The rufous casiornis (Casiornis rufus) is a species of bird in the family Tyrannidae, the tyrant flycatchers. It is found in Argentina, Bolivia, Brazil, Paraguay, Peru, Uruguay, and as a vagrant to Chile. The rufous casiornis was originally described as Thamnophilus rufus, mistakenly placing it in the "typical antbird" family Thamnophilidae. It was later moved to genus Casiornis that was erected in 1856. During the first half of the twentieth century many authors placed that genus in family Cotingidae but starting in the 1970s it was recognized as belonging to Tyrannidae. The rufous casiornis shares the genus with the ash-throated casiornis (C. fuscus) and the two form a superspecies. For a time they were treated as conspecific but early in the twenty-first century they were firmly established as separate species.
The rufous casiornis is monotypic. The rufous casiornis is 17 to 18 cm (6.7 to 7.1 in) long and weighs 22 to 27 g (0.78 to 0.95 oz). The sexes have the same plumage. Adults have a rufous head, upperparts, wings, and tail. Their throat and breast are cinnamon with a whitish middle of the throat. Their belly is pale buffy yellowish...