SELACHIAN-DOMINATED VERTEBRATE FOSSIL ASSEMBLAGE FROM THE UPPER CRETACEOUS ATARQUE SANDSTONE, SEVILLETTA NATIONAL WILDLIFE REFUGE, SOCORRO COUNTY, NEW MEXICO

Abstract

We have relocated and recollected the fossil vertebrate locality in the Upper Cretaceous (Turonian) Atarque Sandstone on the Sevilleta National Wildlife Refuge first documented by Baker and Wolberg in the 1980s. The locality is now NMMNH 5153 and yields numerous teeth and bone fragments from a 0.7-m-thick localized intrabasinal ferruginous conglomerate of limestone, tooth, bone, bivalve shell and chert pebbles in a section of finegrained sandstone near the top of the Atarque Sandstone. Virtually all of the teeth and bones from this bed were broken prior to fossilization, so based on the lithjology of the bonebed and the preservation of the fossils, we interpret this fossil site as an allochthonous assemblage in a storm deposit. The following selachian taxa were previously known to be present in this assemblage: Hybodus sp., Ptychodus whipplei , P . cf. P . mammillaris , Chiloscyllium greeni , Scapanorhynchus raphiodon, Cretodus semiplicatus , cf. Paranomodon sp., Squalicorax falcatus, Rhinobatos sp., Pseudohypolophus mcnultyi, Ischyrhiza schneideri and Ptychotrygon triangularis . Our collection duplicates many of the selachian taxa previously known from this assemblage, and also includes numerous teleost, especially pycnodonts. Turtle bones and dromaeosaur teeth are also present, indicating a freshwater/terrestrial component to the assemblage. Scapanorhynchus dominates the assemblage, and the sedimentology, terrestrial taxa, assemblage diversity and rarity of Ptychodus suggest a relatively nearshore association.