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Paleo-Profile: Livyatan melvillei

Macrophyseter

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The modern sperm whale Physeter macrocephalus (which means "long-headed blower") has been celebrated and feared in classic literature, often being depicted as ruthless ship-destroyers, most famous of these literature was Herman Melville's novel Moby Dick. But fossil discoveries in the early 2000s beg to differ, revealing a massive leviathan as big as the sperm whale but with powerful and gigantic jaws spawning teeth bigger than a human arm and an appetite that would make Moby Dick resemble a minnow. A whale that would wreck ships for sport rather than defense, its name was Livyatan melvillei, a name-worthy leviathan that must go down in history as the largest and most powerful tetrapod macropredator of all time.

 

livyatan_melvillei_by_teratophoneus-dao0

Illustration by Teratophoneus

 

Etymology

    Livyatan melvillei literally means "Melville's Leviathan", which easily suggests that L. melvillei was named in honor of the novel Moby Dick. The genus name uses the literal spelling of the Hebrew word לווייתן (livyatán) in reference to the nickname leviathans commonly used on whales, especially from Moby Dick according to the namers, although the Leviathan was also a legendary sea monster from the Hebrew Bible (However, the english spelling leviathan was originally used, but was later discarded due to the name already being taken). The Latin species name melvillei was named after Moby Dick author Herman Melville.

   Although unnecessary, the genus name can be broken down even further to the original meaning of לווייתן (livyatán), which literally means "wreathed" or "twisted", thus making the most literal meaning of L. melvillei be "Melville's wreathed".

 

Discovery

    For over a century, gigantic teeth whale teeth, some claimed to reach lengths of 40 centimeters, have been found all over South America, most notably Chile and Peru (and according to some sources California, but there is no deeper explanation to this). In November of 2008, a team of international scientists uncovered a 75% complete skull of a giant cetacean in the Pisco Formation of the Cerro Colorado desert in Peru (In an interview, the scientists remarked that they found the skull at the very last day or their trip upside-down and broken up). Taken back to Lima for examination, it was deemed a new type of cetacean and was given the taxon Leviathan melvillei in their papers published two years later. However, quickly after publication it was pointed out that the genus Leviathan was already a synonym for a mastodon. Because strict taxonomy rules do not allow any name to be used twice (Even if the already existing name is a synonym), the genus was renamed to Livyatan.

    In 2016, a fossil enthusiast Murray Orr discovered a giant 30+ centimeter tooth off the shores of Beaumaris Bay near Melbourne in Australia. Realizing that this find may be important, he quickly contacted the Victorian Museum, where it was discovered that the tooth was indeed important and belonged to that of Livyatan. Although the morphology of the tooth itself is identical to that of L. melvillei, it is pointed out that Beaumaris was a Pliocene-age formation and thousands of miles away from Peru, suggesting that Livyatan or possibly just L. melvillei was much more diverse and existed much longer.

 

Biology

Total Body Length

    Because only the skull has been discovered, the rest of L. melvillei's body -and size- is still yet to be debated and thoroughly confirmed. As of now, two other physeteroids have been officially to determine the size of the L. melvillei holotype, with a third one used by some. In general, the total body length is generally said to be up to 18 meters in length.

    Using the modern sperm whale as reference, the total body length of the holotype was calculated to be 13.5 meters long, making it somewhat a bit smaller compared to modern whales. However, P. macrocephalus is unique for having a elongated head and a shorter body compared to other physeteroids, and because of the shorter, more robust form of the L. melvillei holotype skull, it may not be the most accurate reference. The P. macrocephalus reference is commonly used as the lower estimate of L. melvillei

    Another, more closer relative with a fully complete skeleton known, Zygophyseter varolai, can be used as reference to yield a much larger and impressive 17.5 meters, which rivals the length of P. macrocephalus itself. Because of L. melvillei being more closely related to Z. varolai than P. macrocephalus, plus the unusual and unique body dimensions of the latter, this estimate is probably more accurate than the lower 13.5. Many in the science community and media simply round the estimate to 18 meters.

    A third, but unofficial reference what was once frequently used is Brygmophyseter shigensis, which is known from a near-complete skeleton. A paleoartist referenced the body of the B. shingensis holotype to the L. melvillei skull and calculated a length of 15.4 meters. Although this estimate may be credible and can be seen to be used with other paleoartists, it is not an official estimate and is largely unused by scientists.

    However, it must be remembered that these size estimates are only based on the holotype, which is the only non-tooth specimen currently found. This means that it is very possible that L. melvillei could reach larger sizes. In fact, isolated teeth already may suggest larger sizes. In a twitter post by one of the scientists in possession of the Beaumaris tooth hinted that it came from an 18-meter Livyatan and was may have even been a subadult. A gigantic Chile tooth from the same post was estimated by someone to come from a L. melvillei that grew to 21 meters long (Using credible tooth/body length ratios).

