oval foramen

The alisphenoid strut, an extension of the alisphenoid bone of the skull which separates two openings in the skull, the buccinator-masticatory foramen and the accessory oval foramen, is usually present, although it is more commonly absent in other Nephelomys.

As the two specimens were "identical in all character states" used in his phylogenetic analysis, were from similar stratigraphic levels and "uniquely share the presence of a triangular coracoid with a large, oval foramen", Senter concluded that NGMC 91 does belong to the species Sinornithosaurus millenii.