Recent Discoveries of Fossil Vertebrates in the Lower Peninsula of Michigan

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Editor's Comments. J. A. Holman is presently Curator Emeritus of Vertebrate Paleontology at the Michigan State University Museum and Daniel O. Fisher is a professor and curator of paleontology in the University of Michigan Museum of Paleontology. This paper (produced because of the encouragement of Ronald O. Kapp) provided an update on records of mastodont and mammoth localities (as well as other Pleistocene vertebrates) and, in doing so, posed several questions, including (1) Why were proboscidean sites in the state so abundant for such a short period of time (12,000 to 10,000 years ago), while other vertebrates were apparently so uncommon? (2) Why did the proboscideans and other mammals become extinct so suddenly? and (3) What was the impact of human hunters on the flora and fauna of Michigan. The "Human Interaction" section in the paper introduced some of D. Fisher's evidence for the butchery of mastodonts by human hunters in Michigan. Fisher soon provided other valuable information about the taphonomy and biology of mastodonts, as well as their human interactions, in a flurry of publications in other journals.

Since the last detailed publication on the Pleistocene vertebrates of Michigan (Wilson 1967), much new information has accumulated: new sites have been found; ranges have been extended; C-14 dates have been obtained; vertebrates have for the first time been identified from a Wisconsinan interstadial interval; and butchering of extinct proboscideans by humans has been demonstrated at several localities. Thus, we believe that the time has come to consolidate this new information in a single location.

Several modern workers have gone beyond the stage of merely salvaging fossil vertebrates, and several of these works are cited here. Nevertheless, compelling problems are still with us such as (1) why proboscidean sites are so abundant from such a short period of time (12,000-10,000 years before the present [hereafter B.P.]), while other vertebrates were apparently so uncommon; (2) why the proboscideans and other large mammals became so suddenly extinct; and (3) what was the impact of the Paleo-Indian population on the flora and fauna of Michigan. We hope that this paper will stimulate additional interest in Michigan Pleistocene vertebrates so that some of these problems may be solved. The following two sections, Paleoecology and Human Interactions, are discussions growing out of consideration of the new records in the Systematic Paleontology section.

PALEOECOLOGY

This section deals with considerations of taphonomy and faunal diversity (Holman) and with the late Pleistocene vegetation and climate (Kapp).

Taphonomy and faunal diversity. -- Seventy-four new records of Michigan late Pleistocene vertebrates are assembled in the Systematic Paleontology section of this paper, superseding the summary of Wilson (1967). A large number of the new records of Michigan late Pleistocene vertebrates are proboscideans (57 of 74 = 77.0%); and in cases where such information was recorded, most of these huge animals came from kettle-like depressions, very often associated with muck or peat deposits. It has previously been assumed (Holman 1975) that these animals became trapped and drowned in these features.

Of the 52 proboscideans that were identified to the specific level 42 (80.8%) were mastodonts, and 10 (19.2%) were mammoths. Other vertebrates reported here include two fishes, one amphibian, one bird, two giant beavers, one muskrat, two meadow voles, one black bear, one peccary, one moose, two Scott's moose, and two whitetailed deer. In a Michigan late Pleistocene vertebrate site, it is usual to find one large animal, sometimes associated with the remains of another species or two. Holman has searched very carefully for microvertebrate remains at many of these sites, and only in one case (Adams Site in Livingston County) has he found small vertebrate remains, representing two fishes and one meadow vole.

Thus one of the unsolved taphonomic questions relating to the late Pleistocene of Michigan is why faunal diversity is so low at these sites. It was suggested to Holman by the late C. W. Hibbard that the reason the smaller animals are not trapped in Michigan bog burials is because these creatures were light enough to run across the tops of the ancient bogs. Data from bog sites in Ohio and Indiana do not bear this out. The Clark Bog site in Darke County, Ohio (about 11,000 B.P.) yielded nine fishes, two turtles, seven birds, and 17 mammals (C. J. Chantell in litt. 8 February 1985, and J. A. Holman 1986); and the Christensen Bog Site in Hancock County, Indiana (about 13,000 B.P.) yielded one frog, three turtles, two birds, and eight mammals (Graham et al. 1983).

Late Pleistocene vegetation and climate. -- The last major continental glaciation, the Wisconsinan, involved several glacial advances separated by ice-free interstadial intervals. At the maximum extent, the glacial lobes completely covered Michigan and expanded into south central Indiana and southwestern Ohio. Pollen analytical evidence indicates that the vegetation of the interstadials was of the boreal forest or forest-tundra type and suggests that the climate was of a glacial character. In two instances vertebrate remains have been recovered from deposits from the Plum Point interstadial interval, bracketed by radiocarbon dates of 32,000-24,000 B.P. in Ontario where such deposits are more extensive and have been studied in detail (Dreimanis 1964).

Recovery, during well drilling, of wood fragments of spruce (Picea) and tamarack (Larix), together with a bone of the Lesser scaup (Aythya affinis), from beneath 17m of glacial overburden gives evidence of the ice-free conditions in Muskegon County at 25,050 [+ or -] 700 B.P. Kapp (1978) concluded that "the regional vegetation was apparently a coniferous forest dominated by spruce and pine, the latter probably Pinus banksiana which had migrated into Michigan during the long ice-free interval."

