The oldest mammals from <scp>A</scp>ntarctica, early <scp>E</scp>ocene of the <scp>L</scp>a <scp>M</scp>eseta <scp>F</scp>ormation, <scp>S</scp>eymour <scp>I</scp>sland

Abstract

Abstract New fossil mammals found at the base of A cantilados II A llomember of the L a M eseta F ormation, from the early E ocene ( Y presian) of S eymour I sland, represent the oldest evidence of this group in A ntarctica. Two specimens are here described; the first belongs to a talonid portion of a lower right molar assigned to the sparnotheriodontid litoptern N otiolofos sp. cf. N . arquinotiensis . Sparnotheriodontid were medium‐ to large‐sized ungulates, with a wide distribution in the E ocene of S outh A merica and A ntarctica. The second specimen is an intermediate phalanx referred to an indeterminate E utheria, probably a S outh A merican native ungulate. These A ntarctic findings in sediments of 55.3 Ma query the minimum age needed for terrestrial mammals to spread from S outh A merica to A ntarctica, which should have occurred before the final break‐up of G ondwana. This event involves the disappearance of the land bridge formed by the W eddellian I sthmus, which connected W est A ntarctica and southern S outh A merica from the L ate C retaceous until sometime in the earliest P alaeogene.