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The mastodons and mammoths of Michigan.

Editor's Comments. Margaret (Skeels) Stevens produced this paper while a student at the University of Michigan. She was a productive scholar and teacher at Lamar University in Beaumont, Texas, before her recent retirement. This is the seminal paper on the mastodonts and mammoths of Michigan. It not only details the known records of these animals in the state, but discusses aspects of their taphonomy (mode of death, burial, and fossilization) and biology. The idea that Skeels put forth--that the deep muck and peat and floating mats of vegetation ("quaking bogs") in the late Pleistocene were natural traps that these heavy animals would have broken through--is still accepted as primary taphonomic event involved in the fossilization of these proboscideans. The fact most fossil proboscideans in Michigan have been excavated from former shallow basins of kettle bog sites attests to this hypothesis.

Nevertheless, the fact that these animals are almost always found as scattered parts rather than whole skeletons indicates that other taphonomic events occurred. Several of these have been addressed by Daniel C. Fisher of the University of Michigan (e.g., Fisher 1984a,b). It is quite possible that the animals merely become stuck, rather than completely buried in bogs. Here they could have died of starvation and been scavenged by humans (see Barondes' 1996 report on the St. Johns, Michigan mastodont excavated by Daniel Fisher and Fisher 1987); or weakened ones could have been killed by human hunters. Then the animals could have been butchered at the site, the edible portions carried away, and the remaining parts discarded in the boggy areas in which they were found. There, fossilization would have occurred.

The lack of smaller vertebrate fossils from proboscidean sites in Michigan was attributed by Skeels to the possibilities that, because of their smaller size, their remains might have been overlooked, considered recent intrusions, or because they look "... very much like pieces of branches or roots that are sometimes present in muck or peat." Since Skeels (1962) many sites have been carefully excavated by professional vertebrate paleontologists, and there is still no question that small vertebrates are exceedingly rare at these localities. I suggest that at least one part of the problem is due to the fact that the highly fibrous plant matrix in which Michigan proboscideans are found is almost impossible to dissociate, thus standard wet-screening methods do not work; and that another part of the problem may be do to the erosion and eventual loss of small vertebrate bones due to the highly acidic conditions of bogs and bog remnants. Most of the C14 dates in this paper are too young.

INTRODUCTION

Fossil mammals are known only from the Late Pleistocene of Michigan. If earlier Cenozoic deposits ever were present in Michigan they were destroyed by glacial ice that four times overrode the state. The American mastodon and Jefferson mammoth were the largest Pleistocene animals to walk on Michigan soil. Most of the information concerning these large mammals in the state must be sought in newspaper reports of individual finds. However, O.P. Hay (1923) reported upon all Michigan Pleistocene mastodon and mammoth remains known to him. Case and others (1935) reported the occurrences of the Jefferson mammoth from Glacial Lake Mogodore in Cass County. Later in the same year, Case and Stanley (1935) reported on the Bloomfield Hills mastodon. Archie MacAlpin (1940) summarized all known finds of the American mastodon in Michigan but did not publish on the mammoths. The purpose of this paper is to place on record all known occurrences of both the American mastodon and Jefferson mammoth in the state, including those discovered since 1940, and to make available to the citizens of Michigan an account of these interesting mammals.

Most of the fossil remains of these animals found in the state have occurred in swamps and bogs. Such areas owe their origin to the manner in which the last glacier melted; the majority of the lake depressions were formed at the time of the retreat of the last ice sheet. As the ice front retreated large blocks of ice were left behind, buried under the glacial outwash sediments. For a time such ice blocks were protected from the warmth of the sun by the gravel, sand, and silt that covered them. Eventually, however, these ice remnants melted, leaving depressions in their place. Although most of these were of small size, others were quite large. Geologists refer to the smaller ones as kettles or kettle holes. If silt or clay washed into these depressions it sealed them, and water would then accumulate to form a pond or lake. In most cases such depressions contained water only in the spring, but if they went below the water table a permanent pond or lake resulted. Over the years such ponds and lakes continued to receive sand, silt, and clay from flood waters, and additional material from vegetation growing around their edges. In time at least some of these bodies of water, particularly the shallower ones, became filled to levels where aquatic and semiaquatic vegetation could encroach upon the open water. Thus a bog was formed where an open pond or lake had once existed. Wherever water was shallow, plant material extended down through the water to the bottom, but where the water deepened the vegetation often formed a mat that floated over part of the water surface. Partially or completely filled depressions of this sort exist in Michigan today and are called "quaking bogs." The process of filling, however, is one that still continues and depressions in all stages can be found in the state. Floating mats of the nature described are unsafe; a heavy animal venturing too far out on one often breaks through. Many times such an animal is unable to climb back onto the mat, becomes mired, and eventually drowns. These bogs apparently were places of retreat for mastodons and some mammoths during the winter months. They would have been protected from strong winds, and the surrounding forest would have offered abundant food. But the deep muck and peat and the floating mats of vegetation, though partly frozen, were potential traps.

