New Mexico Geological Society Annual Spring Meeting — Abstracts

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Extensive Late Cretaceous (Coniacian), Mostly Marine Vertebrate Fossil Assemblages From the Southeastern San Juan Basin, New Mexico

Randy Pence1, Paul May1 and Spencer G. Lucas1

1New Mexico Museum of Natural History, 1801 Mountain Road N.W., Albuquerque, NM, 87104,

An extensive vertebrate faunal assemblage has been collected from anthills that have gathered fossil material from the Upper Cretaceous (Coniacian) Tocito Sandstone. The fossil-bearing deposit is a crossbedded, very coarse grained to pebbly sandstone that was deposited on an offshore bar or barrier island. The fossils mostly represent selachian taxa, are worn and tumbled and thus are allochthonous. This is an ongoing project consisting of sorting and identifying at least 17,000 fossils, and thus far there have been at least 12 selachians, 3 bony fish, four invertebrates, at least two types of reptiles, and one mammal collected. The selachian taxa include Scapanorhynchus raphiodon, Ptychodus mortoni, Squalicorax cf. falcatus, Scindocorax novimexicanus, Cretolamna appendiculata, Ptychotrygon nov. sp., Hybodus sp., Polyacrodus aff. parvidens, Pseudohypolophus ellipsis, rhynobatoidsp., Myledaphus sp.,and Cantioscyllium decipiens, as well as yet to be identified species. The bony fishes include Micropycnodon kansasensis, Anomoeodeus sp., Lepidotes sp.and an unidentified ginglymodian. Inoceramid clams make up the majority of the invertebrates, with the rest being baculites, other ammonites, crinoids (reworked from Paleozoic strata), and gastropods. The reptiles include crocodile, plesiosaur, and mosasaur. The one mammal tooth collected is an incisor of an unknown taxon. Teeth of Scapanorhynchus apparently make up the vast majority of the faunal assemblage (though soem of these teeth, many of which are fragmentary, may represent other taxa), while some other taxa are rare, notably Polyacrodus aff. parvidens, which is known from five or less examples. Almost all of the teeth are very small, less than 10 mm in maximum dimension, but whether this is caused by hydraulic sorting, the ability of the ants to carry material to build up their hills, or the fossil assemblage sourcing a possible shark pupping area is yet to be determined.

pp. 52

2021 New Mexico Geological Society Annual Spring Meeting
April 15-16, 2021, Virtual Meeting

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