Paratheria (mammals)
Encyclopedia
Paratheria is an obsolete term used for a group that included at least the xenarthra
n mammals. It was proposed by Oldfield Thomas
in 1887 to set apart the sloth
s, anteater
s, armadillo
s, and pangolin
s, usually classified as placentals, from both marsupial and placental mammals, an arrangement that received little support from other workers. When Gondwanatheria
were first discovered in Argentina the 1980s, they were thought to be related to xenarthrans, leading to renewed attention to the hypothesis that xenarthrans are not placentals. However, by the early 1990s, gondwanatheres were shown to be unrelated to xenarthrans, and xenarthrans are still considered placentals.
The term was coined by British mammalogist Oldfield Thomas
in 1887 in a review of tooth development
in mammals. He found that the "Edentata"—a group in which he included the anteater
s, armadillo
s, and sloth
s that are still included in Xenarthra
as well as the pangolin
s and the aardvark
—were especially distinctive. He derived edentate teeth from the first stage in his model of mammalian dental evolution, and consequently suggested that they should be given a grouping separate from the other major groupings of mammals, for which terms had been introduced by Thomas Huxley
: Eutheria
(placentals) and Metatheria
(marsupials). For this grouping, he suggested the name Paratheria "to indicate their position by the side
of, but separate from, the other Mammals" (the Greek παρά para means "beside"). Thomas was unable, however, to provide a satisfactory scenario for the origin of the aardvark's wholly unique dentition, which he could only compare with the teeth of a fish. Thomas's arrangement was foreshadowed by Henri Marie Ducrotay de Blainville
's 1839 classification; he placed edentates (except the sloth Bradypus, which he considered to be a primate) as a major division, the Maldentés ("poorly toothed"), distinct from the other monodelphes (placentals), the Bien dentés ("well-toothed").
Thomas's hypothesis received little support, or even attention, in subsequent years. In 1893, Henry Fairfield Osborn
remarked that new studies of edentate teeth indicated that they were not as distinct as Thomas thought. William Berryman Scott
did, however, place Paratheria as a separate subclass in 1904, although he apparently did not follow Thomas's theories about the origins of edentate teeth. In 1910, William King Gregory
reviewed the interrelationships of mammals and placed edentates among other placentals, though he gave "Paratheria" as an alternative name for his superorder Edentata, which included Xenarthra and tentatively Pholidota (pangolins), Tubulidentata (aardvarks), and the fossil Taeniodonta. In 1976, Eli Minkoff also used "Paratheria" for a placental superorder that included Edentata (i.e., Xenarthra) and Pholidota.
The Paratheria hypothesis enjoyed a brief renaissance when unusual, high-crowned teeth began turning up in the Cretaceous
and Paleocene
fossil record of Argentina. In 1984, Sudamerica ameghinoi, from the Paleocene of Argentina, was assigned to Xenarthra within a cohort Paratheria, Two years later, José Bonaparte
named Gondwanatherium patagonicum from the Late Cretaceous
of Argentina, which he thought to be related to Sudamerica, and tentatively assigned it to the infraclass Paratheria. Bonaparte described an additional related animal, Vucetichia gracilis, from the Argentinean Late Cretaceous in 1990; by then he classified it in an order Gondwanatheria
tentatively assigned to the infraclass Paratheria. Bonaparte argued against George Gaylord Simpson
's 1931 view that xenarthrans derive from the Tertiary Palaeanodonta of North America, and instead suggested that xenarthrans, and perhaps pangolins, split from eutherians as early as the Early Cretaceous
and derived from some early "pantothere
" mammal.
However, Bonaparte himself had abandoned the proposed relationship between xenarthrans and gondwanatherians by 1993. Instead, gondwanatherians were shown to be related to another Late Cretaceous Argentinean animal, Ferugliotherium
(which turned out to be undistinguishable from Vucetichia), and through it to multituberculates. The relation between multituberculates and gondwanatheres later became controversial, but they are no longer thought to be related to xenarthrans. By 1996, "few if any systematists would ... doubt the eutherian affinities of xenarthrans" and molecular data have also supported the placements of Xenarthra within placentals as one of four major clades.
Xenarthra
The superorder Xenarthra is a group of placental mammals , existent today only in the Americas and represented by anteaters, tree sloths, and armadillos. The origins of the order can be traced back as far as the Paleogene in South America...
n mammals. It was proposed by Oldfield Thomas
Oldfield Thomas
Oldfield Thomas FRS was a British zoologist.Thomas worked at the Natural History Museum on mammals, describing about 2,000 new species and sub-species for the first time. He was appointed to the Museum Secretary's office in 1876, transferring to the Zoological Department in 1878...
in 1887 to set apart the sloth
Sloth
Sloths are the six species of medium-sized mammals belonging to the families Megalonychidae and Bradypodidae , part of the order Pilosa and therefore related to armadillos and anteaters, which sport a similar set of specialized claws.They are arboreal residents of the jungles of Central and South...
