70 million years ago, several species shared a nest


Birds and reptiles co-habitated for mutual profit and protection. Nick Carne reports.


Four different microscopic views of enantiornithine eggshells, taken from the shared nest.

Fernandez et al

Birds and reptiles were strategically sharing nest sites at least 70 million years ago, new research suggests.

Analysis of fossilised eggshells unearthed in western Romania has revealed four types of shell and thus four types of previous inhabitants: extinct birds within a group known as enantiornithes, birds of undetermined classification, gecko-like lizards and small predecessors of crocodiles.

The shells – some complete and others broken into thousands of pieces – were densely packed and encased in mudstone that formed part of the remains of a bird breeding colony, probably comprising hundreds of separate nests.

The fossilised remains of two enantiornithine eggs, in the shared nest.

Fernandez et al
And they date from the late-Cretaceous period, making this the earliest known nest site shared by multiple species.

It was found near the city of Sebeș, in the Transylvania region, by local palaeontologist Mátyás Vremir, but the analysis was carried out by an international team led by researchers at the Centro Regional Universitario Bariloche in Argentina.

Their findings are reported in the journal Scientific Reports.

Their paper speculates that this was very much a planned co-habitation.

The area of plain created by seasonal flooding offered the enantiornithes safety from predators, the authors suggest, and this in turn afforded shelter to smaller reptiles which benefitted from the security of the birds guarding their own nests.

The lizard and crocodile type animals were not perceived as a threat to the bird eggs and nestlings, possibly because they were much smaller than the adult birds

“Evidence supporting our theory can still be seen today in Argentina, where lizards … co-habit and lay eggs inside the nests of the caiman crocodile, safe in the knowledge that the female doesn't feed during the incubation of her eggs and poses no threat to the hatchling lizards,” says Christian Laurent, a participating researcher from the University of Southampton in the UK.

  1. https://www.accessscience.com/content/enantiornithes/800660
  2. https://www.nature.com/articles/s41598-018-36305-3
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