The Mazongshan Dinosaur Fauna (MDF) includes all dinosaurs recovered from the late Early Cretaceous Xiagou and Zhonggou formations in the Mazongshan area of Gansu Province in northwestern China. Currently, 11 distinctive dinosaur genera have been recovered in this fauna, representing three theropods, two sauropods, four hadrosauroids, and two neoceratopsians. Four features can be recognized for the MDF: (1) the presence of large herbivorous theropods, such as the therizinosaur Suzhousaurus and ornithomimosaur Beishanlong; (2) the presence of diverse basal hadrosauroids, represented by at least four genera; (3) an abundance of basal neoceratopsians, represented by numerous individuals of Auroraceratops; and (4) an apparent lack of psittacosaurids. The MDF is unique and different from any other known dinosaur faunas, including that from the Jehol Biota.

The Early Cretaceous of northwest China has yielded abundant vertebrates, invertebrates, and plant fossils from numerous intermontane basins. Developing a chronostratigraphic context for these important fossil finds is important to understanding the development of modern terrestrial ecosystems, the evolution of dinosaurs, and the Cretaceous greenhouse climate. This study utilizes carbon isotope chemostratigraphy of the fossil-rich Xinminpu Group in the Yujingzi Basin in northwest Gansu Province. Lithostratigraphic descriptions defined three facies. The lowest is a tan, coarse arkosic sandstone, overlain by gray to variegated mudstones, sandstones, and thin limestones, which transition to red sandstones, conglomerates, and mudstones. Depositional environment interpretation of these lithofacies assisted in refining 450 samples of bulk sedimentary organic carbon as well as charcoal samples to develop a composite curve to correlate to existing carbon isotope curves from the region and to better constrained Cretaceous sections globally. The carbon isotope curve is correlated based on the broad positive excursion associated with carbon isotope fluctuations of the Paquier Episode that spans the late Aptian to early Albian. Based on this correlation, the middle gray mudstone facies, which contains a diverse fauna including theropods, sauropods, and ornithopods, as well as turtles and invertebrates, is placed within the upper Aptian. The upper red sandstone facies, which contains therizinosaurs and the ceratopsian dinosaur Auroraceratops, is placed in the lower Albian.

Auroraceratops rugosus from the Lower Cretaceous Zhonggou Formation, Gansu Province, China is characterized by exquisite external preservation of articulated, often ventrolaterally curled remains found in discrete locations several to hundreds of meters apart. This has prompted a hypothesis that the remains are the result of recurring die-offs and rapid burial in burrows. To test this, rare earth element (REE) concentrations were measured from Auroraceratops bones and surrounding red-bed mudstones via inductively coupled plasma mass spectrometry. Petrographic analysis was conducted to understand the preservation of the bones and surrounding rock. Results suggest early postmortem deterioration of the bone by bacteria and/ or fungal hyphae (Wedl type I tunneling and mineralized remains) and mineralization of hyphae in acidic/reducing conditions. This is supported by Ce-enriched, filamentous ferromanganese oxide coatings on the external and internal bone cavities. Deterioration/dissolution of the bone must have ceased for a period of time, and we suggest that desiccation of the carcasses halted the deterioration of bone. A second mineralization phase occurred as remains came into contact with vadose water, as evident by precipitation of micritic calcite, recrystallization of filamentous apatite in the bone matrix, and bone REE patterns indicating equilibration with alkaline/oxidized fluids. Despite poor histologic preservation, the well-articulated, curled-up positioning of the remains, and similarity to remains from the Upper Cretaceous Nemegt Formation of Mongolia, suggests that the Auroraceratops beds are the result of death in burrows in a seasonally arid environment. The similar taphonomic mode to remains from Nemegt may represent a common preservation mode for faunas from extensional basin deposits.

The basal neoceratopsian dinosaur Auroraceratops rugosus was described based on a single skull from the Gongpoquan Basin in northwestern Gansu Province, China. The genus is now known from over 80 specimens, including many from the neighboring Yujingzi Basin. Auroraceratops is one of the best-known basal neoceratopsians. Auroraceratops can be diagnosed by the following autapomorphies: inflated premaxillary teeth; a fungiform expansion of the lacrimal; large tuber caudodorsally on the dentary near the contact with the surangular; and tubercle on the lateral face of the dentary at about the middle of the mandible. Auroraceratops also has a combination of plesiomorphic and derived characters. It possesses characters plesiomorphic to Neoceratopsia, such as broad nasals (seen in basal ceratopsians, such as Yinlong), the absence of a lateral ridge on the surangular, a relatively high number of premaxillary teeth (three), and rugosity on the dentary, jugal, surangular, and sometimes the postorbital, which is in detail similar to that seen in chaoyangsaurids. At the same time, Auroraceratops possesses derived characters not seen in Liaoceratops, the earliest diverging member of Neoceratopsia. These features include an epijugal and a surangular wall lateral to the mandibular glenoid fossa. The cranial anatomy of the early horned dinosaur Auroraceratops rugosus is described.

