paleoenvironment with the bird Elsornis; dromaeosaurids Mahakala and Velociraptor mongoliensis; and ornithomimid Aepyornithomimus. P. andrewsi is also abundant at Udyn Sayr, where Avimimus and Udanoceratops have been recovered. The relatively low dinosaur paleodiversity, small body size of most dinosaurs, and arid settings of the Djadokhta Formation compared to those of the Nemegt Formation, suggest that Protoceratops and contemporaneous biota lived in a stressed paleoenvironment (physical factors that generate adverse impacts on the ecosystem). In addition, the high occurrence of protoceratopsid fossils in arid-deposited formations indicates that these ceratopsians preferred warm environments. Although P. andrewsi was the predominant protoceratopsid on this formation, tentative remains of P. hellenikorhinus have been reported from the Udyn Sayr and Bor Tolgoi localities, suggesting that both species co-existed. Whereas P. andrewsi is found in aeolian sediments (Bayn Dzak or Tugriken Shireh), P. hellenikorhinus is found in the aeolian-fluvial sediments. As the latter type of sediments is also found in the Bayan Mandahu Formation, it is likely that P. hellenikorhinus preferred environments combining humid and arid conditions. Taphonomy In 1993 Jerzykiewiczz suggested that many articulated Protoceratops specimens died in the process of trying to free themselves from massive sand bodies that trapped them during sandstorms events and were not transported by environmental factors. He cited the distinctive posture of some Protoceratops involving the body and head arched upwards with forelimbs tucked in at their sides—a condition known as "standing" in particular cases—the absence of sedimentary structures in sediments preserving the individuals, and the Fighting Dinosaurs taphonomic history itself as evidence for this catastrophic preservation. Given that this posture is exhibited by populations from both Bayan Mandahu and Djadokhta formations, Jerzykiewiczz indicated that this behavior was not unique to any locality. He also considered it unlikely that these Protoceratops individuals died after burying themselves in the sand given that these specimens are only found in structureless sandstones; an arched posture would pose hard breathing conditions; and burrowers are known to excavate headfirst and sub horizontally. Fastovsky in 1997 examined the geology at Tugriken Shireh providing insights into the taphonomy of Protoceratops. He agreed in that the preservation of Protoceratops specimens indicate that they underwent a catastrophic event such as desert storms, and carcasses were not relocated by scavengers or environmental factors. Several isolated burrows found in sediments at this locality have also been reported penetrating in the bone surface of some buried Protoceratops individuals. Fastovsky pointed out these