Phenacodontidae is an extinct

family Family (from ) is a Social group, group of people related either by consanguinity (by recognized birth) or Affinity (law), affinity (by marriage or other relationship). It forms the basis for social order. Ideally, families offer predictabili ...

of large herbivorous

mammal A mammal () is a vertebrate animal of the Class (biology), class Mammalia (). Mammals are characterised by the presence of milk-producing mammary glands for feeding their young, a broad neocortex region of the brain, fur or hair, and three ...

s traditionally placed in the “

wastebasket taxon Wastebasket taxon (also called a wastebin taxon, dustbin taxon or catch-all taxon) is a term used by some taxonomists to refer to a taxon that has the purpose of classifying organisms that do not fit anywhere else. They are typically defined by e ...

”

Condylarthra 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 wast ...

, which may instead represent early-stage perissodactyls. They lived from the late early

Paleocene The Paleocene ( ), or Palaeocene, is a geological epoch (geology), epoch that lasted from about 66 to 56 mya (unit), million years ago (mya). It is the first epoch of the Paleogene Period (geology), Period in the modern Cenozoic Era (geology), ...

to early middle

Eocene The Eocene ( ) is a geological epoch (geology), epoch that lasted from about 56 to 33.9 million years ago (Ma). It is the second epoch of the Paleogene Period (geology), Period in the modern Cenozoic Era (geology), Era. The name ''Eocene'' comes ...

(about 60–50 million years ago) and their fossil remains have been found in North America and Europe. The only unequivocal Asian phenacodontid is '' Lophocion asiaticus''.

Description

These animals had a variety of body sizes, and could be as small as domestic cats (''

Tetraclaenodon ''Tetraclaenodon'' was a genus of small and early ungulate mammals that was part of the Phenacodontidae family. It is the oldest and most primitive phenacodontid. Its fossils known from the Nacimiento Formation, New Mexico New Mexico ...

'' and ''

Ectocion ''Ectocion'' (sometimes ''Ectocyon'') is an extinct genus of placental mammals of the family Phenacodontidae. The genus was earlier classified as ''Gidleyina'' (Simpson 1935) and ''Prosthecion'' (Patterson and West 1973). Retrieved May 2013. It r ...

'') and as large as sheep (''

Phenacodus ''Phenacodus'' (Greek: "deception" (phenax), "tooth' (odus)) is an extinct genus of mammals from the late Paleocene through middle Eocene, about 55 million years ago. It is one of the earliest and most primitive of the ungulates, typifying the fa ...

''). The skull of phenacodontids is long and narrow, and equipped with a small braincase. The skeleton of phenacodontids show several primitive characteristics (the long and heavy tail for example) but also a number of advanced, Perissodactyla-like adaptations: Their long legs, for example, had five fingers, but the first finger showed a clear reduction, and in some forms (like ''Phenacodus'') the fifth finger was reduced as well. Some species had tapir-like adaptations suggestive of the presence of a short proboscis or a strong prehensile lip. The teeth of phenacodontids, particularly in the latter forms, were quite specialized: The molars and premolars were equipped with low cusps that sometimes joined in ridges, similar to the condition found in some perissodactyls. Some forms, like '' Meniscotherium'', had enlarged ridges. This adaptation is unusual for mammals as old as phenacodontids. Only a few other archaic mammals possessed teeth with similar structures, such as ''

Pleuraspidotherium ''Pleuraspidotherium'' is an extinct genus of condylarth of the family Pleuraspidotheriidae, whose fossils have been found in the Late Paleocene Marnes de Montchenot of France and the Tremp Formation of modern Spain Spain, or the Kingdom ...

''.

Evolution

The phenacodontids evolved in the middle Paleocene in North America. Early forms were usually small; ''

'', for example, was the size of a fox. Later forms were much larger and invaded Europe, although they never became as plentiful as in North America. Towards the beginning of the Eocene these animals slowly disappeared from the fossil record. Only a few forms survived into the middle Eocene: the ''

'' in Europe and North America, ''

Almogaver ''Almogaver'' is an extinct possible odd-toed ungulate genus in the family Phenacodontidae. It was a ground-dwelling herbivore. It is known from the Tremp Basin in Spain Spain, or the Kingdom of Spain, is a country in Southern Europe, Sou ...

'' in Europe and ''

'' in North America. An exception to the scarcity of Eocene phenacodontids is the dog-sized genus '' Meniscotherium'', whose fossils are very abundant.

Classification

Phenacodontids have classically been included in the large group

, now considered

polyphyletic A polyphyletic group is an assemblage that includes organisms with mixed evolutionary origin but does not include their most recent common ancestor. The term is often applied to groups that share similar features known as Homoplasy, homoplasies ...

. In particular, the genus ''Phenacodus'' is often illustrated as a typical example of a "condylarth", due to the remarkable abundance of fossil remains. Ectocion ralstonensis Granger 1

* Subfamily Phenacodontinae Cope, 1881 ** Genus ''

'' Scott, 1893 ***''Tetraclaenodon floverianus'' Cope, 1890 ***''Tetraclaenodon puercensis'' (Cope, 1881) ***''Tetraclaenodon septentrionalis'' Thewissen, 1990 ** Genus ''

Copecion ''Copecion'' was a genus of early herbivorous mammals that was part of the family Phenacodontidae. It reached 6 to 12 kg and was similar in size and morphology to ''Ectocion''. Both these herbivorous ungulates likely occupied similar ecological ni ...

