SAUROCEPHALUS, SAURODON AND PROSAURODON
Sword-eels of the Late Cretaceous
Copyright Š 2004-2007 by Mike Everhart
Created 02/05/2004 - Updated 05/29/2007
LEFT: Painting by Charles Bonner, Keystone Gallery
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SAUROCEPHALUS, SAURODON AND PROSAURODON Sword-eels of the Late Cretaceous Copyright Š 2004-2007 by Mike Everhart Created 02/05/2004 - Updated 05/29/2007 LEFT: Painting by Charles Bonner, Keystone Gallery |
When Lewis and Clark set out in 1804 on their westward trek to explore the Louisiana Purchase, they had no idea that they would also be crossing the expanse of an ancient ocean that once covered the middle of North America. It was early in the trip when they found the only fossil specimen that survives today from the collections made by the expedition along the Missouri River, along the western border of what is now the Harrison County, Iowa. Meriwether Lewis described the remains in a note that survives along with the specimen as "the petrified jaw bone of a fish" (below; see Spamer, et. al., 2000, for a more detailed account). The specimen was eventually presented to the American Philosophical Society where it was studied, and then mis-identified some years later by Dr. Richard Harlan (1824) as a new species of marine reptile, Saurocephalus lanciformis. He believed it to be most closely related to the marine reptiles called ichthyosaurs.
Hays (1830) described a similar specimen from New Jersey but noted that it was clearly the skull of a fish, not a reptile, and declined to use Harlan's mis-leading genus name of Saurocephalus. Instead he established a new genus (Saurodon) and species (leanus).
Later, Joseph Leidy (1857, p. 302) incorrectly noted that the specimen mis-identified by Harlan was a fragment of a "maxillary bone with teeth of peculiar genus of sphyrænoid (barracuda-like - see Protosphyraena) fishes from the Cretaceous formation of the Upper Missouri." The type specimen of Saurocephalus lanciformis (ANSP 5516) was also the first fossil fish and the first vertebrate to be collected, illustrated and described from the Niobrara Formation. Over the years, the number of named Saurodon / Saurocephalus 'species' grew to eleven, but the number was reduced to two by Bardack and Sprinkle ( 1969). Stewart (1999) re-described a third species (Prosaurodon pygmaeus) that had originally been named Saurodon pygmaeus by Loomis in 1900. According to Stewart, Prosaurodon specimens have often been mis-identified as Ichthyodectes.
Saurodontinae is a sub-family of the Ichthyodectidae (Earl Manning, pers. comm., 2004) and includes three genus/species in the Western Interior Sea, of which Prosaurodon is the most primitive.
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Family Ichthyodectidae Sub-family Saurodontinae Prosaurodon pygmaeus (Loomis, 1900) Saurodon leanus Hays, 1830 Saurocephalus lanciformis Harlan, 1824
LEFT: The skull of Saurodon leanus, showing the unusual extension of the lower jaw (predentary) from Stewart (1900). |
All of the species were small to medium-sized (1-2 m / 3-6ft), elongate predatory fish and are uncommon as fossils in the chalk. The most unusual character of these fish is the pre-dentary bone that projected forward from the lower jaw. The function of this under-slung extension of the lower jaw is unknown but it gives a different perspective to the phrase “leading with your chin.” Another characteristic of these fish their flat, blade-like teeth, set in a single row in the jaws. In Saurocephalus and Saurodon, the teeth are closely set, nearly vertical and have a “keyhole-like” notch at the base of each tooth on the inside of the jaws. In Prosaurodon, the teeth have a more rounded cross-section, are more widely set, inclined anteriorly, and do not have the notch found in the other two species. From Stewart’s (1999) phylogenetic analysis, it appears that Gillicus (Ichthyodectidae) is more closely related to Saurodon than to Xiphactinus. (click here for a picture of Gillicus teeth)
The three species apparently occur at differing times in the Western Interior Sea with little overlap. According to Stewart (1999), Saurocephalus lanciformis appears only in the uppermost chalk (Early Campanian) while Saurodon leanus is known from the lower through the middle chalk (Late Coniacian through the Santonian). Prosaurodon pygmaeus appears first about the middle of the chalk and continues upwards into the Sharon Springs Member of the Pierre Shale (Ibid.; Carpenter, 1996). Pre-Niobrara records of the Saurodontidae are unknown in Kansas. However, a much older specimen from the Cenomanian Eagle Ford Group of Texas (Stewart and Friedman, 2001) suggests that family existed for some time before the deposition of the Niobrara.
| RIGHT: A medial view of the right maxilla of the type specimen of Saurocephalus
lanciformis Harlan 1824, including a detail showing a complete tooth. This is the
only surviving fossil specimen collected by the Lewis and Clark Expedition, 1805-1805. It
was found in western Iowa by Patrick Gass on August 6, 1804, and is now in the Academy of
Natural Sciences of Philadelphia (ANSP 5516)
- (Exhibit Label) See also this historical paper: Harlan, R., 1824. On a new fossil genus of the order Enalio sauri, (of Conybeare). Jour. Acad. Nat. Sci. Philadelphia, ser.1, 3(pt. 2):331-337; pl. 12, figs. 1-5. |
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| RIGHT: Figure 1 of Plate 16 illustrating the type specimen of Saurodon
leanus as published by Hays in 1830. Outline of the predentary is added. Hays, I., 1830. Description of a fragment of the head of a new fossil animal, discovered in a marl pit, near Moorestown, New Jersey. Transactions American Philosophical Society, ser. 2, 3(18):471-477, pl. 16. (read Dec. 4, 1829 and Jan. 1, 1830). <EM> |
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| RIGHT: One of the most complete skulls of Saurodon leanus that I have seen. Discovered and prepared by Barbara Shelton and exhibited in the Keystone Gallery collection. |  |
RIGHT: The skull of Saurodon leanus Hays (FHSM VP-168) on exhibit in the Sternberg Museum of Natural History.
