Paul (2002:25) coined Averostra as a taxon containing Dromaeosauridae and theropods that possessed “at least one accessort maxillary opening in the lateral wall of the antorbital fossa that led into a bony mediorstral maxillary sinus.” Like most form-qualified (”apomorphy-based”) stem-based definitions, problems emerge involving homology. In Allosaurus fragilis, two openings and associated spaces are present at the anterior end of the antorbital fossa (Witmer 1997), the openings termed the promaxillary and maxillary fenerstrae. Some basal theropods, however, only have one of these openings, such as the abelisaurid Rugops or the allosauroid Carcharodontosaurus, and it is not always clear which one.

The clade identified as Averostra by Paul (2002:24), furthermore, is not resolved on cladograms by Carrano et al. (2002) and Sereno et al. (2004) that, in contrast, link Ceratosauria (sensu stricto) with Tetanurae. However, given that this arrangement is still controversial (Tykoski and Rowe 2004:fig. 3.12), proposing another taxon (however defined) seems premature.