Details

Autor(en) / Beteiligte

• Ferguson, Ashley Lynn

Titel

Investigating Nests and Eggs of Modern and Fossil Amniotes

Ort / Verlag

ProQuest Dissertations & Theses

Erscheinungsjahr

2022

Quelle

ProQuest Dissertations & Theses A&I

Beschreibungen/Notizen

• 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 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.