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scaling of pre-K/T dinosaur body sizes



A new paper (well, it appeared in May, which does not
age it that much) has appeared, which may be of
interest to those who estimate dinosaur body sizes on
the basis of incomplete skeletons:
Penny S. Reynolds, 2002. How big is a giant? The
importance of method in estimating body size in
extinct mammals. Jour. Mammalogy 83(2):321-332
Thanks to Penny for sending it to me. As she points
out, the use of body size estimations for any extinct
taxon predicated on isometrics is not especially
useful, if one is using interpolations not within
predictor variability ranges (2002:322). And she uses
the case of the extinct Oligocene rhino Indicotherium
as a taxon for which "giant" was incorrect, as well as
the "giant" Pleistocene beaver Castorides ohioensis.
She points out that "giant" is usually not accurate,
revised estimates derived from femora lengths often
produce smaller dimensions. She, like many us, believe
that isolated bones are not especially useful. Needed
are a variety of elements, so that sources of error
are balanced against possible inferences. Body mass
esimates of the Pleistocene beaver were twice those
based on femora lengths. Rodents -- like theropods --
have taxonomically differentiating skulls, but
generalized body shapes. A skull is not subject, she
writes, to gravitational loading, and the ratio of
skull length:body mass will not have the allometric
relationality for axial and appendicular skeleton.
Thus, while theropod skulls may be plesiomorphically
similar in being theropods, like rodents the skulls
have diagnosable templates derived from feeding
strategies, and number and growth patterns of
dentition will proportionately elongate as the size of
the animal increases during maturation. Hence, Penny
states that rodent skull length is not a good metric
for estimating body mass, and I would infer the same
applies to many theropods. She proposes that even if
phylogenetic relationships are incorporated in point
estimates for body size predicated on interspecific
information,  the bias may be lessened, but one still
has problems: "the absurdly wide confidence intervals
generated from Monte Carlo simulations compared with
those from nonphylogenetic models do not suggest that
these methods are any better at quantifying the
uncertainty in the predictions of individual body
masses". 

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