s, anteater
Anteater
Anteaters, also known as antbear, are the four mammal species of the suborder Vermilingua commonly known for eating ants and termites. Together with the sloths, they compose the order Pilosa...
s, armadillo
Armadillo
Armadillos are New World placental mammals, known for having a leathery armor shell. Dasypodidae is the only surviving family in the order Cingulata, part of the superorder Xenarthra along with the anteaters and sloths. The word armadillo is Spanish for "little armored one"...
s, and pangolin
Pangolin
A pangolin , also scaly anteater or Trenggiling, is a mammal of the order Pholidota. There is only one extant family and one genus of pangolins, comprising eight species. There are also a number of extinct taxa. Pangolins have large keratin scales covering their skin and are the only mammals with...
s, usually classified as placentals, from both marsupial and placental mammals, an arrangement that received little support from other workers. When Gondwanatheria
Gondwanatheria
Gondwanatheria is an extinct group of mammals that lived during the Upper Cretaceous through the Eocene in the Southern Hemisphere, including Antarctica...
were first discovered in Argentina the 1980s, they were thought to be related to xenarthrans, leading to renewed attention to the hypothesis that xenarthrans are not placentals. However, by the early 1990s, gondwanatheres were shown to be unrelated to xenarthrans, and xenarthrans are still considered placentals.
The term was coined by British mammalogist Oldfield Thomas
Oldfield Thomas
Oldfield Thomas FRS was a British zoologist.Thomas worked at the Natural History Museum on mammals, describing about 2,000 new species and sub-species for the first time. He was appointed to the Museum Secretary's office in 1876, transferring to the Zoological Department in 1878...
in 1887 in a review of tooth development
Tooth development
Tooth development or odontogenesis is the complex process by which teeth form from embryonic cells, grow, and erupt into the mouth. Although many diverse species have teeth, non-human tooth development is largely the same as in humans...
in mammals. He found that the "Edentata"—a group in which he included the anteater
Anteater
Anteaters, also known as antbear, are the four mammal species of the suborder Vermilingua commonly known for eating ants and termites. Together with the sloths, they compose the order Pilosa...
s, armadillo
Armadillo
Armadillos are New World placental mammals, known for having a leathery armor shell. Dasypodidae is the only surviving family in the order Cingulata, part of the superorder Xenarthra along with the anteaters and sloths. The word armadillo is Spanish for "little armored one"...
s, and sloth
Sloth
Sloths are the six species of medium-sized mammals belonging to the families Megalonychidae and Bradypodidae , part of the order Pilosa and therefore related to armadillos and anteaters, which sport a similar set of specialized claws.They are arboreal residents of the jungles of Central and South...
s that are still included in Xenarthra
Xenarthra
The superorder Xenarthra is a group of placental mammals , existent today only in the Americas and represented by anteaters, tree sloths, and armadillos. The origins of the order can be traced back as far as the Paleogene in South America...
as well as the pangolin
Pangolin
A pangolin , also scaly anteater or Trenggiling, is a mammal of the order Pholidota. There is only one extant family and one genus of pangolins, comprising eight species. There are also a number of extinct taxa. Pangolins have large keratin scales covering their skin and are the only mammals with...
s and the aardvark
Aardvark
The aardvark is a medium-sized, burrowing, nocturnal mammal native to Africa...
—were especially distinctive. He derived edentate teeth from the first stage in his model of mammalian dental evolution, and consequently suggested that they should be given a grouping separate from the other major groupings of mammals, for which terms had been introduced by Thomas Huxley
Thomas Huxley
Thomas Henry Huxley PC FRS was an English biologist, known as "Darwin's Bulldog" for his advocacy of Charles Darwin's theory of evolution....
: Eutheria
Eutheria
Eutheria is a group of mammals consisting of placental mammals plus all extinct mammals that are more closely related to living placentals than to living marsupials . They are distinguished from noneutherians by various features of the feet, ankles, jaws and teeth...
(placentals) and Metatheria
Metatheria
Metatheria is a grouping within the animal class Mammalia. First proposed by Thomas Henry Huxley in 1880, it is nearly synonymous with the earlier taxon Marsupialia though it is slightly wider since it also contains the nearest fossil relatives of marsupial mammals.The earliest known...
(marsupials). For this grouping, he suggested the name Paratheria "to indicate their position by the side
of, but separate from, the other Mammals" (the Greek παρά para means "beside"). Thomas was unable, however, to provide a satisfactory scenario for the origin of the aardvark's wholly unique dentition, which he could only compare with the teeth of a fish. Thomas's arrangement was foreshadowed by Henri Marie Ducrotay de Blainville
Henri Marie Ducrotay de Blainville
Henri Marie Ducrotay de Blainville was a French zoologist and anatomist.Blainville was born at Arques, near Dieppe. In about 1796 he went to Paris to study painting, but he ultimately devoted himself to natural history, and attracted the attention of Georges Cuvier, for whom he occasionally...
