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Subfossils of the common musk turtle (Sternotherus odoratus) from a holocene peat deposit in Northern Indiana.

INTRODUCTION

Although remains of aquatic turtles are commonly reported from Pleistocene deposits, few records exist from Holocene sediments. The dearth of accounts from the Holocene is more likely a result of sampling neglect than an indication of the absence or rarity of turtles. Older sites, perhaps because they harbor more abundant remains of extinct megafauna, seem to attract more attention from palaeoecologists. However, because the presence or absence of turtles can be an important tool in climatic and biogeographic inference, a thorough spatial and temporal record is needed.

While published records of Holocene aquatic turtles in the Midwest are relatively few, records of the common musk turtle, Sternotherus odoratus (Latreille), are particularly uncommon. Indiana records of S. odoratus include the McCullock's Run Site in Bartholomew County (7000-8000 radiocarbon v BP) (Ronald L. Richards, Indiana State Museum, pers. comm.) and the Prairie Creek Site in Daviess County ([approximately]14,000 radiocarbon V BP) (Holman and Richards, 1993). Additionally, Holman (1990) reported a specimen from a marl bed in Shiawassee County, Michigan ([approximately]5800 radiocarbon y BP).

This paper reports the recovery of Holocene remains of Sternotherus odoratus from northern Indiana. The objectives are to report the age and taphonomy of the remains and to discuss the palaeoecology of the site.

STUDY SITE

Little Chapman Bog, occurs in northeastern Kosciusko County, Indiana (T33N, R6E, Section 35). The sub-basin is a kettle associated with Little Chapman Lake. The peatland occupying the kettle is approximately 9 ha and is nestled in late-Wisconsin glacial outwash. The surface of the peatland is dominated by Sphagnum mosses (Sphagnum fimbriatum, S. palustre, S. teres), Vaccinium macrocarpon (American cranberry), Thelypteris palustris (marsh fern) and Osmunda regalis (royal fern) (Swinehart, 1997).

MATERIALS AND METHODS

Prior to coring, the peatland was probed systematically at 25-m intervals with metal rods to determine the deepest areas of the basin. Coring was conducted at the deepest probe location in the peatland (15 m). A modified Hiller corer with a chamber diam of 5 cm was used to collect the sediments. Cores were sectioned into 25-cm lengths and placed into plastic bags. A 20-ml volume was taken from each interval and gently rinsed through a 0.4-mm mesh sieve. The material remaining in the sieve was placed in a petri dish and examined under a dissecting microscope for identification and quantification of macroscopic subfossils. Subfossils are here defined as: (1) remains of once living organisms that are composed, at least in part, of organic material, or (2) inorganic material of biotic origin that has not yet been lithofied (i.e., mollusc shells, Chara tests). Organic subfossils are distinguished from detritus by having been deposited in an environment where complete decay has been permanently inhibited.

The remaining sediment from each sampling interval was also rinsed through a 0.4-mm mesh sieve. The material was then placed into a large, white enamel pan and examined for large, infrequent subfossils such as bones, large seeds, and leaves that might not have been represented in the 20-ml subsamples used for quantification.

Radiocarbon (14C) dating of sediment was conducted at the Purdue Rare Isotope Measurement (PRIME) Laboratory using a mass accelerator.

Representative subfossils from the peatland were placed in vials with a 60% solution of ethanol. Voucher specimens are held by the senior author, with the exception of the Sternotherus remains, which were deposited in the Michigan State University Museum (MSU-VP # 1443).

RESULTS AND DISCUSSION

Six bones of Sternotherus odoratus were recovered in a tight cluster within the 600-625-cm depth interval. These included three peripherals and one costal (Fig. 1), one cranial, and one vertebral. It is presumed that the bones represent the carcass of a single animal, because they were relatively frequent in and exclusive to a single, narrow depth interval (25 cm), and because they were clustered very closely together within that interval. Subfossils associated with the bones included achenes of Najas flexilis (bushy pond weed) and Ceratophyllum demersum (coontail), seeds of Brasenia schreberi (water shield), and fragments of the moss Drepanocladus aduncus. Subfossils from similar sediments above and below the bones included scales of sunfishes (family Centrarchidae), a shell of Gyraulus parvus (wheel snail), seeds of Nymphaea tuberosa (white water lily), and fragments of the mosses Calliergon stramineum and Meesia triquetra.

Vascular plant fragments from the sediment immediately surrounding the bones yielded a radiocarbon (14C) date of 3680 [+ or -] 80 y BP. The turtle represented by the subfossil remains may have been deposited on the bottom of the lake after death, or it may have burrowed into the sediments and died during winter topor. If the latter is true, the radiocarbon date may exceed the date of the turtle remains.

The environment indicated by the subfossil assemblage was a mineral-rich, mud-bottomed lake with abundant submergent macrophytes. The presence of Brasenia schreberi and Ceratophyllum demersum, suggests relatively quiet, protected waters. Such a habitat coincides with that preferred by extant populations of Sternotherus odoratus (see Conant and Collins, 1991).

Acknowledgments. - The figure was prepared by Ms. Teresa Petersen. We thank Mr. Ken Mueller of the Purdue Rare Isotope Measurement Laboratory for providing the radiocarbon date. The senior author wishes to thank the Basil S. Turner Foundation of Elkhart. Indiana, for funding the larger study from which the present paper was derived.

LITERATURE CITED

CONANT, R. AND J. T. COLLINS. 1991. Reptiles and Amphibians of Eastern and Central North America, 3rd ed. Houghton Mifflin, Boston. i-xix + 450 p.

HOLMAN, J. A. 1990. Vertebrates from the Harper Site and rapid climatic warming in Mid-Holocene Michigan. Mich. Acad., 22:205-217.

----- AND R. L. RICHARDS. 1993. Herpetofauna of the Prairie Creek Site, Daviess County, Indiana. Proc. Indiana Acad. Sci., 102:115-131.

SWINEHART, A. L. 1997. The development and ecology of peatlands in Indiana. Ph.D. Dissertation, Purdue University, Department of Forestry and Natural Resources, West Lafayette, Indiana. ixx + 303 p.

ANTHONY L. SWINEHART, Purdue University, Department of Forestry and Natural Resources, West Lafayette, Indiana, 47907-1159, and J. ALAN HOLMAN, Michigan State University Museum, East Lansing, 48824-1045. Submitted 22 June 1998; accepted 24 September 1998.
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Publication:The American Midland Naturalist
Date:Jul 1, 1999
Words:1001
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