Most mastodon remains in southern Michigan are associated with muck, peat, and marl. Chances for preservation are good in bogs because there is immediate burial. The body of an animal that dies on high ground is seldom preserved because predators and scavengers scatter the bones. Such exposed bone usually becomes decayed or badly weathered before it can be carried downslope to a lake or stream to be preserved in the sediments deposited there. Bone that comes from a bog is usually very dark colored, dark brown or black, due to the acids produced by the decaying organic matter.

Because of their larger size, mastodons are the most commonly found mammalian fossils in Pleistocene deposits in Michigan Smaller animals such as elk, deer, wolves, and beavers are probably much more abundant in bog deposits, but because of their smaller size their remains may be overlooked or considered those of recent forms. Moreover, these smaller bones often look very much like the pieces of branches or roots that are sometimes present in the muck or peat. Recovery of the smaller Pleistocene mammals of Michigan would do much to increase our understanding of these Ice Age forms.

THE AMERICAN MASTODON

The ancestors of the American mastodon reached North America from Eurasia via the Bering land bridge during Miocene time, approximately 18 million years ago. These early proboscideans (animals with a trunk) were subtropical forms, not the cold-loving animals that some of their descendants became. During the Ice Age (Pleistocene) the American mastodon gradually became adjusted to cooler conditions, so that by the time of the last of the four glaciations they were well adjusted to life in cold northern (boreal) forests.

Fossil remains indicate that only two species of the Proboscidea lived in Michigan during the Late Pleistocene. These were the American mastodon (Mammut americanum) and the Jefferson mammoth (Mammuthus jeffersoni). These two forms are usually known, collectively, as "mastodons" or "elephants" to the uninformed person. In reality they represent two very different types of animals. The similarities between them are large size, columnar (graviportal or pillar-like) limbs, a proboscis (trunk), and large tusks (specialized incisor teeth). Important differences occur in skull shape and tooth structure, as explained below. Moreover, they lived in quite different habitats.

It is rather unfortunate that the two generic names, Mammut and Mammuthus, are so similar. Both words stem from the barbaric word mammut, which means "earth-burrower" (Lucas 1935, 157). The term is believed to have originated during the Middle Ages when the Eastern European farmers assumed that these beasts were large burrowing monsters because their bones were commonly found buried in the soil. The peasants had never seen a living elephant.

Cuvier's term Mastodon has frequently been used as a generic name for the American mastodon, and "Mastodon americanus" is still used in a loose sense today because it is so prevalent in the literature (Jepsen 1960). However, Blumenbach's (1799) name Mammut is the earlier and accepted generic name.

Following is the classification of the Late Pleistocene mastodon of Michigan.

ORDER PROBOSCIDEA

FAMILY MAMMUTHIDAE

GENUS MAMMUT BLUMENBACH, 1799

Mammut americanum (Kerr). American mastodon

Mastodon giganteus Cuvier. Winchell, 1861, Geol. Surv. Mich., First Biennial Rept. (1860), p. 132.

Mammut americanum (Kerr). Hay, 1930, Carnegie Inst. Wash. Publ. 390, 2: 624.

Mastodon americanus (Kerr). MacAlpin, 1940, PMASAL, 25 (1939): 483.

The foregoing are synonymous names, names that have been used in past years for the American mastodon in Michigan.

Characters of Mammut americanum. -- The tusks are without enamel. The upper tusks are large and round with slightly indicated annular growth rings (Osborn 1936). The lower tusks, when present, are small, straight, and circular in cross section (Plate. II, Figure. 3), but they usually were lost by mature individuals. One specimen (UMMP 37811) in the University of Michigan Museum of Paleontology has the two lower tusks present one in each of the lower jaws. The maximum length of the left lower tusk is 241.0 mm; the maximum transverse diameter, at the base of the tooth, is 47.0 mm. The vertical diameter, at the base of the tooth, is 40.05 mm. The diameter at the tip, which is blunt and polished, is 27.0 mm. The depth of the alveolus (socket) is 170.5 mm. The tusks in mastodons are the upper and lower second incisors; the first and third incisors in each jaw failed to develop.

