Phragmolites

I could have titled this "That One Snail", because that's what Phragmolites seems to have become in my circle of acquaintances; for whatever reason, we remember having seen this distinctive fossil but can't remember what it's called. This is where a common name, something like "sculpted ring snail", might come in handy. If you haven't seen them, they could easily be mistaken for a tiny coiled cephalopod, or some kind of worm tube or crinoid columnal if the specimen is not exposed clearly. They range in size from less than a centimeter to about an inch across and are flat-coiled (planispiral), with the outer coils wider than the inner coils and partially covering them, and a distinct but small keel. There are strong markings on the coils that resemble the sutures of a nautiloid or ammonite.

These little fellas.

Life on Mill Street

We held another Cambrian hike at Interstate State Park on Saturday, and I thought it would be a good time to revisit some ground we covered in June of 2016. Specifically, at that time I glossed over the fossils of the Mill Street Conglomerate, but they're worth another look.

Monoplacophorans

There are some things in life that just don't have a handy name. Take for example the subject of this entry, an obscure group of mollusks known from a few modern deep-water species and a more robust fossil record. Various members of this group have labored under the terms "Monoplacophora", "Tergomya", and "Tryblidiida", all of which could be mistaken for a disease, a planet in a science fiction series, or a piece of anatomy you'd rather not know about. (You can combine all three: "I got monoplacophora in my tryblidiida after I visited Tergomya. It's as bad as it sounds.")  At one point someone suggested that their vernacular name should be "gastroverm", which you'll probably agree was no help at all. The reason for this multitude of names has to do with the rules of classification; visit here or here if you want details (and don't say I didn't warn you), but the basic bit is that Tryblidiida includes all the modern forms, and is classified in Tergomya, which is in turn part of Monoplacophora, and "Monoplacophora" is something of a problem because its traditional definition includes some things that weren't all that closely related. However, everyone was kind of used to Monoplacophora, so they kept it around, except now it can have a precise definition, or be a "state of mind" including various odd extinct things from the Cambrian, which I shall omit. If you want to be picky, this is about tergomyans.