Kentisuchus

Kentisuchus is an extinct genus of gavialoid crocodylian, traditionally regarded as a member of the subfamily Tomistominae. Fossils have been found from England and France that date back to the early Eocene.^[2] The genus has also been recorded from Ukraine, but it unclear whether specimens from Ukraine are referable to Kentisuchus.^[3][4]

Kentisuchus Temporal range: Early Eocene, 55.8–48.6 Ma[1] PreꞒ Ꞓ O S D C P T J K Pg N
K. spenceri fossil at the Tellus Science Museum
Scientific classification
Domain:	Eukaryota
Kingdom:	Animalia
Phylum:	Chordata
Class:	Reptilia
Clade:	Archosauromorpha
Clade:	Archosauriformes
Order:	Crocodilia
Superfamily:	Gavialoidea
Genus:	†Kentisuchus Mook, 1955
Species
†K. astrei Jouve, 2016 †K. spenceri (Buckland, 1836) [originally Crocodylus spenceri] (type)
Synonyms
Crocodylus spenceri Buckland, 1836

Species

K. spenceri skull

The genus Kentisuchus was erected by Charles Mook in 1955 for the species "Crocodylus" toliapicus, described by Richard Owen, in 1849. William Buckland named "Crocodylus" spenceri on the basis of a partial skull found from the Isle of Sheppey in Kent, England.^[5][6][7] In 1888 Richard Lydekker considered "C." toliapicus synonymous with "C." champsoides and "C." arduini, named by De Zigno, and reapplied the name "C." spenceri to all of these species.^[8][9]

The genus name Kentisuchus was constructed only after it was realized that these specimens were clearly distinct from the genus Crocodylus and that some specimens originally assigned to "C." spenceri belonged to entirely different genera and species. "C." arduini was reassigned to the new genus Megadontosuchus in the same paper that Kentisuchus was first described in. A 2007 review of European Eocene tomistomines synonymized K. toliapicus and K. champsoides with K. spenceri.^[10]

Phylogenetics

K. spenceri skull in multiple views

K. spenceri is closely related to Megadontosuchus and Dollosuchoides.^[11][12][13] An apparent close relationship between K. spenceri and Eosuchus lerichei has been used to imply that the latter species was a tomistomine, while it is now thought that Eosuchus is a basal eusuchian that lies outside the crocodilian crown group.^[14]

Below is a cladogram based morphological studies comparing skeletal features that shows Kentisuchus as a member of Tomistominae, related to the false gharial:^[15]

Crocodylidae	Crocodylinae Tomistominae Xaymacachampsa† Megadontosuchus† Kentisuchus† Maroccosuchus† Dollosuchoides† Thecachampsa† Penghusuchus† Toyotamaphimeia† Tomistoma cairense† Maomingosuchus† Tomistoma schlegelii False gharial Gavialosuchus† Tomistoma lusitanicum† Paratomistoma† Tomistoma coppensi†

Based on morphological studies of extinct taxa, the tomistomines (including the living false gharial) were long thought to be classified as crocodiles and not closely related to gavialoids.^[16] However, recent molecular studies using DNA sequencing have consistently indicated that the false gharial (Tomistoma) (and by inference other related extinct forms in Tomistominae) actually belong to Gavialoidea (and Gavialidae).^{[17][18][19][20][21][14][22]}

Below is a cladogram from a 2018 tip dating study by Lee & Yates simultaneously using morphological, molecular (DNA sequencing), and stratigraphic (fossil age) data that shows Kentisuchus as a gavialoid, more basal than the last common ancestor to both the gharial and the false gharial:^[14]

Gavialoidea	Gavialidae Gavialis gangeticus Gharial Gavialis bengawanicus† Gavialis browni† Gryposuchus colombianus† Ikanogavialis† Gryposuchus pachakamue† Piscogavialis† Harpacochampsa† Toyotamaphimeia† Penghusuchus† Gavialosuchus† Tomistoma lusitanicum† Tomistoma schlegelii False gharial (crown group) Tomistoma cairense† Dollosuchoides† Maroccosuchus† Paratomistoma† Kentisuchus†
(total group)

Paleobiology

The close relation of Kentisuchus and Dollosuchoides, which are known from European localities that were on the mainland during the early Eocene, to Megadontosuchus, which is known from Italian localities that were once part of a Tethysian archipelago, suggests that it came to these islands after a dispersal event south from mainland Europe rather than north from Africa.^[23]

