A new basal sauropodomorph (Dinosauria: Saurischia) from Quebrada del Barro Formation (Marayes-El Carrizal Basin), northwestern Argentina - PubMed (original) (raw)

A new basal sauropodomorph (Dinosauria: Saurischia) from Quebrada del Barro Formation (Marayes-El Carrizal Basin), northwestern Argentina

Cecilia Apaldetti et al. PLoS One. 2011.

Abstract

Background: Argentinean basal sauropodomorphs are known by several specimens from different basins; Ischigualasto, El Tranquilo, and Mogna. The Argentinean record is diverse and includes some of the most primitive known sauropodomorphs such as Panphagia and Chromogisaurus, as well as more derived forms, including several massospondylids. Until now, the Massospondylidae were the group of basal sauropodomorphs most widely spread around Pangea with a record in almost all continents, mostly from the southern hemisphere, including the only record from Antarctica.

Methodology/principal finding: We describe here a new basal sauropodomorph, Leyesaurus marayensis gen. et sp. nov., from the Quebrada del Barro Formation, an Upper Triassic-Lower Jurassic unit that crops out in northwestern Argentina. The new taxon is represented by a partial articulated skeleton that includes the skull, vertebral column, scapular and pelvic girdles, and hindlimb. Leyesaurus is diagnosed by a set of unique features, such as a sharply acute angle (50 degrees) formed by the ascending process of the maxilla and the alveolar margin, a straight ascending process of the maxilla with a longitudinal ridge on its lateral surface, noticeably bulging labial side of the maxillary teeth, greatly elongated cervical vertebrae, and proximal articular surface of metatarsal III that is shelf-like and medially deflected. Phylogenetic analysis recovers Leyesaurus as a basal sauropodomorph, sister taxon of Adeopapposaurus within the Massospondylidae. Moreover, the results suggest that massospondylids achieved a higher diversity than previously thought.

Conclusions/significance: Our phylogenetic results differ with respect to previous analyses by rejecting the massospondylid affinities of some taxa from the northern hemisphere (e.g., Seitaad, Sarahsaurus). As a result, the new taxon Leyesaurus, coupled with other recent discoveries, suggests that the diversity of massospondylids in the southern hemisphere was higher than in other regions of Pangea. Finally, the close affinities of Leyesaurus with the Lower Jurassic Massospondylus suggest a younger age for the Quebrada del Barro Formation than previously postulated.

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Conflict of interest statement

Competing Interests: The authors have declared that no competing interests exist.

Figures

Figure 1

Figure 1. Location and Geologic map of the Marayes-El Carrizal Basin (Northwestern Argentina)

. A: Location and geologic map; B: Section of the Marayes group at the type locality. The red circle indicates the site of the holotype of Leyesaurus marayensis gen. et sp. nov., near the top of the Quebrada del Barro Formation. (B: modified from Bossi [23]).

Figure 2

Figure 2. Silhouette reconstruction of the skeleton of Leyesaurus marayensis (PVSJ 706

). Reconstruction only shows preserved bones. Modified from Martinez . Scale bar equals 25 cm.

Figure 3

Figure 3. Skull of the new basal sauropodomorph Leyesaurus marayensis (PVSJ 706).

Photograph of the skull (A) and interpretative drawing (B) in lateral view. Dark grey color represents matrix and light grey color represents foraminae. Abbreviations: a, angular; aoF, antorbital fenestra; aoFo; antorbital fossa; Apmx, ascending process of the maxilla; d, dentary; f, frontal; itF, infratemporal fenestra; j, jugal; l, lacrimal; laoFo; lacrimal antorbital fossa; mF, mandibular fenestra; mx, maxilla; n, nasal; O, orbit; p, parietal; pf, prefrontal; pm, premaxilla; po, postorbital; rug, platform-like rugosities; q, quadrate; qj, quadratejugal; Rmx, ridge of the ascending process of the maxilla; sa, surangular; snf, subnarial foramen. Scale bar equals 1cm.

Figure 4

Figure 4. Skull of the new basal sauropodomorph Leyesaurus marayensis (PVSJ 706).

Photograph of the skull (A) and interpretative drawing (B) in dorsal view. Dark grey color represents matrix and light grey color represents foramina. Abbreviations: Apmx, ascending process of the maxilla; bo, basioccipital; d, dentary; f, frontal; j, jugal; l, lacrimal; mx, maxilla; n, nasal; O, orbit; p, parietal; pf, prefrontal; pm, premaxilla; po, postorbital; sa, surangular; stF, supratemporal fenestra; sq, squamosal. Scale bar equals 1 cm.

Figure 5

Figure 5. Maxillary teeth of basal sauropodomorphs.

