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Adaptive Features of Protoceratopoids (Ornithischia: Neoceratopsia)
The analysis of some morphological characteristics of protoceratopoid skeletons, the extent of mobility of the vertebral column, and the probable adaptive significance of these features suggest that Bagaceratops had a mostly aquatic mode of life, Protoceratops was semiaquatic, Udanoceratops was facultatively aquatic, and Leptoceratops was predominantly terrestrial. Protoceratopoids were quadrupeds, with the prevalence of hind limbs, probably using slow or rapid trotlike gait. An asymmetrical locomotion was most likely impossible. On dry land, Bagaceratops and Protoceratops moved slowly. Udanoceratops and Leptoceratops approximately equally used rapid and slow locomotor modes, although the second could run for a longer time than the first.
Schemes of cross section through the middle part of the tail: (a–d) reconstruction of tail section at 12–15cd: (a) Bagaceratops, (b) Protoceratops, (c) Udanoceratops, (d) Leptoceratops, (e) Alligator mississippiensis, at 21cd (after Frey, 1988, text- figs. 46c, 60c), and (f) Megalobatrachus japonicus, at 11cd. Designations: oblique lines show epaxial muscles, crossing lines are hypaxial muscles, dots are adipose tissue. All figures are given in equal heights of vertebral centers.