Sidersaura marae. Image credit: Gabriel Diaz Yantén
Rebbachisauridae is a family of small to mid-sized sauropod dinosaurs characterized by their highly modified skulls and cervical and dorsal vertebrae with single neural spines. This clade of basal diplodocoid sauropods are known from the early Late Cretaceous of Africa, South America, and Europe. They were part of the sauropod faunas of Argentina together with macronarians (Titanosauriformes) and other diplodocoids (Dicraeosauridae). It was not until 1990 that sauropod specialist John McIntosh realized that a vertebrba described by Franz Nopcsa in 1902, proceeding from the Upper Cretaceous of Neuquen, was anatomically similar to the African Rebbachisaurus garasbae. Later, Bonaparte described Rayososaurus agrioensis, from the Candeleros Formation, Neuquén province, Argentina, and noted some similarities with R. garasbae, and he proposed Rebbachisauridae as a new sauropod clade.
Sidersaura marae, a new specimen from the Huincul Formation (upper Cenomanian – Turonian) of Neuquén Province, Argentina adds new light about the evolutionary history of rebbachisauridae. The holotype (MMCh-Pv 70) includes a partial skull, partial dorsal vertebrae, fourteen caudal vertebrae, five haemal arches, a partial left scapula, pubic peduncle, both tibiae, both distal fibulae, some metatarsals, phalanges, and ungual phalanges. Additional partial specimens were collected from the basal levels of the Huincul Formation. The generic name derived from the Latin word “sider” (star), referring to the peculiar shape of some bones located in the tail, called hemal arches, and the Greek word “saura”, the feminine declination of the word “sauros”, meaning “lizard. The specific name honors Mara Ripoll, director of the “Ernesto Bachmann” Paleontological Museum in recognition of her extensive career in that institution.
Sidersaura marae gen. et sp. nov. anterior to middle haemal arch in anterior view (A); anterior to middle haemal arch in anterior & lateral view (B); middle to posterior haemal arches in anterior & lateral views (C, D). Scale bars: 5 cm. From Lerzo et al., 2024.
Originally discovered in 2012, Sidersaura had dimensions similar to those of the great Diplodocus, reaching an an estimated mass of 15 ton, and 20 m in length. The most distinctive features of Sidersaura are the presence of a frontoparietal foramen (hole in the cranial roof), a trait shared with dicraeosaurids more derived than Kaatedocus, and a particularly hard skull bones. Another striking feature is the presence of a new tarsal condition with a novel calcaneum morphology more resembling to early branching sauropods than to neosauropods.
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Letters from Gondwana. 