An international research team including paleontologists from the Institut Català de Paleontologia Miquel Crusafont (ICP), the University of Edinburgh, and different institutions from the USA (Pittsburgh, Albuquerque, and New York) have shown that Eocene archaic placental mammals such as the tillodont Trogosus retained ancestral brain features in comparison to contemporaneous Eocene crown clades. The study reveals that this genus had a relatively small neocortex, which could have negatively impacted its long-term survival and been linked to the extinction of Tillodontia during the middle Eocene.