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Thryptodus zitteli

The "Battering Ram" Fish

An Unusual Fossil from the Smoky Hill Chalk of Western Kansas

Copyright © 1999-2010 by Mike Everhart

Last  Updated 02/24/2010

 

 

 

LEFT: A diorama at the Sternberg Museum showing the floor of the Western Interior Sea during the Late Cretaceous. The large inoceramid clams are Platyceramus platinus; the smaller bivalves are rudists called Durania maxima. Two small pycnodont fish are visible in the background.

     Fossils have been collected from the Smoky Hill Chalk and Pierre Shale of western Kansas since the late 1860s. There have been many spectacular fossils found, including long necked plesiosaurs (Elasmosaurus platyurus), giant fish (Xiphactinus), mosasaurs and pteranodons.  These are well known and can be readily identified. Many of these fossils are shown on the Oceans of Kansas Paleontology web pages.  Some remains, however, like the two specimens shown below are more difficult to identify (and explain!). 

     These two fossils shown below are examples of the anterior part of the skull (ethmoid and premaxillae) of a strange fish called variously Bananogmius zitteli (Cope) and Thryptodus zitteli (Loomis). Thryptodids belong to an extinct family of fish called plethodids, which includes another species commonly found in the chalk: Bananogmius evolutus.  Note that Taverne (2001) recently removed B. evolutus (Cope 1878) from the genus Bananogmius and placed it into a new genus (Pentanogmius Taverne 2000) as Pentanogmius evolutus (Cope 1878).

For this page, I will use Thryptodus until I can work out the most correct name.  Thryptodids were a primitive group of fish that do not have modern relatives as far as I am aware. In some cases, like Thryptodus and Martinichthys, their skeletons were poorly ossified and were rarely preserved.

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LEFT: Complete skulls of Thryptodus have been found rarely in the chalk. The type specimen of Thryptodus zitteli (from Kansas and described by Loomis, 1900) was in a museum in Germany that was destroyed by Allied bombs during World War II.  In Kansas, these fish are only found in the lower 1/4 of the Smoky Hill Chalk and apparently become extinct by the end of Coniacian time (about 86 mya).  

More recently, Shimada and Schumacher (2003) described what is probably the oldest specimen of Thryptodus (FHSM VP-13996) from the Lincoln Limestone (Middle Cenomanian) Member of the Greenhorn Limestone Formation in Russell County, KS.  

     Unfortunately, the two specimens shown below are the best that I have found so far. The skull of Thryptodus was heavily built, with a rostrum (the ethmoid bone, shown below) that is very massive.  Another unusual feature is the flat surface at the anterior end  (to make the third picture, the two 'noses' were simply stood on their ends) that shows possible wear. I would certainly be interested in hearing about any modern analogs to this fish, or ideas as to what the unusually heavy construction of the skull was used for.  Another fish in this family (also from the Chalk) is Martinichthys.... which also had a heavy rostrum (nose), but one which was more slender and generally showed signs of 'wear' on the anterior end.

thrypt1a.jpg (3173 bytes) A dorsal view of two 'noses' of Thryptodus zitteli  (FHSM VP-15571 / EPC 1995-34 and FHSM VP 15572 / EPC 1999-01), The anterior end is at the bottom of the scan. The size of the two fish must have been about the same.
thrypt2a.jpg (2797 bytes) A ventral view of the same two specimens.   Both of these specimens had other skull material and vertebrae associated with them, including a large, flat parasphenoid bone that covered the roof of the mouth.
thrypt3a.jpg (4018 bytes) The 'business end' of the two specimens showing the flat surface of the 'nose'.  What were these 'battering ram' like adaptations used for? Three views of a recently discovered Texas specimen are shown HERE, HERE, and HERE. Based on specimens I have seen recently from Texas, the species seems to be more common there.

Other Oceans of Kansas webpages on Late Cretaceous fish:

 

Field Guide to Sharks and Bony Fish of the Smoky Hill Chalk

 

Sharks:

Kansas Shark Teeth

Cretoxyrhina and Squalicorax

Ptychodus

Chimaerids

 

Bony Fish

 

Pycnodonts and Hadrodus

 

Plethodids:

Pentanogmius

   Martinichthys

   Thryptodus

  

Bonnerichthys

Protosphyraena

Enchodus

Cimolichthys

Pachyrhizodus

Saurodon and Saurocephalus

Xiphactinus


Suggested references:

Loomis, F. B., 1900. Die anatomie und die verwandtschaft der Ganoid- und Knochen-fische aus der Kreide-Formation von Kansas, U.S.A. Palaeontographica, 46: (partial copy)

Shimada, K. and B. A. Schumacher. 2003. The earliest record of the Late Cretaceous fish, Thryptodus (Teleostei: Tselfatiiformes), from central
Kansas. Kansas Academy of Science, Transactions 106(1-2):54-58.

Taverne, L., 2001. Révision du genre Bananogmius (Teleostei, Tselfatiiformes), poisson marin du Crétecé supérior d'Amérique du Nord et d'Europe. Geodiversitas 23(1):17-40. (Revision of the genus Bananogmius (Teleostei, Tselfatiiformes), marine fish from the Upper Cretaceous of North America and Europe).

Taverne, L. 2003. Redescription critique des genres Thryptodus, Pseudothryptodus et Paranogmius, poissons marins (Telostei, Tselfatiiformes) du Crétecé supérior des Etats-Unis d’ Egypte et de Libye. Belgian Journal of Zoology 133(2):163-173.