Perissodactyla
This article needs additional citations for verification. (October 2021) |
Perissodactyla | |
---|---|
Clockwise from left: plains zebra (Equus quagga), Indian rhinoceros (Rhinoceros unicornis) and Brazilian tapir (Tapirus terrestris) | |
Scientific classification | |
Domain: | Eukaryota |
Kingdom: | Animalia |
Phylum: | Chordata |
Class: | Mammalia |
Clade: | Perissodactylamorpha
|
Order: | Perissodactyla Owen, 1848 |
Families | |
|
Perissodactyla (, do.
The order was considerably more diverse in the past, with notable extinct groups include the
Despite their very different appearances, they were recognized as related families in the 19th century by the zoologist Richard Owen, who also coined the order's name.
Anatomy
The largest odd-toed ungulates are rhinoceroses, and the extinct Paraceratherium, a hornless rhino from the Oligocene, is considered one of the largest land mammals of all time.[4] At the other extreme, an early member of the order, the prehistoric horse Eohippus, had a withers height of only 30 to 60 cm (12 to 24 in).[5] Apart from dwarf varieties of the domestic horse and donkey, living perissodactyls reach a body length of 180–420 cm (71–165 in) and a weight of 150 to 4,500 kg (330 to 9,920 lb).[6] While rhinos have only sparse hair and exhibit a thick epidermis, tapirs and horses have dense, short coats. Most species are grey or brown, although zebras and young tapirs are striped.
Limbs
The main axes of both the front and rear feet pass through the third toe, which is always the largest. The remaining toes have been reduced in size to varying degrees. Tapirs, which are adapted to walking on soft ground, have four toes on their fore feet and three on their hind feet. Living rhinos have three toes on both the front and hind feet. Modern equines possess only a single toe; however, their feet are equipped with hooves, which almost completely cover the toe. Rhinos and tapirs, by contrast, have hooves covering only the leading edge of the toes, with the bottom being soft.
Ungulates have stances that require them to stand on the tips of their toes. Equine ungulates with only one digit or hoof have decreased mobility in their limbs, which allows for faster running speeds and agility. Differences in limb structure and physiology between ungulates and other mammals can be seen in the shape of the humerus. For example, often shorter, thicker, bones belong to the largest and heaviest ungulates like the rhinoceros.[7]
The
Skull and teeth
Odd-toed ungulates have a long upper jaw with an extended diastema between the front and cheek teeth, giving them an elongated head. The various forms of snout between families are due to differences in the form of the premaxilla. The lacrimal bone has projecting cusps in the eye sockets and a wide contact with the nasal bone. The temporomandibular joint is high and the mandible is enlarged.
Rhinos have one or two horns made of
The number and form of the teeth vary according to diet. The incisors and canines can be very small or completely absent, as in the two African species of rhinoceros. In horses, usually only the males possess canines. The surface shape and height of the molars is heavily dependent on whether soft leaves or hard grass make up the main component of their diets. Three or four cheek teeth are present on each jaw half, so the dental formula of odd-toed ungulates is: 0-3 . 0-1 . 2-4 . 31-3 . 1 . 2-4 . 3 × 2 = 30-44
The Guttural Pouch, a small outpocketing of the auditory tube that drains the middle ear, is a characteristic feature of Perissodactyla.[10] The Guttural Pouch is of particular concern in Equine Veterinary practice, due to its frequent involvement in some serious infections. Aspergillosis (infection with Aspergillus mould) of the Guttural Pouch (also called Guttural Pouch Mycosis) can cause serious damage to the tissues of the pouch, as well as surrounding structures including important cranial nerves (Nerves IX-XII: Glossopharyngeal, Vagus, Accessory and Hypoglossal Nerves[10]) and the internal carotid artery.[10] Strangles (Streptococcus equi equi infection) is a highly transmissible respiratory infection of horses[11][12] that can cause pus to accumulate in the Guttural Pouch;[13] horses with S. equi equi colonising their Guttural Pouch can continue to intermittently shed the bacteria for several months,[14] and should be isolated from other horses during this time to prevent transmission. Due to the intermittent nature of S. equi equi shedding, prematurely reintroducing an infected horse may risk exposing other horses to the infection, even though the shedding horse appears well and may have previously returned negative samples. The function of the Guttural Pouch has been difficult to determine, but it is now believed to play a role in cooling blood in the internal carotid artery before it enters the brain.[10]
Gut
All perissodactyls are hindgut fermenters. In contrast to ruminants, hindgut fermenters store digested food that has left the stomach in an enlarged cecum, where the food is digested by bacteria. No gallbladder is present. The stomach of perissodactyls is simply built, while the cecum accommodates up to 90 L (24 US gal) in horses. The intestine is very long, reaching up to 26 m (85 ft) in horses. Extraction of nutrients from food is relatively inefficient, which probably explains why no odd-toed ungulates are small; nutritional requirements per unit of body weight are lower for large animals, as their surface-area-to-volume ratio is smaller.
