| Diacodexis | |
|---|---|
 | |
| Diacodexis pakistanensis and Pakicetus inachus | |
Scientific classification  | |
| Domain: | Eukaryota |
| Kingdom: | Animalia |
| Phylum: | Chordata |
| Class: | Mammalia |
| Order: | Artiodactyla |
| Family: | † Diacodexeidae |
| Genus: | † Diacodexis Cope, 1882 |
| Species | |
| |
Diacodexis is an extinct genus of small herbivorous mammals belonging to the family Diacodexeidae [1] [2] [3] that lived in North America, Europe and Pakistan from 55.4 mya to 46.2 mya and existing for approximately 9.2 million years.
Diacodexis is the oldest known even-toed ungulate. In life, it would have resembled a modern duiker, measuring about 50 centimetres (1.6 ft) in body length, but with a much longer tail. Unlike most later species of artiodactyl, it still had five toes on each foot, although the third and fourth toes were already elongated. It may also have had small hooves on each toe. Its teeth suggest that it was a herbivorous browser. [4]
D. ilicis possessed a very simple neocortex, characterised by an almond-shaped gyrus instead of parallel sulci as some earlier authors had believed. [5]
As suggested by its long legs, Diacodexis is believed to have been fast-running, capable of leaping relatively far.
Diacodexis was widespread, with fossils having been found in Pakistan, Europe, and North America.
Perissodactyla, or odd-toed ungulates, is an order of ungulates. The order includes about 17 living species divided into three families: Equidae, Rhinocerotidae (rhinoceroses), and Tapiridae (tapirs). They typically have reduced the weight-bearing toes to three or one of the five original toes, though tapirs retain four toes on their front feet. The nonweight-bearing toes are either present, absent, vestigial, or positioned posteriorly. By contrast, artiodactyls bear most of their weight equally on four or two of the five toes: their third and fourth toes. Another difference between the two is that perissodactyls digest plant cellulose in their intestines, rather than in one or more stomach chambers as artiodactyls, with the exception of Suina, do.
Ungulates are members of the diverse clade Euungulata, which primarily consists of large mammals with hooves. Once part of the clade "Ungulata" along with the clade Paenungulata, "Ungulata" has since been determined to be a polyphyletic and thereby invalid clade based on molecular data. As a result, true ungulates had since been reclassified to the newer clade Euungulata in 2001 within the clade Laurasiatheria while Paenungulata has been reclassified to a distant clade Afrotheria. Living ungulates are divided into two orders: Perissodactyla including equines, rhinoceroses, and tapirs; and Artiodactyla including cattle, antelope, pigs, giraffes, camels, sheep, deer, and hippopotamuses, among others. Cetaceans such as whales, dolphins, and porpoises are also classified as artiodactyls, although they do not have hooves. Most terrestrial ungulates use the hoofed tips of their toes to support their body weight while standing or moving. Two other orders of ungulates, Notoungulata and Litopterna, both native to South America, became extinct at the end of the Pleistocene, around 12,000 years ago.
Artiodactyls are placental mammals belonging to the order Artiodactyla. Typically, they are ungulates which bear weight equally on two of their five toes. The other three toes are either present, absent, vestigial, or pointing posteriorly. By contrast, most perissodactyls bear weight on an odd number of the five toes. Another difference between the two orders is that many artiodactyls digest plant cellulose in one or more stomach chambers rather than in their intestine. Molecular biology, along with new fossil discoveries, has found that cetaceans fall within this taxonomic branch, being most closely related to hippopotamuses. Some modern taxonomists thus apply the name Cetartiodactyla to this group, while others opt to include cetaceans within the existing name of Artiodactyla. Some researchers use "even-toed ungulates" to exclude cetaceans and only include terrestrial artiodactyls, making the term paraphyletic in nature.
Tylopoda is a suborder of terrestrial herbivorous even-toed ungulates belonging to the order Artiodactyla. They are found in the wild in their native ranges of South America and Asia, while Australian feral camels are introduced. The group has a long fossil history in North America and Eurasia. Tylopoda appeared during the Eocene around 50 million years ago.
