This increase in size within a group animals through time, i.e. larger species and larger species are constantly showing up on the evolutionary state, is a well known rule of biology.  We refer to this pattern as Cope’s Rule, named after an American paleontologist Edward Drinker Cope.  At broad levels, Cope’s Rule is definitely true.  The start of life on this planet was microscopic and now we have whales and redwoods. However, a mixed bag of patterns of increasing, decreasing, and no change is body size is seen in organism as diverse as molluscs and mammals.  Even within a single group like mammals, some groups like rodents show little change with time, while whales get larger with time, and horses get both bigger and smaller.

Godzilla appears to be following Cope’s Rule.  So how big will Godzilla be in 2050?  Rhett Allain at Dot Physics calculates this to be 170 meters.  But I, as nerds debating meaningless things will, disagree.  Allain appears to use multiple dates for each iteration of Godzilla.  For example, the 50 meter Godzilla occurs in movies from 1954-1975 and again in 2001.  In Allain’s plots, 50 meter Godzilla occurs in 1954, 1960, 1970, and 1991.  This artificially weights the analysis and treats separate iterations, i.e. species, of Godzilla the same as a single individual of the same species of Godzilla.  To restate, different sightings, e.g. different movies, of the same individual of Godzilla are put into the analysis multiple times even though they are presumably the same individual. I prefer to use a standard paleontological method, specifically the size at first occurrence.

So redoing the analysis, I first find no actual statistical increase in size with time.  That is because the second smallest Godzilla, 55 meters, did not appear until 1999 (purple dot in the graph), the regression between size and time is not significant with this point included.  I am also not sure why the artist of the plot decided to place the 55 meter purple Godzilla out of temporal order. If purple Godzilla is thrown out of the analysis we get the equation

Log 10 Height = -13.94 + 0.008 Year

So in 2050, I calculate that Godzilla would be 288.4 meters not 170 meters.

So why is Godzilla obtaining ever larger sizes with time?  Skyscrapers.  Skyscraper height has increased dramatically over the last century.  For Godzilla to continue to plow through buildings in major metropolises, a more formidable size is needed.  Of course this size change can only be evolutionarily adaptive if it changes the fitness of Godzilla, i.e. in the simplest case the number of offspring passed to the next generation.  If Godzilla is able to topple buildings this might allow for greater acquisition of resources in this case food in the form of people. This would increase the lifespan of Godzilla allow for more reproduction or allow for greater amount of energy to be passed to the offspring increasing their rate of survival  Or perhaps toppling buildings is a sexual display that sexual partners cue on.  Sexual selection!

Of course the real problem of a 55,000 ton Godzilla is the urine production. Using the handy Kaiju post, we can quickly calculate that, 151,436,928 12,921,400 gallons per day.  That is about 1.8 about quarter of the hold of the largest production oil tankers.

The post The Ever Increasing Size of Godzilla: Implications for Sexual Selection and Urine Production first appeared on Deep Sea News.

Kevin’s wonderful post on the Giant Isopod inspired me to post on a topic I have long pondered. Frequent readers of DSN know that I am fond of Sylvia Earle and the topic of body size. Honestly, it is not just body size is all matter of size related issues. A roadside trip can be quickly diverted by the world’s largest ball of yarn or North America’s largest biscuit. Mmm…biscuits, but I digress. What I want to discuss, and I use this word specifically as after 10 years contemplation I seem no closer to an answer, is why the Giant Isopod is, well, giant?

Mosely noted in 1880

Other [animals] attain under them gigantic proportions. It is especially certain crustacea which exhibit this latter peculiarity, but not all crustacea, for the crayfish like forms in the deep sea are of ordinary size. I have already referred to a gigantic Pycnogonid [sea spider] dredged by us. Mr. Agassiz dredged a gigantic Isopod eleven inches in length. We also dredged a gigantic Ostracod.

For over a 125 years, scientists have contemplated the extreme size of Bathynomus giganteus. Do other isopods attain these sizes? Gigantism is also known in the isopod Serolis but enlargement comes from flattening that increases the effective surface area. B. giganteus appears unique in its extreme gain in bulk.

Why the increase in size? Timofeev (2001) proposed that deep-sea gigantism, for all crustaceans, is a consequence of larger cells sizes obtained under cold temperatures, as has proposed for other groups (e.g. Van Voorhies 1996). In crustaceans, bathymetric gigantism may also in part reflect decreases in temperature leading to longer lifespans and thus larger sizes in indeterminate growers (Timofeev 2001). However, despite little changes in temperature beyond the thermocline, deep-sea invertebrates including isopods continue to show changes in body size.  Alternatively, Chapelle and Peck (1999 and 2004) demonstrated that maximum potential size was significantly correlated with oxygen concentration in the related amphipods. It is suggested this relationship arises because the amount of oxygen available controls the amount of sustainable tissue. This has been shown experimentally in which cell size and cell number both increase with increasing oxygen concentration (Frazier et al. 2001, Peck and Chapelle 2003). Larger sizes in gastropods are also found at more oxygenated sites in the deep sea (McClain and Rex 2001). However, giant isopods are known from the Gulf of Mexico deep where oxygen concentrations are low.

Kevin also brought up another interesting point….

B. giganteus is a scavenger (3, 5, 6), but some suggest it is also a facultative predator (3, 6). Specimens in aquaria have survived 8 weeks between feedings (5) and it speculated that this may be an adaptation for carrying its brood, which would be severely impacted by a full stomach (3). Further support for this hypothesis are the large quantities of lipid reserves in the hepatopancreas (14) and fat bodies (2) of this isopod.

Alternatively, the larger size also increases fasting potential because greater fat reserves can be maintained. Larger size also confers a greater foraging area, important for either a scavenger or a predator.  Both of these are important adaptations in the food-limited deep sea.

Of course all of this is speculative and it remains unclear why Bathynomus is unique among arthropods. Perhaps is size is simply a random walk in evolution and is nonadaptive. Gould noted in reference to another body size pattern, Cope’s Rule…

One would think that issues so fundamental, and so eminently testable, had been conclusively resolved long ago-except for a perverse trait of human psyche. We tend to pick most ‘notable’ cases out of general pools, often for idiosyncratic reasons that can only distort a proper scientific investigation

Is this case for the Giant Isopod? But perhaps the most interesting question is why the Giant Isopod is not larger?

The post Why is The Giant Isopod Giant? first appeared on Deep Sea News.