Lack of carotid rete
Unlike artiodactyls, perissodactyls lack a
Distribution
Most extant perissodactyl species occupy a small fraction of their original range. Members of this group are now found only in Central and South America, eastern and southern Africa, and central, southern, and southeastern Asia.[16] During the peak of odd-toed ungulate existence, from the Eocene to the Oligocene, perissodactyls were distributed over much of the globe, the major exceptions being Australia and Antarctica. Horses and tapirs arrived in South America after the formation of the Isthmus of Panama around 3 million years ago in the Pliocene. Their North American counterparts died out around 10,000 years ago, leaving only Baird's tapir with a range extending to what is now southern Mexico. The tarpans were pushed to extinction in 19th century Europe. Hunting and habitat destruction have reduced the surviving perissodactyl species to fragmented populations. In contrast, domesticated horses and donkeys have gained a worldwide distribution, and feral animals of both species are now also found in regions outside their original range, such as in Australia.
Lifestyle and diet
Perissodactyls inhabit a number of different habitats, leading to different lifestyles. Tapirs are solitary and inhabit mainly tropical rainforests. Rhinos tend to live alone in rather dry savannas, and in Asia, wet marsh or forest areas. Horses inhabit open areas such as grasslands, steppes, or semi-deserts, and live together in groups. Odd-toed ungulates are exclusively herbivores that feed, to varying degrees, on grass, leaves, and other plant parts. A distinction is often made between primarily grass feeders (white rhinos, equines) and leaf feeders (tapirs, other rhinos).
Reproduction and development
Odd-toed ungulates are characterized by a long gestation period and a small litter size, usually delivering a single young. The gestation period is 330–500 days, being longest in rhinos. Newborn perissodactyls are
Taxonomy
Outer taxonomy
Traditionally, the odd-toed ungulates were classified with other mammals such as
Molecular genetic studies, however, have shown the ungulates to be
|
According to studies published in March 2015, odd-toed ungulates are in a close family relationship with at least some of the so-called Meridiungulata, a very diverse group of mammals living from the Paleocene to the Pleistocene in South America, whose systematic unity is largely unexplained. Some of these were classified based on their paleogeographic distribution. However, a close relationship can be worked out to perissodactyls by protein sequencing and comparison with fossil collagen from remnants of phylogenetically young members of the Meridiungulata (specifically Macrauchenia from the Litopterna and Toxodon from the Notoungulata). Both kinship groups, the odd-toed ungulates and the Litopterna-Notoungulata, are now in the higher-level taxon of Panperissodactyla. This kinship group is included among the Euungulata, which also contains the even-toed ungulates and whales (Artiodactyla). The separation of the Litopterna-Notoungulata group from the perissodactyls probably took place before the Cretaceous–Paleogene extinction event. "Condylarths" can probably be considered the starting point for the development of the two groups, as they represent a heterogeneous group of primitive ungulates that mainly inhabited the northern hemisphere in the Paleogene.[23][24]
Modern members
Odd-toed ungulates (Perissodactyla) comprise three living families with around 17 species—in horses, however, the exact count is still controversial. Rhinos and tapirs are more closely related to each other than to horses. The separation of horses from other perissodactyls took place according to molecular genetic analysis in the Paleocene some 56 million years ago, while the rhinos and tapirs split off in the lower-middle Eocene, about 47 million years ago.
|
- Order Perissodactyla
- Suborder Hippomorpha
- Family Equidae: horses and allies, seven species in one genus
- Equus ferus
- Tarpan, †Equus ferus ferus
- Przewalski's horse, Equus ferus przewalskii
- Domestic horse, Equus ferus caballus
- African wild ass, Equus africanus
- Nubian wild ass, Equus africanus africanus
- Somali wild ass, Equus africanus somaliensis
- Domesticated ass (donkey), Equus africanus asinus
- Atlas wild ass, †Equus africanus atlanticus
- Onager or Asiatic wild ass, Equus hemionus
- Mongolian wild ass, Equus hemionus hemionus
- Turkmenian kulan, Equus hemionus kulan
- Persian onager, Equus hemionus onager
- Indian wild ass, Equus hemionus khur
- Syrian wild ass, †Equus hemionus hemippus
- Kiang or Tibetan wild ass, Equus kiang
- Western kiang, Equus kiang kiang
- Eastern kiang, Equus kiang holdereri
- Southern kiang, Equus kiang polyodon
- Plains zebra, Equus quagga
- Quagga, †Equus quagga quagga
- Burchell's zebra, Equus quagga burchellii
- Grant's zebra, Equus quagga boehmi
- Maneless zebra, Equus quagga borensis
- Chapman's zebra, Equus quagga chapmani
- Crawshay's zebra, Equus quagga crawshayi
- Selous' zebra, Equus quagga selousi
- Mountain zebra, Equus zebra
- Cape mountain zebra, Equus zebra zebra
- Hartmann's mountain zebra, Equus zebra hartmannae
- Grévy's zebra, Equus grevyi
- Equus ferus
- Family Equidae: horses and allies, seven species in one genus
- Suborder Ceratomorpha
- Family Tapiridae: tapirs, five species in one genus
- Brazilian tapir, Tapirus terrestris
- Mountain tapir, Tapirus pinchaque
- Baird's tapir, Tapirus bairdii
- Malayan tapir, Tapirus indicus
- Kabomani tapir, Tapirus kabomani
- Family Rhinocerotidae: rhinoceroses, five species in four genera
- Black rhinoceros, Diceros bicornis
- Southern black rhinoceros, †Diceros bicornis bicornis
- North-eastern black rhinoceros, †Diceros bicornis brucii
- Chobe black rhinoceros, Diceros bicornis chobiensis
- Uganda black rhinoceros, Diceros bicornis ladoensis
- Western black rhinoceros, †Diceros bicornis longipes
- Eastern black rhinoceros, Diceros bicornis michaeli
- South-central black rhinoceros, Diceros bicornis minor
- South-western black rhinoceros, Diceros bicornis occidentalis
- White rhinoceros, Ceratotherium simum
- Southern white rhinoceros, Ceratotherium simum simum
- Northern white rhinoceros, Ceratotherium simum cottoni
- Indian rhinoceros, Rhinoceros unicornis
- Javan rhinoceros, Rhinoceros sondaicus
- Indonesian Javan rhinoceros, Rhinoceros sondaicus sondaicus
- Vietnamese Javan rhinoceros, Rhinoceros sondaicus annamiticus
- Indian Javan rhinoceros, †Rhinoceros sondaicus inermis
- Sumatran rhinoceros, Dicerorhinus sumatrensis
- Western Sumatran rhinoceros, Dicerorhinus sumatrensis sumatrensis
- Eastern Sumatran rhinoceros, Dicerorhinus sumatrensis harrissoni
- Northern Sumatran rhinoceros, †Dicerorhinus sumatrensis lasiotis
- Black rhinoceros, Diceros bicornis
- Family Tapiridae: tapirs, five species in one genus
- Suborder Hippomorpha
Prehistoric members
There are many perissodactyl fossils of multivariant form. The major lines of development include the following groups:
- Equoidea (equines) also developed in the Eocene. Palaeotheriidae are known mainly from Europe; their most famous member is Eohippus, which became extinct in the Oligocene. In contrast, the horse family (Equidae) flourished and spread. Over time this group saw a reduction in toe number, extension of the limbs, and the progressive adjustment of the teeth for eating hard grasses.
- Chalicotheriidae and Lophiodontidae. The Chalicotheriidae developed claws instead of hooves and considerable extension of the forelegs. The best-known genera include Chalicotherium and Moropus. Chalicotherioidea died out in the Pleistocene.
