English: Various size estimates of Livyatan melvillei, an extinct macroraptorial sperm whale, compared to the extant sperm whale (Physeter macrocephalus).

• Livyatan was described by Lambert et al. (2010) and is primarily known from a large, fairly complete ~3 metres (9.8 ft) long skull, MUSM 1676. The Livyatan silhouettes in this image represent two different size estimates by Lambert et al., one estimate based on the modern-day sperm whale and the other estimate based on the incompletely known extinct relative Zygophyseter. Because modern-day sperm whales have elongated skulls with variable lengths based on sex and age, Lambert et al. opted to use the bizygomatic width of the skull in relation to body length, but with the skull subtracted, as their guide to estimate the total length of Livyatan. Doing so produced estimates of 13.5 metres (44 ft) based on sperm whales and between 16.2 to 17.5 meters (53 to 57 ft) based on Zygophyseter.^[1][2] The silhouettes were drawn around a reconstruction of the skull (Figure 33, Lambert et al., 2016) but with soft tissues inspired by other whale species. However, because Livyatan is only known from a single skull, it is probable that the silhouettes above will not perfectly reflect the actual size and shape of the animal. Specific soft tissue details that affect the appearance of the head, like the size and shape of the melon and spermaceti organ, are unknown.

• Physical maturity for female sperm whales is around 10.6 to 11 meters (35 to 36 ft) on average, whilst for male sperm whales, it is around 15 to 16 meters (49 to 52 ft) in length. Above-average females have been recorded up around 12 to 13 meters (39 to 43 ft), and the maximum size usually stated for males is males around 18 to 19 meters (59 to 62 ft).^[3][4][5][6] However, based on whaling records, some males have been recorded at even larger sizes on rare occasions. One male caught in 1950 was reported to be 20.7 metres (68 ft) long (shown in the above diagram); some sources regard this as the largest reliably measured.^[4][7][8] Historical claims exist of sperm whales reaching or exceeding ~80 feet (24 m), but sources disagree as to their accuracy or plausibility.^[4][8][9] However, in a review of size variation in marine megafauna, McClain et al. (2015) supported a 24 metres (79 ft) male in the International Whaling Commission's (IWC) records as the 'longest measured length'. Regardless of the exact size of the largest males, exceptionally large sperm whales like these are very rare, with 95% of those measured being below 15 metres (49 ft).^[8]

• Note: Due to the IWC's measuring standards, sperm whales are supposed to be measured from the most forward part of the head to the notch between tail flukes;^[8] this means the tail flukes add additional length to the silhouettes above.

• Human diver silhouette extracted from File:Sperm_whale_size.svg

References