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Evolution of egg shapes in theropods, birds (free pdf)

Ben Creisler

A new paper in open access:

D. Charles Deeming & Marcello Ruta (2014)
Egg shape changes at the theropod–bird transition, and a morphometric
study of amniote eggs.
Royal Society Open Science 1: 140311.
DOI: 10.1098/rsos.140311


The eggs of amniotes exhibit a remarkable variety of shapes, from
spherical to elongate and from symmetrical to asymmetrical. We examine
eggshell geometry in a diverse sample of fossil and living amniotes
using geometric morphometrics and linear measurements. Our goal is to
quantify patterns of morphospace occupation and shape variation in the
eggs of recent through to Mesozoic birds (neornithe plus non-neornithe
avialans), as well as in eggs attributed to non-avialan theropods. In
most amniotes, eggs show significant deviation from sphericity, but
departure from symmetry around the equatorial axis is mostly confined
to theropods and birds. Mesozoic bird eggs differ significantly from
extant bird eggs, but extinct Cenozoic bird eggs do not. This suggests
that the range of egg shapes in extant birds had already been attained
in the Cenozoic. We conclude with a discussion of possible biological
factors imparting variation to egg shapes during their formation in
the oviduct.


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