Skull reconstruction of Effigia okeeffeae (AMNH FR 30587). (a, b) Lateral view, (c) reconstruction, (d, e) dorsal view and (f) reconstruction. Abbreviations: an, angular; d, dentary; f, frontal; j, jugal; l, lacrimal; m, maxilla; mf, mandibular fenestra; n, nasal; p, parietal; pal; palatine; pf, prefrontal; pm, premaxilla; po, postorbital; q, quadrate; qj, quadratojugal; sq, squamosal; sr, surangular.

(a) Phylogenetic positions of Effigia and Shuvosaurus among basal archosaurs. Unique tree shown (81 characters, length=156, RI=0.8320, CI=0.5897). The placement of Effigia within Theropoda requires the addition of 27 steps and the placement sister to ornithomimids requires the addition of 30 steps. The first number is the decay value and the second number is the bootstrap value. (b) The convergences listed below are present in Effigia and are characters that describe the dinosaurian clade and nested theropod clade. (i) Dinosauria. Reduction of arm/leg ration, postfrontal absent, ‘offset femoral head’, elongated parabasisphenoid. (ii) Neotheropoda. Enlargement of the preacetabular process of the ilium, incorporation of additional sacral vertebrae, hollow limbs, ‘antitrochanter’, present on the ilium, fusion of sacral vertebrae into rigid rod, fusion of the sacral neural arches, left and right oppression of the ischium, cervical vertebra pleurocoels. (iii) Coelurosauria. Increased pubic boot size, elongated prezygapophyses in distal caudal vertebrae, preacetabular fossa. (iv) Ornithomimosauria. Enlargement of the orbit, posteroventral rotation of the squamosal, anteroventrally angled quadrate, lacrimal–frontal contact absent. (v) Clade within Ornithomimosauria. Posterior directed process on each diapophysis of the posterior cervical vertebrae, edentulous jaws.

AMNH FR 30587. (a) Skeletal reconstruction of Effigia okeeffeae. The bones in grey are unknown. (b) Posterior caudal vertebrae (AMNH FR 30589) with overlapping prezygapophyses in lateral view. Arrow indicates anterior direction for the vertebrae only. (c) Articulated pelvis in lateral view. (d) Right coracoid in lateral view. (e) Anterior cervical vertebra in lateral view. (f) Incomplete right manus scaled to the right pes in dorsal view. (g) Right pes in dorsal view. (h) Right proximal part of the femur in medial view. (i) Articulation of the right ankle in posterior view. Abbreviations: as, astragalus; c, carpal; ca, calcaneum; cf, coracoid foramen; fi, fibula; gl, glenoid; il, ilium; ns, neural spine; prz, prezygapophysis; pu, pubis; sa, sacrum; ti, tibia. Scales=1 cm.