A report on the Shelton Mastodon Site and a discussion of the numbers of mastodons and mammoths in Michigan.

Originally published in Michigan Academician Vol. XXI, No. 2 (Spring 1989): 115-32

Editor's Comments. J. Shoshani, formerly a professor at Wayne State University in Detroit, is now associated with the University if Asmara, Asmara, Eritria. An energetic researcher on both fossil and modem proboscideans , Dr. Shoshani supervised multidisciplinary excavations of mastodont sites in southeastern Michigan (e.g., Shoshani et al. 1989). This approach has allowed him to discuss the food web of the the mastodont-dominated community as well as the paleoecology of the associated fauna and flora. This paper provides an update to Holman et al. (1986), but the main contribution of the paper reflects on the 5:1 dominance in Michigan of mastodont fossils over mammoths, and suggests that mastodonts were ecological generalists, better adapted to a diversity of habitats than the mammoth, which was more of a specialist. The author postulates that the more or less treeless habitats which the mammoth required were not common enough to support very large populations in Michigan and contrasts Michigan with the Nebr aska plains where the mammoths outnumbered mastodonts about 8 to 1.

INTRODUCTION

Elephants, mammoths, and mastodons (order Proboscidea) have fascinated mankind since the dawn of prehistory. The first report of the American mastodon (Mammut americanum) in Michigan was during the nineteenth century (Lanman 1839). In the intervening 150 years, people have continued to find bones and teeth of the extinct American mastodon and mammoths (Mammuthus sp.). Most of these finds were bones and tooth fragments, and only very few complete or partially complete specimens were discovered. Presently, there are two mounted skeletons of the American mastodon in Michigan; one, probably a female, is at the Exhibit Museum of the University of Michigan, Ann Arbor (Dorr and Eschman 1970), and the other, probably a male, is at the Highland Lakes Campus of Oakland Community College, Union Lake (Dorr et al. 1982).

The vast majority of these proboscidean materials came from occasional

surface finds reported by farmers or amateur collectors (see for example Dorr and Eschman 1970, and Holman et al. 1986, and Appendix A in this paper). When locations are precisely documented, surface finds provide us with important information about past inhabitants and their paleoecology, but only bones and teeth collected in well-defined strarigraphic context can be dated and associated with particular environmental features.

The two mastodons focused upon here were uncovered at the Shelton Mastodon Site (SMS), a well-documented Michigan locality (Shoshani et al., 1989; Shoshani and Zawiskie, unpublished ins.). Field work at the SMS was carried out during the summer months of 1983-1987, following standard techniques as described byJoukowsky (1980), Kummel and Raup (1965), and Rixon (1976). A detailed account of the findings at this site during the years 1983-1986 appears in Shoshani etal. (1989). In this paper, I shall provide a timely summary of the uncovered fauna and macro flora for the entire excavation period and briefly review the significance of the findings. The mastodons listed in Appendix A (which is an update to Holman et al. 1986), provide the basis for my discussion on the numbers of mammoths and mastodons in Michigan.

THE SHELTON MASTODON SITE

The SMS is located in southeastern Michigan, northern Oakland County (Brandon Township SE 1/4 of SE 1/4 of Section 26, T5N R9E, 82[degrees] 20' W longitude, 42[degrees] 50' N latitude, at an elevation of 317 m (1040 ft.) above sea level (Figure 1). During the Port Bruce Stade, Oakland County was covered with a continental ice sheet; subsequent retreat of the Saginaw and Huron-Erie lobes resulted in the deposition of a portion of the Defiance Morainic System in northern Oakland County approximately 14,500 years ago (Farrand and Eschman 1974; Evenson et al. 1976; Eschman and Mickelson 1986). According to Mozola (1954), intermorainal areas contain related till and outwash plains. The Shelton vertebrate faunule was derived from sediments that mantle the Oxford outwash plain. Radiocarbon dates that bracket this faunule indicate correlation with the forest bed of the Twocreekan Substage at the type locality in Wisconsin (Morgan and Morgan 1979). Sediments that overlie the vertebrate-bearing forest bed span the Plei stocene-Holocene boundary.

