Picture* of Xiphactinus used by permission of the author Dan Varner.
This image may not be reproduced without his permission.

Evan De Groot of rural Sioux Center found a lower jaw and some other bones in Cretaceous rocks in the Loess Hills of Plymouth County just South of Westfield, Iowa in the summer of 2001.  The specimen was found in the shales/clay below the hard Greenhorn limestone beds that cap the local hills. I originally thought the rock matrix corresponded best to the description of the Hartland Member of the Greenhorn Formation (Hattin, 1975; Hattin and Siemers 1987) but after corresponding with Brian Witzke of the Iowa Geological Survey, I think the matrix is best classified in this area as part of the Bridge Creek Member of the Greenhorn Formation.  Specimens of large ichthyodectid fish are fairly common in the chalks of the western Interior Seaway, but very few have been found in the eastern exposures of the Seaway in this area (Witzke, 1981).

The most common of the ichthyodectid fish in the younger Niobrara chalks is Xiphactinus which is the largest bony fish of the Cretaceous, sometimes getting up to 20 feet (one of the largest ones was discovered in the same Cretaceous seaway in Western Kansas). Xiphactinus at least sometimes swallowed its prey whole as can be seen in the specimen on display in the Sternberg Museum of natural history.  While this Iowa fish could be Xiphactinus, identification will have to wait until more of the fish is uncovered from the shale. I have been told it would be even more exciting (significant) if it were a different genus.

Evan and I have removed the shale from on top of the fossil.  Evan then made a wooden frame and encased the fossil and shale matrix in plaster of paris.  Click on this link to see our work in extracting the fossil.  This link will take you to a description of the rocks and stratigraphy.


References
Hattin , D.E. 1975. Stratigraphy and depositional environment of  Greenhorn Limestone (Upper Cretaceous) of Kansas.  Kansas Geological Survey Bulletin 209  [1979 reprint edition] 128p.

Hattin, D.E. and C.T. Siemers [assisted by G.F. Stewart] 1987. Guidebook Upper Cretaceous stratigraphy and depositional environments of western Kansas. for Annual meetings of American Association of Petroleum Geologists and Society of Economic Paleontologists and Mineralogists [held at Oklahoma City, Oklahoma on April 1978]. Guidebook series 3 Kansas Geological Survey.  [reprint with modifications of 1978 edition] 55p.

Witzke B.J, 1981. Cretaceous vertebrate fossil of Iowa, and nearby areas of Nebraska, South Dakota, and Minnesota. in R. L. Brenner, R. F. Bretz, B. J. Bunker, D. L. Iles, G. A. Ludvigson, R. M. McKay, D. L. Whitley, B. J. Witzke.  Cretaceous Stratigraphy and sedimentation in Northwest Iowa, Northeast Nebraska, and Southeast South Dakota. Iowa Geological Survey Guidebook Series Number 4. 172 p.


* Picture scanned by Mike Evert.

Web page designed by James Mahaffy on May 28, 2001 (6:04PM)
Last updated on: May 15, 2003 (3:11pm)