Mastodon 2008-06-29 001

A mastodon, from Ancient Greek μαστός (''mastós''), meaning "breast", and ὀδούς (''odoús'') "tooth", is a member of the genus ''Mammut'' (German for 'mammoth'), which was endemic to North America and lived from the late Miocene to the early Holocene. Mastodons belong to the order Proboscidea, the same order as elephants and mammoths (which belong to the family Elephantidae). ''Mammut'' is the type genus of the extinct family Mammutidae, which diverged from the ancestors of modern elephants at least 27–25 million years ago, during the Oligocene.

Like other members of Mammutidae, the molar teeth of mastodons have zygodont morphology (where parallel pairs of cusps are merged into sharp ridges), which strongly differ from those of elephantids. In comparison to its likely ancestor ''Zygolophodon'', ''Mammut'' is characterized by particularly long and upward curving upper tusks, reduced or absent tusks on the lower jaw, as well as the shortening of the mandibular symphysis (the frontmost part of the lower jaw), the latter two traits also having evolved in parallel separately in elephantids. Mastodons had an overall stockier skeletal build, a lower-domed skull, and a longer tail compared to elephantids. Fully grown male ''M. americanum'' are thought to have been have been to at shoulder height and from to in body mass on average. The size estimates suggest that American mastodon males were on average heavier than any living elephant species; they were typically larger than Asian elephants and African forest elephants of both sexes but shorter than male African bush elephants.

''M. americanum'', known as an "American mastodon" or simply "mastodon," had a long and complex paleontological history spanning all the way back to 1705 when the first fossils were uncovered from Claverack, New York, in the American colonies. Because of the uniquely shaped molars with no modern analogues in terms of large animals, the species caught wide attention of European researchers and influential Americans before and after the American Revolution to the point of, according to American historians Paul Semonin and Keith Stewart Thomson, bolstering American nationalism and contributing to a greater understanding of extinctions. Taxonomically, it was first recognized as a distinct species by Robert Kerr in 1792 then classified to its own genus ''Mammut'' by Johann Friedrich Blumenbach in 1799, thus making it amongst the first fossil mammal genera to be erected with undisputed taxonomic authority. The genus served as a wastebasket taxon for proboscidean species with superficially similar molar teeth morphologies but today includes 7 definite species, 1 of questionable affinities, and 4 other species from Eurasia that are pending reassessments to other genera.

Mastodons are considered to have had a predominantly browsing-based diet on leaves, fruits, and woody parts of plants. This allowed mastodons to niche partition with other members of Proboscidea in North America, like gomphotheres and the Columbian mammoth, who had shifted to mixed feeding or grazing by the late Neogene-Quaternary. It is thought that mastodon behaviors were not much different from elephants and mammoths, with females and juveniles living in herds and adult males living largely solitary lives plus entering phases of aggression similar to the musth exhibited by modern elephants. ''Mammut'' achieved maximum species diversity in the Pliocene.

Mastodons for at least a few thousand years prior to their extinction coexisted with Paleoindians, who were the first humans to have inhabited North America. Evidence has been found that Paleoindians (including those of the Clovis culture) hunted mastodons based on the finding of mastodon remains with cut marks and/or with lithic artifacts.

Mastodons disappeared along with many other North American animals, including most of its largest animals (megafauna), as part of the end-Pleistocene extinction event around the end of the Late Pleistocene-early Holocene, the causes typically being attributed to human hunting, severe climatic phases like the Younger Dryas, or some combination of the two. The American mastodon had its last recorded occurrence in the earliest Holocene around 11,000 years ago, which is considerably later than other North American megafauna species. Today, the American mastodon is one of the most well-known fossil species in both academic research and public perception, the result of its inclusion in American popular culture.

Taxonomy

Research history

Earliest finds

In a letter dating to 1713, Edward Hyde, 3rd Earl of Clarendon (known also as Lord Cornbury) from New York reported to the Royal Society learned society of Great Britain that in 1705, a large-sized tooth was found near the side of the Hudson River by a Dutch country-fellow and was sold to New York General Assembly member Van Bruggen for a gill of rum, and Bruggen eventually gave it to Cornbury. He then stated that he sent Johannis Abeel, a recorder of Albany, New York to dig near the original site of the tooth to find more bones.

