A 2020 study of phorusrhacid skull morphology by Degrange found that there were two main morphotypes within the group, derived from a seriema-like ancestor.
A 2020 study on the skull structure of phorusrhacids by Degrange found that these creatures could be categorized into two main forms, which are believed to have originated from an ancestral species similar to the modern-day seriema bird.