Tusks of the mastodon and the mammoth consist of ivory, which is a complex type of dentine. Dentine is not so hard as enamel and therefore does not lend itself as well to fossilization. Well-preserved tusks of mastodons or mammoths have not been found in Michigan. Tusks when found are usually very friable so that the layers of ivory split and break off in small pieces.

One of the differences between the American mastodon and the mammoth is the way the tusks leave the skull. In the mastodon they project more or less horizontally from the skull, curving at first outward and later inward (Plate I, Figure 2) in the course of growth, whereas in the mammoth the tusks leave the skull more nearly vertically, curve downward and outward, then begin the curve that brings their tips inward toward each other (Plate I, Figure 1).

[FIGURE 1 OMITTED]

The size of the tusks in both mastodons and mammoths differs between the sexes. The male individuals of both species possessed heavier, larger, and longer tusks.

Mastodons apparently used their tusks to pry off and possibly to break into small pieces the branches upon which they fed, in much the same way that the living African elephant will rip a limb from a tree, stand on it with both feet, and break it in half with one of its tusks. Only one tusk is used in this operation, never both. Elephants and mastodons were thus "right" or "left handed." When both of the tusks are recovered with the skull of a mastodon, one of them is usually shorter than the other and shows breakage and polish at the tip (Plate I, Figure 2). This has often been overlooked in mounted specimens; tusks have frequently been restored equal in length.

The cheek teeth of the American mastodon consist of six on each side of each jaw. The first three teeth of the six are known as milk or deciduous premolars and the last or hinder three as permanent molars. The individual teeth, exclusive of the tusks (incisors), are designated in the upper jaw as D[p.sup.2], D[p.sup.3], D[p.sup.4], [M.sup.1], [M.sup.2], and [M.sup.3]. The symbol "Dp" stands for deciduous premolar and "M" for permanent molar. The lower individual teeth are designated as D[p.sub.2], D[p.sub.3], D[p.sub.4], [M.sub.1], [M.sub.2], and [M.sub.3]. In a reference to both the upper and lower last molar, for example, the symbol would be written as [M.sub.3.sup.3]. In the American mastodon D[p.sub.4.sup.4], M 1/1, and [M.sub.2.sup.2] each consist of three transverse ridge crests, or lophs, which are formed by two cusps. [M.sub.3.sup.3] has four lophs and a vestigial heel behind the last ridge crest (Figure 1B; Plate II, Figures 1 and 2). In some individuals, there are five lophs across the third molar. Cuvier's term, mastodon, refers to the nature of these cusps. The word when broken down into its Greek roots means "nipple tooth" (Palmer 1904, 401).

The teeth increase in size from the fourth premolar to the last molar. The size of each tooth varies somewhat in different individuals, as well as in the same individual. See Table 1 for measurements of American mastodon teeth in the University of Michigan Museum of Paleontology.

There is no juvenile specimen in the University of Michigan Museum collection. The remains of young mastodons probably are overlooked because of their small size. The recovery of these would contribute greatly to our knowledge of milk teeth and tooth replacement.

A young adult, UMMP 29276, had the fourth upper right premolar in use at the time of death. This tooth is well worn, and the first upper molar shows wear on the anterior pair of cusps. The second molar ([M.sup.2]) had not moved down to the level of the grinding surface of the first upper molar. The crown of the third upper molar ([M.sup.3]) is fully developed, though it had not erupted.

In specimen UMMP 11308, the upper dentition of a young male, the fourth upper premolar had been shed and the first molar had moved forward in the jaw and taken its place. This tooth is well worn. The second molar is worn on its anterior cusps and the third had not moved into occlusal position (contact with opposite tooth). Specimen UMMP 24240 has the second upper molar well worn. The third molar is in occlusal position and shows wear. Mastodons apparently had reached maturity by the time the second and third molars were in use. The University of Michigan Museum of Paleontology has no specimen in which only the third molar was present, although this condition did occur in aged animals (Hay 1914).

Tooth replacement in mastodons continued throughout much of their life. In the majority of mammals milk teeth are pushed out by the upward or downward growth of the permanent teeth that lie at their roots. In the Proboscideans and Sirenians (Manatees and Dugongs) the permanent teeth are formed in the back part of the jaw behind the milk teeth. As the milk teeth are worn down, their replacements have to move forward and upward in the lower jaws and forward and downward in the upper jaws.

Mastodons were neither as large nor as tall as mammoths in overall body size, but the mastodon skull was larger and lacked the high occipital crest so prominent in mammoth skulls (Plate I, Figure 1). The mounted female mastodon in the University of Michigan Museum of Paleontology measures approximately 7 feet, 8 inches tall at the shoulders (Plate I, Figure 2). Adult males are taller.