Abeel reported later that he went to the town of Claverack, New York where the original bones were found. American historian Paul Semonin said that the accounts written by Cornbury and Abeel match up with that written by in the July 30, 1705 entry in ''The Boston News-Letter''. The account reported skeletal evidence of an antediluvian (or biblical) "giant" uncovered from Claverack. The femur and one of the teeth both dissolved before they could be further observed, however.

Big Bone Lick

In 1739, a French military expedition under the command of Charles III Le Moyne (known also as "Longueil") explored the locality of "Big Bone Lick" (located in what is now the US state of Kentucky) and gathered fossil bones and teeth there. The French naturalist Louis Jean-Marie Daubenton examined the fossil collection brought by Longueuil and compared it with specimens of extant elephants and Siberian mammoths in 1762. Daubenton said that the bones were discovered by Native Americans (probably Abenaki hunter-warriors). He came to the conclusion that the femur and tusk belonged to an elephant while the molars (or cheek teeth) came from a separate giant hippopotamus.

In Shawnee tradition, the proboscideans roamed in herds and were hunted by giants, who both eventually died out. The accounts told by the Shawnee individuals in 1762 are the oldest known documented interpretations of the "Ohio" fossils, although the traditions may have had been told for generations.

In 1767, Peter Collinson credited Irish trader George Croghan for having sent him and Benjamin Franklin fossil evidence of the mysterious proboscideans, using them for his studies. He concluded that the peculiar grinders (the molars) were built for herbivorous diets of branches of trees and shrubs as well as other vegetation, a view later followed by Franklin.

In 1768, Scottish anatomist William Hunter recorded that he and his brother John Hunter observed that the teeth were not like those of modern elephants. He determined that the "grinders" from Ohio were of a carnivorous animal but believed that the tusks belonged to the same animal. After examining fossils from Franklin and Lord Shelburne, Hunter was convinced that the "''pseudo-elephant''", or "''animal incognitum''" (shortened as "''incognitum''"), was an animal species separate from elephants that might have also been the same as the proboscideans found in Siberia. He concluded his article with the opinion that although regrettable to philosophers, humanity should be thankful to heaven that the animal, if truly carnivorous, was extinct.

Early American observations

In 1785, Reverend Robert Annan wrote an account recalling an event in which workers discovered bones in his farm near the Hudson River in New York in fall of 1780. The workers found four molars in addition to another that was broken and thrown away. They also uncovered bones, including vertebrae that broke shortly thereafter. Annan expressed his confusion at what the animal could be but speculated based on its "grinders" that it was carnivorous in diet. He speculated also that it was probably extinct due to some catastrophe within the globe.

American statesman Thomas Jefferson stated his thoughts on ''Notes on the State of Virginia'' (published by 1785) that the fossil proboscideans may have been carnivorous, still exist in the northern parts of North America, and are related to mammoths whose remains were found in Siberia. Jefferson referenced the theory of American social degeneracy by Georges-Louis Leclerc, Comte de Buffon, countering it by using extant and extinct animal measurements, including those of "mammoths," as proof that North America faunas were not "degenerative" in size. Semonin pointed out that social degeneracy was an offensive concept to Anglo-American naturalists and that the American proboscidean fossils were used as political tools to inspire American nationalism and counter against the theory of American degeneracy.

In 1799, laborers recovered a thighbone while digging a marl pit at John Masten's farm in Newburgh, New York, and subsequent excavations were observed by a crowd of over a hundred people. American painter and exhibitionist Charles Willson Peale visited the locality in 1801, where he first sketched the fossils then purchased excavation privileges and full ownership of the fossils from Masten and borrowed a loan from the American Philosophical Society (APS) in Philadelphia, Pennsylvania. In addition to the first skeleton, the second was excavated using a mill-like device to drain a deep marl pit. Peale assembled a complete skeleton in his Philadelphia Museum in 1804, and its exhibit was open first to invited members of the American Philosophical Society on December 24 then to the general public on December 25 for an exhibit admission fee in addition to the general admission fee.

