Morphological variability in the skull of dicraeosaurid sauropod dinosaurs

GALLINA, PABLO ARIEL; APESTEGUÍA, SEBASTIÁN; CANALE, JUAN IGNACIO

General Roca

Congreso; 11º Congreso de la Asociación Paleontológica Argentina; 2016

The family Dicraeosauridae includes five taxa but only Dicraeosaurus hansemanni Janensch 1914, Amargasaurus cazaui Salgado and Bonaparte 1991, and Suuwassea emilieae Harris and Dodson 2004, preserve cranial remains. The skull anatomy is mainly known from the posterior region (braincase and dermal roof) in the three taxa; however Dicraeosaurus and, to a lesser extent, Suuwassea provide restricted evidence from the rostral part. The cranial remains of a new dicraeosaurid sauropod (MMCh-PV 75) from the Lower Cretaceous Bajada Colorada Formation (Northern Patagonia, Argentina) expand the knowledge on the skull morphology of this group. These include dermal roof (tooth-bearing, median roofing, circumorbital, and temporal bones) and palatal elements, braincase, and the nearly complete lower jaw. The new taxon exhibits diagnostic characters of Dicraeosauridae such as elongated basipterygoid processes diverging at an angle lesser than 30 degrees, presence of postparietal foramen, supratemporal fenestra laterally exposed and smaller than the foramen magnum, basal tubera narrower than the occipital condyle, and a ventrally directed prong on squamosal. Surprisingly, this new form differs from the other known dicraeosaurids in having a gracile skull with dorsoventrally compressed occipital condyle, basipterygoid processes extremely narrow, squamosal process elongated and slender, postemporal fenestra extended medially, and reduced dentition in the maxilla and dentary. The morphological variability present perception of the anatomy of sauropod dinosaurs. The preserved elements allow inferring the first reliable reconstruction of a dicraeosaurid skull in lateral aspect, showing substantial differences with previous restorations.