THE MANY MYTHS, SOME OLD, SOME NEW, OF ... - Gregory S. Paul

74
G. S. PAUL
(Coombs, 1978a; Halstead and Halstead, 1981; Ostrom, 1987; Padian, 1989; and
Thulborn, 1989, who asserts that shire horses are the biggest gallopers).
Reality: This is a very extensive, complex subject. Here it will be pointed out that a
number of extinct tetrapods of two to 20 plus tonnes have limbs that are more gracile,
more powerfully muscled, and less derived than the highly modified, slow action legs
of elephants. These include large theropods, iguanodonts-hadrosaurs, ceratopsids,
ankylosaurids, titanotheres, giant extinct rhinos, and the indricotheres. In particular,
all of these retain highly mobile ankles and long feet that allow a push off into a
long suspended phase. This suggests that these animals were much faster than
elephants, being capable of a true run with an airborne phase. In the modern fauna,
rhinos are the biggest high speed gallopers.
A number of biomechanic and scaling studies support the possibility that speed can
remain high in large animals if they retain the proper body design, and if they
properly scale limb and body proportions as size increases (Heglund et al., 1982;
McMahon, 1984; Lindstedt et al., 1985; Alexander, 1989). The retention of legs that
are both virtually identical in morphology and increasingly strong and powerful in
ornithomimids and tyrannosaurs of increasing size is one of the best examples of this
phenomenon (Paul, 1988a). In addition, adults are usually as fast or faster than their
young, even when their limbs are stouter and distally shorter, so tyrannosaurs should
not have lost speed as they grew up from their gracile young. Bald assertions that big
animals cannot be fast are therefore obsolete (Figure 3).
Figure 3 The elephantine bulk of 6 tonne Triceratops horridus was not a barrier to galloping because,
unlike elephants, it had the strong boned, powerfully muscled, and flexed jointed limbs needed to propel it
at high speeds.