Built Like a Race Horse, Slow as an Elephant?

[Sim Koning <simkoning@msn.com>]

I remember reading a rather lengthy argument about the top speed of 
elephants on the mailing list a while back, so I thought I would do some 
searching on the net for a video of an elephant in a full charge; I managed 
to find this.

http://youtube.com/watch?v=pek-2s7csP8

I asked the person who was there (I?m assuming based on the comments) how 
fast the elephant was moving, and he/she replied 15 to 25 mph. After 
watching the video several times, that seems to be right, though I think 15 
mph is more accurate. I know Hutchinson has done research on elephants in 
Thailand and measured their top speed to be around 15 mph; I think it?s 
unlikely that African elephants are much faster, since the elephants that 
were tested in Thailand were the fastest elephants they could find.

Hutchinson has stated that the estimated top speed of a T rex (25 mph) is 
possible but unlikely and that 10 to 15 mph was probably a T rex?s top 
speed. But I have to wonder, why would an animal that has the same cursorial 
adaptations found in ostrich mimics be as slow as an elephant? As GSP has 
often pointed out, Tyrannosaurs were elastically similar to much smaller 
ostrich mimics and so their legs should have been able to hold up under the 
stresses of running. Now I know that as animals get bigger, it becomes 
increasingly difficult to run, or even support their weight for that matter, 
since the support from muscles increases in 2 dimensions (cross sectional 
area) while their mass increases in 3 (twice the size, 8 times the weight) 
but why did 6 ton tyrannosaurs have adaptations for running if they could 
not run at all? One possible explanation is that juvenile tyrannosaurs were 
very fast runners and the ability was gradually lost as they grew in size, 
allometrical studies seem to suggest this.

  Juvenile tyrannosaurs seem to have had disproportionately long legs, with 
longer lower leg bones and shorter femurs, while adults have longer femurs 
and shorter lower leg bones; this shift in limb proportions may have been an 
adaptation for the adult tyrannosaur?s decreased ability to run. Adult 
tyrannosaurs may not have been able to run at all, but that still doesn?t 
explain why the femurs of adult tyrannosaurs are elastically similar to fast 
running ornithomimids; with that in consideration, I think it?s logical to 
think that adult T rexes could achieve an aerial faze in a slow run at about 
25 mph for short distances, which Hutchinson?s work seems to suggest. To be 
realistic, 25 mph isn?t really that ?slow? at all, after all, it?s only 5 
mph slower than an emu?s top speed.

It is still scary to think that a full grown T rex could move in a fast walk 
at 10 to 15 mph, this is faster than many people can run for any length of 
time.

Simeon Koning

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