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mumakil energetics & growth



Some commentators have said that the ubercollossal mumakils (aka oliphaunts) 
in The Return of the King are 7 or 8 stories tall, but comparing the height of 
their riders they are more like 50 ft (have not seen an official figure from 
the movie's creators). 5 stories is about the maximum height of sauropods, and 
is probably the tallest land animals can be due to hydrostatic pressure 
problems in the feet. Scaling up from elephants total mass of a mumakil, which 
appear rather long legged, would be over 500 tonnes. That's about 100 times the 
average mass for Loxodonta and five times greater than very large sauropods. 

Resting metabolic rates calculate as kilograms to the 0.75 power times 1400 
equals watts, so a mumakil would run on ~25 million W, or 1.3 million kcal/day 
(a kcal being what is often called a calorie concerning human diets), total 
energy budget would be about twice that. This would actually be a very low 
energy rate per kilogram of tissue, being only 30 times higher than in a 5 
tonne 
elephant, and the low surface area/mass ratio would prevent over heating during 
the day (for those unduly obsessed with the overheating problem due to the 
metabolic rate/surface area issue, scaling elephant MRs up to mumakils would 
result in a 20 fold increase, which remains well in the mammalian zone).

Power needed to support and move an animal calculates simply as kilograms to 
the 0.684 power times 2.5 equals watts needed to move 1 kilometer, a 
horsepower equals 750 W (and is based on the sustained work such a plowing done 
by a 
large workhorse, a galloping warhorse does about 12 hp). This has been observed 
from mice to elephants. Ergo, giant animals are extremely energy efficient in 
locomotary terms and it is no trouble for them to power high speeds. Since 
muscle power scales to muscle cross sectional area which scales to the two 
thirds 
power, and since the power needed to move at a given speed scales to nearly 
the same exponent, top speed remains constant if leg muscle mass remains the 
same percentage of total mass. Again, elephants show no signs of deviating from 
this pattern, they have very small leg muscles making up less than 10% of 
total mass according to what data is available (horses have about twice as much 
leg muscle relative to total mass). The low power production of the small leg 
muscles of elephants contradict the common assumption that land giants suffer 
from severe locomotary problems due to their bulk; if they did then elephants 
would have oversized leg muscles generating high power levels well above those 
predicted by the two thirds exponent (likewise, even supersauropods do not show 
evidence of having oversized leg muscles, instead sauropods tend to be 
isometric and the limbs and pelvis were not able to anchor large muscles). A 5 
tonne 
elephant moving at its top speed of 15 mph is doing just 25 hp, only twice 
that of a much smaller horse, because it has such small leg muscles which due 
to 
scaling issues cannot generate as much wattage per kiogram as smaller animals 
muscles. So each kilogram of leg muscle is generating just 50 or so W, 
compared to 100 or more W for smaller animals moving at their top speeds. The 
mumakils in ROTK seem to be doing well over 15 mph due to their enormous stride 
lengthes. They are probably animated moving too fast for the real world, but it 
is 
possible that such giants would be able to outpace an elephant simply due to 
their 40 ft long legs. A speed of 25 mph would require 1000 hp. Again this is 
actually low in that it would require each kilogram of leg muscle to generate 
just 16 W. 

In terms of sheer height, mass and movement super mumakils may be viable. But 
there are other problems. Daily food requirements would be a few tonnes of 
fresh fodder a day, a serious problem especially for the caretakers of an 
entire 
war herd. It is doubtful that a population of 500 tonne tachyenergetic land 
animals, particularly slow breeding K-strategists, could find sufficient food 
to sustain a viable adult population over the long term. Even fast breeding 
r-strategist sauropods were probably limited to 100 or so tonnes by this 
factor. 

Even worse is the growth rate issue. Continental animals cannot live much 
beyond 60 years because disease, accident and predation knock them off (island 
tortoises can exceed 100 because of the absence of disease vectors and 
predation). Also, reproduction has to start by age 20 or 30 for population 
stability 
reasons. For an animal to reach hundreds of tonnes in just a few decades would 
require growing over 50 kilograms per day, a rate not seen in any living 
animal. So in terms of food consumption and growth supersized mumakils are 
probably 
not viable. 

Also, how humans could capture and master such over sized animals is not 
clear. Even a newborn calf would weigh around 10 tonnes. 

G Paul