Evolutionary and paleobiogeographic implications of new carcharodontosaurian, megaraptorid, and unenlagiine theropod remains from the upper Lower Cretaceous of Victoria, southeast Australia

The Early Cretaceous non-avian theropod body fossil record of Victoria, Australia dominantly comprises isolated dental and postcranial remains. Numerous specimens have been collected from both the upper Strzelecki Group (upper Barremian–lower Aptian) and Eumeralla Formation (upper Aptian–lower Albian), yet theropod diversity in each unit remains poorly resolved. In both deposits, specimens pertaining to Megaraptoridae—a clade seemingly endemic to South America and Australia in the Cretaceous—are most frequently encountered. However, evidence of other typically common Gondwanan theropod groups, including Abelisauridae and Carcharodontosauria, has remained unknown. Herein, we describe five new theropod specimens: three tibiae, and two articulated caudal vertebrae with haemal arches, from the upper Strzelecki Group; and a single tibia from the Eumeralla Formation. Two of these tibiae—one each from the upper Strzelecki Group and the Eumeralla Formation—provide the first evidence for Carcharodontosauria in Australia. Two megaraptorid specimens from the upper Strzelecki Group—a tibia, and two caudal vertebrae with haemal arches—demonstrate that this clade had achieved large body size at the time of its first appearance in the fossil record. A tibia from the upper Strzelecki Group is interpreted to represent the Gondwanan dromaeosaur clade Unenlagiinae. Collectively, the new theropod remains described herein strengthen the evidence for mid-Cretaceous faunal interchange between Australia and South America across Antarctica, and highlight the presence of carcharodontosaurians and unenlagiines at high latitudes in the late Early Cretaceous.