Bagaceratops was among the smallest ceratopsians, growing up to 1–1.5 m (3.3–4.9 ft) in length, with a weight about 22.7–45 kg (50–99 lb). Although emerging late in the reign of the dinosaurs,Bagaceratops had a fairly primitive anatomy—when compared to the much derivedceratopsids—and kept the small body size that characterized early ceratopsians. Unlike its close relative,Protoceratops,Bagaceratops lacked premaxillary teeth (cylindrical, blunt teeth near the tip of the upper jaw).
Fossil localities of Mongolia and the location of Bayan Mandahu;Bagaceratops fossils have been reported from the Bayan Mandahu (bottom right), Hermiin Tsav, Khulsan (both left), and possibly Udyn Sayr (center) localities
During the large field work of the Polish-Mongolian Palaeontological Expeditions in the 1970s, abundant protoceratopsid specimens were discovered on eroded surfaces of the Hermiin Tsav locality of theBarun Goyot Formation,Gobi Desert. This newly collected and rich fossil material is stored in theInstitute of Paleobiology of thePolish Academy of Sciences (Poland). In 1975, two of the expedition's leading scientists, namely Polish paleontologistsTeresa Maryańska andHalszka Osmólska, published a largemonograph dedicated to describe this material where they named the new genus and type species of protoceratopsidBagaceratops rozhdestvenskyi. The selectedholotype isZPAL MgD-I/126, which consists of a relatively medium-sized skull, and a vast majority of the specimens collected by the expeditions were assigned toBagaceratops, including juvenile and sub-adult skulls. The generic name,Bagaceratops, means "small-horned face" and is derived from theMongolianbaga = meaning small; andGreekceratops = meaning horn face. The specific name,B. rozhdestvenskyi, is named in honor of the RussianpaleontologistAnatoly Konstantinovich Rozhdestvensky for his notorious work on dinosaurs.[1]
Diagram ofBagaceratops KID 196Bagaceratops specimen MPC-D 100/551B, which belongs to an indeterminate species
In 1993, the Japan-Mongolia Joint Paleontological Expedition collected an articulated and nearly completeBagaceratops skeleton (MPC-D 100/535) from the Barun Goyot Formation at the Hermiin Tsav locality.[2] In 2010 and 2011 this specimen was examined to analyze several borings (tunnel-like holes) left by invertebrae scavengers on joint areas.[3][4] As of 2019, MPC-D 100/535 remains largely undescribed.[5] In 2019 a partial skeleton (specimen KID 196) ofBagaceratops was described by Bitnara Kim and colleagues, who noted no significant differences between the skeleton ofProtoceratops and the former, with the exception of the anatomy of the skull and the shape and location of theclavicles. 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.[5]
In 2020, Czepiński described new specimens ofBagaceratops andProtoceratops from the Udyn Sayr and Zamyn Khond localities, respectively, of theDjadochta 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 ananagenetic transition fromProtoceratops andrewsi toBagaceratops rozhdestvenskyi.[6]
Juvenile remains, at first tentatively namedProtoceratops kozlowskii,[1] and then renamedBreviceratops kozlowskii by Kurzanov in 1990,[7] were considered to be juvenileBagaceratops.Paul Sereno in 2000 explained this by extrapolating that the juvenileBreviceratops would grow into a matureBagaceratops.[8]
In 2003 Russian paleontologist Vladimir R. Alifanov named the new taxaLamaceratops tereschenkoi andPlatyceratops tatarinovi from the Barun Goyot Formation. Material assigned by Alifanov corresponds to the holotype ofLamaceratops (PIN 4487/26; a partial small-sized skull), recovered from the Khulsan locality, and the holotype ofPlatyceratops (PIN 3142/4; an almost complete medium-sized skull), found in thered beds of the Hermiin Tsav locality. He also coined the family Bagaceratopidae in order to contain these new taxa andBagaceratops.[9] Also during 2003,You Hailu andDong Zhiming described and named the new genus and species of protoceratopsidMagnirostris dodsoni from red beds at the Bayan Mandahu locality of theBayan Mandahu Formation,Inner Mongolia (China). The holotype ofMagnirostris, IVPP V12513, represents a nearly complete skull lacking thefrill region of a large individual and was collected during expeditions led by the Sino-Canadian Dinosaur Project.[10] In 2006 Mackoviky regarded all of these ceratopsians asjunior synonyms ofBagaceratops based on the reasoning that all exhibit anatomical traits already seen on other specimens of this protoceratopsid, and some of them are likely products of preservation.[11]
Skeletal diagram featuring the known elements ofGobiceratops
