DINOSAUR EGGS AND EGGSHELL CHARACTERIZATION FROM SANAGASTA FORMATION, LA RIOJA, ARGENTINA

LUCAS FIORELLI; MARIO HÜNICKEN; SERGIO DE LA VEGA; ROXANA BRIZUELA

Neuquén

Congreso; III Congreso Latinoamericano de Paleontolog¨ªa de Vertebrados; 2008

Universidad Nacional del Comahue

After the initial discovery of the Sanagasta fossils in 2001, numerous dinosaur nests were found in the spring and summer of 2007-2008 in the Sanagasta Geologic Park, La Rioja province, Argentina. The geopaleontological field works in the region discovered an extraordinary paleosite that represents the more important nest site in Latin America outside Patagonia. The sedimentary outcrops of Sanagasta Formation are extremely variable laterally as well as vertically, constituted by several ¨C4 to 5¨C cycles of mudstones, sandstones and conglomerated with a complex stratification and lithology. In the valley crop outs the middle (former Sauces Fm.) and upper member (former Los Llanos Fm.) and this last one is that bearer the frequent nests, eggs and eggshells. The objective of the present work is the characterization, throwing out novel data, the eggs and the eggshell found in the park. Although Tauber (2007) published an original work with the description of an egg and numerous eggshell fragments from this area, his results are different from our own preliminary results. Probably this is due to not representative materials found and described by him. In general, the eggs display a grouped disposition inside the clutches and this range from a minimum of 3 eggs ¨Cpreservation influenced by taphonomic factors¨C, to a maximum of more than 35 mainly complete eggs. The eggs possess a spherical to slightly ovoid macroscopic shape with multiple fractures in their surface, eroded and sometimes collapsed. These have an average diameter of 22 cm and their circumference (slightly variable in each specimen) is 60-62 cm, having calculated a maximum volume of 6300 cm3. The eggshells display extremely variable thicknesses, reaching minimums values of 1.29 mm and maximum values of 7.94 mm (average=4,3952; Me=4,31; ¦Ò2=0,67496; n=1150), as much in the same site as in the same nest. Even more, some eggs have a high variability in eggshell thickness; one for example, had 3.15 mm in the apical poles and 6.35 mm in the equatorial lateral ones, a particular case registered also in similar eggs from the Yaminu¨¦ locality, R¨ªo Negro province, Argentina (Manera de Bianco, 1996); however, in the Yaminu¨¦¡¯s eggs this pole-equatorial thickness variability is smaller. Numerous statistic analyses were carried out to search differences with other oospecies. In addition, although not representing different morphotypes, statistically noticeable differences of thickness were observed between eggshells in two different sites within the Park. The external surface is ornamented with dome-like mammillae, which have variable section but are generally circular. The basic type of egg organization is dinosauroidspherulithic, with a filispherulitic structural morphotype. In summary, and from the preliminary studies, we can conclude that the Sanagasta Geologic Park region represents a great area with a monospecific nesting site; the eggs apparently belonging to the Faveoloolithidae and specifically to Sphaerovun erbeni; however this latter ichnotaxon is actually in revision.