Several canid fossils, which were originally discovered and described in the early 20th century, are known from Early and earliest Middle Pleistocene of Java (Indonesia). Here we revise the taxonomy and relative age of the Javanese canid fossils in light of recent developments in the taxonomy and phylogeny of Canidae, and new insights in the evolution of island mammals. Results show that Cuon was absent during the Early and earliest Middle Pleistocene while the large-sized Xenocyon (previously Megacyon) was present in the Early Pleistocene and replaced by the small-sized Xenocyon (previously Mececyon) during the earliest Middle Pleistocene. The latter is probably an anagenetic dwarf derived from the larger form of the preceding period. The change in body size of Xenocyon on Java over time is likely the effect of increased competition within the carnivore guild within the restricted boundaries of the island. Simultaneously with a pronounced body size shift, a dietary shift from large-sized prey to much smaller prey must have taken place in order to meet energetic constraints. The degree of endemism of terrestrial mammals of the earliest Middle Pleistocene horizon of the site Trinil, which has also yielded Homo erectus fossils, indicates that during this period, Java was marginally isolated which allowed for a corridor dispersal to the island with subsequent vicariance. The nature and degree of isolation may have been similar to that of Late Pleistocene Sicily, but of a longer duration, given the higher degree of dwarfism of the stegodon, antilope and canid. The following continentalisation enabled the invasion by mainland terrestrial mammals, as is seen in younger layers at Trinil, and eventually by Homo sapiens and Cuon in the Late Pleistocene / Holocene.