This ammonite counterpart has made a rather splendid home for a colony of barnacles. What I love about this is the continuity; about 190 million years ago a 10 cm wide ammonite died and was fossilized in the mud of a warm, shallow Jurassic sea. What happened to the remains I don't know, I hope they are in an appreciative fossil collector's drawer, but the counterpart, the impression left by the ammonite's aragonite shell became home to a thriving community of barnacles, the creatures that Charles Darwin studied in enormous depth between 1846 and 1854.
This eight-year intellectual bodyswerve came at the height of Darwin's interest in 'the species question'; Darwin first privately wrote about natural selection in 1842*, his joint paper (written with Alfred Russel Wallace) was read to the Linnaean Society in 1858 and The Origin of Species was published in 1859. Some have suggested that Darwin's interest in this uncharismatic group of creatures was displacement activity (that he was scared to continue his evolutionary work), others that Darwin knew very well what he was doing, becoming intimately acquainted with a little-researched animal and using what he observed to support his burgeoning ideas about evolution by natural selection.
This apparently peaceful, sessile scene, with a dead ammonite's cast, a couple of hundred barnacles, seven limpets and a stray periwinkle is really one of fierce competition to survive.