More evidence Nanotyrannus never existed

[suspsy]

https://advances.sciencemag.org/content/6/1/eaax6250

ABSTRACT: Despite its iconic status as the king of dinosaurs, Tyrannosaurus rex biology is incompletely understood. Here, we examine femur and tibia bone microstructure from two half-grown T. rex specimens, permitting the assessments of age, growth rate, and maturity necessary for investigating the early life history of this giant theropod. Osteohistology reveals these were immature individuals 13 to 15 years of age, exhibiting growth rates similar to extant birds and mammals, and that annual growth was dependent on resource abundance. Together, our results support the synonomization of "Nanotyrannus" into Tyrannosaurus and fail to support the hypothesized presence of a sympatric tyrannosaurid species of markedly smaller adult body size. Our independent data contribute to mounting evidence for a rapid shift in body size associated with ontogenetic niche partitioning late in T. rex ontogeny and suggest that this species singularly exploited mid- to large-sized theropod niches at the end of the Cretaceous.

[Tyto_Theropod]

Interesting but unsurprising - at least for me, as someone who's been in the 'Nanotyrannus is a junior synonym' camp for a while based on what I'd read.  Still, I'm always fascinated at the thought of two growth stages of a single species filling two different niches, and possibly employing different hunting strategies.  AFAIK there isn't really an analogue for this today (which could, of course, be used to argue that this interpretation is a little fanciful).  It's ideas like this that make Tyrannosauridae - and prehistoric animals and ecosystems in general - all the more intriguing.  How alien that past version of Earth sometimes seems!

[Mirroraptor]

How will they explain the difference in absolute forelimb length?
Some Nanotyrannus have forelimbs that are longer and much longer than T.rex, unless they have reversed growth in their forelimbs during development.
Perhaps most of the Nanotyrannus fossils are from the Juvenile Tyrannosaurus rex, but it cannot be ruled out that there is indeed an unidentified group of Tyrannosaurid dinosaurs living in the same area as T rex.

[stargatedalek]

How will they explain the difference in absolute forelimb length?
Some Nanotyrannus have forelimbs that are longer and much longer than T.rex, unless they have reversed growth in their forelimbs during development.
Perhaps most of the Nanotyrannus fossils are from the Juvenile Tyrannosaurus rex, but it cannot be ruled out that there is indeed an unidentified group of Tyrannosaurid dinosaurs living in the same area as T rex.

Larger proportionally, but not larger. The arms of "Nanotyrannus" specimens are smaller than Tyrannosaurus arms, just much larger relative to the body. They simply grew more slowly as the animal aged.

[Mirroraptor]

How will they explain the difference in absolute forelimb length?
Some Nanotyrannus have forelimbs that are longer and much longer than T.rex, unless they have reversed growth in their forelimbs during development.
Perhaps most of the Nanotyrannus fossils are from the Juvenile Tyrannosaurus rex, but it cannot be ruled out that there is indeed an unidentified group of Tyrannosaurid dinosaurs living in the same area as T rex.

Larger proportionally, but not larger. The arms of "Nanotyrannus" specimens are smaller than Tyrannosaurus arms, just much larger relative to the body. They simply grew more slowly as the animal aged.

[stargatedalek]

The "dueling dinosaurs" fossil is not a trustworthy source. It has thus far been examined only by the company trying to sell it, and they are marketing it heavily on it containing "Nanotyrannus". Frankly, I have no doubts they would be willing to fudge numbers if not actually lie to promote their product.

[Avian]

Heres a video that explains a little bit: https://m.youtube.com/watch?v=a-DrKFVE63A

[Mirroraptor]

The "dueling dinosaurs" fossil is not a trustworthy source. It has thus far been examined only by the company trying to sell it, and they are marketing it heavily on it containing "Nanotyrannus". Frankly, I have no doubts they would be willing to fudge numbers if not actually lie to promote their product.

Perhaps this is the case, and we may never know the true answer until the dueling dinosaurs specimens are finally examined by academia.

