If Nanotyrannus is valid, what is it?

[Tarbosaurus]

I'm still on the fence about if Nanotyannus l. is a valid genus or not. I used to be firmly on the "Juvenile T.rex" side with Carr but some arguments such as the odd limb proportions on "Bloody Mary", tooth counts in actual juvenile Tyrannosaurus like "Baby Bob", and there being two "types" of Tyrannosaurid teeth in Hell Creek with overlapping sizes but very different shapes which don't all seem to be cases of it being teeth from different parts of the mouth, have shifted me to being open to both sides. I suppose it does make ecological sense for there to be a medium-size carnivore in the same region as a very large predator as the prey taken would likely differ drastically. So while I'm undecided, I can certainly see either argument being true.

But hypothetically speaking, if Nanotyrannus turns out to be a valid genus, what branch of the family tree exactly would it come from? Based off time and location I'd be tempted to say it's a Tyrannosaurinae like Tarbosaurus or Tyrannosaurus, but last I checked most definite members of that group tended to be a lot more robust. I also recall when it was first described, Gilmore called it a species of Gorgosaurus. The lean build and thinner teeth do align with Albertosaurinae, but they could be convergently evolved I suppose.

Edited December 19, 2018 by Tarbosaurus

[The Amateur Paleontologist]

Hey @Tarbosaurus - welcome to the Forum

You're raising some interesting issues.. I actually hadn't given much thought to the possibility that N. lancensis was an albertosaurine...

-Christian

[Tarbosaurus]

1 hour ago, The Amateur Paleontologist said:

Hey @Tarbosaurus - welcome to the Forum

You're raising some interesting issues.. I actually hadn't given much thought to the possibility that N. lancensis was an albertosaurine...

-Christian

I admit it's based off very little evidence. Only information I'm aware of regarding the possibility of an Albertosaurine surviving into that time and in that region is this.

https://www.jstor.org/stable/1304167

 

It's more surmised based off build and size. From what I can gather, most specimens that might be a Nanotyrannus are not fully grown and could have potentially gotten somewhat larger. This would put them fairly close to the range of Gorgosaurus and Albertosaurus. Additionally reported Nanotyrannus remains have some skeletal traits found in those two genera, but not with Tyrannosaurus or Tarbosaurus. Aside from specifics, it seems Albertosaurines had preportionally longer arms than Tyrannosaurines, especially Gorgosaurus.

 

Source, Comparison of various adult tyrannosaurids: Gorgosaurus libratus (a), Albertosaurus sarcophagus (b), Tyrannosaurus rex (c) and Tarbosaurus bataar (d). Differences are minor at the generic level. Courtesy of Gregory S. Paul.

This seems to match up to how reported Nanotyrannus specimens have noticeably larger arms with "Bloody Mary" have arms larger than "Wyrex" despite being substantially smaller.

 

And just glancing at the general builds from an outside perspective, there are some similarities even if it's just coincidence. Some earlier forms that were more common in previous stages like lambeosaurines did persist into the Maastrichtian stage, just in lower numbers. So I didn't discount the possibility an Albertosaurine did too.

 

Edited December 19, 2018 by Tarbosaurus

[LordTrilobite]

As far as I know Nannotyrannus hasn't been identified as an Albertosaurine for a long time. I forgot but there are some important differences that make it more closely related to T. rex. So even if it's valid it's likely not Albertosaurine.

[ynot]

If Nano is a juvenile Albertosaurine why are they not found where the Albertosaurine  are common? Also - where are the adults that were contemporary to nano?

[Tarbosaurus]

8 hours ago, ynot said:

If Nano is a juvenile Albertosaurine why are they not found where the Albertosaurine  are common? Also - where are the adults that were contemporary to nano?

Again, just an 'off the wall' idea. I'd presume if it turned out to have evidence of such it be a migration (given the locations aren't that far from formations with the likes of Albertosaurus) and bad luck not finding adults yet. I can't quite recall where but I seem to remember something stating the suspected Nano specimens aren't fully grown. Assuming they aren't T.rex.

[ynot]

11 minutes ago, Tarbosaurus said:

given the locations aren't that far from formations with the likes of Albertosaurus)

The locations may be close to each other in distance, but not so close in time.

[Tarbosaurus]

2 hours ago, ynot said:

The locations may be close to each other in distance, but not so close in time.

Not arguing for arguments sake, , but last I checked Albertosaurus was pegged as hanging in there until 68 mya, not that long of a gap. I do believe you that if Nano is a valid genus, it's probably a Tyrannosaurine, I just don't see many family trees listing it to begin with so I wasn't sure how the opinions fell.

[CBchiefski]

Welcome @Tarbosaurus and I would read this thread:

You do not see many trees listing it as most consider it to be a growth stage of T rex, the last decent phylogeny which had it was Holtz 2001 before Jane was discovered and he placed it as a sister taxon to T rex plus made the point that Nano was likely a growth stage of Rex. Now, you are correct in seeing similarities to Albertosaurinae as often times juveniles do look closer to the ancestral state of their group, which seems to be the case with Nano.

If you would like to see the tree I refer to:
Holtz, T.R., Jr. 2001. The phylogeny and taxonomy of the Tyrannosauridae. Pp. 64-83, in D.H. Tanke and K. Carpenter (eds.), Mesozoic Vertebrate Life: New Research Inspired by the Paleontology of Philip J. Currie. Indiana Univ. Press.

Edited December 20, 2018 by CBchiefski
Added call out