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Re: The New Paper That Time Forgot
--- On Sun, 10/12/08, David Marjanovic <firstname.lastname@example.org> wrote:
> P. Martin Sander & Marcus Clauss: Sauropod Gigantism.
> How did sauropod
> dinosaurs reach body sizes that remain unsurpassed in
> land-living animals?,
> Science 322, 200f. (10 October 2008)
> Being a two-page "Perspectives" paper, it has no
> abstract and is already so
> concise that I cannot summarize it unless I do it in one
> sentence. So, here
> are a few quotes:
Being a two page perspective piece, you'd think Science could afford to give
that one out for free.
No matter though.
> "Large body size in endothermic animals is associated
> with a major problem
> of dissipating excess body heat. A long neck also means
> that a large volume
> of air must be moved in the windpipe during ventilation
> before fresh air
> reaches the lung. These problems appear to have been solved
> by an
> evolutionary innovation shared by sauropods and theropods
> [...] and their
> descendants, the birds: a highly heterogeneous avian-style
> system (11) with cross-current gas exchange [uh, no,
> counter-current --
> cross-current is what crocodiles have!]
Actually birds are cross-current. The blood passes by the alveoli at a right
angle. It's not as effective as counter-current, but it is still "better" than
concurrent gas exchange. Especially when coupled with a unidirectional flow of
My question in regard to all of this is do we actually know that any dinosaur
had a cross-current unidirectional system in place? I can accept that the most
bird like dinosaurs (maniraptors, deinonychosaurs etc) probably had the full
suite of avian respiration in place, but I'm less inclined to say the same
thing for dinos further from the avian side of the family.
We have evidence of air sacs, but what evidence do we have for unidirectional
flow of air? Surely one likely came before the other. As there are other
animals today (certain snakes and insects) that have air sacs, but no flow
through system of gas exchange, I'm inclined to think that air sacs came first;
flow through second.
As for the rest of the article, it would appear that Sander and Clauss relied
heavily on the Erickson et al 2001 study, for their assumptions about sauropod
BMR; yet work by Lehman and Woodward (2008) has shown that there are flaws with
the Erickson growth curve for sauropods. Bone histology data suggests that
sauropods like _Apatosaurus_ (used in the Erickson et al study) would have
taken closer to 80 years to reach adult size.
The strangest thing about this is that Sander and Clauss did read the paper, as
they cited it in their work ( 's mine ):
"In addition, one of the studies (23) [Gilooly et al from PLoS Biol] suffers
from poor bone histologic constraints on sauropod growth rates, as does a study
(24) [Lehman and Woodward] arguing against fast growth in
sauropods. Compared to other dinosaurs, the long bones of sauropods rarely
preserve growth marks, probably because bone tissue was deposited too rapidly
to record them (15) [Sander 2000, Paleobiol]. Histologic growth rate studies
using skeletal elements other than long bones may provide more reliable
The authours argued that Lehman and Woodward had based their data strictly off
of long bone studies, but they didn't. Lehman and Woodward used the exact same
specimens that Erickson et al had used. Sander and Clauss obviously had no
problem with those specimens, as Erickson et al was frequently cited, so I see
no reason for them to complain about the Lehman and Woodward study either.
The authours also stated that gastric mills were not present in sauropods. Has
that been confirmed now? Are sauropods officially considered not to have
One last quibble I had was from here:
"In addition, the vulnerability of a long neck (10) makes its
evolution unlikely without protection from predation by superior body size."
An interesting thought, but if true would we not expect sauropod hatchlings and
juveniles to be short necked? At the very least, we might expect early
sauropods to have had short necks. Not to mention the existence of
_Tanystropheus_, which was big, but hardly of "superior" size to contemporary
predators. Then there were the smaller critters like _Hyphalosaurus_. I'm just
not sure how well the large size argument holds up for sauropod necks.