Stereomic microstructure of Clypeasteroida in thin section based on new material from Pleistocene strata in Taiwan

Abstract

 Trabeculae in studied fossils still behave as a single crystal for each ossicle. Plate boundaries can be identified clearly under polarized light microscopes. Galleried and labyrinthic stereom are documented from Taiwanese specimens.

Changing surface ocean circulation caused the local demise of echinoid Scaphechinus mirabilis in Taiwan during the Pleistocene–Holocene transition

“…Stable oxygen isotope values of biogenic carbonate reflect the oceanic conditions at the time of biomineralization. Sand dollar specimens from the Toukoshan Formation are generally well preserved, with little compaction in the internal stereom, and the interconnecting pores still retain their original geometry; at least three types of stereoms are still recognizable 5 . Because more than a thousand intact and incomplete tests were available for this study, only the best-preserved samples were analyzed (see more detail on preservation state and selection criteria in “ Materials and Methods ” section).…”

“…Selections of samples are based on the following criteria: (1) preservation of stereom (Ref. 5 ); (2) no obvious dissolution or organic staining; (3) no deformation and structural features; and (4) avoiding fast growing regions, including lantern and marginal plates, in order to prevent vital effect (Ref. 10 ).…”

“…Over the years, more than 20,000 sand dollar specimens have been collected from the study area by amateurs and researchers, suggesting that the northwestern coast of Taiwan was once a favorable environment for S. mirabilis to thrive. More importantly, fossil assemblages here represent multiple generations and exhibit size variations, ranging from 9.5 to 62.4 mm in size 5 , allowing detailed studies on their ontogenetic changes 6 , 7 . Their living distributions at present, however, occur exclusively in cooler waters north of mainland Taiwan, such as northern China, Japan 8 , Korea, and the Russian Far East 9 .…”

“…Studied specimens are a subset of museum specimens deposited at the Department of Geosciences, National Taiwan University (NTUG) (Ref. 5 ). Map was created with Adobe illustrator CS6 ( https://www.adobe.com/products/illustrator.html ).…”