a circular or semi-circular shape—as previously hypothetized—with a diameter of . Most of the individuals within the nest had nearly the same age, size and growth, suggesting that they belonged to a single nest, rather than an aggregate of individuals. Fastovsky and team also suggested that even though the individuals were young, they were not perinates based on the absence of eggshell fragments and their large size compared to even more smaller juveniles from this locality. The fact that the individuals likely spend some time in the nest after hatching for growth suggests that Protoceratops parents might have cared for their young at nests during at least the early stages of life. As Protoceratops was a relatively basal (primitive) ceratopsian, the finding may imply that other ceratopsians provided care for their young as well. In 2017 Gregory M. Erickson and colleagues determined the incubation periods of P. andrewsi and Hypacrosaurus by using lines of arrested growth (LAGS; lines of growth) of the teeth in embryonic specimens (Protoceratops egg clutch MPC-D 100/1021). The results suggests a mean embryonic tooth replacement period of 30.68 days and relatively plesiomorphically (ancestral-shared) long incubation times for P. andrewsi, with a minimum incubation time of 83.16 days. Norell and team in 2020 analyzed again this clutch and concluded that Protoceratops laid soft-shelled eggs. Most embryos within this clutch have a flexed position and the outlines of eggs are also present, suggesting that they were buried in ovo (in the egg). The outlines of eggs and embryos indicates ellipsoid-shaped eggs in life with dimensions about long and wide. Several of the embryos were associated with a black to white halo (circumference). Norell and team performed histological examinations to its chemical composition, finding traces of proteinaceous eggshells, and when compared to other sauropsids the team concluded that they were not biomineralized in life and thus soft-shelled. Given that soft-shelled eggs are more vulnerable to deshydratation and crushing, Protoceratops may have buried its eggs in moisturized sand or soil. The growing embryos therefore relied on external heat and parental care. Paleopathology In 2018 Tereshchenko examined and described several articulated cervical vertebrae of P. andrewsi and reported the presence of two abnormally fused vertebrae (specimen PIN 3143/9). The fusion of the vertebrae was likely a product of disease or external damage. Predator–prey interactions Barsbold in 1974 shortly described the Fighting Dinosaurs specimen and discussed possible scenarios. The Velociraptor has its