Resumen

VAZQUEZ, Miguel et al. New material of Nothrotheriops sp. (Mammalia: Xenarthra) from the El Cedazo fauna, Aguascalientes, Mexico. Bol. Soc. Geol. Mex [online]. 2025, vol.77, n.1, e021024.  Epub 08-Ago-2025. ISSN 1405-3322.  https://doi.org/10.18268/bsgm2025v77n1a021024.

In the 1970’s, Mooser and Dalquest (1975) described the El Cedazo local fauna recovered from the vicinity of the city of Aguascalientes, which they assigned to an Illinoian age. Among the described mammalian taxa was a small ground sloth identified as Nothrotherium cf. N. shastensis, represented by one tooth and some postcranial material.

Recently, an almost complete lower jaw of Nothrotheriops was collected by one of the authors (MV) in Arroyo Cobos, one of the ravines that yielded the El Cedazo local fauna. The lower jaw preserves three molariforms on each side, unfortunately the mandibular spout is missing. A radius and some vertebrae are associated with the mandible.

Comparison of this new specimen with the Rancholabrean N. shastensis and Irvingtonian N. texanus indicates some differences and similarities. The tooth row is smaller than juvenile sloths of N. shastensis from Rancho La Brea and San Josecito Cave, Rancholabrean but it is similar to N. texanus from the Irvingtonian Leisey Shell Pit 1A. The ratio of total alveolar length of the mandible against the depth of the mandible at the third molariform falls closer to N. texanus than to N. shastensis. Unlike both species of Nothrotheriops, the ascending ramus is elongated posteriorly, it is half of the total length of the lower jaw (without mandibular spout), and it forms an obtuse angle of 136° with respect to the alveolar tooth row. It is possible that these differences are ontogenetic in nature.

The second and third molariforms of both sides of the mandible are sufficiently well preserved for mesowear analysis. Based on the mean mesowear angle 108.8°, this particular individual is inferred to have been a mixed feeder. These results are in contrast to previous studies on the feeding habits of N. shastensis from southwestern United States, which is suggested to have been a browser of xeric shrubs, based on plant remains preserved in fossil dung.

Palabras llave : Nothrotheriops; Fauna Cedazo; Pleistocene; Aguascalientes; México.

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