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Triconodonta

(Infraclass)

Overview

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Triconodonta (also known as Eutriconodonta) is the generic name for a group of early mammals which were close relatives of the ancestors of all present-day mammals. Triconodonts lived between the Triassic and the Cretaceous. They are one of the groups that can be classified as mammals by any definition. Several other extinct groups of Mesozoic animals that are traditionally considered to be mammals (such as Morganucodonta and Docodonta) are now placed just outside Mammalia by those who advocate a 'crown-group' definition of the word "mammal".1]

Illustration of the lower jaw of Triconodon mordax, 1861

Their name, meaning "Three conical teeth", is based on one of their fundamental characteristics. They had the typical morphology of the proto-mammals: small, furry, tetrapod animals with long tails. They probably had a nocturnal lifestyle to avoid dinosaur predators, coming out from their burrows after dusk to hunt for small reptiles and insects[]. However, recent evidence from China suggests that some triconodonts such as Repenomamus were indeed able to take on small dinosaurs. [1].

Phylogeny

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Cladogram after Marisol Montellano, James A. Hopson, James M. Clark (2008)[2] and Thomas Martin & Alexander O. Averianov (2006) for Klameliidae.[3]

Cladogram after Kielan-Jaworowska, Cifelli & Luo (2004),[5] Gao et al. (2010)[6] and Thomas Martin & Alexander O. Averianov (2006) for Klameliidae.[3]

Averianov (2006). "A previously unrecognized group of Middle Jurassic triconodontan mammals from Central Asia". Naturwissenschaften 94 (1): 43?48. doi:10.1007/s00114-006-0155-5. PMID 17016686. http://www.springerlink.com/content/18ug5m3166268505/. 
  • ^ a b A. V. Lopatin, E. N. Maschenko and A. O. Averianov (2010). "A new genus of triconodont mammals from the Early Cretaceous of Western Siberia". Doklady Biological Sciences 433 (1): 282?285. doi:10.1134/S0012496610040137. http://www.springerlink.com/content/071870234w7x4664/. 
  • ^ Haaramo, Mikko: "Triconodonta". Mikko's Phylogeny Archive
  • ^ Chun-Ling Gao, Gregory P. Wilson, Zhe-Xi Luo, A. Murat Maga, Qingjin Meng and Xuri Wang (2010). "A new mammal skull from the Lower Cretaceous of China with implications for the evolution of obtuse-angled molars and 'amphilestid' eutriconodonts". Proceedings of the Royal Society B: Biological sciences 277 (1679): 237?246. doi:10.1098/rspb.2009.1014. PMC 2842676. PMID 19726475. http://rspb.royalsocietypublishing.org/content/277/1679/237.abstract. 
    • b>Triconodonta (also known as Eutriconodonta) is the generic name for a group of early mammals which were close relatives of the ancestors of all present-day mammals. Triconodonts lived between the Triassic and the Cretaceous. They are one of the groups that can be classified as mammals by any definition. Several other extinct groups of Mesozoic animals that are traditionally considered to be mammals (such as Morganucodonta and Docodonta) are now placed just outside Mammalia by those who advocate a 'crown-group' definition of the word "mammal".1]

    Illustration of the lower jaw of Triconodon mordax, 1861

    Their name, meaning "Three conical teeth", is based on one of their fundamental characteristics. They had the typical morphology of the proto-mammals: small, furry, tetrapod animals with long tails. They probably had a nocturnal lifestyle to avoid dinosaur predators, coming out from their burrows after dusk to hunt for small reptiles and insects[]. However, recent evidence from China suggests that some triconodonts such as Repenomamus were indeed able to take on small dinosaurs. [1].

    Phylogeny

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    Cladogram afte r Marisol Montellano, James A. Hopson, James M. Clark (2008)[2] and Thomas Martin & Alexander O. Averianov (2006) for Klameliidae.[3]

    Cladogram after Kielan-Jaworowska, Cifelli & Luo (2004),[5] Gao et al. (2010)[6] and Thomas Martin & Alexander O. Averianov (2006) for Klameliidae.[3]

    Averianov (2006). "A previously unrecognized group of Middle Jurassic triconodontan mammals from Central Asia". Naturwissenschaften 94 (1): 43?48. doi:10.1007/s00114-006-0155-5. PMID 17016686. http://www.springerlink.com/content/18ug5m3166268505/. 
  • ^ a b A. V. Lopatin, E. N. Maschenko and A. O. Averianov (2010). "A new genus of triconodont mammals from the Early Cretaceous of Western Siberia". Doklady Biological Sciences 433 (1): 282?285. doi:10.1134/S0012496610040137. http://www.springerlink.com/content/071870234w7x4664/. 
  • ^ Haaramo, Mikko: "Triconodonta". Mikko's Phylogeny Archive
  • ^ Chun-Ling Gao, Gregory P. Wilson, Zhe-Xi Luo, A. Murat Maga, Qingjin Meng and Xuri Wang (2010). "A new mammal skull from the Lower Cretaceous of China with implications for the evolution of obtuse-angled molars and 'amphilestid' eutriconodonts". Proceedings of the Royal Society B: Biological sciences 277 (1679): 237?246. doi:10.1098/rspb.2009.1014. PMC 2842676. PMID 19726475. http://rspb.royalsocietypublishing.org/content/277/1679/237.abstract. 

