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, 8 (4), e61030

A Large Accumulation of Avian Eggs From the Late Cretaceous of Patagonia (Argentina) Reveals a Novel Nesting Strategy in Mesozoic Birds


A Large Accumulation of Avian Eggs From the Late Cretaceous of Patagonia (Argentina) Reveals a Novel Nesting Strategy in Mesozoic Birds

Mariela S Fernández et al. PLoS One.


We report the first evidence for a nesting colony of mesozoic birds on Gondwana: a fossil accumulation in Late Cretaceous rocks mapped and collected from within the campus of the National University of Comahue, Neuquén City, Patagonia (Argentina). Here, Cretaceous ornithothoracine birds, almost certainly Enanthiornithes, nested in an arid, shallow basinal environment among sand dunes close to an ephemeral water-course. We mapped and collected 65 complete, near-complete, and broken eggs across an area of more than 55 m(2). These eggs were laid either singly, or occasionally in pairs, onto a sandy substrate. All eggs were found apparently in, or close to, their original nest site; they all occur within the same bedding plane and may represent the product of a single nesting season or a short series of nesting attempts. Although there is no evidence for nesting structures, all but one of the Comahue eggs were half-buried upright in the sand with their pointed end downwards, a position that would have exposed the pole containing the air cell and precluded egg turning. This egg position is not seen in living birds, with the exception of the basal galliform megapodes who place their eggs within mounds of vegetation or burrows. This accumulation reveals a novel nesting behaviour in Mesozoic Aves that was perhaps shared with the non-avian and phylogenetically more basal troodontid theropods.

Conflict of interest statement

Competing Interests: The authors have declared that no competing interests exist.


Figure 1
Figure 1. Site location.
Counter-clockwise from top right: map of Argentina and the Comahue region (Neuquén and Río Negro Provinces); map of Neuquén Province; map of Neuquén City; close up of Neuquén City to show the University of Comahue (UNC) campus, and the location of the fossil bird nesting colony (shaded box).
Figure 2
Figure 2. Close-up of site location and in situ egg map.
Top: overview of the Universitary campus showing the location of several paleofaunal elements and the grid corresponding to the nesting colony (shaded purple box). Bottom: grid showing the location of each mapped egg; circles represent upright eggs, ovals represent eggs slightly inclined vertically and the oval that lies with its long axis parallel to the substrate represents an egg found in that position.
Figure 3
Figure 3. Stratigraphic profile.
Bajo de la Carpa Formation, Neuquén Group , to illustrate the diverse biota spread through the horizons within this sequence. Layer containing the eggs discussed in this paper is indicated. Abbreviations: An, Anacleto Formation; Pl, Plottier Formation.
Figure 4
Figure 4. Several in-situ complete and fragmentary eggs from the Comahue campus nesting colony.
These eggs demonstrate spatial arrangement in vertical (a and c), subvertical (d) and horizontal (b) positions.
Figure 5
Figure 5. In situ eggs within the Comahue campus.
In situ association in bedding plane (a), inset of single egg in position (b), egg half-buried in sediment (typical for almost all eggs collected) (c), close up lateral view of same egg showing degree of asymmetry (d).
Figure 6
Figure 6. Partial egg (MUC-Pv 1358) with typically fractured but well preserved eggshell.
Some avian bone fragments are visible inside the egg (arrows).

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    1. Schweitzer MH, Jackson FD, Chiappe LM, Schmitt JG, Calvo JG, et al. (2002) Late Cretaceous avian eggs with embryos from Argentina. Journal of Vertebrate Paleontology 22: 191–195.
    1. Grellet-Tinner G, Norell MA (2002) An avian egg from the Campanian of Bayn Dzak, Mongolia. Journal of Vertebrate Paleontology 22: 719–721.
    1. Zhou Z, Zhang F (2004) A precocial avian embryo from the Lower Cretaceous of China. Science 306: 653. - PubMed
    1. Grellet-Tinner G, Chiappe LM, Norell MA, Bottjer D (2006) Dinosaurs eggs and nesting behaviors: A paleobiological investigation. Palaeogeography, Palaeoclimatology, Palaeoecology 232: 294–321.
    1. Dyke GJ, Vremir M, Kaiser G, Naish DW (2012) A drowned Mesozoic bird breeding colony from Late Cretaceous of Transylvania. Naturwissenschaften 99: 435–442. - PubMed

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Grant support

Funding was provided by the Jurassic Foundation (to RAG), the Secretaría de Gobierno de La Rioja and the Consejo Federal de Ciencia y Tecnología (COFECYT) (SCTIP N°1198/06 – Proyecto LR02/06). The funders had no role in study design, data collection and analysis, decision to publish, or preparation of the manuscript.