Diplocynodon

Diplocynodon is an extinct genus of alligatoroid crocodilian that lived during the Paleocene to Middle Miocene in Europe. Some species may have reached lengths of 3 metres (9.8 ft),^[7] while others probably did not exceed 1 metre (3.3 ft).^[8] They are almost exclusively found in freshwater environments.^[9] The various species are thought to have been opportunistic aquatic predators.^[10]

Diplocynodon Temporal range: Paleocene - Middle Miocene, 59.2–13.8 Ma[1] PreꞒ Ꞓ O S D C P T J K Pg N
Diplocynodon ratelii
Scientific classification
Domain:	Eukaryota
Kingdom:	Animalia
Phylum:	Chordata
Class:	Reptilia
Clade:	Archosauromorpha
Clade:	Archosauriformes
Order:	Crocodilia
Superfamily:	Alligatoroidea
Subfamily:	†Diplocynodontinae Brochu, 1999
Genus:	†Diplocynodon Pomel, 1847
Species
†D. dalpiazi Del Favero, 1999 †D. darwini (Ludvig, 1877) †D. deponiae (Frey, Laemmert & Riess, 1987)[2][3] †D. elavericus Martin, 2010 †D. gervaisi †D. hantoniensis (Wood, 1846) †D. levantinicum Huene & Nikoloff, 1963 †D. kochi (Venczel & Codrea, 2022)[4] †D. muelleri (Kälin, 1936)[5] †D. ratelii Pomel, 1847 (type) †D. tormis †D. ungeri (Prangner, 1845)
Synonyms
Baryphracta Frey, Laemmert & Riess, 1987[2][3] Enneodon Pranger, 1845 Hispanochampsa Kälin, 1936[6][5] Saurocainus

In the nineteenth century, D. steineri was named from Styria, Austria and D. styriacus was named from Austria and France. A third Austrian species, Enneodon ungeri, was placed in its own genus. The Austrian and French species of Diplocynodon were synonymized with E. ungeri in 2011, and because the name Diplocynodon has priority over Enneodon, the species is now called D. ungeri.^[11] Other genera have recently been found to be synonymous with Diplocynodon. Hispanochampsa muelleri of Spain was determined to be synonymous with Diplocynodon in 2006,^[5] and Baryphracta deponaie of Germany was confirmed to be synonymous with Diplocynodon in 2012.^[3]

Well preserved specimens have been found in the Messel Pit and the Geiseltal lignite deposit in Germany. Most articulated Diplocynodon specimens from these localities contain gastroliths. In the Eocene epoch, the German sites were either a swampy freshwater lake (Messel Pit) or a peat bog swamp (Geiseltal).

Species

Species
Species	Age	Location	Unit	Notes	Images
D. dalpiazi	Late Rupelian	Italy	Monteviale		D. darwini from Messel pit, Hesse, Germany, 48 million years old Skull of D. hantoniensis Diplocynodon cf. ratelii
D. darwini	Lutetian	Germany	Messel pit	All specimens are from Messel pit of Germany. Synonyms are: D. ebertsi and D. hallense.
D. deponaie[2][3]	Middle Eocene	Germany	Messel pit	Synonyms are: Baryphracta deponaie.
D. elavericus[12]	Middle Priabonian	France	Domérat	All specimens came from Allier, Massif Central of France.
D. gervaisi	Earliest Rupelian	France	Ronzon	Synonyms are: Saurocainus gervaisi.
D. hantoniensis	Early Priabonian	United Kingdom	Headon Hill Formation	All specimens came from Hordwell, southern England. D. cf. hantoniensis is known from the Oligocene of Dordogne, France.
D. levantinicum[7]	Oligocene (Chattian)	Bulgaria	Maritsa Formation
D. kochi	Eocene (Priabonian)	Romania	Cluj Limestone Formation
D. muelleri[5]	Middle Rupelian	Spain	El Talladell	More than 100 are known, all from Lleida Province, Catalonia. Synonyms are: Hispanochampsa muelleri, D. guerini and D. marini.
D. ratelii	Middle Aquitanian* Late Eocene to Early Miocene	France	Saint-Gérand-le-Puy*	D. ratelii is the type species of Diplocynodon. Most of the specimens came from Allier, Massif Central of France. Synonyms are: D. gracile.
D. tormis	Late Bartonian	Spain	Salamanca
D. ungeri[11]	Middle Miocene	Austria*  France	Pannonian Basin* Paris Basin	Synonyms are: Enneodon ungeri, D. steineri, and D. styriacus (see text).

*Locality and/or horizon of the type specimen.

