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Pachyrhizodus 

A Large Predatory Fish from the Late Cretaceous Western Interior Sea

 

Copyright ?2003-2013 by Mike Everhart

Created 11/11/2003; Last update 07/01/2013

 

LEFT: Two Pachyrhizodus caninus on the hunt. Paleo-art by Ron Garrett; Copyright ?small> Ron Garrett 2004.   Used with permission.


Pachyrhizodus is the genus of medium sized (up to 3m) Late Cretaceous fish found in the Smoky Hill Chalk. First named by Agassiz from specimens collected from the English Chalk, E.D. Cope later named two new species from Kansas (P. caninus and P. leptopsis). A much smaller member of the genus, Pachyrhizodus minimus, was added by Albin Stewart in 1899.

 

garret4b.jpg (20486 bytes) The remains of a least three species of Pachyrhizodus are fairly common finds in the Smoky Hill Chalk of Western Kansas. Two of the species, Pachyrhizodus caninus and P. leptopsis were medium sized predators, up to 6 ft (2m) or more in length. They have large teeth which can be easily confused with those of mosasaurs (see Stewart and Bell, 1994). The third species, P. minimus, probably grew no larger than 3 ft (1 m).  For unknown reasons, P. minimus is often preserved as a complete fish, in some cases with the remains of internal organs and scales.

LEFT: Pachyrhizodus. Paleo-art by Ron Garrett; Copyright ?/big> Ron Garrett 2004.   Used with permission.

cope187a.jpg (14006 bytes) LEFT: (CLICK TO ENLARGE) Pachyrhizodus caninus Cope 1872: Plate L (50) from Cope (1875), The Vertebrata of the Cretaceous Formations of the West. Cope's illustration shows the heavy lower jaws and large teeth that are typical of this species.

RIGHT: The lower jaw and left quadrate of a new Pachyrhizodus caninus specimen from the Smoky Hill Chalk (FHSM VP-18518).

We found our first Pachyrhizodus caninus remains (a very scattered skull and lower jaws)  in the low chalk of Ellis County in 1988 and were really puzzled trying to figure out what they were. 

1988-2a.jpg (14436 bytes) LEFT: A jaw element we found in 1988 looked too heavy to be something from a fish.

RIGHT: Fortunately, David Parris of the New Jersey State Museum was able to identify this fragment as the anterior of a right premaxilla) and provided a figure from Loomis, 1900. We donated the specimen to the NJSM (NJSM 15139). 

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LEFT: FHSM VP-18518 - Note the large overlap of the premaxilla over the maxilla in this photo.... very different from the edge to edge contact in Xiphactinus audax. Pachyrhizodus could do some pretty serious biting... It is no wonder that fragments of these jaws have been misidentified as mosasaur in some museum collections.

RIGHT: FHSM VP-18518 -  Complete right upper jaw of Pachyrhizodus caninus Cope, including maxilla and premaxilla.

In a bit of an understatement, Cope (1872) describes the premaxillary bones of Pachyrhizodus as being "well-developed."  Since then, we've found a number of similar specimens, and it seems that the anterior end of one premaxilla or the other is almost always among the remains.

1991-18a.jpg (10358 bytes) LEFT: A left premaxilla and a fragment of the right dentary of a badly broken and poorly preserved skull of Pachyrhizodus caninus (EPC 1991-18). (Smoky Hill Chalk, Gove County)

RIGHT: A close-up of the fragment of the right dentary showing a complete tooth and the roots of three other teeth (EPC 1991-18).

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     The first specimens of Pachyrhizodus caninus were apparently found by E. D. Cope while in western Kansas in 1871, mentioned briefly in his 1872 note "On the families of fishes of the Cretaceous formation in Kansas," and described more fully by him in 1875. He noted that the skull of one specimen was "about a foot in length by 6 and a half inches wide."   The remains were found in Fossil Springs Canyon, south and east of Fort Wallace (Logan County).

     Pachyrhizodus minimus, was described from a lower jaw found by Alban Stewart in 1899 near Butte Creek in Logan County. As its name implies, it is a much smaller fish than P. caninus. Since then, numerous examples of complete fish of this species have been found in the chalk Miller (1957) reported on a specimen (FHSM VP-326) with preserved intestinal casts found by George Sternberg near Hackberry Creek in SW Trego County. - Photo of specimen in the Sternberg Museum)

     In 1990, while we were collecting with J. D. Stewart in Lane County, my wife Pam found a nearly complete P. minimus eroding from the chalk.  The chalk at this site is somewhat older than that of the type locality (Santonian). J. D. and I uncovered the specimen and then put a plaster jacket over it (See below) .

