The memorization and production of song in songbirds share important parallels with the process of speech acquisition
in humans. In songbirds, these processes are dependent on a group of specialized telencephalic nuclei known
as the song system: HVC (used as a proper name), RA (robust nucleus of arcopallium), LMAN (lateral magnocellular
nucleus of the nidopallium) and striatal Area X. A recent study suggested that the arcopallium of the Sayornis
phoebe, a non vocal learner suboscine species, contains a nucleus with some properties similar to those of songbird
RA, suggesting that the song system may have been present in the last common ancestor of these groups. Here we
report morphological and gene expression evidence that a region with some properties similar to RA is present in another
suboscine, the Amazonian endemic Willisornis poecilinotus. Specifically, a discrete domain with a distinct Nissl
staining pattern and that expresses the RA marker RGS4 was found in the arcopallium where the oscine RA is localized.
Our findings, combined with the previous report on the S. phoebe, suggest that an arcopallial region with some
RA-like properties was present in the ancestor of both Suboscines infraorders Tyranni and Furnarii, and is possibly
an ancestral feature of Passeriformes.
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