The special exhibition attracted thousands of visitors, and the skeleton became a US national symbol. Charles Peale's son Rembrandt Peale took the skeleton to Europe used to promote the fossil proboscidean and have it used as support for Jefferson's final rebuttals against Buffon's arguments for supposed inferiority of American faunas. Author Keith Stewart Thomson argued that the promotion of the "mastodon" skeleton made it a symbol of the strength of American nationalism and that "mammoth" as a term became associated with gigantism. Decades later, the museum bankrupted, and the first skeleton's specimens were sold to some German spectators in around 1848, who eventually sold it to Hessisches Landesmuseum Darmstadt in Germany where it is now displayed. The second skeleton's specimens landed eventually at the American Museum of Natural History.

Other skeletons of ''Mammut americanum'' were excavated within the United States in the first half of the 19th century. One of them was collected by American showman Albert C. Koch in what is today the Mastodon State Historic Site at Missouri in 1839. He hypothesized in 1840 that the proboscidean, which he classified as ''Missourium'', was much larger than an elephant, had horizontal tusks plus trunks, and occupied aquatic habitats. He acquired additional fossils from a spring on the Pomme de Terre River to assemble a mounted skeleton of the "''Missouri Leviathan''" and briefly exhibited it at After exhibiting the skeleton throughout Europe, he sold the skeleton to the British Museum of Natural History. Richard Owen then properly reassembled the skeleton, and it today is on display there.

In 1845, another skeleton was excavated from Newburgh by laborers hired by Nathaniel Brewster initially to remove lacustrine deposits to fertilize the neighboring fields. They were observed by a large number of spectators and uncovered relatively complete fossil evidence of ''M. americanum''. The skeleton was exhibited in New York City and other New England towns then was acquired by John Collins Warren for study. After Warren's death in 1856, the skeleton was sent to Warren's family but was traded to Harvard Medical School for John Warren's skeleton. The "Warren mastodon", under the request of American paleontologist Henry Fairfield Osborn, was purchased by the American financier J. P. Morgan for $30,000 in 1906 and donated to the American Museum of Natural History where it is exhibited today.

Early taxonomic history

In the 1790s, the "''American incognitum''" was subject to research by multiple taxonomists. Scottish writer Robert Kerr erected the species name ''Elephas americanus'' in 1792 based on fossil tusks and "grinders" from the Big Bone Lick locality. He stated that the tusks were similar to elephants while the molars were completely different because they were covered with enamel and had a double row of high conical cusp processes. Kerr was unsure about the taxonomic affinities of the molars and referenced that Thomas Pennant supposed that they belong to an unknown species within the genus ''Elephas'', giving the common name "American elephant".

German naturalist Johann Friedrich Blumenbach also followed up with more taxonomic descriptions of fossil proboscideans in 1799. The first fossil species, recovered from Germany, was described as belonging to the newly erected species ''Elephas primigenius''? (now known as ''Mammuthus primigenius''). The second was what he considered to be an unknown "colossal land monster of the prehistoric world," considering it to be the "mammoth." He created the genus ''Mammut'' and erected the species ''Mammut ohioticum'' based on fossil bones dug up from Ohio in North America. He said that the species was distinguished from other animals of the prehistoric world based on the unusual shapes of the large molars. The genus name "Mammut" refers to the German translation for "mammoth." The naming of the genus ''Mammut'' in 1799 makes it the second or third genus to be recognized with taxonomic authority given that ''Megalonyx'' had been named the same year.

French naturalist Georges Cuvier also described known fossil proboscidean species back in 1796, although his account was later published in 1799. He considered that the remains uncovered from Siberia were true "mammoths" that had similar dentitions to extant elephants but had some morphological differences. He mentioned the fossil remains that were brought back by Longueil from Ohio back in 1739 and several researchers from previous decades who noted the unusual molars and thought that they belonged to different animals like hippopotamuses. He followed recognition in the previously established species "''Elephas americanus''" and argued that the species was different from elephants and mammoths and cannot be found amongst living animals due to extinction from catastrophism.

The proboscidean species was subject to several other species names given by other taxonomists within the earliest 18th century as well as the genus name ''Harpagmotherium'' by the Russian naturalist Gotthelf Fischer von Waldheim in 1808.

