Mylodon was a species of giant ground sloth dating back into the Pleistocene to the Holocene 10,000 years ago.
Discovery[]
Mylodon was named by Richard Owen on the basis of a nearly complete lower jaw with teeth, which was found by Charles Darwin in a consolidated gravel cliff at Bahía Blanca, during the survey expedition of HMS Beagle. At several sites, preserved hide and dung have been discovered, and are in such a state of conservation that the people who first discovered them believed they belonged to a living animal, instead of to an extinct species. The discovery of fresh-looking samples of skin and dung sparked a small wave of expeditions during the early 20th century to search for a living example of the animal. The samples have since been found to be around 10,000 years old, although they look fresh because of the extreme cold and stable conditions in the caves in which they were found.
Fossils assigned to Mylodon have also been found in the Ñuapua Formation of Bolivia. Well preserved samples of Mylodon remains have been discovered in the Cueva del Milodón site in Patagonia, Chile along the southern flank of Cerro Benítez in the year 1896. Associated with bones of other early Patagonian animals, these remains of Mylodon date from an era earlier than 10,000 BC. The American Museum of Natural History has exhibited a sample of Mylodon dung from Argentina with a note that reads "deposited by Theodore Roosevelt.
Description[]
General[]
Mylodon was a large representative of the Mylodontidae.
Skull and dentition features[]
Especially in the construction of the skull, Mylodon differed significantly from other related forms.
The genus name means "peaceful tooth". Mylodon was thought to be a herbivore similiar to most ground sloths, although additional evidence confirmed the species real diet and reassigned it as an Opportunistic Omnivore.[1]
The animal had little osteoderms that helped it protect against predators. The large claws on Mylodon also helped with this as well as helping it to reach vegetation, defend itself as well as capturing any available prey.
The Mylodon lived in Patagonia South America. Presumed Reasons for its extinction are either prehistoric-human hunting and/or climate change which would have changed the flora and habitat.
Distribution and important fossil finds[]
Taxonomy[]
Mylodon's close relatives include the ground sloths of the genera Glossotherium and Paramylodon.
History of research[]
The taxonomic history of Mylodon is complex. It has involved confusion and equivocation with other mylodont forms such as Glossotherium and Paramylodon over a long period of time. Some of this complexity can be attributed to the first describer of the genus itself, who is Richard Owen (1804-1892). Owen, one of the most important explorers of the Victorian era, was concerned from 1836 with fossil finds brought back by Charles Darwin from his pioneering voyage on the HMS Beagle to South America. The collection also included a mandible from Punta Alta near Bahía Blanca in the south of the Argentina Buenos Aires Province (specimen number NHM 16617). The nearly complete specimen was distinguished by a row of teeth consisting of a total of four molar-like Teeth. In an extensive 1840 paper, Owen referred the mandible to the new genus he had created, Mylodon, and named the species M. darwinii (darwinii is the spelling used by Owen, but in modern times darwini is also often used; according to the Regulations of Zoological Nomenclature, the former version is correct.) He related the genus name to the molar-like teeth (from Greek μυλη (myle) for "molar" and ὀδούς (odoús) for "tooth", thus translating as much as "molar tooth"), with the species epithet darwinii honoring Darwin as finder of the voucher specimen. As a second species besides M. darwinii Owen referred in his paper to M. harlani. This form was based on a mandible and clavicle, both of which came from the Big Bone Lick in Boone County in the U.S. state of Kentucky, and which Richard Harlan had already described in 1831 under the species assignment Megalonyx laqueatus. Owen, however, recognized similarities in the construction of the mandible to his M. darwinii and renamed Harlan's form. Harlan used an essay two years later to comment on Owen's choice of name regarding Mylodon, which he felt was not very descriptive. According to him, the name could be applied to almost any extinct mammalian form because almost all of them had the posterior molars. Moreover, the name would be inappropriate because, starting from the Latin version dens molaris for "molar tooth" and the second part of speech don (from dens for "tooth"), there is a duplication that would translate as "molar tooth-tooth". Regardless, Owen's establishment of the genus Mylodon with two species resulted in the extinct sloth representative being distributed in both South and North America.
Glossotherium, Grypotherium, and Paramylodon[]
Owen, in his 1840 work, established the genus Glossotherium in addition to Mylodon, but without designation of a specific species. The basis here was a posterior skull fragment taken from the riverbed of the Arroyo Sarandi in the Uruguay department of Soriano. In contrast to Mylodon, for which Owen assumed a kinship proximity to the other large ground sloths known at the time, such as Megatherium or Megalonyx, he placed Glossotherium in a series with the anteaters and with the pangolins, respectively, and postulated an insectivorous lifestyle for the animals. Two years later, however, Owen discarded the name Glossotherium again. This occurred in the course of processing a nearly complete skeleton that had been discovered the year before in the flood plains of the Río de la Plata north of Buenos Aires. The largely intact skull was characterized by a short and broad snout and by a dentition consisting of a total of 18 teeth, of which the foremost tooth in each case showed a canine design. Based on the similarities in dental structure with the flat, molar-like teeth, Owen placed the skeleton in the genus Mylodon and introduced the new species M. robustus. The skull fragment that he had originally placed in Glossotherium he now associated with M. darwinii. As a result of this study, three species of the genus Mylodon already existed in the 1840s.
