Epipophyses

The epipophyses are bony projections of the cervical vertebrae found in dinosaurs and some fossil basal birds. These paired processes sit above the postzygapophyses on the rear of the vertebral neural arch. Their morphology is variable and ranges from small, simple, hill-like elevations to large, complex, winglike projections. Epipophyses provided large attachment areas for several neck muscles; large epipophyses are therefore indicative of a strong neck musculature.

The presence of epipophyses is a synapomorphy (distinguishing feature) of the group Dinosauria. Epipophyses were present in the basal-most dinosaurs, but absent in closely related ancestors of this group like Marasuchus and Silesaurus. They were typical for most dinosaur lineages; however, they became lost in several derived theropod lineages in the wake of an increasingly S-shaped curvature of the neck.

...
Wikipedia