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| RIGHT: The lower jaw of a Saurodon leanus specimen (VP-3186) in the collection of the Sternberg Museum of Natural History. |  |
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LEFT: The front half of a fairly complete Saurodon leanus (KUVP 180) from the Smoky Hill Chalk. |
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LEFT: A close-up of the anterior skull of KUVP 180, showing the predentary, the dentary, maxilla and premaxilla. |
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LEFT: The damaged back portion of the KUVP 180 specimen, showing the vertebrae that are characteristic of Saurodontidae and Ichthyodectidae. |
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LEFT: A 3-dimensional mount of the upper and lower jaws of a Saurodon leanus skull (unnumbered) in the Museum of Geology, Emporia State University, Emporia, KS. Note that the anterior of the left dentary is not articulated with the predentary as it should be. |
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LEFT: A close-up of the lower jaws / predentary, and partial left upper jaw / premaxilla of Saurodon leanus in medial view from the Fryxell Geology Museum at Augustana College in Rock Island, Illinois. This specimen was collected by George F. Sternberg from the Smoky Hill chalk and acquired from him by Augustana College. A different view of the specimen is HERE. |
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LEFT: This specimen of Saurodon leanus (FHSM VP-74) in the Sternberg Museum collection preserves the upper and and lower jaws, the premaxilla and the predentary. The specimen was collected and prepared by George F. Sternberg. |
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LEFT: This is a photograph of a recently discovered specimen of a saurodontid fish from the Ozan Formation (Upper Campanian), Hempstead County, Arkansas. It is believed that this is the first record of this taxon from the Cretaceous of Arkansas. The initial identification appears to be Saurocephalus lanciformis. Photograph by Kelly Irwin. |
Other Oceans of Kansas webpages on Late Cretaceous fish:
Field Guide to Sharks and Bony Fish of the Smoky Hill Chalk
Sharks:
Bony Fish
Plethodids:
SUGGESTED REFERENCES:
Bardack, D. and G. Sprinkle. 1969. Morphology and relationships of saurocephalid fishes. Fieldiana Geology 16(12):297-340.
Harlan, R. 1824. On a new fossil genus of the order Enalio sauri, (of Conybeare). Journal of the Academy of Natural Sciences of Philadelphia, Series 1, 3(pt. 2):331-337; pl. 12, figs. 1-5.
Hays, I. 1830. Description of a fragment of the head of a new fossil animal, discovered in a marl pit, near Moorestown, New Jersey. Transactions of the American Philosophical Society, Series 2, 3(18):471-477, pl. 16.
Leidy, J. 1856. Notes on the fishes in the collection of the Academy of Natural Sciences of Philadelphia. Proceedings of the Academy of Natural Sciences of Philadelphia, 8:221. (printed in 1857)
Leidy, J. 1857. Remarks on Saurocephalus and its allies. Transactions of the American Philosophical Society, xi pp. 91-95, with pl. vi.
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.
Spamer, E. E., R. M. McCourt, R. Middleton, E. Gilmore and S. B. Duran. 2000. A national treasure: Accounting for the Natural history specimens from the Lewis and Clark Expedition (western North America, 1803-1806) in the Academy of Natural Sciences of Philadelphia. Proceedings of the Academy of Natural Sciences of Philadelphia, 150:47-58.
Stewart, A. 1898. Some notes on the genus Saurodon and allied species. Kansas University Quarterly, 7(4):177-186, pls. XIV, XV, XVI.
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. 1990a. Niobrara Formation vertebrate stratigraphy, pages 19-30, In Bennett, S. C. (ed.), Niobrara Chalk Excursion Guidebook, The University of Kansas Museum of Natural History and the Kansas Geological Survey.
Stewart, J. D. 1999. A new genus of Saurodontidae (Teleostei: Ichthyodectiformes) from Upper Cretaceous rocks of the Western Interior of North America. pp. 335-360, 2 fig. In Arrantia, G. and H-P Schultze (eds.), Mesozoic Fishes 2 - Systematics and Fossil Record, Verlage Dr. Friedrich Pfeil, München, Germany.
Stewart, J. D. and V. Friedman. 2001. Oldest North American record of Saurodontidae (Teleostei: Ichthyodectiformes). Journal of Vertebrate Paleontology 21(Supplement to 3):104A.
Taverne, L. and P. Bronzi. 1999. Les poissons cretaces de Nardō. 9°. Note complementaire sur le saurodontinae (Teleostei, Ichthyodectiformes): Saurodon elongatus, sp. nov. Studi e Ricerche sui Giacimenti Terziari di Bolca. VIII. Memor. Vol. Lorenso Sorbini, Museo Civico di Storia Naturale, Verona, pp. 105-116. (Illustration of a nearly complete fish)
