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Libro de Resumenes de la Reunion de Comunicaciónes de la Asociación Paleontológica Argentina 2023 - Parankylosaurian weaponry gets even stranger: new ankylosaur remains from the La Colonia Formation (Campanian-Maastrichtian) represent the most complete record in Argentina
Congreso
Fecha:
2023Editorial y Lugar de Edición:
Asociación Paleontológica ArgentinaResumen *
Our understanding on diversity and kinship of Gondwanan armored dinosaurs increased with the description of Stegouros eleganssen, the naming of Parankylosauria reuniting Stegouros with Antarctopelta oliveroi and Kunbarrasaurus ieversi, and the descriptions of the basal thyreophoran Jakapil kaniukura and the nodosaurid Patagopelta cristata. Our study describes new ankylosaur remains from La Colonia Formation, MPEF-PV 11534, comprising cranial/postcranial remains, with plates and ossicles, representing an adult of nearly 1,60 m long (additional specimens similar or smaller). The skull roof is wider than long, anteroposteriorly flat, and covered by fused osteoderms. The nasals are more than one third the skull length, as in Kunbarrasaurus; with the nares and nasal vestibule covered by osteoderms. The postorbital is anteroposteriorly and mediolaterally wide, with the prefrontal-postorbital contact extending medially along the eye socket. The supratemporal fenestra is enclosed by the parietal-postorbital-squamosal suture. The skull preserves supraoccipital and otoccipitals in articulation; and an osteoderm covers the jugal, quadratojugal, and quadrate. The right lower jaw is almost complete. The dentary shows an alveolar row medially emarginated and dorsally convex with 14 alveoli and preserved dentition. The mandibular fenestra is closed, and postdentary bones are covered by an osteoderm. Dorsal vertebrae are dorsally lengthened with transverse processes transitionally lowering posteriorly. The fused sacrum preserves four vertebrae and ribs, with a missing presacral rod. The centrum of caudal vertebrae are sub-squared and flattening posteriorly, as the parankylosaurs. Scapula and coracoid are unfused, the preacetabular process is long and curves ventrolaterally. Limb bones are long and slender, with the stylopodium similar in length to the zeugopodium, but the manus three times shorter than the pes. There are 90 complete scutes with varying shapes and sizes, more than a hundred fragments of scutes, and thousands of ossicles, which covered the neck, trunk, tail, and limbs at least proximally. The tail shows a subcilindrical and dorsoventrally flattened weapon with six rows (epaxial, lateral, and hipaxial) of seven rings of fused scutes forming a solid structure housing the seven last caudal vertebrae. The lateral scutes are strongly keeled, and the epaxial and hipaxial osteoderm rows completely enclose the caudal weapon up to the last caudal vertebrae. This weapon is unique amongst ankylosaurs, contrasting with Stegouros, which shows only two lateral rows of strongly-keeled fused scutes. Phylogenetic analyses with four datasets recover this ankylosaur within Parankylosauria, and the presence of numerous autapomorphies including this unprecedently cudgel-like tail weapon, will allow naming a new Gondwanan taxon. Información suministrada por el agente en SIGEVAPalabras Clave
ArgentinaLa Colonia FormationGondwanaParankylosauria