Two New Large Strombid Species From The Lower Miocene Linut-Od Formation In Southern Cebu Island, Philippines
Yolanda Maac-Aguilar1, Tomoki Kase2 and Hiroshi Noda3
1JSPS Fellow, National Science Museum, Tokyo and Mines and Geosciences Bureau, Philippines; 2National Science Museum, Tokyo; 3 c/o Tsukuba University, Tsukuba City
Two new species under genus Oostrombus (Gastropoda: Mollusca) were identified from two sites located in the lower part of the lower Miocene Linu-tod Formation in southern Cebu, Philippines. Both species were found to share common characters such as large, heavy, smooth shells, a thickly calloused columella and a rounded flaring wing slightly exceeding the height of the spire. But, certain distinguishing morphological features were noted which compelled classification into separate species. Oostrombus sp. 1 is rather obconic in shape with rather widespread columellar callus covering the entire apertural facet, whereas Oostrombus sp. 2 has a comparably shorter spire, a rotund, barrel-shaped body with a strongly tapered base and a callus restricted in the columella. Discovery of these new species marks the first large fossil strombids to be recorded in the Philippines and the only Oostrombus species identified in the Indo-Pacific. When compared with other known large strombid congeners, both species categorically fall under the subgenus Oostrombus Sacco, 1893, an extinct Tethyan stock reported from Europe and the Americas. Other large strombid genera like Tricornis Jousseaume, 1886 of modern oceans and Dilatilabrum Cossmann, 1904, another extinct Tethyan taxa, also present close similarities but were distinguished thereof based on differences in surface sculptures and shape of outer lip. These discoveries are considered breakthroughs in paleobiogeography which could fill up important gaps in the distribution of species known only in the western Tethys and Americas. Finding such an extinct European stock in the Philippines indicates a direct connection between the Pacific Ocean and Europe thru the Tethys Sea, giving access to faunal migration as early as early Miocene time or probably even beyond.
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