Outsized animals have been a mainstay of this blog in the past, notable posts can be found here, here and here. While those posts appear to have been relatively popular*, I don't intend to write any more moderately fluffy posts rattling off trivia. I think it would be more worthwhile to determine if animals can reach the lengths claimed for them, see if there are widespread patterns in how outsized animals can be and suggest widespread implications. And I'll probably talk about a lot of other stuff, I never know where these things wind up.
*I guess this isn't saying much, the Nature Blog Network tells me this blog is abysmally unpopular. Oh well...
Unfortunately, there are a lot of issues that need to be brought up before we can start having fun (sic). I'm sure everyone is aware of scaling, but just for the heck of it: when Animal A is twice the length (2^1) of Animal B it will have four times the surface area (2^2) and eight times the mass (2^3). Muscle and bone strength depend on area, so we can anticipate animals being proportionally bulkier at larger sizes - among other allometric changes. Quickly and generally, larger animals exist at lower densities, have larger home ranges, are subjected to less predation, have lower metabolic rates, change temperatures more slowly, are more efficient and faster locomotors, et cetera (Peters 1983). It's an absolutely fundamental measurement and one source stated that "[b]ody size is the single most important axis of biodiversity" (Brown et al. 2007). This post isn't looking at body size in the context of biodiversity, but it seems reasonable to suggest that body size can be very important from an intraspecific perspective.
Despite size being such a useful, nay, pivotal measurement, "fish story" data plagues many sources that should have been substantially more critical. As I discussed previously, the wels catfish (Siluris glanis) is frequently stated to reach 5 meters and ~300 kg* (e.g. Stone 2007); in reality, specimens over 2 meters are noteworthy and the largest accurately measured/well supported specimen was 2.78 m and 144 kg (see here). Statements such as "the wels grows up to 5 m long" and "the wels averages 1.4-1.6 m long" (wiki) create vastly different impressions of the wels' size - the former should outweigh the latter by about 40 times, for one thing. In the past I have also discussed the size of the green anaconda (Eunectes murinus); I can't help but note that some sources state that the anaconda is 6-10 m (~10-33 feet) long (e.g. Burnie and Wilson 2001). A survey of 1000 anacondas did not turn up any snakes longer than 17 feet (5.18 m) and there is still a reward out for any snake longer than 30 feet (see article). How do you report extreme figures as if they are the norm of the species? Unless there is an extreme lack of data (e.g. some ziphiids) there's no reason to give a maximum length instead of the average adult length and mass.
* I'm not sure where this figure originated, it may have been rounded from a 4.6 m/327 kg claim made by Kessler in 1856. The weight is abnormally low (a wels that length should be over twice as heavy), which strongly indicates a fabrication. Alternately, the length could have come from a sturgeon (apparently they can be confused for wels - see here) and the weight could have been a crude estimate (perhaps a linear scaling).
So... why look at outsized animals at all? By definition they will not be numerous, but they may have exaggerated ecological impacts. Larger and older black rockfish (Sebastes melanops) produce greater numbers of larvae over broader periods of time than smaller individuals; their larvae will also be larger, faster growing and more starvation resistant (Birkeland 2005). This will probably not be the norm amongst fish species which reproduce only once or twice in their life or have high turnover rates (Birkeland 2005). Within species there may be significant ecological differences between size classes, e.g. large parrotfish will excavate substratum while smaller ones will not (Birkeland 2005). That's an extreme situation of course, but if an animal is much larger than average it will have to be doing something different in order to sustain itself. Outsized individuals will have the ability to feed on larger prey items and if some individuals get as massive as claimed (i.e. several times heavier than average) they may even be at a distinct trophic level. While the impacts of the average individual are important, looking at all the individuals on the bell curve can give a more complete understanding.
Human exploitation tends to "favor" large individuals and this can cause the average size of an organism to decrease. If there is good historical data of individuals much larger than average, then it may indicate that modern individuals aren't at previous levels of diversity. This is assuming that outsized individuals have a genetic basis since humans with pituitary gigantism tend to have many other medical issues and rather short lifespans. Anyways, let's look at sperm whales (Physeter macrocephalus), which I mentioned in the past.
Wood (1982) states that the average adult bull* is 14.93 m (49 feet) in length, but another source (mentioned here) states that the average length is 16 m (52.5 feet). The difference doesn't look like much, but a 107% difference in length means at least a 123% difference in weight. That's probably a difference of thousands of tons of prey annually. Photographic measurement of 13 bachelor males off New Zealand ranged from 11.7-15.8 m (med. 14.2 m) and 7 males off California ranged from 14.7-18.2 m (med. 16.4) (Jaquet 2006). The sample size is too small to make a fuss over the figures (probably slight overestimates) but there do appear to be regional differences in sperm whale size (and behavior, proportions, markings, etc) (Jaquet 2006). This complicates things since the largest male may not have been as outsized as predicted if it came from a rather large population - a rough estimate will have to do. The record was a 20.7 m (67'11") bull caught off South Georgia in the '48-'49 season, by the way (Wood 1982). Taking the high road (16 m avg.), the record specimen was was about 129% longer than average and at least 217% more massive. So how massive are sperm whales? Wood (1982) estimates his average bull to weigh 36 tonnes (~40 tons) (I have no idea where this figure derives from) and mentions large bulls which were weighed in full at 18 m/53 tonnes (59 feet/58 tons) and 16 m/40 tonnes (52'6"/44 tons). Using these figures, the record bull would weigh at least 96, 81 or 87 tonnes. Wood (1982) also mentioned an 18 m bull which weighed out piecemeal at 53.37 tonnes, hinting that the whale was proportionally heavier in life (maybe 10% due to fluid loss ~ 58 tonnes/64 tons) given an estimate of 81-88 tonnes. Wood's estimate of 80 tonnes for the record bull may be a bit light and I'm not entirely sure how he arrived at this figure in the first place**.
