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Re: Agonized death in dinos - my thoughts.
discussion there is a section that comments on
Which brings me to my real bugaboo with this paper. Under
an apparent phylogenetic signal related to opisthotony. First off, this
has little to do with a phylogenetic signal. <<<
It's both. It is empirically a phylogenetic signal (dinosaurs,
pterosaurs, mammals), and via inference a thermophysiology signal (more
The argument (as Scott had mentioned in a previous post) is that the
creatures with high basal metabolisms, will be more susceptible to the
effects of hypoxia, and result in opisthotonic postures.<<<
Sort of: The arguement is that cerebellar shut-down prior to death
allows muscle contraction to occur uninhibitted, causing the
opisthotonic posture. How quickly the cerebellum shuts down during CNS
disfunction (hypoxia, poisoning, etc) would delimit the amount of time
that uncontrolled muscles spasms occur (or whether they happen at all).
Since ectotherms utilize far less oxygen per unit time, their
cerebellums (cerebelli?) are not going to be effected as quickly by
reduced oxygen flow caused by CNS disfunction. There can be little
question here; organisms with lower oxygen consumption per unit time
are going to have tissues (and therefore organs) that are less
suceptible to reduced oxygen availability than organisms with high
oxygen consumption rates. Unless you challenge the entire causal
mechanism postulated for opisthotony, it's hard to see how this is much
of a leap. And again, there is strong empirical support based on the
distribution of opisthotony in fossil organisms (see below) .
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
The authours mention that there are crocodyliformes that show
limitation imposed by the dorsal osteoderms? This was taken into
account when attempting to explain why opisthotony is so rarely seen
Is there any reason to think dermal armor would effect crocodilian
dorsoflexion? At a totally annecdotal level, crocs picked up by
television "naturalists" don't seem to have any problems with their
tails curving dorsally when picked up by them (although they don't seem
pleased, either...). They authors reasonable cite ossified tendons in
derived ornithiscians as one limiting cause (although primitive
ornithiscians that lack ossified tendons do exhibit opisthotony), and
limit the roll of ornithiscian armor to stegosaurs, whose plates surely
would have done more to hamper movement that crocodillian armor.
Pleurothotony is the exact same thing as opisthotony, only the neck
and tail arch to the side, instead of
over the back.<<<
But are they the same? The consistent opisthotonic pose results from
stronger dorsal musculature "out contracting" ventral musculature; what
explanation is there for lateral motion? Opisthotonic death poses are
the specific result of tissue contraction, but pleurotonic postures can
just as easily result from water motion or other physical disturbance.
Don't get me wrong, I agree that it should be studied more (I'm
interested in any references you have on induced pleurotony), but
pleurotony has a whole range of potential causes that don't requre
(althogh could include) spasmatic muscle contraction, while opisthotony
apparently has a consistent cause, so is not as succeptible to
confounding environmental signals.
hits another snag when they tested it in
The argument that opisthotony only occurs in automatic endotherms,
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.<<<
It isn't ambiguous if it just means that basal mammals consumed less
oxygen. Even amongst extant mammals non-placentals have lower oxygen
consumption rates (on average) than placentals (on average).
mention of the different body design of
Finally, the biggest problem I noted was that there was never a
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.<<<
Except pterosaurs are dorsal-ventrally compressed, yet still
demonstrate opisthotonic posture. Extant birds cannot really be
described as "laterally compressed", yet show opisthotony. And
notably, people are extremely dorsoventrally compressed, yet apparently
also exhibit opisthotony.
If this were presented as an acid-test for thermal physiological signal
in the face of counter evidence I would agree with Jason's skpeticism,
but the empirical distribution is consistent with other lines of
evidence, and is in fact seen across groups with different body shapes.
Additional research is (always!) a good idea, but the conclusions seem
in line with their data, as well as independent lines of data about
dinosaur and pterosaur physiology, and I feel the paper is better for
having included it.
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