[Dinoxels]

Heres a video that explains a little bit: https://m.youtube.com/watch?v=a-DrKFVE63A

I think you mean:
this episode

[Avian]

You're right. My bad.

[Huskies]

I wonder if this means that t-rex didn't live in groups just like lions considering if the adults were after different kinds of preys than the juveniles.

[Gwangi]

Interesting but unsurprising - at least for me, as someone who's been in the 'Nanotyrannus is a junior synonym' camp for a while based on what I'd read.  Still, I'm always fascinated at the thought of two growth stages of a single species filling two different niches, and possibly employing different hunting strategies.  AFAIK there isn't really an analogue for this today (which could, of course, be used to argue that this interpretation is a little fanciful).  It's ideas like this that make Tyrannosauridae - and prehistoric animals and ecosystems in general - all the more intriguing.  How alien that past version of Earth sometimes seems!

There are reptiles alive today that live drastically different lives as adults than they did as juveniles. Komodo dragons come to mind, where the young are arboreal, in part to stay away from their cannibalistic parents.

[Tyto_Theropod]

Interesting but unsurprising - at least for me, as someone who's been in the 'Nanotyrannus is a junior synonym' camp for a while based on what I'd read.  Still, I'm always fascinated at the thought of two growth stages of a single species filling two different niches, and possibly employing different hunting strategies.  AFAIK there isn't really an analogue for this today (which could, of course, be used to argue that this interpretation is a little fanciful).  It's ideas like this that make Tyrannosauridae - and prehistoric animals and ecosystems in general - all the more intriguing.  How alien that past version of Earth sometimes seems!

There are reptiles alive today that live drastically different lives as adults than they did as juveniles. Komodo dragons come to mind, where the young are arboreal, in part to stay away from their cannibalistic parents.

Well derp.  I knew that about komodos and had completely forgotten!  Better go and hand back my biology degree!   Regardless, thanks for another reminder that nature is amazing.

The cannibalism aspect is an interesting speculation for Tyrannosaurs as well.  There is some evidence of this behaviour, so perhaps their social structure (or lack thereof) was at least to some extent komodo-like?

[stargatedalek]

I think cannibalism in Tyrannosaurus is often overstated. We find a great deal of evidence of non-lethal fighting, almost always directed at biting the other around the nasal crest. This just seems far to deliberate for random acts of hunting.

Additionally, most predators will eat dead members of their own species, even if they won't kill them. It's cannibalism but a far different context than we typically think of. Given the amount of Tyrannosaurus fossils we have it only makes sense some are going to show evidence of having been scavenged by the only large carnivore in the region.

[suspsy]

I agree with stargate. Crocodilians are known to engage in cannibalism, but it's really not all that frequent among any of the 22 different species. You don't see Nile crocodiles actively attacking each on a regular basis. Such behaviour isn't healthy from an evolutionary perspective.

Same goes for bears. Males will sometimes try to go after cubs, and there's been at least one instance where a male polar bear killed a female that was defending her cubs and then devoured part of her, but again, such behaviour isn't rampant.

[Tyto_Theropod]

Very good points, @stargatedalek and @suspsy.  It was just an interesting thought. 

Certainly cannibalism doesn't benefit the species on a broad scale, and it makes even less sense when you keep in mind that most if not all extant Archosaurs exhibit some form of parental care.  Then again, you could also argue that a) on a smaller scale, evolution is governed by survival of the fittest individuals and b) dinosaurs are a very diverse group and not all of them need have behaved like modern relatives.  It's also worth pointing out that crocodiles and bears do no show the extreme niche partitioning between adults and juveniles that komodo dragons do, and that Tyrannosaurs seem to have done. 

However, for the most part I completely agree with you on it being unlikely.  I definitely don't imagine that individual T. rex regularly killed each other - animals are all about self-preservation, so it's far more likely that, as with the majority of species, most fights would have broken up before life-threatening injuries were inflicted. 

