Featured Fossil: Lake Jacksboro Nautiloids

by Sean Moran, Florida Museum of Natural History

Sean Moran and others fossil hunting at Lake Jacksboro
Sean Moran and others fossil hunting at Lake Jacksboro

In the days preceding the large Society of Vertebrate Paleontology conference in Dallas, Texas, the FOSSIL Project held a two day mini-conference in conjunction with the Dallas Paleontological Society (DPS). The first day of the meeting, October 12, was filled with a variety of presentations, socializing, and breakout discussion sessions. On October 13 we were lucky enough to join the DPS for a day of fossil collecting at two Pennsylvanian localities west of the Dallas-Fort Worth area. The second site we visited, though not the focus of this article should also be mentioned. The site is located in the city of Mineral Wells and very recently was designated as a fossil park. Over the hour and a half the group spent at the park, most field trip attendees found crinoid calyces, brachiopods, and fragments of trilobites despite much recent collecting activity and low rainfall.

Earlier in the day, well before sunrise, the group loaded up on caffeine and donuts before leaving on a charter bus from Brookhaven College to the first site at Lake Jacksboro. During the ride Mark McKinzie, a DPS member with years of experience searching for fossils in Texas, helped to put the localities in context and note what fossils we were likely to find. This first site we visited, an outcrop of Finis Shale known alternatively as the Lost Creek Dam Spillway site, is very well known for its Pennsylvanian nautiloids as well as other fossils such as primitive sharks. Our large group of approximately 50 people fanned out across the outcrop and spent a couple hours collecting the light beige fossils in the eroding shale and siltstone. It seemed the most sought after fossils were the many species of cephalopods and the few shark teeth that were found. However, crinoids, brachiopods, gastropods, corals, and bryozoans were found in abundance.

Though these other fossils were more plentiful, most of the group focused on the nautiloids. I personally collected a handful of coiled species, including Gonioloboceras sp., Metacoceras sp., and Tainoceras sp., and straight-shelled species, such as Euloxoceras sp. and Mooreceras sp.. While the orthocone nautiloids were strewn across the outcrop and were as common as any other fossil at the site, the coiled cephalopods were more difficult to find. By the end of the collecting trip at Lake Jacksboro a handful of cephalopod fragments were discovered as well as a few complete specimens, including a beautifully preserved specimen of Gonioloboceras sp.. The trip was a great way to wrap up the FOSSIL mini-conference and open the SVP meeting. It provided a wonderful opportunity to collect Texas fossils and get to know members of a dozen different fossil clubs and professionals from several institutions just by conversing together on the outcrop.

 

 

Coiled nautiloids
Coiled nautiloids

Gonioloboceras and Metacoceras
Gonioloboceras and Metacoceras

Orthocone nautiloids
Orthocone nautiloids