Diplocynodon

Species

*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.

Below is a more detailed cladogram of Diplocynodon:

In a 2025 study, Jules D. Walter and colleagues argue that many character states previously thought to be diagnostic for alligatoroids were actually much more widespread. In their analysis several genera traditionally viewed as basal alligatoroids, among them Diplocynodon, were found to not only fall outside of Alligatoroidea but to not even be true crocodilians, instead representing derived non-crocodilian eusuchians.

Palaeobiology

Osteohistological analysis of D. hantoniensis suggests that it had a similar pattern of growth to the modern American alligator, exhibiting a determinate, seasonally-controlled rate of growth. Additionally, D. hantoniensis was allometrically very similar to American alligators, with the femoral length and femoral circumference scaling in a similar fashion in both species.

CT scans of D. tormis reconstruct internal structures of its snout and a portion of its brain, with implications for its sensory and cognitive capabilities. The relative sizes of the olfactory bulbs overlap with alligatoroids and fall short of true crocodiles, adding to anatomical evidence for a closer relationship to alligatoroids. The optic lobes and reptile encephalization quotient are proportionally smaller than other medium-sized crocodilians, though this could be influenced by incomplete preservation at the back of the skull.

Palaeoecology

Based on skull shape analysis of the crocodylians known from the Lutetian site of Geiseltal, Diplocynodon was a small generalist carnivore that partitioned its resources with the larger Asiatosuchus. According to enamel δ13C values from specimens from the Late Oligocene site of Enspel, the Diplocynodon living in the palaeoenvironment fed primarily on aquatic vertebrates.

References

• Fossils (Smithsonian Handbooks) by David Ward (Page 243)

References

1. (6 September 2021). "Phylogenetic analysis of a new morphological dataset elucidates the evolutionary history of Crocodylia and resolves the long-standing gharial problem". [[PeerJ]].
2. (1999). "Die Krokodil-Fauna der Fossillagerstätte Grube Messel". Ein aktueller Überblick., Natur und Museum, Frankfurt am Main.
3. (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.
4. (2022). "A new late Eocene alligatoroid crocodyliform from Transylvania". Comptes Rendus Palevol.
5. (2006). "''Diplocynodon muelleri'' comb. nov., an Oligocene diplocynodontine alligatoroid from Catalonia (Ebro Basin, Lleida Province, Spain)". Journal of Vertebrate Paleontology.
6. (1936). "''Hispanochampsa mülleri'' nov. gen. nov. sp.". Abh. Schweizer. Palaeontol. Gesellschaft.
7. (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.
8. (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.
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. (March 2015). "Late Oligocene ambient temperatures reconstructed by stable isotope analysis of terrestrial and aquatic vertebrate fossils of Enspel, Germany". Palaeobiodiversity and Palaeoenvironments.
11. (2011). "Taxonomic clarification of ''Diplocynodon'' Pomel, 1847 (Crocodilia) from the Miocene of Styria, Austria". Neues Jahrbuch für Geologie und Paläontologie - Abhandlungen.
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.
13. Michael S. Y. Lee. (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]].
14. (2019). "A new alligatoroid from the Eocene of Vietnam highlights an extinct Asian clade independent from extant ''Alligator sinensis''". PeerJ.
15. (2025). "Expanded phylogeny elucidates ''Deinosuchus relationships'', crocodylian osmoregulation and body-size evolution". Communications Biology.
16. (9 February 2025). "Evolution of growth strategy in alligators and caimans informed by osteohistology of the late Eocene early-diverging alligatoroid crocodylian Diplocynodon hantoniensis". [[Journal of Anatomy]].
17. (2025-02-24). "New data on the inner skull cavities of Diplocynodon tormis (Crocodylia, Diplocynodontinae) from the Duero Basin (Iberian Peninsula, Spain)". Fossil Record.
18. (January 2017). "Evidence for prey preference partitioning in the middle Eocene high-diversity crocodylian assemblage of the Geiseltal-Fossillagerstätte, Germany utilizing skull shape analysis". [[Geological Magazine]].
19. (12 February 2015). "Late Oligocene ambient temperatures reconstructed by stable isotope analysis of terrestrial and aquatic vertebrate fossils of Enspel, Germany". Palaeobiodiversity and Palaeoenvironments.