Condylarth

Condylarths Temporal range: Late Cretaceous - Oligocene, 65.5–23Ma PreЄ Є O S D C P T J K Pg N
Arctocyon, a plantigrade condylarth
Scientific classification
Kingdom:	Animalia
Phylum:	Chordata
Class:	Mammalia
Infraclass:	Eutheria
Superorder:	Laurasiatheria?
Order:	†Condylarthra Cope 1881
Families
†Arctocyonidae †Periptychidae †Hyopsodontidae †Meniscotheriidae †Mioclaenidae †Phenacodontidae †Didolodontidae †Sparnotheriodontidae?

Condylarthra is an order of extinct placental mammals known primarily from the Paleocene and Eocene epochs. Condylarths are among the most characteristic Paleocene mammals and they illustrate the evolutionary level of the Paleocene mammal fauna.

When compared to today's mammals, condylarths are relatively unspecialized placental mammals. However, in comparison to their insectivorous ancestors, members of the Condylarthra show the first signs of specializing to become omnivores or even herbivores.

Evolutionary history

Ectocion, small plant-eating condylarths found in Wyoming

Since larger land-bound herbivores were absent following the extinction of the dinosaurs, the shift in diet from insectivorous to more herbivorous trophic categories triggered 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.

Here, the term Ungulata refers to a subgroup of placental mammals that are descendants of a common ancestor (i.e. homologous to), the most primitive condylarth. 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 hoofs, this feature does not define the Ungulata. Indeed, some condylarths had small hoofs 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. This raises the possibility that Condylarthra itself is polyphyletic: the several condylarth groups may not be closely related to each other at all. Indeed, condylarths are increasingly regarded as a 'wastebasket' taxon, though 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.

Condylarthra always was a problematic group; both paraphyletic and polyphyletic. When Condylarthra was first described by Cope 1881, Phenacodontidae was the type and only family therein. Cope 1885, however, raised Condylarthra to an order and included a wide range of diverse placentals with generalized dentitions and postcrania. 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.

Prothero, Manning & Fischer 1988 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
• head of astragalus is short and robust

Taxonomy

• Family Arctocyonidae
  • Genus Arctocyon
  • Genus Chriacus
• Family Periptychidae
  • Genus Ectoconus
  • Genus Oxyacodon
• Family Hyopsodontidae
  • 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
  • Subfamily Meniscotheriinae
    • Genus Ectocion
    • Genus Meniscotherium
    • Genus Orthaspidotherium
    • Genus Pleuraspidotherium
  • Genus Almogaver
  • Genus Copecion
  • Genus Eodesmatodon
  • Genus Phenacodus
• Family Didolodontidae
• Family Sparnotheriodontidae?
• Genus Tingamarra?
• Genus Protungulatum
• Genus Kharmerungulatum

See also

• Evolution of mammals
• List of prehistoric mammals

References

• Cope, E. D. (1881). "A new type of Perissodactyla". American Naturalist 15: 1017–20. OCLC 45953517. 
• Cope, E. D. (1885). "The Vertebrata of the Tertiary Formations of the West". U. S. Geological Survey of the Territories 3: 1–1009. OCLC 3934701. Retrieved April 2013. 
• Janis, C.M. (1993). "Tertiary Mammal Evolution in the Context of Changing Climates, Vegetation, and Tectonic Events". Annual Review of Ecology and Systematics 24: 467–500. doi:10.1146/annurev.es.24.110193.002343. 
• Madsen, O.; Scally, M.; Douady, C.J.; Kao, D.; DeBry, R.W.; Adkins, R.; Amrine, H.M.; Stanhope, M.J.; de Jong, W.W.; Springer, M.S. (2001). "Parallel adaptive radiations in two major clades of placental mammals". Nature 409 (6820): 610–614. doi:10.1038/35054544. PMID 11214318. 
• McKenna, M.C.; Bell, S.K. (1997). Classification of Mammals Above the Species Level. Columbia University Press. ISBN 0-231-11012-X. 
• Murphy, W.J.; Eizirik, E.; O'Brien, S.J.; Madsen, O.; Scally, M.; Douady, C.J.; Teeling, E.C.; Ryder, O.A.; Stanhope, M.J.; de Jong, W.W.; Springer, M.S. (2001). "Resolution of the early placental mammal radiation using Bayesian phylogenetics". Science 294 (5550): 2348–2351. doi:10.1126/science.1067179. PMID 11743200. 
• Novacek, M.J. (1986). "The skull of leptictid insectivorans and the higher-level classification of eutherian mammals". Bulletin of the American Museum of Natural History 183 (1): 1–111. hdl:2246/1628. 
• Prothero, D.R.; Manning, E.M.; Fischer, M. (1988). "The phylogeny of the ungulates". In Benton, M. J. The phylogeny and classification of the tetrapods. 2: mammals. Systematics Association Special Volume 35B. Oxford: Clarendon Press. pp. 201–234. ISBN 9780198577126. Retrieved May 2013. 
• Thewissen, J.G.M. (1990). Evolution of Paleocene and Eocene Phenacodontidae (Mammalia, Condylarthra). Papers on Paleontology 29. Museum of Paleontology, The University of Michigan. OCLC 742731818. 
• Van Valen, L.M. (1966). "Deltatheridia, a new order of mammals". Bulletin of the American Museum of Natural History 132 (1): 1–126. hdl:2246/1126. 
• Van Valen, L.M. (1988). "Paleocene dinosaurs or Cretaceous ungulates in South America?". Evolutionary Monographs 10: 1–79.