The First Occurrence in the Fossil Record of an Aquatic Avian Twig-Nest with Phoenicopteriformes Eggs: Evolutionary Implications

Abstract

BackgroundWe describe the first occurrence in the fossil record of an aquatic avian twig-nest with five eggs in situ (Early Miocene Tudela Formation, Ebro Basin, Spain). Extensive outcrops of this formation reveal autochthonous avian osteological and oological fossils that represent a single taxon identified as a basal phoenicopterid. Although the eggshell structure is definitively phoenicopterid, the characteristics of both the nest and the eggs are similar to those of modern grebes. These observations allow us to address the origin of the disparities between the sister taxa Podicipedidae and Phoenicopteridae crown clades, and traces the evolution of the nesting and reproductive environments for phoenicopteriforms.Methodology/Principal FindingsMulti-disciplinary analyses performed on fossilized vegetation and eggshells from the eggs in the nest and its embedding sediments indicate that this new phoenicopterid thrived under a semi-arid climate in an oligohaline (seasonally mesohaline) shallow endorheic lacustine environment. High-end microcharacterizations including SEM, TEM, and EBSD techniques were pivotal to identifying these phoenicopterid eggshells. Anatomical comparisons of the fossil bones with those of Phoenicopteriformes and Podicipediformes crown clades and extinct palaelodids confirm that this avian fossil assemblage belongs to a new and basal phoenicopterid.Conclusions/SignificanceAlthough the Podicipediformes-Phoenicopteriformes sister group relationship is now well supported, flamingos and grebes exhibit feeding, reproductive, and nesting strategies that diverge significantly. Our multi-disciplinary study is the first to reveal that the phoenicopteriform reproductive behaviour, nesting ecology and nest characteristics derived from grebe-like type strategies to reach the extremely specialized conditions observed in modern flamingo crown groups. Furthermore, our study enables us to map ecological and reproductive characters on the Phoenicopteriformes evolutionary lineage. Our results demonstrate that the nesting paleoenvironments of flamingos were closely linked to the unique ecology of this locality, which is a direct result of special climatic (high evaporitic regime) and geological (fault system) conditions.

Aqueous Transport of Gull Nests and Eggs: Taphonomic Implications for Fossil Amniote Nests

“…Convincing evidence exists only for three fossil theropod nests (Varricchio et al 1997;Zelenitsky and Therrien 2008;Grellet-Tinner et al 2012) and six sauropod nests (Chiappe et al 2004). When a fossil nest structure composed of vegetation is discovered, paleontologists should consider the possibility that it was transported from its original location prior to fossilization.…”

“…All such nests are subject to disruption by flooding, wave action, storm surges, or tsunamis (Sidle et al 1992;Flint and Grand 1996;Viera et al 2006;BirdLife International 2012) resulting in the possibility of transport. Recently, Grellet-Tinner et al (2012) reported the discovery of what was interpreted to have been a floating nest constructed of twigs belonging to an extinct flamingo (order Phoenicopteriformes) from an early Miocene formation in Spain. The nest contained five well-preserved eggs.…”

“…Analyses of fossilized vegetation from the nest, the eggshells, and surrounding sediments suggest the nest was constructed in a shallow, endorheic, lacustrine habitat in a semiarid climate. The report by Grellet-Tinner et al (2012) highlights the potential for the initial transport and subsequent fossilization of nest structures composed of vegetation, even though in this specific case the nest may not have been moved from its original location. The report demonstrates the potential of a nest to serve as a transport vessel for eggs and young prior to preservation, even if the nest itself did not fossilize.…”

First bird footprints from the lower Miocene Lerín Formation, Ebro Basin, Spain

“…However, Mlíkovský (2002) affirmed that important differences from vulturids were mentioned in the description, and he relegated this taxon to the Aves incertae sedis until its holotype is located and restudied. In other locality, bones and eggs were found and were assigned to Phoenicopteridae indeterminate (Murelaga, 2000;Grellet-Tinner et al, 2012).…”

“…Avian fossil record from the early Miocene in the Iberian Peninsula. All the information is extracted from Sán-chez-Marco (1999, 2006, Mlíkovský (2002), Grellet-Tinner et al (2012), andDíaz-Martínez et al (2015). Only the most recent taxonomic/ichnotaxonomic determination is considered.…”