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New basal dinosauromorph records from the Dockum Group of Texas, USA

Volkan Sarıgül

Plain Language Abstract

After several significant fossil discoveries, the dinosauromorphs of the Late Triassic Epoch (ca. 237-201 million years ago) have recently become one of the hot topics in vertebrate palaeontology. The dinosauromorph clade covers all dinosaurs (both avian and non-avian) and their sister groups, termed basal dinosauromorphs. The Dockum Group of Texas, USA, a thick terrestrial geological unit that is made of fluvial sediments, is one of the main areas where the Late Triassic dinosauromorphs were relatively abundant with high taxonomic diversity. This work introduces nine hitherto unpublished basal dinosauromorph specimens from the Dockum Group of Texas (from Randall and Garza counties). Most of these specimens are assigned to two species of an already known genus (Dromomeron romeri and Dromomeron gregorii), demonstrating their temporal range is wider than previously thought, and that they probably co-existed together without replacing each other during the Late Triassic. Two additional calf bone specimens display a strong resemblance to that of an Argentinean basal dinosauromorph (Marasuchus lilloensis), but around three times larger in size.

Resumen en Español

Nuevos registros de dinosauromorfos basales del Grupo Dockum de Tejas, USA

Los dinosauromorfos basales constituyen un componente importante de la diversidad de dinosauromorfos del Triásico tardío del Grupo Dockum. Este estudio presenta nueve elementos hasta ahora inéditos de las extremidades traseras de dinosauromorfos basales de los condados de Garza y Randall en Texas. La mayoría de estos especímenes consisten en fragmentos de fémur y tibia pertenecientes a Dromomeron, mientras que una fíbula completa y otra parcial tienen una morfología semejante a la que presenta Marasuchus lilloensis, pero con un tamaño mucho más grande, y se asignan a dinosauriformes indeterminados. El descubrimiento de tres especímenes de Dromomeron en la Formación Tecovas de Palo Duro Canyon es particularmente notable porque estos son los registros más antiguos de Dromomeron romeri y Dromomeron gregorii, y el primer caso de solapamiento bioestratigráfico de los dos taxones. El rango taxonómico ampliado de D. romeri desafía la propuesta que fue sugerida sobre la sustitución de D. gregorii en el cambio de fauna del Triásico tardío (Adamaniense-Revueltiense).

Palabras clave: Triásico tardío; Texas; Dockum; Dinosauromorpha; grupos basales; bioestratigrafía

Traducción: Enrique Peñalver (Sociedad Española de Paleontología)

Résumé en Français

Nouvelles occurrences de dinosauromorphes basaux du groupe de Dockum, Texas, USA

Les dinosauromorphes basaux constituent une composante importante de la diversité des dinosauromorphes du Trias récent de Dockum. Cette étude présente neuf éléments non publiés du membre postérieur de dinosauromorphes basaux provenant des comtés de Garza et Randall au Texas. La plupart de ces spécimens se composent de fragments de fémurs et de tibias attribués à Dromomeron, alors qu'un péroné complet et d'un péroné partiel montrent une morphologie ressemblant à celle de Marasuchus lilloensis, mais avec une taille plus importante, et sont attribués à des dinosauriformes indéterminés. La découverte de trois spécimens de Dromomeron dans la formation de Tecovas du canyon de Palo Duro est particulièrement remarquable car ce sont les occurrences de Dromomeron romeri et Dromomeron gregorii les plus basses stratigraphiquement, et le premier chevauchement biostratigraphique signalé pour ces deux taxons. La distribution taxinomique étendue de D. romeri remet en cause son supposé remplacement par D. gregorii lors du renouvellement faunique du Trias récent (Adamanien-Revueltien).

Mots-clés : Trias récent ; Texas ; Dockum ; Dinosauromorpha ; groupes basaux ; biostratigraphie

Translator: Antoine Souron

Deutsche Zusammenfassung

Neue Nachweise basaler Dinosauromorphen aus der Dockum Gruppe von Texas, USA

Die basalen Dinosauromorphen sind eine wichtige Komponente der spätriassischen Dockum Diversität. Diese Studie stellt neun bisher unveröffentlichte Hinterbein-Elemente von basalen Dinosauromorphen aus den Garza und Randall Counties in Texas vor. Die meisten dieser Stücke bestehen aus femoralen und tibialen Fragmenten die Dromomeron zugeschrieben werden, wohingegen eine komplette und eine partielle Fibula der Morphologie von Marasuchus lilloensis ähneln, jedoch größer sind und als Dinosauriformes indet. eingeordnet werden. Die Entdeckung von drei Dromomeron-Stücken in der Tecovas Formation des Palo Duro Canyons ist besonders bemerkenswert, da es sich hierbei um das unterste Auftreten von Dromomeron romeri und Dromomeron gregorii handelt, sowie um den ersten Nachweis einer biostratigraphischen Überlappung dieser beiden Taxa. Die erweiterte taxonomische Reichweite von D. romeri stellt seinen vorgeschlagenen Ersatz für D. gregorii im spättriassischen (Adamanium-Revueltianium) Faunen-Austausch in Frage.

Schlüsselwörter: Späte Trias; Texas; Dockum; Dinosauromorpha; basale Gruppen; Biostratigraphie

Translator: Eva Gebauer

Arabic

Translator: Ashraf M.T. Elewa

 

 

FIGURE 1. The Dockum Group exposures (highlighted in grey) in western Texas and eastern New Mexico (modified after Lehman, 1994a). Fossil localities are spotted (yellow-filled circles) within the corresponding counties of Garza, Howard and Randall (marked in red).

