[Date Prev][Date Next][Thread Prev][Thread Next][Date Index][Thread Index][Subject Index][Author Index]

Eggshell Porosity Provides Insight on Evolution of Nesting in Dinosaurs

Ben Creisler

New in PLoS ONE:

Kohei Tanaka, Darla K. Zelenitsky & François Therrien (2015)
Eggshell Porosity Provides Insight on Evolution of Nesting in Dinosaurs.
PLoS ONE 10(11): e0142829
doi: 10.1371/journal.pone.0142829

Knowledge about the types of nests built by dinosaurs can provide
insight into the evolution of nesting and reproductive behaviors among
archosaurs. However, the low preservation potential of their nesting
materials and nesting structures means that most information can only
be gleaned indirectly through comparison with extant archosaurs. Two
general nest types are recognized among living archosaurs: 1) covered
nests, in which eggs are incubated while fully covered by nesting
material (as in crocodylians and megapodes), and 2) open nests, in
which eggs are exposed in the nest and brooded (as in most birds).
Previously, dinosaur nest types had been inferred by estimating the
water vapor conductance (i.e., diffusive capacity) of their eggs,
based on the premise that high conductance corresponds to covered
nests and low conductance to open nests. However, a lack of
statistical rigor and inconsistencies in this method render its
application problematic and its validity questionable. As an
alternative we propose a statistically rigorous approach to infer nest
type based on large datasets of eggshell porosity and egg mass
compiled for over 120 extant archosaur species and 29 archosaur
extinct taxa/ootaxa. The presence of a strong correlation between
eggshell porosity and nest type among extant archosaurs indicates that
eggshell porosity can be used as a proxy for nest type, and thus
discriminant analyses can help predict nest type in extinct taxa. Our
results suggest that: 1) covered nests are likely the primitive
condition for dinosaurs (and probably archosaurs), and 2) open nests
first evolved among non-avian theropods more derived than
Lourinhanosaurus and were likely widespread in non-avian
maniraptorans, well before the appearance of birds. Although
taphonomic evidence suggests that basal open nesters (i.e.,
oviraptorosaurs and troodontids) were potentially the first dinosaurs
to brood their clutches, they still partially buried their eggs in
sediment. Open nests with fully exposed eggs only became widespread
among Euornithes. A potential co-evolution of open nests and brooding
behavior among maniraptorans may have freed theropods from the
ground-based restrictions inherent to covered nests and allowed the
exploitation of alternate nesting locations. These changes in nesting
styles and behaviors thus may have played a role in the evolutionary
success of maniraptorans (including birds).