Figure Open Access
Bakker, R. T.,; Williams, M.; Currie, P. J.
Figure 2—Branching diagram of the tyrannosaurids and fheir close allies, with lateral views of the skulls shown in correct stratigraphic sequence. Nodes and the derived characters that define them: 1) Neotheropoda (Late Jurassic- Latest Cretaceous) — premaxillary tooth crowns strongly assymmetrical, with inner (lingual) face nearly flat and outer (buccal) face strongly convex; premax. symphysis U-shaped in dorsal view; intramandibular joint fully developed, with anterior prong of the angular penetrating into the cavity between the dentary and splenial. 2) Ceratosauridae (Late Jurassic) — premaxillary tooth count reduced to three; premaxillary incisors with thick, strong sulci and ridges on the inner face. 3) Advanced neotheropods (Late Jurassic-Latest Cretaceous) — occiput much deeper above the foramen magnum, as seen in posterior view; accessory antorbital fenestra present; posterior shafts of cervical ribs do not overlap one another; presacral column compresssed fore- to-aft relative to femur length; scapula blade very narrow throughout its length. 4) Allosauridae (Late Jurassic) — parocdpital process bent downwards strongly; basituber with a deep notch in the posterior-ventral edge for the ilio-costalis cervicis-capitis muscle; sphenethmoid ossification weak. 5) Very advanced neotheropods (Early Cretaceous-Latest Cretaceous) — ascending process of astragulus very tall, wide transversely and thin front-to-back; nasals narrow. 6) Dromaeosauridae (Early Cretaceous-Latest Cretaceous (Deinonychus) — pubis turned backwards; second hindclaw very large and sickle-shaped; distal half of tail encased within basketwork of bony rods developed from chevrons and prezygapophyses. 7) Tyrannosauroidea (Early Cretaceous-Latest Cretaceous) — paroccipital process very deep top-to-bottom at the root; large excavation around the fenestra ovalis and pneumatization of the paroccipital root. 8) Acrocanthosaurids (Early Cretaceous) — neural spine of cervicals and dorsals elongated. 9) Advanced tvrannosauroids (Late Cretaceous) — occiput deeper above the supraoccipital wedge; metatarsal bundle very long and compressed side-to-side, with strong pinching of the proximal end of metatarsal III. 10) Ornithomimids + troödontids + birds +?oviraptorids (?Latest Jurassic-Latest Cretaceous) — periotic region with large depression and highly pneumatic. 11) Tyrannosauridae (Late Cretaceous) — adductor muscle scar developed forward over the frontals to a position opposite the orbits; squamosal-quadratojugal suture very long, straight and nearly parallel to the long axis of the skull, as seen in side view; supraoccipital ' wedge with two tabs of bone placed in tandem; first maxillary tooth like the four premaxillary teeth; all incisiform teeth very crowded and narrow across buccal face; parietal occipital wings very tall above the supraoccipital; large oval foramen in jugal. 12) Nanotyrannus (Latest Cretaceous, Lanciat Faunal Age) —very wide basicranial boxwork with flat ventral floor; verv wide frontal-orbital region with very narrow snout; parietal wing of occiput with sharp angle between dorsal and lateral edges. 13) Rough-snouted tyrannosaurids (Late Cretaceous) — dorsal surface of nasals very rough, with irregular longitucinal striae and ridges. 14) Daspletosaurus torosus (Late Cretaceous, Judithan Faunal Age) — snout and mandible short front-toback and deep; teeth large and reduced in number; lachrimal horn developed into blunt triangular apex. 15) Tyrannosaurids with anterior pneumatic foramina in basicranial boxwork (Late Cretaceous). 16) Ahoramus (Late Cretaceous, Nemegt Fauna) — multiple oval hornlets on nasals. 17) Massive snouted tyrannosaurids with anterior basicranial foramina (Late Cretaceous) — snouts and mandibles short and deep; tooth count reduced. 18) New genus and species from the Horseshoe Canyon Formation Late Cretaceous) — orbit closed off from below by prong of postorbital. 19) Tyrannosaurids with large anterior foramina. 20) Gorgosaurus (Late Cretaceous, Judithan Faunal Age) — lachrimal horn developed into apex that is directed forward. 21) Tyrannosaurids with large foramina and wide basicrania (Late Cretaceous) — orbit closed off from below by postorbital; lachrimal and postorbital swollen above orbits; lachrimal swollen around pneumatic foramen; maxillary tooth row curved more strongly; maxillary tooth count reduced; mandible deeper; basicranial boxwork wider; first maxillary tooth enlarged. 22) Tarbosaurus (Late Cretaceous, Nemegt Fauna) — tooth crowns swollen and thick for their height. 23) Tyrannosaurus (Latest Cretaceous, Lancian Fauna) — teeth strongly procumbent; mandible very deep; lachrimal and postorbital very swollen above and behind orbit; muscle attachment surface, for anterior pterygoideus, at posterior-dorsal corner of antorbital fenestra eliminated by swelling of lachrimal; pneumatic foramen in lachrimal surrounded by grossly swollen bone; basicranium compressed fore-to-aft and basitubera displaced forward against basipterygoid processes