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FIGURE 2. Generalized columnar sections of the Dockum Group in Texas in Randall, Garza and Howard counties, including the stratigraphic positions of the cited quarries in bold (modified after Ash, 1976; Lucas and Anderson, 1993b; Martz, 2008; Martz et al., 2013; and Bill Mueller, personal commun., 2014, 2015). Unit numbers and lithostratigraphic correlatives for the Garza County section are taken from Martz et al. (2013).

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FIGURE 3.1, Location map of the "lower Sunday Canyon" Site within the Palo Duro Canyon State Park (bordered in red on the map, taken from Google Earth 2016); 2, Field photograph of the "lower Sunday Canyon" Site, indicated by the red arrow (Photo credit: Bill Mueller).

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FIGURE 4. Complete listing of hitherto published Dockum non-dinosaurian dinosauromorph specimens from the Dockum Group of Texas with voucher information and representing elements, and their stratigraphic distribution. Lithologic thicknesses are not to scale.

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FIGURE 5.Dromomeron gregorii (TTU-P18331), proximal end of left femur in 1, anterior view; 2, medial view; 3, posterior view; 4, lateral view; 5, proximal view. Abbreviations: at, anterior trochanter; fh, femoral head (note that the femoral is broken); ft, fourth trochanter; pmt, posteromedial tuber; tf, trochanteric fossa; ts, trochanteric shelf. Hatching indicates the damaged areas. Arrow indicates anterior side.

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FIGURE 6.Dromomeron gregorii (TTU-P20046), distal end of left femur in 1, anterior view; 2, medial view; 3, posterior view; 4, lateral view; 5, distal view. Abbreviations: fc, fibular condyle; ig, intercondylar groove; lc, lateral condyle; mc, medial condyle; r, ridge; s, scar. Hatching indicates the damaged areas. Arrow indicates anterior side.

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FIGURE 7.Dromomeron gregorii (WTAMU-V-8302), proximal end of right femur in 1, anterior view; 2, medial view; 3, posterior view; 4, lateral view; 5, proximal view. Abbreviations: at, anterior trochanter; fh, femoral head; ft, fourth trochanter; pmt, posteromedial tuber; tf, trochanteric fossa; ts, trochanteric shelf; ve, ventral emargination. Hatching indicates the damaged areas. Arrow indicates anterior side.

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FIGURE 8.Dromomeron gregorii (WTAMU-V-8303), proximal end of right tibia in 1, lateral view; 2, anterior view; 3, medial view; 4, posterior view; 5, proximal view. Abbreviations: cc, cnemial crest; lc, lateral crest; mc, medial crest; r, ridge. Arrow indicates anterior side.

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FIGURE 9.Dromomeron romeri (TTU-P12537X), proximal end of right tibia in 1, anterior view; 2, lateral view; 3, posterior view; 4, medial view; 5, proximal view. Abbreviations: cc, cnemial crest; lc, lateral condyle; mc, medial condyle. Hatching indicates the damaged areas. Arrow indicates anterior side.

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FIGURE 10.Dromomeron romeri (WTAMU-V-8301), distal end of right femur in 1, anterior view; 2, medial view; 3, posterior view; 4, lateral view; 5, distal view. Abbreviations: amr, anteromedial ridge (sensu Irmis et al., 2007b); fc, fibular condyle; ig, intercondylar groove; lc, lateral condyle; mc, medial condyle; mlr, mediolateral ridge. Arrow indicates anterior side.

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FIGURE 11.Dromomeron sp. (TTU-P12539X), proximal end of right femur in 1, anterior view; 2, medial view; 3, posterior view; 4, lateral view; 5, proximal view. Abbreviations: fh, femoral head (note that the femoral head is broken); pmt, posteromedial tuber; tf, trochanteric fossa; ve, ventral emargination. Hatching indicates the damaged areas. Arrow indicates anterior side.

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FIGURE 12. Dinosauriformes gen. and sp. indet. (TTU-P10546), left fibula in 1, anterior view; 2, lateral view; 3, posterior view; 4, medial view; 5, proximal view; 6, distal view. Abbreviations: bs, beveled surface; da, damaged anterior part; dm, damaged posterior part; lf, lateral facet; mf, medial facet; pp, posterior process; py, pyramidal process. Arrow indicates anterior side.

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FIGURE 13. Dinosauriformes gen. and sp. indet. (TTU-P19803), distal end of left fibula in 1, anterior view; 2, lateral view; 3, posterior view; 4, medial view; 5, distal view. Abbreviations: as, articular surface for astragalus and calcaneum; bs, beveled surface; pp, posterior process; py, pyramidal process. Hatching indicates the damaged areas. Arrow indicates anterior side.

figure13

 

authorVolkan Sarıgül. Museum of Texas Tech University, 4th Street, Box 43191, Lubbock, Texas, 79409. This email address is being protected from spambots. You need JavaScript enabled to view it.

Born in 1987, Volkan earned his B.Sc. (2009) and M.Sc. (2011) in geology from Istanbul Technical University and his Ph.D. (2014) in geosciences from Texas Tech University, and he becomes the first and so far the only Turkish palaeontologist who studies archosaurs. He conducted the first comprehensive study on Dockum dinosauromorphs of Texas as a Ph.D. dissertation. His current research focuses mainly on Mesozoic archosaurs and other coeval tetrapods from Turkey and surrounding regions.