Evidently Midland County was also deglaciated during the Plum Point interstadial, because mandible fragments and teeth of a Jefferson mammoth were discovered near Coleman and were dated at 24,000 [+ or -] 4000 B.P. (Kapp 1970). These remains were found in stream gravels and no associated macrofossil remains or microfossil-rich sediments were found from which paleoecological inferences might be derived. To date all evidence indicates that the mid-Wisconsinan interstadials in the Great Lakes region were characterized by a glacial climate. Pollen records from such deposits are dominated by conifer pollen, commonly with abundant spruce and pine (to 70%), and herbaceous pollen, including sedges. Some climatic amelioration is suggested by presence of thermophilous deciduous species (Kapp 1977), especially in Ontario. Of the large, extinct, Pleistocene vertebrates at least the mammoth occupied Michigan during the Plum Point interstadial.

The Wisconsinan late-glacial interval is defined as the period following final glacial retreat which was characterized by glacial climate. The ice sheets began to shrink from southern Ohio and Indiana after 16,000 B.P., and several counties (Cass, St. Joseph, Branch, Hillsdale, Kalamazoo, Calhoun, and Jackson) in south central Michigan were completely or partially deglaciated by 14,800 B.P. (Farrand and Eschman 1974). By 13,800 B.P. approximately one-half of the land surface of the lower peninsula was deglaciated with the hilly topography of the areas between the major glacial lobes already exposed. It is primarily in such regions of recessional moraines, closed depressions, and poor drainage that most vertebrate fossils have been recovered. Approximately one-half of the new vertebrate localities reported in this report (Figure 1) were found in the interlobate morainal belt between the Saginaw and Erie glacial lobes (Washtenaw, Ingham, Livingston, Oakland, Genesee, Lapeer, and Sanilac Counties). Commonly the remains were recovered during trenching for installation of tile lines to drain shallow depressions on agricultural land. In other instances ponds, marshes, bogs, or fens were being excavated in order to create larger ponds with open water. The sediments associated with the vertebrate fossils usually reveal that marl accumulated for a period after deglaciation, probably stimulated by influx of carbonate-rich groundwater from recently deposited glacial till. In many instances peat (sedge and/or Sphagnum type) accumulated subsequently, producing an organic-rich muck when tilled.

A review and summarization of pollen analytical studies is presented in order to determine, on a regional and time-trangressive basis, the type of vegetation associated with the fossil vertebrate fauna. These data are presented in simplified form in Tables 1 and 2. In each instance pollen studies were completed on sediments in direct association with the vertebrate fossils or from stratigraphic units which were equivalent or somewhat younger in age. The pollen reports have been tabulated in simplified form by grouping ecologically similar types (spruce/fir: boreal, pine:north temperate, deciduous:temperate, non-tree:open landscape). More detailed palynological reports are available for many of the specimens (1 Thaller: Held and Kapp 1969; 2, 3, and B Pitt, Smith and Flint: Oltz and Kapp 1963; 5 Pontiac: Stoutmire and Benninghoff 1964; 10 Wells: Gooding and Ogden 1965; 11 Christensen: Whitehead et al. 1982; 12 Orleton Farms: Sears and Clisby 1952; Thomas 1952; 13 Pontius Farms: Ogden and Hay 1967; E Coville Farm: Benninghoff and Hibbard 1961). In other instances manuscript reports which are in preparation have been consulted (4 Rappuhn: Kapp; 8 Powers: Garland and Cogswell 1985; 9 Kolarik: Jackson et al. 1986). In addition, palynological results are reported from several additional sites, some very recently discovered (6 Sheathelm, 7 Heisler, A Henry, C Mead, C Harper); detailed pollen spectra from these deposits are presented in Table 3.

[FIGURE 1 OMITTED]

Except at the Pitt mastodont site, the pollen spectra associated with mastodonts in Michigan, Indiana, and Ohio all contain at least 40% spruce and fir pollen. This clearly represents a boreal forest or forest/tundra type of environment, with these northern forest types present in the region near the depositional site. At sites with lower frequencies of spruce/fir pollen, the other dominant pollen type is usually pine (e.g., Pitt, Smith, Orleton Farms); these probably are from the period of declining spruce pollen, with concomitant increase in pine, which typifies the end of the late-glacial in pollen diagrams from the Great Lakes region. Three sites (Rappuhn, Sheathelm, Heisler) have significant quantities of deciduous tree pollen. The deciduous types are primarily in the suite of cold-tolerant species which characterize the end of the late-glacial and early postglacial in regional pollen diagrams: black ash (Fraxinus nigra), birch (Betula), ironwood or blue beech (Ostrya/Carpinus), and oak (Quercus) (see Table 3). In three records (Pontiac, Wells, and Christensen mastodonts and, most notably, Henry mammoth), the non-tree pollen frequencies are very high; this indicates an open vegetation of the forest/tundra type or extensive open sedge marsh. The Henry mammoth site, located only a short distance from the Lake Huron shores, seems to record an expanse of nonforested wetland.

In summary, the pollen data associated with all of the mastodont, mammoth, and musk ox sites reveal that the contemporaneous vegetation was most like that of modern areas considerably north of southern Michigan, Indiana, and Ohio localities. Coniferous forests, …