Diplocynodon is an extinct genus of eusuchian, either an alligatoroid crocodilian or a stem-group 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). The largest species D.hantoniensis measured 5.9 m (19.5 ft) in length. 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).

*Locality and/or horizon of the type specimen.

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.

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.