Geoscience Reference
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humans—are emus of Australia (
Dromaius novaehollandiae
), which can move as
fast as 40 mph (64 kph), and rheas of South America (
Rhea americana
and
R. pen-
nata
)atabout35mph(56kph).Andbecausealloftheseflightlessbirdsareactually
moderntheropods,theyactasmarvelousproxiesforhowsomeMesozoictheropods
could have reached similar speeds when running.
Ofcourse,modernanimals havetheirlimits whenappliedtothegeologicpast,
especiallyoncewestartlookingatgiganticdinosaurs,forwhichwehavenomodern
analog. Hence, one of the more imaginative scientific questions applied to running
dinosaurs has to be one posed of nearly everyone's favorite dinosaur,
Tyrannosaur-
us rex
. The question was this: If
T. rex
could run at about 45 mph—as depicted so
memorably in the first
Jurassic Park
movie—what would have happened to it if it
tripped? One paleontologist, Jim Farlow, and two other colleagues figured out that
given the average mass of an adult
T. rex
(about 6 tons) and a speed of 45 mph,
its forward momentum, halted suddenly by a fall, would have instantly killed it.
Giventhis,thenotionofaflat-outrunning
T. rex
,howeverentertaining(orfrighten-
ing), is not very likely if it or any other large predatory theropod died every time it
tripped while running at full speed—which, let's face it, is a poor adaptive strategy
for passing on genes. However, we should also keep in mind that animals run fast
in terrains and substrates conducive to such behavior, but do not in, say, gooey mud
or ice-covered lakes.
Otherscientistsfiguredouthowmuchmusculaturea
T. rex
wouldhaveneeded
tomovesuchamassivebodyathighspeedsandcameupwithnumbersforthemass
of muscles for its legs and around its tail. What they found was that a 45-mph-run-
ning
T. rex
would have required about 85% of its entire body mass concentrated in
its legs and muscles around its tail, giving this dinosaur more than just a little “junk
in the trunk.” Based on their calculations of more realistic proportions of muscle
massinthoseareasthatcorrelatedtospeed,theyinsteadproposedthat
T. rex
moved
at speeds of about 10 to 25 mph.
