... The Late Cretaceous Los Alamitos Formation (Maastrichtian; Franchi and Sepúlveda, 1983;Bonaparte et al., 1984;Andreis, 1987;Franchi et al., 2001) is a well-known stratigraphical unit, mostly because of the abundant vertebrate record (Bonaparte et al., 1984;Bonaparte, 1987Bonaparte, , 2002. These include pipoid and calyptocephalellid anurans, diverse madtsoiid snakes and chelid turtles, meiolaniid tortoises, sphenodontians, sauropod, non-avian theropods and birds, abundant specimens of the hadrosaurid dinosaur Huallasaurus australis, and particularly diverse mammals, including a dozen of species belonging to dryolestoids, including meridiolestidans, gondwanatherians, and taxa of uncertain affinities (Bonaparte et al., 1984;Bonaparte, 1986Bonaparte, , 1987Bonaparte, , 1994Bonaparte, , 2002Báez, 1987;Broin, 1987;Powell, 1987Powell, , 2003Albino, 1987Albino, , 2000Apesteguía, 2005;Agnolin and Martinelli, 2009;Gómez, 2016;Rougier et al., 2021;Rozadilla et al., 2021). ...