are generally recognized, although the membership of these groups varies somewhat from study to study and some coronosaurs may not fit in any of them. One group can be called Protoceratopsidae and includes Protoceratops and its closest relatives, all Asian. Another group, Leptoceratopsidae, includes mostly North American animals that are more closely related to Leptoceratops. The third group, Ceratopsoidea, includes the family Ceratopsidae and closely related animals like Zuniceratops. Ceratopsidae itself includes Triceratops and all the large North American ceratopsians and is further divided into the subfamilies Centrosaurinae and Chasmosaurinae. All previously published neoceratopsian phylogenetic analyses were incorporated into the analysis of Eric M. Morschhauser and colleagues in 2019, along with all previously published diagnostic species excluding the incomplete juvenile Archaeoceratops yujingziensis and the problematic genera Bainoceratops, Lamaceratops, Platyceratops and Gobiceratops that are very closely related to and potentially synonymous with Bagaceratops. While there were many unresolved areas of the strict consensus, including all of Leptoceratopsidae, a single most parsimonious tree was found that was most consistent with the relative ages of the taxa included, which is shown below. Paleobiology Unlike almost all other dinosaur groups, skulls are the most commonly preserved elements of ceratopsian skeletons and many species are known only from skulls. There is a great deal of variation between and even within ceratopsian species. Complete growth series from embryo to adult are known for Psittacosaurus and Protoceratops, allowing the study of ontogenetic variation in these species. Most restorations of ceratopsians show them with erect hindlimbs but semi-sprawling forelimbs, which suggest that they were not fast movers. But Paul and Christiansen (2000) argued that at least the later ceratopsians had upright forelimbs and the larger species may have been as fast as rhinos, which can run at up to 56 km or 35 miles per hour. A nocturnal lifestyle has been suggested for the primitive ceratopsian Protoceratops. However, comparisons between the scleral rings of Protoceratops and Psittacosaurus and modern birds and reptiles indicate that they may have been cathemeral, active throughout the day at short intervals. Paleoecology Paleobiogeography Ceratopsia appears to have originated in Asia, as all of the earliest members are found there. Fragmentary remains, including teeth, which appear to be neoceratopsian, are found in North America from the Albian stage (112 to 100 million years ago), indicating that the group had dispersed across what is now the Bering Strait by the middle of the Cretaceous Period.