SYSTEMATICS OF THE STENOMYLINI, THE NORTH AMERICAN, OLIGOCENE- MIOCENE, GAZELLE-LIKE CAMELS (MAMMALIA: ARTIODACTYLA: CAMELIDAE: STENOMYLINAE: STENOMYLINI)

The stenomylines, known as the “gazelle-like camels”, were a group of North American camels spanning the late Oligocene through the early Miocene. The subfamily Stenomylinae (Matthew, 1910) was comprised of 6 genera and within the subfamily, the tribe Stenomylini included four of the more derived genera: Stenomylus (Peterson, 1906), Wyomylus (Cassiliano, 2008), Blickomylus (Frick and Taylor, 1968), and Rakomylus (Frick 1937). This research presents a systematic revision of the tribe Stenomylini, which has not been reviewed at the generic level since Frick and Taylor (1968). In particular, the eponymous genus, Stenomylus, needs to be re-assessed due to questionable separation of species within the genus. S. gracilis (Peterson, 1906) and S. hitchcocki (Loomis, 1910) were mostly distinguished on the basis of relative size. However, standard dentition measurements of the premolar-to-molar length ratios reveal considerable overlap between the two species and statistical tests do not support a significant difference between the two. Even more, they are both known from the lower beds of the Harrison Formation. We find that there is no justification for the separation of S. gracilis and S. hitchcocki, making the latter a junior synonym. As a result, all museum exhibits, books, and websites that mention S. hitchcocki (the species name used for specimens from Stenomylus Quarry), will need to be updated. Thus, we recognize the 4 original genera, each of which is monotypic, except for Stenomylus, consisting of S. gracilis and S. keelinensis. With the systematics of the Stenomylini revised, it will be necessary to update the various paleobiological databases, which are currently full of outdated, invalid taxa, not only in the Stenomylini, but in most other camel groups too.