The Megalodon may have neem slimmer but longer than this illustration shows.
Catmando/Shutterstock
A scientific principle that creationists seem to find baffling, is based on the intellectually honest position that opinion must be guided by evidence. It is that scientific opinion is always provisional and subject to change if the evidence changes, so evidence is frequently re-examined and reassesses, and scientific opinion is adjusted accordingly. This is why science textbooks are revised periodically and new editions produced, incorporating the newer thinking,
A simple analogy is that of driving to an airport to catch an important flight. You might check the expected driving time by checking in an old route planner from the 1950's, which might tell you the journey, in the days before traffic congestion, would take about 90 minutes, then you might check a few days before the flight, using an online route planner and learn that the journey will take about 2 hours at that time of day.
Do you just regard the 1950's version as an indisputable fact and plan your journey accordingly? How about the one a few days ago? No! A sensible person, regards both those as provisional pending more up-to-date information, and checks again on the day, when they might discover that there is a road closure and a diversion in place, or there is a serious incident on the motorway, reducing the traffic to a slow crawl for 20 miles, so the journey will now take 3 hours. Was the first estimate wrong? Which is the best estimate to go with now? The old ones based on information available at that time, which might have caused you to miss your flight, or the new one based on updated information?
On that analogy, creationists are in the position of using information not from the 1950s, but from the Bronze Age, some of it from a time before even the wheel was invented, let alone air-transport, motor cars or motorways!
In 2022, based on very scant information (a tooth and some vertebrae), a team of researchers estimated the size of an extinct shark, the megalodon (big tooth) shark, Otodus megalodon, to be at least 50 feet long, and possibly as much as 65 feet. This was based in the assumption that O. megalodon was like a scaled up great white shark, Carcharodon carcharias, so its dimensions could be estimated by comparing what they had with those of C. carcharias.
Now a team or researchers co-led by biologist, Phillip Sternes of the University of California Riverside (UCR), and DePaul University paleobiology, Professor Kenshu Shimada, have reassessed the evidence and concludes that O. megalodon was slimmer than the great white but probably considerably longer than the earlier estimate. This greater length would probably have meant a more efficient digestive system having longer to digest food and extract nutrients from it, so its hunting and predation would have had less impact on the ecosystem than first thought. It would still have been an apex predator but maybe not as voracious as first thought.
Their research is published in the journal Palaeontologia Electronica, an explained in a UCR news release:
And more technical details are given in the team's open access paper in Palaeontologia Electronica:For the new study … a team of 26 scientists from around the world, co-led by Sternes and DePaul University paleobiology professor Kenshu Shimada, was inspired by differences in previously estimated body lengths for the Megalodon.Our team reexamined the fossil record, and discovered the Megalodon was more slender and possibly even longer than we thought. Therefore, a better model might be the modern mako shark. It still would have been a formidable predator at the top of the ancient marine food chain, but it would have behaved differently based on this new understanding of its body.
Phillip Sternes, first author
Biologist
University of California at Riverside (UCR)
The team then weighed in on a new comparison of Megalodon vertebra fossils to those of living lamniform shark relatives. “We measured the whole vertebral skeleton of a living great white shark with a CT scanner and compared that to the previous reconstruction of the Megalodon vertebral column,” Sternes said. “It was still a giant, predatory shark. But the results strongly suggest that the Megalodon was not merely a larger version of the modern great white shark.” A revised understanding of the Megalodon body type would in turn affect scientists’ understanding not only of the giant shark itself, but also of its impact on the ecology and evolution of marine ecosystems that shaped the present-day oceans. There is no doubt the Megalodon is one of the largest marine predators ever to have lived. But a slimmer and more elongated body would suggest the Megalodon also had a longer digestive canal. Sternes explained that in this case, the sharks might have enjoyed enhanced absorption of nutrients, and may not have had to eat as often as previously believed. “With increased ability to digest its food, it could have gone for longer without needing to hunt. This means less predation pressure on other marine creatures,” Sternes said. “If I only have to eat one whale every so often, whale populations would remain more stable over time.” Some shark scientists have theorized that a natural decrease in prey led to the extinction of Megalodons. However, Sternes has another theory, in part supported by the revised understanding of its shape.It was a ‘eureka-moment’ when our research team realized the discrepancy between two previously published lengths for the same Megalodon specimen.
