FIRST RECORD OF ORGANIC REMAINS IN UPPER CRETACEOUS ORNITHOID EGG, FROM RÍO NEGRO, ARGENTINA

FERNÁNDEZ, MARIELA S.; GARCÍA, RODOLFO A.; SALGADO, LEONARDO

Zapala-Villa El Chocón

Jornada; Jornadas Argentinas de Paleontología de Vertebrados; 2014

Comisión Organizadora

We report the first record of organic remains in an ornithoid egg from Río Negro Province, in Upper Cretaceous (Campanian-Maastrichtian) rocks of the Allen Formation (Salitral Ojo de Agua). The egg is exceptionally preserved, including fibers of the testaceous membrane. The fibers are flattened, with a thickness of 1.1μm and a width of 4.8μm each. The fibers have an arrangement similar to those seen in living crocodiles, and display a random arrangement. The preservation of the testaceous membrane suggests extraordinary site conditions. EDAX analysis reported that fibers are enriched in trace of Mg, Al, Si, P, F, and K, element that are also present in one or more examples of both extant and fossil shell membrane. The egg preserved a single pole, of smooth surface. Its measurements are 5.38 cm in length (long axis) and 3.06 cm in width (short axis). Three samples of eggshells have been observed under scanning electron microscope. The ultrastructure of the eggshells reveals that these eggs have an ornithoid basic type, and a ratite morphotype. The well-developed mammilary cones are 154μm thick and the squamatic layer is 251 μm. The complete thickness of the eggshell is about 400μm. The shell microstructure of this egg is consistent with Laevisoolithidae, an ootaxon traditionally associated with enantiornithid birds.