New Mexico Geological Society Annual Spring Meeting — Abstracts

The Upper Pennsylvanian Tinajas Member of the Atrasado Formation is of Missourian age and yields vertebrate coprolites from the Kinney Brick Quarry Lagerstätte in the Manzanita Mountains of Bernalillo County and the Tinajas Lagerstätte in the Cerros de Amado of Socorro County. A new locality (NMMN locality L-9096), also in the Cerros de Amado, contains a very large sample of coprolites. Most specimens are found as a weathering lag that eroded from a shale although, a small number of specimens occur in situ in thin limestone beds. The majority of coprolites are spiral in morphology (heteropolar, amphipolar, scroll). Five ichnotaxa are heteropolar spiral in morphology and include Crassocoprus mcallesteri, Kalocoprus oteroensis, two ichnospecies of Heteropolacopros and ?Speirocoprus isp. There are numerous specimens of Crassocoprus mcallesteri, which was previously only known from one specimen from the Tinajas Lagerstätte. Heteropolar microspiral coprolites are assigned to Heteropolacopros, but there is a need for an ichnotaxonomic review of this ichnogenus. Amphipolar coprolites are represented by Hyronocopros amphipola. There are several specimens of the scroll coprolite Bibliocoprus beemanensis, which is identified beyond its type locality for the first time. Four bromalite faunas of Missourian age in New Mexico represent an ecological transect from estuarine to shallow marine: (1) Kinney Brick Quarry Lagerstätte – estuarine; (2) Tinajas Lagerstätte – lagoonal ; (3) NMMN locality L-9096 – nearshore marine; and (4) Sacramento Mountains – offshore marine. The Kinney ichnofauna preserves a diverse bromalite ichnoassemblage comprising seven morphotypes of coprolites, regurgitalites and a consumulite. Most specimens are sub-ovoid, laterally compressed, non-spiral in morphology and preserved in matrix. The sample size from the Tinajas Lagerstätte is smaller but it yields 12 morphotypes of bromalites (11 coprolites, 1 regurgitalite) including Conchobromus kinneyensis, Crassocoprus mcallesteri, Spierocoprus socorroensis, Elongatocoprus amadoensis, Elacacoprus williamsi and Crustacoprus tinajaensis. Most specimens are preserved in matrix, and a higher percentage are of spiral morphology than at Kinney. The Sacramento Mountains ichnofauna derives from the Beeman Formation and consists entirely of spiral coprolites that have weathered out of shale. Beeman specimens represent Liassocoprus hawkinsi, Heteropolacopros texaniensis, Hyronocoprus amphipola, Kalocoprus oteroensis, Bibliocoprus beemanensis and unassigned morphotypes. There are clear trends through these ichnofaunas (Kinney-Tinajas-L-9096-Sacramentos); (1) flattened preservation in matrix to isolated three dimensional; (2) diverse bromalites to only coprolites; and (3) increasing proportion of spiral coprolites. The new locality is transitional in all these aspects between Tinajas and the Sacramentos. The ichnofauna of the Beeman Formation is representative of the Shark Surplus Paradox, in which there is an apparent disproportionate diversity and abundance of spiral (probably chondrichthyan) coprolites relative to the fish fauna (preserved or inferred). The ichnofaunas from the Missourian of New Mexico are potentially important for understanding the causes of the Shark Surplus Paradox.