The teeth of sea urchins comprise a variety of different structural entities, all of which are composed of magnesium-bearing calcite together with a small amount of organic material. The teeth are worn down continuously, but in such a way that they remain sharp and functional. Here we describe aspects of the structural, compositional and micromechanical properties of the teeth of Paracentrotus ...

Human beings have a natural interest in their origins. We are vertebrates, within the craniates, within the chordates. Fossils indicate how the chordates separated, in early Palaeozoic times or before, from their latest common ancestor with the echinoderms. The most primitive known fossil chordates retained a calcitic skeleton of echinoderm type (calcichordates) and some of these, the mitrates,...

Sponges show the highest diversity of associated bacteria among marine invertebrates. Immunological evidence traces the origin of the sponge bacterial symbioses to the Precambrian era. Hence, sponges appear to be ideally suited for studying the evolutionary origins of prokaryote-metazoan associations. Sponges produce either calcareous or siliceous skeletons, which only coexist in a relict group...

The ability to form mineral structures under biological control is widespread among animals. In several species, specific proteins have been shown to be involved in biomineralization, but it is uncertain how they influence the shape of the growing biomineral and the resulting skeleton. Calcareous sponges are the only sponges that form calcitic spicules, which, based on the number of rays (actin...

The aim of this study was to analyze yields, biological efficiency, earliness (expressed as days to first harvest), and precociousness and establish models for the mushroom growing according to these parameters. The experiment followed a double factorial design with four sources of calcium (calcitic limestone, calcitic limestone + gypsum, dolomitic limestone and dolomitic limestone + gypsum) an...

A new δ(18)O Phanerozoic database, based on 24,000 low-Mg calcitic fossil shells, yields a prominent 32 Ma oscillation with a secondary 175 Ma frequency modulation. The periodicities and phases of these oscillations are consistent with parameters postulated for the vertical motion of the solar system across the galactic plane, modulated by the radial epicyclic motion. We propose therefore that ...

A thin (3–25 cm), persistent conglomerate-sandstone unit occurs at the base of the transgressive systems tract of an Upper Pennsylvanian cyclothem below a transgressive limestone in outcrop and subsurface in SE Kansas and NE Oklahoma. It has an erosional base and a sharp top, and is composed of calcitic clasts, some shell fragments and quartz sand, and rare coal fragments. Clasts are rounded, e...