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, (63), 55-81

A New Herrerasaurid (Dinosauria, Saurischia) From the Upper Triassic Ischigualasto Formation of Northwestern Argentina

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A New Herrerasaurid (Dinosauria, Saurischia) From the Upper Triassic Ischigualasto Formation of Northwestern Argentina

Oscar A Alcober et al. Zookeys.

Abstract

Herrerasauridae comprises a basal clade of dinosaurs best known from the Upper Triassic of Argentina and Brazil, which have yielded remains of Herrerasaurus ischigualastensis and Staurikosaurus pricei, respectively. Systematic opinion regarding the position of Herrerasauridae at the base of Dinosauria has varied. Here we describe a new herrerasaurid, Sanjuansaurus gordilloi gen. n., sp. n., based on a partial skeleton from Carnian-age strata of the the Upper Triassic Ischigualasto Formation of northwestern Argentina. The new taxon is diagnosed by numerous features, including long, band-shaped and posterolaterally oriented transverse process on the posterior cervical vertebrae; neural spines of the sixth to eighth dorsal vertebrae, at least, bearing acute anterior and posterior processes; scapula and coracoid with everted lateral margins of the glenoid; and short pubis (63% of the femoral length). Phylogenetic analysis placed Sanjuansaurus within a monophyletic Herrerasauridae, at the base of Theropoda and including Herrerasaurus and Staurikosaurus. The presence of Sanjuansaurus at the base of the Ischigualasto Formation, along with other dinosaurs such as Herrerasaurus, Eoraptor, Panphagia, and Chromogisaurus suggests that saurischian dinosaurs in southwestern Pangea were already widely diversified by the late Carnian rather than increasing in diversity across the Carnian-Norian boundary.

Keywords: Carnian; Dinosauria; Herrerasauridae; Ischigualasto; Saurischia.

