Article · Wikipedia archive · Last revised Jun 16, 2026

Splenial

The splenial is a small bone in the lower jaw of reptiles, amphibians and birds, usually located on the lingual side between the angular and surangular. The splenial and coronoid are together known as the paradental elements. In non-tetrapod vertebrates, the splenial is known as the first infradentary and forms part of the infradentary series along with the postsplenial and angular. The earliest known taxon with infradentary bones is the placoderm Entelognathus, while they were absent in the earlier-diverging Qilinyu. Splenials are present in non-mammalian synapsids, but lost in mammals, though there are some claims of a vestigial splenial in some early mammals.

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Hemimandible of Trimerorhachis; the splenial (labeled "sp") is visible on the interior surface source ↗
Skull and jaws diagram of the primitive synapsid Dimetrodon, showing location of the splenial source ↗

The splenial is a small bone in the lower jaw of reptiles, amphibians and birds, usually located on the lingual side (closest to the tongue) between the angular and surangular.12 The splenial and coronoid are together known as the paradental elements.3 In non-tetrapod vertebrates, the splenial is known as the first infradentary and forms part of the infradentary series along with the postsplenial and angular.45 The earliest known taxon with infradentary bones is the placoderm Entelognathus, while they were absent in the earlier-diverging Qilinyu.6 Splenials are present in non-mammalian synapsids, but lost in mammals, though there are some claims of a vestigial splenial in some early mammals.3

References

References

  1. Romer, A. S. (1956). Osteology of the Reptiles. 772 pp. Chicago & London.
  2. Watson, D. M. S. (1912). LXVII.—On some reptilian lower jaws. Journal of Natural History, 10(60), 573-587.
  3. Rougier, Guillermo W.; Martinelli, Agustín G.; Forasiepi, Analía M.; Novacek, Michael J. (2007). "New Jurassic Mammals from Patagonia, Argentina: A Reappraisal of Australosphenidan Morphology and Interrelationships". American Museum Novitates. 3566 (1): 1. doi:10.1206/0003-0082(2007)507[1:NJMFPA]2.0.CO;2. ISSN 0003-0082.
  4. Jeffery, Jonathan E (2003). "Mandibles of rhizodontids: anatomy, function and evolution within the tetrapod stem-group". Transactions of the Royal Society of Edinburgh: Earth Sciences. 93: 255–276.
  5. Zhu, You-An; Ahlberg, Per A.; Zhu, Min (2018-12-31). "The Evolution of Vertebrate Dermal Jaw Bones in the Light of Maxillate Placoderms". In Johanson, Zerina; Underwood, Charlie; Richter, Martha (eds.). Evolution and Development of Fishes (1 ed.). Cambridge University Press. pp. 71–86. doi:10.1017/9781316832172.005. ISBN 978-1-316-83217-2.
  6. Zhu, Min; Ahlberg, Per E.; Pan, Zhaohui; Zhu, Youan; Qiao, Tuo; Zhao, Wenjin; Jia, Liantao; Lu, Jing (2016-10-21). "A Silurian maxillate placoderm illuminates jaw evolution". Science. 354 (6310): 334–336. doi:10.1126/science.aah3764. eISSN 1095-9203. ISSN 0036-8075.