FIRST RECORD OF INDALECIA (MAMMALIA, LITOPTERNA?, INDALECIIDAE) IN THE RÍO LORO FORMATION (EARLY PALEOGENE, TUCUMÁN PROVINCE, ARGENTINA)

Abstract

The Río Loro Formation (early Paleogene, Tucumán Province, northwestern Argentina) has yielded several endemic vertebrates, including turtles, crocodiles, and mammals. The age of this unit is currently under discussion given the lack of absolute chronological data, although recent works favored a middle Paleocene–early Eocene age. In this contribution, we present a left maxillary fragment (PVL 5901), preserving part of the M1 and the M2. A first analysis indicates a close relationship with Indalecia (Litopterna?, Indaleciidae), a genus previously recorded for the Lower Lumbrera Formation (?Ypresian; Salta Province, northwestern Argentina). Given that the Indaleciidae and the representatives of Amilnedwardsidae and Notonychopidae were considered related in the context of the order Notopterna, a comparison was made between PVL 5901 and these taxa, confirming its resemblance with Indalecia. However, PVL 5901 differs from Indalecia grandensis (type and only species of the genus) by the presence of a cuspule on the base of the ectoflexus, the absence of a small fossette mesial to the distolabial fossette, and a conspicuous entoflexus. Hence, we refer PVL 5901 to Indalecia sp. This is the first common faunal element between the Río Loro and Lower Lumbrera formations. Nevertheless, the marked taxonomic discrepancies between the Río Loro vertebrate assemblage and other early Paleogene units contrast with this single common record, and a partial temporal correspondence between the Río Loro and Lower Lumbrera formations is not supported here. Instead, this record indicates a more extended temporal and geographical distribution for the genus Indalecia in northwestern Argentina.

Keywords

• Río Loro Formation
• Lubrera Inferior Formation
• Notopterna
• Biostratigraphy
• Northwestern Argentina