- Rhinocerotoidea (rhino relatives) included a large variety of forms from the Eocene up to the Oligocene, including dog-size leaf feeders, semiaquatic animals, and also huge long-necked animals. Only a few had horns on the nose. The Amynodontidae were hippo-like, aquatic animals. Hyracodontidae developed long limbs and long necks that were most pronounced in the Paraceratherium (formerly known as Baluchitherium or Indricotherium), the second largest known land mammal ever to have lived (after Palaeoloxodon namadicus[28]). The rhinos (Rhinocerotidae) emerged in the Middle Eocene; five species survive to the present day.
- Tapiroidea reached their greatest diversity in the Eocene, when several families lived in Eurasia and North America. They retained a primitive physique and were noted for developing a trunk. The extinct families within this group include the Helaletidae.[citation needed]
- Several mammal groups traditionally classified as , are now understood to be part of the odd-toed ungulate assemblage. Phenacodontids seem to be stem-perissodactyls, while hyopsodontids are closely related to horses and brontotheres, despite their more primitive overall appearance.
- Desmostylia[29] and Anthracobunidae have traditionally been placed among the afrotheres, but they may actually represent stem-perissodactyls. They are an early lineage of mammals that took to the water, spreading across semi-aquatic to fully marine niches in the Tethys Ocean and the northern Pacific. However, later studies have shown that, while anthracobunids are definite perissodactyls, desmostylians have enough mixed characters to suggest that a position among the Afrotheria is not out of the question.[30]
- Order Perissodactyla[31]
- Superfamily Brontotherioidea
- Suborder Hippomorpha
- †Hyopsodontidae[32]
- †Pachynolophidae[33]
- Superfamily Equoidea
- †Indolophidae[34]
- †Palaeotheriidae (might be a basal perissodactyl grade instead)
- Clade Tapiromorpha
- †Isectolophidae[35] (a basal family of Tapiromorpha; from the Eocene epoch)
- †Suborder Ancylopoda
- †Lophiodontidae
- Superfamily Chalicotherioidea
- †Eomoropidae (basal grade of chalicotheroids)
- †Chalicotheriidae
- Suborder Ceratomorpha
- Superfamily Rhinocerotoidea
- Superfamily Tapiroidea
- †Deperetellidae
- †Rhodopagidae (sometimes recognized as a subfamily of deperetellids)
- †Lophialetidae[36]
- †Eoletidae (sometimes recognized as a subfamily of lophialetids)
- †Anthracobunidae[37] (a family of stem-perissodactyls; from the Early to Middle Eocene epoch)
- †Phenacodontidae[37] (a clade of stem-perissodactyls; from the Early Palaeocene to the Middle Eocene epoch)
Higher classification of perissodactyls
|
Relationships within the large group of odd-toed ungulates are not fully understood. Initially, after the establishment of "Perissodactyla" by Richard Owen in 1848, the present-day representatives were considered equal in rank. In the first half of the 20th century, a more systematic differentiation of odd-toed ungulates began, based on a consideration of fossil forms, and they were placed in two major suborders: Hippomorpha and Ceratomorpha. The Hippomorpha comprises today's horses and their extinct members (Equoidea); the Ceratomorpha consist of tapirs and rhinos plus their extinct members (Tapiroidea and Rhinocerotoidea).[39] The names Hippomorpha and Ceratomorpha were introduced in 1937 by Horace Elmer Wood, in response to criticism of the name "Solidungula" that he proposed three years previously. It had been based on the grouping of horses and Tridactyla and on the rhinoceros/tapir complex.[40][41] The extinct brontotheriidae were also classified under Hippomorpha and therefore possess a close relationship to horses. Some researchers accept this assignment because of similar dental features, but there is also the view that a very basal position within the odd-toed ungulates places them rather in the group of Titanotheriomorpha.[38][42]
Originally, the
Evolutionary history
Origins
The evolutionary development of Perissodactyla is well documented in the fossil record. Numerous finds are evidence of the adaptive radiation of this group, which was once much more varied and widely dispersed. Radinskya from the late Paleocene of East Asia is often considered to be one of the oldest close relatives of the ungulates.[47] Its 8 cm skull must have belonged to a very small and primitive animal with a π-shaped crown pattern on the enamel of its rear molars similar to that of perissodactyls and their relatives, especially the rhinos.[48] Finds of Cambaytherium and Kalitherium in the Cambay shale of western India indicate an origin in Asia dating to the Lower Eocene roughly 54.5 million years ago.[49][50] Their teeth also show similarities to Radinskya as well as to the Tethytheria clade.[51][52] The saddle-shaped configuration of the navicular joints and the mesaxonic construction of the front and hind feet also indicates a close relationship to Tethytheria.[citation needed] However, this construction deviates from that of Cambaytherium, indicating that it is actually a member of a sister group. Ancestors of Perissodactyla may have arrived via an island bridge from the Afro-Arab landmass onto the Indian subcontinent as it drifted north towards Asia.[53] A study on Cambaytherium suggests an origin in India prior or near its collision with Asia.[54]
The alignment of hyopsodontids and phenacodontids to Perissodactyla in general suggests an older Laurasian origin and distribution for the clade, dispersed across the northern continents already in the early Paleocene. These forms already show a fairly well-developed molar morphology, with no intermediary forms as evidence of the course of its development.
