Feeding the media mouth-fulls of scale-raising jaws, challenging the fear factor of caged adrenalin junkies and curbing the idea of a family beach day — sharks have gone beyond their marine domain as apex predators and deliver a presence in the realms of the media and academics. Their 450 million-year existence catalyzed the staggering number of species dominating the earth’s waters and has made for an extensive fossil record detailing the long history of its kind. However, the mystery lies within the prehistoric mighty-tooth shark, the megalodon. Due to the megalodon’s limited fossil record, research led by UCR Biologist Phillip C. Sternes and his team worked to unveil the megalodon’s morphology, eventually proposing a slimmer body form than the stocky build that was previously assumed.
Sharks remain one of the most acknowledged fish in the animal kingdom due to their grandiose teeth, agile predation and tertiary status in the food chain, features best represented by the shark world’s primadonna, “Otodus megalodon,” more widely referred to as the megalodon. Primarily recognized for its mega-sized jaw, lined with serrated teeth and for being the largest shark to have ever existed, the megalodon’s physical image continues to be showered with acknowledgment by paleontologists, furthering the research towards its unknown anatomy.
The ever-growing enigma of the megalodon’s frame has long been challenged by paleontologists’ interpretations of the existing, yet limited, fossil record of teeth and an incomplete set of vertebrae. Given the need for a model, the great white shark was used to assume early 2D and recent 3D renditions of the megalodon’s body. According to Sternes, the standard lay in both sharks’ shared similarities — serrated teeth, similar diets, food chain status and their regional endothermy (regional warm-bloodedness). Using the white shark as a template rendered a megalodon model that was similarly stout and heavy set, a research result widely accepted in academia and the media that would inevitably be countered.
The assumptions being made about the megalodon’s build based on a limited fossil record, Sternes’ explained his childhood passion for sharks, “my passion for sharks happened once I was five or six years old … Yeah, I watched ‘Jaws’ for the first time … and I watched that [‘Jaws’] I don’t know how many times … I was captivated by them,” and a team of 26 scientists behind him with similar ideas, pushed for new research.
Efforts to challenge the presumed stocky build, rendered by UK biologist Jack A. Cooper’s 2020 research article, “Body dimensions of the extinct giant shark Otodus megalodon: a 2D reconstruction” and 2022 research article “The extinct shark Otodus megalodon was a transoceanic superpredator: Inferences from 3D modeling” on the megalodon, led Sternes and his team towards the central question — Did the megalodon look like a larger great white shark? Sternes states, “the first step was to go back and look at both the 2020 and 2022 papers [and ask myself] why are they still following this assumption [ that megalodons look like larger great whites] in the first place.”
Aided by a Belgium megalodon shark named IRSNB P 9893, vertebral centra, preserved extant species, and the given available Computed Tomography (CT) scans and images, Sternes, and his team were able to answer this question by addressing four discrepancies in Cooper’s proposals — the construction of the vertebral column, jaw size, ontogenetic concerns and body form reconstruction.
Cooper’s suggestions about the megalodon, brought upon by his research, remain to raise concerns by Sternes and those alike. These concerns were first addressed by Sternes and his team when responding to Cooper’s reconstruction of the megalodon vertebral column using an incomplete vertebrae set that was assigned numbers without the consideration for missing pieces from the sequence. Thus, leaving room for an underestimated column length as Sternes comes to suggest, “Yeah, the vertebral sets are incomplete to begin with. So at minimum, this vertebral set is 36 feet long. There [are] probably even more vertebrae that were missing in the first place. So that [vertebral column] could be even longer than that.”
Cooper’s reconstruction also features the largest vertebrae at the first position of the column, an assumption inconsistent with shark anatomy, according to Sternes, “you see in both extinct sharks, and the living sharks, the largest vertebrae is always in the stockist portion of the shark. But what Jeff Cooper and others did is they put the largest vertebrae directly in the first position.”
Sternes’ team next recognizes discrepancies in Cooper’s megalodon jaw size. Comparisons began with the ratios between two exact white shark jaw sizes and their largest vertebrae, with a ratio of 8.3, and the megalodon’s 3D jaw size and its largest vertebrae, possessing a ratio of 10.6. Comparing the two ratios, Sternes’ team realized differences in the ratios revealing that megalodons had an oversized jaw.
Next, ontogenetic concerns were acknowledged, revolving around Cooper’s use of a juvenile white shark as the model for the megalodon. Sternes’ team argues for the lack of consideration for allometric change, that is, the change in the juvenile shark’s morphology as it ages. The use of a young shark, as the team protests, works against the idea of negative allometry.
The last discrepancy addressed by Sternes’ team was Cooper’s rendition of the megalodon’s build. Cooper’s team used two megalodon specimens from different regions of the world from two different periods and combined one tooth set and vertebrae set.
After recognizing the discrepancies, Sternes and his team rendered their new interpretation of the megalodon’s body. Despite the argument behind these discrepancies, Sternes and his team acknowledge that the exact body of the megalodon cannot be reconstructed based on the available fossil record. Further driven by Cooper’s research claims, Sternes mentions his and his team’s desire to counter these discrepancies, “These fundamental assumptions that the 2022 paper relied on … we attacked … because those key points were very important for building a 3D model in the first place. So those are the ones we’re going after … Those are the only four issues we caught at the moment.”
Sterne’s research goes ahead and argues that the megalodon’s body form is more elongated than that of an extant white shark. The original vertebral column length of 11.1+meters and the maximum diameter of the Belgium megalodon vertebrae suggest that the vertebral column was thinner than extant white sharks and more slender than smaller lamnidae. It was also considered that the megalodon could have had a more oval cross-sectional geometry, a more elongated body form closer to that of extant sharks, as opposed to Cooper’s rectangular anatomy.
Offering the public a chance at a new perspective revolving around the world’s beloved mega-shark, Sternes highlights the purpose of his team’s research, “I strive for both the scientific community and the public alike to understand what [the] megalodon looks like. We say it’s [a] more slender-looking shark. That’s what we propose.” The overall impact of this research not only leaves an open floor for those wishing to counter its results but also opens the door to further explore the megalodon’s influence on the history of marine life. Diving into new projects soon, Sternes hopes to continue to influence shark research.
