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PeerJ. 2017 Aug 29;5:e3706. doi: 10.7717/peerj.3706. eCollection 2017.

Dinosaur origin of egg color: oviraptors laid blue-green eggs.

Author information

1
Division of Palaeontology, Steinmann Institute of Geology, Mineralogy and Palaeontology, University of Bonn, Bonn, Germany.
2
Department of Geology & Geophysics, Yale University, New Haven, CT, United States of America.
3
Life and Medical Sciences Institute, University of Bonn, Bonn, Germany.
4
Department of Chemistry, University of California, Berkeley, United States of America.
5
Pharmaceutical Institute, Pharmaceutical Chemistry I, University of Bonn, Bonn, Germany.
6
Kekulé Institute for Organic Chemistry and Biochemistry, University of Bonn, Bonn, Germany.

Abstract

Protoporphyrin (PP) and biliverdin (BV) give rise to the enormous diversity in avian egg coloration. Egg color serves several ecological purposes, including post-mating signaling and camouflage. Egg camouflage represents a major character of open-nesting birds which accomplish protection of their unhatched offspring against visually oriented predators by cryptic egg coloration. Cryptic coloration evolved to match the predominant shades of color found in the nesting environment. Such a selection pressure for the evolution of colored or cryptic eggs should be present in all open nesting birds and relatives. Many birds are open-nesting, but protect their eggs by continuous brooding, and thus exhibit no or minimal eggshell pigmentation. Their closest extant relatives, crocodiles, protect their eggs by burial and have unpigmented eggs. This phylogenetic pattern led to the assumption that colored eggs evolved within crown birds. The mosaic evolution of supposedly avian traits in non-avian theropod dinosaurs, however, such as the supposed evolution of partially open nesting behavior in oviraptorids, argues against this long-established theory. Using a double-checking liquid chromatography ESI-Q-TOF mass spectrometry routine, we traced the origin of colored eggs to their non-avian dinosaur ancestors by providing the first record of the avian eggshell pigments protoporphyrin and biliverdin in the eggshells of Late Cretaceous oviraptorid dinosaurs. The eggshell parataxon Macroolithus yaotunensis can be assigned to the oviraptor Heyuannia huangi based on exceptionally preserved, late developmental stage embryo remains. The analyzed eggshells are from three Late Cretaceous fluvial deposits ranging from eastern to southernmost China. Reevaluation of these taphonomic settings, and a consideration of patterns in the porosity of completely preserved eggs support an at least partially open nesting behavior for oviraptorosaurs. Such a nest arrangement corresponds with our reconstruction of blue-green eggs for oviraptors. According to the sexual signaling hypothesis, the reconstructed blue-green eggs support the origin of previously hypothesized avian paternal care in oviraptorid dinosaurs. Preserved dinosaur egg color not only pushes the current limits of the vertebrate molecular and associated soft tissue fossil record, but also provides a perspective on the potential application of this unexplored paleontological resource.

KEYWORDS:

Biliverdin; Dinosaur paternal care; Egg color evolution; Eggshell taphonomy; Macroolithus yaotunensis; Protoporphyrin; Reproduction

Conflict of interest statement

The authors declare there are no competing interests.

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