|Skeleton of Toxodon in Buenos Aires|
|Genus:||† Toxodon |
Toxodon (meaning "bow tooth" in reference to the curvature of the teeth) is an extinct genus of South American mammals from the Late Miocene to early Holocene epochs (Mayoan to Lujanian in the SALMA classification) (about 11.6 million to 11,000 years ago).It is a member of Notoungulata, one of several now extinct orders of South American native ungulates distinct from living perissodactyls and artiodactyls. It was among the largest and last members of its order, and was probably the most common large hoofed mammal in South America of its time.
Toxodon was one of the last members of Notoungulata, a group of ungulates that had been part of the fauna of South America since the Paleocene. Toxodon was a member of Toxodontidae a large bodied group including similar, vaguely rhinoceros like forms.
Charles Darwin was one of the first to collect Toxodon fossils, after paying 18 pence for a T. platensis skull from a farmer in Uruguay. In The Voyage of the Beagle Darwin wrote, "November 26th – I set out on my return in a direct line for Montevideo. Having heard of some giant's bones at a neighbouring farm-house on the Sarandis, a small stream entering the Rio Negro, I rode there accompanied by my host, and purchased for the value of eighteen pence the head of the Toxodon." Since Darwin discovered that the fossils of similar mammals of South America were different from those in Europe, he invoked many debates about the evolution and natural selection of animals.
In his own words, Darwin wrote down in his journal,
Lastly, the Toxodon, perhaps one of the strangest animals ever discovered: In size it equaled an elephant or megatherium, but the structure of its teeth, as Mr. Owen states, proves indisputably that it was intimately related to the Gnawers, the order which, at the present day, includes most of the smallest quadrupeds: In many details it is allied to the Pachydermata: Judging from the position of its eyes, ears, and nostrils, it was probably aquatic, like the Dugong and Manatee, to which it is also allied. How wonderfully are the different Orders, at the present time so well separated, blended together in different points of the structure of the Toxodon!
Analysis of collagen sequences obtained from Toxodon as well as from Macrauchenia found that South America's native notoungulates and litopterns form a sister group to perissodactyls, making them true ungulates.This finding has been corroborated by an analysis of mitochondrial DNA extracted from a Macrauchenia fossil, which yielded a date of 66 Ma for the time of the split with perissodactyls.
The species Toxodon chapalmalensis is known from the Pliocene (Montehermosan-Chapadmalalan) of Argentina,while Toxodon platensis, the type species, is known from the Pleistocene.
In 2014, a study identifying a new species of toxodontid resolved the phylogenetic relations of the toxodontids, including to Toxodon. The below cladogram was found by the study:
Toxodon was about 2.7 m (8 ft 10 in) in body length, with an estimated weight up to 1,415 kg (3,120 lb) and about 1.5 m (4 ft 11 in) high at the shoulder and resembled a heavy rhinoceros, with a short and vaguely hippopotamus-like head. Because of the position of its nasal openings, it is believed that Toxodon had a well-developed snout.[ citation needed ]Toxodon possessed a large, barrel shaped body. It had short stout legs with plantigrade feet with three functional relatively short toes. The hind limbs are longer and raised higher than the front limbs, giving a sloped appearance to the body. Like horses, it had a stay apparatus allowing the knees to be passively locked while standing.
The vertebrae were equipped with high apophyses, which most likely supported the massive weight and muscles as well as its powerful head.[ citation needed ]Toxodon had broad jaws which were filled with bow shaped teeth and incisors. The molar teeth of Toxodon have no roots and are ever-growing (euhypsodont), like the incisors of rodents and lagomorphs, and often exhibit enamel hypoplasia.
Toxodon is suggested to have been capable of running at considerable speed.
Toxodon is believed to have been ecologically plastic, with its diet varying according to local conditions,with an almost totally C3 browsing diet in the Amazon rainforest, mixed feeding C3 in Bahia and the Pampas to almost completely C4 dominated grazing diet in the Chaco.
Toxodon became extinct at the end of the Late Pleistocene around 12,000 years as part of the Quaternary extinction event, alongside almost all other large animals in South America. Previous mid-Holocene dates are now thought to be in error.Remains from the Arroyo Seco 2 site in the Pampas are associated with butchered megafauna, but it is unclear if the Toxodon itself was actually butchered or the remains were naturally transported to the site.
Toxodon had a wide distribution in South America during the Late Pleistocene, extending from the Pampas into the Amazon rainforest.
