The first enantiornithines to be discovered were incorrectly referred to modern bird groups. For example, the first known enantiornithine, "Gobipteryx minuta", was originally considered a paleognath related to ostriches and tinamou. Enantiornithines were first recognized as a distinct lineage, or "subclass" of birds, by Cyril A. Walker in 1981. Walker made this discovery based on some partial remains from the late Cretaceous period of what is now Argentina, which he assigned to a new genus, "Enantiornis", giving the entire group its name. Since the 1990s, many more complete enantiornithines have been discovered, and it was determined that a few previously described "birds" (e.g. "Iberomesornis", "Cathayornis", and "Sinornis") were also enantiornithines.