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Scansoriopteryx revisited



    Jaime Headden has, on 27 September, graciously
outlined some of his reasons for not considering
Scansoriopteryx [unfortunately plain text does not
allow proper italicization of genus/species names, so
presume they are here] a neonate, even though Stephen
Czerkas and Chongxi Yuan have spent considerable time
with the actual specimen, CAGS02-IG-gausa-1/DM 607,
and have not changed their conclusion of the animal
having been 2-3 weeks old when it died. (I shall avoid
the question of priority re: this taxon and
Epidendrosaurus, and am hoping either Jaime or Mickey
will present, in this forum, a detailed comparative
osteology, faster and more accessible than waiting
months for over-priced copies of JVP.)
    However, I do wish to return to my comments of
recent days re: the anatomical morphogenesis of these
theropods. I am using the Ricklefs/Starck/Konarzewski
chapter 11 as my springboard (plundering their pages
with gratitude). In morphogenesis following hatching,
a small, feathered theropod's inner organ systems
would see greatest growth in the digestive tract, so
that, at a certain stage, growth of other organs would
then commence. I have long thought the size of these
little dinosaurs are good estimators of their basal
metablic rates, although, using living dinosaurs,
biosynthesis (namely respiration) is a notoriously
difficult "thing" to measure. Robert Ricklefs, in a
series of fine papers in the 1970s (especially his
1973 paper Patterns of growth in birds, and in 1974
Energetics of reproduction in birds), posited
digestive tract development (remember, children: no
food = starvation) being 33% energy composition of
cellular tissue, although A.J. Webster in 1985 thought
it slightly higher (36%)for fat buildup in dinosaur
neonate tissue and 125% for protein synthesis.
    As a neonate dinosaur's growth slowed (rates
higher in altricial theropods than precocial
theropods), BMRs/thermoregulation/body activity
increased. However, looking carefully at the
Czerkas/Yuan photographs, and assuming the digestive
tract and stomach are where one would expect, the
inferred mass of the gut in those areas does not
necessarily indicate functionality. In fact, among all
living dinosaurs after hatching, the intestines are
larger than the stomach. Ricklefs, in his research
during the 1980s, found relatively little difference
(after scaling for various body sizes) in proportions
of stomach mass in infant dinosaurs. Still poorly
understood:  precocial baby dinosaurs have high
metabolism/activity, but how this controlled in the
capacity of the gut's metabolizing energy is not yet
known.
    To eat is to live and grow; all food ingested is
used entirely for cell maintenance.  Among precocial
theropods (who have slower growth rates), metabolized
energy, at the cellular level, is lower than
maintenance -- and variations in growth speeds require
little extra energy. In other words, the
stomach/intestinal system in dinosaurs after hatching
are flexible in terms of what their bodies require
rather than interfering with energy increase and
growth. J.M. Starck, in his excellent chapter in Avian
growth & development (1998), elucidates the known data
on how dinosaur skeletons develop. Among living
dinosaurs, e.g., embryonic skeletal and cartilage
development is fairly uniform among all taxa.
Precocial dinosaurs require greater biomechanical
strength in their bones slows growth rates.
   I remain, needless to say, unconvinced that these
little Czerkas dinosaurs are adults, but I am equally
sure that, because of their sizes, their food
assimilation, oxygenization of tissues, and waste
removal was constrained by smallness of inner organs.
As they grew, behavioural systems changed concurrently
with organ maturation. Altricial and precocial
dinosaurs today display differences in organ
functionalities.
   And, it is likely that, in using living dinosaurs
as a guide to anatomy of these earlier dinosaurs, we
just might be able to infer more than what some have
thought. After all, John Hutchinson's biomechanical
extrapolations of tyrannosaur musculature are not done
in a vacuum, but are linked, so to speak, to the
muscles of other taxa. The 18th/19th centuries
conceptualizations of "actualism" -- inferring
paleoecomorphologies from ongoing
macro/microevolutionary processes -- are, in fact,
still useful. Inner anatomy, including bone
proportions relative to organs, provides, as it were,
glimpses into probable behaviours, and I do not think
it "reckless" to take "wild" guesses, if one has an
operable grasp of form/function complexes.

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