| Nests and eggs represent the beginning of life for many vertebrates. Determining the
nesting strategies of extant amniotes is crucial in elucidating the evolution and diversification of
reproductive traits as nesting materials are poorly preserved in the fossil record. Avian and
chelonian nests are particularly rare compared to non-avian dinosaurs.
The goal of this dissertation is to investigate and describe the sedimentology, taphonomy,
and ecology of two fossil nesting localities and examine modern eggshell porosity via micro-CT
images. I characterized two nesting localities, one from the Late Cretaceous Kaiparowits
Formation in Grand Staircase-Escalante National Monument outside of Escalante, Utah, the
second in the Eocene Bridger Formation east of Lyman, Wyoming, in terms of sedimentology
and stratigraphy and taphonomy.
Eggshell from the Kaiparowits Formation is identified as testudine and unique
characteristics of the shell unit height-to-width ratio, egg size, eggshell thickness, and
ornamentation warrant the naming of a new ootaxa, Testudoolithus tuberi. The distribution of
eggshell is interpreted as resulting from nest predation. The Bridger Formation eggshell material
is similar since the distribution and preservation of half eggs is interpreted as being caused by
predation. Both of the nesting localities are imbedded in greenish-gray mudstones overlying and
under lithic sandstones, suggesting flood-plain deposition. The avian eggshell is named a new
ootaxon as well, (Doolithus bridgerensis), from the number of observable ultrastructural layers.
Micro-CT images of modern rigid-shelled amniotes, including birds, crocodylians, a
tortoise, and a gecko, reveals a complex network of internal pores that do not connect to the
external surface of the eggshell. The functional pores tend to be cylindrical to trumpet-shaped in
birds and pear-shaped in the tortoise, but are bowl-shaped in the gecko, conical in the
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crocodylian genera Crocodylus and Osteolaemus, and globular in Melanosuchus niger. Eggs in
open and closed nesting strategies have generally similar functional eggshell porosity ranges of
0.1-0.8% sample volume. However, covered nesters generally have higher total porosities of 2.9-
16.1%. The internal porosity arises from the interstitial spaces between mineralized egg units.
The functional value of the internal porosity is yet unknown, but may improve properties of shell
insulation and retention of water vapor.
Keywords: Kaiparowits, Bridger, eggs, taphonomy, porosity, nesting |