In 2008 Alifanov described and named another ceratopsian taxon from the Barun Goyot Formation,Gobiceratops minitus. Its holotype (PIN 3142/299) is represented by a very small and juvenile skull that was collected from the Hermiin Tsav locality near the end of the 1970s by the Joint Soviet–Mongolian Paleontological Expedition. Though Alifanov used this skull to erect the newGobiceratops, it had already been displayed for several years at theMoscow Paleontological Museum under the nameBagaceratops rozhdestvenskyi.[12]
A comprehensive study on the intraspecific variation in morphology ofB. rozhdestvenskyi was conducted by Polish paleontologist Łukasz Czepiński in2019, where he concluded that the previously namedGobiceratops minutus,Lamaceratops tereschenkoi,Platyceratops tatarinovi andMagnirostris dodsoni represent additional specimens and growth stages ofB. rozhdestvenskyi and therefore, junior synonyms. Czepiński reexamined many of the specimens originally described by Maryańska and Osmólska, as well as the respective holotypes of these taxa, providing evidence that all traits used to separate them are, in fact, indistinguishably present onBagaceratops and they fall within the large intraspecific variation of this taxon. He also consideredBreviceratops to be a distinct and separate genus of protoceratopsid, from bothBagaceratops andProtoceratops, as it features a combination of basal (primitive) and derived (advanced) traits.[13]
Bagaceratops specimens compared to a 1.8 m (5.9 ft) tall human
Bagaceratops was a small-sized protoceratopsid, reaching adult dimensions of about 1–1.5 m (3.3–4.9 ft) in length[14][5] and 22.7–45 kg (50–99 lb) in body mass based onMaginostris.[15] It had a smaller frill, about ten grinding teeth per jaw, and more triangular skull than its close relative,Protoceratops. Although bothBagaceratops andProtoceratops were very similar (mostly in the postcranial skeleton), the former had a much derived (advanced) skull morphology.Bagaceratops lacked primitivepremaxillary teeth, had paired (fused) nasal bones, and an oval-shaped fenestra (hole) was developed in themaxilla—otherwise known as accessoryantorbital fenestra.[1][13]
Bagaceratops belonged toCeratopsia, a group of herbivorous dinosaurs withparrot-like beaks which thrived inNorth America andAsia during the Cretaceous Period, which ended roughly 66 million years ago.
In 2019 Czepiński analyzed a vast majority of referred specimens to the ceratopsiansBagaceratops andBreviceratops, and concluded that most were in fact specimens of the former. Although the generaGobiceratops,Lamaceratops,Magnirostris, andPlatyceratops, were long considered valid and distinct taxa, and sometimes placed withinProtoceratopsidae, Czepiński found the diagnostic features used to distinguish these taxa to be largely present inBagaceratops and thus becoming synonyms of this genus. Under this reasoning, Protoceratopsidae consists ofBagaceratops,Breviceratops, andProtoceratops. Based on cranial characters such as presence or absence of premaxillary teeth and an antorbital fenestra,P. andrewsi is the basal-most protoceratopsid andBagaceratops the derived-most one. Below are the proposed phylogenetic relationships within Protoceratopsidae by Czepiński:[13]
TheBarun Goyot Formation, based onsediments, is regarded asLate Cretaceous in age (Middle-UpperCampanian) and has virtually yielded the bulk of material for whichBagaceratops is known.[16][13] This formation is mostly characterized by series ofred beds, mostly light-colouredsands (yellowish, grey-brown, and rarely reddish) that are locally cemented. Sandyclaystones (often red-coloured),siltstones,conglomerates, and large-scale troughcross-stratification in sands are also common across the unit. In addition, structureless, medium-grained, fine-grained and very fine-grainedsandstones predominate in sediments of the Barun Goyot Formation. The sediments of this formation were deposited inalluvial plain (flat land consisting of sediments deposited by highlandrivers),lacustrine, andaeolian paleoenvironments, under relativelyarid tosemiarid climates.[17][18][16]
TheBayan Mandahu Formation, which yieldedMagnirostris (now synonym ofBagaceratops),[13] is considered to be Late Cretaceous in age, roughlyCampanian. The dominantlithology is reddish-brown, poorly cemented, fine grained sandstone with some conglomerate, andcaliche. Other facies includealluvial (stream-deposited) and aeolian (wind-deposited) sediments. It is likely that sediments at Bayan Mandahu were deposited by short-lived rivers andlakes on an alluvial plain with a combination ofdune field paleoenvironments, under a semi-arid climate. The formation is known for its vertebrate fossils in life-like poses, most of which are preserved in unstructured sandstone, indicating a catastrophic rapid burial.[33][34]
^Watabe, M., Suzuki, S., 2000a. Report on the Japan-Mongolia Joint Paleontological Expedition to the Gobi desert, 1993. Hayashibara Museum of Natural SciencesResearch Bulletin 1, 17 29.