Professor Kenshu Shimada, co-author
Department of Biological Sciences
DePaul University, Chicago, Illinois, USA.The research team of shark experts from the U.S., UK, Austria, France, Japan, Mexico, Brazil, and Australia all feel that a revised understanding of ancient marine life would have a cascading effect on the oceans that are still visible today. “Now that we know it was a thinner shark, we need to reinvestigate its lifestyle, how it really lived, and what caused it to go extinct,” Sternes said. “This study represents a major stepping stone for others to follow up on.”I believe there were a combination of factors that led to the extinction, but one of them may have been the emergence of the great white shark, which was possibly more agile, making it an even better predator than the Megalodon. That competition for food may have been a major factor in its demise.
Philip Sternes.
ABSTRACTCreationists seem not to be able to work out that a later opinion, based on up-to-date evidence is more likely to be correct than an ancient opinion based on little more than guessworkk by people who believed in magic and thought Earth was small and flat and at the center of the Universe, and stars were stuck to a dome over it.
The megatooth shark, †Otodus megalodon, which likely reached at least 15 m in total length, is an iconic extinct shark represented primarily by its gigantic teeth in the Neogene fossil record. As one of the largest marine carnivores to ever exist, understanding the biology, evolution, and extinction of †O. megalodon is important because it had a significant impact on the ecology and evolution of marine ecosystems that shaped the present-day oceans. Some attempts inferring the body form of †O. megalodon have been carried out, but they are all speculative due to the lack of any complete skeleton. Here we highlight the fact that the previous total body length estimated from vertebral diameters of the extant white shark (Carcharodon carcharias)for an †O. megalodon individual represented by an incomplete vertebral column is much shorter than the sum of anteroposterior lengths of those fossil vertebrae. This factual evidence indicates that †O. megalodon had an elongated body relative to the body of the modern white shark. Although its exact body form remains unknown, this proposition represents the most parsimonious empirical evidence, which is a significant step towards deciphering the body form of †O. megalodon.
INTRODUCTION
The extinct megatooth shark, †Otodus megalodon (Lamniformes: †Otodontidae), is an iconic prehistoric shark that has captured the attention of both scientists and the public due to its large teeth. Yet, one major challenge palaeontologists have faced is exactly what †O. megalodon looked like because no complete skeleton of the fossil species is known to date. Traditionally, the extant white shark (Carcharodon carcharias) has been used as a model species to reconstruct the body form of †O. megalodon (e.g., Gottfried et al., 1996). The most recent attempts have been the 2D reconstruction work by Cooper et al. (2020), followed by Cooper et al.’s (2022) 3D model of the body of †O. megalodon. Cooper et al. (2020, 2022) used the extant white shark as a model representation of †O. megalodon because the fossil shark has been inferred to be regionally endothermic like the extant lamnid sharks that include the white shark (Ferrόn, 2017). In particular, Cooper et al. (2022) used an extant juvenile white shark specimen to generate a 3D model of †O. megalodon first, and then conducted a ‘model adjustment’ using all the extant lamnids because of the uncertainty in the phylogenetic position of †O. megalodon within Lamniformes.Based on their body form reconstruction, they concluded that †O. megalodon was a fast-cruising shark much like the extant lamnids. However, using the extant white shark or other lamnids as a template to reconstruct the body form of †O. megalodon lacks empirical fossil support (Sternes et al., 2023.4). Furthermore, it is also tenuous on the phylogenetic basis because †O. megalodon, as an otodontid, lies outside of the Lamnidae and may not be closely related to the family at all (Sternes et al., 2023.4; Figure 1A; but see also Appendix 1).
One key question is: “Did †O. megalodon look like a large extant white shark?” It is true that the extant white shark has generally been used to estimate the body size of †O. megalodon (Shimada, 2019; Perez et al., 2021), but unlike preserved teeth that are at least tangibly comparable, the lack of any complete skeleton, or even a complete cranial skeleton or vertebral column, makes any skeletal or body reconstruction speculative. However, there are three critical pieces of information relevant to addressing the question that have become available since Cooper et al.’s (2022) study. First, on the basis of geochemical evidence, the endothermic physiology in †O. megalodon (specifically, likely regional endothermy) is empirically confirmed (Griffiths et al., 2023). Second, the newly described placoid scales of †O. megalodon, particularly the scales’ interkeel distances that vary independent of body sizes in sharks, indicate that the general cruising speed of †O. megalodon was likely slower than the cruising speeds of extant lamnids, including the white shark (Shimada et al., 2023.1). Third, and more significantly, two other lamniform species, the extant planktivorous basking shark (Cetorhinus maximus), which has traditionally been regarded as a sluggish shark, as well as the deepwater, benthopelagic smalltooth sand tiger (Odontaspis ferox) have both been reinterpreted to be endothermic (also likely regional endothermy: Dolton et al., 2023.1a, 2023.2b; despite at least O. ferox is suggested to be ectothermic based on isotopic analyses by Griffiths et al., 2023). Hence, while †O. megalodon was indeed ‘endothermic’ (Griffiths et al., 2023), the new palaeontological (Shimada et al., 2023.1) and neontological (at least Dolton et al., 2023.2a, at present) evidence do not corroborate the previous assumption and its rationale that †O. megalodon must have physically resembled the extant white shark or lamnids in general (Cooper et al., 2020, 2022). Therefore, the purpose of this paper is two-fold: 1) to re-evaluate the validity of the most recently proposed body form reconstruction of †O. megalodon; and 2) to provide a new hypothesis on the body form of †O. megalodon based on available evidence.
FIGURE 1. Simplified family-level phylogenetic hypothesis of Lamniformes showing all extant clades and †Otodontidae (A: dagger [†] indicates extinct), and silhouette depiction of fossil vertebral column of †Otodus megalodon (B). A, Current understanding of lamniform phylogeny demonstrating that a large portion of the phylogenetic tree remains unresolved due to conflicting results based on various molecular and morphological studies (Sternes et al., 2023.4 and references therein); although the placement of †Otodontidae is tentative and other extinct families are not depicted in this tree, the main point of this illustration is to demonstrate that †Otodontidae lies outside of Lamnidae (both clades highlighted in bold letters) where clades containing one or more species with regional endothermy (indicated by an asterisk [*]) do not share an immediate common ancestry (Sternes et al., 2023.4). B, Reconstructed vertebral column and its total measured length by Cooper et al. (2022) based on an incomplete associated vertebral set from the Miocene of Belgium; this specific specimen (IRSNB P 9893) was previously estimated to have come from an individual that measured 9.2 m in total length, including the head and caudal fin (Gottfried et al., 1996) based on the modern white shark, not accounted for by Cooper et al.
FIGURE 3. Photographic (*) and CT images (**) of preserved specimens of extant white shark (Carcharodon carcharias) and salmon shark (Lamna ditropis). A, Complete specimen of 126-cm-TL male C. carcharias caught off central California, USA (LACM 43805-1): from top to bottom, external body* and skeleton** in left lateral view and external body** and skeleton** in ventral view. B, Complete specimen of 151 cm TL male L. ditropis caught off central California (FMNH 117475): from top to bottom, external body* and skeleton** in left lateral view and external body* and skeleton** in dorsal view. C, Head specimen of estimated 271-cm-TL male C. carcharias caught off southern Florida, USA (FMNH 38335): from top to bottom, external head* and cranial skeleton** in left lateral view and external head* and cranial skeleton** in dorsal view. All scale bars equal 10 cm.
FIGURE 4. Previous and new schematic interpretations of †Otodus megalodon body form. A dark grey silhouette depicting the previously reconstructed †O. megalodon body form by Cooper et al. (2022) based on the extant white shark, superimposing a light grey outline showing the newly interpreted body form of †O. megalodon which is more elongated than the extant white shark. Note: it must be emphasized that this illustration should be strictly regarded as schematic as the exact extent of body elongation, the shape of the head, and the morphology and positions of the fins remain unknown based on the present fossil record.Sternes, Phillip C., Jambura, Patrick L., Türtscher, Julia, et al.
White shark comparison reveals a slender body for the extinct megatooth shark, Otodus megalodon (Lamniformes: Otodontidae).
Palaeontologia Electronica, 27(1):a7. https://doi.org/10.26879/1345
Copyright: © 2024 The authors.
Published by Palaeontological Association. Open access.
Reprinted under a Creative Commons Attribution-NonCommercial-ShareAlike 4.0 International license (CC BY-NC-SA 4.0)
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