Improving the knowledge of the dental ontogeny of dinomyds (Rodentia, Hystricognathi)

NASIF, N. L.; ABDALA, F.

Mendoza

Congreso; 4th International Paleontological Congress: THE HISTORY OF LIFE: A VIEW FROM THE SOUTHERN HEMISPHERE; 2014

IANIGLA, CCT-CONICET

4th INTERNATIONAL PALAEONTOLOGICAL CONGRESS, Mendoza, Argentina. 2014 763Open sessions / PosterIMPROVING THE KNOWLEDGE OF THE DENTAL ONTOGENY OF DINOMYDS (RODENTIA, HYSTRICOGNATHI)Norma Nasif1 and Fernando Abdala21. Facultad de Ciencias naturales, Universidad Nacional de Tucumán,Miguel Lillo 205, 4000, San Miguel de Tucumán.2. Evolutionary Studies Institute, University of the Witwatersrand, South Africa.Nestor.abdala@wits.ac.zaINTERNATIONAL PALAEONTOLOGICAL CONGRESS, Mendoza, Argentina. 2014 763The Family Dinomyidae (Hystricognathi, Caviomorpha), with only one extant species, Dinomys branickii (the pacarana), has an important late Oligocene to Pliocene fossil record in South America, with its highest diversity during the late Miocene. They include a wide range of body-sizes, from small to gigantic, and different degrees of molar hypsodonty. Despite its important diversity in the past, information about anatomy and ontogeny of dinomyds is scarce. We are presenting here new data on dental ontogeny produced by new fossils and by small (young) specimens of the living pacarana. A deciduous upper third premolar (dP3) is present in the dental development of dinomyds, a condition represented in Branisamys from the Bolivian late Oligocene, the earliest representative of the family, and also in one of the youngest specimens of the living pacarana. In both cases the dP3 is a tiny, rooted, non-molariform tooth located in front and very close to the dP4. The dP3 is shed and not replaced and its alveolus becomes ossified. Shed of the dP3 in Branisamys would occur in an advanced stage of development, before or during the replacement of the dP4, whereas Dinomys will shed this tooth in a very early postnatal stage where dP4 and M1 are eruptingshowing an incipient occlusal worn. Replacement of the dP4 and dp4 in euphypsodont dinomyd fossils is corroborated. In brachydont dinomyds with unilateral hypsodonty and, eventually, the first protohypsodonts (Branisamys and Drytomomys) replacement of dP4/dp4 occurs after M3/m3 is functioning. In the late Miocene protohypsodont Potamarchinae (Paranamys), replacement of the dP4/dp4 occurs before eruption of M3/m3, whereas in euhypsodontid forms (late Miocene of northwestern Argentina) replacement only occurs when the last molar is erupting and did not reach the occlusal surface, or when M3/m3 is totally functional as in the pacarana. The presence of the dP3 in the oldest representatives and in the only living form, suggests their putative presence during stages of the ontogeny of each lineage of the family, even though they are not documented in thefossil record of several taxa. The presence of this tooth would support the hypothesis of a basal position of dinomyds in the context of South American hystricognathes. In the dental evolution of dinomyds, heterochrony in the dental replacement sequence of the dP4/dp4 in relation to the M3/m3 is related with development of hypsodonty and with the retention of deciduous premolar in a more prolonged time during the ontogeny.