Oldest known eutherian stapes and a marsupial petrosal bone from the Late Cretaceous of North America

Abstract

Cranial remains of Late Cretaceous therian mammals are rarely found in North America and are usually limited to isolated petrosal bones. The oldest known associated stapes and petrosal bone of a Late Cretaceous eutherian are reported here. Comparison with a Late Cretaceous marsupial petrosal bone gives a further indication of the probable condition of several character states of the ancestral mammalian (or at least therian) middle ear, and also indicates the antiquity of various aspects of the middle ear of extant eutherians and marsupials.