
University
of Manchester biologists used lasers to measure the minimum amount of skin requisite
to enfold around the skeletons of modern-day mammals, including reindeer, polar
bears, giraffes and elephants.
They exposed
that the animals had almost exactly 21% more body mass than the minimum emaciated
'skin and bone' wrap volume, and applied this to a giant Brachiosaur skeleton
in Berlin's Museum für Naturkunde.
Previous
estimates of this Brachiosaur's weight have varied, with estimates as high as
80 tonnes, but the Manchester team's calculations published in the magazine
Biology Letters abridged that figure to just 23 tonnes. The team says the new method
will apply to all dinosaur weight capacity.
Direct
author Dr Bill Sellers said: "One of the most important things
palaeobiologists require to know about fossilized animals is how much they
weighed. This is astonishingly difficult, so we have been testing a new
approach. We laser scanned various large creature skeletons, including polar
bear, giraffe and elephant, and calculated the minimum packaging volume of the
main skeletal sections.
"We
showed that the actual volume is reliably 21% more than this value, so we then
laser scanned the Berlin Brachiosaur, Giraffatitan brancai, calculating the
skin and bone packaging volume and added 21%. We found that the giant herbivore
weighed 23 tonnes, sustaining the view that these animals were much lighter
than usually thought.
Dr
Sellers, based in Manchester's Faculty of Life Sciences, explained that body
mass was a critical limit used to constrain biomechanical and physiological
traits of organisms.
He said:
"Volumetric methods are becoming more common as techniques for estimating
the body masses of fossil vertebrates but they are often accused of extreme
subjective input when estimating the width of missing soft tissue.
"Here,
we display an alternative loom where a minimum convex hull is derived exactly
from the point cloud generated by laser-scanning mounted skeletons. This has
the benefit of requiring minimal user interference and is therefore more
objective and far quicker.
"We
tested this method on 14 large-bodied mammalian skeletons and established that
it consistently underestimate body mass by 21%. We suggest that this is a
robust method of estimating body mass where a mounted skeletal reconstruction
is available and show its usage to predict the body mass of one of the main, comparatively
complete sauropod dinosaurs, Giraffatitan brancai, as 23,200 kg.
"The
value we got for Giraffatitan is at the low range of preceding estimates;
although it is still huge, some of the huge estimates of the past 80 tonnes in
1962 are overstated. Our method provides a much more accurate gauge and shows
dinosaurs, while still huge, is not as big as earlier thought."
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