Linwood Mine, located just east of Buffalo in Scott County, Iowa, has been the site of a recent discovery of some of the earliest tetrapods known. It is a very unique site and there are only a handful of locations around the world that contain similar fossils. These include Delta, Iowa, and deposits exposed in Scotland, Australia, Greenland and Russia. The fossils in Linwood Mine are preserved in middle-Devonian (380 million years ago) limestone, where ancient caves have been filled with deposits of limestone, chert and some sandstone, along with the tetrapod bones, fish teeth and small marine invertebrates. Some of the chert pebbles are well rounded, which suggests that they and the tetrapods may have been carried some distance before they were deposited. The cave fill is sandwiched between highly layered limestone. This further supports the fill’s origin from a high intensity event, such as a flood.
The actual tetrapod pieces are poorly preserved and are represented by small bone fragments. Unfortunately, the pieces found thus far have been too dismembered to identify more specifically. The teeth found are almost certainly ptyctodont teeth. Ptyctodonts belong to the dominant group of fish from Devonian time called placoderms. They had armored plates in their skin, and most had a bony shield covering their head. The problems that are associated with this find revolve mostly around the fact that there is so little known about these tetrapods because of their rarity. Work has been done to try to determine the evolutionary affinities of these creatures, and whether they exhibit shared or derived characteristics. My work will focus on recovering more materials and trying to aid in the search for more clues to these tetrapods’ evolutionary pasts.
Andrea Wirth, ’01 Kaukauna, WI
Majors: Geology, Economics and Business
Sponsor: Benjamin Greenstein