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First record of organic remains in Upper Cretaceous ornithoid egg, from Río Negro, Argentina
Zapala y Chocón
Jornada; XXVIII Jornadas Argentinas de Paleontologia de Vertebrados; 2014
Institución organizadora:
Museo Paleontologico Ernosto Bachman, Museo Carmen Funes y Museo Provincial de Ciencias Naturales Prof. Dr. Juan A. Olsacher
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.