Body length estimation of Neogene macrophagous lamniform sharks (Carcharodon and Otodus) derived from associated fossil dentitions

Abstract

The megatooth shark, Otodus megalodon, is widely accepted as the largest macrophagous shark that ever lived; and yet, despite over a century of research, its size is still debated. The great white shark, Carcharodon carcharias, is regarded as the best living ecological analog to the extinct megatooth shark and has been the basis for all body length estimates to date. The most widely accepted and applied method for estimating body size of O. megalodon was based upon a linear relationship between tooth crown height and total body length in C. carcharias. However, when applying this method to an associated dentition of O. megalodon (UF-VP-311000), the estimates for this single individual ranged from 11.4 to 41.1 m. These widely variable estimates showed a distinct pattern, in which anterior teeth resulted in lower estimates than posterior teeth. Consequently, previous paleoecological analyses based on body size estimates of O. megalodon may be subject to misinterpretation. Herein, we describe a novel method based on the summed crown width of associated fossil dentitions, which mitigates the variability associated with different tooth positions. The method assumes direct proportionality between the ratio of summed crown width to body length in ecologically and taxonomically related fossil and modern species. Total body lengths were estimated from 11 individuals, representing five lamniform species: Otodus megalodon, Otodus chubutensis, Carcharodon carcharias, Carcharodon hubbelli, and Carcharodon hastalis. The method was extrapolated for the largest known isolated upper tooth of O. megalodon, resulting in a maximum body length estimate of 20 m.

Tooth morphology elucidates shark evolution across the end-Cretaceous mass extinction

“…This accords with our morphospace overlap of anacoracids and hexanchids (Fig P in S1 Text ) and is further compatible with some modern shark communities, in which the hexanchid, Notorynchus cepedianus , is known to invade apex predator niches once vacated by the lamnid, Carcharodon carcharias [ 93 ]. Unfortunately, shark body size is difficult to estimate accurately from fossil shark teeth [ 94 , 95 ], and the paleoecology of Cretaceous anacoracids and hexanchids is poorly understood. Irrespectively, the persistence of larger-bodied selachimorphs across the K/Pg boundary infers size-based niche continuity, a pattern consistent with static dental disparity (this study and [ 21 ]), and, thus, the likelihood that other drivers, including diet, habitat preference, and reproductive strategy [ 96 ], were influential in selecting for selachimorph extinction susceptibility.…”

A megatoothed shark (Carcharocles angustidens) nursery in the Oligocene Charleston Embayment, South Carolina, USA

“…In the absence of complete skeletons permitting measurement of body length, Carcharodon carcharias is a reasonable modern analog for reconstructing body length from otodontid tooth dimensions (Pimiento et al, 2010). Note, however, that a recent study suggests that these estimates might underestimate the maximum body length, and that posterior teeth overestimate body length versus anterior teeth (Perez et al, 2021). Because the goal of this study is to evaluate the relative size, and not evaluate different methods, we follow Pimiento et al (2010) and Shimada et al (2020) in using the equations from Shimada (2002).…”

“…If the tooth position is incorrect, body length estimates might be overestimated. In order to exclude tooth posi-tion as a variable, each tooth was identified to approximate position based on comparison with the only known dentition of C. angustidens (OU 22261, Gottfried and Fordyce, 2001), but use A3 over I1 (intermediate) and include the posteriors as a continuation of the laterals after Shimada (2002) and Perez et al (2021). Anterior teeth are the largest, and generally have the longest (relative to root width) and most symmetrical crowns; lateral teeth are relatively smaller than anteriors and have proportionally shorter and more distally inclined crowns, and increasingly have proportionally smaller crowns in further distal tooth positions closer to the commissure (=posteriors of some authors, e.g., Gottfried and Fordyce, 2001).…”

“…3-4) and do not represent trees derived from cladistic analyses of morphological data. Though subsequent studies have followed this taxonomic decision (e.g., Boessenecker et al, 2019;Cooper et al, 2020;Herraiz et al, 2020;Perez et al, 2021), not all have (e.g., Godfrey et al, 2018;Kent, 2018;Perez et al, 2019). An exhaustive review of this subject is provided by Kent (2018: 80-85).…”

Feeding ecology has shaped the evolution of modern sharks

“…48 Lamniforms, on the other hand, segregated into only a few distinctive dental morphologies that suffered synchronized disparity contractions during the mid-Miocene-early Pliocene (Figure 2A)-a time frame commenced by the global mid-Miocene climatic disruption. 49 These contractions are most evident among lamnids and otodontids (Figures S3B and S7), 8 which are lineages typified by apex predators, such as Otodus megalodon with an estimated maximum body length of 20 m. 50 Otodus megalodon possessed high-crowned triangular teeth that closely resemble those of Carcharodon carcharias and was probably likewise specialized for feeding on marine tetrapods (e.g., cetaceans and pinnipeds) as an adult. The decline of lamniform apex predators across the mid-Miocene-early Pliocene has been attributed to climate change and competition [51][52][53] but was possibly also influenced by niche specialization limiting their responsive capacity to environmental alterations.…”