    • References

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    Taxonomy

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    The Infraclass Triconodonta is a member of the Subclass Theriiformes. Here is the complete "parentage" of Triconodonta:

    • Domain: Eukaryota Whittaker & Margulis,1978 - eukaryotes
      • Kingdom: Animalia C. Linnaeus, 1758 - animals
        • Subkingdom: Bilateria (Hatschek, 1888) Cavalier-Smith, 1983 - bilaterians
          • Branch: Deuterostomia Grobben, 1908 - Deuterostomes
            • Infrakingdom: Chordonia (Haeckel, 1874) Cavalier-Smith, 1998
              • Phylum: Chordata Bateson, 1885 - Chordates

    The Infraclass Triconodonta is further organized into finer groupings including:

    Orders

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    Therapsida

    Therapsida is a group of the most advanced synapsids, and include the ancestors of mammals. Many of the traits today seen as unique to mammals had their origin within early therapsids, including hair, lactation, and an erect posture. The earliest fossil attributed to Therapsida is believed to be Tetraceratops insignis (Lower Permian). Therapsids evolved from 'pelycosaurs' (specifically sphenacodonts) 275 million years ago. They replaced the pelycosaurs as the dominant large land animals in the Middle Permian. They remained the dominant fauna until replaced by archosaurs and rhynchosaurs in the Middle Triassic although some therapsids, the kannemeyeriiforms for example, remained diverse in the Late Triassic. The therapsids included the cynodonts, the group that gave rise to mammals in the Late Triassic around 225 million years ago. Of the non-mammalian therapsids, only cynodonts and dicynodonts survived the Triassic?Jurassic extinction event. The last of the non-mammalian therapsids, the cynodont tritylodontids, became extinct in the Early Cretaceous, approximately 100 million years ago. [more]

    At least 1,057 species and subspecies belong to the Order Therapsida.

    More info about the Order Therapsida may be found here.

    References

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    Footnotes

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    Triconodonta (also known as Eutriconodonta) is the generic name for a group of early mammals which were close relatives of the ancestors of all present-day mammals. Triconodonts lived between the Triassic and the Cretaceous. They are one of the groups that can be classified as mammals by any definition. Several other extinct groups of Mesozoic animals that are traditionally considered to be mammals (such as Morganucodonta and Docodonta) are now placed just outside Mammalia by those who advocate a 'crown-group' definition of the word "mammal".1]

    Illustration of the lower jaw of Triconodon mordax, 1861

    Their name, meaning "Three conical teeth", is based on one of their fundamenta l characteristics. They had the typical morphology of the proto-mammals: small, furry, tetrapod animals with long tails. They probably had a nocturnal lifestyle to avoid dinosaur predators, coming out from their burrows after dusk to hunt for small reptiles and insects[]. However, recent evidence from China suggests that some triconodonts such as Repenomamus were indeed able to take on small dinosaurs. [1].

    Phylogeny

    [ Back to top ]

    Cladogram after Marisol Montellano, James A. Hopson, James M. Clark (2008)[2] and Thomas Martin & Alexander O. Averianov (2006) for Klameliidae.[3]

    Cladogram after Kielan-Jaworowska, Cifelli & Luo (2004),[5] Gao et al. (2010)[6] and Thomas Martin & Alexander O. Averianov (2006) for Klameliidae.[3]

    Averianov (2006). "A previously unrecognized group of Middle Jurassic triconodontan mammals from Central Asia". Naturwissenschaften 94 (1): 43?48. doi:10.1007/s00114-006-0155-5. PMID 17016686. http://www.springerlink.com/content/18ug5m3166268505/. 
  • ^ a b A. V. Lopatin, E. N. Maschenko and A. O. Averianov (2010). "A new genus of triconodont mammals from the Early Cretaceous of Western Siberia". Doklady Biological Sciences 433 (1): 282?285. doi:10.1134/S0012496610040137. http://www.springerlink.com/content/071870234w7x4664/. 
  • ^ Haaramo, Mikko: "Triconodonta". Mikko's Phylogeny Archive
  • ^ Chun-Ling Gao, Gregory P. Wilson , Zhe-Xi Luo, A. Murat Maga, Qingjin Meng and Xuri Wang (2010). "A new mammal skull from the Lower Cretaceous of China with implications for the evolution of obtuse-angled molars and 'amphilestid' eutriconodonts". Proceedings of the Royal Society B: Biological sciences 277 (1679): 237?246. doi:10.1098/rspb.2009.1014. PMC 2842676. PMID 19726475. http://rspb.royalsocietypublishing.org/content/277/1679/237.abstract. 

    • Sources

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    • The text on this page is licensed under the GNU Free Documentation License. It includes material from Wikipedia retrieved Wednesday, April 25, 2012.
    • Photographs on this page are copyrighted by individual photographers, and individual copyrights apply.
    • The technology underlying this page, including the controls behind Keep Exploring, is owned by the BayScience Foundation. All rights are reserved.
    Last Revised: August 24, 2012
    2012/08/24 17:25:27