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RE: "running" elephants - locomotary analoges



Hutchinson made an interesting comment that reveals a flaw with his 
methodology. It is the digital versus the real world problem. 

"I'm not a big fan of using particular extant animals as "models", analogs, 
or what have you for dinosaurs.  I prefer understanding the principles and 
mechanisms that make living animals work, and using multiple lines of 
evidence to see how those principles might apply to extinct animals.  I don't 
find analogs/models as very testable (even indirectly) or insightful.  They 
mostly head toward dead ends, not in new or fertile research directions." 

H appears to be pretty much abandoning what is far and away the best real 
world method for investigating animal locomotion, comparative anatomy and 
function. in favor of speculative digital simulations. Rather shocking 
actually. 

For example let's say that someone published a paper that tried to estimate 
the flight performance of extinct giants via computer simulations of required 
muscle mass, bone strength or whatever. Let's say the paper correctly 
calculated the flight parameters of a pigeon, and then went on to conclude 
that Quetzalcoatlus would have been incapable of any flight because it was 
too big and its thin walled bones too weak (prior to the discovery of super 
pterosaurs there were calculations "showing" that fliers could not be larger 
than pterandonts). Such a study would clearly be incorrect because the 
anatomical form of Quetz was obviously adapted for flight. This would be true 
even if the methodology latter correctly calculated the performance 
parameters of larger living fliers, since the anatomical flight adaptations 
of the extinct giant cannot be refuted. It would be necessary to conclude 
that the methodology used to estimate the performance of super pterosaurs 
were errant - not surprising since vertebrate locomotion is extremely complex 
and remains poorly understood in many regards, so attempts to reconstruct 
extinct forms via detailed computer simulations are prone to serious mistake 
(much as until recently the flight of bees was not explainable with know 
aerodynamics). 

Turning to running animals, Hutchinson and so forth are basically trying to 
estimate the required power output of leg muscles needed to support animals 
and move that at varying speeds via digital simulations. Actually, this is 
not even necessary since the power output of locomoting animals has been 
measured in a very large sample of animals from mice to elephants. The 
equation is body mass in kg to the 0.684 power x 2.5 x speed in km/h = the 
watts needed to move at that speed. There you go, the power needed to move 
almost any type and size of land animal (saltors excepted) at any speed and 
no need for computer simulations to figur eit out. So the leg muscles of a 
horse need to generate about 11,000 W or 15 hp to support and propel the 
animal at nearly 40 mph to win a race (= 750 W, a hp ~= the work that can be 
sustained by a large horse indefinitely, such a plowing a field or turning a 
mill; a work straining to pull a sledge a few feet at a county fair is doing 
around 20 hp). The mass specific power required to support an animal and move 
at a given speed declines dramatically with size from mice to elephants (and 
correctly extended to researchers to sauropods), and that this scales to 
about the same 2/3s power as does the cross-sectional area of the leg muscles 
is what determines power production. So, in order to maintain a constant top 
speed, muscles mass needs to remain a constant % of body mass, not increase. 
Although counterintuative it is too well demonstrated by actual animals to be 
contradicted with speculative digital simulations (also note that the 
power/speed relationship is essentially linear in the great majority of 
animals, so running at 30 mph requires ~30 times as much power as running 1 
mph). So slow elephants have small leg muscles no proportionally larger than 
those of similarly slow small mammals. The anatomy of elephants, which are 
giant fermenting vats with modest legs attached, prevents them from having 
the large leg muscles needed to run fast. Combined with their lack of flexed 
joints and long mobile feet to push off with they are unable to achieve the 
fully suspended phase needed to run fast. Fast mammals and birds logically 
have proportionally larger leg muscles, up to and over a quarter of body 
mass, big galloping rhinos actually have rather small leg muscles. Having 
flexed joints and longer, mobile feet, runners can use the power of their 
large leg muscles to achieve a full suspended phase. Note that being 
quadrupedal versus bipedal has little if any effect on total locomotary 
muscle power and size requirements in walkers versus runners since fast 
running mammal locomotary muscles approach those of birds in percent of body 
mass. 

For example, we know a lot of things for certain about your 100 tonne 
sauropod. The power its leg muscles would need to support its mass and move 
at 15 mph would be 150,000 W or 200 hp, within a range 130-260 (the observed 
variation at a given body size). This is just 7 times the power output of a 
galloping horse. If the sauropod consisted of 10% leg muscles, then there is 
no doubt they could produce the needed 130-250 hp, it being a mere 15 or so W 
per kg of leg muscle which is actually trivial. There is no need to do 
digital simulations in order to restore what is obvious - that an elephant 
limbed super dinosaur was able to produce the power needed to keep from 
collapsing as it moved at the same top speed as an elephant. Science can be 
easy. 

