Colonial ground nesting by Archaeopteryx suggests wing evolution in primal association with nesting and the ground up evolution of flight

Guimaraes, M. J.

doi:10.1101/2023.05.30.542892

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bioRxiv · 10.1101/2023.05.30.542892

Colonial ground nesting by Archaeopteryx suggests wing evolution in primal association with nesting and the ground up evolution of flight

Guimaraes, M. J.

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Abstract

Following an investigation into the hypothesis that the iconic Berlin specimen of Archaeopteryx fossilized in nesting position, which led to the discovery not only of its association with soft eggs and several hatchlings, but also similar findings in a second Archaeopteryx specimen, an attempt to characterize the entire Berlin specimen nest and estimate its number of eggs is reported here. The Berlin specimen arranged and brooded its eggs on the ground. Its clutch size appears to have exceeded one hundred eggs. Egg littering found not only in its fossil bed but also in the sediment layer immediately above it, inclusively with evidence that a subsequent generation nested over the specimen, is consistent with repeated usage of a ground nesting site. All Archaeopteryx specimens fossilized in different views of a similar pose that is compatible with a nesting posture, and evidence of eggs of consistent size with the 2D outlines of 3D flattened eggs is present not only in the Berlin, Teylers, Thermopolis and Maxberg specimens, but also in the isolated Archaeopteryx feather fossil. In addition, egg and hatchling littering are present in the Berlin, Teylers and isolated Archaeopteryx feather fossils. Taken together, these findings are indicative of colonial ground nesting behavior by Archaeopteryx in Solnhofen. Egg littering, eggs dorsal to the Berlin specimen torso and limb rotations in the London and Thermopolis Archaeopteryx specimens can all be explained by nesting in reentrances located at the margins or in sand banks of marine lagoons in Solnhofen, which would have been flooded, causing the subsequent collapse of the nest and the still-life preservation of its content. The discovery of colonial ground nesting in a winged Jurassic bird relative favors the evolution of birds from the ground up and suggests that wings and their elongated feathers were primarily associated with ground nest protection and only secondarily with flight.

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Guimaraes, M. J.. 2023-06-01. Colonial ground nesting by Archaeopteryx suggests wing evolution in primal association with nesting and the ground up evolution of flight. https://doi.org/10.1101/2023.05.30.542892

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