New Mexico Geological Society Annual Spring Meeting — Abstracts

A campaign to collect microvertebrates in the Fossil Forest Research Natural (FFRNA) Area and the Bisti/De-na-zin Wilderness (BDNZ) of the San Juan Basin over the past 3 (1998-2000) has resulted in recovery of numerous microvertebrate fossils from existing and new fossil sites.

Upper Fruitland Formation and lower Kirtland Formation (Hunter Wash Member; Hunter Wash local fauna) sites include L-4276 (="Quarry 1"), 4616 (probably = "Quarry 2"), 4010, and 3490. These sites yield a diverse assemblage of chondrichthyes (e.g., Squatirhina, Cantioscyllium, Lissodus, Hybodus, Myledaphus) and osteichthyes (e.g., Paralbula, Lepisosteidae, Amiidae, Melvius), squamates, Chelonia, Crocodylia, Dinosauria (e.g., Ceratopsidae, Hadrosauridae, Tyrannosauridae, Troodon, Sauromitholestes, Dromaeosaurus, Richardoestesia, Paronychodon), and Mammalia.

De-na-zin Member, Kirtland Formation sites (Willow Wash local fauna) include L-3228, 4541, and 4543. Microvertebrate sites in the De-na-zin Member tend to be in sand channel facies, where fossils are dispersed and may be highly abraded. Recent recovery efforts have resulted in promising localities, however.

Uppermost Kirtland Formation (Naashoibito Member; Alamo Wash local fauna) sites include L-929 (= BUNM 675), 4005, and 4534. These yield Lepisosteidae, Amiidae, Crocodylia, Squamata, Dinosauria (e.g., Ceratopsidae, Hadrosauridae, Sauropoda, cf. T. rex, Troodon, Richardoestesia), and mammals (e.g., Alphadon and Essonodon browni).

The microvertebrate component of the Hunter Wash and Willow Wash local faunas are similar to those described from late Campanian faunas in west Texas (Terlingua local fauna), Utah (Kaiparowits Formation), Montana and southern Alberta (Judith River Group). The Alamo Wash local fauna microsites yield a microfauna most similar to latest Maastrichtian microfaunas of the northern Rocky Mountain Region. They differ in lacking chondrichthyans and in containing Sauropoda, as represented by abundant postcranial fragments and isolated teeth. The Naashoibito Member microfaunas are especially significant because they are by far the most diverse and best-preserved Maastrichtian microvertebrate faunas yet identified in North America south of Wyoming.