LOST COMPSOGNATHID INTEGUMENT

[darren.naish@port.ac.uk]

Re: integument in small theropods...

Tim suggested that, because feathers/fuzz/fur is missing in 
_Compsognathus_, it might be due to secondary loss. In 
other words, what we see in the skeletons represents the life 
condition. In response Pete said....

> I am not sure if it's all that clear Compsognathus lacked feathers.  The 
> specimen, as it is, doesn't preserve any skin to speak of.  So as they say, 
> absense of evidence is not evidence of absense.

I'm with Pete on this one (and Greg Paul, and other 
rearchers who have stated similar). The absence of 
integument in _Compsognathus_ (and _Scipionyx_) is 
taphonomic - remember that dinosaur skeletons represent 
rotting corpses, not pristine animals that just died. Having 
spent most of last year immersed in vertebrate taphonomy 
and little else (sigh) I can confirm that some very odd things 
can happen regarding integument prior to, during and after 
burial. 

Importantly, corpses of furry/feathery animals can lose ALL 
of their fur/feathers prior to burial. The most graphic case I 
witnessed was that in which a fox (_Vulpes vulpes_) corpse 
on the strand-line of a beach lost ALL of its fur while 
rolling around in the surf, yet otherwise remained more-or-
less fully intact (with all soft tissues). When the corpse was 
finally entombed in sediment, it was fully naked. A similar 
thing can happen in birds BUT the remiges and rectrices 
generally stay attached to the skeleton for such a long time 
that these feathers generally remain. This was shown by 
Paul Davis and Schafer:  Schafer shows a tern corpse that 
illustrates this perfectly (it's reproduced in Wellnhofer's 
pterosaur book). However, given that (?) non-maniraptoran 
theropods lacked strongly 'rooted' remiges and rectrices, we 
should not expect to find such feathers when all others are 
absent.

Another thing that can happen (this time after burial) is total 
decomposition of ALL integument even when autolithified 
internal organs remain. This must have occurred in 
_Scipionyx_ where the guts are intact but there is no shred 
of integument of any sort and a similar process could 
explain the absence of feathers and/or scales on 
_Compsognathus_. Today, bacteria generally cannot break 
down the beta keratins that constitute feathers and for this 
reason some workers have asserted that such a model is 
unlikely. However, feathers in fact incorporate both alpha 
and beta keratins, raising the possibility that the more 
primitive fibres of compsognathids etc. were made up of 
more alpha than beta keratin. If this were the case (it's easy 
to test but to my knowledge no-one has yet done the tests on 
_Sinosauropteryx_) then bacterial decay of compsognathid 
fibres along with the rest of the integument would not be 
unlikely and could have occurred.

Bottom line: we are looking at 'artificially naked' corpses, 
NOT live animals.

-- 
Darren Naish
School of Earth & Environmental Sciences
University of Portsmouth UK, PO1 3QL

email: darren.naish@port.ac.uk
tel: 023 92846045