Revisiting old data to unveil the history and age of the Itaboraí Basin fossil mammals

• Published in: Journal of mammalian evolution 2024-12, Vol.31 (4), p.42, Article 42
• Main Authors: Bergqvist, Lílian Paglarelli, Carneiro, Leonardo M., Zanesco, Tábata, Castro, Luis Otávio Resende, de Oliveira, João Alves
• Format: Article
• Language: English
• Subjects: Animal Genetics and Genomics; Anthropology; Biomedical and Life Sciences; Eocene; Evolutionary Biology; Fossil mammals; Human Genetics; Life Sciences; Paleocene; Topography
• ISSN: 1064-7554; 1573-7055
• DOI: 10.1007/s10914-024-09738-z

The fossil mammalian assemblage of the Itaboraí Basin, located in the state of Rio de Janeiro, Brazil, was recovered from fissure fill deposits that vertically cut its limestone beds. Previous studies have considered the abundant and diversified fossil mammals excavated from such deposits of this small basin to have been deposited synchronously. An analysis comparing the whole Itaboraí mammalian assemblage with that of the Las Flores Formation, Argentina, estimated its age as early Eocene. The purpose of this study is to test the hypothesis of an asynchronous formation and infilling of the fissures and to conduct faunistic comparisons with other South American local faunas, considering the mammals of each Itaboraí fissure (MN, MCT-1 and MCT-2) separately, as these fissures were formed in distinct areas of the basin and in different topographic levels. To evaluate the faunal similarities between the Itaboraí fissures and other South American local faunas, cluster analysis and parsimony analysis of endemicity were undertaken. Both methods nest all three Itaboraí fissures with the Yacimiento Las Flores fauna, but some analysis show two fissures (MN and MCT-1) to be closer to it than the third. Based on the topographic levels of the fissures, their fossil mammals (diversity, presence/absence, and abundance), marsupial trophic structure and evolutionary stage, we conclude that the Itaboraí mammal assemblage is composed of faunas of different ages/stages: the fauna of the fissure discovered in 1968 (MCT-2) is the oldest (probably late Paleocene to earliest Eocene), and the fissure discovered in 1949 (MCT-1) is the youngest (early Eocene).