 

Morphology

    L. melvillei was a physeteroid, but unlike other raptorials, had a large, box-shaped head. While this feature is common in other physeteroids, it should be noted that the other raptorials with known skulls, Zygophyseter, Brygmophyseter, and Acrophyseter, all had smaller heads and a snout which resembles dolphins, while L. melvillei does not. This is because the holotype skull shows the supercranial basin curving to the end of the skull like that of P. macrocephalus, while the others have their supercranial basins limited to the face, thus creating their snout.

    With a giant supercranial basin, this means that L. melvillei had a massive supply of hypertrophied tissue (spermaceti and melon), suggesting that the whale possessed some abilities. The large spermaceti was a trait that was theorized to possible explain P. macrocephalus's ability to dive deep, suggesting that L. melvillei too, had the ability to dive deep. But with L. melvillei being more possibly a surface hunter, another, more accepted usage would be advanced echolocation as seen in P. macrocephalus. Another possible usage would be ramming, which is also a behavior P. macrocephalus has been seen doing. Although the two whales have very similar traits in the morphology of the head, this does not suggest that they are very closely related to each other, as the traits are merely a result of parallel evolution.

    As the L. melvillei holotype only consisted of a skull, the morphology of the rest of the body is unknown. Multiple theories of the body plan have circulated, but the most accepted one is a large and robust body, as hinted by the small but robust skull, and based on the other raptorial sperm whales, which all have a similar body plan of a small, robust head and a large body.

    L. melvillei, like all raptorials, had functional teeth on both jaws. With the presence of functional teeth in the upper jaw, it shows that L. melvillei was macropredatory. The teeth also grow up to 36 centimeters, being the largest functional teeth in the animal kingdom (tusks are considered teeth, which are obviously larger, but they are not functional for eating and do not count). Having such large teeth, it has been suggested that L. melvillei probably also had a powerful bite force to deliver a more deadly blow to its prey. Your hand would merely be squashed by a tooth of L. melvillei if it were ever to bite it! With all of these features, it all points to the conclusion that L. melvillei was an efficient apex predator, which hunted whales, sharks, and anything else it could grab.

 

Hunting

    L. melvillei's preferred prey is believed to be animals up to 10 meters in length including large whales, sharks, and other large animals. Because all the animals L. melvillei prey on lived by the surface, it meant that it was a surface hunter. Currently, it is believed that L. melvillei would attack from below, diving deep to gain momentum, then accelerating up and ramming the victim, stunning it before the jaws deliver the kill. Unfortunately, there is currently no fossils with feeding marks left by L. melvillei, so the current theories are based on the morphology of L. melvillei alone. 

    With the data of the skull morphology along with the continuous pattern of the hunting methods of large ocean predators, we can draw an image of how exactly L. melvillei could have hunted- A lone 6-meter Cetotherium cruises alone at the shore, away from the safety of a pod. Nearby, a hungry 18-meter L. melvillei senses prey through its echolocation and draws closer. Seeing the whale, it quickly descends as the Cetotherium obliviously continues to swim on. Having swum deep enough, the L. melvillei then rushes towards the whale, increasing speed every moment until its strong head rams into the Cetotherium's underside, sending both into the surface and quickly fall back in the water. Suffering major broken bones in the ribs, tail, and spine, the unconscious and paralyzed Ceototherium sinks hopelessly as the victorious L. melvillei turns back towards the dying whale and bites it, driving its 30 centimeter teeth deep into the flesh and destroying the vital organs, putting the Cetotherium out of its misery. The killer has won its meal, and what was left of the victim sinks to the bottom of the ocean, resting on the ancient seabed as nourishment for any lingering scavengers.

 

Environment

    The L. melvillei holotype was dated 9.9-8.9 million years old. Isolated teeth from other parts of Peru and Chile show a temporal range of 11.6-7.2 million years, and the Beaumaris tooth extends it further to 5 million years ago. The temporal range based on South American examples sits right during a golden age of cetaceans- the diversity of mysticetes and odontocetes alike are seeing its highest level of diversity. Moreover, fossil records show mysticete population being the highest in Peru and Australia, right where L. melvillei fossils have been found. In fact, this pattern of L. melvillei teeth being found in the greatest cetacean hotspots suggest that it was a specialized hunter, designed to thrive in overpopulated oceans and could afford to evolve huge builds backed by such a fertile supply of prey (Hence, L. melvillei was the largest macropredatory tetrapod).

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Diversity of mysticetes. Original graph by G. Bianucci (University of Pisa).

