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Re: "Cursoriality", etc.
Michael asserts that elephants can fast walk (amble) well over 20 mph. This
is simply not possible. When an animal cannot achieve a suspended phase, and
elephants cannot (even juvenile elephants doing the best they can cannot
run), then speed is simply a function of stride length versus stride
frequency. Although elephant legs are long, they have limited excursion arcs
because they are so big. Maximum walking stride frequency is also limited by
size. For an elephant to walk at 25 mph would require that its stride
frequency be twice as high as possible.
I carefully timed an Asian elephant that won an elephant race in Thailand. It
was the biggest bull in the bunch. It was obviously going full tilt. Speed
was 12 mph. This is similar to the top speed Alexander observed chasing
African elephants. They used film to measure the speed. Speedometer speeds
are notoriously unreliable for a number of reasons and generally no longer
used in scientific studies. As for humans being run down by elephants, most
people cannot run very fast, especially on irregular ground. Able to achieve
long suspended phases, most trained sprinters could easily outrun an
elephant. Using antecdotal accounts of humans being squished by elephants is
not a scientific way to estimate their speed.
Also note that energy efficiency is largely independent of speed at any given
body mass. The dramatic increase of energy efficiency in hopping kangaroos is
extremely unusual. Bigger animals are relatively more energy efficient than
smaller ones, recent measurements on elephants confirm this.
Finally, animals are excellent at accelerating. Rhinos reach top speed in
just a few seconds.