How much urine can a Kaiju produce? And other fun information

The response to the Kaiju post has been amazing and of course everyone has suggested alterations to the calculations.

For background, biologists know that much of an animal’s biology, everything from limb length, heart volume, lung capacity, territorial range, and urine production, all scale with body size. We use an equation, based on data from lots of animals, to calculate all of these. The equation usually takes the form of Variable of interest = a (mass)^b. a the intercept usually varies among groups like birds, mammals, frogs, carnivores, nocturnal, carnivores, etc.. b the slope can as well but usually scales as a multiple of 0.25.

By knowing the mass of an animal, we can gain some insights even in the absence of direct observation, like how many people a day a Kaiju would consume.

Many people questioned basing my equations on Komodo Dragons, arguing that Kaiju were more like mammals, other reptiles, birds, fish, or crustaceans. A commenter also noted that the weights of each Kaiju are known.

So with actual weights and assuming that Kaiju are like different types of organisms in their physiology, the number of people per day needed to sustain a Kaiju is

Kaiju Name	Category	Kaiju Weight (tons)	Komodo Dragon	Mammal	Bird	Reptile	Marine Fish	Crustacean
Onibaba	II	2040	11.6	64.4	35.1	2.9	14.7	8.0
Knifehead	III	2700	14.2	79.4	42.4	3.6	18.3	9.9
Leatherback	IV	2025	11.5	64.1	34.9	2.9	14.6	7.9
Otachi	IV	2690	14.2	79.2	42.3	3.6	18.2	9.9
Scunner	IV	3230	16.2	90.7	47.9	4.1	21.1	11.4
Raiju	IV	3475	17.1	95.8	50.4	4.3	22.3	12.1
Mutavore	III	2630	13.9	77.8	41.7	3.5	17.9	9.7
Trespasser	III	2700	14.2	79.4	42.4	3.6	18.3	9.9
Slattern	V	6750	27.8	157.1	79.1	7.2	37.7	20.3

Of course I assumed that the tons were not metric tons but long tons. At least one commenter disagreed. If we use metric tons instead

Kaiju Name	Category	Kaiju Weight (tons)	Komodo Dragon	Mammal	Bird	Reptile	Marine Fish	Crustacean
Onibaba	II	2040	12.4	69.3	37.5	3.1	15.8	8.6
Knifehead	III	2700	15.3	85.4	45.3	3.9	19.8	10.7
Leatherback	IV	2025	12.3	68.9	37.3	3.1	15.7	8.6
Otachi	IV	2690	15.2	85.1	45.2	3.9	19.7	10.7
Scunner	IV	3230	17.4	97.6	51.2	4.4	22.8	12.3
Raiju	IV	3475	18.4	103.0	53.8	4.7	24.1	13.1
Mutavore	III	2630	15.0	83.7	44.5	3.8	19.4	10.5
Trespasser	III	2700	15.3	85.4	45.3	3.9	19.8	10.7
Slattern	V	6750	29.9	168.9	84.5	7.7	40.8	22.0

A commenter also suggested that digestive efficiency would not be 100%, i.e. a that all the energy of human would not be accessible to a Kaiju. Perhaps Kaiju are complete crap at digesting bone or their guts are just designed really poorly. Assuming they have an efficiency of 50% and long tons

Kaiju Name	Category	Kaiju Weight (tons)	Komodo Dragon	Mammal	Bird	Reptile	Marine Fish	Crustacean
Onibaba	II	2040	23.1	128.8	70.1	5.8	29.3	15.9
Knifehead	III	2700	28.4	158.8	84.8	7.2	36.6	19.8
Leatherback	IV	2025	23.0	128.1	69.8	5.8	29.2	15.8
Otachi	IV	2690	28.3	158.3	84.6	7.2	36.5	19.8
Scunner	IV	3230	32.4	181.5	95.8	8.2	42.2	22.8
Raiju	IV	3475	34.2	191.6	100.7	8.7	44.7	24.2
Mutavore	III	2630	27.9	155.7	83.3	7.1	35.8	19.4
Trespasser	III	2700	28.4	158.8	84.8	7.2	36.6	19.8
Slattern	V	6750	55.7	314.2	158.2	14.3	75.5	40.7

So if Kaiju are essentially mammals, complete rubbish at digestion, and assuming long tons, then the largest Kaiju, Slattern at 6,750 tons, would require 314.2 people per day. In 61.7 years it could eat its way through Hong Kong, assuming of course there were no births and no other non-Kaiju related deaths. Who has time for sex when they’re running from a 6750 ton alien?