References

1. Rio, Jonathan P.; Mannion, Philip D. (6 September 2021). "Phylogenetic analysis of a new morphological dataset elucidates the evolutionary history of Crocodylia and resolves the long-standing gharial problem". PeerJ. 9: e12094. doi:10.7717/peerj.12094. PMC 8428266. PMID 34567843.
2. Stéphane Jouve (2016). "A new basal tomistomine (Crocodylia, Crocodyloidea) from Issel (Middle Eocene; France): palaeobiogeography of basal tomistomines and palaeogeographic consequences". Zoological Journal of the Linnean Society 177 (1): 165–182. doi:10.1111/zoj.12357.
3. Efimov, M. B. (1993). The Eocene crocodiles of the GUS — a history of development. Kaupia 3:23–25.
4. Zvonok, E. A.; Skutschas, P. P. (2011). "On a tomistomine crocodile (Crocodylidae, Tomistominae) from the Middle Eocene of Ukraine". Paleontological Journal. 45 (6): 661–664. Bibcode:2011PalJ...45..661Z. doi:10.1134/S0031030111060165. S2CID 140135377.
5. Mook, C. C. (1955). Two new genera of Eocene crocodilians. American Museum Novitates 1727:1-4.
6. Buckland, W. (1836). Geology and Mineralogy Considered with Reference to Natural Theology. 618 pp. Pickering, London.
7. OWEN, R. 1850. Monograph on the fossil Reptilia of the London Clay, and of the Bracklesham and other Tertiary beds, part II: Crocodilia (Crocodilus, etc.). Monograph of the Palaeontographical Society, London, 50 pp.
8. De Zigno, A. (1880). Sopra un cranio di coccodrillo scoperto nel terreno Eoceno del Veronese. Mem. R. Accad. Lincei, ser. 3, Cl. Sci. Fip., Mat., Nat., vol. 5, pp. 65-72.
9. Lydekker, R. (1888). Catalogue of the fossil Reptilia in the British Museum. London, pp. 60-63.
10. Brochu, C. A. (2007). Systematics and taxonomy of Eocene tomistomine crocodylians from Britain and Northern Europe. Palaeontology 50(4):917-928
11. Piras, P., Delfino, M., Del Favero, L., and Kotsakis, T. (2007). Phylogenetic position of the crocodylian Megadontosuchus arduini and tomistomine palaeobiogeography. Acta Palaeontologica Polonica 52(2):315–328.
12. Jouve, S. (2004). Etude des crocodyliformes fini Crétace−Paléogène du Bassin de Oulad Abdoun (Maroc) et comparaison avec les faunes africaines contemporaines: systématique, phylogénie et paléobiogéographie. Ph.D. thesis. 652 pp. Muséum National d’Histoire Naturelle de Paris, Paris.
13. Delfino, M., Piras, P., and Smith, T. (2005). Anatomy and phylogeny of the gavialoid crocodylian Eosuchus lerichei from the Paleocene of Europe. Acta Palaeontologica Polonica 50:565–580.
14. Michael S. Y. Lee; Adam M. Yates (27 June 2018). "Tip-dating and homoplasy: reconciling the shallow molecular divergences of modern gharials with their long fossil". Proceedings of the Royal Society B. 285 (1881). doi:10.1098/rspb.2018.1071. PMC 6030529. PMID 30051855.
15. Iijima, Masaya; Momohara, Arata; Kobayashi, Yoshitsugu; Hayashi, Shoji; Ikeda, Tadahiro; Taruno, Hiroyuki; Watanabe, Katsunori; Tanimoto, Masahiro; Furui, Sora (2018-05-01). "Toyotamaphimeia cf. machikanensis (Crocodylia, Tomistominae) from the Middle Pleistocene of Osaka, Japan, and crocodylian survivorship through the Pliocene-Pleistocene climatic oscillations". Palaeogeography, Palaeoclimatology, Palaeoecology. 496: 346–360. Bibcode:2018PPP...496..346I. doi:10.1016/j.palaeo.2018.02.002. ISSN 0031-0182.
16. Brochu, C.A.; Gingerich, P.D. (2000). "New tomistomine crocodylian from the Middle Eocene (Bartonian) of Wadi Hitan, Fayum Province, Egypt". University of Michigan Contributions from the Museum of Paleontology. 30 (10): 251–268.
17. Harshman, J.; Huddleston, C. J.; Bollback, J. P.; Parsons, T. J.; Braun, M. J. (2003). "True and false gharials: A nuclear gene phylogeny of crocodylia". Systematic Biology. 52 (3): 386–402. doi:10.1080/10635150309323. PMID 12775527.
18. Gatesy, Jorge; Amato, G.; Norell, M.; DeSalle, R.; Hayashi, C. (2003). "Combined support for wholesale taxic atavism in gavialine crocodylians" (PDF). Systematic Biology. 52 (3): 403–422. doi:10.1080/10635150309329. PMID 12775528.
19. Willis, R. E.; McAliley, L. R.; Neeley, E. D.; Densmore Ld, L. D. (June 2007). "Evidence for placing the false gharial (Tomistoma schlegelii) into the family Gavialidae: Inferences from nuclear gene sequences". Molecular Phylogenetics and Evolution. 43 (3): 787–794. doi:10.1016/j.ympev.2007.02.005. PMID 17433721.
20. Gatesy, J.; Amato, G. (2008). "The rapid accumulation of consistent molecular support for intergeneric crocodylian relationships". Molecular Phylogenetics and Evolution. 48 (3): 1232–1237. doi:10.1016/j.ympev.2008.02.009. PMID 18372192.
21. Erickson, G. M.; Gignac, P. M.; Steppan, S. J.; Lappin, A. K.; Vliet, K. A.; Brueggen, J. A.; Inouye, B. D.; Kledzik, D.; Webb, G. J. W. (2012). Claessens, Leon (ed.). "Insights into the ecology and evolutionary success of crocodilians revealed through bite-force and tooth-pressure experimentation". PLOS ONE. 7 (3): e31781. Bibcode:2012PLoSO...731781E. doi:10.1371/journal.pone.0031781. PMC 3303775. PMID 22431965.
22. Hekkala, E.; Gatesy, J.; Narechania, A.; Meredith, R.; Russello, M.; Aardema, M. L.; Jensen, E.; Montanari, S.; Brochu, C.; Norell, M.; Amato, G. (2021-04-27). "Paleogenomics illuminates the evolutionary history of the extinct Holocene "horned" crocodile of Madagascar, Voay robustus". Communications Biology. 4 (1): 505. doi:10.1038/s42003-021-02017-0. ISSN 2399-3642. PMC 8079395. PMID 33907305.
23. Kotsakis, T., Delfino, M., and Piras, P. (2004). Italian Cenozoic crocodilians: taxa, timing and palaeobiogeographic implications. Palaeogeography, Palaeoclimatology, Palaeoecology 210(1):67-87.

External links

• Kentisuchus in the Paleobiology Database

• Paleontology portal