarbosaurus providing only about 5% of all footprints.
Yep, as first noted by the JMJPE over a decade ago.


Tarbosaurus, like T. rex, devouring the entire prey animal
Dunno of they ate the larger limb elements. IIRC one study concluded they didn't.


Edit: The discrepancy in the Nemegt between the number of prey fossils found versus the number of Tarbosaurs, and then the inverse number of footprints, still seems odd.
The bulk of Nemegtian tracks are from hadrosaurs, presumably S. angustirostris. I suspect one reason they're so abundant (absolutely and relative to T. baatar tracks) is that hadrosaurs lived close to rivers (where tracks are most likely made) whereas tyrannosaurs lived and hunted in all environments with suitable prey.
As for skeletal ratios, I once suggested the drier Nemegtian environment, relative to the Hell Creek, played a role. Droughts were hell on juvenile tyrannosaurs, as smaller beasts heat up more quickly.They probably suffered high mortality and were preserved by sediments from returning rains and floods.
 
Mar 2017
873
Colorado
At only one point in time can we say that there were an unbelievably large number of predators in relation to their prey, and that is in the last days during the extinction, when eventually there were no prey, only starving predators. However, the fossils in the Nemegt are from before the extinction, not during it.
The Triassic, allegedly, had ONLY predators. I still find that kind of hard to believe.

African lions stuff themselves catatonic. In the hot sun, carcasses deteriorate rapidly: jackals, hyenas, and about a dozen different species of vulture finish them off --- carcasses in a healthy environment don't last 24 hrs.

American mt lions feed, usually bury their prey, and come back to feed over a period of days until it becomes too rancid. The biggest bird scavengers are ravens and a very few hawks/eagles. Coyotes find lion country a bit risky, but foxes will steal what they can (but not much). I've moved whole carcasses that weren't buried. So ... a T.rex doesn't have to eat prey all at once.

Length of the digestive system seems pretty critical. The shorter the intestines, the more decay a predator/scavenger can stand.
----
There was a neighborhood dog that was grabbed by a lion. The lion was full, but couldn't resist the prey, and promptly buried it ... somewhat alive. The dog gained enough sense to dig out and drag itself home ... with puncture wounds in its skull. That's not the typical ending of dog:lion encounters.



...and yet, another speculation:
Some raptors drop entire kills in their nests and share them with the young. A big T.rex kill could feed a T.rex for multiple days, plus a large amount of progeny (presuming parental care, of course). Not many T.rex's, right? Species with low success rate of young growing to adulthood tend to have large broods ... and in spite of that, typically only replace themselves in their lifetime. Think of frogs laying 100's of eggs over their lifetime, and only JUST replacing the adults when it's all said and done. So, there COULD have been lots of little T.rex tykes, sharing a kill, only to be snapped up by anything big enough to swallow them.
 
Last edited:

Corvidius

Ad Honorem
Jul 2017
3,047
Crows nest
I think the Permian was a bit carnivore heavy with the Edaphosauridae being the notable exception.