'' Gingerich, 1989 ***''Copecion brachypternus'' (Cope, 1882) ***''Copecion davisi'' Gingerich, 1989 ** Genus ''

'' Cope, 1882 ***''Ectocion cedrus'' Thewissen, 1990 ***''Ectocion collinus'' Russell, 1929 ***''Ectocion ignotum'' Novacek et al., 1991 ***''Ectocion major'' (Patteron & West, 1973) ***''Ectocion mediotuber'' Thewissen, 1990 ***''Ectocion osbornianus'' (Cope, 1882) ***''Ectocion parvus'' Granger, 1915 ***''Ectocion superstes'' Granger, 1915 ** Genus ''

'' Cope, 1873 ***''Phenacodus bisonensis'' Gazin, 1956 ***''Phenacodus condali'' (Crusafont i Villalta, 1955) ***''Phenacodus grangeri'' Simpson, 1935 ***''Phenacodus intermedius'' Granger, 1915 ***''Phenacodus lemoinei'' Thewissen, 1990 ***''Phenacodus magnus'' Thewissen, 1990 ***''Phenacodus matthewi'' Simpson, 1835 ***''Phenacodus primaevus'' Cope, 1873 ***''Phenacodus teilhardi'' Simpson, 1929 ***''Phenacodus trilobatus'' Cope, 1882 ***''Phenacodus vortmani'' (Cope, 1880) ** Genus '' Lophocion'' Wang and Tong 1997 ***''Lophocion asiaticus'' Wang and Tong 1997 ***''Lophocion grangeri'' Bai et al. 2019 * Subfamiliy Meniscotheriinae Cope, 1882 ** Genus '' Meniscotherium'' Cope, 1874 ***''Meniscotherium chamense'' Cope, 1874 ***''Meniscotherium tapiacitum'' Cope, 1882 ** Genus ''

Orthaspidotherium ''Orthaspidotherium'' was a European Paleocene genus of early herbivorous mammals of the family Pleuraspidotheriidae. It was included in the family Meniscotheriidae by Teilhard de Chardin in 1921-1922 and was subsequently separated into the famil ...

'' Lemoine, 1878 ***''Orthaspidotherium edwardsi'' Lemoine, 1878 Some

phylogenetic In biology, phylogenetics () is the study of the evolutionary history of life using observable characteristics of organisms (or genes), which is known as phylogenetic inference. It infers the relationship among organisms based on empirical dat ...

analyses have revealed effective relationships between the various groups of "condylarths". One phylogeny suggests there may be close correlations between a

clade In biology, a clade (), also known as a Monophyly, monophyletic group or natural group, is a group of organisms that is composed of a common ancestor and all of its descendants. Clades are the fundamental unit of cladistics, a modern approach t ...

containing

proboscidea Proboscidea (; , ) is a taxonomic order of afrotherian mammals containing one living family (Elephantidae) and several extinct families. First described by J. Illiger in 1811, it encompasses the elephants and their close relatives. Three l ...

ns, hyracoids, perissodactyls and phenacodontids and another clade with ''

Microhyus ''Microhyus'' is a genus of true weevils in the beetle family Curculionidae The Curculionidae are a family of weevils, commonly called snout beetles or true weevils. They are one of the largest animal families with 6,800 genera and 83,000 spec ...

'' and the macroscelids.Tabuce, R., Coiffait, B., Coiffait, P.E., Mahboubi, M. & Jaeger, J.J. "2001" A new genus of Macroscelidea (Mammalia) from the Eocene of Algeria: a possible origin for elephant-shrews." ''Journal of Vertebrate Paleontology'' 21, 535-546. The clade including these forms would be analogous to the clade Taxeopoda, proposed in 1998.Archibald, DJ; 1998 "Carnivores, Ungulates, and Ungulatelike Mammals." ''Cambridge University Press'', pp. 292-331. According to more recent views, instead of a

monophyletic In biological cladistics for the classification of organisms, monophyly is the condition of a taxonomic grouping being a clade – that is, a grouping of organisms which meets these criteria: # the grouping contains its own most recent co ...

, the condylarths are better understood as an

evolutionary grade A grade is a taxon united by a level of morphological or physiological complexity. The term was coined by British biologist Julian Huxley, to contrast with clade, a strictly phylogenetic unit. Phylogenetics The concept of evolutionary grades ...

that lead to the true

ungulate Ungulates ( ) are members of the diverse clade Euungulata ("true ungulates"), which primarily consists of large mammals with Hoof, hooves. Once part of the clade "Ungulata" along with the clade Paenungulata, "Ungulata" has since been determined ...

Phylogenetic analysis In biology, phylogenetics () is the study of the evolutionary history of life using observable characteristics of organisms (or genes), which is known as phylogenetic inference. It infers the relationship among organisms based on empirical data ...

of 2012 recover phenacodontids as a series of sister taxa to the

Altungulata Altungulata or Pantomesaxonia ('' sensu'' and later authors) is an invalid clade ( mirorder) of ungulate mammals comprising the perissodactyls, hyracoids, and tethytheres ( sirenians, proboscideans, and related extinct taxa). The name "Pant ...

clade. Later phylogenetic studies confirm that phenacodonts were most closely related to modern

odd-toed ungulate Perissodactyla (, ), or odd-toed ungulates, is an order of ungulates. The order includes about 17 living species divided into three families: Equidae (horses, asses, and zebras), Rhinocerotidae (rhinoceroses), and Tapiridae (tapirs). They t ...

Paleobiology

The specialized teeth found in at least some phenacodontids seem to indicate a primary

herbivorous A herbivore is an animal anatomically and physiologically evolved to feed on plants, especially upon vascular tissues such as foliage, fruits or seeds, as the main component of its diet. These more broadly also encompass animals that eat n ...

lifestyle. The shape of the legs indicated that some phenacodontids (like ''Phenacodus'') were swift runners.

Notes

References

* * * * * *

External links

* {{Authority control Condylarths Panperissodactyla Paleocene mammals Eocene mammals Paleocene first appearances Eocene extinctions Prehistoric mammal families