Habitat and food. -- Mammut americanum was a forest animal, browsing on the forest vegetation along bogs and streams (Hibbard 1951). In the early days before scientific investigation, however, people who found mastodon teeth thought them to have belonged to some large flesh-eating monster (Jepsen 1960). Benjamin Franklin, who was one of the first to study such teeth systematically, concluded that it would have been impossible for the American mastodon to have eaten meat.

The following quotations are taken from Warren (1852), who mentions three accounts of mastodon finds associated with materials which were probably stomach contents.
 Near Newburgh, in the State of New York, an American mastodon was
 discovered in 1845. During the excavation of this animal, a mass of
 material resembling crushed branches of trees was discovered.


According to Warren, a medical doctor, this material received little attention at the time. Another man, Dr. Prime, was present at the time of excavation and described the mass as follows:
 In the midst of the ribs, imbedded in the marl and unmixed with shells
 or carbonate of lime, was a mass of matter, composed principally of
 twigs of trees broken into pieces of about two inches in length, and
 varying in size from very small twigs to half an inch in diameter.
 There was mixed with these a large quantity of finer vegetable
 substance, like finely divided leaves; the whole amounting to from
 four to six bushels. From the appearance of this, and its situation
 (position in the skeleton), it was supposed to be the contents of the
 stomach; and this opinion was confirmed on removing the pelvis,
 underneath which, in the direction of the last of the intestines, was
 a train of the same material, about three feet in length and four
 inches in diameter. Microscopic examination of this matter revealed
 that the twigs were terminal branches of coniferous trees.


Another mastodon from Chester, near Goshen, Orange County, New York, had been discovered with similar vegetable material. Professor Mitchell described it thus:
 Beneath the bones, and immediately around them, was a stratum of
 coarse vegetable stems and films resembling chopped straw, or rather
 drift stuff of the sea; for it seemed to be mixed with broken fibers
 of conferva, like those of the Atlantic shore.


[FIGURE 2 OMITTED]

The third occurrence reported was that of a mastodon from Wythe County, Virginia, that was found associated with "half-masticated reeds, twigs, and grass or leaves," according to Bishop Madison in a letter to Dr. V. S. Barton.

The preservation of masticated vegetable matter from the stomach should not be regarded as improbable because the finds are associated with peat. Peat is an accumulation of vegetable material that has been subjected to compaction for a very long period of time in bogs. It is often well preserved, even to the extent that pollen grains occurring within it can be examined and the genera of plants determined. Peat deposits consist mostly of fine organic materials. Branches of trees are not uncommon in such deposits, but these would never be "broken into pieces of about two inches in length."

Location of finds of mastodon remains in Michigan. -- MacAlpin (1940) listed 114 specimens of the American mastodon that had been found in Michigan. He concluded that these represented considerably fewer than half of those collected in the state since 1839. Forty-nine new discoveries have since been reported. All of the recorded occurrences within the state are shown in Figure 2. Following is a list of the new records since 1939, obtained from newspaper articles, letters, and museum specimens.

ALLEGAN COUNTY

1. Plainwell, 4 1/2 miles northeast. Gunplains Township, Sec. 10, T.1 N., R.11 W. Most of a skeleton, lower jaw with teeth, many vertebrae, no skull, fragments of ribs, sacrum, foot bones, etc., found at a depth of 5 1/2 feet in marl.

2. South Haven, just north. Caseo Township, Sec. 32 T. 1 N., R.16 W. Lower jaws, at a depth of 6 feet in marl.

BERRIEN COUNTY

1. Watervliet, NW 1/4 NE 1/4, Sec. 1, T.3 S., R.17 W. One skull, UMMP 24240. Donated to the University of Michigan by Mrs. Beulah King and Mrs. Elizebeth Acton.

2. Hager Township, SE 1/4 NE 1/4, Sec. 22, T.3 S., R.18 W. Skull fragment with four teeth, UMMP 26865. Gift of Mr. and Mrs. William Walsh McNeill.

3. On the farm of Rudy Adams. Third molar, in marl around 1912.

CALHOUN COUNTY

1. Along Rice Creek. One tooth, found around 1834 or 1835. Specimen at the Grand Rapids Public Museum, No. 12359.

CLINTON COUNTY

1. St. Johns, on Avery Road. One tooth.

GENESEE COUNTY

1. Flushing, W 1/2 W 1/2 of NE 1/4, Sec. 24, T.8 N., R.5 E. One tooth and possibly other bones, UMMP 23606. Gift of J. R. Roberts.

