New thylacinid species of Badjcinus, Nimbacinus, and Ngamalacinus are described from upper Oligocene deposits of the Riversleigh World Heritage Area, northwestern Queensland. Badjcinus timfaulkneri, Nimbacinus peterbridgei, and Ngamalacinus nigelmarveni are among the oldest thylacinids yet known and indicate an earlier diversification of the family than previously understood. Maximum parsimony analysis supports a sister group relationship between Ng. nigelmarveni and Ng. timmulvaneyi, but the relationships of the two other new taxa are unresolved. Bayesian dated total evidence analysis using morphological and molecular data supports the generic assignment of B. timfaulkneri and Ng. nigelmarveni but not that of Ni. peterbridgei. Both phylogenies herein support a taxonomic reassignment of Thylacinus macknessi to the genus Wabulacinus, a conclusion also supported by the results of previous studies. Body mass estimates based on molar size regressions indicate body sizes ranging from 3.7 kg to 11.4 kg for the new thylacinid species. Badjcinus timfaulkneri exhibits an extremely deep jaw compared with other thylacinids, with mandibular bending strength analysis suggesting that it was a highly durophagous carnivore much like the modern dasyurid Sarcophilus harrisii. This analysis also suggests Ni. peterbridgei had a dentary more similar in shape to that of plesiomorphic thylacinid faunivores such as Ni. dicksoni and T. cynocephalus suggesting that it had a relatively more generalist faunivorous diet. The molars of Ng. nigelmarveni suggest they were better suited for longitudinal slicing than the molars of B. timfaulkneri and Ni. peterbridgei, indicating a more hypercarnivorous diet compared with that of those species.