    However, the appearance of L. melvillei during this time is still a wonder, because around this time the giant shark Carcharocles megalodon was already the apex predator of all seas. What's even more amazing is that not only did the two coexist, they also hunted the very same prey. In most situations, the pure pressure of competition would have an environment only allow one apex species, but the appearance of two equal apexes proves that there were so many whales at the time that the competition levels wouldn't strain if another one appeared. If the cetaceans were less diverse, then L. melvillei or even C. megalodon would not have existed, because it was only to the huge supply of prey that allowed them to evolve a build that requires immense amounts of eating. But it seems that L. melvillei might have been too reliant on mysticete overpopulation, as the former only appeared in areas of the highest mysticete concentrations (Western South America and Australia), while C. megalodon had a cosmopolitan distribution. This could be because the sheer size of L. melvillei was relatively huge for a hypercarnivorous mammal. Mammals, being warm-blooded require more metabolism than cold-blooded animals for the extra energy to be able to regulate its body. (While the largest animals are indeed mammals, they have easy access to food while macropredators need to hunt evasive animals which require more energy. It's no question that the largest hypercarnivores today are relatively small compared to those from past times. The advantage of being small is that you don't need as much metabolism as bigger predators and can easily adapt to a sparsely populated environment) This is no exception for L. melvillei. It's possible that the reliance of such a huge population of prey restrict their distribution to the most populated areas, and any other place with less population of cetaceans will provide too little prey for a bulky 18-meter whale to survive in.

 

Extinction

    Due to such a poor fossil record, it is unknown when exactly L. melvillei went extinct (There is an accepted temporal range, but abnormal examples like the Beaumaris tooth are constantly changing it), but we do know that it arose during the high-tide of whales during the Miocene and vanished sometime during the Pliocene or later.

    During the Pliocene, a major cooling in the earth's climate occurred which created the modern-day polar ice caps. With much of the waters once warm becoming colder, it led to a chain reaction of mass extinctions. An estimated 36% of Pliocene genera went extinct. This is also when mysticete population saw a huge drop in diversity, with more than 13 different genera disappearing. Because of L. melvillei's dependence and overspecialization on such a huge population of whales, a drop in numbers could essential kill off L. melvillei via starvation, let alone the disappearance of almost half of all mysticetes.

    The Pliocene also gave rise to a new group of hypercarnivores- raptorial dolphins (Orcininaes). Although having been living in the shadows of the huge L. melvillei for millions of years, they have proven to be successful even with a drop in marine diversity. With these intelligent predators proving their success in a short period of time, there is no reason why they would not have pressured even more competition onto L. melvillei. With the latter being so overspecialized for an overpopulated environment, it failed to adapt to a sudden drop in prey unlike the former, who were versatile hunters able to adapt to most changes, and quickly went extinct. Raptorial dolphins, on the other hand, still exist today as the ocean's apex predator and remain unthreatened as a whole species.

 

Phylogeny

    L. melvillei currently does not have a stable place in the phylogenic tree and is still deemed incertae sedis like all other raptorial sperm whales. When the first raptorial physeteroid B. shingensis was known to the public in 1995, it was unlike any cetacean, with a physeteroid-resembling body but with raptorial jaws not seen by any before. Even after the discovery of the other known raptorials during the early 2000s, we still don't have enough knowledge to make an exact placement, although we do have a basic idea of where they would go into. L. melvillei is currently a unique physeteroid, sharing no direct relatives (subfamilies), although its closest relatives are the other raptorial physeteroids Zygophyseter and Brygmophyseter.

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Cladogram by G. Bianucci (University of Pisa). L. melvillei is spelled Leviathan.

 

Reference

-Lambert, O., Bianucci, G., Post, K., Muizon, C. D., Salas-Gismondi, R., Urbina, M., & Reumer, J. (2010). The giant bite of a new raptorial sperm whale from the Miocene epoch of Peru. Nature, 466(7310), 1134-1134. doi:10.1038/nature09381

-Fang, J. (2010, June 30). Call me Leviathan melvillei. Retrieved from https://www.nature.com/news/2010/100630/full/news.2010.322.html

-Lambert, Olivier; Bianucci, Giovanni; De Muizon, Christian (2016-09-01). Macroraptorial sperm whales (Cetacea, Odontoceti, Physeteroidea) from the Miocene of Peru. Zoological Journal of the Linnean Society: n/a–n/a. ISSN 1096-3642. doi:10.1111/zoj.12456.

 

 

Purple text uses unofficial but possibly credible sources. These can range from accurate calculations by random people online to paleoartist's opinions on morphology. They may or may not be accurate, so you must see for yourself.

Red text uses speculation. Do not take any red text seriously unless you believe it may be credible.



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Macrophyseter

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That was my first attempt at making a Paleo-Profile, hope you enjoyed. Because I wasn't able to organize my facts well while making this, there may be inaccuracies and spoofs. Please let me know if you see any of them. I have not cited any purple text sources in the references, so I may post them if you want.

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