Abstract
The limited fossil record of Australian Cretaceous theropods is dominated by megaraptorids, reported from associated and isolated material from the Early Cretaceous of Victoria and the ‘Mid’-Cretaceous of central-north New South Wales and central Queensland. Here, we report on new postcranial theropod material from the early Late Cretaceous Griman Creek Formation at Lightning Ridge. Among this new material is an associated set consisting of two anterior caudal vertebrae and a pubic peduncle of the ilium, to which a morphologically similar partial vertebral centra from a separate locality is tentatively referred. These elements display a combination of characteristics that are present in megaraptorid and carcharodontosaurid theropods, including camellate internal organization of the vertebral centra, ventrally keeled anterior caudal centra and a pubic peduncle of the ilium with a ventral surface approximately twice as long anteroposteriorly as mediolaterally wide. Unfortunately, a lack of unambiguous synapomorphies precludes accurate taxonomic placement; however, avetheropodan affinities are inferred. This new material represents the second instance of a medium-sized theropod from this interval, and only the third known example of associated preservation in an Australian theropod. Additional isolated theropod material is also described, including an avetheropodan femoral head that shows similarities to Allosaurus and Australovenator, and a mid-caudal vertebral centrum bearing pneumatic foraminae and extensive camellae that is referrable to Megaraptora and represents the first axial skeletal element of a megaraptorid described from Lightning Ridge.
Highlights
The fossil record of Australian Cretaceous theropods is scarce and is composed almost exclusively of isolated and fragmentary remains [1]
A re-evaluation of the problematic Victorian elements is beyond the scope of this present study; the new Lightning Ridge theropod material described here further highlights the preponderance of basal avetheropodangrade theropods from the Mid-Cretaceous of eastern Australia
New associated and isolated material from the Upper Cretaceous Griman Creek Formation of Lightning Ridge contributes to the scant fossil record of Australian theropods and underscores the predominance of basal avetheropodan-grade theropods during this interval
Summary
The fossil record of Australian Cretaceous theropods is scarce and is composed almost exclusively of isolated and fragmentary remains [1]. Despite the evidence for a high diversity of theropods in Australia, the record of apex theropod predators appears to be dominated by megaraptorids This is in contrast to the contemporaneous theropod fossil record of Patagonia, at roughly the same palaeolatitude, which hosted a diverse range of abelisaurids, with a smaller component of the fauna consisting of carcharodontosaurids and megaraptorids [13]. The first named Australian theropod, Rapator ornitholestoides, was described on the basis of a single metacarpal I discovered in the GCF in the vicinity of Lightning Ridge [16] While this taxon is considered to be a nomen dubium, subsequent comparisons with the same element in Australovenator and Megaraptor indicate megaraptorid affinities for Rapator [1,12,17].
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