RE: "running" elephants - locomotary analoges

[GSP1954@aol.com]

In his post on my comments on differing methodologies for investigating the 
locomotion of extinct animals John does not entirely accurately characterize 
my position, and deal with tangential and semantic issues that do not get to 
the core of the problem. 

So far John's published work on tyrannosaurs has empahsized attempts to using 
biomechanical models to estimate their locomotary performance in terms of 
required muscle masses and power outputs. Since these were calculated 
extrapolations run through a computer, and were not compared to actual leg 
muscle masses and power needs in big animals, I labeled them digital 
simulations, which is correct. This is far different from what I prefer, 
which is too see by direct observation what animals small and big actually do 
and what they really need to achieve a given level of performance, and apply 
that to fossil forms. 

Also, John's work appears to deemphasive the importance of anatomical 
adapatations for speed - so his tyrannosaurs are not dramatically faster than 
elephants despite their extreme differences in form based on biomechanical 
simulations - while I emphasie such comparisions so my tyrannosaurs are much 
faster in the big bird/rhino analogy than slow elephants. So he is minimizing 
the importance of comparative anatomy relative to alternative methods. 

But the main issue remains that John's biomechanical work whatever we choose 
to call it is producing results strongly divergent from reality. In the 
Nature paper it is estimated that a juv tyranno would need almost twice as 
much leg muscles to run as fast as are actually present in emus and 
ostriches. 

The Nature paper estimated that a gorgosaur sized tyranno would need over 
half its mass to be leg muscles to run fast. But the horsepower that a 
similar, rhino sized animal needs to run fast is well known and is not very 
high, rhinos do gallop - perhaps as fast as horses - and there is no way that 
short legged rhinos have leg muscles proportionally larger than horses, if 
anything they are significantly smaller according to my comparisons. Leg 
muscle mass and power requirements to move at a given speed are broadly 
similar in bipeds and quadrupeds (in emus and running dogs 25% of body mass 
is locomotary muscles). Gorgosaurs could easily have had leg muscles as 
proportionally large as those of rhinos, and probably much larger, and could 
therefore produce as much if not greater horse power. Gorgosaurs also had 
longer, more gracile legs than rhinos. So there is no sound reason to 
conclude that gorgosaurs were slower than rhinos, there are good  reasons to 
think that if anything they were faster, and they would have needed only a 
fifth or so of body mass to be leg muscles to achieve speeds comparable to 
those of running birds and fast ungulates. 

Same is true of Tyrannosaurus. We know elephants need to produce only two to 
three times as much hp as a fast galloping horse to achieve their top speed 
of 15 mph. It is also apparent that the amount of leg muscles needed to 
produce this power is only a small % of total mass, and this matches what is 
known of leg masses in elephants. There is no reason to think that if an 
animal the same size of an elephant had leg muscles two to three times as 
large a % of the total mass that it would not be able to run at least twice 
as fast. Having leg muscles proportionally two to more times larger than an 
elephant remains within the observed maximum. Not having a big fat gut to 
carry around plus extreme nonlocomotary weight adaptations means that 
Tyrannosaurus easily had leg muscles two or more times larger than an 
elephant, and it was anatomically adapted to run, so the avepod could run two 
or three time faster gnerating only about half a dozen times more hp than a 
horse a dozen times smaller. This is true even if we assume that 
Tyrannosaurus was as power inefficient as possible for an animal of its size, 
but there is no reason to conclude it was so, or was less energy efficient 
than elephants which are close to the norm. 

Key points here are that the above conclusion is about as close to true as 
one can get without a time machine, and that there is no need at all to do 
intricate biomechanical calculations to reach it. The data in the literature 
on the scaling and variation in power requirements, combined with data on 
proportional locomotary muscle mass and anatomical/speed  correlations, are 
sufficient. Nor can biomechanical simulations falsify the above conclusions 
since the latter are based on observed reality, the former on a set of 
assumptions. Instead the observed data falsifies the Nature study and related 
work. What biomechanical studies can do if well done is explains details of 
how tyrannosaurs moved far faster than elephants, they cannot be used to 
estimate the basic performance level. 

But much of the biomechanical work so far done on the subject has been Rube 
Golbergian spinning of wheels that produce wildly inaccurate results. Since 
the results of the Nature paper are so divergent from the real pattern it is 
necessary to question if that set of biomechanical results qualify as scienc
e. After all, it's basic in science to show that ones method is in strong 
accord with observed reality before applying to dramatically different 
subjects. The good thing about the study is that its results were so strange 
that it motivated me to figure out why, and to finally establish beyond 
reasonable doubt that tyrannosaurs of all sizes were far faster than 
elephants, as fast a large ground birds and ungulates, and did not decline in 
speed with size.  

As for the supposed need to increase leg muscle mass as size increases in 
order to maintain a constant top speed, baby elephants are no faster than the 
adults. Yet what data exists indicates that juvs have proportionally larger 
leg muscles. This makes sense since its the little ones that have the 
proportionally longer  legs to hang more muscles on. The same applies to 
running animals in general, its the youngsters that are wee bodies on stilts, 
and probably proportionally bigger leg muscles, yet the grown ups are as fast 
or faster. Unfortunately there is little if any data on this important 
question. 

So it's great that John et al are doing observational work on living 
elephants etc. And that's what we need more of, lots of basic data (incl leg 
muscle masses in a wide variety of animals), fundamental information that 
should have been gathered a long time ago - as far as I know no one has cut 
apart a bunch of horses to find out exactly how much leg muscles they have! 
Even muscle mass data on humans is hard to get. Measuring living animals and 
their locomotion will tell us a lot more about locomotion than biomechanical 
simulations that over estimate the leg muscle masses of fast running 
tyrannosaurs by a factor of two to five. 

G Paul