Re: prosauropod growth & metabolics

["Jaime A. Headden" <qilongia@yahoo.com>]

Greg Paul (GSP1954@aol.com) wrote:

<That at least some prosauropods experienced reptilian growth as demonstrated
by Sander & Klein in Nature is not surprising.>

  I would have liked a lot more corroboration and a treatment that may have
been related to variable climate or taxonomic diversity lumped into *P.
engelhardti*. The authors assumed a singular, cohesive group for their sample
size, so this may affect their results as a variable outcome.

<pretridactyl theropods as well as protodinosaurs - retained small ilia that
were incapable of anchoring the very large thigh muscles present on more
derived dinosaurs, including birds, as well as mammals with large ilial plates
(this is discussed in DA etc).>

  Yes, the complex large ilia of more advanced archosaurs such as
rauisuchids/prestosuchids, neornithischians, non-herrerasaurid theropods, and
titanosaurian sauropods would be more distinct, related to larger degree of leg
muscle and thigh mass, aside from the fact that there is a correlation between
the bigger or more massive the animal and the larger the ilium, especially when
the limb in question is bipedal. In quadrupeds, you also get massive scapulae
to go along with the ilia. It takes that much more muscle just to move the
animal.

  I am not familiar with some of the terms used herein, have they been defined?

  "pretridactyl" is a no-brainer, but wouldn't "non-avepod" be more consistent
with _Dinosaurs of the Air_? All this would seem to exclude would be
Herrerasauridae, since *Eoraptor* seems to have a more tridactly pes than
*Herrerasaurus* did, which itself doesn't resemble the feet of animals like
*Marasuchus* or *Silesaurus* and implies a reversal, rather than ancestral
condition, anyway.

  "protodinosaur" comes to us from _Predatory Dinosaurs of the World_, but
wouldn't some more clade-specific or taxon-specific term work?

  "brevischian" and "longoschian" -- these seem new to me, are they defined
somehow? I know that sauropods develop a long ischium in some clades, while
titanosaurs develop a shorter one. How does this weigh on their effectiveness,
or the effectiveness of the terms for ornithischians, who possess often greatly
enlarged ischia ('cept for ankylosaurs, of course).

<When they suggest that Plateosaurus was an ectotherm is seems doubtful that
they really mean it was largely dependent upon external heat as the word
actually means.>

  While the word itself bears this in the etymology, the term is used for a
grouping of features, as was made clear during the discussion on metabolic/heat
source terminology discussed earlier this year. A word's eymology and its
meaning/application should be separated, since not all words can be so
cohesively (or through brevity) convey the concept the author is trying to put
forth.

<Instead they appear to be denying that it had the well developed
thermorgulatory system present in birds and mammals, which is probably correct
but in no way means that the first dinosaurs were ectotherms.>

  Actually, given their undeveloped hips, tiny ilia, simple femora, more medial
fourth trochanter, relatively shorter expression of the size and extent of the
knee and elbow joints, and the more complex proximal tarsals, longer first toe
which would possibly have contacted the substrate, and simpler
vertebral/pelvic/rib system relating to breathing, would should expect most
early dinosaurs (including "protodinosaurs" and herrerasaurids) to have had a
MUCH more basal and croc-like breathing and metabolic system than the more
active later organisms. The same parallels can be found in early to later
rauisuchians and other groups of crocodylomorphans.

<Meanwhile, Feduccia in a commentary on the new, advanced Early Cretaceous
wading bird from China says it was an endotherm, implying that it was a fully
avian endotherm, even though more basal birds almost certainly were endotherms
that made most of their body heat internally even if they lacked the entire
avian suite of thermorgulatory adaptations.>

  Only one bird was tested for this paradigm, *Confuciusornis*, so Feduccia
could also be correct in this assertion, as by analogy, in comparing the wading
bird's anatomy to that of living birds or others whom are considered active
enough to be fully endothermic, such as ornithuromorphans.

<The need for an overhaul of the energetic physiological terminology is
reinforced.>

  Only if we ignore the use of the terminology today and stop letting people be
sloppy about what they are calling what. Lack of strict adherence of the terms
we DO have, or concious knowledge of how they are defined, has probably led
many researchers to develop their own terminology, ot to be very loose on them,
such as perhaps Feduccia had done. If we enforce the current terminology, the
need for an "overhaul" will disappear.

  Possibly. Make a new year's resolution on it.

  Cheers,

Jaime A. Headden

"Innocent, unbiased observation is a myth." --- P.B. Medawar (1969)


                
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