HEAD, SKULL–NECK AND EXTRINSIC EYE MUSCULATURE OF THE DICRAEOSAURID SAUROPOD BAJADASAURUS PRONUSPINAX

Cranial muscles perform important roles triggering diverse paleobiological faculties, such as feeding, communication, alert postures, etc. Within Sauropoda, a clade with high specializations in skull architectures, and several partially complete skulls recovered, detailed reconstructions of the cranial muscles are mainly limited to two of the most famous taxa of the clade: Diplodocus and Camarasaurus. The cranial musculature for Dicraeosauridae, a minor group within the clade, has been gingerly described, based on the few suitable specimens. Herein, the craniomandibular, extrinsic eye, and cervicocranial musculatures of Bajadasaurus pronuspinax are inferred, resulting in the first detailed reconstruction for Dicraeosauridae on these muscular groups, and these are compared with previous inferences in Dicraeosauridae and with other Sauropoda and non-avian dinosaurs. The musculature of Bajadasaurus shows a shift of angle in the temporal musculature when passing through the inferior temporal window (probably indicating the presence of a cartilage for support), an important role of the orbitotemporal muscles in a hypothetical cranial kinesis (which, if true, would allow pseudo-palinal movements in a rostral directionduring the feeding process), an avian-like configuration of the eye muscles, and high lateroflexor moment arms for the skull-neck complex. Dicraeosauridae show clear osteological correlates for a high number of the craniomandibular and cervicocranial muscles, albeit some of these correlates might not be exclusively dedicated for musculature, and could be indicating the presence of alternative soft tissues.