's 1839 classification; he placed edentates (except the sloth Bradypus, which he considered to be a primate) as a major division, the Maldentés ("poorly toothed"), distinct from the other monodelphes (placentals), the Bien dentés ("well-toothed").
Thomas's hypothesis received little support, or even attention, in subsequent years. In 1893, Henry Fairfield Osborn
Henry Fairfield Osborn
Henry Fairfield Osborn, Sr. ForMemRS was an American geologist, paleontologist, and eugenicist.-Early life and career:...
remarked that new studies of edentate teeth indicated that they were not as distinct as Thomas thought. William Berryman Scott
William Berryman Scott
William Berryman Scott was an American vertebrate paleontologist, authority on mammals, and principal author of the White River Oligocene monographs. He was a professor of geology and paleontology at Princeton University....
did, however, place Paratheria as a separate subclass in 1904, although he apparently did not follow Thomas's theories about the origins of edentate teeth. In 1910, William King Gregory
William King Gregory
William King Gregory was an American zoologist, renowned as a primatologist, paleontologist, and functional and comparative morphologist. He was an expert on mammalian dentition, and a leading contributor to theories of evolution...
reviewed the interrelationships of mammals and placed edentates among other placentals, though he gave "Paratheria" as an alternative name for his superorder Edentata, which included Xenarthra and tentatively Pholidota (pangolins), Tubulidentata (aardvarks), and the fossil Taeniodonta. In 1976, Eli Minkoff also used "Paratheria" for a placental superorder that included Edentata (i.e., Xenarthra) and Pholidota.
The Paratheria hypothesis enjoyed a brief renaissance when unusual, high-crowned teeth began turning up in the Cretaceous
Cretaceous
The Cretaceous , derived from the Latin "creta" , usually abbreviated K for its German translation Kreide , is a geologic period and system from circa to million years ago. In the geologic timescale, the Cretaceous follows the Jurassic period and is followed by the Paleogene period of the...
and Paleocene
Paleocene
The Paleocene or Palaeocene, the "early recent", is a geologic epoch that lasted from about . It is the first epoch of the Palaeogene Period in the modern Cenozoic Era...
fossil record of Argentina. In 1984, Sudamerica ameghinoi, from the Paleocene of Argentina, was assigned to Xenarthra within a cohort Paratheria, Two years later, José Bonaparte
José Bonaparte
José Fernando Bonaparte, Ph.D. , is an Argentine paleontologist who discovered a plethora of South American dinosaurs and mentored a new generation of Argentine paleontologists like Rodolfo Coria...
named Gondwanatherium patagonicum from the Late Cretaceous
Late Cretaceous
The Late Cretaceous is the younger of two epochs into which the Cretaceous period is divided in the geologic timescale. Rock strata from this epoch form the Upper Cretaceous series...
of Argentina, which he thought to be related to Sudamerica, and tentatively assigned it to the infraclass Paratheria. Bonaparte described an additional related animal, Vucetichia gracilis, from the Argentinean Late Cretaceous in 1990; by then he classified it in an order Gondwanatheria
Gondwanatheria
Gondwanatheria is an extinct group of mammals that lived during the Upper Cretaceous through the Eocene in the Southern Hemisphere, including Antarctica...
tentatively assigned to the infraclass Paratheria. Bonaparte argued against George Gaylord Simpson
George Gaylord Simpson
George Gaylord Simpson was an American paleontologist. Simpson was perhaps the most influential paleontologist of the twentieth century, and a major participant in the modern evolutionary synthesis, contributing Tempo and mode in evolution , The meaning of evolution and The major features of...
's 1931 view that xenarthrans derive from the Tertiary Palaeanodonta of North America, and instead suggested that xenarthrans, and perhaps pangolins, split from eutherians as early as the Early Cretaceous
Early Cretaceous
The Early Cretaceous or the Lower Cretaceous , is the earlier or lower of the two major divisions of the Cretaceous...
and derived from some early "pantothere
Pantotheria
Pantotheria is an abandoned taxon of Mesozoic mammals. This group is now considered an informal "wastebasket" taxon and has been replaced by Dryolestida as well as other groups...
" mammal.
However, Bonaparte himself had abandoned the proposed relationship between xenarthrans and gondwanatherians by 1993. Instead, gondwanatherians were shown to be related to another Late Cretaceous Argentinean animal, Ferugliotherium
Ferugliotherium
Ferugliotherium is a fossil mammal from the Campanian and/or Maastrichtian of Argentina in the family Ferugliotheriidae. The genus contains a single species, Ferugliotherium windhauseni, which was first described in 1986...
(which turned out to be undistinguishable from Vucetichia), and through it to multituberculates. The relation between multituberculates and gondwanatheres later became controversial, but they are no longer thought to be related to xenarthrans. By 1996, "few if any systematists would ... doubt the eutherian affinities of xenarthrans" and molecular data have also supported the placements of Xenarthra within placentals as one of four major clades.