title: Tyrannosaurid skeletal design first evolved at small body size.
abstract: Nearly all of the large-bodied predators (>2.5 tons) on northern continents during the Late Cretaceous were tyrannosaurid dinosaurs. We show that their most conspicuous functional specializations--a proportionately large skull, incisiform premaxillary teeth, expanded jaw-closing musculature, diminutive forelimbs, and hindlimbs with cursorial proportions--were present in a new, small-bodied, basal tyrannosauroid from Lower Cretaceous rocks in northeastern China. These specializations, which were later scaled up in Late Cretaceous tyrannosaurids with body masses approaching 100 times greater, drove the most dominant radiation of macropredators of the Mesozoic.
authors.affiliation: Department of Organismal Biology and Anatomy, University of Chicago, Chicago, IL 60637, USA. dinosaur@uchicago.edu
authors.forename: Paul C
authors.initials: PC
authors.lastname: Sereno
authors.forename: Lin
authors.initials: L
authors.lastname: Tan
authors.forename: Stephen L
authors.initials: SL
authors.lastname: Brusatte
authors.forename: Henry J
authors.initials: HJ
authors.lastname: Kriegstein
authors.forename: Xijin
authors.initials: X
authors.lastname: Zhao
authors.forename: Karen
authors.initials: K
authors.lastname: Cloward
mesh_terms: D000818:Animals; D005075:Biological Evolution; D049628:Body Size; D001842:Bone and Bones / Q000033:anatomy & histology*; D054022:Cerebrum / Q000033:anatomy & histology; D002681:China; D025061:Dinosaurs / Q000033:anatomy & histology / Q000145:classification; D005552:Forelimb / Q000033:anatomy & histology; D005580:Fossils; D006614:Hindlimb / Q000033:anatomy & histology; D010802:Phylogeny; D012863:Skeleton; D012886:Skull / Q000033:anatomy & histology; D014070:Tooth / Q000033:anatomy & histology