2. Flint, exact locality not known, but somewhere near Flint. Tooth fragment, in gravel.

3. Davison, exact locality not known. One molar.

4. Richfield Township, no other data. Scapula.

GRATIOT COUNTY

1. St. Louis, about 3 miles southeast. T.2 W., R.11 N. One tooth, in muck on gravel.

2. Alma, Sec. 17 T.11 N., R.2 E. Skull parts, tooth fragments, axis, three dorsal vertebrae, ribs, and part of pelvis. Specimen at Alma College.

3. Ithaca, north of E 1/2 SW 1/4, Sec. 5, T.11 N., R.2 W. Part of a skeleton.

HILLSDALE COUNTY

1. Near Hemlock Lake, Sec. 5, T. 7 S., R.4 W. Vertebrae, UMMP 38622, found in marl while digging a boat canal to Hemlock Lake. Donated by Mr. and Mrs. Herschel H. Hall.

INGHAM COUNTY

1. Fowlerville, west of. Exact locality not known. Bone scraps, found in sand 23 feet below the surface.

IONIA COUNTY

1. Mullikin, 2 miles west and 1 north. Lower jaw and most of the skeleton. Specimen at the Michigan State University Museum, No. 1130.

JACKSON COUNTY

1. Jackson, 6 miles northwest. Broken tusk. Michigan State University Museum 7745.

KALAMAZOO COUNTY

1. Near Battle Creek, 12 miles west, at the west end of Sherman Lake. Sec. 30 or 31, T.1 S., R.9 W. Fragment of jaw with two teeth, in a drainage canal.

2. Fort Custer Military Reservation, Sec. 1 or 2, T.2 S., R.9 W. Palatal part of skull with four cheek teeth, tusk, vertebrae, ribs, etc., in a drainage ditch to Eagle Lake. Skeleton at the Kingman Museum, Battle Creek.

KENT COUNTY

1. Bowen Township, northeastern part. Three lower molar teeth, in sand.

2. Exact locality unknown. Parts of a skeleton. Specimen at the Michigan State University Museum.

3. Exact locality unknown, but north of Grand Rapids. Humerus and a few carpals. Specimen at the Grand Rapids Public Museum.

LAPEER COUNTY

1. Near Lapeer, about 5 miles southeast, Sec. 14, T.7 N., R.10 E. Lower jaw with six cheek teeth and two small tusks, part of pelvis, sacrum, two scapulae, 17 vertebrae, about 20 ribs, foot bones, parts of radius, ulna, humerus, and femurs (UMMP 37811). A [C.sup.14] date was obtained from this specimen. The date is 5950 [+ or -] 300 years before the present (B.P.).

2. Clifford, 2 miles south. NE 1/4 SW 1/4 Sec. 21, T.10 N., R.11 E. Part of a lower jaw with one tooth.

LENAWEE COUNTY

1. Seneca Township, Sec. 5, T.8 S., R. 2E. Maxillary teeth, fourth premolar to third molar, and one tusk, UMMP 29276. A [C.sup.14] date of the inner part of the tusk (No. M-280) is 7,070 [+ or -] 240 B.P. Donated by J. M. Bruggeman.

2. Tecumseh, a few miles northeast. Sec. 18, T. 5 S., R. 5 E. One tooth, UMMP 26864, on the surface of a peat bog. Gift of Ralph Schafer.

LIVINGSTON COUNTY

1. Putnam Township, SW 1/4, Sec. 36, T. 1 N., R. 4 E. About three or four rods north of the Washtenaw-Livingston County line. Neural spine, UMMP 23499.

2. Near Fowlerville. Dorsal vertebrae, UMMP 25780.

MIDLAND COUNTY

1. Near the Midland County Club, Sec. 9, T.14 N., R.2 E. Part of the palate with second and third molars, UMMP 27730. Gift of Dan Smick.

MONTCALM COUNTY

1. Near Stanton, exact locality unknown. Broken humerus, UMMP 31054. Gift of Clifford Wright.

NEWAYGO COUNTY

1. Near Fremont, 6 miles northwest. Broken premolar, UMMP 24836, in gravel. Gift of Don Vander Werp.

OAKLAND COUNTY

1. Near Holly, Sec. 27 or 32, T.5 N., R.7 E. Four teeth and a jaw fragment.

OTTAWA COUNTY

1. Holland, at Big Creek, a few miles east of Holland. Jaw, teeth, ribs, long bones, and vertebrae.

SAGINAW COUNTY

1. Near Freeland. W 1/2, NW 1/4 Sec. 29, T. 13 N., R. 3 E. Broken jaw, two teeth, and part of pelvis, in marl.

2. Frankenmuth, 8 or 9 miles south. SW corner of Sec. 32, T.10 N., R.6 E. One tooth, in sandy loam.

3. Near St. Charles, locality not known. One molar tooth, UMMP 22271.

SANILAC COUNTY

1. Argyle, 2 miles north and 1 east. One rib, a long bone, and several foot bones, in a drainage ditch in marl.

2. Croswell, exact locality not known. One tooth, in a swamp.

SHIAWASSEE COUNTY

1. Henderson, Rush Township, Sec. 16, T. 6 N., R. 2 E. Part of skull and most of the skeleton, UMMP 23498, at a depth of 6 or 7 feet in marl.

