In large enough quantities, the minute shells of these bivalves can affect environmental conditions, and this change in conditions can positively affect the ability of organic remains in the immediate environment to fossilize (one aspect of
taphonomy). For example, in the
Dinosaur Park Formation, the fossil remains of
hadrosaur eggshells are rare. This is because the breakdown of
tannins from the local
coniferous vegetation caused the ancient waters to be acidic, and therefore usually eggshell fragments dissolved in the water before they had a chance to be fossilized. Hadrosaur eggshell fragments are however present in two
microfossil sites in the area. Both of these sites are dominated by preserved shells of invertebrate life, primarily shells of pisidiids. The slow dissolution of these minute bivalve shells released
calcium carbonate into the water, raising the water's
pH high enough that it prevented the hadrosaur eggshell fragments from dissolving before they could be fossilized. Image:Pisidium moitessierianum.svg|Drawing of the right valve external view of
Pisidium moitessierianum Image:Pisidium moitessierianum 3.svg|Drawing of the right valve internal view of
Pisidium moitessierianum Image:Pisidium moitessierianum 2.svg|Drawing of the right valve lateral view of
Pisidium moitessierianum Image:Pisidium sp.jpg|SEM image of
Pisidium sp. ==Extant subgenera and species==