[HD-man]

Interesting but unsurprising - at least for me, as someone who's been in the 'Nanotyrannus is a junior synonym' camp for a while based on what I'd read.  Still, I'm always fascinated at the thought of two growth stages of a single species filling two different niches, and possibly employing different hunting strategies.  AFAIK there isn't really an analogue for this today (which could, of course, be used to argue that this interpretation is a little fanciful).  It's ideas like this that make Tyrannosauridae - and prehistoric animals and ecosystems in general - all the more intriguing.  How alien that past version of Earth sometimes seems!

There are reptiles alive today that live drastically different lives as adults than they did as juveniles. Komodo dragons come to mind, where the young are arboreal, in part to stay away from their cannibalistic parents.

Don't forget about crocodilians (See the Bakker quote).

Well derp.  I knew that about komodos and had completely forgotten!  Better go and hand back my biology degree!   Regardless, thanks for another reminder that nature is amazing.

The cannibalism aspect is an interesting speculation for Tyrannosaurs as well.  There is some evidence of this behaviour, so perhaps their social structure (or lack thereof) was at least to some extent komodo-like?

Probably more croc-like than Komodo-like (I.e. Crocs protect their young, but don't feed them).

Quoting Bakker ( https://www.amazon.com/Dinofest-International-Proceedings-Symposium-University/dp/0935868941 ):

A striking difference exists in modern communities between cold-blooded predators and hot-blooded predators. Most bird and mammal species feed their young until the youngsters are almost full size; then and only then do the young set out to hunt on their own. Consequently, the very young mammals and birds do not chose food items independently of the parents. Young lions and eagles feed on parts of carcasses from relatively large prey killed by the parents. Most snakes, lizards, and turtles do not feed the young after birth, and the new-born reptiles must find prey suitably diminutive to fit the size of the baby reptilian jaws and teeth. A single individual lizard during its lifetime usually feeds over a much wider size range of prey than a single individual weasel or hawk, because the lizard begins its life hunting independently.
Therefore, a predatory guild of three lizard species with adult weights 10g, 100g and 1000g would require a much wider range of prey size than a guild of three mammal predator species with the same adult weights. If allosaurs had a lizard-like parental behavior, then each individual allosaur would require a wide size range in prey as it grew up. The evidence of the Como lair sites strongly suggests that the dinosaur predatory guild was constructed more like that of hot-blooded carnivores than that of lizards or snakes.
This theory receives support from the shape of the baby allosaur teeth. In many cold-blooded reptilian predators today, the crown shape in the very young is quite different from the adult crown shape. For example, hatchling alligators have the same number of tooth sockets in each jaw as do the adults, but the hatchling crowns are very much sharper and more delicate. In the hatchling all the teeth are nearly the same shape, and the young gators have less differentiation of crown size and shape along the tooth row; the hatchlings lack the massive, projecting canine teeth and the very broad, acorn-shaped posterior crowns of the adults. Young gators feed extensively on water insects, and the sharp crowns are designed for such insectivorous habits. Adult gator species use their canine teeth for killing large prey, such as deer, and employ the acorn crowns to crush large water snails and turtles (Chabreck, 1971; Delaney and Abercrombie, 1986; McNease and Joanen, 1977; Web et al, 1987).
If allosaur hatchlings fed independent of adults, I would not expect the hatchling tooth crowns to be the same over-all shape as that of the adult. However, the over-all tooth crown shape in the tiniest allosaur IS identical to that of the adult (figs. 3,4). Thus it appears that hatchlings were feeding on prey tissue of the same general texture and consistency as that fed upon by adults.

[Tyto_Theropod]

H @HD-man From that point of view, it would be interesting to do a study of tooth crown size and shape over the lifetime of Tyrannosaurus.  Definitely going to do a Google Scholar search and see if anyone's done a study on this when I get the time!

[GojiraGuy1954]

http://www.thefossilforum.com/index.php?/topic/93287-the-case-for-nanotyrannus/&;

[suspsy]

http://www.thefossilforum.com/index.php?/topic/93287-the-case-for-nanotyrannus/&

If Pete Larson wants his arguments to be taken seriously by the paleontological community, then he needs to write a formal paper and get it published. This post comes off as little more than yet another desperate advertisement for the Dueling Dinosaurs.