*I should point out that the total length of a whale is taken from the snout to the notch in the tail fluke, some less than scrupulous authorities in the past got larger figures by measuring the flukes or even taking a measurement along the curve of the body.
**The largest sperm whale in the southern hemisphere was 19.5 m, and if you scale up Wood's 14.93 m/36 tonne animal to this size the estimated weight is 80.2 tonnes.
There's a world of difference between a ~40 tonne 16 m whale and a ~90 tonne 19.5 m whale, and incredibly much larger animals have been reported in the past. People are generally full of crap when it comes to extreme animal sizes and I'm extremely distrustful of any claims before the era of photography, but the case for giant sperm whales is unique. Wood (1982) mentions that the British Museum has a mandible measuring 5 m (16'4.75") in length, however there is apparently a 5.5 m (18') mandible in the Nantucket Whaling Museum (see here and here). The sperm whale jaw seems rather short when viewed externally (see here) but it seems much longer proportionally when the animal is viewed as a skeleton (see here). Why bring thus up? Well, Wood (1982) cites a source that claims a mandible:body ratio of 1:6.2 in a 14.7 m whale and a 1:5.4 ratio in an old 16.28 m whale. These may be measurements of the externally visible jaw, but I'm in desperate need of a peer-reviewed information on sperm whale mandible:body proportion. Wood (1982) used a 1:5.1 proportion for the animal to derive a figure of, gulp, 25.5 meters (83'8") and a 1:5 estimate for a 5.5 m jaw gives a length of 27.5 meters (90 feet). So let's say that Wood's estimate for sperm whale mandible:body length proportion is wrong and it is something like 1:4 - in this case the 5.5 meter mandible would still belong to a 22 m (72 foot) whale 106% longer and 120% heavier than the record specimen and close to triple the weight of the average sperm whale at something like 110 tonnes/120 tons. The record sperm whale was caught in 1950 and the mandibles are probably from much earlier (the 5 m one was from 1851) so it could be possible that the average shrank substantially since then. Wood's 25.5 m (83'8") sperm whale would be something like 170 tonnes/185 tons and if there was ever a 27.5 m sperm whale (90 feet) it would weigh something like 210 tonnes/230 tons. I'm not going to seriously entertain the notion that sperm whales rivaling blue whales for the largest animal actually existed, but it does seem like the average Physeter macrocephalus was considerably larger before heavy exploitation.
So are there patterns as to how large the largest outsized animals can be? Maurice Burton apparently stated that outsized specimens are 68% longer than the average size and 40% longer than the unusual large (Heuvelmans 1968 - from Burton's Living Fossils?). An animal 168% longer than average would also weigh around 5 times more - it would be a marvel for the bauplan of a species to expand to such extravagant sizes and work well enough for the animal to survive in nature. I'm not really a big believer in any self-proclaimed zoological "laws" or "rules" (I guess "Zoological Loose Guideline" doesn't have the same ring), but it is worth noting out that a population of sperm whales with 16 m long bulls could theoretically have an outsized specimen 26.88 m long. This pattern does not emerge with record-sized land mammals - the largest bush elephant (Loxodonta africana) was ~125% taller than average (~4 m vs. 3.2 m) and the largest Masai giraffe (Giraffa tippelskirchi) was a mere 111% taller than average (5.87 m vs. 5.3 m) assuming it was measured correctly (i.e. without the horns) (data from Wood 1982). Perhaps aquatic animals can tolerate outsized specimens more - the aforementioned record Wels catfish (2.78 m) was about 185% longer than average (~1.5 m).
Topics such as this one are certainly not going to be resolved in one blog post, so I'll end it here to get on to other things. There is a great deal of data out there, particularly on state record fish, that might be interesting to go through, but I think the rough picture here is sufficient. While incredible size may offer advantages such as resistance to predation and increased offspring health, tradeoffs will exist. Increased food acquisition comes to mind and there could be morphological issues as well. There are reasons that the outsize isn't the norm, but if situations change it could be adopted as a new norm. Australian giant feral cats are a possible example - emphasis on possible. Outsized animals aren't critical to understanding evolution and ecology but they can make for a potentially very interesting topic.
Birkeland, Charles and Dayton, Paul K. 2005. The importance in fishery management of leaving the big ones. TRENDS in Ecology and Evolution 20, 356-358
Brown, James H. et al. 2007. The metabolic theory of ecology and the role of body size in marine and freshwater ecosystems. In:I Hildrew, A. G. et al. 2007 (Ed.) Body Size: The Structure and Function of Aquatic Ecosystems. Cambridge University Press. pp. 1-15.
Burnie, David and Wilson, Don E. 2001. Animal: The Definitive Visual Guide. Dorling Kindersley, London and New York.
Heuvelmans, Bernard. 1968. In the Wake of the Sea-Serpents. Hill and Wang, New York.
Hutchings, Peter A. 2005. Life history consequences of overexploitation to population recovery in Northwest Atlantic cod (Gadus morhua). Can. J. Fish. Aquat. Sci. 62, 824–832
Jaquet, Nathalie. 2006. A simple photogrammetric technique to measure sperm whales at sea. Marine Mammal Science 22, 862-879.
Peters, Robert Henry. 1983. The Ecological Implications of Body Size. Cambridge studies in Ecology.
Stone, Richard. 2007. The Last of the Leviathans. Science 316, 1684-1688
Wood, Gerald. 1982. Guinness book of Animal Facts and Feats. Guinness Superlatives, Middlesex.