sample of P. andrewsi specimens, primarily confluding that the neck frill of Protoceratops has no indicators or evidence for being sexually dimorphic. Obtained results showed instead that several regions of the skull of Protoceratops independently varied in their rate of growth, ontogenetic shape and morphology; a high growth of the frill during ontogeny in relation to other body regions; and a large variability of the neck frill independent of size. Knapp and team noted that results of the frill indicate that this structure had a major role in signaling within the species, consistent with selection of potential mates with quality ornamentation and hence reproductive success, or dominance signaling. Such use of the frill may suggest that intraspecific social behavior was highly important for Protoceratops. Results also support the general hypothesis that the neck frill of ceratopsians functioned as a socio-sexual signal structure. Reproduction In 1989, Walter P. Coombs concluded that crocodilians, ratite and megapode birds were suitable modern analogs for dinosaur nesting behavior. He largely considered elongatoolithid eggs to belong to Protoceratops because adult skeletons were found in close proximity to nests, interpreting this as an evidence for parental care. Furthermore, Coombs considered the large concentration of Protoceratops eggs at small regions as an indicator of marked philopatric nesting (nesting in the same area). The nest of Protoceratops would have been excavated with the hindlimbs and was built in a mound-like, crater-shaped center structure with the eggs arranged in semicircular fashion. Richard A. Thulborn in 1992 analyzed the different types of eggs and nests—the majority of them, in fact, elongatoolithid—referred to Protoceratops and their structure. He identified types A and B, both of them sharing the elongated shape. Type A eggs differed from type B eggs in having a pinched end. Based on comparisons with other ornithischian dinosaurs such as Maiasaura and Orodromeus—known from more complete nests—Thulborn concluded that most depictions of Protoceratops nests were based on incompletely preserved clutches and mostly on type A eggs, which were more likely to have been laid by an ornithopod. He concluded that nests were built in a shallow mound with the eggs laid radially, contrary to popular restorations of crater-like Protoceratops nests. In 2011 the first authentic nest of Protoceratops (MPC-D 100/530) from the Tugriken Shireh locality was described by David E. Fastovsky and team. As some individuals are closely appressed along the well-defined margin of the nest, it may have had