Material and data collected at the SMS have been the subject of intensive multidisciplinary investigation. Following is the roster of studies that have been conducted: the fauna and flora up to the 1986 season and its paleoecology (Shoshani et al. 1989), palynology (Snyder and Shoshani, in preparation), wood anatomy (Newsom and Shoshani, in preparation), fish (Smith and Shoshani, in preparation), amphibians (DeFauw and Shoshani 1991), co-leopteran insects (Morgan et al., in preparation), molluscans (Thurlow and Shoshani, submitted), diatoms (Stoermeret al. 1988), Early Archaic projectile points (Shoshani et al. 1989), and stratigraphy and paleoecology (Shoshani and Zawiskie, unpulished ms.). Figures 2 and 3 provide a summary of our finds during the five field sessions.

A typical cross-section at the site reveals three distinctive units above the glacial deposits (Figure 2). This figure also incorporates six of the twelve radiocarbon dates (all given as years "before present" = B.P.) obtained from wood and bones collected at the SMS. The bottom of Unit II includes the forest floor, located on top of the massive blue-grey clay (Unit I), and it is clearly evidenced by a laterally continuous bed of spruce needles, cones, horizontal logs, charcoaled wood, in situ spruce tree stumps, stones, and cobbles. The rocks and boulders are of glacial origin, probably from the adjacent morainic highland. The mastodon (Mammut americanum), the Scott's moose (Cervalces scotti), and other species in the vertebrate faunule occur at this level (Unit II) and were buried during episodic sedimentation events, probably following fires that periodically denuded the morainal highlands. The faunistic and floristic data from the SMS reveal pond-margin lacustrine environment at about 11,500 B.P. Deep fis sures, apparently in a polygonal pattern, occurred in the upper surface of Unit II (Figure 3). This is evidence of intense frost riving at the end of the climatically severe late-glacial, possibly during the Great Lakean glacial stade.

The climate subsequently moderated, pines became prominent in the forests of the region, and peat developed in a bog environment.

POPULATIONS AND THE HABITAT PREFERENCE OF MASTODONS AND MAMMOTHS

Proboscidean Censuses

The remains of the two mastodons found at the SMS are two of 219 specimens of M. americanum found in Michigan. Mammuthus specimens in Michigan, on the other hand, number only 47 (Figure 4). This observation raises the question as to whether or not these numbers accurately portray the Pleistocene ratios of these extinct taxa..

Hay's (1923) counts of mastodons and mammoths in Michigan were 27 and 7, respectively. MacAlpin's (1939) survey of mastodons in Michigan totaled 117 (no mammoths were included). Skeels (1962) and subsequent workers included both proboscidean genera. A summary of these censuses and the ratios between Mammut and Mammuthus is given in Table 1A.

Some current explanation for such a 5:1 (actually 4.65:1) ratio is that a bias may exist in the fossil-forming processes due to the habitats which these two species occupied. I shall argue that, in addition to taphonomic bias, which is a part of this phenomenon, the skeletal anatomy (in conjunction with the manner in which the skeleton manifests itself in the ecological preference) of the species under consideration should be considered as another parameter which determines population density. Based on the argument that I will outline below, it is entirely plausible that the differences in numbers of specimens for Mammut and Mammuthus represent a true ecological scenario of the populations of these two genera during the late Pleistocene of Michigan. Stated otherwise, the observed numerical differences are a reflection of a complex of ecological interactions between anatomical and habitat differences between mastodons and mammoths. For comparative purposes, similar numbers are provided for Nebraska (Table 1B); in Nebraska the ratio of mastodons to mammoths is approximately 1:8. The numbers were obtained from records in museums or other public institutions and from only a few which were held in private collections. Nebraska was chosen because a greater portion of its Pleistocene habitat was open grassland or savanna, in contrast to a mosaic of diverse habitats in southern Michigan (Davis 1969, 1976; Wright 1983; Delcourt and Delcourt 1984).

A close examination of the data in Table 1 shows that the "harvest" of mastodons and mammoths in Michigan per year varies from 0 to 5 and from 0 to 1, respectively. Similarly, these figures for Nebraska are 0 to 2 and 5 to 12. The most striking feature of this table is the consistency in ratios of Mammut to Mammuthus over a period of 65 years (from 1923 to 1988).

Interestingly, in Illinois (Table 1 C), located between Nebraska and Michigan, the ratio is 1:1, intermediate between the ratios in the two states. Similarly in Florida, the ratio of mastodons and mammoths was 1:1 (Table 1 D).

