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New Paper (taphonomy)

Dear list,

Here is a new taphonomy paper  from the last issue of Paleobiology, which is 
(somewhat) dinosaur-related. Looks  like very interesting stuff too...

Marshall Faux, C., & K. Padian,  2007 : The opisthotonic posture of 
vertebrate skeletons: postmortem contraction  or death throes? Paleobiology 33 
(2), pp. 

Abstract: An extreme,  dorsally hyperextended posture of the spine 
(opisthotonus), characterized
by  the skull and neck recurved over the back, and with strong extension of 
the  tail, is observed in
many well-preserved, articulated amniote skeletons  (birds and other 
dinosaurs, pterosaurs, and at
least placental mammals).  Postmortem water transport may explain some cases 
of spinal curvature
in  fossil tetrapods, but we show how these can be distinguished from causes 
of the  opisthotonic
posture, which is a biotic syndrome. Traditional biotic  explanations nearly 
all involve postmortem
causes, and have included rigor  mortis, desiccation, and contraction of 
tendons and ligaments.
However,  examination of the process of rigor mortis and experimental 
observations of  drying and
salinity in carcasses of extant animals show that these  explanations of the 
ââdead birdââ (opisthotonic)
posture account for few or  no cases. Differential contraction of cervical 
ligaments after death
also  does not produce the opisthotonic posture. It is not postmortem 
contraction but  perimortem
muscle spasms resulting from various afflictions of the central  nervous 
system that cause these
extreme postures. That is, the opisthotonic  posture is the result of ââ
death throes,ââ not postmortem
processes, and  individuals so afflicted assumed the posture before death, 
not afterward. The  clinical
literature has long recognized that such afflicted individuals  perish from 
asphyxiation, lack of
nourishment or essential nutrients,  environmental toxins, or viral 
infections, among other causes.
Accepting the  actual causes of the opisthotonic posture as perimortem and 
not postmortem  provides
insights into the causes of death of fossilized specimens, and also  revises 
interpretations of
paleoenvironmental conditions of many fossil  deposits. The opisthotonic 
posture tells us more
about the circumstances  surrounding death than about what happened after 
death. Finally,  the
opisthotonic posture appears to have a phylogenetic signal: it is so far  
reported entirely in ornithodiran
archosaurs (dinosaurs and pterosaurs) and  in crown-group placentals, though 
the distribution
in mammals may expand with  further study. It seems important that the 
opisthotonic posture
has been  observed extensively only in clades of animals that are known or 
thought to  have
high basal metabolic rates: hypoxia and related diseases would be most  
likely to affect animals
with high oxygen use rates.

FÃlix  Landry
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