Sedimentological Analyses of Eggshell Transport and Deposition: Implication and Application to Eggshell Taphonomy

Abstract

The interpretation of fossil eggshells can be problematic because eggshells may be transported by hydraulic flow in floodplains, making it difficult to interpret the reproductive behavior and ecology of parent animals. A series of flume studies was conducted to establish analytical techniques for assessing eggshell hydraulic transport in the fossil record. We investigated preferred eggshell orientation after transport, the relationship of flow competence with eggshell height and volume, and the size of clastic sediment expected to be associated with transported eggshells. Goose, emu, and ostrich eggshell fragments were released in a flume with decelerating flow. The transport of each eggshell was observed five times on each of four substrates (coarse sand, sparse gravel, dense gravel, and polyvinyl chloride). At eggshell deposition, eggshell orientation and flow depths were recorded. Critical bed shear stress for eggshell deposition was estimated based on the flow depth at the point of eggshell deposition, tested relative to eggshell height and volume, and used to estimate the size of hydraulically equivalent particles. The probability of concave-down orientation after transport was .

Taphonomy of Extant Desert Tortoise (Gopherus Agassizii) and Loggerhead Sea Turtle (Caretta Caretta) Nesting Sites: Implications for Interpreting the Fossil Record

“…In contrast, a subsurface assemblage at a tern colony show a marked decrease in concave-up eggshells, with 42% CU and 58% CD (Wang et al 2014), a value similar to that obtained through experiments with chick trampling (Hayward et al 2011). In contrast, hydraulically transported assemblages produce very skewed assemblages with usually under 20% of the eggshell oriented concave up (Hayward et al 2011;Imai 2013).…”

“…Because tortoise carapaces cause extensive eggshell damage during hatching, this orientation likely reflected fragmentation of the upper, predominantly concave-down 75% of the eggs. Taken separately, these two fractions in the egg bottoms and surrounding sediment are both significantly different from 50:50 and 20:80 ratios (i.e., transported material; Hayward et al 2011;Imai 2013) as evaluated by a chi-square test, with the eggshells from the surrounding sediment also differing from 60:40. Thus, in assessing fossil assemblages for eggshell orientation and location, one needs a large sample size (e.g., n .…”

“…For example, Horner (1994) compares the distribution and size ranges of skeletal remains from dinosaur nesting sites in the Upper Cretaceous Two Medicine Formation to extant avian colonial nesting sites at Lake Bowdoin National Wildlife Refuge in Montana. In addition, several papers report results of experiments related to egg and eggshell fragment transport and examine the ratio of concave-up to concave-down eggshell fragments at modern avian nesting sites for comparison to fossil localities (Hayward et al 1997(Hayward et al , 2011Oser and Jackson 2014;Wang et al 2014;Imai 2013). Hayward et al (2000) use location of openings in eggs (pole versus equator) to distinguish hatched from depredated eggs of ground nesting birds.…”

Taphonomical and palaeoecological investigation of the Late Cretaceous (Maastrichtian) Tuştea vertebrate assemblage (Romania; Haţeg Basin) - insights into a unique dinosaur nesting locality

“…5C). This position indicates that the eggs were most probably preserved and buried in situ, in their original positions, since material transported and deposited by water would favour concavedown orientations over those that are concave-up, as being more stable in fluid flow conditions (Hayward et al, 2000(Hayward et al, , 2011Imai et al, 2015). Trampling can probably be excluded as a significant fragmentation agent in the case of the eggshell and egg accumulations of Tuştea, because this mechanism also creates concave-down rather than concave-up orientation, and would have led to a more advanced destruction of the eggs themselves.…”

A mixed vertebrate eggshell assemblage from the Transylvanian Late Cretaceous

“…Specifically, non-transported eggshell fragments at hatching and predation sites tend to rest CU rather than CD 39 . Therefore, trampled fragments and fragments transported by wind and water favour CD over CU orientations 40,60,61 . The CU:CD orientation ratio (42:58) in our study is statistically distinguishable from both the 60:40 ratio typical of in situ nests and the 15:85 ratio of transported nests when evaluated with a chi-square test 60,62 and from those nests that are buried under substrate with a relation of CU:CD orientation (38:62).…”