Gastropods are commonly preserved as steinkerns (internal casts), a mode of fossilization that leads to loss of external morphological features. This loss of information is problematic for taxonomic identification and ecological inference in evaluating assemblages where original shell material is not preserved. We seek to quantify how closely gastropod steinkerns represent the morphology of their original shells. We investigated this relationship experimentally by fabricating steinkerns in silicone from modern gastropod shells and comparing their geometry to that of the shells we used to create them. In addition to recording traces of ornamentation such as ribs and spines, we used a theoretical morphospace framework to evaluate the fidelity of shell-coiling parameters in steinkerns. Our results show that some morphotypes reflect their taxonomic identification more accurately than others, indicating that steinkern fidelity is highly variable. Experimental steinkerns consistently cluster less reliably by morphotype than their original shell counterparts. Additionally, we find that shell thickness is an important factor in determining steinkern fidelity. The fidelity of the high-spired Duplicaria duplicata, for example, is significantly lower than the average value for the morphotypes investigated whereas the fidelity of planispiral Haplotrema concavum and open-coiling Epitonium is significantly higher, a trend related to shell thickness. Thus, taxonomic identification and subsequent analyses, such as community composition, of steinkern assemblages must recognize this differential fidelity to counter preservational biases.

Globally, scleractinian coral diversity peaked in the Early Miocene (Burdigalian) and declined afterwards. In contrast to this global trend, scleractinian coral diversity in the Lower to Middle Miocene was low in the Red Sea, which had begun to open in the Oligocene and experienced its first marine incursion in the Burdigalian. Here, we report on coral diversity of reefs assigned to the Burdigalian to Langhian Wadi Waqb Member (Jabal Kibrit Formation) from outcrops exposed in the foothills behind the Red Sea coastline near Umluj, Saudi Arabia. Compared to the global records from the Paleobiology Database and the literature, the fossil record from the Wadi Waqb member suggests a relation of the taxonomic spectrum to the Arabian Gulf and the Mediterranean. No clear relation to the taxonomic spectrum to the Indian Ocean is observed. These faunal differences are consistent with the hypothesis that the young Red Sea was connected to the Arabian Gulf via the Mediterranean through the Gulf of Suez, but there was no connection between the Red Sea and the Indian Ocean because of the Afar mantle plume that uplifted the southern area of the Red Sea rift and blocked direct exchange of marine biota.