Livyatan

''Livyatan'' is an extinct genus of macroraptorial sperm whale containing one known species: ''L. melvillei''. The genus name was inspired by the biblical sea monster Leviathan, and the species name by Herman Melville, the author of the famous novel ''Moby-Dick'' about a white bull sperm whale. It is mainly known from the Pisco Formation of Peru during the Tortonian stage of the Miocene epoch, about 9.9–8.9 million years ago (mya); however, finds of isolated teeth from other locations such as Chile, Argentina, South Africa, and Australia imply that either it or a close relative survived into the Pliocenes (or "raptorial sperm whales") and was probably an apex predator, preying on whales, seals, and so forth. Characteristically of raptorial sperm whales, ''Livyatan'' had functional, enamel-coated teeth on the upper and lower jaws, as well as several features suitable for hunting large prey.

''Livyatan''s total length has been estimated to be about , similar to that of the modern sperm whale (''Physeter macrocephalus''), making it one of the largest predators known to have existed. The teeth of ''Livyatan'' measured , and are the largest biting teeth of any known animal, excluding tusks. It is distinguished from the other raptorial sperm whales by the basin on the skull, spanning the length of the snout. The spermaceti organ, contained in that basin is thought to have been used in echolocation and communication, or for ramming prey and other sperm whales. The whale may have interacted with the large extinct shark Megalodon (''Otodus megalodon''), competing with it for a similar food source. Its extinction was probably caused by a cooling event at the end of the Miocene period causing a reduction in food populations. The geological formation where the whale has been found has also preserved a large assemblage of marine life, such as sharks and marine mammals.

Taxonomy

Research history

In November 2008, a partially preserved skull, as well as teeth and the lower jaw, belonging to ''L. melvillei'', the holotype specimen MUSM 1676, were discovered in the coastal desert of Peru in the sediments of the Pisco Formation, southwest of the city of Ica. Klaas Post, a researcher for the Natural History Museum Rotterdam in the Netherlands, stumbled across them on the final day of a field trip. The fossils were prepared in Lima, and are now part of the collection of the Museum of Natural History, Lima of National University of San Marcos.

The discoverers originally assigned—in July 2010—the English name of the biblical monster, Leviathan, to the whale as ''Leviathan melvillei''. However, the scientific name ''Leviathan'' was also the junior synonym for the mastodon (''Mammut''), so, in August 2010, the authors rectified this situation by coining a new genus name for the whale, ''Livyatan'', from the original Hebrew name of the monster. The species name ''melvillei'' is a reference to Herman Melville, author of the book ''Moby-Dick'', which features a gigantic sperm whale as the main antagonist. The first ''Livyatan'' fossils from Peru were initially dated to around 13–12 million years ago (mya) in the Serravallian Age of the Miocene, but this was revised to 9.9–8.9 mya in the Tortonian Age of the Miocene.

During the late 2010s, fossils of large isolated sperm whale teeth were reported from various Miocene and Pliocene localities along the Southern Hemisphere. These teeth have been identified to be of similar size and shape with that of the ''L. melvillei'' holotype and may be species of ''Livyatan''. However, it is commonplace that authors do not identify such teeth as a conclusive species of ''Livyatan'', instead opting to assign an open nomenclature in which the biological classifications of the specimens are restricted to comparisons or affinities with ''Livyatan''. This is mostly because isolated teeth tend to not be informative enough to be identified at the species level, meaning that there is some undeterminable possibility that they belong to an undescribed close relative of ''Livyatan'' rather than ''Livyatan'' itself.

In 2016 in Beaumaris Bay, Australia, a large sperm whale tooth measuring , specimen NMV P16205, was discovered in Pliocene strata by a local named Murray Orr, and was nicknamed the "Beaumaris sperm whale" or the "giant sperm whale". The tooth was donated to Museums Victoria at Melbourne. Though it has not been given a species designation, the tooth looks similar to those of ''L. melvillei'', indicating it was a close relative. The tooth is dated to around 5mya, and so is younger than the ''L. melvillei'' holotype by around 4or 5million years.

In 2018, palaeontologists led by David Sebastian Piazza, while revising the collections of the Bariloche Paleontological Museum and the Municipal Paleontological Museum of Lamarque, uncovered two incomplete sperm whale teeth cataloged as MML 882 and BAR-2601 that were recovered from the Saladar Member of the Gran Bajo del Gualicho Formation in the Río Negro Province of Argentina, a deposit that dates between around 20-14 mya. The partial teeth measure and in height respectively. Anatomical analyses of the specimens found that much of their characteristics are identical to ''L. melvillei'' except in width, in which the diameter of both teeth are smaller. Because of this, along with only isolated teeth being available, the palaeontologists chose to assign an open nomenclature, identifying both specimens as ''aff. Livyatan sp.''

In 2019, palaeontologist Romala Govender reported the discovery of two large sperm whale teeth from Pliocene deposits near the Hondeklip Bay village of Namaqualand in South Africa. The pair of teeth, which are stored in the Iziko South African Museum and cataloged as SAM-PQHB-433 and SAM-PQHB-1519, measure and in height respectively, the latter having its crown missing. Both teeth have open pulp cavities, indicating that both whales were young. The teeth are very similar in shape and size to the mandibular teeth of the ''L. melvillei'' holotype, and were identified as ''cf. Livyatan''. Like the Beaumaris specimen, the South African teeth are dated to around 5mya.

Phylogeny

''Livyatan'' was part of a fossil stem group of hyper-predatory sperm whales commonly known as macroraptorial sperm whales, or raptorial sperm whales, alongside the extinct whales ''Brygmophyseter'', ''Acrophyseter'', and ''Zygophyseter''. This group is known for having large, functional teeth in both the upper and lower jaws, which were used in capturing large prey, and had an enamel coating. Conversely, the modern sperm whale (''Physeter macrocephalus'') lacks teeth in the upper jaw, and the ability to use its teeth to catch prey. ''Livyatan'' belongs to a different lineage in respect to the other raptorial sperm whales, and the size increase and the development of the spermaceti organ, an organ that is characteristic of sperm whales, are thought to have evolved independently from other raptorial sperm whales. The large teeth of the raptorial sperm whales either evolved once in the group with a basilosaurid-like common ancestor, or independently in ''Livyatan''. The large temporal fossa in the skull of raptorial sperm whales is thought to a plesiomorphic feature, that is, a trait inherited from a common ancestor. Since the teeth of foetal modern sperm whales (''Physeter macrocephalus'') have enamel on them before being coated with cementum, it is thought that the enamel is also an ancient characteristic ( basal). The appearance of raptorial sperm whales in the fossil record coincides with the diversification of baleen whales in the Miocene, implying that they evolved specifically to exploit baleen whales. It has also been suggested that the raptorial sperm whales should be placed into the subfamily Hoplocetinae, alongside the genera ''Diaphorocetus'', ''Scaldicetus'', and '' Hoplocetus'', which are known from the Miocene to the lower Pliocene

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