An articulated specimen of the basal titanosaurian (Dinosauria: Sauropoda) Epachthosaurus sciuttoi from the early Late Cretaceous Bajo Barreal Formation of Chubut Province, Argentina

ABSTRACT

We describe an articulated specimen of the titanosaurian sauropod Epachthosaurus sciuttoi from the early Late Cretaceous Bajo Barreal Formation of Chubut Province, central Patagonia, Argentina. The skeleton was found in tuffaceous sandstone, with its hindlimbs flexed and its forelimbs widely extended. It is slightly deformed on its left side. The skull, neck, four or five cranial dorsal vertebrae, and several distal caudals are missing.

Epachthosaurus is diagnosed by the following autapomorphies: middle and caudal dorsal vertebrae with accessory articular processes extending ventrolaterally from the hyposphene, a strongly developed intraprezygapophyseal lamina, and aliform processes projecting laterally from the dorsal portion of the spinodiapophyseal lamina; hyposphene-hypantrum articulations in caudals 1–14; and a pedal phalangeal formula of 2-2-3-2-0. The genus shares the following apomorphies with various titanosaurians: caudal dorsal vertebrae with ventrally expanded posterior centrodiapophyseal laminae; six sacral vertebrae; an ossified ligament or tendon dorsal to the sacral neural spines; procoelous proximal, middle, and distal caudal centra with well-developed distal articular condyles; semilunar sternal plates with cranioventral ridges; humeri with squared proximolateral margins and proximolateral processes; unossified carpals; strongly reduced manual phalanges; craniolaterally expanded, nearly horizontal iliac preacetabular processes; pubes proximodistally longer than ischia; and transversely expanded ischia. Epachthosaurus is considered the most basal titanosaurian known with procoelous caudal vertebrae.