Among prehistoric sharks, none are more famous than the giant Megalodon,
a fearsome predator that stalked the ancient oceans for almost 20 million years. This
enormous shark was a ruthless killer of extinct whales and other marine animals,
feeding on almost anything it could get its jaws around. Surely,
nothing in our planet’s oceans could ever have competed with such an extraordinary creature?
Well, this is the fossil record we’re talking about,
so of course something incredible and unexpected was bound to turn
up eventually - something that could even have rivalled Megalodon itself.
Another giant prehistoric killer of large-bodied marine prey was announced in 2010 - a huge,
macro-raptorial sperm whale called Livyatan. This animal lived from about 10 to 5 million years ago,
towards the latter part of Megalodon’s reign, and has been found in the very
same locations that the giant shark lived in. The diets of these two animals seem
to have overlapped as well, and so with two massive predators living in the same
areas and eating the same things, it appears to have been inevitable
that these giants of prehistory would have clashed at some point or another.
The rivalry between Megalodon and Livyatan seems almost too spectacular,
too much like some over-the-top B movie,
to be true - and yet this competition was a very real thing and has been written about in
several scientific papers on these animals. It’s also a very enticing topic for a video,
so what better way to close out Shark Week 2023 than to look at Megalodon’s nemesis - Livyatan.
The feeding ecology of Megalodon - technically called Otodus megalodon - has been extensively
studied, with much fossil evidence contributing to our understanding of what this fish ate. These
fossil finds include bones from both large and small-bodied prehistoric whales that display bite
marks and traces thought to have been inflicted by Megalodon teeth, as well as such marks on
bones belonging to seals, sea lions, turtles and manatees. One vertebra from a large whale
found in the Caribbean even preserves a Megalodon tooth embedded in it, showing with certainty that
the big fishy of death was certainly capable of tackling large whales, but it wasn’t restricted
to hunting only these animals and was just as happy to feed on whatever was available.
A great deal of isotopic evidence from the fossils has been investigated, too. By looking at various
different isotope compositions of the teeth from this shark, palaeontologists have been
able to tell a lot about Megalodon's diet and position within the prehistoric oceans' food webs.
Calcium isotopes have been used to show that Megalodon occupied a slightly higher trophic
position than modern-day Great White Sharks - meaning they were higher up in the food
chain and were able to feed on other large predators that Great Whites cannot. However,
this contrasts slightly with other evidence from Zinc isotopes showing that towards the
end of Megalodon’s time, there was actually quite a lot of overlap in
the trophic level of this shark and Great Whites, with both species actually feeding
on animals lower down in the food web such as small, filter-feeding cetaceans.
Yet another isotope analysis has been used to show that Megalodon was very
generalist in its diet, though - this time by looking at nitrogen isotope compositions. This
research found that there was a large spread of nitrogen isotope values among samples of
Megalodon teeth, with some showing extremely high values - higher than any other marine predator,
in fact - others had quite low values, implying that these sharks had a variety
of prey preferences. This further supports the fossil evidence mentioned earlier,
showing Megalodon was capable of feeding on whatever it pleased.
But what about Livyatan? Well, from the moment this giant was described, it was clear to
palaeontologists that it was also a predator of large marine animals. Unlike modern Sperm Whales,
to which Livyatan is only distantly related, this prehistoric killer had massive teeth in
both the upper and lower jaws - whereas sperm whales only have teeth on the lower
jaw. This points towards a very different feeding strategy between the whales, and whereas sperm
whales obtain prey through suction-feeding, Livyatan most likely fed more like an orca,
taking big chunks of flesh out of the unfortunate creatures it targeted.
The fossil evidence we have for Livyatan’s existence is actually fairly limited,
with just the holotype partial skull and several isolated teeth from around the world
being referred to this cetacean. For over a hundred years, exceptionally large teeth
that appeared similar in structure to a sperm whale’s were occasionally being found at various
fossil localities, but the creature these teeth were coming from remained unknown to science,
as no known whale matched the enormous size of the dentition. Then, while on a field
trip to an exposure of the Miocene-aged Pisco Formation of Peru in November 2008,
palaeontologists uncovered the magnificent, 3-metre-long skull of a macro-raptorial
sperm whale preserved with these same, terrifying giant teeth. At last, the culprit had been found.