Phylogeny

Diplocynodon is one of the basal-most members of the superfamily Alligatoroidea. Diplocynodon's placement within Alligatoroidea can be shown in the cladogram below, based on a 2018 tip dating study by Lee & Yates that simultaneously used morphological, molecular (DNA sequencing), and stratigraphic (fossil age) data.^[13]

Crocodylia

Alligatoroidea Leidyosuchus† Diplocynodontinae† Diplocynodon† Globidonta Stangerochampsa† Brachychampsa† Navajosuchus† Alligatoridae Caimaninae Caiman Melanosuchus Paleosuchus Alligatorinae Alligator extinct basal Crocodilians† (including Mekosuchinae†) Longirostres Crocodyloidea extinct basal crocodiles† Crocodylidae Crocodylus Mecistops Osteolaemus Gavialoidea extinct basal Gavialoids† Gavialidae Gavialis Tomistoma

Below is a more detailed cladogram of Diplocynodon:^[14]

Diplocynodon	Diplocynodon deponiae Diplocynodon darwini Diplocynodon hantoniensis Diplocynodon ratelii Diplocynodon tormis Diplocynodon muelleri

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. Rossmann, T.; Blume, M. (1999). "Die Krokodil-Fauna der Fossillagerstätte Grube Messel". Ein aktueller Überblick., Natur und Museum, Frankfurt am Main. 129 (9): 261–270.
3. Massimo Delfino; Thierry Smith (2012). "Reappraisal of the morphology and phylogenetic relationships of the middle Eocene alligatoroid Diplocynodon deponiae (Frey, Laemmert, and Riess, 1987) based on a three-dimensional specimen". Journal of Vertebrate Paleontology. 32 (6): 1358–1369. Bibcode:2012JVPal..32.1358D. doi:10.1080/02724634.2012.699484. S2CID 84977303.
4. Venczel M, Codrea VA (2022). "A new late Eocene alligatoroid crocodyliform from Transylvania". Comptes Rendus Palevol. 21 (20): 411–429. doi:10.5852/cr-palevol2022v21a20. S2CID 248879850.
5. Paolo Pirasa; Angela D. Buscalionib (2006). "Diplocynodon muelleri comb. nov., an Oligocene diplocynodontine alligatoroid from Catalonia (Ebro Basin, Lleida Province, Spain)" (PDF). Journal of Vertebrate Paleontology. 26 (3): 608–620. doi:10.1671/0272-4634(2006)26[608:DMCNAO]2.0.CO;2. S2CID 86181419.
6. Kälin, J. A. (1936). "Hispanochampsa mülleri nov. gen. nov. sp". Abh. Schweizer. Palaeontol. Gesellschaft. 58: 1–39.
7. Massonne, Tobias; Böhme, Madelaine (2022-11-09). "Re-evaluation of the morphology and phylogeny of Diplocynodon levantinicum Huene & Nikoloff, 1963 and the stratigraphic age of the West Maritsa coal field (Upper Thrace Basin, Bulgaria)". PeerJ. 10: e14167. doi:10.7717/peerj.14167. ISSN 2167-8359. PMC 9653056. PMID 36389401.
8. Delfino, Massimo; Smith, Thierry (November 2012). "Reappraisal of the morphology and phylogenetic relationships of the middle Eocene alligatoroid Diplocynodon deponiae (Frey, Laemmert, and Riess, 1987) based on a three-dimensional specimen". Journal of Vertebrate Paleontology. 32 (6): 1358–1369. Bibcode:2012JVPal..32.1358D. doi:10.1080/02724634.2012.699484. ISSN 0272-4634. S2CID 84977303.
9. Sabău I, Venczel M, Codrea VA, Bordeianu M. 2021. Diplocynodon: a salt water eocene crocodile from Transylvania? North-Western Journal of Zoology 17(1):117-121
10. Tütken, Thomas; Absolon, Julia (March 2015). "Late Oligocene ambient temperatures reconstructed by stable isotope analysis of terrestrial and aquatic vertebrate fossils of Enspel, Germany". Palaeobiodiversity and Palaeoenvironments. 95 (1): 17–31. Bibcode:2015PdPe...95...17T. doi:10.1007/s12549-014-0183-7. ISSN 1867-1594. S2CID 129654808.
11. Jeremy E. Martin; Martin Gross (2011). "Taxonomic clarification of Diplocynodon Pomel, 1847 (Crocodilia) from the Miocene of Styria, Austria". Neues Jahrbuch für Geologie und Paläontologie - Abhandlungen. 261 (2): 177–193. doi:10.1127/0077-7749/2011/0159.
12. Jeremy E. Martin (2010). "A new species of Diplocynodon (Crocodylia, Alligatoroidea) from the Late Eocene of the Massif Central, France, and the evolution of the genus in the climatic context of the Late Palaeogene". Geological Magazine. 147 (4): 596–610. Bibcode:2010GeoM..147..596M. doi:10.1017/S0016756809990161. S2CID 140593139.
13. 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.
14. Tobias Massonne; Davit Vasilyan; Márton Rabi; Madelaine Böhme (2019). "A new alligatoroid from the Eocene of Vietnam highlights an extinct Asian clade independent from extant Alligator sinensis". PeerJ. 7: e7562. doi:10.7717/peerj.7562. PMC 6839522. PMID 31720094.

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