Cuvier's taxonomy

In 1806, Cuvier wrote multiple extended research articles on fossil proboscideans of Eurasia and the Americas. He stated that the bones that Buffon previously described from North America were not of elephants but another animal that he referred to as the "''mastodonte''," or the "''animal of Ohio''." He reinforced the idea that the extinct "mastodon" was an animal close in relationship to elephants that differed by jaws with large tubercles. He suggested that "mammoth" and "carnivorous elephant" be discontinued as names for the species and that it receive a new genus name instead. Cuvier said that for "''mastodonte''," he derived the name's etymology (compound (, "breast") + (, "tooth")) from Ancient Greek to mean "nipple tooth," since he thought that it expressed the characteristic form of the teeth.

In 1817, the French naturalist officially established the genus name ''Mastodon'', reaffirming that it is extinct and has left no living descendants. He established that it had an overall body form similar to elephants but had molars more similar to hippopotamuses and pigs that did not serve to grind meat. The first species he erected within ''Mastodon'' was ''Mastodon giganteum'', giving it the informal name "great mastodon" and writing that that it is designated to the Ohio proboscidean with abundant fossil evidence, equal size but greater proportions to modern elephants, and diamond-shaped points of the molars. The naturalist also created the second species name ''Mastodon angustidens'' and gave it the informal name "narrow-toothed mastodon," diagnosing it as having narrower molars, smaller sizes compared to ''M. giganteum'', and range distributions in Europe and South America. Cuvier also erected several other species of ''Mastodon'' originating from other continents in 1824. Despite Cuvier's genus name being younger than multiple other genus names, ''Mastodon'' became the most commonly used genus name for the 19th century.

Taxonomic problems

"''Mastodon''" was riddled with major taxonomic problems since species now determined as belonging to other proboscidean genera were classified to ''Mastodon'' on the basis of similar dentitions to that of "''Mastodon giganteum''" (= ''Mammut americanum''), effectively making it a wastebasket taxon. Various fossil proboscidean species were classified into ''Mastodon'' in the 19th century before eventually being reclassified into distinct genera. In addition to still-valid species names, several synonymous or dubious species names ultimately belonging to different genera were erected within the Americas as well throughout the 19th century. Also, many species names erected based on ''M. americanum'' remains were erected. As a result, ''M. americanum'' has many synonymous names. The issue of synonymous species names were especially apparent in the first half of the 19th century.

Today, the genera that include species formerly classified into ''Mastodon'' include ''Gomphotherium'' (''G. angustidens'', ''G. pyrenaicum'', ''G. productum'', ''G. libycum'', ''G. subtapiroideum'', ''G. steinheimense''), ''Zygolophodon'' (''Z. turicensis'', ''Z. proavus''), ''Cuvieronius'' (''C. hyodon''), ''Stegodon'' (''S. elephantoides''), ''Stegolophodon'' (''S. latidens'', ''S. cautleyi''), ''Anancus'' (''A. avernensis'', ''A. sivalensis'', ''A. perimensis''), ''Tetralophodon'' (''T. longirostris''), ''Choerolophodon'' (''C. pentelici''), ''Stegomastodon'' (''S. mirificus''), ''Rhynchotherium'' ("''R.''" ''euhypodon''), ''Stenobelodon'' (''S. floridanus''), and ''Notiomastodon'' (''N. platensis'').

In 1830, American naturalist John Davidson Godman created the genus ''Tetracaulodon'' plus its species ''T. Mastodontoideum'' based on what he determined to be differences between it and ''Mastodon'' based on the skull and dentition. Both Richard Harlan and William Cooper pointed out that except for the tusks, all other characteristics of the specimens were consistent with ''M. giganteum''. They therefore argued that there was no reason to assume that the tusks were not just individual variations, a view followed also by George William Featherstonhaugh. Isaac Hays comparatively defended Godman's taxon, which led to a bitter debate regarding the validity of the genus amongst American naturalists.