Phylogeny
The Perissodactyla appeared relatively abruptly at the beginning of the Lower Paleocene about 63 million years ago, both in North America and Asia, in the form of
More successful lines of odd-toed ungulates emerged at the end of the Eocene when dense jungles gave way to steppe, such as the chalicotheriid rhinos, and their immediate relatives; their development also began with very small forms. Paraceratherium, one of the largest mammals ever to walk the earth, evolved during this era.[63][64] They weighed up to 20 metric tons (22 short tons) and lived throughout the Oligocene in Eurasia. About 20 million years ago, at the onset of the Miocene, the perissodactyls first reached Africa when it became connected to Eurasia because of the closing of the Tethys Ocean. For the same reason, however, new animals such as the mammoths also entered the ancient settlement areas of odd-toed ungulates, creating competition that led to the extinction of some of their lines. The rise of ruminants, which occupied similar ecological niches and had a much more efficient digestive system, is also associated with the decline in diversity of odd-toed ungulates. A significant cause for the decline of perissodactyls was climate change during the Miocene, leading to a cooler and drier climate accompanied by the spread of open landscapes. However, some lines flourished, such as the horses and rhinos; anatomical adaptations made it possible for them to consume tougher grass food. This led to open land forms that dominated newly created landscapes. With the emergence of the Isthmus of Panama in the Pliocene, perissodactyls and other megafauna were given access to one of their last habitable continents: South America.[65][66] However, many perissodactyls became extinct at the end of the ice ages, including American horses and the Elasmotherium. Whether over-hunting by humans (overkill hypothesis), climatic change, or a combination of both factors was responsible for the extinction of ice age mega-fauna, remains controversial.[31]
Research history
In 1758, in his seminal work Systema Naturae,
In 1861, Henri Marie Ducrotay de Blainville (1777–1850) classified ungulates by the structure of their feet, differentiating those with an even number of toes from those with an odd number. He moved the horses as solidungulate over to the tapirs and rhinos as multungulate animals and referred to all of them together as onguligrades à doigts impairs, coming close to the concept of the odd-toed ungulate as a systematic unit. Richard Owen (1804–1892) quoted Blainville in his study on fossil mammals of the Isle of Wight and introduced the name Perissodactyla.[39][42]
In 1884,
Interactions with humans
The domestic horse and the donkey play an important role in human history, particularly as transport, work and pack animals. The domestication of both species began several millennia BCE. Due to the motorisation of agriculture and the spread of automobile traffic, such use has declined sharply in Western industrial countries; riding is usually undertaken more as a hobby or sport. In less developed regions of the world, traditional uses for these animals are, however, still widespread. To a lesser extent, horses and donkeys are also kept for their meat and their milk.
In contrast, the existence in the wild of almost all other odd-toed ungulates species has declined dramatically because of hunting and habitat destruction. The quagga is extinct and Przewalski's horse was once eradicated in the wild.
Present threat levels, according to the International Union for Conservation of Nature (2012):[73]
- Four species are considered critically endangered: the Javan rhinoceros, the Sumatran rhinoceros, the black rhinoceros and the African wild ass.
- Six species are endangered: the mountain tapir, the Central American tapir, the Malayan tapir, the wild horse and Grévy's zebra.
- Three species are considered vulnerable: the Indian rhinoceros, the South American tapir and the mountain zebra.
