CHRONISTER SITE INVESTIGATIONS:
NEW INFORMATION ON THE CRETACEOUS OF MISSOURI
David Parris

INTRODUCTION

More than half a century after its discovery, the Chronister Site continues to challenge investigators. A source of great pride to Missourians, and the primary inspiration for the Bollinger County Museum of Natural History, it is also the provenience for the Missouri State Dinosaur, designated as the original specimen of Hypsibema missouriense. All who have contributed to the study of the site have derived much satisfaction from their participation, and the finds of the last few years have rewarded their dedicated service. Now organized as the Missouri Ozark Dinosaur Project, Inc., the excavations there will undoubtedly continue to produce valuable information on the Cretaceous faunas of the eastern subcontinent.

HISTORY OF INVESTIGATIONS

The discovery and narrative of the Chronister Site is well known and has been periodically reviewed in publications, and only the major events need be included here. The dinosaur material was published by Gilmore and Stewart (1945) and the specimen originally reported by them was the only faunal material for nearly four decades, receiving attention primarily by taxonomic reassignments (Baird and Horner, 1979). Renewed investigations by geologist Bruce Stinchcomb, the property owner, resulted in additional faunal material. Joined by collaborators from the New Jersey State Museum, a broader investigation of the geology and paleontology was soon published (Stinchcomb et al., 1994). Excavations since that time have been conducted by the Missouri Ozark Dinosaur Project, Inc., from which the principal investigators have periodically reported the results (Fix and Darrough, 2004). We continue to refine our views of the paleoenvironment of this important site.

METHODS

As reported by Fix and Darrough (2004), the excavations are now protected by an enclosure, preventing water damage and disruption. As a result, plaster jacket removal has become feasible, essentially for the first time. The obscure and much-deformed clay strata made such removal virtually impossible previously. With ample opportunity to expose a meaningful portion of the bone-bearing deposit, the possibility of getting large segments of material to a laboratory for preparation has now become a reality. With the use of mechanical lifting devices, we now have been able to remove jacket specimens weighing more than 400 kg. Recovery of large specimen blocks for laboratory preparation is likely to result in better microfaunal specimens as well as recovery of large bones. A prime example of large specimen recovery is illustrated here. A jacket nicknamed “Gargantua” was recovered during the past year. With semi-articulated specimens, including vertebrae and a probable scapula, this jacket was excavated from the wall of the excavation, which is well below the original ground surface. It was jacketed in place, and lifted by block and tackle, then lowered onto a padded pallet. It was pulled up a ramp that was built for the purpose, using a cable drawn by a truck.

At the opposite end of the spectrum, the washing and screening approach to small specimens has also been refined to the extent that items of considerably less than one millimeter in dimension have now been recovered. We have thus been able to get further information on the smaller aquatic vertebrate taxa.

RESULTS

A revised faunal list for the site is given in Table 1. The microfaunal identifications are based on a sample estimated at 1000 specimens. Most notable among microfaunal identifications are probable hybodont sharks, based on cephalic hooks, tooth fragments, and spines. The minute size of the specimens suggests that they are from small juvenile individuals. The possible environmental implications of hybodonts are noted in the discussion. Batoids have previously been reported from the Chronister Site.

Among large specimens, the most significant new item thus far recognized is a major portion of a lower dentition of a hadrosaurid. We are pleased to attribute the prospective identification to John R. Horner, who noted the breadth and carinae of the teeth and suggested comparison to Gryposaurus. (See Horner, 1992)

DISCUSSION - INTERPRETATIONS

Previous interpretations of the Chronister paleoenvironment generally involved a paleokarst, a minor deposit of clay in a sinkhole terrain (Stinchcomb et al., 1994). Contributing to this traditional view is the fact that the Cretaceous deposits of the immediate area are all of small size, and scattered through a carbonate-dominated terrain. The Chronister Site is as yet the only one that has yielded fossil vertebrates. It has seemed likely that it represented a coastal plain edpression that served as an entrapment, particularly when the fauna consisted of one dinosaur. Although marine Cretaceous deposits are found not far away (Gallagher et al., 2005), there are no obvious connections. However, the overview of the fauna now recorded suggests that other interpretations should be considered. The fauna is highly aquatic and some of the taxa, such as Trionyx, are not to be expected in small pond environments. A sizeable coastal plain lacustrine environment seems a much more likely interpretation for Chronister, Consistent with all taxa of the fauna now known. External drainage to the marginal marine environment is likely.

