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The microfauna of the Upper Triassic Ojo Huelos Member, San Pedro Arroyo Formation, central New Mexico, U.S.A.

ASU Author/Contributor (non-ASU co-authors, if there are any, appear on document)
Andrew B. Heckert Ph.D., Assistant Professor of Geology (Creator)
Appalachian State University (ASU )
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Abstract: Three fossiliferous horizons at the type section of the Upper Triassic Ojo Huelos Member of the San Pedro Arroyo Formation yield a microfauna of ostracodes, “spirorbids,” sharks, bony fish, and tetrapods. These fossils represent a rare lacustrine microfossil assemblage near the base of the Upper Triassic Chinle Group. The fossiliferous interval consists primarily of pisolitic limestone and sandy mudstone. The fauna includes the ostracodes Darwinula sp., and Gerdalia sp., “spirorbid polychaetes,” the hybodont shark Lissodus humblei, several morphotypes of actinopterygian fish, including redfieldiids and semionotids, fragmentary labyrinthodont amphibians, and indeterminate reptiles. Darwinula is the most common fossil. Numerically, Lissodus, known from dozens of teeth, dominates the vertebrate fauna, followed by actinopterygians. The smallest teeth of Lissodus from this locality are the smallest teeth known for the genus. This assemblage is consistent with an early Late Triassic (Carnian) age, and lithostratigraphic position suggests that this fauna is probably of Adamanian (latest Carnian) age. Carbonates of definitive lacustrine origin are rare in the Chinle, and this fauna documents the first discovery of microvertebrate tetrapods in lacustrine limestones of the Chinle Group. Because this microvertebrate fauna is clearly from an aquatic environment, this favors an aquatic (not scatologic) origin for similar fish-dominated microvertebrate faunas in the Chinle.

Additional Information

Heckert, A.B., and Lucas, S.G. (2002) The microfauna of the Upper Triassic Ojo Huelos Member, San Pedro Arroyo Formation, central New Mexico, U.S.A. New Mexico Museum of Natural History and Science Bulletin 21, p. 77-85. (ISSN 1524-4156) Archived in NC DOCKS with permission of the editor. The version of record is available at:
Language: English
Date: 2002