Lonchidion

Credit: R.J. Palmer.

*Lonchidion* is an extinct genus of hybodontiforme sharks that lived in Africa, Asia, Europe and the Americas from the Triassic to the Cretaceous.

## Description

Being one of the last hybodonts, *Lonchidion* is known from its distinctive serrated fine spines that are found among iconic fauna of the Upper Hell Creek Formation, such as *Tyrannosaurus* and *Triceratops*. This formation preserves *L. selachos* (recovered from Montana and North/South Dakota), with ~40 specimens recovered and making 0.4% of the Hell Creek vertebrate record. R. Estes (1964) named *L. selachas* as the type, with Jan Fischer, Sebastian Voigt, Jörg W. Schneider, Michael Buchwitz and Silke Voigt (2011) naming *L. ferganensis* based on fossil teeth and egg capsules. *L. humblei* are known from the Upper Carnian-aged Dockum Group of Texas. This species exhibits a tooth morphology which, when compared, leads authors to believe other species were more derived. These are: a prominent labial buttress, a low crown, a smooth sculpture and lacking in accessory cusps.

*L. selachos* are known from the Late Cretaceous Lance Formation of Eastern Wyoming, among other locations (Saskatchewan, Colorado, Montana, New Mexico, North Dakota, South Dakota and Texas). *L. selachos* is, also, known from the Sue locality alongside *Myledaphus pustulosus* and the Aguja Formation, where 9 specimens (including 4 with full crowns and 5 fragments lacking roots) were recovered. In the Aguja Formation, it is differentiated as a gracile form when compared to *Vectiselachos*, *Lissodus* and *Hylaeobatis*, as it has minute cusplets. *L. anitae* is differentiated by being smaller and having a cuspate transverse ridge from Albian-aged strata. *L. selachos* has a greater mesiodistal width and lower crown height from Campanian-aged strata. Hundreds of Lonchidion specimens are reported from the Terlingua fauna. *L. derenzii* is reported from the Late Triassic of Spain by Esther Manzanares, Cristina Pla, Carlos Martínez-Pérez, Humberto Ferrón and Héctor Botella (2017).

## Paleobiology

*L. ferganensis* materials were found in a selachian nursery site from the Middle-Late Triassic Madygen Formation, Kyrgyzstan. Alongside *L. ferganensis* were *L. ferganensis*, *Palaeoxyris alterna* (teeth) and *Fayolia sharovi* with *L. ferganensis* (egg capsules), which were all named with *L. ferganensis*. The *L. ferganensis* teeth were found, almost exclusively, in pelecypod-rich shallow lacustrine mudstone, belonging to juvenile individuals. The authors suggested this site is a hybodont/xenacanthid nursery, occupying a littoral zone of a lake to spawn. Additionally, the lack of adults further solidifies the spawnpoint classification. Oviposition strategies observed from fossil egg capsules are very much similar to extant sharks, suggesting they originated well before the Cenozoic. *L. anitae* are known from the Holly Creek Formation.

## Species

* *L. anitae*
* *L. babulskii*
* *L. breve*
* *L. crenulatum*
* *L. delsatei*
* *L. derenzii*
* *L. griffisi*
* *L. humblei*
* *L. indicus*
* *L. inflexum*
* *L. khoratensis*
* *L. marocensis*
* *L. microselachos*
* *L. monteschi*
* *L. selachas*
* *L. selachos*
* *L. striatum*
* *L. weltoni*

## References

1. ↑ https://www.sciencedirect.com/science/article/abs/pii/S0195667120301695?via%3Dihub
2. ↑ https://www.jstor.org/stable/1304274
3. ↑ https://shark-references.com/species/view/Lonchidion-selachos
4. ↑ https://paleobiodb.org/classic/basicTaxonInfo?taxon\_no=67744
5. ↑ https://www.cambridge.org/core/journals/journal-of-paleontology/article/abs/new-sharks-and-other-chondrichthyans-from-the-latest-maastrichtian-late-cretaceous-of-north-america/03C9F86EA8FE0C54C70BFB7783FC8AA2
6. ↑ https://www.sciencedirect.com/science/article/abs/pii/S0195667116301690?via%3Dihub
7. ↑ https://bioone.org/journals/journal-of-vertebrate-paleontology/volume-37/issue-1/02724634.2017.1253585/Lonchidion-derenzii-sp-nov-a-New-Lonchidiid-Shark-Chondrichthyes-Hybodontiforms/10.1080/02724634.2017.1253585.short
8. ↑ https://www.tandfonline.com/doi/abs/10.1080/02724634.2011.601729
9. ↑ https://peerj.com/articles/12242/?utm\_source=PeerJ&utm\_medium=twitter&utm\_campaign=12242&utm\_id=Social#p-57
10. ↑ 10.00 10.01 10.02 10.03 10.04 10.05 10.06 10.07 10.08 10.09 10.10 10.11 10.12 10.13 10.14 10.15 10.16 10.17 http://fossilworks.org/bridge.pl?taxon\_no=56537&action=taxonInfo