Tokyo, steinkerns, and sinistrality

Last night I returned from two Tokyo museums; the National Science Museum and the University Museum of the University of Tokyo. I spent three days looking through three gastropod collections and saw a lot of snails! Here is a summary.

This is the invertebrate fossil specimen room of the National Science Museum of Tokyo. The atmosphere in this room and in most paleontology collections in general is really wonderful. It is hard to explain, but the smell of fossils in dusty drawers, there is nothing like it.The anticipation when you open each drawer too. Just magnificent!Here I am searching for buccinids.One of the amazing specimens I came across was this one, which looks like "just" a round rock, but...has a snail fossil inside! This kind of rock-surrounding-a-fossil is called a concretion.Another interesting fossil I found lots of is a steinkern, or the internal mold, of a skeletal part or parts. In this case, I found the steinkerns of snails. Although the calcium carbonate shell can be very resistant and able to fossilize, in these cases the empty shell was filled in with sediment that became more resistant that the shell itself, which dissolved away leaving only the internal snail-shaped cemented sediment behind. Sugoi!The shell collection that I was most interested in at the Museum of the University of Tokyo was organized like this.Here are some of the specimens I examined.Perhaps you trying to figure out what looks odd about these snails. Does the one below look more "normal"?The first three images were of sinistral or left-coiling snails! The image above is of the more common dextral, or right-coiling shell. Sinistrality can be a characteristic of a species as it is with the three above or it can occur as a developmental anomaly in an otherwise right-coiling species. Here are some anomalous sinistral examples.