Talenkauen

Talenkauen (meaning "small skull" in Aonikenk, referring to the proportionally small skull) is a genus of basal iguanodont dinosaur from the Maastrichtian-age Upper Cretaceous Pari Aike Formation of Lake Viedma, Santa Cruz, Argentina. It is based on MPM-10001, a partial articulated skeleton missing the rear part of the skull, the tail, and the hands. Its most unusual feature is the presence of several thin mineralized plates along the sides of the ribs

Description
Talenkauen was rather like Dryosaurus in shape and build, but with a proportionally longer neck. The full length of the body is estimated at no more than 4 meters (13 feet). Unlike more derived iguanodontians, it still had teeth in the tip of the beak (premaxillary teeth), and a first toe. More derived iguanodonts lose this toe, retaining only the three middle toes. The humerus has reduced areas for muscle attachment, a featured shared with other South American ornithopods like Notohypsilophodon and Anabisetia. This and other similarities to South American ornithopods suggests that there may have been a distinct Southern Hemisphere ornithopod group, but the authors cautioned that all of the evidence together does not permit such an interpretation. The authors, through cladistic analysis, found the new genus to be more basal than Dryosaurus and Anabisetia, but more derived than Tenontosaurus and Gasparinisaura.[1] More recently, the describers of Macrogryphosaurus found their genus and Talenkauen to be related, and coined the clade Elasmaria for the two genera.

Mineralized plates
Talenkauen's most distinct feature is a set of smooth, ovoid plates found along the side of the rib cage. These plates can be long (180 millimeters, or 7.1 in), but are very thin (only 3 millimeters thick [0.1 in]). They were present with at least the first eight ribs, attaching along the middle portion of a rib and lying flat.[1] Several other dinosaurs are known to have had similar plates, including Hypsilophodon, Othnielosaurus, Parksosaurus, Thescelosaurus,[3] and Macrogryphosaurus (also from Argentina, but from somewhat older rocks), which may have been related.[2] Because of the fragility of the plates, and the fact that they may not have always turned to bone in the living animal, they may have been more widespread than currently known. Novas and colleagues suggested that the plates may be homologous to uncinate processes, strip-like bony projections found on the ribs of a variety of animals including the tuatara, crocodiles, birds, and some maniraptoran theropod dinosaurs. In birds, uncinate processes help to ventilate the lungs, working with rib cage muscles, and Novas and colleagues proposed a similar function for the plates of Talenkauen.[1] This homology was rejected in a more recent study by Richard Butler and Peter Galton because of the plates' form.[3] The plates were too thin and limited in location to have been very useful as defensive devices.

Paleobiology
Talenkauen, as a basal iguanodont, would have been a small, bipedal herbivore.[4] Other dinosaurs from the Pari Aike Formation include the giant titanosaurid Puertasaurus[5] and the predatory neovenatorid Orkoraptor.