What Did Megalodon Eat? – The Bristol Dinosaur Challenge

Visitor Writer: Jack Cooper, MSc
UoB Graduate / PhD Pupil, College of Swansea

As we’ve seen to this point, there have been adjustments and updates to the scientific consensus of Megalodon’s taxonomic task and most physique dimension. Nevertheless, its favorite snack is one thing that’s universally agreed upon within the scientific neighborhood. In one other rarity, it’s one thing that’s often portrayed with fairly good accuracy in fiction. Enable me to introduce a shark that ate whales – precise whales!

Lots of at present’s giant macropredatory sharks are identified for consuming marine mammals, particularly our previous good friend the good white shark. A number of the most iconic images of this shark embody it hurling itself out of the water with its newest sufferer between its jaws (Fig. 1). Nevertheless, juvenile white sharks don’t eat seals proper from the get-go. As an alternative, they begin off consuming fish and smaller sharks [1]. If we glance once more on the Gatun formation in Panama, we discover loads of fossil sharks, rays and otoliths (buildings from the interior ears of fish), as nicely a plethora of invertebrates like molluscs [2,3].

One thing we don’t discover, nevertheless, is fossil marine mammals. This appears to point that Megalodon younger have been additionally consuming fish and smaller sharks moderately than instantly going after marine mammals. That is one thing referred to as an ontogenetic shift in weight-reduction plan, which means that the shark adjustments its most well-liked meals supply because it grows. By consuming bigger meals, and doubtless plenty of it, because it reached its grownup dimension, Megalodon would’ve been capable of preserve the metabolic calls for of being so giant. It might’ve accomplished this by consuming not solely whales, however absolutely anything it got here throughout.

Determine 1: An incredible white shark catching an unfortunate Cape fur seal by way of its “breaching” predation behaviour, a tactic the place the shark propels itself from the water to shortly snatch prey. This photograph was taken in False Bay, South Africa, one of many primary aggregation websites of white sharks. Picture by Chris Fallows.

Given how a lot meals Megalodon would’ve wanted to eat to justify its monumental dimension, it was nearly actually an opportunistic feeder. The fossil document is our greatest information right here. That is as a result of presence of hint fossils, that are geological data of organic exercise. This will vary from dinosaur footprints to scratches on bones indicating that one thing bit the animal that bone belonged to. And Megalodon left just a few of those hint fossils behind, offering key proof of its kills.

A number of fossils have been discovered belonging to quite a lot of cetaceans with notable chew marks on them. One well-cited instance comes from the Yorktown formation in Maryland, the place a number of whale bones had chew marks that had clearly been made by giant serrated tooth [4]. In actual fact, Megalodon tooth are typically discovered straight related to these bones [5].

Sharks lose and exchange tooth 1000’s of instances all through their lives, and thus sharks incessantly lose tooth when making a violent kill. This can be a key motive why shark tooth are such widespread fossils. The presence of the shark’s tooth proper by a scratched whale bone does point out that feeding was happening. However, one thing that palaeontologists ought to at all times take into account when these fossils are discovered is: was this really predation? Or was it maybe scavenging?

Scavenging is a standard feeding behaviour in trendy macropredatory sharks equivalent to nice whites (Fig. 2) and tiger sharks [6,7]. When these sharks encounter lifeless whales floating on the floor, it’s an all-you-can-eat buffet. Critically, scavenging requires no power expenditure, one thing that may be wasted on a failed predation try. Provided that Megalodon wanted to have the ability to preserve its monumental dimension, it wouldn’t make a lot sense to move on a free meal if it encountered a lifeless whale. Thus, by proxy of how giant trendy sharks feed, most of us can be keen to guess that Megalodon most likely did scavenge when given an opportunity.

Determine 2: An incredible white shark scavenging on a whale carcass. This will nicely have been a standard prevalence for the Megalodon within the Miocene and Pliocene. Picture by Matt Dicken.

This stated, there may be one significantly exceptional fossil that implicates Megalodon in a predation try. And, crucially, we all know this primarily as a result of its try failed. A paper printed in 2010 [8] described a partial rib Pliocene fossil belonging to a cetacean from the Yorktown formation in North Carolina (yep, two Yorktown formations). This fossil additionally confirmed harm resembling chew marks, however notably there gave the impression to be a woven bone protecting over these marks. The authors interpreted this as an indication of an an infection that had occurred whereas the animal had been recovering from bone trauma attributable to these chew marks. These marks matched up nicely with a serrated chew, suggesting that the attacker had serrated tooth – identical to Megalodon. The research subsequently recommended {that a} Megalodon, or one other giant shark, had attacked the animal the fossil had come from, however the sufferer had survived the try solely to die of an an infection from its damage six weeks later [8].

Much more just lately, the primary ever fossil chew marks discovered within the southern hemisphere attributed to Megalodon have been present in Peru’s Pisco formation [9]. Maybe it was meant to be, as this is identical website the place Gordon Hubbell discovered his distinctive Carcharodon fossil (mentioned in Q1). The bitten materials discovered right here included cranium and rib stays, suggesting that the shark had bitten its goal from the facet. Most importantly, the stays have been recognized to a person species for the primary time – that species being Piscobalaena nana, a small baleen whale. Like within the different hint fossils, the chew marks matched up nicely to giant serrated tooth – a very good case for accusing Megalodon of the assault (Fig. 3). It subsequently appeared that Megalodon was additionally able to concentrating on smaller whales (be it predation or scavenging), very a lot in step with options that it possible additionally focused dolphins, sea turtles and different smaller prey [9].

