[Date Prev][Date Next][Thread Prev][Thread Next][Date Index][Thread Index][Subject Index][Author Index]


>Sometimes it's tricky to tell whether or not uncinate processes on 
>maniraptoran ribs had their own, separate centres of ossification. If 
>you look closely at the uncinate processes in some ratites - 
>particularly moa, and I have seen it in cassowaries and I think 
>ostriches too (emus, like GSP says, do not have uncinates on their 
>ribs... I checked lots of specimens hoping to disprove this:)) - the 
>uncinate is not fused to the rib.

The "fighting" Velociraptor and perhaps some of the oviraptorosaur 
specimens from the Gobi all show this same condition.  This is an 
interesting paradox that also brings up some problems in basal bird 
evolution: if dromaeosaurs and perhaps oviraptorosaurs had uncinates, 
why were they lost in Archaeopteryx and the enantornithines but 
"regained" in the ornithurines?  Is this paradox perhaps evidence for a 
monophyletic Sauriurae (where the lack or incomplete calcification of 
uncinates is evidence of common descent)?  

>This is a problem in curation and exhibition, because of course the 
>uncinates then drop off and can get lost, so lots of curated ratite 
>specimens have the uncinates stapled or wired onto the rib. This 
>problem is superbly illustrated by the _Dinornis_ on display in the 
>main hall of the NHM (London) (where one of the fibulae, >incidentally, 
has already fallen off its natural position).

A similiar problem is found in Opisthocomus.  According to Storrs Olson, 
there is a second phalanx on the alular digit in adults that is lost 
frequently in preparation.  

>If palaeognaths do have a basal position in Neornithes (i.e. are the 
>sister-group to Neognathae), then might 'uncinates fully fused to 
>ribs' be a neognathan character? Or have ratites reversed a primitive 
>ornithurine condition? Diagrams of hesperornithiformes, 
>ichthyornithiformes and of course _Chaoyangia_ seem to show the 
>uncinates as unfused, so maybe the former idea is the best 
>one. I'm really despairing at how little I know.

Your former idea sounds most reasonable and probably correct.  

Another case where uncinates can be useful for finding relations is the 
case of diatrymids and anhimids (screamers).  They both lack uncinates, 
have thickened orbital rims, presence of an enlarged distal tubercle on 
the deltoid crest, cribiform anterior carpal fossa, elongate proximal 
metacarpal symphysis, elongate alular metacarpal, and pectineal process 
of pubis represented by low convexity.  Andors (1992) interpreted these 
characters as convergences mainly because he considered diatrymids 
intermediate between galliforms and anseriforms.  However, two recent 
analyses take anseriforms away from the galliforms (one, I think by 
Brian Livezey, supports anseriforms as flamingo relatives within the 
Ciconiiformes!).  Unfortunately, I ran out of change (and time) before I 
could get to the articles (they both were in the December 1997 
Zoological Journal of the Linnaen Society I believe).  When I get around 
to getting them I'll enlighten everybody here. 

Diatrymids=giant screamers?  Hmm.  

Matt Troutman

Get Your Private, Free Email at http://www.hotmail.com