^Alifanov, V. R. (2003). "Two new dinosaurs of the infraorder Neoceratopsia (Ornithischia) from the Upper Cretaceous of the Nemegt Depression, Mongolian People's Republic".Paleontological Journal.37 (5):524–534.
^abcdefgCzepiński, Ł. (2019). "Ontogeny and variation of a protoceratopsid dinosaurBagaceratops rozhdestvenskyi from the Late Cretaceous of the Gobi Desert".Historical Biology.32 (10):1394–1421.doi:10.1080/08912963.2019.1593404.S2CID132780322.
^abEberth, D. A. (2018). "Stratigraphy and paleoenvironmental evolution of the dinosaur-rich Baruungoyot-Nemegt succession (Upper Cretaceous), Nemegt Basin, southern Mongolia".Palaeogeography, Palaeoclimatology, Palaeoecology.494:29–50.Bibcode:2018PPP...494...29E.doi:10.1016/j.palaeo.2017.11.018.
^Arbour, V. M.; Currie, P. J.; Badamgarav, D. (2014). "The ankylosaurid dinosaurs of the Upper Cretaceous Baruungoyot and Nemegt formations of Mongolia".Zoological Journal of the Linnean Society.172 (3): 631−652.doi:10.1111/zoj.12185.
^Averianov, A. O.; Lopatin, A. V. (2022). "A re-appraisal of Parvicursor remotus from the Late Cretaceous of Mongolia: implications for the phylogeny and taxonomy of alvarezsaurid theropod dinosaurs".Journal of Systematic Palaeontology.19 (16):1097–1128.doi:10.1080/14772019.2021.2013965.S2CID247222017.
^Funston, G. F.; Mendonca, S. E.; Currie, P. J.; Barsbold, R.; Barsbold, R. (2018). "Oviraptorosaur anatomy, diversity and ecology in the Nemegt Basin".Palaeogeography, Palaeoclimatology, Palaeoecology.494:101–120.Bibcode:2018PPP...494..101F.doi:10.1016/j.palaeo.2017.10.023.
^Gradziński, R.; Jerzykiewicz, T. (1974). "Dinosaur- and mammal-bearing aeolian and associated deposits of the Upper Cretaceous in the Gobi Desert (Mongolia)".Sedimentary Geology.12 (4):249–278.Bibcode:1974SedG...12..249G.doi:10.1016/0037-0738(74)90021-9.
^Eberth, D. A. (1993). "Depositional environments and facies transitions of dinosaur-bearing Upper Cretaceous redbeds at Bayan Mandahu (Inner Mongolia, People's Republic of China)".Canadian Journal of Earth Sciences.30 (10): 2196−2213.Bibcode:1993CaJES..30.2196E.doi:10.1139/e93-191.
^Godefroit, P.; Currie, P. J.; Li, H.; Shang, C. Y.; Dong, Z.-M. (2008). "A new species of Velociraptor (Dinosauria: Dromaeosauridae) from the Upper Cretaceous of northern China".Journal of Vertebrate Paleontology.28 (2):432–438.doi:10.1671/0272-4634(2008)28[432:ANSOVD]2.0.CO;2.JSTOR20490961.S2CID129414074.
^Pei, R.; Qin, Yuying; Wen, Aishu; Zhao, Q.; Wang, Z.; Liu, Z.; Guo, W.; Liu, P.; Ye, W.; Wang, L.; Yin, Z.; Dai, R.; Xu, X. (2022). "A new troodontid from the Upper Cretaceous Gobi Basin of inner Mongolia, China".Cretaceous Research.130 (105052) 105052.Bibcode:2022CrRes.13005052P.doi:10.1016/j.cretres.2021.105052.S2CID244186762.
^Gao, K.; Hou, L. (1996). "Systematics and taxonomic diversity of squamates from the Upper Cretaceous Djadochta Formation, Bayan Mandahu, Gobi Desert, People's Republic of China".Canadian Journal of Earth Sciences.33 (4): 578−598.Bibcode:1996CaJES..33..578G.doi:10.1139/e96-043.
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