- The onager, the plains zebra and the white rhinoceros are near-threatened; however, the northern subspecies, Ceratotherium simum cottoni (northern white rhinoceros) is close to extinction.
- The kiang is not considered at risk (least concern).
References
- ^ "PBDB". paleobiodb.org. Retrieved 18 July 2021.
- S2CID 84391276.
- ^ "Glossary. American Museum of Natural History". Archived from the original on 20 November 2021.
- ^ "The Largest Beasts to Walk the Earth". Phenomena. National Geographic Society. 14 July 2015. Archived from the original on 15 July 2015.
- ^ "Dawn horse". Encyclopædia Britannica. Retrieved 7 September 2016.
- ISBN 9780982261965.
- ^ Hall, Brian K. (2006). Fins into Limbs. University of Chicago Press. ISBN 978-0-226-31337-5.
- S2CID 34568531.
- PMID 31373392.
- ^ ISBN 978-0-323442640.
- ^ Rush, Bonnie. "Strangles (Distemper) in Horses - MSD Veterinary Manual". MSD Veterinary Manual. MSD. Retrieved 25 September 2023.
- ^ Lascola, Kara. "Strangles in Horses - Respiratory Diseases of Horses - MSD Veterinary Manual". MSD Veterinary Manual. MSD. Retrieved 25 September 2023.
- ISBN 978-0-323442640.
- ^ Freeman, Paul. "Strangles" (PDF). Strangles. NSW Government - Department of Primary Industries. Retrieved 25 September 2023.
- ^ PMID 18426746.
- ^ "Perissodactyl | Definition, Characteristics, Species, Examples, Habitat, & Facts | Britannica". www.britannica.com. Retrieved 16 May 2023.
- ^ Zookeeping: An Introduction to the Science and Technology. Chicago: University of Chicago Press. 2013. p. 273.
- ^ Williams, Jennifer (15 December 2008). "Understand Normal Mare and Foal Behavior". equusmagazine.com. Archived from the original on 13 May 2017. Retrieved 4 February 2019.
- ^ Ballenger, Liz; Myers, Phil. "Rhinocerotidae (rhinoceroses)". Animal Diversity Web. Retrieved 2021-03-27."Ballenger, Liz; Myers, Phil. "Rhinocerotidae (rhinoceroses)". Animal Diversity Web. Retrieved 2021-03-27.
- ^ PMID 9126561.
- S2CID 30067369.
- PMID 16785431.
- ^ S2CID 4467386.
- ^ Ross MacPhee; Frido Welker; Jessica Thomas; Selina Brace; Enrico Cappellini; Samuel Turvey; Ian Barnes; Marcelo Reguero; Javier Gelfo; Alejandro Kramarz (2014). "Ancient protein sequencing Resolves litoptern and notoungulate superordinal affinities". The History of Life: A View from the Southern Hemisphere: 186.
- PMID 11286489.
- .
- .
- .
- PMID 25295875.
- PMID 27384169.
- ^ .
- S2CID 84391276.
- .
- S2CID 84061253.
- ^ .
- S2CID 214053761.
- ^ PMID 25295875.
- ^ S2CID 84351811.
- ^ a b c George Gaylord (1945). "The Principles of Classification and a Classification of Mammals". Bulletin of the American Museum of Natural History: 252–258.
- ^ Horace Elmer Wood (1934). "Revision of the Hyrachyidae". Bulletin of the American Museum of Natural History: 181–295.
- .
- ^ a b c d Robert M. Schoch (1989). "A brief historical review of perissodactyl classification". The Evolution of Perissodactyls. Oxford University Press. pp. 13–23.
- JSTOR 1005518.
- ^ Leonard B. Radinsky (1964). "Paleomoropus, a new early Eocene chalicothere (Mammalia, Perissodactyla), and a revision of Eocene chalicotheres". American Museum Novitates: 1–28.
- .
- ^ Robert Milton Schoch (1984). "Two unusual specimens of the Yale Peabody Museum Helaletes in collections, and some comments on the ancestry of the Tapiridae (Perissodactyla, Mammalia)". Peabody Museum, Yale University: 1–20.
{{cite journal}}
: Cite journal requires|journal=
(help) - ^ Malcolm C. McKenna; Chow Minna; Suyin Ting; Luo Zhexi (1989). "Radinskya yupingae, a perissodactyl-like mammal from the Late Palaeocene of China". The Evolution of Perissodactyls. Oxford University Press. pp. 24–36.