Condylarthra is an informal group – previously considered an order – of extinct placental mammals, known primarily from the Paleocene and Eocene epochs. They are considered early, primitive ungulates and is now largely considered to be a wastebasket taxon, having served as a dumping ground for classifying ungulates which had not been clearly established as part of either Perissodactyla or Artiodactyla, being composed thus of several unrelated lineages.
Dichobunidae is an extinct family of basal artiodactyl mammals from the early Eocene to late Oligocene of North America, Europe, and Asia. The Dichobunidae include some of the earliest known artiodactyls, such as Diacodexis.
The Raoellidae, previously grouped within Helohyidae, are an extinct family of semiaquatic digitigrade artiodactyls in the clade Whippomorpha. Fossils of raoellids are found in Eocene strata of South Asia and Southeast Asia.
Anoplotherium is the type genus of the extinct Palaeogene artiodactyl family Anoplotheriidae, which was endemic to Western Europe. It lived from the Late Eocene to the earliest Oligocene. It was the fifth fossil mammal genus to be described with official taxonomic authority, with a history extending back to 1804 when its fossils from Montmartre in Paris, France were first described by the French naturalist Georges Cuvier. Discoveries of incomplete skeletons of A. commune in 1807 led Cuvier to thoroughly describe unusual features for which there are no modern analogues. His drawn skeletal and muscle reconstructions of A. commune in 1812 were amongst the first instances of anatomical reconstructions based on fossil evidence. Cuvier's contributions to palaeontology based on his works on the genus were revolutionary for the field, not only proving the developing ideas of extinction and ecological succession but also paving the way for subfields such as palaeoneurology. Today, there are four known species.
Anoplotheriidae is an extinct family of artiodactyl ungulates. They were endemic to Europe during the Eocene and Oligocene epochs about 44—30 million years ago. Its name is derived from the Ancient Greek: ἂνοπλος ("unarmed") and θήριον ("beast"), translating as "unarmed beast".
Duerotherium is an extinct genus of artiodactyl that lived during the Middle Eocene and is only known from the Iberian Peninsula. The genus is a member of the family Anoplotheriidae and the subfamily Anoplotheriinae, and contains one species, D. sudrei. Like other anoplotheriids, it was endemic to Western Europe. The genus was described based on a left fragment of a maxilla from the Mazaterón Formation of the Duero Basin, from which its name derives, in 2009. Its dentition is mostly typical of the Anoplotheriinae but differs from related genera in the elongated and triangular third upper premolar and traits of the molars. It is thought to have been part of an endemic fauna that evolved in the Iberian Peninsula during the Middle Eocene, when climates were subtropical.
Xiphodon is the type genus of the extinct Palaeogene artiodactyl family Xiphodontidae. It, like other xiphodonts, was endemic to Western Europe and lived from the middle Eocene up to the earliest Oligocene. Fossils from Montmartre in Paris, France that belonged to X. gracilis were first described by the French naturalist Georges Cuvier in 1804. Although he assigned the species to Anoplotherium, he recognized that it differed from A. commune by its dentition and limb bones, later moving it to its own subgenus in 1822. Xiphodon was promoted to genus rank by other naturalists in later decades. It is today defined by the type species X. gracilis and two other species, X. castrensis and X. intermedium.
Homacodontidae is an extinct family of basal artiodactyl mammals from the early Eocene to late Oligocene of North America, Europe, and Asia.
Dichodon is an extinct genus of Palaeogene artiodactyls belonging to the family Xiphodontidae. It was endemic to Western Europe and lived from the middle Eocene up to the earliest Oligocene. The genus was first erected by the British naturalist Richard Owen in 1848 based on dental remains from the fossil beds in Hordle, England. He noticed similar dentitions to contemporary artiodactyls like those of the Anoplotheriidae and Dichobunidae and references the name of the genus Dichobune. Eventually, it was found to be more closely related to Xiphodon and now includes 11 species, although one of them may be synonymous.
Diacodexeidae is an extinct family of basal artiodactyl mammals from the Eocene of North America, Europe, and Asia. The family includes some of the earliest known artiodactyls, such as Diacodexis. They were small animals with short snouts, and closely related to the dichobunids, with which they were formerly classified.