Fossils of Toxodon have been found in:
Megatherium is an extinct genus of ground sloths endemic to South America that lived from the Early Pliocene through the end of the Pleistocene. It is best known for the elephant-sized type species M. americanum, sometimes called the giant ground sloth, or the megathere, native to the Pampas through southern Bolivia during the Pleistocene. Various other smaller species belonging to the subgenus Pseudomegatherium are known from the Andes.
Litopterna is an extinct order of South American native ungulates. Like other endemic South American mammals, their relationship to other mammal groups had long been unclear, but recent genetic and proteomic evidence indicates that their closest living relatives are Perissodactyls including horses, rhinoceros, and tapirs, and that litopterns are closely related to notoungulates, another widespread group of South American ungulates.
Notoungulata is an extinct order of mammalian ungulates that inhabited South America from the early Paleocene to the Holocene, living from approximately 61 million to 11,000 years ago. Notoungulates were morphologically diverse, with forms resembling animals as disparate as rabbits and rhinoceroses. Notoungulata are the largest group of South American native ungulates, with over 150 genera in 14 families having been described, divided into two major subgroupings, Typotheria and Toxodontia. Notoungulates first diversified during the Eocene. Their diversity declined during the Late Neogene, with only the large toxodontids persisting until the end of the Pleistocene, perishing as part of the Quaternary extinction event among with most other large mammals in the Americas. Collagen analysis suggests that notoungulates are closely related to litopterns, another group of South American ungulates, and their closest living relatives being perissodactyls, including rhinoceroses, tapirs and equines. However their relationships to other South American ungulates are uncertain. Several groups of notoungulates separately evolved ever-growing cheek teeth.
South American native ungulates, commonly abbreviated as SANUs, are extinct ungulate-like mammals of controversial affinities that were indigenous to South America prior to the Great American Biotic Interchange. They comprise five major groups conventionally ranked as orders—Astrapotheria, Litopterna, Notoungulata, Pyrotheria, and Xenungulata—as well as the primitive "condylarth" groups Didolodontidae and Kollpaniinae. It has been proposed that some or all of the members of this group form a clade, named Meridiungulata, though the relationships of South American ungulates remain largely unresolved. The two largest groups of South American ungulates, the notoungulates and the litopterns, were the only groups to persist beyond the mid Miocene. Only a few of the largest species of notoungulates and litopterns survived until the end-Pleistocene extinctions.
Macrauchenia was a large, long-necked and long-limbed, three-toed native South American ungulate in the order Litopterna. The genus gives its name to its family, the Macraucheniidae or "robust litopterns". Like other litopterns, it is most closely related to the odd-toed ungulates (Perissodactyla), from which litopterns diverged approximately 66 million years ago. The oldest fossils in the genus date to the late Miocene, around seven million years ago, and M. patachonica disappears from the fossil record during the late Pleistocene, around 20,000-10,000 years ago. M. patachonica is one of the last and best known member of the family and is known primarily from the Luján Formation in Argentina, but is known from localities across southern South America. Another genus of macraucheniid Xenorhinotherium was present in northeast Brazil and Venezuela during the Late Pleistocene. The type specimen was discovered by Charles Darwin during the voyage of the Beagle. In life, Macrauchenia may have resembled a humpless camel, though the two taxa are not closely related. It fed on plants in a variety of environments across what is now South America. Among the species described, M. patachonica and M. ullomensis are considered valid; M. boliviensis is considered a nomen dubium; and M. antiqua has been moved to the genus Promacrauchenia.
Macraucheniidae is a family in the extinct South American ungulate order Litopterna, that resembled various camelids. The reduced nasal bones of their skulls was originally suggested to have housed a small proboscis, similar to that of the saiga antelope. However, one study suggested that they were openings for large moose-like nostrils. Conversely, prehistoric pictographs by indigenous people seems to depict animals interpreted as macraucheniids with trunks. Their hooves were similar to those of rhinoceroses today, with a simple ankle joint and three digits on each foot. Thus, they may have been capable of rapid directional change when running away from predators, such as large phorusrhacid terror birds, sparassodont metatherians, giant short-faced bears (Arctotherium) and saber-toothed cats (Smilodon). Macraucheniids probably lived in large herds to gain protection against these predators, as well as to facilitate finding mates for reproduction.
