Fossils of Mammut americanum, the American Mastodont, have been recovered from a stream in the Chattahoochee River drainage basin. These fossils imply that at least some local stream terraces are of Pleistocene age

Schwimmer, David R.

English

Columbus State University

81FIRST MASTODONT REMAINS FROM THECHATTAHOOCHEE RIVER VALLEY IN WESTERN GEORGIA,WITH IMPLICATIONS FOR THE AGE OFADJACENT STREAM TERRACESDavid R. Schwimmer, Department of Chemistry and GeologyColumbus College, Columbus, Georgia 31993-2399ABSTRACTFossils of Mammut americanum, the American Mastodont, havebeen recovered from a stream in the Chattahoochee River drainagebasin. These fossils imply that at least some local stream terraces are ofPleistocene age.INTRODUCTIONFossils from the Pleistocene Epoch are widely distributed in Georgia [see (1)for a synoptic literature review]. These fossils are especially common in somesoutheastern Georgia counties with coastal marine tidal channels and subtidaldredge spoils (see 2, 3 for illustrated summaries) and in the northwestern part ofthe state in cave deposits (4-6). An additional diverse Pleistocene fauna isChattahqpchee_Cq.Stewart Co.Figure 1. Locality map, showing the position of Hannahatchee Creek relative to theChattahoochee River. Fossils discussed here were collected in the streambed betweenUnion and Omaha; precise localities are indeterminable.GA J SCI 49: 81-8682 SCHWIMMERdescribed from a Piedmont stream terrace deposit in the central part of the state(7). Pleistocene fossils have not been reported previously from the southwesternmargin of the state which lies within the valley of the Chattahoochee River. Thislack of evidence for Pleistocene fossils has left the age of the upper stream terracesalong the Chattahoochee and its tributaries in doubt. Indeed, the apparent absenceof fossils suggested that regional stream terraces were most likely older than thePleistocene, since fossils of large Ice-age mammals are abundant in geologicallyyoung deposits. The only dated stream terrace deposits in central-western Georgiaare in the Flint River basin, Taylor County, where the age is mid-Pliocene(Hemphillian land mammal age) based on fossil horse teeth (8).The discovery of mastodont remains reported here suggests that at least somesedimentary deposits near the Chattahoochee are of Pleistocene age (Fig. 1). Atooth-specimen of Mammut americanU»i\s taxonomically unequivocal, and asdescribed below, this species occurs characteristically in sediments from the laterPleistocene.MATERIALSSystematic PaleontologyOrder PROBOSCIDEAFamily MAMMUTIDAE Cabrera, 1929Genus Mammut Blumenbach, 1799 (= Mastodon Cuvier, 1817)Mammut americanum (Kerr, 1791)(Figures 2.1-2.6)Material: a left upper third molar (M3) [replica cataloged as CCQ-90-X-Xc]. A left(?) tibial fragment, preserving approximately one-third of distal shaft and ablatedcondyles.Localities: lag deposits in Hannahatchee Creek, Stewart County, Georgia. Thetooth was collected approximately one Km west of Union, and the tibial fragmentwas collected in an area near Omaha. Localities of original deposition are unknown.Repositories: both specimens are retained in private collections. The tooth wascollected by Jimmy Stafford of Lumpkin, Georgia: a cast of the specimen isreposited in the research collections of Columbus College. The limb fragment wascollected by Len and Josephine Lee of Omaha, Georgia.Discussion: The molar features a complete crown and nearly complete roots(Figure 2.1-2.3) with distinctively blue-black mineralization evident in the crownenamel. The tooth is of typical morphology with four complete lophs bisected bythe median sulcus to from eight cusps, an incomplete fifth transverse ridgecomposed of several conules, and a tubercule on the posterior border. Discrimina-tion of isolated upper from lower third molars in Mammut americanum may bebased on several criteria (9) including relative widths of the first two lophs and thepresence of a three-part root in uppers. This is an upper third molar (M3,) in thelarger range of adult sizes, measuring 184 mm antero-posteriorly (i.e. mesio-distally)FIRST MASTODONT REMAINS 83Figure 2. Afammur americanum. J-3, /e/f third upper molar, lingual, buccal, x 1/3,occlusal, x 2/5. 