Sister group relationship of grebes and flamingos is well supported by both molecular and morphological data. Surprisingly, most of the morphological characters now recognized as synapomorphies of grebes and flamingos have long been known in both taxa, but they were never considered to be homologous. The same is true of two additional synapomorphies discussed here, the presence of nail-like ungual phalanges and prominent caudolateral projections on the ventral side of the cervical vertebrae (processus ventrales).
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