Notohypsilophodon

From 1985 onwards the Laboratorio de Paleovertebrados of the Universidad Nacional de la Patagonia "San Juan Bosco" organised excavations in the late Cenomanian-early Turonian-age Bajo Barreal Formation of the San Jorge Basin, northern Chubut, Patagonia. At Buen Pasto near Comodoro Rivadavia a partial juvenile skeleton lacking the skull, was found.[2]

In 1998 this find was named and described by Rubén D. Martínez as the type species Notohypsilophodon comodorensis. The generic name combines a Greek νότος, notos, "south wind" with the name of the genus Hypsilophodon. The specific name refers to Comodoro Rivadavia.[2]

Notohypsilophodon is based on the holotype specimen UNPSJB — PV 942, a partial skeleton including four neck, seven back, five hip, and six tail vertebrae, four rib fragments, a partial left scapula (shoulder blade), partial right coracoid, a right humerus (upper arm bone), both ulnae, and most of a left leg (minus the foot), a right fibula and astragalus, and thirteen phalanges. Because the neural arches are not fused to the bodies of the vertebrae, its describer regarded the individual as not fully grown.[2]

As a "hypsilophodontid" or other basal ornithopod, Notohypsilophodon would have been a bipedal herbivore. Its size was not estimated in the describing article, but as most adult hypsilophodonts were 1 to 2 meters (3.3 to 6.6 ft) long,[3] this genus would probably have been of similar size. In 2010 Gregory S. Paul gave an estimation of 1.3 metres (4.3 ft) for the length, 6 kilograms (13 lb) for the weight of the animal.[4]

Martínez found no evidence that Notohypsilophodon was an iguanodont, and instead assigned it to the more basal Hypsilophodontidae, which made it at the time the only South American hypsilophodont.[2] A hypsilophodontid assignment was supported by Rodolfo Coria in a 1999 review of South American ornithopods,[5] but a more recent review of basal ornithopods found the fossil remains to be too fragmentary for classification beyond Euornithopoda, a clade within Ornithopoda including the "hypsilophodonts" and iguanodonts.[3] Moreover, the Hypsilophodontidae are today considered to be a paraphyletic group, not consisting of directly related species forming a separate branch, but representing a series of successive branches splitting off the main euornithopod tree.[3] A recent redescription of Notohypsilophodon found it to be basal in Ornithopoda, more primitive than Gasparinisaura.[6] In 2015, it was found to be part of the clade Elasmaria along with other Antarctic and Patagonian ornithopods.[7]

Cladogram based in the phylogenetic analysis of Rozadilla et al., 2015: