RE: TOROSAURUS/TRICERATOPS FRILLS

[jconrad@lib.drury.edu]

First, THANKS to those who took time to respond!!

I actually knew that _Avaceratops_ and _Brachyceratops_ were considered
centrosaurines, I just don't know what characters place them there.  Both
animals are rather poorly known, but I don't know exactly what basis was
used to place them as basal centrosaurines.  

> Brachyceratops and Avaceratops are closely related, but neither of those 
> are closely related to Triceratops. Brachyceratops and Avaceratops are 
> members of the Centrosaurinae, the more primitive subfamily of the 
> Ceratopsidae. There is some debate over whether or not the frill of 
> Avaceratops was solid, but I have seen the type specimen for it, and if 
> there were fenestrae they were dang small.

> My opinion, backed up by many characters, is that Triceratops and 
> Avaceratops independently lost their parietal fenestrae. Based on other 
> characters in the skull, it seems that Triceratops is more closely 
> related to Chasmosaurus and Torosaurus than others. (see below).

This sounds reasonable.  
 
>>They are basal Centrosaurinae, and Toro/Trike may be
> advanced Chasmosaurinae. Some skulls of Trike are very similar to
> centrosaurines, like *T. "obtusus"* and *T. "serratus"*, so they may
> be basal, and the semi-solid (very thin on both trikes and Brachy and
> Ada) mid parietals are quitre similar.
 
> I only partly agree here. "T. obtusus" and "T. serratus" are probably 
> not basal, but about as advanced as you could get. I agree that the 
> parietals are similar, but they were acquired independently. My 
> examination of the specimens shows that Avaceratops and Triceratops have 
> few if any other similarities. The shape of the squamosal is 
> characteristically centrosaurine in Avaceratops, and Triceratops has a 
> chasmosaurine, although short, squamosal (I'll add here that there is 
> some variation in that, too. I'm doing research on it at present).

Cool, thanks for the info.  Have a great day!
 
> The Torosaurus Home Page
> http://www.geocities.com/CapeCanaveral/Hangar/3404

Jack Conrad