4-6. (?) left tibial fragment, posterior, medial, anterior, x 1/6.84 SCHW1MMERby 104 mm transversely (i.e. bucco-lingually) across the metaloph. Bucco-lingualwidth across the protoloph is 95 mm. Cingula are moderately developed onbuccal and lingual margins, and only weakly-developed cristae interrupt transversevalleys behind the pretrite cusp; collectively, these features categorize this toothas the "smooth variety" (9, 10). The tooth was fully erupted at the time of death.This tooth has partially worn anterior cusps which shows that the individual wasmature. The excellent preservation of most tooth surfaces, especially someterminal roots, suggests that this mastodont's original burial locality was near thesite where the molar was dredged from the stream bed.The limb-shaft fragment is badly water-worn and uninformative at the assumedproximal end of the shaft. The distal end retains a vestige of the medial (?)condylar surface. This appears to be a left tibial fragment with a maximum shaftcross-dimension of 241 mm distally. The size of this fragment suggests theindividual was of typical adult size (9-13). The length of the fragment as preservedis 407 mm (Figures 2.4-2.6). It may, therefore, have come from the sameindividual as the tooth, given that stream traction-load transport could haverolled the tubular bone fragment several km downstream from the tooth site.Both specimens show relatively little chemical-physical alteration, other than thestriking blue-black mineral coloration of cortical bone in the tibial fragment and ofthe enamel in the molar. However, the tooth roots retain the typical off-whitecolor of fresh ivory. The tibial fragment shows no permineralization on eithertrabecular bone regions or the medullary cavity.ANALYSISM. americanum is reported from North American deposits as old as the laterBlancan mammal age of the late Pliocene (maximum 3.5 million years beforepresent [yr. BP]) in the Pacific Northwest and Florida (13-14), and as young as7000 yr BP in Florida (15). Nevertheless, the species was apparently rare in theeastern continent in deposits from before the Rancholabrean land mammal age ofthe late Pleistocene [beginning ca. 400,000 yr BP (13-14)], after which time itbecame extraordinarily abundant until becoming abruptly exinct in the earlyHolocene. Discovery of American mastodont remains in deposits within theChattahoochee River basin therefore implies that at least some of the regionalsediments are from the later Pleistocene. The excellent preservation of the molar,as well as the lack of mineral infilling in the tibia, further suggest that these fossilshave come from the younger range of M. americanum dates.It would be clearly useful to find the original depositional site(s) for these fossils.The tooth specimen must come from deposits either in the highest banks aboveHannahatchee Creek or, more likely, in a streamside bog along the stretchbetween Louvale and Union, GA. The tooth was collected in the Fall of 1990following previous seasons of unusually heavy precipitation. Therefore, it is likelythat the tooth washed into Hannahatchee Creek recently via a swollen, perhapsintermittent tributary drainage.The ages of terrace deposits along the Chattahoochee River and its tributariesare very poorly constrained. Fluvial terraces on the Georgia Coastal Plain aretopographically separable and measurable, and they may be in part correlativeFIRST MASTODONT REMAINS 85with coastal terraces (16); however, each drainage's isostatic history may distortgeodetic relationships. The Chattahoochee Valley, in particular, has undergonesignificant entrenchment and rebound in recent geologic history (8, 16). TheseAmerican mastodont fossils are therefore a useful