# 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), while others probably did not exceed 1 metre (3.3 ft). They are almost exclusively found in freshwater environments. The various species are thought to have been opportunistic aquatic predators.
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. Other genera have recently been found to be synonymous with Diplocynodon. Hispanochampsa muelleri of Spain was determined to be synonymous with Diplocynodon in 2006, and Baryphracta deponaie of Germany was confirmed to be synonymous with Diplocynodon in 2012.
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. darwini from Messel pit, Hesse, Germany, 48 million years old Skull of D. hantoniensis Diplocynodon cf. ratelii |
| D. deponaie | Middle Eocene | Germany | Messel pit | Synonyms are: Baryphracta deponaie. | D. darwini from Messel pit, Hesse, Germany, 48 million years old Skull of D. hantoniensis Diplocynodon cf. ratelii |
| D. elavericus | Middle Priabonian | France | Domérat | All specimens came from Allier, Massif Central of France. | D. darwini from Messel pit, Hesse, Germany, 48 million years old Skull of D. hantoniensis Diplocynodon cf. ratelii |
| D. gervaisi | Earliest Rupelian | France | Ronzon | Synonyms are: Saurocainus gervaisi. | D. darwini from Messel pit, Hesse, Germany, 48 million years old Skull of D. hantoniensis Diplocynodon cf. ratelii |
| 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. darwini from Messel pit, Hesse, Germany, 48 million years old Skull of D. hantoniensis Diplocynodon cf. ratelii |
| D. levantinicum | Oligocene (Chattian) | Bulgaria | Maritsa Formation | | D. darwini from Messel pit, Hesse, Germany, 48 million years old Skull of D. hantoniensis Diplocynodon cf. ratelii |
| D. kochi | Eocene (Priabonian) | Romania | Cluj Limestone Formation | | D. darwini from Messel pit, Hesse, Germany, 48 million years old Skull of D. hantoniensis Diplocynodon cf. ratelii |
| D. muelleri | 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. darwini from Messel pit, Hesse, Germany, 48 million years old Skull of D. hantoniensis Diplocynodon cf. ratelii |
| 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. darwini from Messel pit, Hesse, Germany, 48 million years old Skull of D. hantoniensis Diplocynodon cf. ratelii |
| D. tormis | Late Bartonian | Spain | Salamanca | | D. darwini from Messel pit, Hesse, Germany, 48 million years old Skull of D. hantoniensis Diplocynodon cf. ratelii |
| D. ungeri | Middle Miocene | Austria*  France | Pannonian Basin* Paris Basin | Synonyms are: Enneodon ungeri, D. steineri, and D. styriacus (see text). | D. darwini from Messel pit, Hesse, Germany, 48 million years old Skull of D. hantoniensis Diplocynodon cf. ratelii |
*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:

## 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 δ$^{13}$C values from specimens from the Late Oligocene site of Enspel, the Diplocynodon living in the palaeoenvironment fed primarily on aquatic vertebrates.