Clearly, there is an overall simplification in this approach because not all the remains of mammoths and mastodons were contemporaneous or found in the same depositional layer. Not all the specimens collected in Michigan lived at the same time; therefore, the ratios may have changed as each species approached extinction during the 4,000 years that both lived together following glacial retreat from southern Michigan. Radiocarbon dates from sites where Mammut and Mammuthus were found clearly indicate that the species were contemporaries. Furthermore, although not a common occurrence, there are excavation sites in Illinois (J. J. Saunders, personal communication) and Florida (G. Morgan, personal communication) in which both mammoths and mastodons were found together.

Students of taphonomy (see, for example, articles in the books edited by Behrensmeyer and Hill 1980 and Martin and Klein 1984) agree, on the whole, that the bones of animals that die close to the wetland or a lake may have a better chance of being preserved than those that die in an open grassland or dry savanna. In the latter habitats, the bones are exposed to more natural weathering and spreading than in the former habitats where the chemistry (e.g., pH) may be a factor, and sedimentation rates and burial are more rapid. I concur that taphonomic processes play a significant role in bone preservation. General statements may be misleading, however, because the complexity of a particular scenario may be compounded by local variations. For example, good depositional settings such as rivers, ponds, and moist depressions can occur in an open, dry grassland which, overall, has a less-favorable preservation habitat than does forested wetland.

It appears that, despite the theoretically less-favorable preservation conditions in the open habitat, it is possible that enough buried skeletal elements remain that are identifiable to give a reasonable inference of past populations. This is especially true when the species under consideration is elephant sized rather than the size of a small mammal. A second argument holds that human development (such as housing projects and road constructions) that is conducted more often and in greater intensity in drylands provides opportunities for finding bones in greater frequency than in wetlands (West and Dallman 1980).

HABITAT PREFERENCE

Over the decades, as more and more bones and teeth have been discovered and as parallel studies have been conducted, it has become possible to make inferences about the habitats of American mastodon (M. americanum) and the mammoth (Mammuthus sp.). Many authors (e.g., Warren 1852; Skeels 1962; Oltz and Kapp 1963; Stoutamire and Benninghoff 1964; Saunders 1977; West and Dallman 1980; Graham et al. 1983; Garland and Cogswell 1985; Holman et al. 1986; Kapp 1986; Koch and Fisher 1986; Bearss and Kapp 1987; Holman et al. 1988) have detailed the flora and fauna associated with Mammut and Mammuthus in Michigan and the Great Lakes Region. Good summaries are those of Skeels (1962), Dorr and Eschman (1970), Kurten and Anderson (1980), articles in the volume edited by Martin and Klein (1984), and the recent paper by Miller (1987).

The emerging picture is that mastodons had broad tolerance for diverse ecosystems (ranging from coniferous and deciduous forests to swamps and open grassland intermixed with sedges, and from lowland to highland habitats), whereas mammoths roamed more uniform, generally treeless or open forest habitats (prairies, tundras, and taigas). The terms diverse and uniform are used here in the broad sense. That is, the mastodon could have been more adaptive in terms of latitude, but, on the finer scale, it might have been restricted to a given alluvial plain, an ecotone, or a gallery forest. The uniform habitat of the mammoth, although it is generally less diverse than that of the mastodon, might have been a mosaic savanna or steppe. These generalized diverse versus uniform habitat requirements and the related feeding adaptations of Mammut and Mammuthus, respectively, are manifested in the structure and function of their teeth and skeletons (Olsen 1972; Shoshani, in press).

The underlying principle in this relationship may be called the generalist versus specialist hypothesis. Inferences can, thus, be made with regard to the relative numbers of individual mastodons and mammoths (and perhaps with any pair of mammalian taxa) based upon their anatomy and the types of their habitats in a given area. Similarly, once the numbers and the anatomical adaptations are known, the habitat requirements can be predicted.