2. Henderson, Rush Township, Sec. 16, T. 6 N., R. 2 E. Left ulna, 200 yards from No. 23498.

3. Corunna, New Haven Township. Sec. 24, T. 8S., R. 3 E. One-half tooth, in gravel.

4. Bryon, exact locality not known. Part of a tusk, in a drainage ditch.

VAN BUREN COUNTY

1. Near Hartford, 3 miles east and 1 mile south. Two teeth, Michigan State University Museum 5296, in a peat bog.

2. Almena Township, Sec. 33, T.2 S., R.13 W. Part of a tusk, in marl.

WASHTENAW COUNTY

1. Milan, Augusta Township, Sec. 29, T. 4 S., R. 7 E. Part of right ramus of lower jaw with six teeth, UMMP 34127, in a drainage ditch. Gift of Joseph S. Zabo.

2. Lodi Township, SW 1/4 SW 1/4, Sec. 17, T. 3 S., R. 5 E. One jaw, atlas, axis, and palate, UMMP 24241. Gift of Fred Grob, 1947.

3. Freedom Township, NE 1/4 Sec. 4, T. 3 S., R. 4 E. Fragment of tusk (M-67, [C.sup.14] dated), in Cary outwash gravels.

WAYNE COUNTY

1. Monguegon Township, NE 1/4 NE 1/2 Sec. 12. Base of skull, lower jaw, several teeth, one tusk in poor condition, scapula, humerus, ulna, foot bones, ribs, and vertebrae, UMMP 3483, in a county drainage ditch.

THE JEFFERSON MAMMOTH

The mammoth arrived in North America from Eurasia much later than the mastodon. The earliest records to date are from the early Middle Pleistocene (Kansan deposits). This ancestral stock probably gave rise to the Imperial mammoth and the Columbian mammoth (both southern forms) and the Jefferson mammoth (a more northern species). The well-known Woolly mammoth, a tundra dweller, arrived in North America much later in the Pleistocene.

Following is the classification of the Jefferson mammoth.

ORDER PROBOSCIDEA

FAMILY ELEPHANTIDAE

GENUS MAMMUTHUS BURNETT, 1830

Mammuthus jeffersoni (Osborn), Jefferson mammoth

Elephas primigenius Blumenbach. Hay, 1923, Carnegie Inst. Publ. 322, p. 137 (not of Blumenbach).

E. columbi Falconer. Hay, 1923, Carnegie Inst. Publ. 322, p. 151 (not of Falconer).

E. boreus Hay. Sherzer, 1927, Science, 65, No. 1695:616 (not of Hay).

E. primigenius americanus (DeKay). Case and others, 1935, PMASAL, 20, p. 449 (not of DeKay).

Parelephas jeffersonii (Osborn). Osborn, 1936, Proboscidea, V. 2, p. 1083.

A census of the remains of Mammuthus jeffersoni has not previously been reported for Michigan. Individual remains of this mammoth have in the past been identified as the "Woolly" mammoth (M. primigenius) or the Columbian mammoth (M. columbi). Hibbard (1951) only briefly mentioned M. jeffersoni as occurring in the state.

Characters of Mammuthus jeffersoni. -- The teeth of mammoths, as well as those of the living elephants to which the mammoths are related, consist of alternating cement, dentine, and enamel ridge plates (Figure 1A; Plate III, Figures 1 and 2). These plates are transverse to the long axis of the tooth. The number of ridge plates present in the tooth per 100 mm, the thickness of the enamel, and the distance of the enamel plates from one another are used to distinguish the different species. The premolars are smaller than the molars and hence possess fewer ridge plates. The third molar is the largest tooth and has the most plates; for the Jefferson mammoth, there are generally 25 in the upper and 24 in the lower (M3 25/24). The symbols denoting the position of the teeth are the same as those used to describe mastodon teeth. For mammoths and elephants, however, after the symbol designating the tooth appears a notation of the maximum number of ridge plates known for the upper and lower teeth. The number of ridge plates observed in the upper tooth is written above the line and the number in the lower tooth below the line.

