Data from: The shape of avian eggs: assessment of a novel metric for quantifying eggshell conicality

Studying avian egg shape and other aspects of its morphology has recently
undergone a renaissance. Yet, most studies rely solely on two metrics for
the quantification of egg shape: elongation and asymmetry. The difficulty
of additionally quantifying the curvature of an eggshell has yielded many
attempts including those with complex equations and spatial modeling
techniques based on digitized images. These have lacked an independent
single-variable metric, hampering comparative studies. We propose a metric
for one common quality of egg shape, conicality, which is notably variable
in diverse species’ calcareous shells including shorebirds and non-avian
theropods. This metric utilizes multiple measurements of the slope along
an eggs profile to produce a distribution of angular measurements, which
can be analyzed with a Kurtosis (K) value. This metric was tested with
sets of computer modeled and 3D printed egg forms, where elongation, the
percentage of conicality, and the relative curvature of the shell profile
were controlled. For applicability to natural eggs and their diversity
across taxa, the Kurtosis value was used to quantify the gradient of
conicality across a focal avian family, Alcidae, where the Kurtosis value
successfully identified the most conical eggs using qualitative
descriptions from well-established literature. Given the significance of
egg morphology and profile curvature to structural integrity, surface-area
to volume ratio, egg mobility/stability, nesting behavior, and embryonic
development, our proposed measure of conicality could prove a useful
variable to the study of avian and non-avian egg-producing
species.