SUMMARY AND CONCLUSION

Pleistocene sediments at the Shelton Mastodon Site were deposited in open lacustrine to forested marginal lacustrine habitats while the Holocene deposits represent a bog environment (Figure 3). The vertebrate fauna was recovered from the forest zone (Unit II). Radiocarbon dates bracket most elements of this fauna between 12,320 [+ or -] 110 to 11,770 [+ or -] 110 B.P. The invertebrates were derived from the open lacustrine and vertebrate-bearing marginal lacustrine deposits (Units I and II). The molluscan taxa are all extant gill-breathing gastropods and filter-feeding bivalves; they indicate fairly well-oxygenated, nutrient-rich waters with some current action. Modem counterparts live on vegetation in a variety of aquatic habitats. A nearly continuous record of the macroflora was recovered from the Pleistocene marginal lacustrine and Holocene bog sediments (Unit II and III).

Our data indicate that a pre-Twocreekan intermorainal lake developed at the site and that it was eventually infilled by clastic sediment during Twocreekan to early Holocene time. During the deposition of the Pleistocene Unit II (Fig. 2) a spruce-dominated forest existed in the area, supporting a diverse boreal vertebrate fauna. Two of the nine vertebrate species (Mammut americanum and Cervalces scotti) are presently extinct and three (Esox lucius, Perca flavescens, Rana sp.) have not been previously reported from Pleistocene sediments in Michigan (Holman et al. 1986). The transition to Holocene time is indicated by a bog-bottom radiocarbon date of 9,640 [+ or -] 120 B.P. and is marked by a shift to birch and then pine-dominated forest in the surrounding, better-drained highlands. Two Early Archaic projectile points, inferred to be over 9,000 years old (Fitting 1975; Shoshani et al. in press) were recovered from the upper levels of the bog sediments.

Thus, the multidisciplinary study summarized here provides the first detailed reference section of Huron-Saginaw lobe sediments in Michigan, that can be correlated with the substages of the Michigan lobe Twocreekan sediments of Wisconsin. The food web and the paleoecology of the associated fauna and flora are also an important contribution to the past history of the Great Lakes Region.

The 5 to 1 dominance in Michigan of mastodon (Mammut) fossils over mammoths (Mammuthus) was documented to have persisted over the entire period for which vertebrate fossil censuses have been published. It is postulated that the mastodon was, ecologically, a "generalist," better adapted to the diversity of habitats in Michigan. In contrast, the mammoth was more of a "specialist," ecologically. The open, more-or-less treeless habitats which it required were less frequent in Michigan, supporting relatively smaller populations of mammoths. The opposite circumstance applied in Nebraska where mammoths outnumbered mastodons approximately 8 to 1. In keeping with the generalist-specialist hypothesis, the specialized skeletal adaptations of mammoths to ecological niches in treeless or savanna biomes would be expected to lead to their dominance on the Nebraska plains.

APPENDIX A

An update on specimens of mastodons and mammoths in Michigan (latest report was that of Holman et al. 1986).

ORDER PROBOSCIDEA

FAMILY MAMMUTIDAE

Mammut americanum (Kerr) American mastodon

CALHOUN COUNTY

1. Heisler Site, near Springport, Clarence Township, SE 1/4, NE 1/4, NE 1/4 of Section 14, T 1 S, R 4 W. Age: 11,160 [+ or -] 110 B.P. on wood sample, and 10,740 [+ or -] 300 B.P. on "sediment sample." Material: cranium (with one tusk, the other broken), mandible, about half of the vertebral column and associated ribs or parts of them, portion of pelvis, a few long bones, and some footbones. Collected by Jim and Lester Heisler and J. .A. Holman, November 1984. The bones are presently at the University of Michigan (Ann Arbor). Remarks: this material was reported by Holman et al. (1986: 456-7) under "Proboscidea indeterminate." Literature: Holman et al. (1986), Bearss and Kapp (1987), D. C. Fisher (pers. comm.), R. O. Kapp (pers. comm.).

GENESEE COUNTY

1. Johnson Site, Richfield Township, Section 9, T 7 N, R 8 E. Age: 12,500 [+ or -] 500 B.P. Material: scapula, about 15 vertebrae and some associated ribs or parts of them, part of the sternum, humerus, two radii, two ulnae, one femur, patella, and some phalanges. Collected by C. Paulsen, G. R. Smith, D. C. Fisher and party, October 1979 and May 1980, and presently kept at Mott Community College, Flint. Remarks: Holman et al. (1986:447) reported about the material at the Sloan Museum belonging to one individual M. americanum. According to C. H. Wilson, one stylohyoid bone belongs to a second individual mastodon which was excavated "300 feet from the other animal," the other two stylohyoidea belong to the mastodon reported by Holman et al. (1986). All three stylonhyoid bones were studied by Shoshani (in press) and are now at the Museum of Paleontology, University of Michigan, Department of Paleontology. Literature: Holman et al. (1986), C. H. Wilson (pers. comm.), D.C. Fisher (pers. comm.).

