Chronister Mesozoic Vertebrate Fossil Site Bollinger County, Missouri
CHRONISTER VERTEBRATE SITE
Bruce L. Stinchcomb
One of Missouris geologic anomalies is the Chronister Mesozoic vertebrate fossil Site. Anomalous because most of the state is underlain by Paleozoic or Precambrian rocks rather than Mesozoic and also because the rocks of the site are non-marine or continental deposits to quote E. B. Branson who mentioned the site in his Geology of Missouri, 1944.
Mesozoic strata were unknown in Missouri prior to the 1930s. In the mid 30s Willard Farrar and Lyle McManamy working on a WPA financed program with the Missouri Geological Survey, geologically mapped Stoddard County and discovered the presence of Cretaceous clays which was reported in their 1937 Geology of Stoddard County. Interest in the geology of the southeastern part of Missouri continued with a mapping program and thesis (Heller, 1943) extending north of Stoddard County into the Ozark region of Bollinger County. Dan Steward, coming on board with the Missouri Geological Survey in 1940 engaged in geologic mapping of an area in the vicinity of Glen Allen which Robert Heller also was investigating at the same time. In 1941 they mapped a structurally complex area along Crooked Creek near Glen Allen west of Marble Hill and Lutesville in Bollinger County. Steward was shown a group of bones which had been recovered from clay while digging a cistern in the back of the house of Lula Chronister. Already aware of blue-grey clays in the banks of nearby Crooked Creek, Steward was open to the possibility that such clay might be of Mesozoic (Cretaceous) age, in light of the fact that marine Cretaceous sediments had been discovered in Stoddard County a few years earlier.
Steward took some of the bones to Rolla, where Chief Buehler, the State Geologist at the time, is reported to have barked out Why those are only old cow bones. Convinced that they were fossils and possibly dinosaur, Steward collaborated with Maurice Mehl of the University of Missouri, (the only University of Missouri at that time in Columbia) in determining what they had. Mehl had worked with Mesozoic vertebrate fossils in Wyoming and affirmed that the bones were indeed dinosaur. Steward and Mehl planned to do a paper on the fossils, however, the fall of 1941 saw the beginning of World War II and things changed. Steward focused on strategic mineral deposits of the Joplin area. Willard Farrar was killed in the war (UMRs Farrar Residence Hall is named after him) and the paper on the Chronister site remained in limbo until after the war when it was published in the Journal of Paleontology. Maurice Mehl had contacted Charles Gilmore of the U. S. National Museum regarding the bones and in 1945 Gilmore authored the paper on the site with Steward (Gilmore and Steward, 1945).
Little activity took place at the site until 1972 when the author investigated it and found one of the sons of John and Lula Chronister living nearby who expressed considerable interest in my interest in the site. Attracted to it because of an interest and curiosity with Ozark outliers and their fossils, it was decided that a back hoe could probe the area around the now abandoned cistern for additional material. Obtaining a small grant from the St. Louis Academy of Science, we probed the site and at first found nothing in blackish-grey clay. Later digging found bones of dinosaur and turtle in grey and yellow clay. A few years after our initial investigations, Oli Chronister offered to sell the site to me at a reasonable price and seeing how other fossil sites are often made unavailable or lost by ownership changes, I purchased it. Aware that a site such as this has considerable hands on educational as well as scientific value, a number of interested persons became involved, including Guy Darrough and Mike Fix. Finding that the site was difficult to work as a consequence of drainage problems and slumping of the clay when wet, the solution for a more or less permanent dig was found in covering the dig site with a plastic tarp-like greenhouse. This is what is currently being utilized to cover the dig and to expose the bone bearing clay.
FOSSIL TAXA FOUND AT THE SITE
The original fossils found in the digging of the cistern in 1940 consisted of 14 caudal (tail) vertebrae of a dinosaur. These were the specimens figured in the Gilmore and Steward paper and were the basis for establishment of what they considered to be a Cretaceous sauropod to which they gave the name Neosaurus missourensis. The genus Neosaurus was coined in view of their belief that it was the youngest known sauropod, however known only by its tail vertebrae. When excavations of the mid 1970s produced additional material, assistance in dinosaur taxonomy and anatomy was acquired from David Parris of the New Jersey State Museum. It was found that most of the material recovered was of hadrosaur origin (duckbilled dinos), specifically of the genus Hypsibema sp. Neosaurus, the genus established by Gilmore and Stewart had been placed in synonymy under the genera Parrosaurus sp. and Hypselbema sp. Other dinosaur material which was found consisted of carnosaur bone and teeth (Albertasaurus sp.) and gastroliths.
