Notoungulata

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Notoungulata
Temporal range: early Paleocene (Danian)-Late Pleistocene
~61–0.012  Ma
Toxodon skeleton.jpg
Skeleton of Toxodon (Toxodontidae)
Propachyrucos ameghinorum AMNH.jpg
Skeleton of Prosotherium (Hegetotheriidae)
Scientific classification OOjs UI icon edit-ltr.svg
Domain: Eukaryota
Kingdom: Animalia
Phylum: Chordata
Class: Mammalia
Clade: Panperissodactyla
Order: Notoungulata
Roth 1903
Suborders and families

See text

Notoungulata is an extinct order of ungulates that inhabited South America from the early Paleocene to the end of the Pleistocene, living from approximately 61 million to 11,000 years ago. [1] 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 from the late Neogene onwards, with only the large toxodontids persisting until the end of the Pleistocene (with Mixotoxodon expanding into Central America and southern North America), perishing as part of the Late Pleistocene megafauna extinctions along with most other large mammals across the Americas. Collagen sequence analysis suggests that notoungulates are closely related to litopterns, another group of South American ungulates, and their closest living relatives being perissodactyls (odd-toed ungulates), including rhinoceroses, tapirs and equines as part of the clade Panperissodactyla. However their relationships to other South American ungulates are uncertain. Several groups of notoungulates separately evolved ever-growing cheek teeth.

Contents

Taxonomy

Notoungulata is divided into two major suborders, Typotheria and Toxodontia, alongside some basal groups (Notostylopidae and Henricosborniidae) which are potentially paraphyletic. [2] Notoungulates make up over half the described diversity of indigenous South American ungulates, [2] with over 150 genera in 14 different families. [3]

This order is proposed to be united with other South American native ungulates in the super-order Meridiungulata. The notoungulate and litoptern native ungulates of South America have been shown by studies of collagen and mitochondrial DNA sequences to be a sister group to the perissodactyls, making them true ungulates. [4] [5] [6] The estimated divergence date is 66 million years ago. [6] This conflicts with the results of some morphological analyses which posited them as afrotherians. It is in line with some more recent morphological analyses which suggested they were basal euungulates. Panperissodactyla has been proposed as the name of an unranked clade to include perissodactyls and their extinct South American ungulate relatives. [4]

Cifelli has argued that Notioprogonia is paraphyletic, as it would include the ancestors of the remaining suborders. Similarly, Cifelli indicated that Typotheria would be paraphyletic if it excluded Hegetotheria and he advocated inclusion of Archaeohyracidae and Hegetotheriidae in Typotheria. [7]

Notoungulata were for many years taken to include the order Arctostylopida, whose fossils are found mainly in China. Recent studies, however, have concluded that Arctostylopida are more properly classified as gliriforms, and that the notoungulates were therefore never found outside South and Central America. [8]

Based on an analysis of 133 morphological characters in 50 notoungulate genera, Billet in 2011 concluded that Homalodotheriidae, Leontiniidae, Toxodontidae, Interatheriidae, Mesotheriidae, and Hegetotheriidae are the only monophyletic families of notoungulates. Some studies have suggested that Pyrotheria, often ranked as an independent order, should also be included within Notoungulata. [9]

Phylogeny

Notoungulata

Classification

Ecology

Notoungulates varied widely in body size, with early diverging notoungulates like Simpsonotus, and some hegetotheriid and interatheriid typotherians having a body mass of approximately 1–2 kilograms (2.2–4.4 lb), while the toxodontid Toxodon is suggested to have had a body mass exceeding 1,000 kilograms (2,200 lb). Typotheres generally occupied small-medium body size niches, while toxodontians were generally medium-large sized animals. [2] The families Interatheriidae, Hegetotheriidae, Mesotheriidae and Toxodontidae separately evolved high crowned (hypsodont) ever-growing cheek teeth, [10] with high crowned species constituting the majority of notoungulates from the Late Oligocene onward. [2] This adaptation was historically suggested to be the result of a diet increasingly incorporating grass, but this has been questioned, and other authors suggesting that it may have been due to the increasing intake of abrasive particles from volcanic sources. [2] [10] Many typotheres have bodyforms convergent on rodents, hyraxes and rabbits, [11] with some rabbit-like hegetotheriids suggested to have developed a rabbit-like bounding locomotion. [12] The basal notungulate Notostylops and the mesotheriids are suggested to have engaged in digging, with mesotheriids suggested to have had an ecology similar to wombats. [2] Toxodontids have sometimes been compared to rhinoceroses and hippopotamuses in overall bodyform and tooth morphology. [11] The Miocene toxodontian Homalodotherium had claws on its forelimbs and is thought to have had an ecology similar to the extinct chalicotheres, rearing on its hindlegs to feed. [2] Like perissodactyls, notoungulates were likely primitively hindgut fermenters, [13] but it has also been proposed that some of them may have had fermentation more similar to ruminants based on their skeletal anatomy, though this is uncertain. [11]

Evolutionary history

The oldest notoungulates appeared during the Paleocene, [1] probably originating from "condylarth" ancestors that had migrated from North America. Notoungulates and other South American native ungulates reached their apex of diversity during the Eocene and Oligocene. Notoungulate species diversity was stable during the Miocene, though 45% of the family diversity of the group became extinct during the interval, including Homalodotheriidae, Leontiniidae, and Interatheriidae. The diversity of the group declined during the Pliocene and Pleistocene, which is coeval in time with the Great American Interchange, which allowed ungulates and other mammals from North America to enter South America. This decline has historically been attributed to competition with the new North American arrivals, though earlier views had probably overstated the importance of this, [2] with climatic change also likely being an important factor. [14] As part of the Great American interchange, the toxodontid Mixotoxodon migrated into Central and North America, with its furthest northern record being in Texas. [15] The last hegetotheriids are known from the Early Pleistocene (with a supposed Middle Pleistocene record being considered questionable). [14] The youngest known member of Typotheria, the mesotheriid Mesotherium , has its last records in the late Middle Pleistocene, around 220,000 years ago. [16] The last notoungulates, the toxodontids Toxodon, Mixotoxodon and Piauhytherium became extinct at the end of the Late Pleistocene around 12,000 years ago as part of the Late Pleistocene megafauna extinctions, along with most other large mammals in the Americas. The extinction coincides with the arrival of the first humans to the Americas and they are suggested to have been a causal factor in the extinction. [2]

