Zbigniew M. Bocheński, Teresa Tomek, Krzysztof Wertz and Ewa Świdnicka (2013). «The third nearly complete passerine bird from the early Oligocene of Europe». Journal of Ornithology154 (4): 923-931. doi:10.1007/s10336-013-0958-z.
F. Keith Barker, Alice Cibois, Peter Schikler, Julie Feinstein< & Joel Cracraft: Phylogeny and diversification of the largest avian radiation. PNAS, 27 de julio, 2004, Vol. 101, no. 30, PDF