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 wastebasket taxon, having served as a dumping ground for classifying ungulates which had not been clearly established as part of either Perissodactyla or Cetartiodactyla, being composed thus of several unrelated lineages.

Taxonomic history

Condylarthra always was a problematic group. When Condylarthra was first described by , Phenacodontidae was the type and only family therein. , however, raised Condylarthra to an order and included a wide range of diverse placentals with generalized dentitions and postcranial skeletons. More recent researchers (i.e. post-WW2) have been more restrictive; either including only a limited number of taxa, or proposing that the term should be abandoned altogether. Due to their primitive characteristics condylarths have been considered ancestral to several ungulate orders, including the living Artiodactyla, Cetacea, Perissodactyla, Hyracoidea, Sirenia, and Proboscidea, as well as the extinct Desmostylia, Embrithopoda, Litopterna, Notoungulata, and Astrapotheria.

delimited condylarths as those having the following characters, but lacking the specializations present in more derived orders:
* superior ramus of stapedial artery shifted to petrosal or lost
* mastoid foramen lost
* bulla if present composed of ectotympanic
* relatively bunodont teeth with low cusp relief
* trigonids of lower molars shortened anteroposteriorly
* large, posteriorly projecting hypoconulid on M₃ (lower third molar)
* head of astragalus is short and robust

Evolutionary history

The disappearance of the dinosaurs opened up an ecological niche for large mammalian herbivores. Some condylarths evolved to fill the niche, while others remained insectivorous. This may explain, in part, the tremendous evolutionary radiation of the condylarths that we can observe throughout the Paleocene, resulting in the different groups of ungulates (or " hoofed mammals") that form the dominant herbivores in most Cenozoic animal communities on land, except on the island continent of Australia.

Among recent mammals, Paenungulata ( hyraxes, elephants, and sea cows), Perissodactyla (horses, rhinoceroses, and tapirs), Artiodactyla ( pigs, deer, antelope, cows, camels, hippos, and their relatives), Cetacea (whales), and Tubulidentata ( aardvarks) are traditionally regarded as members of the Ungulata. Besides these, several extinct animals also belong to this group, especially the endemic South American orders of ungulates, ( Meridiungulata). Although many ungulates have hooves, this feature does not define the Ungulata. Indeed, some condylarths had small hooves on their feet, but the most primitive forms are clawed.

Recent molecular and DNA research has reorganised the picture of mammalian evolution. Paenungulates and tubulidentates are seen as afrotherians, and no longer seen as closely related to the laurasiatherian perissodactyls, artiodactyls, and cetaceans, implying that hooves were acquired independently (i.e. were analogous) by at least two different mammalian lineages, once in the Afrotheria and once in the Laurasiatheria. Condylarthra itself, therefore, is polyphyletic: the several condylarth groups are not closely related to each other at all. Indeed, Condylarthra is sometimes regarded as a 'wastebasket' taxon. True relationships remain in many cases unresolved.

In addition to meridiungulates and living ungulates, a condylarthran ancestry has been proposed for several other extinct groups of mammals, including Mesonychia and Dinocerata.

Taxonomy

*Family Arctocyonidae (possibly polyphyletic assemblage)
**Genus '' Arctocyon''
**Genus ''Chriacus''
*Family Periptychidae
**Genus ''Ectoconus''
**Genus '' Oxyacodon''
*Family Hyopsodontidae (now established as within Perissodactyla)
**Subfamily '' Tricuspiodontinae''
***Genus '' Litomylus''
***Genus '' Paratricuspiodon''
***Genus '' Tricuspiodon''
**Genus '' Aletodon''
**Genus '' Decoredon''
**Genus '' Dipavali''
**Genus '' Dorraletes''
**Genus '' Haplaletes''
**Genus '' Haplomylus''
**Genus '' Hyopsodus''
**Genus '' Louisina''
**Genus ''Microhyus''
**Genus '' Midiagnus''
**Genus '' Oxyprimus''
**Genus '' Palasiodon''
**Genus ''Paschatherium''
**Genus '' Utemylus''
**Genus '' Yuodon''
*Family Mioclaenidae
*Family Phenacodontidae (established as stem- Perissodactyla)
**Subfamily Meniscotheriinae
***Genus '' Ectocion''
***Genus '' Meniscotherium''
**Genus '' Almogaver''
**Genus '' Copecion''
**Genus ''Eodesmatodon''
**Genus '' Phenacodus''
*Family Pleuraspidotheriidae
**Genus '' Hilalia''
**Genus '' Orthaspidotherium''
**Genus '' Parabunodon''
**Genus ''Pleuraspidotherium''
*Family Didolodontidae (stem- Meridiungulata)
*Family Sparnotheriodontidae? ( Litopterna)
*Genus '' Tingamarra''? (non-descript therian mammal)
*Genus '' Protungulatum'' (either non-placental eutherian or basal artiodactyl).
*Genus ''Kharmerungulatum'' (a zhelestidJames David Archibald · Alexander Olegovich Averianov
Phylogenetic analysis, taxonomic revision, and dental ontogeny of the Cretaceous Zhelestidae (Mammalia: Eutheria)
Article · Feb 2012 · Zoological Journal of the Linnean Society)

See also

* Evolution of mammals
* List of prehistoric mammals

Notes

References

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External links

{{Authority control

Obsolete mammal taxa