- ^ Kenneth D. Rose (2006). The Beginning of the Age of Mammals. Johns Hopkins University Press. pp. 242–267.
- ^ Sunil Bajpai; Vivesh Kapur; Debasis P. Das; BN Tiwari; N. Saravanan; Ritu Sharma (2005). "Early Eocene Land Mammals from Vastan Lignite Mine, District Surat (Gujarat), western India" (PDF). Journal of the Palaeontological Society of India: 101–113.
- ^ Sunil Bajpai; Vivesh Kapur; JGM Thewissen; Debasis P. Das; BN Tiwari (2006). "New Early Eocene cambaythere (Perissodactyla, Mammalia) from the Vastan Lignite Mine (Gujarat, India) and on evaluation of cambaythere relationships". Journal of the Palaeontological Society of India: 101–110.
- S2CID 86206151.
- ^ Kishor Kumar (2005). "Comments on 'Early Eocene Land Mammals from Vastan Lignite Mine, District Surat (Gujarat), western India' by Bajpai". Journal of the Palaeontological Society of India: 101–113, 2005.
- PMID 25410701.
- S2CID 226263139.
- PMID 27384169.
- PMID 27358361.
- S2CID 4603597.
- .
- hdl:1854/LU-3178691.
- S2CID 129473193.
- ^ Hlawatsch, Kerstin; Erfurt, Jörg (2007). "Zahnmorphologie und stratigraphische Verbreitung von Hyrachyus minimus (Perissodactyla, Mammalia) in den eozänen Geiseltalschichten" [Tooth morphology and stratigraphic distribution of Hyrachyus minimus (Perissodactyla, Mammalia) in the Eocene Geiseltal layers]. Hallesches Jahrbuch für Geowissenschaften. Suppl. 23: 161–173.
- ISBN 978-3-540-72421-6.
- ISBN 0-412-73810-4.
- .
- ^ Matthew Colbert (2007). "New Fossil Discoveries and the History of Tapirus". Tapir Conservation: 12–14.
- PMID 20007379.
- ^ Étienne Geoffroy Saint-Hilaire; Georges Cuvier (1795). "Memoire sur une nouvelle division of Mammifères, et sur les principes qui doivent servir de base dans cette sorte de travail". Magasin Encyclopédique: 164–190.
- ^ Georges Cuvier (1817). "Le Règne Animal distribue d'après son organisation pour servir de base à l'histoire naturelle des animaux". Introduction à l'Anatomie Comparée. 1: 1–540.
- ^ Johann Friedrich Blumenbach (1779). Handbook of Natural History. pp. 168–448.
- ^ Georges Cuvier (1798). "Tableau Elementaire de l'histoire naturelle des animaux": 1–710.
{{cite journal}}
: Cite journal requires|journal=
(help) - ^ Donald R. Prothero; Robert M. Schoch (1989). "Classification of the Perissodactyla". The Evolution of Perissodactyls. Oxford University Press. pp. 530–537.
- PMID 17329227.
- ^ International Union for Conservation of Nature. "IUCN redlist".
Further reading
- Martin S. Fischer: Mesaxonia (Perissodactyla) Perissodactyla. In: Wilfried Westheide, Reinhard Rieger (eds.): Systematic Zoology. Part 2: Vortex or craniotes. Spektrum Akademischer Verlag, Heidelberg and Berlin 2004, pp 646–655, ISBN 3-8274-0307-3.
- Ronald M. Nowak: Walker's Mammals of the World. 6th edition. Johns Hopkins University Press, Baltimore 1999, ISBN 0-8018-5789-9.
- Thomas S. Kemp: The Origin & Evolution of Mammals Oxford University Press, Oxford, 2005. ISBN 0-19-850761-5.
- AH Müller: Textbook of Paleozoology, Volume III: vertebrates, Part 3: Mammalia. 2nd edition. Gustav Fischer Verlag, Jena and Stuttgart 1989. ISBN 3-334-00223-3.
- Don E. Wilson, DeeAnn M. Reeder (eds.): ISBN 0-8018-8221-4.
- Ronald M. Nowak (1999), Walker's Mammals of the World (6th ed.), Baltimore: Johns Hopkins University Press, LCCN 98023686