Palaehoplophorini glyptodonts (Xenarthra, Glyptodontidae) from the Puerto Madryn Formation (Late Miocene), Argentine Patagonia: Diversity and biochronological implications in southern South America

Abstract

Palaehoplophorini is a poorly known lineage of glyptodonts that appeared during the Middle Miocene in Patagonia. Their diversity is considered low with respect to other glyptodont groups, including only two well-characterized species from the Middle-Late Miocene of Patagonia (ca. 12 Ma): Palaehoplophorus meridionalis and Palaehoplophoroides rothi. The putative Late Miocene Palaehoplophorini Palaehoplophorus antiquus and Aspidocalyptus castroi from the Mesopotamian and Pampean regions, respectively, were defined based on fragmentary materials without relevant diagnostic characters. Here, we describe several Late Miocene (ca. 9.4 Ma) Palaehoplophorini remains coming from the upper levels of the Puerto Madryn Formation (Península Valdés, Chubut Province, Argentina). Material includes carapace osteoderms, caudal rings, and tube fragments, all assigned to Palaehoplophorini. A right femur one-third larger than that of Kelenkura castroi (Chasicoan Stage/Age) was also identified, suggesting an estimated body mass of ca. 320 kg. These fossil remains confirm the persistence of Palaehoplophorini during the Late Miocene, at least in Patagonia. Our analysis also discards the Pampean region as a “refuge” for the last Palaehoplophorini as it was previously proposed. Lastly, anatomical comparisons reflect a correlation between body mass and latitudinal distribution of late Tortonian glyptodonts in South America, with a size decrease towards low latitudes.