Editing Protoceratops (section)

===Movement===
[[File:Protoceratops juvenile and adult differences.jpg|thumb|left|Key differences between ''Protoceratops'' adults and juveniles]]
In 1996, Tereshchenko reconstructed the walking model of ''Protoceratops'' where he considered the most likely scenario to be ''Protoceratops'' as an obligate [[quadruped]] given the proportions of its limbs. The main gait of ''Protoceratops'' was probably [[trot]]-like mostly using its hindlimbs and it is unlikely to have used an asymmetric gait. If trapped in a specific situation (like danger or foraging), ''Protoceratops'' could have employed a rapid, [[facultative bipedalism]]. He also noted that the flat and wide pedal unguals of ''Protoceratops'' may have allowed efficient walking through loose terrain, such as [[sand]] which was common on its surroundings. Tereshchenko using [[speed]] [[equation]]s also estimated the average maximum walking speed of ''Protoceratops'' at about 3&nbsp;km/h ([[kilometres per hour]]).<ref>{{cite journal|last1=Tereschhenko|first1=V. S.|date=1996|title=A Reconstruction of the Locomotion of Protoceratops|journal=Paleontological Journal|volume=30|issue=2|pages=232–245|url=https://www.researchgate.net/publication/288362836}}</ref>

Upon the analysis of the forelimbs of several ceratopsians, Phil Senter in 2007 suggested that the hands of ''Protoceratops'' could reach the ground when the hindlimbs were upright, and the overall forelimb morphology and range of motion may reflect that it was at least a facultative (optional) quadruped. The forelimbs of ''Protoceratops'' could sprawl laterally but not for quadrupedal locomotion, which was accomplished with the elbows tucked in.<ref>{{cite journal|last1=Senter|first1=P.|date=2007|title=Analysis of forelimb function in basal ceratopsians|journal=Journal of Zoology|volume=273|issue=3|pages=305–314|doi=10.1111/j.1469-7998.2007.00329.x}}</ref> In 2010 Alexander Kuznetsov and Tereshchenko analyzed several vertebrae series of ''Protoceratops'' to estimate overall mobility, and concluded that ''Protoceratops'' had greater lateral mobility in the presacral (pre-hip) vertebrae series and reduced vertical mobility in the cervical (neck) region.<ref name=Kuznetsov2010/> The fossilized footprint associated with the specimen ZPAL Mg D-II/3 described by Niedźwiedzki in 2012 indicates that ''Protoceratops'' was [[digitigrade]], meaning that it walked with its toes supporting the body weight.<ref name=Nied2012/>

In 2019 however, Słowiak and team described the limb elements of ZPAL Mg D-II/3, which represents a sub-adult individual, and noted a mix of characters typical of [[bipedal]] ceratopsians such as a narrow glenoid with scapular blade and an arched femur. The absence of these traits in mature individuals indicates that young ''Protoceratops'' were capable of facultative bipedal locomotion and adults had an obligate quadrupedal stance. Even though adult ''Protoceratops'' were stocky and quadruped, their tibia-femur length ratio—the tibia being longer than femur, a trait present in bipedal ceratopsians—suggests the ability to occasionally stand on their hindlimbs. Słowiak and team also suggested that the flat and wide hand unguals (claw bone) of ''Protoceratops'' may have been useful for moving on loose terrain (such as sand) without sinking.<ref name=Justyna2019/>