KENT COUNTY

1. Smith Site, Grandville Township, Section 18, T 6 N, R 12 W. Age: 11,320 [+ or -] 140 B.P. based on maxillary bone fragment, and 10,920 [+ or -] 190 B.P. based on tusk cementum material. Material: cranium, two tusks, approximately two thirds of the vertebral column and associated ribs or parts of them. Discovered October 3, 1985, at a home construction site on the property of Mark and Debbie Smith in Grandville. A team headed by R. Flanders from Grand Valley State University in Allendale has excavated the bones and is now holding them. Remarks: bones were discovered "in a pile of clay"; also found with this material are "a number of seashells." Literature: Detroit News, October 5, 1985; Detroit News, February 14, 1985; R. Flanders (pers. comm.).

MONTCALM COUNTY

1. Eldridge Site, Crystal Township, Section 17 T 10 N, R 5 W. Age: possibly late Pleistocene. Material: cranium, mandible, about two thirds of the vertebral column, three fourths of the ribs, scapula, pelvis, and most of the long bones. Discovered June 9, 1986, by R. Rutherford (of Patterson Construction Co., Crystal) while excavating a trench with a backhoe in the field owned by Walter and Ida Eldridge. S. Beld, R. Bowker, D.C. Fisher, J. A. Holman, and R. O. Kapp joined the excavating team. Skeletal material is presently at the University of Michigan (Ann Arbor) for studies. Remarks: a burial bog; D. C. Fisher believes this specimen is a female. Sediment samples were collected by R. O. Kapp for pollen study. Literature: Daily News (the newspaper of Greenville, Belding & Montcalm County) June 10, 1986; Daily News, July 2,1986; J. A. Holman (pers. comm.), D. C. Fisher (pers. comm.). R. 0. Kapp et al., in press.

OAKLAND COUNTY

1. Mosher Site, Oxford Township, SW 1/4, NW 1/4 of Section 18, T 5 N, R 10 E. Age: Possibly late Pleistocene. Material: fourth [+ or -] 1 right rib, collected about 1980 by Marlin E. Marshall on Wayne Mosher farm on Baldwin Road across from "Rainbow Acres." Remarks: a pond/marsh with much peat deposit on site, many Indian arrowheads and other artifacts found in the vicinity; this site is about 5.5 km from the Shelton Site (see below). This rib is currently in the possession of J. and S. Shoshani (it will eventually be donated to Cranbrook Institute of Science). Literature: M. E. Marshall (pers.comm.).

2. Shelton Site, Brandon Township, SE 1/4 of SE 1/4 of Section 26, T 5 N, RE 9. Age: from 12,320 [+ or -] 110 to 10,020 [+ or -] 80 B.P., based on wood and bone samples associated with the bone-bearing layer. Material: a tusk. Remarks: five field seasons (1983-1987) were conducted at this site under the sponsorship of Cranbrook Institute of Science (CIS), Oakland Community College (Highland Lakes Campus), and Wayne State University. Of the two tusks (reported by Holman et al. 1986:451), the larger fits well into the only alveolus on the cranium of the subadult mastodon (the left alveolus is filled with osseous material). The small tusk (discovered in 1983) may be part of a larger tusk, or it may be of a juvenile Mammuthus but until definite Mammuthus material is found on this site, we shall refer to these elements as belonging to a juvenile Mammut. The skeletal elements of the subadult M. americanum from this site were reported by Shoshani (1986) and Holman et al. (1986:451). All material collected at the She lton Site will eventually be deposited at CIS. Literature: Holman et al. (1986), Shoshani et al. 1989, and this paper.

