[Paleontology • 2015] Eggshell Porosity Provides Insight on Evolution of Nesting in Dinosaurs
Abstract
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).
The nests of most
dinosaurs, including duck-billed hadrosaurs, consisted of eggs covered
under mounds of vegetation and dirt. The vegetation mound is not
represented in this illustration to display the eggs. (Art by Julius T.
Csotonyi.)
RoyalTyrrellMuseum.wordpress.com @RoyalTyrrell
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A duckbill
dinosaur (left) next to its eggs buried in the ground, and a birdlike
oviraptorid dinosaur (right) incubating its eggs in an open nest.
Illustration: Julius Csotonyi DOI: 10.1371/journal.pone.0142829
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The nest of a birdlike dinosaur from the Late Cretaceous of China.
photo: Kohei Tanaka
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Kohei Tanaka, Darla K. Zelenitsky and François Therrien. 2015. Eggshell
Porosity Provides Insight on Evolution of Nesting in Dinosaurs. PLoS ONE. DOI: 10.1371/journal.pone.0142829
Fossilized Eggshells Provide Insight into the Evolution of Nesting https://royaltyrrellmuseum.wordpress.com/2015/11/26/fossilized-eggshells-provide-insight-into-the-evolution-of-nesting/
Missing link between dinosaur nests and bird nests http://news.sciencemag.org/paleontology/2015/11/missing-link-between-dinosaur-nests-and-bird-nests
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