Argillochelys cuneiceps was an early marine chelonioid with a broad skull and a relatively short snout. Its jaws carried a moderately developed secondary palate with a deep central groove and paired blunt swellings on the crushing surface. This combination suggests a turtle able to grip and process food firmly rather than simply snatching very soft prey, but the exact balance of fishes, invertebrates or other marine food in its diet remains uncertain.

The species is securely known from cranial material rather than an associated shell. Its marine swimming habit is therefore inferred from its close chelonioid relationships and specialised skull rather than from directly preserved limbs in this species. It formed part of the diverse early Eocene radiation of sea turtles inhabiting warm coastal seas.