The Eocene to Oligocene Nimravinae was the first radiation of cat-like carnivorans. This radiation was centered in North America. Generic and specific taxonomy and temporal ranges are discussed. Eleven North American species, in six genera, are recognized as valid. Cladistic analysis based on a preliminary character analysis provides strong support for clades consisting of Nimravus and Dinaelurus (Nimravini) and the species referred to Hoplophoneus and Eusmilus (Hoplophoneini). Pogonodon and the Hoplophoneini are sister taxa, and Dinictis and Hoplophoneus are probably paraphyletic. Dinictis, Pogonodon and the Hoplophoneini display moderate to extreme development of sabertooth morphologies, whereas the Nimravini lacks these cranial and mandibular features and Dinaelurus crassus has conical teeth. Species diversity increased from the Chadronian to the Whitney an and declined in the early Arikareean. Although the postcranial skeleton of the nimravines most resembles that of modern carnivorans that inhabit closed forest habitats, the diversification of the group coincided with the initial stages of the development of grassland habitats in central North America during the Eocene to Oligocene transition. Nonetheless, the extinction of the clade at the end of the early Arikareean might be associated with the widespread establishment of grassland ecosystems in the late Oligocene.
The Nimravidae are cat-like, predominately sabertoothed, carnivorans of late Eocene to late Miocene age that are known from North America, Europe, Asia, and Africa. Nimravids superficially resemble the true cats (Felidae) in their cranial morphology, hypercarnivorous dentition, and retractile claws.
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