Doedicurus is an extinct genus of glyptodont from South America containing one species, D. clavicaudatus. Glyptodonts are a member of the family Chlamyphoridae, which also includes some modern armadillo species, and they are classified in the superorder Xenarthra alongside sloths and anteaters. Being a glyptodont, it was a rotund animal with heavy armor and a carapace. Averaging at an approximate 1,400 kg (3,100 lb), it was one of the largest glyptodonts to have ever lived. Though glyptodonts were quadrupeds, large ones like Doedicurus may have been able to stand on two legs like other xenarthrans. It notably sported a spiked tail club, which may have weighed 40 or 65 kg in life, and it may have swung this in defense against predators or in fights with other Doedicurus at speeds of perhaps 11 m/s.
Xenorhinotherium is an extinct genus of macraucheniine macraucheniids, closely related to Macrauchenia of Patagonia. The type species is X. bahiense.
Scalabrinitherium is an extinct genus of mammals of the family Macraucheniidae. Fossils of this animal were found among the fossils of prehistoric xenarthrans in the Ituzaingó Formation of Argentina.
Astrapotheria is an extinct order of South American and Antarctic hoofed mammals that existed from the late Paleocene to the Middle Miocene,. Astrapotheres were large, rhinoceros-like animals and have been called one of the most bizarre orders of mammals with an enigmatic evolutionary history.
Toxodontidae is an extinct family of notoungulate mammals, known from the Oligocene to the Holocene of South America, with one genus, Mixotoxodon, also known from the Pleistocene of Central America and southern North America. Member of the family were medium to large-sized, and had medium to high-crowned dentition, which in derived members of the group evolved into ever-growing cheek teeth. Isotopic analyses have led to the conclusion that Pleistocene members of the family were flexible mixed feeders.
Mesotheriidae is an extinct family of notoungulate mammals known from the Oligocene through the Pleistocene of South America. Mesotheriids were small to medium-sized herbivorous mammals adapted for digging.
Mixotoxodon is an extinct genus of notoungulate of the family Toxodontidae inhabiting South America, Central America and parts of southern North America during the Pleistocene epoch, from 1,800,000—12,000 years ago.
Nesodon is a genus of Miocene mammal belonging to the extinct order Notoungulata which inhabited southern South America during the Late Oligocene to Miocene living from 29.0 to 16.3 Ma and existed for approximately. It had a relatively large size, weighing up to 554 kg (1221 lbs) and reaching 1.5 m in height.
Glyptodon is a genus of glyptodontine in the family Chlamyphoridae that lived from the Pliocene, around 3.2 million years ago, to the early Holocene, around 11,000 years ago, in Brazil, Uruguay, Paraguay, Bolivia, Peru, Argentina, and Colombia. It is one of, if not the, best known genus of glyptodont. Glyptodon has a long and storied past, being the first named extinct cingulate and the type genus of the subfamily Glyptodontinae. Fossils of Glyptodon have been recorded as early as 1814 from Pleistocene aged deposits from Uruguay, though many were incorrectly referred to the ground sloth Megatherium by early paleontologists.
Eutatus is an extinct genus of large armadillos of the family Chlamyphoridae. It was endemic to South America from the Early Miocene to Late Pleistocene, living from 17.5 Ma-11,000 years ago, with possible survival into the early Holocene and existing for approximately. Based on carbon isotope ratios, it is thought to have been an herbivore that fed on grasses.
Dusicyon avus is an extinct species of cerdocyonine canid in the genus Dusicyon, native to South America during the Pleistocene and Holocene epochs. It was medium to large, about the size of a German shepherd. It was closely related to the Falkland Islands wolf (Dusicyon australis), which descended from a population of D. avus. It appears to have survived until very recently, perhaps 400 years ago.
Piauhytherium is an extinct genus of herbivorous notoungulate mammal of the family Toxodontidae. It lived during the Late Pleistocene; fossils have been found in Brazil. The only known species is Piauhytherium capivarae.
This paleomammalogy list records new fossil mammal taxa that were described during the year 2019, as well as notes other significant paleomammalogy discoveries and events which occurred during that year.
Neolicaphrium is an extinct genus of ungulate mammal belonging to the extinct order Litopterna. This animal lived from the Late Pliocene (Chapadmalalan) to the Late Pleistocene (Lujanian) in southern South America, being the last survivor of the family Proterotheriidae.
Read, 19th April 1837. A detailed account will appear in the first part of the zoology of Voyage of the Beagle .