Steve Boss

A few weeks ago, with help from geology professor Steve Boss, I wrote about the geological evolution of the Ozarks. Boss explained how this massive geographical area, which stretches from near St. Louis in the northeast all the way down to the Arkansas River in the south, lifted out of a shallow sea. This process occurred over a very long geological period more than 200 million years ago.

Soon after we published this blog post, a friend of mine told me he’d found some impressive fossils in bluff strata near Wesley, 15 miles east of Fayetteville. He brought home some samples, and he asked me if I knew anyone at the university who could look at them and perhaps confirm that several triangular-shaped fossils might be shark teeth.

My friend gave me three samples, which I took to Boss. Below is his thoughtful reply:

Given that these are from near Wesley, I think it’s the Pitkin limestone, but it could be Brentwood limestone. I’d have to see the outcrop to be more certain.

Samples of Pitkin or Brentwood limestone taken from bluff strata near Wesley, Arkansas.

It is a “fossil hash” – a rock full of fossils. The red circles denote the triangular objects you asked about. Unfortunately, they are not shark teeth. ? These are conic cross sections of a crinoid stem. Crinoids are marine animals related to star fish and sea urchins. (Crinoids still live today. You can learn a lot about them online.) The triangular shape occurs because crinoid stems are circular columns. If you slice a circular column obliquely, you get that cone-shaped, or triangular cross section. The yellow circle is a crinoid stem in cross-section along the axis of the stem. There are also a lot of cross-sections perpendicular to the axis of columns – all the small, whitish circular things.

The green circles are cross-sections of animals called brachiopods. They look like clams, with two shells, but are not at all related to clams. They aren’t even mollusks but rather a completely different group of organisms.

“It’s a pretty rock,” Boss said. “Would polish nicely.”