Abstract
Inferring the size of extinct animals is fraught with danger, especially when they were much larger than their modern relatives. Such extrapolations are particularly risky when allometry is present. The extinct giant shark †Otodus megalodon is known almost exclusively from fossilised teeth. Estimates of †O. megalodon body size have been made from its teeth, using the great white shark (Carcharodon carcharias) as the only modern analogue. This can be problematic as the two species likely belong to different families, and the position of the †Otodus lineage within Lamniformes is unclear. Here, we infer †O. megalodon body dimensions based on anatomical measurements of five ecologically and physiologically similar extant lamniforms: Carcharodon carcharias, Isurus oxyrinchus, Isurus paucus, Lamna ditropis and Lamna nasus. We first assessed for allometry in all analogues using linear regressions and geometric morphometric analyses. Finding no evidence of allometry, we made morphological extrapolations to infer body dimensions of †O. megalodon at different sizes. Our results suggest that a 16 m †O. megalodon likely had a head ~ 4.65 m long, a dorsal fin ~ 1.62 m tall and a tail ~ 3.85 m high. Morphometric analyses further suggest that its dorsal and caudal fins were adapted for swift predatory locomotion and long-swimming periods.
Highlights
Inferring the size of extinct animals is fraught with danger, especially when they were much larger than their modern relatives
Based on its fossil teeth and using the modern great white shark (Carcharodon carcharias) as an analogue, it has been calculated that it reached a maximum total length (TL) of ~ 15 to 18 m3–5
This uncertainty, coupled with the fact that sharks of different sizes have been reported as being geometrically similar in body p rofile[26, 27], suggests that other macropredatory lamniforms, in addition to C. carcharias, could serve as modern analogues
Summary
Inferring the size of extinct animals is fraught with danger, especially when they were much larger than their modern relatives. Estimates of †O. megalodon body size have been made from its teeth, using the great white shark (Carcharodon carcharias) as the only modern analogue This can be problematic as the two species likely belong to different families, and the position of the †Otodus lineage within Lamniformes is unclear. Despite the fact that the placement of †O. megalodon in the family †Otodontidae has been widely e xplored[22], the interrelationships between otodontids and other lamniforms remain questionable[25] This uncertainty, coupled with the fact that sharks of different sizes have been reported as being geometrically similar in body p rofile[26, 27], suggests that other macropredatory lamniforms, in addition to C. carcharias, could serve as modern analogues. The estimates of body dimensions of this extinct species have the potential to inform future anatomical, physiological and ecological reconstructions
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