Search

Eomysticetidae (Chaeomysticeti clade) is an archaic family of baleen whales that originated and diversified during the Oligocene epoch. The fossil record of this family is represented by at least 11 formally described species, including records in Baja California Sur (Mexico), Kaiserswerth (Germany), Kitakyushu (Japan), South Carolina (United States), and South Island (New Zealand). Baja California Sur (BCS) possesses important marine deposits from the upper Oligocene, which document a rich diversity of fossil mysticetes, including members of the family Eomysticetidae. In this work, we report a whale specimen collected in the upper Oligocene San Juan Member, El Cien Formation, from the so-called "Ten Minute locality", San Hilario, about 100 km NW of La Paz, Baja California Sur. The studied specimen consists of an incomplete skull, in which most of the rostrum and part of the occipital shield are missing but preserving one tympanic bulla in situ. This specimen is identified as belonging to the family Eomysticetidae based on both an elongated skull and nasals and transversely narrow and long intertemporal region with a wide exposure of parietals and frontals. The lack of more diagnostic regions precludes its identification at generic/specific levels. The specimen represents the first description of an eomysticetid for the San Hilario area, increasing our knowledge of the evolution of this group of mysticetes and its record in the Pacific basin from the late Oligocene of BCS. [ABSTRACT FROM AUTHOR]

The Oligocene species ascribed to the Calappidae H. Milne Edwards, 1837, housed in the palaeontological collections of the Museum "G. Maini" of Ovada (Alessandria, Piemonte, NW Italy) from the Ligure Piemontese Basin, are herein revised in order to verify their systematic assignment. Two additional specimens are ascribed to Calappilia guttata n. sp., whereas one specimen previously ascribed to M. pustulosus is herein assigned to Calappilia sp. The revision allows us to provide an emended diagnosis and new description of Mursiopsis pustulosus Ristori, 1889. Finally the assignment of Stenodromia mainii (Allasinaz, 1987) and Calappilia vicetina Fabiani, 1910, is briefly discussed. [ABSTRACT FROM AUTHOR]

The Oligocene Upper Panalillo Ignimbrite is widely distributed in the San Luis Potosí Volcanic Field, in the southeastern portion of the Mesa Central province of Mexico. It crops out sporadically over a ∼15,000 km2 area. The best exposures of the ignimbrite were sampled for paleomagnetic and geochronological studies, with sites grouped in five zones according to their geographic distribution and structural setting. The five zones are: northwest or La Pendencia (1); north or Valle Umbroso (2); center-north or Mexquitic (3); east or Panalillo (4); and, south or Bledos Graben (5). We determined virtual paleomagnetic poles (VGPs) and mean directions for each sampling site and for each one of the five zones. VGPs for the Upper Panalillo Ignimbrite were combined with published paleomagnetic data for the San Luis Potosí volcanic field in order to determine an Oligocene paleomagnetic pole located at 72.1°N - 165.5°E (N = 17, K = 228.2, A95 = 6.8°), which was in turn compared with the North America reference pole. We determined rotation (R) and flattening (F) parameters for the region. The study was supplemented by seven radiometric ages for the ignimbrite, three are single crystal total fusion LASER 40Ar/39Ar ages and four are K/Ar for saninide separates. The combination of paleomagnetic data and isotopic age determinations suggests that the Upper Panalillo Ignimbrite is composed of at least two flow units with different paleomagnetic and radiometric ages. One unit is approximately 26.5 Ma and it is mostly present in La Pendencia area; the other is ca. 28 Ma, and crops out around the city of San Luis Potosí. The overall mean for individual units of the volcanic field suggests that the region has experienced a counter-clockwise rotation of 7.9° ± 9.6° with respect to the North America craton since the Oligocene. However, the estimate of rotation is not statistically significant, and it can be interpreted as an apparent tectonic rotation consequence of complex faulting that affected the region during Paleogene time. [ABSTRACT FROM AUTHOR]