The only two specimens of Diabloceratops eatoni were recovered at the Wahweap Formation, in Kane County, Utah. Type specimen UMNH VP 16699 was collected by Don DeBlieux in 2002, at the Last Chance Creek locality of this formation, in intraclastic sandstone that was deposited during the Campanianstage of the Cretaceous period, approximately 81 to 76 million years ago. It consists of a partial skull with a piece of the lower jaw, with the right side being intact and part of the left side, which has been weathered. Another specimen UMNH VP 16704 was discovered years earlier in 1998 by Joshua A. Smith of the same formation, but was not described until 2010, when it was assigned to Diabloceratops. These specimens are housed in the collection of the Natural History Museum of Utah.
Description
Diabloceratops was built like a typical ceratopsian in that it had a large neck frill made of bone. It had a small horn on the nose, perhaps a second horn in front of that, and a pair of relatively small horns above the eyes. The skull is deeper and shorter than that of any other centrosaurines. Upon the frill it also had a pair of very long spikes as in Einiosaurus and Styracosaurus. It being one of the earliest centrosaurine ceratopsids, Kirkland noted a character Diabloceratops shared with the more "primitive" protoceratopsid forms. Both possess an accessory opening in the skull that would become much reduced or disappear in later, more advanced ceratopsids. Kirkland saw this as an indication that the earlier species were not together included in some single natural group but instead presented a gradual sequence of ever more derived forms, increasingly closer related to the Ceratopsidae.
The Wahweap Formation has been radiometrically dated as being between 81 and 76 million years old. During the time that Diabloceratops lived, the Western Interior Seaway was at its widest extent, almost completely isolating southern Laramidia from the rest of North America. The area where dinosaurs lived included lakes, floodplains, and east-flowing rivers. The Wahweap Formation is part of the Grand Staircase region, an immense sequence of sedimentary rock layers that stretch south from Bryce Canyon National Park through Zion National Park and into the Grand Canyon. The presence of rapid sedimentation and other evidence suggests a wet, seasonal climate.
Paleofauna
Diabloceratops shared its paleoenvironment with other dinosaurs, such as the hadrosaurAcristavus gagslarsoni, and the lambeosaurAdelolophus hutchisoni, unnamed ankylosaurs and pachycephalosaurs, and the theropodLythronax argestes, which was likely the apex predator in its ecosystem. Vertebrates present in the Wahweap Formation at the time of Diabloceratops included freshwater fish, bowfins, abundant rays and sharks, turtles like Compsemys, crocodilians, and lungfish. A fair number of mammals lived in this region, which included several genera of multituberculates, cladotherians, marsupials, and placentalinsectivores. The mammals are more primitive than those that lived in the area that is now the Kaiparowits Formation. Trace fossils are relatively abundant in the Wahweap Formation, and suggest the presence of crocodylomorphs, as well as ornithischian and theropod dinosaurs. In 2010 a unique trace fossil was discovered that suggests a predator-prey relationship between dinosaurs and primitive mammals. The trace fossil includes at least two fossilized mammalian den complexes as well as associated digging grooves presumably caused by a maniraptoran dinosaur. The proximity indicates a case of probable active predation of the burrow inhabitants by the animals that made the claw marks. Invertebrate activity in this formation ranged from fossilized insect burrows in petrified logs to various mollusks, large crabs, and a wide diversity of gastropods and ostracods.
