Tyrannosaurids are a significant part of the Latest Cretaceous Dinosaur faunas of Asia and North America, and include the giant predators Tyrannosaurus rex and Tarbosaurus bataar, as well as a variety of smaller forms. However, almost all known Tyrannosaurids are known from the last ten million years of the Cretaceous, with only one older species known, the 80 million-year-old Lythronax argestes, from the Wahweap Formation of Utah. This has the effect that, while the relationship of the Tyrannosaurids to other Theropod groups is well understood, exactly how they rose to dominance is somewhat of a mystery.
In a paper published in the journal PeerJ on 9 October 2018, Andrew McDonald of the Western Science Center, Douglas Wolfe of the Zuni Dinosaur Institute for Geosciences, and Alton Dooley, also of the Western Science Center describe a new species of Tyrannosaurid from the upper part of the 84.0–78.5 million-year-old Menefee Formation of San Juan County, New Mexico.
The new species is named Dynamoterror dynastes, where ‘Dynamoterror’ means ‘powerful terror’ and ‘dynastes’ means ‘ruler’. The species is described from fragmentary remains comprising the left and right frontals, four fragmentary vertebral centra, fragments of the dorsal ribs, the right metacarpal II, the supraacetabular crest of the right ilium, several unidentifiable fragments of long bones, phalanx 2 of left pedal digit IV, and phalanx 4 of left pedal digit IV. These fragments were found as float (i.e. they were loose on the surface) and excavations at the site could find no further material. All of the fragments were found together, and are consistent in size, leading McDonald et al. to conclude that they come from a single animal, interpreted to be a medium sized Tyrannosaurid Dinosaur, about nine metres in length.
The new species is named Dynamoterror dynastes, where ‘Dynamoterror’ means ‘powerful terror’ and ‘dynastes’ means ‘ruler’. The species is described from fragmentary remains comprising the left and right frontals, four fragmentary vertebral centra, fragments of the dorsal ribs, the right metacarpal II, the supraacetabular crest of the right ilium, several unidentifiable fragments of long bones, phalanx 2 of left pedal digit IV, and phalanx 4 of left pedal digit IV. These fragments were found as float (i.e. they were loose on the surface) and excavations at the site could find no further material. All of the fragments were found together, and are consistent in size, leading McDonald et al. to conclude that they come from a single animal, interpreted to be a medium sized Tyrannosaurid Dinosaur, about nine metres in length.
Frontals of Dynamoterror dynastes in rostral view. Photographs and 3-D models of right (A), (B) and left (C), (D). Abbreviations: bnp, basal of nasal process; cnc, caudal extent of nasal cavity; plp, prefrontolacrimal process; pnp, prefrontonasal process; rpos, rostral part of postorbital suture; vls, ventrolateral part of lacrimal suture. Scale bars equal five cm. McDonald et al. (2018).
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