There is likewise not doubt that for a 6 t tyrannosaur to run at 30 mph its 
leg muscles would have to generate 70 hp or 50,000 W, within a range from 
50-100 hp. This is just half a dozen times the power output of a horse at the 
same speed. Tyrannosaurs are anatomically configured to concentrate mass in 
the legs (pneumatic skull, neck and trunk, small belly, atrophied arms), so 
the leg muscles should have been large as in runners, making up 20% or more 
of the tyrannosaur's total mass. If so the muscles could easily generate 
50-100 hp, the per kilogram of leg musle power production being if anything 
less than that which occurs in galloping, small legged rhinos. In fact the 
leg muscles should have been able to produce enough power to propel 
Tyrannosaurus at racehorse speeds, but whether anything other than a cheetah 
achieves such speeds in the wild is questionable. So again there is no need 
to generate digital simulations in order to determine that a bird-limbed 
super theropod could generate the power needed to propel itself at bird like 
speeds. If, has has been estimated, over 80% of a Tyrannosaurus was leg 
muscles, then the 5 tonnes of muscle would be able to put out 300 hp, 
sufficient to exceed 100 mph. To conclude that a tyrannosaur with with 20% 
leg muscles would not be able to run fast is simply not logical.  

Because tyrannosaurs has all the basic high speed anatomical running 
adaptations, and must have had 20% leg muscles considering the enormous size 
of the pelvis, long legs, and extensive nonleg weight reduction adaptations, 
there is no more doubt that all tyrannosaurs could reach or exceed 30 mph 
just as there is no doubt Quetz could fly. With 1.2+ tonnes of leg muscles 
Tyrannosaurus simply had too much power not to be able to run fast when the 
muscles' power was fully utilized. If it were as slow as an elephant then it 
should have had a similarly low maximum leg mass and power output, about 30 
hp, and would have the low speed skeletal adaptations I detailed back in PDW. 

Hutchinson's claim that his methodology is more testable than anatomical 
comparisons is spurious, since there is no way to observe if they are 
correctly reconstructing the actual performance of fossil organisms that have 
no directly comparable living examples. In fact, the actual power output of 
leg muscles needed to run at a given speed in an animal of given size 
directly tests Hutchinson's methodology for estimating the same, and 
convincingly falsifies it. 

Hutchinson also suggests that the bouncing gait of elephants "costs more 
energy per step because of the more flexed limbs." Again this is digital s
imulation being stated as though it were reality. The real world cost of 
locomotion in elephants plots a little below the standard line so if anything 
they are energy efficent. The supposed extra cost of walking with flexed legs 
is based on experiments in which humans move with abnormal gaits, and 
abnormal gaits are always energy inefficient compared to the norm. If 
ostrichs could be compelled to walk with their leg joints held straight they 
would probably be less energy efficient than with their normally flexed legs. 
Although it is again counterintuitive, it has never been demonstrated that 
leg posture has a significant and consistent influence on power requirments, 
since many flexed legged animals are more energy efficient than straight 
kneed humans and elephants. 

So far the locomotary digital simulations by Hutchinson and others have been 
so far out of line with the actual power and performance parameters of 
animals that they stand as evidence that the methodologies are deeply flawed. 
This will change as the general understanding of animal locomotion improves 
and/or those using digital simulations better apply the given level of 
knowledge. In any case it is already clear that tyrannosaurs of all sizes 
were strongly flexed limbed runners adapted both in terms of anatomy and 
power output to run at very high speeds, and that there is no evidence of a 
decline in speed as size increased in the group. High fidelity computer 
simulations of the future will only fill in details -- for example how 
strongly flexed joints do not increase power requirement, how inertial mass 
limited maneuverability of giant tyrannosaurs --  they are not crucial to 
estimating the gross speed performance of the group.  

Although giant tyrannosaurs definitely could run fast enough, perhaps enough 
to press a field horse with rider, there are questions we will probably never 
be able to answer no matter what methodlogy is employed. For example whether 
some or all were sprinters of distance runners is strongly dependent upon 
muscle fiber composition (lots of white fiber means short range, lots of red 
long range), which as far as I know is not preserved directly or indirectly 
in the fossil record. 

G Paul