BackgroundModern flamingos (Phoenicopteridae) occupy a highly specialized ecology unique among birds and represent a potentially powerful model system for informing the mechanisms by which a lineage of birds adapts and radiates. However, despite a rich fossil record and well-studied feeding morphology, molecular investigations of the evolutionary progression among modern flamingos have been limited. Here, using three mitochondrial (mtDNA) markers, we present the first DNA sequence-based study of population genetic variation in the widely distributed Chilean Flamingo and, using two mtDNA and 10 nuclear (nDNA) markers, recover the species tree and divergence time estimates for the six extant species of flamingos. Phylogenetic analyses include likelihood and Bayesian frameworks and account for potential gene tree discordance. Analyses of divergence times are fossil calibrated at the divergence of Mirandornithes (flamingos + grebes) and the divergence of crown grebes.ResultsmtDNA sequences confirmed the presence of a single metapopulation represented by two minimally varying mtDNA barcodes in Chilean flamingos. Likelihood and Bayesian methods recovered identical phylogenies with flamingos falling into shallow-keeled (comprising the Greater, American and Chilean Flamingos) and deep-keeled (comprising the Lesser, Andean and James’s Flamingos) sub-clades. The initial divergence among flamingos occurred at or shortly after the Mio-Pliocene boundary (6–3 Ma) followed by quick consecutive divergences throughout the Plio-Pleistocene. There is significant incongruence between the ages recovered by the mtDNA and nDNA datasets, likely due to mutational saturation occurring in the mtDNA loci.ConclusionThe finding of a single metapopulation in the widespread Chilean Flamingo confirms similar findings in other widespread flamingo species. The robust species phylogeny is congruent with previous classifications of flamingos based on feeding morphology. Modern phoenicopterids likely originated in the New World with each sub-clade dispersing across the Atlantic at least once. Our divergence time estimates place flamingos among the youngest families of birds, counter to the classical notion of flamingos as among the oldest based on biogeography and the fossil record. Finally, we designate ‘Phoeniconaias’ as a junior synonym of ‘Phoenicoparrus’ and redefine the latter genus as containing all flamingos more closely related to Phoenicoparrus andinus than Phoenicopterus roseus.

Understanding of the Asian early Paleogene avifauna is limited relative to that of North American and European avifauna of the same period. While major patterns of mammalian faunal exchange among these three regions across the Paleocene/Eocene boundary have been described, much less is known about the dynamics of bird diversity over the same time inter¬ val. Here, we report bird fossils from the earliest Eocene Bumban Member of the Naranbulag Formation in central Mongolia that add to the known record from Asia from just after this boundary. Most of this material, collected by the joint American Museum of Natural History/ Mongolia Academy of Sciences expeditions, is referable to a previously described taxon in Presbyornithidae (Anseriformes). However, five isolated elements are identified as compris¬ ing at least four species from at least three other major avian clades. While further inclusive phylogenetic analyses of each of these clades are necessary, the new remains represent possible earliest occurrences in Asia of these clades. The material includes a humerus and a furcula from shorebirds (Pan-Charadriiformes), a quadrate from a stem member of the flamingogrebe lineage (Pan-Mirandornithes), and a coracoid from a stem galliform (Pangalliformes). We also report a humerus with uncertain phylogenetic affinities but with similarities to core Gruiformes. These new fossils expand our knowledge of the Asian avifauna during this time and have the potential to further inform our understanding of the early biogeography of these clades. The shorebird and flamingo-grebe material indicate that both these lineages were pres¬ ent in Asia by the earliest Eocene. The pan-mirandornithine quadrate provides insight into the early feeding ecology of the flamingo-grebe clade.

The Oligo-Miocene flamingo Harrisonavis croizeti represents an intermediate form between the highly specialized extant flamingo cranial morphology and the more generalized ancestral phoenicopteriform one, characterized by the extinct taxon Palaelodus. However, the original description of H. croizeti lacked detail and the lectotypic skull was lost; thus, it is not known how the ancestral phoenicopterid cranial morphology differed from that of recent forms. Here, we describe new cranial material from Oligo-Miocene deposits of France, including a mostly complete skull with an articulated upper bill, a disarticulated upper bill, and pieces of lower bill. We assign this material to H. croizeti and compare it to all previously reported fossil flamingo cranial material as well as to all six living species. We also use 3D computed tomographic data to reconstruct the skull of H. croizeti in three dimensions. The skull and bill of H. croizeti are similar to those of living species, although they display less specialized filter feeding traits, including a straighter bill with less surface area for filtration lamellae and points of articulation with the lower bill which are less developed. The less specialized form of H. croizeti suggests the extant Phoenicopterus retains a skull morphology more similar to the ancestral condition of crown group flamingos, and the extant Phoenicoparrus form is more derived.