How are tinamous related to ratites such as ostriches and rheas?

Tinamous are closely related to ratites—a group of large, flightless birds that includes ostriches, rheas, emus, and cassowaries.

Scientific interest in tinamous stems from numerous anatomical and biological features that link them to these birds. Specifically, the structure of the bony palate—a key taxonomic feature—clearly connects tinamous to ratites. This relationship is further supported by DNA and protein analysis. Despite these strong evolutionary ties, most authorities classify tinamous in their own order, Tinamiformes, while grouping ratites within the order Struthioniformes. Additionally, young tinamous exhibit physical similarities to young rheas, as both are able to run shortly after hatching and share similar streaked and blotched appearances.1