Lonchidion#Species

{{short description|Extinct genus of hybodont shark}}

{{Automatic taxobox

| fossil_range = Middle Triassic to Late Cretaceous
{{fossilrange|Ladinian|Maastrichtian}}

| image = Lonchidion sp. - Tendaguru Formation, Tanzania.jpg

| image_caption = Teeth of an indeterminate species from the Tendaguru Formation

| taxon = Lonchidion

| authority = Estes, 1964

}}

Lonchidion is a genus of extinct hybodont in the family Lonchidiidae. The genus first appears in the fossil record during the Middle Triassic (Ladinian){{Cite journal |last=Johns |first=Marjorie J. |last2=Albanesi |first2=Guillermo L. |last3=Voldman |first3=Gustavo G. |date=2014-04-16 |title=Freshwater shark teeth (Family Lonchidiidae) from the Middle-Upper Triassic (Ladinian-Carnian) Paramillo Formation in the Mendoza Precordillera, Argentina |url=http://www.tandfonline.com/doi/abs/10.1080/02724634.2013.803976 |journal=Journal of Vertebrate Paleontology |language=en |volume=34 |issue=3 |pages=512–523 |doi=10.1080/02724634.2013.803976 |issn=0272-4634|hdl=11336/32116 |hdl-access=free }} and was among the last surviving hybodont genera, with its youngest known fossils dating to the very end of the Cretaceous (Maastrichtian).{{Cite journal |last=Gates |first=Terry A. |last2=Gorscak |first2=Eric |last3=Makovicky |first3=Peter J. |date=May 2019 |title=New sharks and other chondrichthyans from the latest Maastrichtian (Late Cretaceous) of North America |url=https://www.cambridge.org/core/product/identifier/S0022336018000926/type/journal_article |journal=Journal of Paleontology |language=en |volume=93 |issue=3 |pages=512–530 |doi=10.1017/jpa.2018.92 |issn=0022-3360|doi-access=free }}

Lonchidion was first described by Richard Estes in 1964, and the type species is L. selachas. Fossils of Lonchidion have been found worldwide. The genus has been proposed to be euryhaline, and is often found in freshwater and brackish deposits.{{Cite journal |last=Manzanares |first=Esther |last2=Pla |first2=Cristina |last3=Martínez-Pérez |first3=Carlos |last4=Ferrón |first4=Humberto |last5=Botella |first5=Héctor |date=2017-01-02 |title=Lonchidion derenzii, sp. nov., a new lonchidiid shark (Chondrichthyes, Hybodontiforms) from the Upper Triassic of Spain, with remarks on lonchidiid enameloid |url=https://www.tandfonline.com/doi/full/10.1080/02724634.2017.1253585 |journal=Journal of Vertebrate Paleontology |language=en |volume=37 |issue=1 |pages=e1253585 |doi=10.1080/02724634.2017.1253585 |issn=0272-4634|hdl=10550/85565 |hdl-access=free }} Hybodont egg cases (Palaeoxyris) associated with juvenile teeth of L. ferganensis in the Triassic lake deposits of the Madygen Formation of Kyrgyzstan suggests that this species spawned in freshwater environments,Jan Fischer, Sebastian Voigt, Jörg W. Schneider, Michael Buchwitz and Silke Voigt (2011). "A selachian freshwater fauna from the Triassic of Kyrgyzstan and its implication for Mesozoic shark nurseries". Journal of Vertebrate Paleontology 31 (5): 937–953. {{doi|10.1080/02724634.2011.601729}}. with Palaeoxyris egg cases found in freshwater deposits of the Late Triassic Chinle Formation in North America suggested to have been produced by Lonchidion humblei.{{Cite journal |last=Fischer |first=Jan |last2=Axsmith |first2=Brian J. |last3=Ash |first3=Sidney R. |date=2010-03-01 |title=First unequivocal record of the hybodont shark egg capsule Palaeoxyris in the Mesozoic of North America |url=http://dx.doi.org/10.1127/0077-7749/2009/0028 |journal=Neues Jahrbuch für Geologie und Paläontologie - Abhandlungen |volume=255 |issue=3 |pages=327–344 |doi=10.1127/0077-7749/2009/0028 |issn=0077-7749}}

While the genus is primarily known from teeth, a preserved body impression of a subadult individual is known from the Early Cretaceous freshwater Las Hoyas site in Spain. This specimen is among the smallest known elasmobranchs, at around {{Convert|3.5|cm|in}} in length.{{Cite journal |last=Marugán-Lobón |first=Jesús |last2=Martín-Abad |first2=Hugo |last3=Buscalioni |first3=Ángela D. |date=2023-05-05 |title=The Las Hoyas Lagerstätte: a palaeontological view of an Early Cretaceous wetland |url=https://www.lyellcollection.org/doi/10.1144/jgs2022-079 |journal=Journal of the Geological Society |language=en |volume=180 |issue=3 |doi=10.1144/jgs2022-079 |issn=0016-7649|doi-access=free |hdl=10486/710760 |hdl-access=free }} Other possible body remains of Lonchidion have been reported from other Early Cretaceous sites in Spain.GOMEZ-PALLEROLA, J. E. 1985. Nuevos Hybodóntidos del Cretácico Inferior de Santa María de Meyá (Lérida) [New Hybodontids from the Early Cretaceous of Santa María de Meyá (Lérida)]. Boletin Geologico y Minero, 96(4):372–380.GOMEZ-PALLEROLA, J. E. 1992. [https://info.igme.es/biblioteca/ficheros/BGM/Boletin%20103_5_1992.pdf Nota sobre los tiburones hybodontos de las calizas litográficas del Cretácico Inferior del Montsec (Lérida).] [Note on hybodont sharks from the Lower Cretaceous lithographic limestones of Montsec (Lérida)] Boletin Geologico y Minero, 103:3–33. Lonchidion humblei is suggested to have reached an adult length of {{Convert|25|cm|in}}.{{Cite journal |last=Vullo |first=Romain |last2=Néraudeau |first2=Didier |last3=Dépré |first3=Eric |date=October 2013 |title=Vertebrate remains from the Cenomanian (Late Cretaceous) plant-bearing Lagerstätte of Puy-Puy (Charente-Maritime, France) |url=https://linkinghub.elsevier.com/retrieve/pii/S0195667113001043 |journal=Cretaceous Research |language=en |volume=45 |pages=314–320 |doi=10.1016/j.cretres.2013.06.002}}

The teeth of the genus are low crowned, and probably served to grind hard prey (durophagy).{{Cite journal |last=Bermúdez-Rochas |first=David Didier |date=November 2009 |title=New hybodont shark assemblage from the Early Cretaceous of the Basque-Cantabrian Basin |url=https://linkinghub.elsevier.com/retrieve/pii/S0016699509000771 |journal=Geobios |language=en |volume=42 |issue=6 |pages=675–686 |doi=10.1016/j.geobios.2009.06.004}} Some authors have proposed that Lonchidion is not a valid genus, and that its teeth instead represent a morphological type present among many juvenile hybodonts but that is later lost in adults.{{Cite journal |last=Voris |first=Jared T. |last2=Heckert |first2=Andrew B. |date=2017 |title=Ontogenetic heterodonty in Reticulodus synergus (Chondrichthyes, Hybodontiformes) from the Upper Triassic of the southwestern U.S.A., with a redescription of the genus |url=https://www.jstor.org/stable/44866041 |journal=Journal of Vertebrate Paleontology |volume=37 |issue=4 |pages=1–12 |issn=0272-4634}}