CONICET | Buscador de Institutos y Recursos Humanos

Pneumatic structures among presacral vertebrae arepresent in the dorsal series of non-Sauropoda Sauropodomorpha (e.g., Eucnemesaurus, Aardonyx) and in the cervico-dorsal transition ofGravisauria and more derived Eusauropoda. Recently were known twonon-eusauropod sauropodomorphs (the lessemsaurids Lessemsaurus and Ingentia)with pneumatic structures among their cervico-dorsal vertebral transition,which represent the earliest sauropodomorphs with pneumatic cervical vertebrae and/orcervico-dorsal transition. Here we present a new Sauropodiformes specimen (PVSJ908) from the Late Triassic Quebrada del Barro Formation (Marayes-El CarrizalBasin, Northwestern Argentina) with novel pneumatic structures in its cervico-dorsalvertebrae. This new pneumatic pattern includes the presence of deep fossae withinternal subfossae (=internal chambers) on the pre and postzygapophysealcentrodiapophyseal fossa (prcdf and pocdf) on the posterior cervical (C9-10)and anterior dorsal (D1-5) vertebrae, which are unambiguously identified aspneumatic in origin. The presence of invasive pneumatic complex?fossae withinfossae?observed among lessemsaurids and in the new sauropodiform (PVSJ 908) showa new pattern of pneumatization in an unprecedented region (i.e., prcdf) throughout the presacralregion, and an improved pneumatic system among the cervico-dorsal transitionthat evolved well before the origin of Eusauropoda. Because only cervical andabdominal air sacs and lungs are able to produce pneumatic diverticula thatinvade the vertebrae, the presence of a sophisticated pneumatic complex on theneck of these taxa suggests that a cervical air sac system, and hence animproved avian-style respiratory system, were well developed already at thebase of Sauropoda.