Agonized death in dinos - my thoughts.

[Jura <pristichampsus@yahoo.com>]

I finally had a chance to get a hold of and read the
Faux, Padian opisthotonous paper (thanks to HP Richard
Hing for the copy). 

Overall I think it does a fine job of dispelling the
old notion of post-mortem repositioning, and provides
of strong case for suffering prior to death. I
question the use of "kitchen science" in all of the
news reports. True, Faux did use beef tendons acquired
from a local grocer, but leaving dead birds out on a
table for 3 months? That's not something I would be
doing in my kitchen any time soon. Just imagine the
smell.

I question the use of figures 3CD & E
(_Rhamphorhynchus_ _Pterodactylus_ and _Dorygnathus_
respectively) as examples of opisthotony. While the
authours acknowledge the ambiguity of _Dorygnathus_,
and one could argue the inclusion of that
_Pterodactylus_ specimen,  there is no mention of why
they used that particular _Rhamphorhynchus_ specimen
when its neck is curving very obviously to the side,
and not over the back.  

Which brings me to my real bugaboo with this paper.
Under discussion there is a section that comments on
an apparent phylogenetic signal related to
opisthotony. First off, this has little to do with a
phylogenetic signal. This is more of an implied
thermophysiological signal. Their argument is that
opisthotony only occurs in automatic endotherms (i.e.
"warm-blooded" critters). The argument (as Scott had
mentioned in a previous post) is that the CNS in
creatures with high basal metabolisms, will be more
susceptible to the effects of hypoxia, and result in
opisthotonic postures. However, as noted in the paper
itself, hypoxia is just one example where opisthotony
can occur. Other possible causes of opisthotony
include poisoning from chemicals that affect the CNS,
infection/injury of the meninges, or a congenital
disease. The authours even report on a case of
opisthotony (in _Allosaurus_) that probably resulted
from a CNS disease. If opisthotony is something that
only occurs in automatic endotherms, then are we to
assume that congential CNS diseases, meningitis, or
CNS poisoning never occurred in bradymetabolic
animals; or that if it did, the effects were much less
pronounced? In other words, if hypoxia can't explain
all cases of opisthotony, then one is forced to
explain why it has never been found in known (or
assumed) bradymetabolic animals.

Then again, maybe it has. The authours mention that
there are crocodyliformes that show opisthotonic
positions. They discounted 3 out of 4 mentioned by
Lortet (1892), because the back and tail showed little
arching. Did they not consider the possible anatomical
limitation imposed by the dorsal osteoderms? This was
taken into account when attempting to explain why
opisthotony is so rarely seen among ornithischians. It
shouldn't have been that hard to think the same would
be true for a crocodyliforme. There is also a
pristichampsid that is preserved in almost exactly the
same manner as the _Compsognathus_ in fig 1B (see pg
35. of the book: Crocodiles & Alligators, 1989) albeit
with a shorter, and less arched neck. All other
examples of "agonized death" in bradymetabolic
critters (including fish like the one Jerry Harris
mentioned) are believed to be cases of pleurothotony.

Pleurothotony is the exact same thing as opisthotony,
only the neck and tail arch to the side, instead of
over the back. The _Hyphalosaurus_ and _Keichousaurus_
 pictures that I posted before, are prime examples of
this position. The authours even give mention to the
former species and its dramatic pleurothotonic
position. However they sought to seperate
pleurothotony from opisthotony. The former is less
well studied, yet all cases of induced pleurothotony
resulted from damage to the CNS. Regardless, the
authours take the stance that since there is no
established relationship between the two positions,
they can ignore it. I find this shocking, given the
leap they already took in this section, as well as the
fact that these choristoderes are found in the same
environments that gave us the opisthotonic dinosaurs
and pterosaurs. If anything, they could have mentioned
the need to further study pleurothotonic positions and
whether or not they result from the same scenarios
that give opisthotonic positions (the fact that one
can find both in the same environments, should at
least be suggestive).

The argument that opisthotony only occurs in automatic
endotherms, hits another snag when they tested it in
mammals. Many of their cases were ambiguous. There
were clear cut examples of placental mammals showing
this trait, but basal mammals were harder to come by.
When the authours compared animals from the
Jehol-Biota, they found dinosaurs and pterosaurs
showing opisthotony, while mammals and other reptiles
did not. Even when they compare Eocene faunal
assemblages, the results wind up hazy. Most of the
mammals in the assemblages chosen, don't show
opisthotony, or only show slight signs of it (compared
to all the birds that apparently show it). Even the
pterosaurs they tested, showed conflicting results
(sometimes Rhamphorhynchoids had it. Sometimes they
didn't).

Finally, the biggest problem I noted was that there
was never a mention of the different body design of
mammals and dinosaurs, compared to most reptiles.
Mammals and dinosaurs are laterally compressed
animals. When they die they fall to their sides. Most
reptiles are dorsoventrally compressed. When they die,
they die on their stomachs. Opisthotony is going to be
selectively preserved in dinos and mammals, more often
than other reptiles, simply for the fact that the
hypercontracted muscles aren't fighting the constant
tug of gravity. For that same reason, one would expect
pleurothotonic positions to be more preservationally
biased in squat reptiles like _Hyphalosaurus_. Note
how figs 3C & D both show a pleurothotonic position in
the two pterosaurs that died on their backs/stomachs
(one might argue D, but not C).

The overall premise of the paper, is a sound one. It
does a fine job of testing and invalidating many
previous explanations for these classic death poses.
It's just that small section of the paper that
attempts to link opisthotonic death with high
metabolic rates which is problematic. It has far too
much speculation without enough data to back it up
(something the authours give slight mention to at the
end). The paper would have been better without this
section. 

Jason

"I am impressed by the fact that we know less about many modern [reptile] types 
than we do of many fossil groups." - Alfred S. Romer


 
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