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XENICIBIS & PALS



Ron asked me to send more information on _Xenicibis_, possibly the 
only facultatively quadrupedal bird ever, so here goes. I do not have the 
literature to hand, nor have I in fact seen the paper where Olson 
suggests quadrupedality in this animal: I'm going from what I learnt off 
Julian Hume (an ornithologist who specialises in Mascarene birds: see 
_Smithsonian_ 30 (12), March 2000). 

_Xenicibis xympithecus_ Olson and Wetmore 1976 is from Jamaica. It 
apparently resembled other robust ibises but for its wings. These are 
really peculiar, with uniquely modified ulnae and carpometacarpi. The 
ulnae have markedly attenuated distal ends and are fairly straight; the 
carpometacarpi are large fused clubs, totally unlike those of any other 
bird. Accordingly, Olson suggested that these might have been used in 
supporting the animal in a quadrupedal pose. I understand this was 
published in a short paper (or extended abstract?) presented at an 
American ornithological convention. The idea is not mentioned in the 
_Proc. Biol. Soc. Washington_ paper that first described this bird.

>From the global perspective, what's interesting about _Xenicibis_ is 
that it has helped demonstrate the weirdness potential of ibises. For 
decades, all known ibises were pretty much the same, and despite their 
geographical and ecological success, they all looked pretty similar. It is 
only within the last 20 years that extinct island endemics have changed 
this view - we now know that ibises evolved flightlessness on the 
Hawaiian islands (_Apteribis_) and in the Caribbean. The Mascarene 
form _Borbonibis_, now regarded as the origin of the Reunion 
solitaire (_Ornithaptera_/_Victoriornis_) myth (more on that to appear 
in print soon), was not flightless and has recently been regarded as 
possibly congeneric with _Threskiornis_. At least some of these forms, 
like _Xenicibis_, were morphologically absurd as birds go. 

Finally, what are ibises? Most recent parsinomy analyses of Cainozoic 
bird taxa find that the traditional clades of Gadow and Wetmore (e.g., 
Gruiformes, Coraciiformes, Pelecaniformes) are supported 
empirically, whereas rather more unorthodox alternatives (e.g., that 
falconids are closest to musophagids, that herons are gruiforms, that 
anseriforms are charadriiforms etc.) are not. To my knowlegde no 
study has yet been holistic enough to look at ciconiiforms as well as 
palaeognaths, gruiforms and other groups, but I suppose people are 
working on it. Where ibises fall into all this will be interesting - and 
here we go back to the polyphyletic ratites thing - because Olson has 
suggested that kiwis might be modified ibises. I suppose I should also 
note that we might consider spoonbills as modified ibises too.

Finally finally, are there any onychophoran experts out there?

DARREN NAISH 
PALAEOBIOLOGY RESEARCH GROUP
School of Earth, Environmental & Physical Sciences
UNIVERSITY OF PORTSMOUTH
Burnaby Building
Burnaby Road                           email: darren.naish@port.ac.uk
Portsmouth UK                          tel: 01703 446718
P01 3QL