Retro-acupuncture: Craniocervical musculature of Bajadasaurus pronuspinax

JUAN PABLO GARDERES; MARIANO MILITELLO; JOHN ANDREW WHITLOCK; NÉSTOR TOLEDO; PABLO ARIEL GALLINA

Congreso; 82nd Anual Meeting SVP; 2022

Among non-avian dinosaurs, craniocervical musculature,defined as the axial musculature attaching to the skull andresponsible of positioning and moving the head, is poorlyknown. This is due in large part to the lack of intraspecimenassociation of cranial and cervical remains, and also to issuesregarding homologies of these muscles among extant taxa.Previous studies on dinosaurs were mainly focused ontheropods, such as Tyrannosaurus and Allosaurus, andceratopsians. Among sauropods, only the craniocervicalmusculature of Camarasaurus and Diplodocus has beenstudied so far, showing similar configurations. In thiscontribution, a preliminary reconstruction of the craniocervicalmuscle groups in the dicraeosaurid Bajadasaurus is presented.Among the primary dorsiflexor muscles, the medial part oftransversospinalis capitis is the medial-most muscle of thisgroup, attaching to the sagittal crest laterally and invading thepost-temporal fossa. The lateral part of transversospinaliscapitis attaches along the caudal edge of the parietal wing. Themedial portion of the splenius capitis inserts along thelaterocaudal part of the sagittal crest, dorsal to the proatlantalfacets. The lateral part of splenius capitis attaches along thedorsomedial surface of the paroccipital process, but does notinvade the post-temporal fossa. Among the primarylateroflexor muscles, longissimus capitis superficialis isinferred to attach to the caudomedial surface of the distalportion of the paroccipital process, although leaving noosteological correlate. Rectus capitis lateralis attaches to theventral and distal portions of the paroccipital process, leavingan L-shaped osteological correlate. Among the primaryventroflexor muscles, rectus capitis ventralis is the medialmost muscle of the group, attaching to the ventral surface ofthe basal tubera, leaving no clear osteological correlate. Rectuscapitis dorsalis is inferred to attach to the caudomedial surfaceof the basal tubera, leaving no clear osteological correlate. Theoverall configuration of the craniocervical musculature inBajadasaurus resembles that of other sauropods, excepting theabsence of a fossa for iliocostalis capitis lateral to the foramen magnum in a depression, probably related to the atlantooccipital capsule. This reconstruction represents the firstinference in Dicraeosauridae, expanding the knowledge of thecraniocervical musculature in flagellicaudatan sauropods.