Related Research Articles

<i>Toxodon</i> Extinct genus of notoungulates

Toxodon is an extinct genus of large ungulate native to South America from the Late Miocene to early Holocene epochs. Toxodon is a member of Notoungulata, an order of extinct South American native ungulates distinct from the two living ungulate orders that had been indigenous to the continent for over 60 million years since the early Cenozoic, prior to the arrival of living ungulates into South America around 2.5 million years ago during the Great American Interchange. Toxodon is a member of the family Toxodontidae, which includes medium to large sized herbivores. Toxodon was one of the largest members of Toxodontidae and Notoungulata, with Toxodon platensis having an estimated body mass of 1,000–1,200 kilograms (2,200–2,600 lb).

<span class="mw-page-title-main">Toxodontia</span> Extinct suborder of mammals

Toxodontia is a suborder of the meridiungulate order Notoungulata. Most of the members of the five included families, including the largest notoungulates, share several dental, auditory and tarsal specializations. The group is named after Toxodon, the first example of the group to be discovered by science.

<span class="mw-page-title-main">South American native ungulates</span> Extinct clade of mammals

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 extinction event around 12,000 years ago where they became extinct with most other large mammals in the Americas, shortly after the first arrival of humans into the region.

<span class="mw-page-title-main">Leontiniidae</span> Extinct family of mammals

Leontiniidae is an extinct family comprising eighteen genera of notoungulate mammals known from the Middle Eocene (Mustersan) to Late Miocene (Huayquerian) of South America.

<span class="mw-page-title-main">Toxodontidae</span> Extinct family of notoungulate mammals

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, ranging from around 350–400 kilograms (770–880 lb) in Nesodon to 1,000–1,200 kilograms (2,200–2,600 lb) in Toxodon, 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.

<span class="mw-page-title-main">Mesotheriidae</span> Extinct family of mammals

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.

<i>Mixotoxodon</i> Extinct genus of mammals

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.

<span class="mw-page-title-main">Typotheria</span> Extinct suborder of mammals

Typotheria is a suborder of the extinct mammalian order Notoungulata and includes five families: Archaeopithecidae, Campanorcidae, Interatheriidae, Mesotheriidae, and Oldfieldthomasiidae. Cifelli indicated that Typotheria would be paraphyletic if it excluded members of the suborder Hegetotheria and he advocated inclusion of the hegetothere families Archaeohyracidae and Hegetotheriidae in Typotheria.

<i>Mesotherium</i> Extinct genus of notoungulates

Mesotherium is an extinct genus of mesotheriid, a long-lasting family of superficially rodent-like, burrowing notoungulates from South America. It one of the youngest notoungulates, and the last known member of Typotheria. It was first named by Étienne Serres in 1867, and only contains a single species, Mesotherium cristatum, spanning the Early-Middle Pleistocene.

<i>Huilatherium</i> Extinct genus of mammals

Huilatherium is an extinct genus of leontiniid, a group of hoofed mammals belonging to the order Notoungulata, that comprises other South American ungulate families that evolved in parallel with some mammals of the Northern hemisphere. The leontiinids were a family of herbivorous species comprising medium to large browsers, with relatively short skulls and robust limbs, somewhat similar to their relatives, the best known toxodontids.

<i>Piauhytherium</i> Extinct genus of mammals

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.

Fiandraia is an extinct monotypic genus of notoungulate that lived in Uruguay during the Oligocene and the Early Miocene. It was found in the Fray Bentos Formation, in rocks dated back from the Deseadan period.

Eohyrax is an extinct genus of Notoungulate, belonging to the suborder Typotheria. It lived during the Middle Eocene, and its remains were discovered in South America.

<i>Pseudotypotherium</i> Extinct genus of notoungulates

Pseudotypotherium is an extinct genus of Notoungulates, belonging to the suborder Typotheria. It lived from the Late Miocene to the Late Pliocene, and its fossilized remains were discovered in South America.

<i>Plesiotypotherium</i> Extinct genus of notoungulates

Plesiotypotherium is an extinct genus of Notoungulate, belonging to the suborder Typotheria. It lived from the Middle to the Late Miocene, and its fossilized remains were discovered in South America.

Colbertia is an extinct genus of oldfieldthomasiid notoungulate. It lived from the Early to the Middle Eocene, and its fossilized remains were discovered in Argentina and Brazil.

Oldfieldthomasia is an extinct genus of Notoungulate, probably related to the suborder Typotheria. It lived during the Middle Eocene, in what is today South America.

Ultrapithecus is an extinct genus of oldfieldthomasiid notoungulate that lived during the Middle Eocene of what is now Argentina.

<i>Notopithecus</i> Extinct genus of notoungulates

Notopithecus is an extinct genus of Notoungulate, belonging to the suborder Typotheria. It lived from the Middle to the Late Eocene and its fossilized remains were discovered in South America.

Rosendo is an extinct genus of notohippid notoungulates that lived during the Early Oligocene in what is now Argentina and Chile. Fossils of this genus have been found in the Sarmiento Formation and the Abanico Formations of Argentina and Chile.

References

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Bibliography

Further reading