Bagaceratops
Bagaceratops (meaning "small-horned face") is a genus of ceratopsian dinosaur that lived in what is now the Barun Goyot Formation and Bayan Mandahu Formation, during the Late Cretaceous. One specimen may argue the possible presence of "Bagaceratops" in the Djadochta Formation. Although emerging late in the reign of the dinosaurs, "Bagaceratops" had a fairly primitive anatomy—when compared to other much derived ceratopsians—and kept the small body size that characterized early ceratopsians. History of discovery. The first remains of "Bagaceratops" were discovered in the Gobi Desert during the 1970s by a joint expedition composed of Mongolian and  Polish scientists and it was described in 1975 by two of the expedition's leading scientists, Teresa Maryanska and Halszka Osmólska. Several of these "Bagaceratops" specimens are at Poland's Paleobiological Institute in Warsaw. The holotype is ZPAL MgD-I/126, a medium-sized skull from the Hermiin Tsav locality of the Barun Goyot Formation, during the Campanian stage of the Late Cretaceous. The generic name, "Bagaceratops", means "small-horned face" and is derived from the Mongolian "Baga" = "small"; Greek "ceratops" = "horn face". The type and only species, "B. rozhdestvenskyi", was named in honor of the Russian paleontologist Anatoly  Konstantinovich Rozhdestvensky. "Bagaceratops" is known from five complete and twenty partial crania, the longest of which is 17 cm long. The skulls are spread throughout the life stages of the animal, with the smallest being only 4.7 cm long, so the growth stages are relatively well understood. The smaller juvenile skulls were about the same size as a golf ball. Only fragmentary remains of "Bagaceratops" post-cranial anatomy have been found. Juvenile remains, at first tentatively named "Protoceratops kozlowskii", and then renamed "Breviceratops kozlowskii" by Kurzanov in 1990 are now felt to be juvenile "Bagaceratops". Paul Sereno in 2000 explained  this by extrapolating that the juvenile "Breviceratops" would grow into a mature "Bagaceratops". In 1993, JMPJE collected the articulated and nearly complete "Bagaceratops" skeleton (MPC-D 100/535) from the Barun Goyot Formation at the Hermiin Tsav locality. In 2010 and 2011 this specimen was examined to analyze several borings (tunnel-like holes) left by invertebrae scavengers on joint areas. As of 2019, MPC-D 100/535 remains largely undescribed. In 2019 a partial skeleton (specimen KID 196) of "Bagaceratops" was described by Bitnara Kim and colleagues, who noted no significant diifferences between the skeleton of "Protoceratops" and the former. This specimen  was discovered in 2007 also from the Hermiin Tsav locality of the Barun Goyot Formation, and includes a partially preserved skull with partial skeleton of an adult individual. A study on the nature of the observed variation in morphology and size of skulls of "Bagaceratops" was performed by Łukasz Czepiński in 2019, who also considered the species "Gobiceratops minutus", "Lamaceratops tereschenkoi", "Platyceratops tatarinovi" and "Magnirostris dodsoni" to be potential growth stages of "B. rozhdestvenskyi" and therefore, junior synonyms. In 2020, Czepiński described new specimens of "Bagaceratops" and "Protoceratops" from the Üüden Sair and Zamyn Khond localities of the Barun Goyot  Formation or Djadochta Formation, and evaluated the implications of these specimens for correlation of fossil sites of the latter formation. He considered one of these specimens in particular, MPC-D 100/551B, as a potential evidence of an anagenetic transition from "Protoceratops andrewsi" to "Bagaceratops rozhdestvenskyi". Description. "Bagaceratops" grew to an adult size of about long, high, and weighed around . It had a smaller frill (which lacked fenestrae), and only ten grinding teeth per jaw, and more triangular skull than its close relative, "Protoceratops". "Bagaceratops" evolved later but retains more primitive characteristics than its earlier relative. Otherwise the two dinosaurs were  very similar, each had a beak but no brow horns, and a small horn-like prominence on the snout. Classification. "Bagaceratops" belonged to the Ceratopsia, a group of herbivorous dinosaurs with parrot-like beaks which thrived in North America and Asia during the Cretaceous Period, which ended roughly 66 million years ago. In 2019 Czepiński analyzed a vast majority of referred specimens to the ceratopsians "Bagaceratops" and "Breviceratops", and concluded that most were in fact specimens of the former. Although the genera "Gobiceratops", "Lamaceratops", "Magnirostris", and "Platyceratops", were long considered valid and distinct taxa, and sometimes placed within Protoceratopsidae, Czepiński  found the diagnostic features used to distinguish these taxa to be largely present in "Bagaceratops" and thus becoming synonyms of this genus. Under this reasoning, Protoceratopsidae consists of "Bagaceratops", "Breviceratops", and "Protoceratops". Based on cranial characters such as presence or absence of premaxillary teeth and an antorbital fenestra, "P. andrewsi" is the basal-most protoceratopsid and "Bagaceratops" the derived-most one. Below are the proposed phylogenetic relationships within Protoceratopsidae by Czepiński: Diet. "Bagaceratops", like all ceratopsians, was a herbivore. During the Cretaceous, flowering plants were "geographically limited on the landscape", and so it is likely that this dinosaur fed on  the predominant plants of the era: ferns, cycads and conifers. It would have used its sharp ceratopsian beak to bite off the leaves or needles.