Figures

Figure 1.
Figure 1.
Geological map of the Ischigualasto – Villa Unión Basin (northwestern Argentina) and section of the Ischigualasto Formation at the type locality. The red star indicates the site of the holotype of Sanjuansaurus gordilloi (PVSJ 605), near the base of the Ischigualasto Formation.
Figure 2.
Figure 2.
Preserved bones of Sanjuansaurus gordilloi (PVSJ 605), positioned as they were found in the field. Abbreviations: ca1–15, caudal vertebrae 1–15; c2–9, cervical vertebrae 2–9; d1–14, dorsal vertebrae 1–14; l Fe, left femur; l il, left ilium; l MII, left metatarsal II; l Sc, left scapula and coracoid; l Ti, left tibia; l Ul, left ulna; Ph, manual phalanx; R, rib; r As-Ca, right astragalus and calcaneum; r Fe, right femur; r Fi, right fibula; r Fe, right femur; r Mx, right maxilla; r Pu, right pubis; r Sc, right scapula and coracoid; r Ti, right tibia; s1–3, sacral vertebrae 1–3. Scale bars equals 20 cm.
Figure 3.
Figure 3.
Silhouette reconstruction of the skeletons of the best known herrerasaurids.Sanjuansaurus gordilloi (PVSJ 605) (A) Herrerasaurus ischigualastensis (B) Staurikosaurus pricei (C) Scale bars equals 20 cm. A: missing bones of Sanjuansaurus modified from Sereno 1994; B: from Sereno 1994; C: from Novas 1997.
Figure 4.
Figure 4.
Maxilla of Sanjuansaurus gordilloi (PVSJ 605). Left maxilla of Sanjuansaurus in lateral view (A) Skull of Herrerasaurus (PVSJ 407) in left lateral view (B) Left maxilla of Herrerasaurus (PVSJ 053) in lateral view (C) Abbreviations: af, antorbital fossa; dp, dorsal process; ip, internarial process; J, jugal; jp, jugal process; M, maxilla; of, oval fenestra; pf, promaxillary fenestra; PO, postorbital. Scale bars equals 5 cm.
Figure 5.
Figure 5.
Axial skeleton of Sanjuansaurus gordilloi (PVSJ 605). Nine anterior cervical and two anterior dorsal vertebrae in left lateral view (A). Cervical vertebrae 7, 8 and 9 in left lateral view (B). Dorsal vertebra 1 to caudal vertebra 1 in left lateral view (C). Reconstruction of the sacrum in left lateral view (D). Caudal vertebra 1 to 12 in left lateral view (E). Abbreviations: acdl, anterior centrodiapophyseal lamina; ai, axis intercentrum; ap, anterior process of dorsal neural spine; ca1–12, caudal vertebrae 1 to 12; c2–9, cervical vertebrae 2 to 9; d, diapophysis; d1–13, dorsal vertebrae 1 to 13; ep, epipophysis; ns, neural spine; od, odontoides; p, parapophysis; pcdl, posterior centrodiapophyseal lamina; prz, prezygapophysis; poz, postzygapophysis; pp, posterior process of dorsal neural spine; s1–3, sacral vertebrae 1 to 3; sr1–3, sacral ribs 1 to 3; st, spine table; t, tooth; tp, transverse process; vk, ventral keel. Scale bar equals 5 cm.
Figure 6.
Figure 6.
Preserved shoulder blade and forelimb bones of Sanjuansaurus gordilloi (PVSJ 605). Left scapula and coracoid inposterior(A), and lateral (B) views. Left ulna in lateral (C), medial (D), and anterior views (E). Ungual phalanx of digit III in proximal (F) and lateral view (G). Abbreviations: ac, acromion; ar, anterior ridge; C, coracoid; cg, collateral groove; Cf, coracoid foramen; Cl, coracoid lip; g, glenoid surface; Haf, humeral articular facet; lc, lateral crest; lp, lateral prominence; lr, lateral ridge; ls, ligament scars; lp, lateral prominence; ol, olecranon ; ovd, oval depression; pvp, posteroventral process; Raf, radius articular facet; S, scapula; Sl, scapular lip; Uaf, ulnare articular facet. Scale bar equals 5 cm.
Figure 7.
Figure 7.
Pelvic and hind limb bones of Sanjuansaurus gordilloi (PVSJ 605). Right pubis in anterodorsal (A), lateral (B), and medial views (C). Left femur articulated with the preacetabular portion of the ilium and proximal end of the pubis in lateral view (D). Right femur in medial view (E). Right femur head in proximal view (F). Proximal end of the right femur in anteromedial view (G). Distal end of the left femur in distal view (H). Left tibia in lateral (I), medial (J), anterior (K), posterior (L), proximal (M), and distal views (N). Left metatarsal II in anterior view (O). Distal end of the right tibia in posterior view (P). Abbreviations: aa, acetabular area; ao, abnormal outgrowth in posteroventral process; cc, cnemial crest; ctf, crista tibiofibularis; 4t, fourth trochanter; fc, fibular condyle; fh, femoral head; gt, greater trochanter; Isaf, ischium articular facet; Il, illium; Isaf, ischium articular facet; lc, lateral condyle; mae, ambiens muscle eminence; mCFLs, scars for attachment of muscle caudifemoralis longus; of, obturator foramen; pf, pubic foot; pv, posteroventral process; rP, right pubis; sac, supraacetabular crest; tc, tibial condyle; ts, trochanteric shelf. Scale bar equals 5 cm.
Figure 8.
Figure 8.
Right astragalus and calcaneum of Sanjuansaurus gordilloi (PVSJ 605). Right astragalus and calcaneum in proximal (A), distal (B), anterior (C), posterior (D), lateral (E), and medial views (F). Abbreviations: A, astragalus; ap, ascending process; C, calcaneum; f, foramen; pmb, posteromedial border; ps, posterior shelf; r, ridge. Scale bar equals 2 cm.
Figure 9.
Figure 9.
Single most parsimonious tree (MPT) resulting from the present parsimony analysis (tree length 190 steps; consistency index 0.553, retention index 0.593).

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