I've been looking at my visit logs and I've seen a big uptick in activity - largely due to my adventure with Steve Austin. I think that points to a needed activity for this blog: more discussion of what the folks at "Answers in Genesis" are up to. This is even more important, IMO, given their attempts at "addressing" some of the standard geological facts that are used to demonstrate this diluvian model is hooey. It's no use trotting out standard arguments if the creationists feel like they have a perfectly valid counter. It's time to update our database of counter-counter-claims.
But parrying YEC's is tedious, and no fun if it's all that all the time. So it's time to bring things back to some snails. Particularly Ice Age snails and the modern snail fauna of the Upper Mississippi Valley. Consider the following two photos:
Some recent woodland snails from southwestern Wisconsin:
Common late Pleistocene (ca. 20ka) snails from southwestern Wisconsin and southeastern Minnesota:
Three important points - one of which requires some background info, which I've touched upon in much earlier posts (and we'll revisit in the future). The other two can be seen in the above photos. One is that the "modern" snail fauna is much more diverse and second, the modern fauna displays a very wide range in body shape and size with a much bigger "upper limit." Just from this observed fact, we can start to ask some questions:
- What was the timing of snail dispersal? Did the modern fauna appear before the ice age snails left?
- Was this faunal transition all-at-once, or did individual species expand/adjust their range according to their own needs?
- Do the changes in snail fauna (body size, range limits, etc.) imply something about climate change?
- How are fossil shells preserved in the sedimentary record, and how does this affect our ability to use their shells as clues to ancient conditions?
Okay, that's enough for now. A big hello to all my new visitors - feel free to peruse the archives, leave a message, or whatever.
I am glad to see you are blogging again.
ReplyDeleteBased on the snail species in your photos, I would speculate that the plant cover during late Pleistocene was different than that now. The polgyrids & Anguispira at the bottom (if that's what that is) are mainly woodland snails, while the species on the penny, Hawaiia & Pupilla(?) are species of grassy fields. In northern North America there aren't many large snail species that inhabit open areas.
Aydin,
ReplyDeleteYou are right about the "modern" snails - they were collected from the base of a rather steep hill, where the bigger shells were probably brought downslope via gravity into an open area (where some of the smaller species were hiding).