Tyrannosauroidea is a relatively derived group of theropod dinosaurs more closely related to birds than to other large theropods such as allosauroids and spinosaurids. The clade originated in the Middle Jurassic, approximately 165 million years ago, and for most of their evolutionary history, tyrannosauroids were mostly small-bodied animals that only reached gigantic size during the final 20 million years of the Cretaceous. Until recently, all tyrannosaurs fossils were limited to Asia and North America, but the latest discoveries suggest a more cosmopolitan distribution during their early evolution.
All tyrannosaurs were bipedal predators characterized by premaxillary teeth with a D-shaped cross section, fused nasals, extreme pneumaticity in the skull roof and lower jaws, a pronounced muscle attachment ridge on the ilium, and an elevated femoral head. The clade was a dominant component of the dinosaur faunas of the American West shortly after the emplacement of the Western Interior Seaway (about 99.5 Mya).
Dynamoterror dynastes, the most recent taxon described from the lower Campanian of northwestern New Mexico, provides additional data on the morphology and diversity of early tyrannosaurines in Laramidia. The new specimen lived during the Late Cretaceous period, approximately 78 million years ago. The name derived from Greek word dynamis (“power”) and the Latin word terror. The specific name is a Latin word meaning “ruler. Dynamoterror was collected in San Juan County, New Mexico, and is the first associated tyrannosaurid skeleton reported from the Menefee Formation.
The holotype (UMNH VP 28348) is an incomplete associated skeleton including the left and right frontals, four fragmentary vertebral centra, fragments of dorsal ribs, right metacarpal II, supraacetabular crest of the right ilium, unidentifiable fragments of long bones, phalanx 2 of left pedal digit IV, and phalanx 4 of left pedal digit IV. The right and left frontals both are incomplete; the dimensions of the right frontal are similar to a subadult specimen of Tyrannosaurus rex, suggesting that UMNH VP 28348 represents a subadult or adult individual. The reconstructed skull roof of Dynamoterror present several tyrannosaurine features, such as large supratemporal fossae and a tall sagittal crest on the frontals, providing an expanded attachment area for enormous jaw-closing muscles.
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