The validities of both ''Tetracaulodon'' and ''Missourium'' were rejected by Owen in 1842, although he retained the former name informally. By 1869, American paleontologist Joseph Leidy determined that ''Mastodon americanus'' is the senior species synonym and listed ''M. giganteum'' as a junior synonym. He also listed ''Mammut'', ''Harpagmotherium'', ''Mastotherium'', ''Missourium'', and ''Leviathan'' as synonyms of ''Mastodon''. He also noted that ''M. americanum'' as a species was highly variable in morphology.

In 1902, American paleontologist Oliver Perry Hay listed ''Mammut'' as the prioritized genus name given its status as the oldest genus name, making ''Mastodon'', ''Tetracaulodon'', and ''Missourium'' classified as junior synonyms. He also established ''M. americanum'' as the type species. The genus name ''Mastodon'' was subsequently abandoned by many American paleontologists in favor of ''Mammut'' within the early 20th century. In 1942, American paleontologist George Gaylord Simpson said that for his study, he prioritized the historic plus taxonomically correct name ''Mammut'' over ''Mastodon''. He continued prioritizing ''Mammut'' in 1945, stating that people were generally aware of its taxonomic priorities over ''Mastodon'' and that people had refused to use it. He stated that he did not want to either but reluctantly set aside his personal preferences to follow taxonomic rules.

Additional species

In 1921, Osborn created the species name ''Mastodon matthewi'' based on distinct molars from the Snake Creek Formation of western Nebraska, naming it in honor of William Diller Matthew. He also erected another species ''M. merriami'' from the Thousand Creek Formation in Nevada, which was eventually synonymized with ''Zygolophodon proavus''. Osborn in 1926 followed up for ''Mastodon matthewi'' by establishing the genus ''Pliomastodon'' for the species based on cranial differences from "''Miomastodon''" (= ''Zygolophodon'').

In 1930, Matthew erected a second species for ''Pliomastodon'' named ''P. vexillarius'' based on fossil material from the locality of Elephant Hill in California, determining that it differs from ''Mammut'' by differences in the skull and that the etymology of the species name was made in honor of paleontological contributions by the Standard Oil Company of California.

In 1933, Childs Frick named the species ''Mastodon raki'' from the locality of Truth or Consequences, New Mexico based on differences on the heel and M₃ tooth from ''M. americanus'', otherwise having proportions similar to it. In 1936, Chester Stock published the species name ''Pliomastodon nevadanus'' based on fossils from the Thousand Creek Beds of northwestern Nevada. In 1937, John R. Schultz created the species name ''Pliomastodon? cosoensis'', naming it after the Coso Mountains in Inyo County, California where skull fossils were recovered.

In 1963, J. Arnold Shotwell and Donald E. Russell designated another species ''Mammut (Pliomastodon) furlongi'', assigning it to fossils collected from the Juntura Formation of Oregon. The species name was created in honor of Eustace L. Furlong, who made early fossil collections from the western side of the Juntura Basin.

The genus ''Pliomastodon'' was synonymized with ''Mammut'' while ''Miomastodon'' was synonymized with ''Zygolophodon'' by Jeheskel Shoshani and Pascal Tassy in a 1996 appendix, a view that was followed by other authors in later years.

In 2019, Alton C. Dooley Jr. et al. established ''Mammut pacificus'' based on fossils collected from the Diamond Valley Lake in Hemet, California. They also stated that ''M. oregonense'' is a ''nomen dubium'' and that further analysis needs to be done to confirm whether or not ''M. furlongi'' belongs to ''Zygolophodon'' instead.

In 2023, Wighart von Koenigswald et al. reviewed the North American species of ''Zygolophodon'' and ''Mammut''. They synonymized ''P. adamsi'' and ''P. sellardsi'' with ''Mammut matthewi'' and emended ''M. nevadanus'' and ''M. pacificus'' to ''M. nevadanum'' and ''M. pacificum'', respectively. They also said that they were uncertain of the taxonomic status of ''M. furlongi'', specifically whether or not it was a variant of sexual dimorphism of ''Z. proavus''. Some authors have considered ''M. nevadanum'' to be synonymous with ''M. matthewi'' while others had retained validity of the species name.