                                   SYSTEMATIC PALEONTOLOGY

Class Osteichthyes

     Infraclass Teleostei

         Superorder Elopomorpha

               Order Elopiformes

                    Suborder Elopoidei

                         Family Pachyrhizodontidae Cope 1872

                              Genus Pachyrhizodus Agassiz 1835 (in Poissons Fossiles)

                              Pachyrhizodus caninus Cope 1872

                             Pachyrhizodus leptopsis Cope 1874

                             Pachyrhizodus minimus Stewart 1899

 

pachy1a.jpg (20514 bytes) The heavy, toothy jaws of Pachyrhizodus leptopsis Cope 1874 have been responsible for some confusion among paleontologists.  Specimens from the Late Cretaceous (Cenomanian) of Texas were described by Stenzel (1944) as very early mosasaurs. Thurmond (1969) described a specimen as the jaw of an early mosasaur.  Stewart (1989) and Stewart and Bell (1994) showed convincingly that the jaws originally described as being from the earliest mosasaurs in North America actually came from Pachyrhizodus leptopsis. In that regard, Martin and Stewart (1977) reported that the earliest known North American mosasaurs are actually from the Fairport Chalk Member (Middle Turonian) of the Carlile Shale in Kansas.

LEFT: A Pachyrhizodus caninus at the Rocky Mountain Dinosaur Resource Center.

The heavy, toothy jaws of Pachyrhizodus leptopsis Cope 1874 have been responsible for some confusion among paleontologists.  Specimens from the Late Cretaceous (Cenomanian) of Texas were described by Stenzel (1944) as very early mosasaurs. Thurmond (1969) described a specimen as the jaw of an early mosasaur.  Stewart (1989) and Stewart and Bell (1994) showed convincingly that the jaws originally described as being from the earliest mosasaurs in North America actually came from Pachyrhizodus leptopsis. In that regard, Martin and Stewart (1977) reported that the earliest known North American mosasaurs are actually from the Fairport Chalk Member (Middle Turonian) of the Carlile Shale in Kansas.

VP-2189Y.jpg (18718 bytes) LEFT: The skull of a very large Pachyrhizodus caninus specimen (FHSM VP-2189) in collection of the Sternberg Museum of Natural History. The skull is 56 cm (22 in) long.

RIGHT: A close up of the jaws and teeth of VP-2189; the lower jaw measures 52 cm (20.5 in.) and the largest teeth are 4 cm (1.6 cm) tall. 

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VP-2189Ga.jpg (24871 bytes) LEFT: An early photograph of the large Pachyrhizodus caninus (FHSM VP-2189) collected by Orville Bonner in December, 1965, from the Greenhorn Limestone near Russell, Kansas. A note with this picture indicates that specimen is 8.5 feet (2.6 m) long.
pachyrha.jpg (14309 bytes) LEFT: Plate LXIX from Stewart, 1900 showing the lower jaw and partial skull of Pachyrhizodus.

RIGHT: The lower jaws of Pachyrhizodus minimus from Stewart, 1899. This is the holotype specimen (KUVP-327) in the collection of the University of Kansas.

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A DIG FOR A COMPLETE PACHYRHIZODUS MINIMUS   

packy01a.jpg (20079 bytes) LEFT: A nearly complete Pachyrhizodus minimus found in Lane County by Pam Everhart in 1990. The fish was 22 inches long.

RIGHT: J. D. Stewart and Mike Everhart breathe a sigh of relief after rolling the jacket containing the small fish.  Everything stayed in place.

packy00a.jpg (13884 bytes)
packy02a.jpg (9329 bytes) LEFT: Pam Everhart doing some of the initial prep work on the specimen. The material was later donated to the Cincinnati Museum Center where it is curated as CMC VP-7552.

RIGHT: Views of two anterior vertebrae from two different specimens of Pachyrhizodus caninus from the chalk in Gove County. This specimen was donated to the Cincinnati Museum Center (CMC 7552).

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cmc7552a.jpg (12950 bytes) cmc7552x.jpg (11930 bytes) Close-ups of the skull and pectoral fins of CMC 7552 cmc7552y.jpg (15956 bytes) cmc7552z.jpg (14229 bytes)

 

PACHHEAA.jpg (13295 bytes) LEFT: A reconstruction of the skull of Pachyrhizodus megalops (Woodward) from the English Chalk (Turonian). Adapted from Forey, 1977.  This species is similar to P. minimus from the Smoky Hill Chalk.
vp-326c.jpg (19449 bytes) LEFT: A close up of the Pachyrhizodus minimus (FHSM VP-326) described by Miller (1957) - Currently on exhibit at the Sternberg Museum. Click here for a large picture of the complete specimen.

