further argument on the validity of ‘Nanotyrannus’

[sauroid]

Dentary groove morphology does not distinguish 'Nanotyrannus' as a valid taxon of tyrannosauroid dinosaur.
http://www.sciencedirect.com/science/article/pii/S0195667116300192

[SBell]

The genus is looking more and more like it is a synonym. But then this is how science should work--some puts out a hypothesis (novel genus) based on observations (taxon description). Other people test to see if it holds up (so far, not so much).

No matter how much people want there to be a pygmy tyrannosaur!

[Simon]

The genus is looking more and more like it is a synonym. But then this is how science should work--some puts out a hypothesis (novel genus) based on observations (taxon description). Other people test to see if it holds up (so far, not so much).

No matter how much people want there to be a pygmy tyrannosaur!

Much as I would like to see confirmation of a "Nanotyrannus" as a separate species, I must concur with your statement based on currently available evidence.

However, "pygmy" Tyrannosaurs of a sort DID indeed exist in this ecosystem - but they were the immature individuals of the same species as TRex.  That fact may have precluded a "true" "pygmy" TRex from evolving because they dominated the niche already, based on age/size instead of being a different species ...

[SBell]

The genus is looking more and more like it is a synonym. But then this is how science should work--some puts out a hypothesis (novel genus) based on observations (taxon description). Other people test to see if it holds up (so far, not so much).

No matter how much people want there to be a pygmy tyrannosaur!

Much as I would like to see confirmation of a "Nanotyrannus" as a separate species, I must concur with your statement based on currently available evidence.

However, "pygmy" Tyrannosaurs of a sort DID indeed exist in this ecosystem - but they were the immature individuals of the same species as TRex.  That fact may have precluded a "true" "pygmy" TRex from evolving because they dominated the niche already, based on age/size instead of being a different species ...

That same niche differentiation has been put out there to explain the total lack of a stratified carnivore guild like was usually seen! For example, in the Morrison, where you have a huge range of theropods of different sizes, from medium to huge. In the late Cretaceous Hell Creek-Frenchman Fm, you get small dromaeosaur-like animals, and then T rex, with nothing in between! There aren't even big crocs or something to explain it. Other than younger T.rex individuals.

[Simon]

Yeah ... in a way it seems to support, indirectly, that within its ecosystem, TRex was the most successful carnivorous theropod of the entire dinosaur epoch ... which jibes with the visual and morphological evidence (most muscled, most powerful bite, etc) ... put another way, Allosauroids could tackle sauropods but there is no way they could have "handled" Triceratops or Ankylosaurus like TRex was equipped to do ...

[SBell]

Yeah ... in a way it seems to support, indirectly, that within its ecosystem, TRex was the most successful carnivorous theropod of the entire dinosaur epoch ... which jibes with the visual and morphological evidence (most muscled, most powerful bite, etc) ... put another way, Allosauroids could tackle sauropods but there is no way they could have "handled" Triceratops or Ankylosaurus like TRex was equipped to do ...

And, at the same time, found a way to keep out smaller-niche competition by dominating the field for large ornithomimids and other medium-size prey!

[stargatedalek]

If anything I'd say it was most likely changes in herbivores that drove out the "mid tier" niche carnivores and not Tyrannosaurus.

[Yutyrannus]

That same niche differentiation has been put out there to explain the total lack of a stratified carnivore guild like was usually seen! For example, in the Morrison, where you have a huge range of theropods of different sizes, from medium to huge. In the late Cretaceous Hell Creek-Frenchman Fm, you get small dromaeosaur-like animals, and then T rex, with nothing in between! There aren't even big crocs or something to explain it. Other than younger T.rex individuals.

There was something in between: Dakotaraptor .

[SBell]

That same niche differentiation has been put out there to explain the total lack of a stratified carnivore guild like was usually seen! For example, in the Morrison, where you have a huge range of theropods of different sizes, from medium to huge. In the late Cretaceous Hell Creek-Frenchman Fm, you get small dromaeosaur-like animals, and then T rex, with nothing in between! There aren't even big crocs or something to explain it. Other than younger T.rex individuals.

There was something in between: Dakotaraptor .

Well, compared to the diverse Morrison theropod guild, or even the preceeding Campanian, even one mid-size non-T. rex is pretty minimal.

[sauroid]

related article
https://qilong.wordpress.com/2016/04/05/nano-keeps-on-slipping-slipping/