Robiatherium is an extinct genus of Palaeogene artiodactyls containing one species R. cournovense. The genus name derives from the locality of Robiac in France where some of its fossil were described plus the Greek θήρ/therium meaning "beast" or "wild animal". It was known only from the middle Eocene and, like other anoplotheriids, was endemic to Western Europe. The genus was erected by Jean Sudre in 1988 for a species originally attributed to the xiphodont genus Paraxiphodon in 1978. Robiatherium had dentitions typical of the subfamily Anoplotheriinae, differing from other genera by specific differences in the molars. It is one of the earliest-appearing anoplotheriine species in the fossil record as well as the earliest to have appeared in Central Europe.
Mixtotherium is an extinct genus of Palaeogene artiodactyls belonging to the monotypic family Mixtotheriidae. Known informally as mixtotheriids or mixtotheres, these artiodactyls were endemic to western Europe and occurred from the middle to late Eocene. The genus and type species were both first established by the French naturalist Henri Filhol in 1880. Several species are well known by good skull fossils, which were informative enough to allow for classifications of the species to their own family. The Mixtotheriidae, first recognized by Helga Sharpe Pearson in 1927, is currently known by 7 valid species, although M. priscum is thought by several authors to be synonymous with M. gresslyi. The affinities of the Mixtotheriidae in relation to other artiodactyl families is uncertain, but it is currently thought to have been related to the Cainotherioidea and Anoplotheriidae.
Haplomeryx is an extinct genus of Palaeogene artiodactyls belonging to the family Xiphodontidae. It was endemic to Western Europe and lived from the middle Eocene up to the earliest Oligocene. Haplomeryx was first established as a genus by the German naturalist Max Schlosser in 1886 based on a molar tooth set from Quercy Phosphorites deposits. Three additional species were erected and classified to the xiphodontid genus while one other species, first recognized in 1822, was tentatively classified to it and remains unresolved in affinity.
Amphimeryx is an extinct genus of Palaeogene artiodactyls belonging to the Amphimerycidae that was endemic to the central region of western Europe and lived from the Late Eocene to the Early Oligocene. It was erected in 1848 by the French palaeontologist Auguste Pomel, who argued that its dentition was roughly similar to those of ruminants. Hence, the etymology of the genus name means "near ruminant," of which it derives from the ancient Greek words ἀμφί (near) and μήρυξ (ruminant). The type species A. murinus was previously recognized as a species of Dichobune by the French palaeontologist Georges Cuvier in 1822 before its eventual reclassification to its own genus. Two other species A. collotarsus and A. riparius are recognized also today although the former may be synonymous with A. murinus while the latter is known solely by a now-lost fossil specimen.
Pseudamphimeryx is an extinct genus of Palaeogene artiodactyls belonging to the Amphimerycidae that was endemic to the central region of western Europe and lived from the Middle to Late Eocene. It was first erected in 1910 by the Swiss palaeontologist Hans Georg Stehlin, who assigned to it multiple species and noted specific differences from another amphimerycid Amphimeryx. As of present, it is known by six species, although the validity of P. valdensis has been questioned while the earliest-appearing species P. schosseri has been suggested to not be an amphimerycid.
Amphimerycidae is an extinct family of artiodactyls that was endemic to western Europe that lived from the Middle Eocene to the Early Oligocene. With a taxonomic history extending as far back as 1804, the family was formally recognized by the Swiss palaeontologist Hans Georg Stehlin in 1910 and contains two genera: Amphimeryx and Pseudamphimeryx. Both amphimerycid genera are very similar to each other in terms of skull and dental anatomy but do have specific differences from each other. Both genera are best known from their fused cuboid bone and navicular bone, which together make up a single "cubonavicular bone" of the hind legs. This trait had long been used in support of the idea that they were ruminants by taxonomists. However, their classification to the Ruminantia had also been rejected by other taxonomists later on due to differences in dentition; the systematic position of the Amphimerycidae and close relatives in relation to the wider Artiodactyla, as a result, is unclear.
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