Stratigraphy, age, and systematics of two new fossil whales from Angola and stable isotope geochemistry of chicken eggshell, dinosaur eggshell, and paleosol carbonates: Early burial diagenesis in late cretaceous sediments of the Gobi basin, Mongolia

Ongoing field work in Angola, under auspices of Projecto PaleoAngola, has yielded fossil cetaceans from deposits of Miocene age, providing new insights into the early diversification of cetaceans along the western African coast. Here two new taxa of mysticete whales are described. PA 165 comprises a partial articulated skull, an unfused cervical vertebra, and a partial thoracic vertebra. The skull includes the nasals, proximal premaxillae and maxillae, the supraoccipital shield, left squamosal, exoccipital, periotic, and frontal. Portions of both dentaries are present. PA 166 comprises a partial articulated skull including the region posterior to and including the nasals. The proximal portions of the maxillae and premaxillae are present. Both specimens were recovered from what appears to be the Luanda Formation, a calcareous sandstone of late Miocene age. Phylogenetic analysis indicates these fossils represent two new taxa nested with Caperea marginata, the pygmy right whale, in the Neobalaenidae, a family currently restricted to one living species inhabiting cold temperature Southern Hemisphere waters and one fossil species, Miocaperea pulchra, from South America. Three characters unite the new Angolan taxa with Caperea, including the posterolateral corner of the exoccipital projecting posterior to the occipital condyle, the anterior portion of the supraoccipital articulating with the rostral bones and overlaying the frontal and parietal at the vertex of the skull, and the anterior projection of the parietal dorsal to the supraorbital process of the frontal. Two characters distinguish the Angolan taxa from Caperea , including the lateral and medial margins of the ascending process of the maxilla remain parallel terminating in a squared posterior margin and the ventrolaterally oriented postglenoid process in posterior view. Neobalaenidae is a sister group to Eschrichtiidae and Balaenopteridae. These new taxa are two new fossil representatives of Neobalaenidae and they extend the families range into the Miocene phase of the Benguela Large Marine Ecosystem.;Fragmentary fossil eggshell is often used for isotopic analysis when complete eggshell is not available. These analyses are carried out under the assumption that inorganic eggshell carbonate has a homogenous isotopic composition. Isotopic analyses of three modern chicken (Gallus gallus) eggshells to test the homogeneity of the isotopic composition of the eggshell carbonate. Twenty-five samples were collected along three major axes of all three eggshells for the analyses. Standard deviations for &dgr;13C values are about 0.6‰ and standard deviations of &dgr;18O are about 0.15‰. These low standard deviations suggest that the isotopic composition of the eggshell carbonate is homogenous and that spot sampling fossil eggshell for isotopic analysis produces an isotopic composition representative of the entire eggshell.;Khermeen Tsav, Bugin Tsav, Altan Ula, Nugin Tsav, Narin Bulak, and Gurlin Tsav are fossil-rich localities of southwest Mongolia comprised of Campanian-Maastrichtian strata within the Barungoyot and Nemegt Formations. The light stable carbon and oxygen isotopic compositions of fossil eggshells and paleosol carbonates recovered from these localities were analyzed to evaluate the diagenetic history of this locality and to assess whether an original paleoenvironmental signal is preserved. Fourty-two paleosol carbonate samples and sixty fossil eggshell calcite samples were analyzed petrographically to delineate a paragenetic sequence of diagenetic cementation. Diagenesis was recognized within several generations of luminescent calcite growth. Paleosol carbonate &dgr; 13C and &dgr;18O values range from -0.7 to -8.4‰ and 5.6 to -12.2‰ respectively and eggshell calcite &dgr;13 C and &dgr;18O values range from -14.5 to 2.8‰ and -16.6 to 0.7‰ respectively. The eggshell calcite of both luminescent and non-luminescent samples show isotopic signatures that are similar to those of the paleosol carbonates, suggesting a diagenetic signature affects many of the samples analyzed. Two trends were recognized within the isotopic data, an enrichment of &dgr;18O values due to diagenetic alteration within the vadose zone and and enrichment of &dgr;13C values due to diagenetic alteration within the phreatic zone. The geochemical and petrographic analysis of the paleosol carbonates suggests that meteoric waters are responsible for the secondary diagenetic signature occurring during early burial. &dgr;13C values of these eggshell and paleosol carbonate samples that are least altered confirm the presence of C3 plants upon a semiarid Late Cretaceous landscape. Cathodoluminescence and petrographic analyses revealed that there were varying degrees of secondary alteration within the eggshells. This study provides a record of early diagenesis within the Gobi Basin and will provide a new methodology to determine the extent of alteration within fossil eggshell in general.