Teratophoneus
Teratophoneus ("monstrous murderer"; Greek: "teras", "monster" and "phoneus", "murderer") is a genus of tyrannosaurid dinosaur which lived during the late Cretaceous period (late Campanian age, about 77 to 76 million years ago) in what is now Utah, United States, containing a single known species, T. curriei. It is known from an incomplete skull and postcranial skeleton recovered from the Kaiparowits Formation. It was specifically named "T. curriei" in honor of Philip J. Currie. Discovery and naming. Fossils of "Teratophoneus" were first found in the Kaiparowits Formation of southern Utah. Later, fossils from the same formation were discovered and identified  as the genus. Argon-argon radiometric dating indicates that the Kaiparowits Formation was deposited between 76.1 and 74.0 million years ago, during the Campanian stage of the Late Cretaceous period. This date means that "Teratophoneus" lived in the middle of the Campanian stage of the Late Cretaceous. Several fossils of "Teratophoneus" have been found. Originally, "Teratophoneus" was described based on the holotype BYU 8120. More recently, the specimens UMNH VP 16690 and UMNP VP 16691 have been assigned to it. In 2017, a new specimen of "Teratophoneus" was discovered in the Grand Staircase-Escalante National Monument and airlifted to the  Natural History Museum of Utah in Salt Lake City. Later, in 2021, fossils belonging to 4 or 5 individuals were described in the same study. "Teratophoneus" was named by Thomas D. Carr, Thomas E. Williamson, Brooks B. Britt and Ken Stadtman in 2011. The type and only species was named "T. curriei". The generic name is derived from the Greek "teras", "monster", and "phoneus", "murderer." The specific name honors Philip J. Currie. Description. The holotype of "Teratophoneus" consists of a fragmentary skull and parts of the postcranial skeleton. The fossils were originally assigned to four different individuals, but are probably  only of a single subadult animal. The specimen of "Teratophoneus" was not fully grown: according to an estimate by Carr "et al". was about in length and in weight. In 2016, Molina-Pérez and Larramendi estimated it to be in length and in weight. Gregory S. Paul gave a higher estimation of and . Compared to the skull of an "Albertosaurus", "Teratophoneus" is roughly twenty-three percent shorter in proportion between the lacrimal bone of the and the tip of the snout. The skull of "Teratophoneus" is also comparably deeper. It is unclear if there was a specific reason for these  differences, but the extra depth may have allowed for stronger jaw muscles, increasing the bite force of "Teratophoneus". Classification. Loewen "et al." (2013) conducted a phylogenetic analysis of the family Tyrannosauridae, and confirmed the assignment of "Teratophoneus" to the tyrannosaurid sub-family Tyrannosaurinae. They concluded that "Teratophoneus" was closely related to both "Tarbosaurus" and "Tyrannosaurus", but placed in a more basal position within the family, though more derived than "Daspletosaurus". Below is the cladogram based on the phylogenetic analysis conducted by Loewen "et al." in 2013. In 2020, when describing the genus "Thanatotheristes", Voris "et al.", 2020 found "Teratophoneus" to  be in a subclade alongside "Dynamoterror" and "Lythronax". The clade remains unnamed. Paleobiology. Social Behavior. A bone bed of fossils from the Rainbows and Unicorns Quarry in Southern Utah's Kaiparowits Formation described in 2021 attributed to "Teratophoneus" suggests that the genus was a social pack-hunter. The fossils, consisting of four or possibly five animals ranging from 4-22 years of age, suggest a mass mortality event, possibly caused by flooding, or less likely by cyanobacterial toxicosis, fire or drought. The fact that all of the animals preserved died within a short time period further strengthens the argument for  gregarious behavior in tyrannosaurids, with bone beds of "Teratophoneus", "Albertosaurus", and "Daspletosaurus" showcasing the potential behavior may have been widespread amongst tyrannosaurs in general. Paleoecology. The holotype of "Teratophoneus" were recovered at the Kaiparowits Formation, in southern Utah. Argon-argon radiometric dating indicates that the fossils were buried during the Campanian stage of the Late Cretaceous period. During the Late Cretaceous period, the site within the Kaiparowits Formation was located on Laramidia near its eastern shore on the Western Interior Seaway, a large inland sea that split North America into two landmasses, the other being Appalachia to the east. The  plateau where dinosaurs lived was an ancient floodplain dominated by large channels and an abundance of wetland peat swamps, ponds and lakes, and was bordered by highlands. The climate was wet and humid, and supported an array of different and diverse groups of organisms. This formation contains one of the best and most continuous records of Late Cretaceous terrestrial life in the world. "Teratophoneus curriei" shared its paleoenvironment with theropods such as dromaeosaurids, the troodontid "Talos sampsoni", ornithomimids like "Ornithomimus velox", armored ankylosaurids, the duckbilled hadrosaurs "Parasaurolophus cyrtocristatus" and "Gryposaurus monumentensis", the ceratopsians "Utahceratops gettyi", "Nasutoceratops titusi", and "Kosmoceratops richardsoni , as well as the oviraptorosaurian Hagryphus giganteus". Paleofauna present in the Kaiparowits Formation included chondrichthyans (sharks and rays), frogs, salamanders, turtles, lizards, and crocodilians. A variety of early mammals were present including multituberculates, marsupials, and insectivorans.