Such anisotropy and inhomogeneity are consistent with the nanoindentation tests. Ostrich eggshell exhibits strong texture in the thickness direction, whereas chicken eggshell has little. The EBSD shows that eggshell is anisotropic and non-homogeneous, and different species have different degrees of crystal orientation and texture. We find that the mineral content ranges between 83.1% (Zebra finch) and 96.5% (ostrich) and is positively correlated with EFEM-23.28 GPa (Zebra finch) and 47.76 GPa (ostrich). We measure the mineral content by acid-base titration, and crystallographic characteristics by electron backscatter diffraction (EBSD), on representative species. We study the elastic moduli using three metrics: (i) effective Young’s modulus, EFEM, by a combined experimental and numerical method (ii) elastic modulus, Enano, by nanoindentation, and (iii) theoretical Young’s modulus, Etheory. We analyze 700 freshly-laid eggs from 58 species (22 families and 13 orders) across three orders of magnitude in egg mass. Although poorly represented by dinosaur osteological remains, the lower Two Medicine Formation locality yields egg types that suggest a significant difference in faunal composition compared to the middle and upper portions of the formation. canadensis may occur elsewhere in the middle and upper strata of the Two Medicine and Oldman formations of Montana and Alberta, respectively. tetonensis, and Krokolithes are unique to the lowermost Two Medicine Formation, whereas C. Continuoolithus canadensisZelenitsky et al., 1996 and KrokolithesHirsch, 1985. Four additional ootaxa occurred at the First Find Microsite (OTM 99-19): Prismatoolithus hirschi, oosp. These symmetrical 30 mm × 75 mm prismatic eggs exhibit three structural layers of calcite and round tubercles on the shell surface.
The quarry also produced Triprismatoolithus stephensi, oogen. However, we refer this eggshell to the Spheroolithidae Zhao, 1979, as Spheroolithus choteauensis, oosp. Spherulitic eggshells from a quarry at this locality are similar to Spheruprismatoolithus candensusBray, 1999, which were assigned to the oofamily Prismatoolithidae. This site in the Sevenmile Hill outcrops south of Choteau, Montana, lies immediately above a volcanic tuff and bentonite, dated as 80.0 Ma. Here, we describe a fossil egg-bearing stratum that occurs approximately 105 m above the base of the formation. In the last 30 years, the Two Medicine Formation of western Montana has provided a wealth of information about dinosaur reproductive biology. The Phaethontidae share derived characters with the Procellariiformes, which might support a sister group relationship between the two taxa. The shared derived characters of Scopidae, Balaenicipitidae and Steganopodes are furthermore less easily explained by convergent evolution than by the few characters which support monophyly of the taxon (Phaethontidae + Steganopodes). Monophyly of the taxon (Scopidae + (Balaenicipitidae + Steganopodes)) is better supported by morphological evidence than monophyly of the taxon (Procellariiformes + (Phaethontidae + Steganopodes)) which was established by Cracraft (1985). Derived characters which support the resulting phylogeny are discussed.
A cladistic analysis of 54 anatomical characters resulted in monophyly of the taxon (Scopidae + (Balaenicipitidae + Steganopodes (sensu Cracraft 1985))) and showed both Ciconiiformes and Pelecaniformes to be polyphyletic. The phylogenetic affinities between the shoebill (Balaenicipitidae) and pelecaniform and ciconiiform birds are analysed.
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