RATITE UNCINATES

[darren.naish@port.ac.uk]

Matt Troutman wrote..

> The uncinate processes in dromaeosaurs are 
> secondary ossifications (not extentions of the thoracic ribs in 
> ornithurine birds).  

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. 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).

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.

"Slimy? Mudhole? My _home_ this is"

DARREN NAISH
darren.naish@port.ac.uk