A skull including mandible found at Pergamino in Buenos Aires Province served the Danish zoologist Johannes Theodor Reinhardt (1816-1882) in 1879 as the basis for a comprehensive description. Characteristic of the skull was the narrow snout and a closed nasal arch, which was formed by the firm adhesion of the nasal bone to the middle jaw bone. Furthermore, the dentition consisted of a total of 16 teeth, the upper front canine-like tooth was reduced in each case, in the lower jaw, however, sat four molar-like teeth each. Reinhardt noticed similarities to M. darwinii in the construction of the lower jaw, but in the skull design his find deviated clearly from the broad-nosed M. robustus by the narrow snout. However, according to Reinhardt, there were matches in Owen's Glossotherium skull fragment with corresponding skull sections in M. robustus. Based on the clear parallels between M. darwinii and his narrow-beaked skull finding, Reinhardt propagated the new genus Grypotherium with Grypotherium darwinii as the type species. A different approach was taken by Florentino Ameghino (1854-1911) about ten years later. He confirmed in 1889, the separation of both M. darwinii and M. robustus not only at the species level, but also at the genus level. Deviating from Reinhardt, but agreeing with Owen, he considered the mandible of M. darwinii and the skull fragment of Glossotherium to belong together. Since in this scenario Glossotherium possessed priority over Mylodon (Owen mentioned the former over the latter in 1840) and Grypotherium, Ameghino introduced the species Glossotherium darwinii. In contrast, he left the status of M. robustus untouched. Arthur Smith Woodward (1864-1944), in turn, followed Reinhardt's reasoning. In a paper published in 1900, he presented findings from ground sloths of southern Patagonia and at the same time revised Charles Darwin's collection. In doing so, he equated the mandible of M. darwinii with Reinhardt's Grypotherium and subsequently recovered Grypotherium darwinii. Smith Woodward assigned the skull fragment of Glossotherium to M. robustus by analogy with Reinhardt.
Paleobiology[]
The mylodontids (particularly Mylodon itself) are often considered to be pronounced grazers because of their dental structure with flat chewing surfaces on the molar-like teeth. This is also supported by the high (hypsodont) tooth crowns and the wide mouth with numerous shapes. The ungulates are mostly used as analogous examples, in which shapes with high tooth crowns and broad-lipped mouths are usually grass-eating, such as various cattle, horses or the white rhinoceros. In contrast, those with low tooth crowns and narrow snouts such as the duiker or the black rhinoceros feed largely selective from various leaves and other soft vegetable foods. In contrast to other large mylodontid sloths such as Glossotherium, Paramylodon, or Lestodon, the mouth of Mylodon is relatively narrow. A special feature is the closed nasal arch, which is heavily roughened in its front area and thus offers muscle attachment points for a mobile upper lip. Something similar can be said about individual depressions in the vicinity of the infraorbital foramen, which also functioned as starting points for individual muscle strands in the nose and lip area. Maybe Mylodon was more well-adapted to a mixed-vegetation diet, which was picked up with the help of a movable upper lip. The loss of the front teeth in the upper row of teeth also leads to the assumption that, comparable to cattle, there was a horn-like structure on the middle jawbone that could be used to pluck the food.
The entire anterior cranial structure of Mylodon is relatively solid, combined with a partially ossified nasal septum, it can be assumed that relatively high chewing forces acted when the food was chopped up. In contrast to the sometimes huge representatives of the Megatheriidae, the joint between the lower jaw and the skull of the Mylodonts was relatively low, roughly at the chewing level of the teeth. The resulting decreasing lever arm of the masseter muscle experiences through the structure of the zygomatic arch, mainly of the descending process, a certain compensation, so that there should have been only minor differences to the Megatheria with regard to the biting force. The extended mandibular joint allows a wide freedom of movement when chewing. Against this, however, is the zygomatic arch, which is not closed and therefore could only withstand the opposing forces of the masseter and musculus pterygoideus to a limited extent. It can therefore be assumed that forwards and backwards directed chewing movements dominated in Mylodon. The flat tooth crowns lead to a comparatively small size of the total available chewing surface. In Mylodon, this amounts to a good 1320 mm² corresponding to other mylodonts of the same size. The Indian rhinoceros, which is comparable in terms of its dimensions, has, on the other hand, double to four times the value with 2660 to 5190 mm². The situation is similar with the hippopotamus, the total surface area of which is between 3290 and 5410 mm². The small total occlusal surface of the teeth in Mylodon probably resulted in a rather low processing capacity for the food in the mouth. This can result in either a high rate of fermentation in the gastrointestinal tract and/or a very slow metabolism concluded. The latter is the case with today's sloths. This is due to the long passage time of the food of up to a week through the large, multi-chambered stomach. It can be assumed that this also applies to the extinct sloths. Possibly this made the stomach of the mylodonts a functional equivalent to the complex stomach of the ruminants, whereby a long passage time of the food enabled efficient digestion, in which even more difficult to access nutrients could be provided, for example from foods with a greater fiber content. Such a digestive system could reduce the amount of processed food in the mouth and thus ultimately also the small total sales area with Mylodonhave balanced.
Direct analysis of the food resources used is possible, among many other things, due to the numerous dung residues in the form of coprolites. These are available not only from the Cueva del Milodón in the Chilean part of Patagonia, but also from other caves. The coprolites of Mylodon have a diameter of up to 18 cm. Investigations of the plant residues showed 80 to 95% sweet grasses and 5 to 20% sour grasses. Herbaceous plants, on the other hand, could only be detected in traces. Accordingly, Mylodon led, at least in southwestern Patagonia, a diet consisting almost exclusively of grasses. The food is reflected in the paleohabitat, as pollen analyzes show that the landscape at that time was tundra-like in character and was therefore almost free of trees with only a few low bushes. Occasional evidence of false beeches is interpreted as pollen carried by the wind.
A 2021 study on stable isotope ratios concluded that Mylodon must have been at least sporadically omnivorous.
Gallery[]
