New Mexico Geological Society Annual Spring Meeting — Abstracts

New Mexico’s Early Permian vertebrate track record has received considerable attention over the last decade and is now recognized as a global standard. However, its Early Permian invertebrate ichnofaunas are less well known and have been relatively understudied. Here, we document an occurrence of Hamipes, an invertebrate ichnotaxon that has previously been unreported from New Mexico.

The specimen (NMMNH P-32661) is from New Mexico Museum of Natural History locality 1339, which is in the upper part of the Sangre de Cristo Formation (Wolfcampian) of San Miguel County, New Mexico. A diverse vertebrate ichnofauna is present, dominated by typical Early Permian ichnogenera such as Dromopus and Batrachichnus. An invertebrate ichnofauna is also present, consisting of ichnogenera such as Paleohelcura and Dendroidichnites. The paleoenvironment is interpreted as a sheet-flood deposit on an extensive floodplain.

P-32661 is preserved in convex hyporelief, with only a single-track row shown on the slab. This is either a partial specimen or undertracks in which a second track row did not impress. The track row width is 20 mm, and the total length is 20 cm. The track row contains regular, paired, thin, slightly curved scratch mark impressions, which terminate in commashaped mounds. The individual impressions are 25 mm long, with a repeat distance of 25 mm. We refer P-32661 to the ichnogenus Hamipes Hitchcock, 1858, based on the similarity of this specimen to the type material. Due to the large size of this specimen, the probable arthropod track-maker was a crustacean and not an insect.

There are three separate invertebrate ichnofaunal assemblages in the Lower Permian strata of New Mexico, which are located on a north-to-south transect of the state. The southernmost ichnoassemblage, centered near Las Cruces, is found in coastal tidal flat facies of the Robledo Mountains Formation that show periodic freshwater influence. This diverse ichnoassemblage is distinct in having four arthropod ichnotaxa, including Tonganoxichnus robledoensis, which are known only from their type localities within the Robledo Mountains Formation. Another ichnoassemblage, from the central part of the state around the Lucero uplift and Socorro, is low in ichnodiversity. It is found in transitional brackish waterinfluenced facies low in the Abo Formation. The characteristic ichnotaxon within this ichnoassemblage is Palaeophycus, an infaunal burrow attributed to polychaete makers. Another ichnoassemblage occurs in the northern part of the state, near Villanueva in San Miguel County. It is found within floodplain facies of the Sangre de Cristo Formation that were far inland during Wolfcampian time. The ichnodiversity of this arthropod-dominated ichnoassemblage is less than that of the southern ichnoassemblage. However, it may contain different ichnotaxa in addition to Hamipes. Continued investigation is needed to further determine the compositional similarities and differences between these ichnoassemblages.