Osborn (1936) gives the ridge plate formulae for Mammuthus jeffersoni as: Dp3 [8+]/?, Dp4 12/13, M1 11/?, M2 [18-19]/19, and M3 25/24. Seven to ten of these plates occur in the distance of 100 mm in the third molar (see Figure 1A).

Very few specimens of the Jefferson mammoth are in museum collections in Michigan. The few remains that have been collected in the state consist mostly of jaws with teeth or of isolated teeth. There are remains of 3 individuals in the Grand Rapids Public Museum, 7 in the Michigan State University Museum, and 9 in the University of Michigan Museum of Paleontology. The most complete specimen yet found in the state is represented by a partial skeleton (No. 8238) at the Michigan State University Museum. This mammoth was found approximately 10 miles southeast of Eaton Rapids on the Losey farm and consists of both lower jaws, one tusk, many vertebrae, most of the ribs, the shoulder blades, and a few leg bones. No skull or pelvis was found.

A lower jaw with two teeth, UMMP 22798, was found one mile north of Assyria, in Barry County. This jaw was donated to the University of Michigan Museum of Paleontology by Robert Hughes in 1942. It is from an old individual; the anterior ridge plates of the last molars ([M.sub.3]) are worn down to their roots. The greatest anteroposterior length of the left third molar (L[M.sub.3]) is 265.0 mm and the R[M.sub.3] is 255.0 mm. Both of these teeth have 18 ridge plates forming the occlusal surface. L[M.sub.3] has 7 1/2 ridge plates in 100 mm and R[M.sub.3] has 7. The maximum width of R[M.sub.3] is 109 mm, as taken across the eighth ridge plate, and the maximum width of L[M.sub.3] is 118.5 mm, as taken across the 10th ridge plate. The distance between the grinding surface of the two teeth anteriorly is 35.8 mm. The maximum width of the groove above the rostrum is 70 mm, and the rostrum projects 80.4 mm beyond the symphysis. The rostral groove between the jaws is constricted dorsally. The greatest width of the jaws is 648.0 mm and the length is 542.0 mm. The depth of the jaw, taken from the occlusal surface at the 13th ridge plate to the base, is 223.0 mm. The mandibular condyles are 437.0 mm above the base of the jaw.

Four associated teeth, UMMP 11735, a gift of George Wagner, were found near the Chapel Hill School in Cass County. These are the upper and lower third molars. L[M.sup.3] has 26 ridge plates, of which 18 make up the grinding surface. In 100 mm there are 9 plates. R[M.sup.3] consists of 26+ plates, with 18 making up the occlusal surface and 10 occurring within 100 mm. L[M.sub.3] consists of 25 plates plus one which has broken off. The occlusal surface consists of 16 plates and there are 7 1/2 plates in 100 mm. R[M.sub.3] has 26 ridge plates, 17 of which form the grinding surface. No accurate count could be made of the ridge plates occurring in 100 mm because the tooth is slightly pathological.

As the above data show, there is considerable variation in ridge-plate number, even in the same individual. The thickness of the enamel forming the ridge plates, the number of these plates per tooth, and the number occurring in 100 mm are the chief means by which the various species of Mammuthus are distinguished. The specific distinctions between the Woolly mammoth, the Columbian mammoth, and the Jefferson mammoth, as set forth by Osborn (1936) may be summarized as follows:

The Woolly mammoth Mammuthus primigenius is the animal that today is found frozen in the Arctic regions of North America and Asia. It roamed the tundra in great numbers late in the Pleistocene. It was somewhat smaller than the Jefferson mammoth. The upper and lower third molars have from 24-27 ridge plates, and from 9-13 plates per 100 mm, with an average of 10 in most individuals. In comparison with the third molars of the Jefferson mammoth, those of the Woolly mammoth generally had more plates and were more compressed (which produced the higher plate count per 100 mm).

Mammuthus columbi, the Columbian mammoth, was restricted to southern North America, where it apparently was very abundant, particularly in Florida. This species was larger than the Jefferson mammoth. The enamel ridge-plate numbers for the third molars are [18-19+]/[15-16+], and there are usually only 6 1/2 plates per 100 mm (Osborn 1936, 1071). The enamel forming the ridge plates is thicker than in either the Woolly or Jefferson mammoth.

Habitat and food. -- The mammoths were herbivores, as are the living elephants to which all the mammoths are closely related. They grazed on grasses of various kinds. Probably these animals confined themselves to open grasslands and seldom entered deeply forested areas. The Jefferson mammoth was apparently rather rare in Michigan. This scarcity may be accounted for by limited meadow areas, which would reduce the number able to live in the state. The rarity of finds may be due, in part, to the mammoths' preference for an upland habitat, where their remains would seldom be preserved.