Determine 3: A palaeoartistic rendering of a Megalodon preying on a small baleen whale (P. nana), recreating the occasion that will have led to the Pisco chew mark fossils. Art work by Alberto Gennari. Picture additionally used as determine in Collareta et al. 2017 [9].

Whereas predation methods are onerous to interpret from fossils, trendy sharks might give us an concept of how Megalodon hunted. Its chew pressure would’ve been exceptionally highly effective for damaging whale bones. A pc mannequin of a white shark cranium has proposed that it has a chew pressure exceeding c. 1.8 tonnes, giving it one of many strongest chew forces of any dwelling animal [10]. By extension, this research suggests Megalodon’s chew pressure was even bigger, estimating at a unprecedented 108,514-182,201 N.

Scientists have additionally made makes an attempt at calculating Megalodon’s swimming pace, which can assist give us a sign of the way it hunted. Sharks can have a burst pace, which is a fast jolt of quick swimming, sometimes used for grabbing prey. However their common pace for his or her informal swims are what we name sustained swimming speeds. This varies between species, however one research led by David Jacoby [11] mixed information on 26 species from 64 prior research to develop a mannequin that will predict a scaling relationship between sustained swim pace and the shark’s metabolism and physique mass. Their mannequin incorporating metabolism revealed a scaling exponent of 0.173, summarised as the next equation:

Swim Pace (ms ¯¹) ∝ Mass (kg)^0.173

After they corrected the info for phylogeny, nevertheless, they discovered that minimal swim speeds scaled with physique mass on the barely decrease exponent of 0.15. The above equation moreover assumes a relentless of 1 to match the proportions however the information revealed that this fixed was really 0.266. They subsequently constructed the ability equation:

Swim Pace (ms ¯¹) = 0.266 Mass (kg) ^0.15

From this, they’re able to calculate the sustained swimming pace of Megalodon relying on its mass. For instance, the ~48,000 kg Megalodon calculated because the mass of a 15.9 m shark in Gottfried’s work [12] would reveal a shark swimming repeatedly at 1.34 m/s – roughly 4.8 km/hr [11,13]. Making use of this to a 52,000 kg Megalodon reveals a sustained swim pace of 1.36 m/s or 4.9 km/hr whereas if we went actually excessive and simulated a 100,000 kg shark, this mannequin would lead to a swim pace of 1.50 m/s or 5.4 km/hr. This mannequin has confirmed very efficient not simply in calculating Megalodon swim pace, but in addition in offering a mannequin for a number of shark species (Fig. 4) [11].

Determine 4: The scaling relationship of shark swim pace with physique mass throughout 26 species, fitted with each the linear mannequin (stable line) and 95% CIs (dashed traces). Knowledge for the brown smooth-hound (photograph by Butko CC BY-SA) and basking sharks (photograph by Greg Skomal) are highlighted with arrows. Taken from Jacoby et al. 2015 [11].

Nevertheless, it’s the burst pace that sharks use to shortly snatch their prey. White sharks utilise this for his or her “breaching behaviour” wherein they propel themselves out of the water by speeding prey from under to catch them without warning (Fig. 1) [14]. They will do that as a result of they’re nicely camouflaged attributable to countershading. So, as a result of Megalodon was possible countershaded as nicely, and had comparable ecology and physique construction to white sharks [15], this begs the query: was Megalodon able to breaching too?

Perhaps. White shark burst pace is powered by a physiological adaptation referred to as mesothermy [14]. That is one thing Megalodon has just lately been recommended to have had as nicely (to be mentioned intimately in Q5). Mesothermic fishes usually have quicker sustained and burst swimming speeds than ectothermic fishes [16], and this has been used to recommend that Megalodon might have had a burst pace of as much as 37.15 km/hr [17].

That extremely fast pace for such a big shark could be sufficient to have the ability to breach. Past this, the basking shark (Cetorhinus maximus), at present’s second largest shark, has additionally been noticed breaching [18]. Maybe the large Megalodon was certainly able to leaping out of the water because it grabbed its newest meal. We simply don’t know but, however my private and (considerably) skilled opinion is that it could nicely have been doable.

With such a broad menu to select from, Megalodon was an apex predator, with no identified predators of its personal. This implies two vital issues. Firstly, it possible had stiff competitors for its prey, one thing that will have finally contributed to its extinction. Secondly, as an apex predator, Megalodon would’ve been of utmost significance to its ecosystem as it might’ve stored its prey populations in test and thus preserved a wholesome ecosystem.

Because of this sharks of at present are so vital to marine environments. The lack of an apex predatory shark produces irreversible cascading results that change the neighborhood it leaves behind [19]. As such, our marine ecosystems are the best way they’re partially as a result of Megalodon is now not part of it. And the large whales of recent oceans can relaxation simple consequently.


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Edited by Rhys Charles

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