Phenacodontidae is an extinct

family Family (from la, familia) is a group of people related either by consanguinity (by recognized birth) or affinity (by marriage or other relationship). The purpose of the family is to maintain the well-being of its members and of society. Idea ...

of large herbivorous

mammal Mammals () are a group of vertebrate animals constituting the class Mammalia (), characterized by the presence of mammary glands which in females produce milk for feeding (nursing) their young, a neocortex (a region of the brain), fur ...

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 sole purpose of classifying organisms that do not fit anywhere else. They are typically defined ...

”

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. It is now largely considered to be a wast ...

, which may instead represent early-stage perissodactyls. They lived in the Paleocene and Eocene epochs (about 60–50 million years ago) and their fossil remains have been found in North America and Europe.

Description

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

'') and as large as sheep ('' Phenacodus''). 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 , image_flag ...

''.

Evolution

The phenacodontids evolved in the middle Paleocene in North America. Early forms were usually small; '' Tetraclaenodon'', 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 '' Phenacodus'' in Europe and North America, '' Almogaver'' 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 of organisms or other evolving elements that is of mixed evolutionary origin. The term is often applied to groups that share similar features known as homoplasies, which are explained as a result of conver ...

. 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 '' Tetraclaenodon'' Scott, 1893 ***''Tetraclaenodon floverianus'' Cope, 1890 ***''Tetraclaenodon puercensis'' (Cope, 1881) ***''Tetraclaenodon septentrionalis'' Thewissen, 1990 ** Genus '' Copecion'' 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 '' Phenacodus'' 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'' Lemoine, 1878 ***''Orthaspidotherium edwardsi'' Lemoine, 1878 Some

phylogenetic In biology, phylogenetics (; from Greek φυλή/ φῦλον [] "tribe, clan, race", and wikt:γενετικός, γενετικός [] "origin, source, birth") is the study of the evolutionary history and relationships among or within groups ...

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

clade A clade (), also known as a monophyletic group or natural group, is a group of organisms that are monophyletic – that is, composed of a common ancestor and all its lineal descendants – on a phylogenetic tree. Rather than the English ter ...

containing

proboscidea The Proboscidea (; , ) are 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. Fr ...

ns,

hyracoids Hyraxes (), also called dassies, are small, thickset, herbivorous mammals in the order Hyracoidea. Hyraxes are well-furred, rotund animals with short tails. Typically, they measure between long and weigh between . They are superficially simila ...

, 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 spe ...

'' and the macroscelidsTaxeopoda, proposed in 1998.monophyletic In cladistics for a group of organisms, monophyly is the condition of being a clade—that is, a group of taxa composed only of a common ancestor (or more precisely an ancestral population) and all of its lineal descendants. Monophyletic gr ...

Description

Evolution

Classification

Paleobiology

See also

Notes

References