Several mammutid species outside of North America are classified to ''Mammut'' (or "''Pliomastodon''"), namely ''M. borsoni'', ''M. obliquelophus'', ''M. zhupengensis'', and ''M. lufugense'' (possibly synonymous with ''M. obliquelophus''). Recent research such as that of von Koenigswald et al. in 2023 warned that the genus ''Mammut'' should be carefully used for non-North American species.

Classification and evolution

''Mammut'' is the type genus of the Mammutidae, the sole family of the elephantimorph clade Mammutida (the other elephantimorph clade is Elephantida). The Mammutidae is characterized by molars with zygodont-form crests, which have remained morphologically conservative throughout the evolutionary history of the family. ''Mammut'' is considered to be a derived genus of the family because of strong zygodont development. As a family of the Elephantimorpha clade, it is only distantly related to the Deinotheriidae due to major differences in dentition and emergence of adult teeth. The Mammutidae is identified as a monophyletic clade, meaning that it did not leave any derived descendant groups in its evolutionary history. The monophyly of the Mammutidae makes it differ from the Elephantida, where the Gomphotheriidae is paraphyletic (or ancestral to more derived descendant groups in the cladistic sense) in relation to the derived elephantoid families Stegodontidae and Elephantidae (elephants, mammoths, and relatives).

Although the separation of the Mammutida and Elephantida is strongly supported based on morphological differences, their origins within the late Paleogene remain uncertain. One hypothesis asserts that the Elephantimorpha is monophyletic if the primitive Elephantiformes genus ''Phiomia'' was truly ancestral to both the Elephantida and Mammutida. An alternate hypothesis suggests that the Elephantimorpha is diphyletic because ''Phiomia'' is ancestral to gomphotheres while ''Palaeomastodon'' is ancestral to mammutids. The earliest undisputed mammutid genus ''Losodokodon'' is recorded in Kenya, Africa and firmly establishes the earliest presence of mammutids in the late Oligocene (~27-24 Ma). The Mammutidae, like other Paleogene proboscideans, was therefore an endemic radiation within the continent akin to other endemic mammals like arsinoitheres, hyracoids, and catarrhine primates plus non-endemics such as anthracotheres and hyaenodonts.

In the early Neogene phase of evolution, ''Eozygodon'' made an appearance in the earliest Miocene (~23-20 Ma) of Africa after ''Losodokodon''. ''Eozygodon'' was subsequently succeeded by ''Zygolophodon'' by the early Miocene, and the latter dispersed into Eurasia by around 19-18 million years ago, and into North America by the middle Miocene. The dispersal of mammutids between Africa and Eurasia may have occurred multiple times. The Mammutidae eventually went extinct in Africa prior to the late Miocene.

''Mammut'' as currently defined ''sensu lato'' (in a broad sense) is most likely polyphyletic (comprising several unrelated groups). This is because the inclusion of Eurasian mammutid species into ''Mammut'' implies that they share a common origin with North American ''Mammut'', but this relationship has been doubted. As a result, these Eurasian species may belong to either other existing mammutid genera or entirely new genera. ''"Mammut" borsoni,'' the last Eurasian mammutid, became extinct during the earliest Pleistocene, around 2.5-2 million years ago.

The oldest evidence of mammutids in North America is of a fragmentary molar of ''Zygolophodon'' sp. from Massacre Lake, Nevada, dating to 16.5-16.4 Ma (during the Hemingfordian stage of the North American land mammal ages (NALMA)). The only definitively defined species of ''Zygolophodon'' from North America is ''Z. proavus'', which occurs in the Barstovian and Clarendonian stages. ''M? furlongi'' from the Black Butte in Oregon also dates back to the Clarendonian stage, but the affinities of the species remains unclear. If it truly is a species of ''Mammut'', then its earliest temporal range is recorded at about 10 Ma. The earliest undisputed appearance of ''Mammut'' is of ''M. nevadanum'' from Thousand Creek Beds, dating back to the early Hemphillian, or 8.0-7.1 Ma. Historically, North American paleontologists considered that North American ''Zygolophodon'' evolved into ''Mammut'' in an endemic fashion while European workers generally thought that ''Mammut'' was a Eurasian immigrant that replaced North American ''Zygolophodon'' during the Miocene or Pliocene

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