| Jacksboro, Texas - Pennsylvanian Finis Shale |
| This well-known locality at Lake Jacksboro spillway represents a marine "shelf" deposit. This locality contains an abundant marine macro and microfaunal assemblage which allows for detailed regional and global correlation. In addition to the abundant marine fossils, it is also repleat with plant fossils washed in from the continent. The presence of plant fossils throughout the section gives paleontologists the ability to connect the already well-studied and detailed marine stratigraphy with continental deposits elsewhere. |
| Ammonoids |
|
 |
Cardiella sp. - a pyritized Goniatite Ammonoid. |
|
|
|
 |
Cardiella sp. - Lateral view - A better picture of the same specimen as above showing the beautiful suture patterns of Cardiella. |
|
|
|
 |
Cardiella sp. - Apertural view showing the intricate septa. |
|
|
|
 |
Ventral view close-up of the suture patterns. |
|
|
|
 |
Overall ventral view with mm scale. |
|
|
|
 |
A larger lateral view with mm scale. |
|
|
|
 |
Upper portion of Gonioloboceras, a goniatite ammonoid. There are two characterisitics of this specimen that indicate it might have been predated by a vertebrate such as a shark: punctuation marks (arrows) and the general shape (as if part of a bite). These are fairly common at Jacksboro and a paper has been written on the subject (referenced below). |
|
|
Mapes, R.H., Sims, M.S., and Boardman, D.R. II, 1995, Predation on the Pennsylvanian ammonoid Gonioloboceras and its implications for allochthonous vs. autochthonous accumulations of goniatites and other ammonoids: Journal of Paleontology, volume 69, number 3, p. 441-446. |
|
|
|
 |
Glaphyrites sp? - One of my favorite Ammonoids, this one shows all the different aspects of the Ammonoid shell structure! Almost like one of those cut-away drawings. |
|
|
|
 |
A great image illustrating the various aspects of this specimen. Notice the encrusting bryozoans. For you students out there, the presence of encrusting bryozoans indicates that this portion of the animal sat this side up in the sediment at a depth where encrusting bryozoans could grow, albeit temporarily. What an interesting specimen! Here's a close-up of the primary and secondary ribs. |
|
|
Maeda et. al., (2003) discusses "beached" cephalopods with similar preservation characteristics as this particular specimen. |
|
|
|
 |
Another Glaphyrites - pyritized. |
|
|
|
 |
Anterior view of the same specimen. |
|
|
|
 |
Glaphyrites - Lateral view - better picture of this specimen. |
|
|
|
 |
Glaphyrites - Ventral view - When studying Ammonoids, paleontologists make tracings of the suture patterns of each species to aid in identification, it's almost like a "species fingerprint." Here I have traced a typical Glaphyrites suture pattern to show you how it's done. |
|
|
|
 |
Apertural view (looking towards what would have been the aperture in the living animal) - This view also shows the septa. |
| Conularids |
|
 |
After all these years of study have yet to produce a reasonable explanation as to what these things were. Some think they were filter-feeding coral-like animals. |
| Plants |
|
 |
A Pennsylvanian seed! Semi-rare at Jacksboro, very rare for Pennsylvanian fossil localities as a whole! |
|
|
|
 |
Side view of the same specimen. |
| . |
| References |
 |
Boardman, Darwin R., II. Biostratigraphy of Middle and Late Pennsylvanian (Desmoinesian-Virgilian) ammonoids. Bulletin 232 - Kansas Geological Survey, 1994 (Good for identifying goniatites from OK, KS, NM, AR, and TX). |
|
Dunn, Michael T. On Paleozoic plants from marine strata; Hexaloba finisensia new genus and species, a trigonocarpalean ovule from the Virgilian (Upper Pennsylvanian, Gzhelian) Finis Shale of Texas. Journal of Paleontology, January 2002, Vol. 76, Issue 1, pp.173-180 |
|
Linsley, R. M. Some new Paleozoic gastropod opercula (Pennsylvanian, Texas). Journal of Paleontology, March 1989, Vol. 63, Issue 2, pp.206-211 |
|
Lobza, Vadec The influence of sea level changes and possible pycnocline shifts on benthic communities in the Finis Shale (Virgilian) near Jacksboro, north-central Texas. Memoir - Canadian Society of Petroleum Geologists, December 1994, Vol. 17, pp.927-947 |
|
Maeda, Haruyoshi Taphonomic features of a Lower Permian beached cephalopod assemblage from central Texas. Palaios. Oct. 2003. v. 18, issue 4-5, pp. 421-434. |
| . |
|
|
Return to the main paleo page. |
| . |
