Macrofossils discovered in the Battye Glacier Formation (Pagodroma Group) of the Prince Charles Mountains, East Antarctica, provide important insight into marine life of the mid-Tertiary, rarely preserved elsewhere on the continent. Recorded are five species of macroinvertebrates; these are Adamussium n. sp.? cf. colbecki (Smith, 1902) (Bivalvia), Laternula? sp. (Laternulidae), Mytilidae genus and species indeterminate (Bivalvia), Bivalvia genus and species indeterminate, and Polychaeta genus and species indeterminate. Based on stratigraphical data and faunal composition, the clasts are dated as no younger than Early Miocene. This is one of the oldest reports of Adamussium from Antarctica, previously known from the Late Pliocene to Recent with a possible record in the Late Oligocene–Early Miocene. Palaeoecological data and facies analysis indicate that these taxa inhabited a shallow- to mid-shelf marine environment of normal salinity that was oligotrophic. The substrate was a soft, pebbly and sandy bottom that was sufficiently mobile to sponsor deep burrowing forms.