animals, led the saber-toothed cats of each time period to extinction. As per Van Valkenburgh, the adaptations that made saber-toothed cats successful also made the creatures vulnerable to extinction. In her example, trends toward an increase in size, along with greater specialization, acted as a "macro-evolutionary ratchet": when large prey became scarce or extinct, these creatures would be unable to adapt to smaller prey or consume other sources of food, and would be unable to reduce their size so as to need less food. More recently, it has been suggested that Thylacosmilus differed radically from its placental counterparts in possessing differently shaped canines and lacking incisors. This suggests that it was not ecologically analogous to other saber-teeth and possibly an entrail specialist. Another study has found that other saber toothed species similarly had diverse lifestyles and that superficial anatomical similarities obscure them. Phylogeny of feliform saber-tooths The following cladogram shows the relationships between the feliform saber-tooths, including the Nimravidae, Barbourofelidae and Machairodontinae.Piras P, Maiorino L, Teresi L, Meloro C, Lucci F, Kotsakis T, Raia P (2013) Data from: Bite of the cats: relationships between functional integration and mechanical performance as revealed by mandible geometry. Dryad Digital Repository. https://dx.doi.org/10.5061/dryad.kp8t3 Saber-toothed groups are marked with background colors. Saber-tooth genera Saber-tooth taxonomy All saber-toothed mammals lived between 33.7 million and 9,000 years ago, but the evolutionary lines that led to the various saber-tooth genera started to diverge much earlier. It is thus a polyphyletic grouping. The lineage that led to Thylacosmilus was the first to split off, in the late Cretaceous. It is a metatherian, and thus more closely related to kangaroos and opossums than the felines. The hyaenodonts diverged next, possibly before Laurasiatheria, then the oxyaenids, and then the nimravids, before the diversification of the truly feline saber-tooths. Class: Mammalia Clade: Metatheria (diverged ?, in the Cretaceous) Order: †Deltatheroida (an extinct group of metatherian carnivores) Family: †Deltatheridiidae †Lotheridium Order: †Sparassodonta (an extinct group of metatherian carnivores) Family: †Thylacosmilidae †Patagosmilus †Anachlysictis †Thylacosmilus Subclass: Placentalia Order: †Hyaenodonta †Boualitomus Family: †Sinopidae Genus: †Sinopa Superfamily: †Hyaenodontoidea Family: †Hyaenodontidae Subfamily: †Hyaenodontinae Tribe: †Hyaenodontini Genus: †Hyaenodon Family: †Proviverridae †Parvagula Superfamily: †Hyainailouroidea Family: †Hyainailouridae (paraphyletic family) Subfamily: †Hyainailourinae (paraphyletic subfamily) Tribe: †Leakitheriini Genus: †Leakitherium Tribe: †Metapterodontini Genus: †Metapterodon Order: †Oxyaenodonta Family: †Oxyaenidae Subfamily: †Machaeroidinae Genus: †Apataelurus Genus: †Machaeroides Order Carnivora Family †Nimravidae (diverged from the feliforms 48–55 Ma BP, in the late Eocene) Subfamily †Nimravinae (Dinictis) Subfamily †Hoplophoninae Suborder