[Date Prev][Date Next][Thread Prev][Thread Next][Date Index][Thread Index][Subject Index][Author Index]
Re: Brachiosaurid metabolism?
David Marjanovic writes:
> > If you take e.g. a smaller european sauropod _Hypselosaurus_ with
> > a mass of some 5300 kg when it was adult, compare it to the
> > hatchling weight of the same genus (2,4 kg) and use the
> > calculated grow rate,
> Wait, wait, wait.
> Firstly, *H.* is a quite fragmentary affair. Remember that mass
> estimates of *Brachiosaurus*, for which the complete skeleton can
> be reconstructed from a few individuals, range from 15 to 75 t
> (ignoring even higher outliers for the moment), and then have
> another look at *H.*...
Just to say that you can ignore the 15 tonne outlier (Russell et
al. 1980), too, since this estimate was made on the basis of an
extremely crude limb-bone allometry formula. Furthermore, you can
pretty much ignore the 29 tonne estimate (Anderson et al. 1985) for
the same reason -- they didn't make and measure a model, just
extrapolated relationships that hold for smaller animals. What's
more, you can discard the 78 tonne estimate (Colbert 1962) which was
based on a grotesquely fat model, and the most more recent 74 tonne
estimate (Gunga et al. 1995) which used a computer model built
assuming that the torso, neck, etc. were circular in cross-section.
That leaves as credible estimates 32 tonnes (Paul 1988), 37 tonnes
(Christiansen 1997), 26 tonnes (Henderson 2003), all based on models
or on scale drawing. And perhaps 47 tonnes (Alexander 1985), although
as shown by Paul (1997), that was based on a pretty bad model.
So that still leaves a factor of 47/26 = 1.8, but the situation is not
quite so hopeless as it initially appeared.
Anyway, to get back to the original question:
Vladimír Socha writes:
> recently I've noticed an unresolved(?) debate on brachiosaur
> metabolism with implications for the sauropod longevity in the
> archives [...] the estimated time they would have taken to reach
> adult size would have been much more than one century, perhaps even
Nuh-uh. Sander's (2000) study of Tendaguru sauropod long-bone
histology showed (in a paper that has perhaps the most boring sequence
of figures I've ever seen) showed that _Janenschia_ seemed to read
sexual maturity at 11 years, maximum size at 26 years and death at 38
years (all approximate). Although Sander didn't reach any similar
conclusions regarding _Brachiosaurus_, there's no reason to think its
ages would have been dramatically different from those of
_Janenschia_, which is good-sized sauropod.
Weaver (1983) sought to show that _Brachiosaurus_ could not be
endothermic by demonstrating that it could not have processed enough
food to support a fast metabolism. His calculations all look good to
me, but the paper is fatally flawed by the assumption that _B._
couldn't eat more quickly that a giraffe -- an assumption that is
manifestly absurd to anyone who's seen skulls of both animals. Not to
mention that giraffes have to waste a lot of time chewing whereas
_B_. most likely swallowed without chewing.
Finally, Paul (1998) argues that endothermy is _necessary_ for large
animals such as sauropods, not only to grow but also just to maintain
large bodies. And it's certainly true that the evidence of extant
animals bears that out.
Have fun investigating this!
/o ) \/ Mike Taylor <firstname.lastname@example.org> http://www.miketaylor.org.uk
)_v__/\ "Covenant strode pustulatingly across the gibbous room, the
preternatural sun playing lambently across his gloaming features"
-- Steven Donaldson, "Lord Lambent's Bane"
Alexander, R. McNeill. 1985. Mechanics of posture and gait of some
large dinosaurs: Zoological Journal of the Linnean Society 83: 1-25.
Anderson, J. F., A. Hall-Martin and D. A. Russell. 1985. Long-bone
circumference and weight in mammals, birds and dinosaurs. Journal of
Zoology 207: 53-61.
Christiansen, Per. 1997. Locomotion in sauropod dinosaurs. Gaia 14:
Colbert, Edwin H. 1962. The weights of dinosaurs. American Museum
Novitates, 2076, pp. 1-16.
Gunga, H. C., K. A. Kirsch, F. Baartz, L. Rocker, W.-D. Heinrich,
W. Lisowski, A. Wiedemann and J. Albertz. 1995. New Data on the
Dimensions of Brachiosaurus brancai and Their Physiological
Implications. Naturwissenschaften 82: 190-192.
Henderson, Donald M. 2003. Tipsy punters: sauropod dinosaur
pneumaticity, bouyancy and aquatic habits. Proceedings of the Royal
Society of London, B (Supplement) 271: 180-183. DOI
Paul, G. S. 1988. The brachiosaur giants of the Morrison and Tendaguru
with a description of a new subgenus, Giraffatitan, and a comparison
of the world's largest dinosaurs. Hunteria 2 (3): 1-14.
Paul, G. S. 1997. Dinosaur models: the good, the bad, and using them
to estimate the mass of dinosaurs. Pp. 129-154 in D. L. Wolberg,
E. Stump, and G. D. Rosenberg, eds. DinoFest International:
Proceedings of a Symposium Sponsored by Arizona State
University. Academy of Natural Sciences, Philadelphia.
Paul, G.S. (1998). Terramegathermy and Cope's Rule in the land
of titans. Modern Geology 23:179-217.
Russell, D., P. Beland and J. S. McIntosh. 1980. Paleoecology of the
dinosaurs of Tendaguru (Tanzania). Memoires de la Societe Geologique
de France 139: 169-175.
Sander, P. Martin (2000). Longbone histology of the Tendaguru
sauropods: implications for growth and biology. Paleobiology, 26(3),
2000, pp. 466-488
Weaver, Jan. 1983. The Improbable Endotherm - The Energetics of
Brachiosaurus. Paleobiology 9(2):173-182.