Preliminary reinterpretation of tail myology of Macrogryphosaurus gondwanicus (Dinosauria: Ornithopoda)

GONZÁLEZ-DIONIS, JAVIER; MÉNDEZ, ARIEL H.; CALVO, JORGE O.; CRUZADO-CABALLERO, PENÉLOPE

Salta

Otro; Reunión de Comunicaciones de la Asociación Paleontológica Argentina; 2022

Asociación Paleontológica Argentina

The increase in recent years of the fossil record of the Ornithopoda from Argentina has made possible to conduct more specific research. In this case, we present a new preliminaryreinterpretation of the tail myology of the elasmarian ornithopod, Macrogryphosaurus gondwanicus (MUCPv-321). Holotype is deposited in the Proyecto Dino Collection in Lago Barreales, Neuquén. Its remains were recovered from the Bajo de la Carpa Formation, Upper Cretaceous (Santonian) of west coast of Mari Menuco Lake, Neuquén Basin, Patagonia, Argentina. Regarding the tail material, we analysed scars and structures of three isolated anterior caudal vertebrae (probably Ca 1-3), several anterior haemal arches and the articulated posterior caudal vertebrae (six elements and its haemal arches). The EPB approach is the methodology chosen to determine which muscle group is most probable to be present. A general view shows that scars are present throughout the lateral of the centra, and haemal arches, but these are variable in intensity. Anteriormost caudal vertebraepresent longitudinal scars at the ends of both lateral sides of the centra, but these are poorly marked, whereas, in the articulated most posterior caudals, scars are most noticeable. This fact, together with the apparent reduction of attachment structures in the posterior caudals, could be the evidence that establishes the insertion and transition between M. caudofemoralis longus to M. ilioischiocaudalis. Therefore, in the anterior caudal vertebrae, we can observe more scars above (M. longissimus) and below (M. caudofemoralis longus) of the transverse process, below of prezygapophysis processes (M. caudofemoralis brevis) and in the base of neural spine toward to postzygapophysis processes (M. tendinoarticularis or M. longissimus). On the other hand, haemal arches present two different morphologies in lateral view, the most anterior is straight (without anterior or posterior process), whereas the posterior ones present a gradual expansion with anterior and posterior processes. We can see a similar morphology in other elasmarians like Gasparinisaura and in other dinosaurs like coelurosaur theropods or sauropods. Also, the haemal arches present some dorsoventral scars throughout distal surface and anterior and posterior processes, highlighting the ones present in the anterior process of the last haemal arch (M. ilioischiocaudalis). Future analyses will correlate these observations with possible palaeobiological implications.