The palaeontologists published their discovery in July of 2010,
naming it Leviathan melvillei - after both the biblical sea creature, as well as Herman Melville,
author of Moby-Dick. Unfortunately, it turned out that the name Leviathan
couldn’t be used for this animal, as it was preoccupied since it had been used as an
alternate published name for the Mastodon back in 1841. Although it is now an invalid genus name,
this still means that Leviathan can’t ever be used as the scientific name of an animal,
which really is a shame. Anyway, in response the authors published a correction in August of 2010,
changing the name to Livyatan - the original Hebrew word for Leviathan.
Livyatan was a very interesting and unique animal. As I already mentioned, when looking at its
evolutionary relationships among the sperm whale superfamily - called Physeteroidea - it was found
to belong to an entirely separate lineage from the one containing the modern sperm whale, and
also in a separate position from the living dwarf and pygmy sperm whales, the Kogiids. Livyatan also
falls into a distinct lineage by itself even when compared to the other known macro-raptorial sperm
whales, such as Acrophyseter, Brygmophyseter and Zygophyseter. Albicetus (meaning ‘white whale’,
again in reference to Moby-Dick) was named in 2015 and found to be somewhat
closely allied with Livyatan, though, but the exact relationship is still unclear.
Livyatan differs from some of these other raptorial physeteroids in that the supracranial
basin - the distinct, bowl-shaped depression on the top surface of the skull that would have
housed the spermaceti organ - actually extends all the way along to the front of the upper jaws,
like in the modern sperm whale. In Acrophyseter and Zygophyseter,
though, the supracranial basin is more restricted, and a protruding
snout would have been present in life as the spermaceti organ didn’t reach as far forward.
The skull of Livyatan was found in rocks dating to between about 11.6 and 9 million years ago,
but teeth matching this whale, or at least being very similar to it, have been recovered
from deposits ranging up to just 5 million years ago. And not only did this whale cross over in
time with Megalodon - which lived from around 23 to 3.6 million years ago - but they crossed over
geographically, too. Like Megalodon, Livyatan appears to have had a global distribution,
with teeth being recovered from Chile, Argentina, South Africa, Australia, and even California.
The locality in Peru from which the skull was recovered has also produced
teeth belonging to Megalodon, with the authors who initially described
Livyatan suggesting that the combination of these two enormous predators in the same
environment must have had a major impact on the composition of marine food webs.
In fact, one such impact of the presence of Megalodon and Livyatan was found within a
population of physeteroids known from fossils in North Carolina. A 2018 study looked at a large
sample of sperm whale teeth from the US Atlantic coastal plain that date to around 5 million years
ago and found something very interesting. The teeth that they sampled all belonged to
raptorial sperm whales and though they couldn’t be classified exactly, the presence of wear
facets on the teeth indicated these whales all had teeth in both upper and lower jaws,
so they were different to the modern sperm whale and likely had a comparable ecology to
orcas. These particular physeteroids were also all about the same size as an orca,
reaching 8 to 10 metres in length, and by looking at growth layers within the teeth
the researchers were able to determine at what age these whales had died.
Somewhat surprisingly, they discovered that these sperm whales only rarely lived longer
than 20 years, whereas modern orcas and sperm whales regularly live for more than
65 years. So it seems these fossil sperm whales had an accelerated life history,
growing quickly and not living very long - which the authors attribute to the intense
predation pressure inflicted on these cetaceans by superpredators such as Megalodon and Livyatan.
Whereas in our modern oceans killer whales sit at the top of the food web
and can enjoy long lifespans since nothing else really threatens them,
back in the Neogene things were very different. Orca-sized raptorial sperm whales were not
the top predators of their time, and so they were forced to grow fast in order to survive.
These prehistoric oceans must therefore have had some unique properties in order
to support so many large macropredators in coastal environments. Primary production
rates must have been significantly higher in certain coastal regions than they are today,
and it appears that there were a few extra steps in the marine food webs
that added a complexity to these systems which is not seen in the modern world.
So clearly the presence of two superpredators in the Neogene oceans was having trickle-down
effects on other organisms - but what about on the superpredators themselves?