marker to show that at leastone deposit proximal to the Chattahoochee River is of probable Pleistocene age.The notably blue coloration of both mastodont fossils bears on anotherquestion in regional Pleistocene studies. The term "blue clay" is a popular usagefor deposits containing artifacts and fossil bones along both sides of theChattahoochee Valley (e.g. 17). The origin of this term is obscure, and individualsin the region are heard frequently using the term to describe all local darker-colored deposits, including those of Cretaceous age. Nevertheless, an un-discovered Pleistocene overbank peat or other paludal sedimentary environmentalong the Chattahoochee drainageway may be both the source of the mastodontfossils considered here and the "blue clay" term.ACKNOWLEDGMENTSI thank Jimmy Stafford for providing the opportunity to study the mastodonmolar and I likewise thank Len and Josephine Lee for loan of the tibial specimen. Ialso thank Robert A. Martin of Berry College and Frank Schnell of the ColumbusMuseum for providing useful discussions and background literature. Kim Sangsterand Jon Haney of Columbus College were instrumental to the report byproviding, respectively, literature acquisition and graphics reproduction assistance.REFERENCES1. Lipps EL, Purdy RW and Martin RA: An annotated bibliography of thePleistocene vertebrates of Georgia. Georgia Jour Sci 46(2): 109-148, 1988.2. Hurst VJ: Prehistoric vertebrates of the Georgia Coastal Plain. NewsletterGeorgia Mineral Soc, 10:77-93, 1957.3. Voorhees MR: Vertebrate fossils of coastal Georgia: a field geologist's guide,in Frey RW (ed) The Neogene of the Georgia coast. Guidebook 8th Ann FieldTrip Georgia Geol Soc, p81-102, 197.4. Lipps L and Ray CE: The Pleistocene fossiliferous deposit at Ladds, BartowCounty, Georgia. Bull Georgia Acad Sci 25, 113-119, 1967.5. Ray CE: Pleistocene mammals from Ladds, Bartow County, Georgia. BullGeorgia Acad Sci 25, 120-150, 1967.6. Martin RA and Sneed JM: Late Pleistocene records of caribou and elk fromGeorgia and Alabama. Georgia Jour Sci 47:117-122.7. Voorhies MR: Pleistocene vertebrates with boreal affinities in the GeorgiaPiedmont. Quat Research, 4, 85-93, 1974.8. Voorhies MR: The Pleistocene horse Nannippus minor in Georgia: geologicimplications. Tulane Stud Geol Paleont, 11(2): 109-113, 1974.9. Saunders JJ: Late Pleistocene vertebrates of the western Ozark highland,Missouri. Illinois State Mus Rpt Investig, 33, Springfield 111, pl!8, 1977.10. King JE and Saunders JJ: Environmental insularity and the extinction of theAmerican mastodont, in Martin PS and Klein RG (eds) Pleistocene extinc-86 SCHWIMMERfions. Univ Arizona Press, Tucson AZ, p315-339, 1984.11. Osborn HF: The Proboscidea, Volume I: Moeritherioidea, Deinotherioidea,Mastodontoidea. Amer Mus Nat Hist Press, New York, 1936, p801.12. Olsen SJ: Osteology for the Archaeologist No. 3: The American Mastodonand the Woolly Mammoth. Papers Peabody Mus Archaeol Ethnol, HarvardUniv, 56(3), p56, 1979.13. Kurten B and Anderson E: Pleistocene mammals of North America. ColumbiaUniv Press, New York, 1980, p442.14. Savage DE and Russell DE: Mammalian paleofaunas of the world. Addison-Wesley, Reading, MA, 1983, p432.15. Martin RA and Webb SD: Late Pleistocene mammals from the Devil's Denfauna, Levy County, p. 114-145 in Webb, SD (ed), Pleistocene mammals ofFlorida. Univ. Fla Press, 1974, p270.16. Carver RE and Waters SA: Fluvial terraces and late Pleistocene tectonism inGeorgia. Southeast Geol, 25(2): 117-122, 1984.17. Smith BA: Southwestern Georgia prehistory: an overview. Early Georgia,5(1, 2): 61-63, 1977.

First mastodont remains from the Chattahoochee River valley in western Georgia, with implications for the age of adjacent stream terraces

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First mastodont remains from the Chattahoochee River valley in western Georgia, with implications for the age of adjacent stream terraces

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