Leptoceratopsidae

Leptoceratopsidae is an extinct family of neoceratopsian dinosaurs whose fossils have been found in Asia, North America, and possibly Europe. These animals looked similar to and were closely related to other neoceratopsians—like the families Protoceratopsidae and Ceratopsidae—but they were more primitive and usually smaller. The group was first described in 1923 by Franz Nopcsa von Felső-Szilvás as a subfamily called Leptoceratopsinae, with *Leptoceratops gracilis* as the type species. Note that the family-level name Leptoceratopsidae was not formally established until later by a different author.

In 2001, Mackovicky redefined Leptoceratopsidae as a stem-based family, including *Leptoceratops gracilis* and every species more closely related to it than to *Triceratops horridus*. A 2019 study by Eric M. Morschhauser and colleagues combined all earlier neoceratopsian phylogenetic analyses, excluding the incomplete juvenile *Archaeoceratops yujingziensis* and the problematic genera *Bainoceratops*, *Lamaceratops*, *Platyceratops*, and *Gobiceratops* (which are very close to, and possibly the same as, *Bagaceratops*). The strict consensus had many unresolved areas, including the whole of Leptoceratopsidae, but a single most parsimonious tree was found that best matched the relative ages of the included species.

Definitive leptoceratopsids lived in Asia and western North America during the Late Cretaceous, roughly 83 to 66 million years ago. However, material from the early Campanian of North Carolina and Sweden—referred to this family—may extend their range into eastern North America and Europe. A possible leptoceratopsid ulna called *Serendipaceratops* was found in Australia, but it is not universally accepted as such; it is often considered a nomen dubium because the fragmentary holotype cannot be confidently assigned to any ornithischian group, and it might even belong to an ankylosaur.

The oldest known leptoceratopsid is *Gryphoceratops*, from the late Santonian of Alberta, Canada, named from a partial left dentary. It is also probably the smallest adult ceratopsian known from North America. The youngest leptoceratopsid is *Leptoceratops*, which lived right at the end of the Cretaceous in the late Maastrichtian. In eastern North America, a partial maxilla from the early Campanian of North Carolina represents the first known ceratopsian from that region.