The extreme rareness of Sardinian fossil sites older than Middle and Late Pleistocene makes the Monte Tuttavista karst complex (E Sardinia, Italy) very important. Remarkable lagomorph material, recovered from several fissure infillings of Monte Tuttavista referable to the Capo Figari/Orosei 1 and Orosei 2 faunal sub-complexes (early Pleistocene, ~2.1/1.9–1.1 Ma), allowed us to describe a new endemic insular leporid, Sardolagus obscurus n. gen. n. sp. The new taxon is characterized by a peculiar combination of an advanced p3 (Lepus-type) and a primitive P2 lacking deep flexa. The origin of such discrepancy, unprecedented among continental and insular endemic European leporids, is unclear. It could be the result of: (1) an independent evolution of p3 from an ancestor bearing the primitive P2/p3 (e.g., Alilepus, Hypolagus), or (2) a selective reversal morphocline from an Oryctolagus/Lepus-like leporine. The lack of data about the phylogenetic origin of the new taxon makes any inference about its possible arrival to Sardinia problematic. Crossing the European leporid records and evidence of migrations to Sardinia, we hypothesize three possible ages in which the ancestor of Sardolagus obscurus could have arrived in Sardinia, restricted to the late Miocene–early/late Pliocene (~8–3.6 Ma). The phylogenetic relationship between Sardolagus obscurus n. gen. n. sp. and the oldest Sardinian leporid, recorded from Capo Mannu D1 and dated at the early/late Pliocene boundary (~3.6 Ma), is unclear at present, however it is quite likely that they pertain to the same lineage.