RIGHT: A large specimen of Pachyrhizodus caninus in the collection of the University of Kansas. (Scale = cm) 

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denpacha.jpg (14235 bytes) LEFT: A complete Pachyrhizodus minimus from the Smoky Hill Chalk of Kansas on exhibit in the Denver Museum of Nature and Science. (Size is about 3 ft / 1 m)
BONNER7A.jpg (19571 bytes) LEFT: A complete specimen of Pachyrhizodus minimus in the Keystone Gallery collection.

 

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

Chimaeroids

 

Bony Fish

 

Pycnodonts and Hadrodus

 

Plethodids:

Pentanogmius

   Martinichthys

   Thryptodus

  

Bonnerichthys

Protosphyraena

Enchodus

Cimolichthys

Pachyrhizodus

Saurodon and Saurocephalus

Xiphactinus

 


SUGGESTED REFERENCES:

Agassiz, J.L.R. 1833-1844. Recherches sur les Poissons Fossiles. 3: pp. vii + 390 + 32, Neuch鄑el and Soleure.

Cope, E. D. 1872. On the fossil reptiles and fishes of the Cretaceous rocks of Kansas. Art. 6, pp. 385-424 (no figs.) of Pt. 4, Special Reports, 4th Ann. Rpt., U.S. Geological Survey Territories (Hayden), 511 p.

Cope, E. D. 1872. Note of some Cretaceous vertebrata in the State Agricultural College of Kansas. Proceedings of the American Philosophical Society 12(87):168-170. (for Oct. 20, 1871 meeting)

Cope, E. D. 1872. On the families of fishes of the Cretaceous formation in Kansas. Proceedings of the American Philosophical Society 12(88):327-357.

Cope, E. D. 1875. The vertebrata of the Cretaceous formations of the West. Report, U. S. Geological Survey Territory (Hayden). 2:302 p, 57 pls.

Dixon, F. 1850. Geology and fossils of the Tertiary and Cretaceous formations of Sussex. pp. i-xvi; 1-422.

Forey, P. L. 1977. The osteology of Notelops Woodward, Rhacolepis Agassiz and Pachyrhizodus Dixon (Pisces: Teleostei). Bulletin of the British Museum (Natural History), Geology, 28(2):125-204.

Hay, O. P. 1903. On certain genera and species of North American Cretaceous actinopterous fishes. Bulletin American Museum Natural History XIX 1-95, pls. i-v, 72 text-figs.

Jordon, D. S. 1924. A collection of fossil fishes in the University of Kansas from the Niobrara Formation of the Cretaceous. University Kansas Science Bulletin, 15(2): 219-245.

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:

Martin, L. D. and J. D. Stewart. 1977. The oldest (Turonian) mosasaurs from Kansas. Journal of Paleontology 51(5):973-975.

Miller, H. W. 1957. Intestinal casts in Pachyrhizodus, an Elopid fish, from the Niobrara Formation of Kansas. Kansas Academy of Science, Transactions 60(4):399-401.

Stewart, A. 1898. A preliminary description of seven new species of fish from the Cretaceous of Kansas. Kansas University Quarterly 7(4):189-196, pl. XVII. (Protosphyraena recurvirostris sp. nov., Enchodus parvus sp. nov., Enchodus amicrodus sp. nov., Pachyrhizodus leptognathus sp. nov., Pachyrhizodus velox sp. nov., Beryx polymicrodus sp. nov. and Beryx multidentatus sp. nov.) 

Stewart, A. 1899. Pachyrhizodus minimus, a new species of fish from the Cretaceous of Kansas. Kansas University Quarterly 8(1):37-38.

Stewart, A. 1900. Teleosts of the Upper Cretaceous. The University Geological Survey of Kansas. Topeka VI 257-403, 6 figs., pls. XXXIII-LXXVIII.

Stewart, J. D. 1989. The earliest reputed North American mosasaur records are not mosasaurs. Journal of Vertebrate Paleontology (Abstracts) 9:39A.

Stewart, J. D. and G. L. Bell, Jr. 1994. North America’s oldest mosasaurs are teleosts. Contributions to Science, Natural History Museum of Los Angeles County, 441:1-9.

Credits: Earl Manning, Tulane University provided references and comments on the content of this webpage.


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