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TYRANNOSAUR LIPS



I'm just about still alive. Nick Longrich, I think, musing about beaks or cheeks
in certain dinosaurs, wrote..
 
>  After perusing through the Dinosauria a little more, I did find some 
> of those little holes illustrated on other animals, noticeably the 
> prosauropods and the hypsilophpodont Tenontosaurus, not on the beak part 
> but on the cheek part, although one did show a series of these ending 
> just behind the predentary. So maybe the vascularization could support 
> either, or maybe segnosaurs had big lips, not beaks? At any rate, it's 
> not cut and dry. 

_Tenontosaurus_ is not a hypsilophodont, but a basal member of the iguanodont
clade (if, like me, you agree with Paul Sereno and Katherine Forster).

Emargination of the tooth row in the segnosaurs strongly suggests that they had
cheeks, but this is controversial (see the chapter in Weish-Dod-Os). If they
did, then they evolved them convergently with ornithischians (apparently some
prosauropods (anchisaurids in particular) have incipient cheeks too but I'm not
convinced). Characteristics of the premaxilla and dentary suggest that
segnosaurs had beaks too, and this is further augmented by their phylogenetic
bracket (maniraptorans and bullatosaurs certainly have/had beaks). Extensive
cheeks (the most cranial-ward point of emargination indicates the start of the
cheek tissue) are not compatible with extensive beaks, so as a compromise my
segnosaurs have beaks going back to the start of the cheeks (as in ornithopods).

> as opposed to the bare t. rex teeth Greg draws. 

Except where they have beaks, all of Greg's theropods have lips. Those little
holes you are talking about are nutritive foramina - they aren't too useful
(ASAICT) in telling you about soft-tissue or keratin anatomy, as they appear
widely in vertebrates with lips, with cheeks, and with beaks. As they are not
diagnostic, other characteristics must be looked at (e.g. tooth row
emargination). It is also worth pointing out that blood vessels and nerves pass
through nutritive foramina - they are not 'whisker pits' as some writers
gleefully exclaimed back in the 1970s. 

Incidentally, extensive vascularisation indicated by a large number of nutritive
foramina does not prove the presence of well-vascularised soft tissue. Keratin-
sheathed structures like ungulate horns are often highly vascularised, and some
pterosaur beaks (see figures of the spoonbill-pterosaur whose name I've
forgotten) support large numbers of foramina.

"Help help help. I feel life coming to take me away when all I want to do is
die" - M. Monroe

Extensive memory loss is painful.

DARREN NAISH