Well, as we’ve seen, the oceans were capable of supporting both species,
with those extra tiers in the food webs and highly productive primary producers enabling
the evolution of such enormous carnivores. But Megalodon and Livyatan were still likely going
after the same prey. Although Megalodon seems to have been fairly generalist,
the evidence shows that it would have hunted baleen whales - the
mysticetes - and these are also thought to have been the favoured prey of Livyatan.
So, it’s entirely possible that - just as the countless videos on the subject like to talk about
- Megalodon and Livyatan may have fought each other. Of course, like any animal competing over a
source of food, conflict with another dangerous predator would most likely have been avoided
until no other course of action was possible, and physical attacks would be a last resort. Still,
towards the end of Livyatan’s temporal range, perhaps conflicts with other large predators
such as Megalodon would have been intensified as the medium-sized mysticetes favoured as prey
by the sperm whales became rarer and eventually disappeared, and larger baleen whales evolved.
In the paper describing Livyatan, it’s proposed that the whale would have specifically targeted
these smaller mysticetes since they had the high-energy content needed to sustain such a large
endothermic predator within their thick layers of blubber. Plus, the abundance and diversity
of these mysticetes in the same formation as Livyatan make them logical prey items.
Interestingly, a very recent paper from June of 2023 has found that Megalodon, too, had intensive
energy demands as it turns out to have also been endothermic - maintaining an internal body
temperature that was higher than the surrounding environmental temperature. Megalodon likely had a
different kind of endothermy to cetaceans, though, known as regional endothermy - in which only
certain parts of the body were kept warm. Still, it seems reasonable to assume that this giant,
regionally endothermic shark would also have required calorific prey such as mysticetes in
order to maintain itself - another reason for potential conflict with Livyatan.
More, very cool direct evidence for conflicts between prehistoric sperm whales and large sharks
has also been found - as described in a 2021 paper. A single tooth from a physeteroid was
found in North Carolina that displays something very interesting. The tooth has 3 gouges across
its surface, and based on the traces of a serrated tooth edge, the size of the bites
and the spacing between them, they could only have been inflicted by a member of the Otodus genus.
Now, this may have been Otodus megalodon itself, or it could have been Otodus chubutensis - a
close relative of Megalodon that was still pretty large - as both of these species have been found
in the same formation this tooth comes from. Based on the size of the physeteroid tooth,
it’s estimated that the animal this came from was around 4 metres in total length - so nothing like
the size of Livyatan, which has been estimated at between about 14 to over 17 metres long.
There’s also no way to know for sure if the bite marks made by the shark were the result
of an active predation attempt, or if they were from a shark scavenging on the whale’s carcass.
However, the palaeontologists favour the active predation explanation,
as the shark was clearly targeting the jaws of this cetacean if it then left marks on the teeth,
and biting the jaws would make more sense if an attacker was trying to disable live prey,
rather than scavenging on this part of the body that has relatively little flesh on it compared
to other regions. Another thing to note here is that the gouge labelled 3 on the tooth is
on a part that would have been embedded in the jaw of the living whale - so when
this shark bit down on the cetacean, it would have had to first break through the
jaw bone to inflict this mark, showing how powerfully these sharks could bite.
Although it’s not a tooth from Livyatan and it’s not definitely a bite from Megalodon itself,
it nevertheless shows that sharks of the Otodus genus would sometimes have targeted physeteroids,
too - and that opens up the possibility of sharks such as Megalodon going after even larger ones.
So, the Neogene oceans were undoubtedly a terrifying place with not just one,
but at least two huge superpredators ruling those prehistoric waves. The presence of these
carnivores has also taught palaeontologists a lot about the structure of ancient marine food webs,
and it’s very interesting to think that the arrangement back then would have been quite
different to our modern oceans, with a few extra tiers to consider. And, yes, it’s just plain
cool to think that Megalodon and Livyatan may have fought over the same prey - and what a battle that
would have been. There’s a lot more I could say about Livyatan, especially in regard to what it
means for sperm whale evolution, so let me know if you’d like to see a video dedicated just to that.
And so that marks the end of Shark Week 2023, I really hope you’ve enjoyed the videos this year,
and let me know in the comments your suggestions for topics for Shark Week 2024. Also be sure to
head on over to my mum’s channel, One World, to watch her shark week video on sharks in captivity.