Rocky Mountain - 55th Annual Meeting (May 7-9, 2003)

Paper No. 4
Presentation Time: 9:20 AM


JOHNSON, Sally C., New Mexico Museum of Nat History and Sci, 1801 Mountain Road NW, Albuquerque, NM 87104 and LUCAS, Spencer G., New Mexico Museum of Nat History, Albuquerque, NM 87104,

In central New Mexico, Turonian selachian fossil assemblages from the stratigraphic interval Semilla Sandstone Member of the Carlile Shale to the Juana Lopez Member of the Mancos Shale are nearly monospecific. These assemblages are dominated by the teeth of Ptychodus whipplei with rare occurrences of Squalicorax sp. and Scapanorhynchus raphidon. The selachian-producing units are interpreted as shoals in deep water. This may indicate that Ptychodus whipplei was a deep water shark that came to these shoals to feed. By comparison, the onshore equivalents of the Semilla through the Juana Lopez interval, which include the Atarque Sandstone Member of the Tres Hermanos Formation, yield a diverse selachian assemblage. Although Wolberg (1985) reported 22 species from the Atarque Sandstone, it only contains 11 of the species that he reported: Scapanorhynchus raphidon, Squalicorax falcatus, Ptychodus whipplei, Ptychodus anonymus, Hybodus sp., Chiloscyllium greeni, Cretodus semiplicatus, Ptychotrygon triangularis, Ischyrhiza avonicola, Pseudohypolophus mcnultyi and Rhinobatos sp. This assemblage is dominated by the teeth of the pelagic sharks Scapanorhynchus raphidon and Squalicorax falcatus, and the benthic ray Pseudohypolophus mcnultyi. Ptychodus whipplei is present, but it is a very small component of the Atarque selachian assemblage. The differences in the two age equivalent Turonian assemblages gives insight into the different habitats preferred by these Cretaceous sharks.