The Early Cretaceous basal neoceratopsian dinosaur Auroraceratops rugosus was described based on a single skull recovered from the Gonpoquan Basin in northwestern Gansu Province, China. The genus is now known from cranial and postcranial remains representing at least 80 individuals, many of which come from the neighboring Yujingzi Basin, with an age of Aptian to earliest Albian (126-115 Ma). Among the new material were four syncervicals, representing the phylogenetically and temporally earliest occurrence of a syncervical in Ceratopsia. The anatomy of the syncervical matches that described in leptoceratopsids and protoceratopsids, with the first segment formed from a small atlas centrum, a much larger atlantal intercentrum, and a splint-like, divided atlantal neural arch. The axis bears a large hatchet-shaped neural spine and facets for a double-headed cervical rib. The centra of the first three cervical vertebrae and the first two intercentra are fused, though the boundaries of the individual elements are discernable. The relatively early temporal and phylogenetic appearance of a syncervical supports recent work that shows that the syncervical of ceratopsians is unrelated to the larger head size and cranial ornamentation characteristic of later appearing ceratopsian clades.

The species Auroraceratops rugosus was originally described based upon a single skull. With the recovery of over 80 individuals, a complete description of the postcranial skeleton is presented. Auroraceratops is currently the most complete exemplar we have of ceratopsian postcranial anatomy between Psittacosaurus and Leptoceratops. Adult Auroraceratops had a length of approximately 125 cm and an approximate hip height of 44 cm. Osteological correlates of stance in the fore- and hind limb unequivocally indicate a bipedal gait. The phylogenetically corrected quadrupedal massestimation equation modified for mass estimation of bipedal terrestrial vertebrates estimates an average mass of Auroraceratops at 15.5 kg. It has the phylogenetically and temporally earliest documentation of the syncervical in Ceratopsia. The mid-caudal neural spines are elongate and erect, a feature previously only known in Leptoceratopsidae and Protoceratopsidae. Despite being longer than in most ceratopsians, the mid-caudal neural spines are not as tall as in some leptoceratopsids. Most of the phylogenetically relevant characters of the postcranial skeleton in Auroraceratops are a mosaic of features plesiomorphic to Neoceratopsia and features previously considered to be unique to later diverging clades, such as Leptoceratopsidae and Protoceratopsidae.

Basal neoceratopsians are a relatively diverse group of small- to medium-sized herbivorous dinosaurs from the Early to Late Cretaceous of Asia and North America. Although known for over a century, this group has only relatively recently received intense independent study, tied to the rapid increase in known diversity since 1997. Auroraceratops rugosus is one of these recently discovered species and is one of the best-known basal neoceratopsians, being represented by over 80 specimens, and is also the most completely represented neoceratopsian from the Early Cretaceous. A phylogenetic analysis focusing on non-ceratopsid ceratopsians examines the phylogenetic context of Auroraceratops. The analysis is based on a new matrix of 41 taxa and 257 characters. The results recover an Auroraceratops-Aquilops-ZPAL MgD-I/156 clade within basal Neoceratopsia that is sister to a clade composed of Asiaceratops, Yamaceratops, Mosaiceratops, and the larger clades Leptoceratopsidae and Coronosauria. This phylogeny recovers a monophyletic Coronosauria, Leptoceratopsidae, and Protoceratopsidae. Helioceratops is recovered as sister to the rest of Leptoceratopsidae, Ischioceratops is recovered nested within Leptoceratopsidae, and the enigmatic genus Mosaiceratops is recovered as a basal neoceratopsian, sister to Yamaceratops. Yinlong, and Hualianceratops are recovered in an expanded Chaoyangsauridae, and the genus Psittacosaurus is recovered as the earliest diverging lineage in Ceratopsia. Ajkaceratops, the only European ceratopsian, is robustly recovered as sister to the rest of Ceratopsoidea.