ELOPTERYX REVISITED

[darren.naish@port.ac.uk]

Mickey Mortimer wrote..

> If Elopteryx has a crista trochanteris (which is what happens when the
> lesser and greater trochantors fuse, if I remember correctly), doesn't this
> narrow down it's possible classification somewhat?  As far as I know, only
> troodontids, mononykines, Rahonavis and pygostylians have a trochanteric
> crest.

Unfortunately, neither _Elopteryx_ femora have the distal end 
preserved (which might be helpful.. especially seeing as _Mononykus_ 
lacks an extensor groove). And I wish someone would do a good 
description of troodontid limb bones. I checked Csiki and 
Grigorescu's (1998) figures the other day and, John is right, the 
figures aren't that helpful, nor are the bones really described. I 
was playing with the idea of redescribing the _Elopteryx_ femora but 
I don't think I understand proximal femoral morphology well enough to 
make a useful contribution.
 
> All of the above groups also have well-developed posterior trochantors
> (except for ornithurans, and I'm not sure about confuciusornithids).  So,
> Elopteryx is most probably a troodontid, mononykine or a non-ornithuran
> member of the Rahonavis+pygostylian clade.  

Hmm.. this is something to think about. The idea of an alvarezsaurid 
affinity is _very_ interesting (for reasons I cannot presently 
discuss). Eric Buffetaut's recent description of enantiornithine 
femora from France (again in _Orcytos_ 1) pointed to the 
caudolaterally 'open' excavation delimited distally by a prominent 
posterior trochanter, and I assume that this is true of all(?) 
enantiornithines (will have to check figures). This 'excavation' has 
got to be homologous with the hollow on the caudolateral part of the 
two _Elopteryx_ femora I described in a previous email. However,
that in the _Elopteryx_ specimens it is very shallow and not clearly 
delimited distally by a very well-defined posterior trochanter 
*indicates*, I suppose, that _Elopteryx_ is not enantiornithine. 

> Does anyone know of any other features that would help characterize it 
> further?

Well, there are certainly other features worthy of comment on the 
femora, but whether or not they are unique to these specimens is 
doubtful. In A1235 there is a proximodistally elongate concavity 
running along the cranial face of the shaft from just distal to the 
level of the caput to about half way down. I cannot recall a 
structure as marked as this in any bird femur that I've seen. 

On the caudal surface there is a small concavity (it is labelled a 
sulcus in my diagrams) lateral to the caput and distal to the crista 
trochanteris: a shallow channel then runs from this area 
distolaterally. What this is, I haven't a clue, but that neither 
features are seen in BMNH A1234 suggests it is subject to individual 
variation. Distal to this channel there are two projections from the 
caudal surface of A1235's shaft: a short, low ridge with a blunt 
crest on the caudomedial edge of the bone, and further distally a 
long, sharp low ridge that is in the approximate area of a fourth 
trochanter. The distal end of this latter ridge is closer to the 
lateral side than is the ridge's proximal end (in other words, it 
has a kind of diagonal slant to it). 

I'm very sorry if my garbled descriptive narrative is hard to follow: 
things would help if I could show you the diagrams and point to the 
things I am talking about! Maybe there is a paper in this after all:)

Comments from people who know what they are talking about would be 
much appreciated!

DARREN NAISH 
PALAEOBIOLOGY RESEARCH GROUP
School of Earth, Environmental & Physical Sciences
UNIVERSITY OF PORTSMOUTH
Burnaby Building
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