either a collapsed dune or sandstorm. Skin impressions and footprints During the Third Central Asiatic Expedition in 1923, a nearly complete Protoceratops skeleton (specimen AMNH 6418) was collected at the Flaming Cliffs. Unlike other specimens, it was discovered in a rolled-up position with its skull preserving a thin, hard, and wrinkled layer of matrix (surrounding sediments). This specimen was later described in 1940 by Brown and Schlaikjer, who discussed the nature of the matrix portion. They stated that this layer had a very skin-like texture and covered mostly the left side of the skull from the snout to the neck frill. Brown and Schlaikjer discarded the idea of possible skin impressions as this skin-like layer was likely a product of the decay and burial of the individual, making the sediments become highly attached to the skull. The potential importance of these remains were not recognized and given attention, and by 2020 the specimen has already been completely prepared losing all traces of this skin-like layer. Some elements were damaged in the process such as the rostrum. In 2022 Phil R. Bell and colleagues briefly described these potential soft tissues based on the photographs provided by Brown and Schlaikjer, as well as other ceratopsian soft tissues. However, although the initial perception was that the entire skin-like layer had been removed, photographs shared by Czepiński during the same year have revealed that the right side of the skull remains intact, retaining much of this layer and pending further analysis. Also from the context of the Polish-Mongolian paleontological expeditions, in 1965 an articulated subadult Protoceratops skeleton (specimen ZPAL Mg D-II/3) was collected from the Bayn Dzak locality of the Djadokhta Formation. In the 2000s during the preparation of the specimen, a fossilized cast of a four-toed digitigrade footprint was found below the pelvic girdle. This footprint was described in 2012 by Grzegorz Niedźwiedzki and colleagues who considered it to represent one of the first reported finds of a dinosaur footprint in association with an articulated skeleton, and also the first one reported for Protoceratops. The limb elements of the skeleton of ZPAL Mg D-II/3 were described in 2019 by paleontologists Justyna Słowiak, Victor S. Tereshchenko and Łucja Fostowicz-Frelik. Tereshchenko in 2021 fully described the axial skeleton of this specimen. Description Protoceratops was a relatively small-sized ceratopsian, with both P. andrewsi and P. hellenikorhinus estimated up to in length, and around in body mass.