A, photograph of the teeth of Leyesaurus marayensis (PVSJ 706), the circle shows fifth maxillary tooth in distal view; B, Cross-sections at mid-height of an anterior maxillary tooth of Leyesaurus PVSJ 706 (a), Adeopapposaurus PVSJ 568 (b), Massospondylus SAM-PK-K1314 (c), and Riojasaurus PVSJ 849 (d). Red lines represent the maximum mesiodistal length and labiolingual width at mid-height of the tooth. Abbreviations: r, ratio between mesiodistal length and labiolingual width. Scale bar equals 2 mm.

Figure 6

Figure 6. Atlas-axis complex of the new basal sauropodomorph Leyesaurus marayensis (PVSJ 706).

A, right proatlas in medial view; B, odontoid in dorsal view; C, intercentrum in dorsal view; D, right atlantal neural arch in medial view; E–F, axis in dorsal (E) and lateral (F) view. Abbreviations: Apax, articular projection with the axis; Apoc, articular projection with the occipital; Asan, articular surface with the atlantal neural arch; Asfm, articular surface with the lateral region of the foramen magnum; Asin, articular surface with the intercentrum; Asoc, articular surface with the occipital; epi, epipophysis; fr, foramen; k, keel; nc, neural canal; ns, neural spine; pap, parapophysis; poz, postzygapophysis; prz, prezygapophysis. Scale bar equals 1 cm.

Figure 7

Figure 7. Cervical vertebrae of the new basal sauropodomorph Leyesaurus marayensis (PVSJ 706).

A, neck vertebrae from C3–C7; B, sixth cervical vertebra in lateral view. Abbreviations: C3_–_7, cervical vertebrae; epi, epipophysis; k, keel; ns, neural spine; prz, prezygapophysis; r, ribs. Scale bar equals 1 cm.

Figure 8

Figure 8. Caudal vertebrae of the new basal sauropodomorph Leyesaurus marayensis (PVSJ 706).

A–B, anterior caudal vertebra in lateral (A) and anterior (B) view; C–F, middle caudal vertebra in lateral (C), anterior (D), posterior (E), and ventral (F) view. Abbreviations: nc, neural canal; ns, neural spine; poz, postzygapophysis; tp, transverse process; vf, ventral furrow. Scale bar equals 1 cm.

Figure 9

Figure 9. Preserved elements of the pectoral girdle of the new basal sauropodomorph Leyesaurus marayensis (PVSJ 706).

A–B, left scapula, coracoid, and humerus in medial (A) and lateral (B) view. Abbreviations: co, coracoid; cofr, coracoid foramen; gl, glenoid surface; h, humerus; hH, humeral head; sc, scapula. Scale bar equals 1 cm.

Figure 10

Figure 10. Preserved elements of the pelvic girdle of the new basal sauropodomorph Leyesaurus marayensis (PVSJ 706).

A, right pubic apron in dorsal view; B–C, proximal portion of the left ischium in proximal (B) and lateral (C) view. Abbreviations: dnis, dorsal notch of the ischial symphysis; ilAs, iliac articular surface of the ischium; lmp, lateral margin of the pubic apron; pb, pubic apron; pisp, proximal ischial portion; r, ribs; vk, ventral keel of the ischial shaft. Scale bar equals 1 cm.

Figure 11

Figure 11. Foot elements of the new basal sauropodomorph Leyesaurus marayensis (PVSJ 706).

A–B, left distal tarsal III in dorsal (A) and posterior (B) view; C–D, left distal tarsal IV in dorsal (C) and posterior (D) view; E–G, left metatarsal III (E), IV (F), and V (G) in proximal, dorsal and distal view; H–J, left pedal phalanges: first phalanx of digit I (H), second phalanx of digit II (I), and second phalanx of digit IV (J) in dorsal view. Abbreviations: pt, ligament pit. Scale bar equals 1 cm.

Figure 12

Figure 12. Metatarsal III of the new basal sauropodomorph Leyesaurus marayensis (PVSJ 706).

A–B, photograph of the proximal half of metatarsal III in dorsal (A) and dorsomedial (B) view; C, interpretative drawing showing the medial shelf-like deflection of metatarlas III. Abbreviations: As mtII, articular surface for the metatarsal II; fr, foramen; msh, medial shelf of the metatarsal III; pAs, proximal articular surface; st, shaft of the metatarsal III. Scale bar equals 1 cm.

Figure 13

Figure 13. Strict consensus of the phylogenetic analysis of sauropodomorph dinosaurs.

Analysis was based on the dataset of Yates modified by other authors , – and including Leyesaurus marayensis gen. et sp. nov., showing the strict consensus of 18 MPTs. Bremer decay indices greater than 1 are listed above nodes and Bootstrap values greater than 50% are listed below nodes.

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