Condylarth

Condylarthra is an informal group – previously considered an order – of extinct placental mammals, known primarily from the Paleocene and Eocene epochs.[1] 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.[2][3][4]

Taxonomic history

Condylarthra always was a problematic group. 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 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.[5] 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.[6]

Prothero, Manning & Fischer 1988 delimited condylarths as those having the following characters, but lacking the specializations present in more derived orders:[5]

Evolutionary history
Ectocion, small plant-eating condylarths found in Wyoming

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.[1][7] 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,[8][9] 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.[4] 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[10] and Dinocerata.[11]

    Taxonomy
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    See also

    Notes
    1. McKenna & Bell 1997
    2. Naish, Darren (8 August 2013). "Phenacodontidae, I feel like I know you". Tetrapod Zoology. Scientific American. Archived from the original on 10 March 2014.
    3. Cooper, L. N.; Seiffert, E. R.; Clementz, M.; Madar, S. I.; Bajpai, S.; Hussain, S. T.; Thewissen, J. G. M. (2014-10-08). "Anthracobunids from the Middle Eocene of India and Pakistan Are Stem Perissodactyls". PLOS ONE. 9 (10): e109232. doi:10.1371/journal.pone.0109232. PMC 4189980. PMID 25295875.CS1 maint: ref=harv (link)
    4. Janis 1993
    5. Thewissen 1990, p. 20
    6. Rose, Kenneth D. (2006). "Archaic Ungulates". The beginning of the Age of Mammals. Baltimore: Johns Hopkins University Press. ISBN 9780801892219.
    7. Novacek 1986
    8. Madsen et al. 2001
    9. Murphy et al. 2001
    10. Van Valen 1966
    11. Van Valen 1988
    12. Smith, De Bast. "Reassessment of the Small ‘Arctocyonid’ Prolatidens waudruae from the Early Paleocene of Belgium, and Its Phylogenetic Relationships with Ungulate-Like Mammals". Journal of Vertebrate Paleontology. Retrieved August 2013
    13. Ravel, Anthony; Orliac, Maeva (2014). "The inner ear morphology of the 'condylarthran' Hyopsodus lepidus". Historical Biology. 27 (8): 8. doi:10.1080/08912963.2014.915823.
    14. Cooper, L. N.; Seiffert, E. R.; Clementz, M.; Madar, S. I.; Bajpai, S.; Hussain, S. T.; Thewissen, J. G. M. (2014). "Anthracobunids from the Middle Eocene of India and Pakistan Are Stem Perissodactyls". PLOS ONE. 9 (10): e109232. doi:10.1371/journal.pone.0109232. PMC 4189980. PMID 25295875.
    15. Archibald, J. David; Zhang, Yue; Harper, Tony; Cifelli, Richard L. (May 6, 2011). "Protungulatum, confirmed Cretaceous occurrence of an otherwise Paleocene eutherian (placental?) mammal" (PDF). Journal of Mammalian Evolution. 18 (3): 153–161. doi:10.1007/s10914-011-9162-1. Archived from the original (PDF) on March 3, 2016. Retrieved April 28, 2013.
    16. James 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

    References
    • Cope, E. D. (1881). "A new type of Perissodactyla". American Naturalist. 15 (12): 1017–20. doi:10.1086/272983. OCLC 45953517.CS1 maint: ref=harv (link)
    • Cope, E. D. (1885). "The Vertebrata of the Tertiary Formations of the West". U. S. Geological Survey of the Territories. 3 (9): 1–1009. doi:10.1017/s0016756800467208. OCLC 3934701. Retrieved April 2013. Check date values in: |accessdate= (help)CS1 maint: ref=harv (link)
    • 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.CS1 maint: ref=harv (link)
    • 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.CS1 maint: multiple names: authors list (link) CS1 maint: ref=harv (link)
    • McKenna, M.C.; Bell, S.K. (1997). Classification of Mammals Above the Species Level. Columbia University Press. ISBN 978-0-231-11012-9.CS1 maint: ref=harv (link)
    • 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.CS1 maint: multiple names: authors list (link) CS1 maint: ref=harv (link)
    • 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.CS1 maint: ref=harv (link)
    • Prothero, D.R.; Manning, E.M.; Fischer, M. (1988). "The phylogeny of the ungulates" (PDF). In Benton, M. J. (ed.). 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. Check date values in: |accessdate= (help)CS1 maint: ref=harv (link)
    • Thewissen, J.G.M. (1990). Evolution of Paleocene and Eocene Phenacodontidae (Mammalia, Condylarthra). Papers on Paleontology. 29. Museum of Paleontology, The University of Michigan. hdl:2027.42/48629. OCLC 742731818.CS1 maint: ref=harv (link)
    • 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.CS1 maint: ref=harv (link)
    • Van Valen, L.M. (1988). "Paleocene dinosaurs or Cretaceous ungulates in South America?". Evolutionary Monographs. 10: 1–79.CS1 maint: ref=harv (link)
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