This latter possibility is intriguing, assuming that our identifications of the chondrichthyan taxa are correct. Although batoids and hybodontids are known to have been found in non-marine paleoenvironments, these are generally believed to be proximal to (or remnants of) marine connections. This will be considered as our work continues.

ACKNOWLEDGEMENTS

We thank our many volunteer co-workers, notably Bill Teeters, whose logistical help was critical in the removal of large jacket specimens. Advice and discussions from Jack Horner, Phil Currie, Judy-Gail Armstrong-Hall, Russ Jacobson and Bob Denton have been helpful during recent years. Bruce Stinchcomb has graciously permitted and promoted work on the site, which he owns. State Representative Rod Jetton has provided us with public support and grants critical to our work, including the sponsorship of the original Chronister specimen as Missouri’s State Dinosaur!

The ultimate repository of the Chronister Site specimens is designated as the Bollinger County Museum, whose support (coordinated by Eva Dunn) we gratefully acknowledge. Work has previously been supported by grants from the Saint Louis Academy of Sciences.

REFERENCES

Armstrong-Hall, J. G., 1999, Amiid and Pyctodontid Remains in the Cretaceous Fauna of Missouri, Journal of Vertebrate Paleontology 19: 30A.

Baird, D. and Horner, J. R., 1979, Cretaceous Dinosaurs of North Carolina, Brimleyana 2: 1-28.

Darrough, G., Fix, M., Parris, D. and Grandstaff, B., 2005, Chronister Dinosaur Site Investigations: New Information on the Cretaceous of Missouri, Journal of Vertebrate Paleontology 25: 49A-50A.

Fix, M. F. and Darrough, G. E., 2004, Dinosauria and Associated Vertebrate Fauna of the Late Cretaceous Chronister Site of Southeast Missouri, Geological Society of America Abstracts with Programs 36 (3): 14.

Gallagher, W. B., Campbell, C. E., Jagt, J. W. M. and Mulder, E. W. A., 2005, Mosasaur (Reptila, Squamata) Material from the Cretaceous-Tertiary Boundary Interval in Missouri, Journal of Vertebrate Paleontology 25: 473-475.

Gilmore, C. W. and Stewart, D. R., 1945, A New Sauropod Dinosaur from the Upper Cretaceous of Missouri, Journal of Paleontology 19: 23-29.

Horner, J. R., 1992, Cranial Morphology of Prosaurolophus (Ornithischia: Hadrosauridae) with Descriptions of Two New Hadrosaurid Species and an Evaluation of Hadrosaurid Phylogenetic Relationships, Museum of the Rockies Occasional Paper 2: 1-119.

Parris, D. C., Grandstaff, B. S., Stinchcomb, B. L. and Denton, R. K. Jr., 1988, Chronister: The Missouri Dinosaur Site, Journal of Vertebrate Paleontology 8: 23A.

Stinchcomb, B. L., Parris, D. C., Grandstaff, B. S. and Denton, R. Jr., 1994, The Chronister Site (Cretaceous of Missouri) and Its Vertebrate Fauna, Mid-America Paleontology Society Digest 17 (4): 46-63.

TABLE 1

CHRONISTER SITE FAUNA

Class Chondrichthyes
Order Hybodontoidea
Family Hybodontidae
cf. Lissodus sp.

Class Chondrichthyes
Order Batoidea
Family undetermined

Class Osteichthyes
Order Semionotoidea
Family Lepisosteidae
Lepisosteus sp.

Class Osteichthyes
Order Amioidea
Family Amiidae
Platacodon nanus

Class Reptilia
Order Chelonia
Family Dermatemydidae
Adocus sp.
Naomichelys speciosa Hay

Class Reptilia
Order Chelonia
Family Trionychidae
Trionyx sp.

Class Reptilia
Order Crocodylia
Family Crocodylidae
cf. Leidyosuchus sp.

Class Reptilia
Order Saurischia
Family Ornithomimidae
cf. ornithomimid

Class Reptilia
Order Saurischia
Family Tyrannosauridae
tyrannosaurid, genus undetermined

Class Reptilia
Order Saurischia
Family Dromaeosauridae
dromaeosaurid, genus undetermined

Class Reptilia
Order Ornithischia
Family Hadrosauridae
Hypsibema missouriensis Gilmore
cf. Gryposaurus sp.

Additionally, eggshell specimens, as yet unattributed to particular vertebrate groups, have been recovered at the Chronister Site.

Association of Missouri Geologists
Guide to Field Trips - Field Trip 1, Friday, October 6, 2006  [ pdf ]

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