RE: Rapetosaurus Skull

[MarkSabercat@aol.com]

In response to Chris Collinson's question earlier question regarding the 
extent of Rapetosaurus' antorbital fenestra, I can affirm that it IS actually 
this large, as unusual as it seems. In addition to photos of the individual 
skull elements of the juvenile and adult specimens, I viewed  the cranial and 
postcranial elements while I was working with Kristi-Curry-Rogers at SMM in 
February of last year on the skeletal reconstruction we did for Nature, and 
the a.f. is very different from that of any other known sauropod. I'm 
presently stumped as to the reason for its huge size. Just touching on the 
somewhat related news about dinosaur nostril placement, I have to say that I 
disagree with the restoration of a diplodocid with extremely rostral external 
nares, as shown in Nature. Although the external dorsal surfaces on the 
premaxilla/maxilla of diplodocids like Diplodocus and Apatosaurus show 
prominent rugosities, there is no evidence of  tubular depressions that would 
form a support for   cartilagenous or otherwise fleshy tubes going up to the 
narial opening on the skull; if these forms had anterior rostral outer nares, 
why wouln't these be covered by narial bones, and why would the nares have 
retreated to the top of the skull? Some of the other sauropod taxa are a 
different case, however, and there could be the advantage to the anterior 
position that Dr. Witmer has suggested. I'm inclined to think that one 
possibility for the dorso-posterior openings for the nares on many sauropods 
could partly relate to the need for some of the long necked forms to breathe 
while they took the time required to drink; raising and lowering the neck 
frequently from an extreme low position would have played havoc with their 
blood pressure, and once the head was down to drink it would be best to stay 
down until enough water had been taken in. Backwardly positioned nares would 
fit in with this, although there were probably other reasons for these as 
well. What does everyone else think?

Mark Hallett
marksabercat@yahoo.com