WAYNE COUNTY

1. Near or on Belle Isle, City of Detroit, T 2 S, R 12 E. Age: possibly late Pleistocene. Material: left radius of an adult individual, retrieved by David J. Lowrie from the old Bath House, Detroit, about 1968, and presently held at the Geology Department, Wayne State University. Remarks: "local people said that there were many bones at the Bath House, including a skull; all were well preserved" (Lowrie, pets. comm.). The only known remaining specimen was presented to D. Lowrie. It is possible that these bones originated from the Natural History Museum in the old Detroit City County Building which was torn down in 1961 (Fabbri-Tucker, pets. comm.). Literature: D.J. Lowrie (pets. comm.), L. Fabbri-Tucker (pets. comm.).

FAMILY ELEPHANTIDAE

Mammuthus sp. Burnett, 1830, a mammoth

Species identification is not given here because the material reported is either fragmentary or cannot be absolutely relegated to a particular Mammuthus species. There are two possible species occurrences of Mammuthus species in Michigan, namely, M. primigenius and M. columbi. The Jefferson mammoth (M. jeffersoni) is, according to Maglio (1973, 63), a synonym of the Columbian mammoth (M. columbi).

WASHTENAW COUNTY

1. Near Pleasant Lake Drain, Sharon Township, Section 26, T 3 S, R 3 E. Age: possible late Pleistocene. Material: a tooth fragment measuring 15 cm long, 8 cm wide, and 10 cm high, collected just off Peckins Road between Chelsea and Manchester, about 1975, and currently in the possession of Lawrence Engler (1529 S. Sashabaw, Ortonville, Michigan). Remarks: "plowed in muck soil about 9 inches deep and marl underneath." Literature: L. Engler and J. S. Crimes (pers. comm.).

Summary for Appendix A

Holman et al. (1986) bring the total of Mammut and Mammuthus specimens found in Michigan to 212 and 46, respectively; this report updates the totals to 219 and 47. There are still four "Proboscidea Indeterminate" specimens awaiting identification (see Holman et al. 1986, 456-7). In addition, the material excavated from the Johnson Site (listed under Genesee County in Holman et al. 1986,447, and in this report) needs to be examined in detail, for it may include additional individual proboscideans (pers. observations; D. C. Fisher, pers. comm.; C. H. Wilson, pers. comm.).

TABLE 1

Numbers of Mastodons (Mammut) and Mammoths (Mammuthus) Remains Found in
Michigan (A), Nebraska (B), Illinois (C), and Florida (D). Ratios Were
Rounded to the Nearest Tenths.

    Source               Mastodons  Mammoths  Ratio

A.  MICHIGAN
    Hay, 1923                27         7      4:1
    MacAlpin, 1938          117         -       -
    Skeels, 1962            166        32      5:1
    Wilson, 1967            170        36      5:1
    Holman et al., 1986     212        46      5:1
    This Study, 1988        219        47      5:1
B.  NEBRASKA
    Hay, 1923                 6        35      1:6
    Schultz, 1934            21       154      1:8
    This Study, 1988         49       408      1:8
C.  ILLINOIS
    Hay, 1923                27        26      1:1
    This Study, 1988         48        45      1:1
D.  FLORIDA
    Hay, 1923                20        30      1:1
    This Study              249       290      1:1

ACKNOWLEDGMENTS

I am greatly indebted to the owner of the SMS, Mr. K. Harold Shelton, for his limitless cooperation. I also thank the sponsoring institutions: Cranbrook Institute of Science, Oakland Community College (Highland Lakes Campus), and Wayne State University. Special thanks to J. M. Zawiskie and S. J. Thurlow for their invaluable help with the stratigraphy and the molluscan studies, respectively. The list of people who helped us in many ways is very long; I wish to single out the following individuals: W. S. Benninghoff, H. P. Davis, J. F. Eisenberg, J. P. Dudley, L. Fabbri-Tucker, W. R. Farrand, D. C. Fisher, R, Flanders, R. and J. Grimes, R. W. Graham, G. L. Grosscup, J. A. Holman, R. O. Kapp, D. J. Lowrie, L. S. Luckinbill, M. E. Marshall, A. V. Morgan, G. Morgan, J. L. Pierce, A. R. Pilling, J. J. Saunders, S. L. Shoshani, R. M. Smith, W. L. Thompson, M. R. Voorhies, C. H. Wilson, and F. H. Zoch. (A complete acknowledgment will appear in Shoshani et al., in press.)

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