Considerable amount of fossil turtle remains were also recovered, usually in a fragmentary condition. Most of this turtle material is from the genus Adocus sp., a common late Mesozoic turtle related to the still living fresh water turtle Trionyx sp., a peculiar beaded turtle of the genus Naomichelys sp. was also found, a type of turtle more common in the Jurassic than to the Cretaceous. A portion of the site not covered by the greenhouse was found to yield a large number of specimens of Adocus sp. where a novel mechanism explaining their high concentration was suggested by Forir and Stinchcomb, 1996.
The site is considered to have originally been a watering hole as many of the bones exhibit bite marks of two types, one associated with scavenging, the other with predation, Forir, 2001. The sites location appears to be in association with a major fault and was probably preserved by downfaulting in a graben (Fix, 2001).
LOCAL STRUCTURE AND SEDIMENTS OF THE SITE AREA
Cretaceous sediments of the Chronister site have been considered to have been preserved by the following phenomena:
A. A filled sink hole or paleokarst developed in carbonate rocks of the Roubidoux and Jefferson City formations
B. A sediment filled graben associated with extensive southeastern Missouri faulting and preserved from erosion in a down-dropped fault block. The fault is one of many in the Marble Hill-Glen Allen area.
C. A combination of both A and B, that is a fault block along which there was considerable solution of surrounding carbonate rocks accompanied by filling of the graben by Late Cretaceous (Campanian) sediments.
One of the puzzles of the site is the presence of large boulders of exotic rocks embedded in the bone bearing clay. These boulders consist primarily of sandstone layers of the Everton Formation, boulders of the Plattin Limestone and possibly the Bainbridge and Bailey formations. Rock surrounding and outside of the Chronister site valley is the older Lower Ordovician Roubidoux and Jefferson City formations. One suggestion explaining such exotic boulders proposes that a cliff face of younger rock once surrounded the site which during the Campanian was a depression. Boulders of the younger rock on the cliff face would fall into this depression, become buried by the clay along with the fossil bones of animals attracted to what is considered to have been a watering hole (Forir and Stinchcomb, 1996).
.Investigation of the site is an ongoing activity. With additional excavation and fossil recovery from other clay lenses at the site, additional (and possibly different) material might be obtained. Other outliers of clay in Bollinger and Butler counties, some of which are shown on the 1979 state geological map, may also yield additional fossil vertebrate and plant material, possibly some of different age than the Campanian age strata of the Chronister site.
Farrar, Willard and Mc Manamy, Lyle, 1937, The Geology of Stoddard County, Missouri, Appendix VI, 59th Biennial Report, Missouri Geological Survey and Water Resources.
Fix, Michael F., 2001, (abstract) Dinosauria and Associated Vertebrate Fauna of the Late Cretaceous Chronister Site of Missouri. Abstract of 7th North American Paleontological Convention, Univ. of California, Berkley.
Forir, Matthew and Stinchcomb, Bruce, 1996, Pecular Occcurrence of the Cretaceous Turtle Adocus at the Chronister Site, Bollinger County, Missouri, Sixth North American Paleontological Convention Abstracts of Papers, The Paleontological Society Special Publication No. 8, p. 126.
Forir, Matthew, 2001, (abstract) Using Taphonomy to Determine Paleontological Parameters of the Chronister Local Fauna, Bollinger County, Missouri, Abstracts of 7th North American Paleontological Convention-2001, Univ. of California, Berkley.
Gilmore, Charles W. and Steward, Dan, 1945, A New Sauropod Dinosaur from the Upper Cretaceous of Missouri, Journal of Paleontology, Vol. 19 pg 23-29.
Heller, Robert, 1943, Geology of the Marble Hill Area, Bollinger County, Missouri: Unpublished Master of Arts Thesis, Graduate School of the University of Missouri, Columbia, 109 pg. map.
Parris, David C., Grandstaff, Barbara and Stinchcomb, Bruce, 1988, (abstract) Chronister: The Missouri Dinosaur Site, Journal of Vertebrate Paleontology Vol. 8, Supplement to No. 3, Society of Vertebrate Paleontology, Tyrrell Museum of Paleontology, Drumheller, Alberta.
Association of Missouri Geologists
Guide to Field Trips - Field Trip 1, Friday, October 6, 2006 [ pdf ]
Lead by: Dr. Bruce L. Stinchcomb
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