But what about other aspects of Kaiju biology?

Slattern
Weight (tons)	6,750.00
Weight (kg)	6,123,498.75
Pulse (beats/sec)	0.08	Mammal
Pulse (beats/sec)	0.07	Bird
Stride Frequency (seconds)	0.50	Mammal
Skin Mass (tons)	379.03	Mammal
Lung Mass (tons)	37.58	Bird
Lung Mass (tons)	61.29	Mammal
Lung Mass (tons)	202.50	Reptile
Brain Mass (ton)	0.92	Mammal
Brain Mass (ton)	0.07	Bird
Brain Mass (ton)	0.67	Primate
Brain Mass (ton)	0.03	Fish
Heart Mass (ton)	30.43	Mammal
Heart Mass (ton)	3.83	Bird
Heart Mass (ton)	22.41	Fish
Heart Mass (ton)	27.71	Turtle
Heart Mass (ton)	1.98	Shark
Litter Size	0.03	Mammal
Litter Size	0.00	Bird
Litter Size	169,008,565.50	Reptile
Gestation Time (years)	1.55	Carnivorous Mammal
Incubation Time (days)	4.61	Bird
Lifespan (years)	264.53	Mammal
Lifespan (years)	399.29	Bird
Urine Production (gallons per day)	1,966.75	Mammal
Urine Production (gallons per day)	1,489,082.95	Frog
Density (no. per square kilometer)	0.00	Mammal	21,859.1	No. supported on Earth
Density (no. per square kilometer)	0.32	Bird	162,342,390.0	No. supported on Earth
Density (no. per square kilometer)	27.43	Aquatic Invertebrate	13,991,321,452.0	No. supported on Earth
Territory (square kilometer)	2,761,876,776.05	Carnivorous Mammal	0.2	No. supported on Earth
Territory (square kilometer)	90,246.21	Hunting primate	5651.2	No. supported on Earth
Territory (square kilometer)	16,412,303,719.57	Carnivorous Bird	0.0	No. supported on Earth
Territory (square kilometer)	339,183.74	Lizard	1503.6	No. supported on Earth

In the table above, I calculate different biological features of the largest Kaiju, Slattern, based on different animals (mammals, birds, frogs, fish, etc.). Slattern’s heart beat would be an order of magnitude slower than most humans, beating less than 5 times per minute. The heart would be anywhere from 2 tons upwards of 30.5 tons. Based on either birds or mammals, it wouldn’t even be able to even muster a single offspring per birthing event. On the other hand if Kaiju are reptilian, we are all severely screwed. Lifespan would be measured in 100’s of years.

Piss…how much would it produce? Every day a Kaiju, if mammalian, would produce about 40 barrels worth of urine. If Kaiju are like frogs, then Slattern would produce 92 Olympic swimming pools worth of urine per day (roughly 0.8% of flow rate of the River Thames).

With the scariness of that settling in, the density of Slatterns supported on Earth could be alarming. At the smallest this would still top out over 20,000. It strikes me that Kaiju are probably territorial. Why else would they always be so damn angry and smashing things all the time? If this is true then the numbers drop radically. If they are avian or mammalian, then Earth could support one, like beta fish in an aquarium. If on the other hand they are like hunting primates or lizards, we are looking at thousands.

McNab, B.K. (2009) Resources and energetics determined dinosaur maximal size. PNAS 106:12184-12188

Nagy, K.A., Girand, I.A., and Brown, T.K. (1999) Energetics of free-ranging mammals, reptiles, and birds. Annu. Rev. Nutr. 19:247-277

Peters, R.J. (1983) The ecological implications of body size. Cambridge University Press.