Stomach contents are known only from frozen bodies of the Woolly mammoths (Farrand 1961). Felix (1912) reported a frozen Woolly mammoth from Siberia that had within its stomach various tundra grasses, such as red bent grass and alpine foxtail. The needles of conifers were rare in the material examined. Heintz (1955) mentioned the types of vegetation found in the stomach of a frozen Woolly mammoth as being mosses and grasses. A pollen analysis of the stomach contents of the Beresovka-mammoth (Heintz 1955) showed that 97.09 percent of the pollen belonged to grasses and only 0.17 percent belonged to trees (fir, alder, birch, willow). The rest of the pollen belonged to various other meadow plants.

There is no reason to believe that the Jefferson mammoth deviated from a herbivorous, grazing mode of life. The species of plants for this mammoth would be different from those forming the diet of the Woolly mammoth, but most were probably grasses. Possibly in the winter months some alder, willow, and birch supplemented this fare. In character the teeth in the Jefferson mammoth are most like those of the Asiatic elephant, which is almost exclusively a grazer.

Location of finds of the Jefferson mammoth in Michigan. -- Thirty-two Jefferson mammoth remains have been recorded in Michigan since 1839. As in the case of the mastodon, this number probably represents considerably fewer than the remains actually found in the state. Recorded occurrences are shown in Figure 3 and listed below.

[FIGURE 3 OMITTED]

ARENAC COUNTY

1. 2 1/2 miles north of Au Gres. One tooth (letter of W. A. Kelly, September 24, 1935). Specimen at Michigan State University.

BARRY COUNTY

1. Assyria, 1 mile north. NW 1/4 Sec. 15, T.1 N., R.7 W. Tusk, jaw, scapula, vertebrae, and foot bones (UMMP 22798), in muck. Gift of Robert Hughes in 1942.

BERRIEN COUNTY

1. Galien Township, NE 1/4 Sec. 6, T.8 S., R.19 W. Lower third molar. Specimen in the Chamberlin Memorial Museum, Three Oaks (Dice 1920).

2. Bakerstown marsh, south and west of Buchanan. One tooth, found during the digging of a drainage ditch (Hay 1923, 171).

3. Southwest part of Lake Township. Fragment of a tooth, found in the spring of 1943.

4. Three Oaks, 2 miles southeast. Two upper and two lower third molars, found around 1900. Specimens at the Chamberlin Memorial Museum, Three Oaks (Dice 1920; Hay 1923).

5. Exact locality unknown. One tooth. Present location unknown (Dice 1920.)

CASS COUNTY

1. Jones, near Chapel Hill schoolhouse. Sec. 32, Porter Township, T.7 S., R.13 W. Two good humeri, broken femur, broken tibia, scapula, pelvis, ribs, some vertebrae, foot bones, four teeth, etc. (UMMP 11735). Gift of George Wagner.

EATON COUNTY

1. Eaton Rapids, 2 miles south. Jaws (UMMP 11732) with one tooth each, in the bed of Grand River in 1904. This is No. 8260 reported by Hay (1923, 137).

2. Near Grand Ledge. Three teeth and a tusk, a foot below the surface in muck (Lane 1902; Hay 1923).

3. Near Eaton Rapids, on Wilcox road. One tooth, in muck.

4. Charlotte, exact locality not known. One left lower third molar (UMMP 13639), in muck of the Thornapple River.

GLADWIN COUNTY

1. Remains found in Gladwin County, locality not known (Sherzer 1927).

GRATIOT COUNTY

1. Ithaca, 7 miles west. Sec. 2, T.10 N., R.4 W. Tooth and parts of the skeleton, 2 1/2 feet below the surface in muck lying on gravel.

INGHAM COUNTY

1. Leslie, 3 miles west. Scapula, femur, tibia, and ulna, under peat in marl.

IONIA COUNTY

1. Hubbardston, bed of Fish Creek near electric power plant. Fragment of tooth (UMMP 13362). Gift of Dr. M. B. Robinson.

JACKSON COUNTY

1. Near Eaton Rapids, 9 1/2 miles southeast. Both lower jaws; one tusk; cervical, thoracic, and lumbar vertebrae; most of the ribs; both shoulder blades; and two or three leg bones, in marl. Specimen at the Michigan State University Museum, No. 8238.

2. Locality not known, somewhere in the northern part of Jackson County. One molar (UMMP 3163), in peat.

KENT COUNTY

1. Grand Rapids, approximately 5 miles south on Plaster Creek. One tooth.

2. Rockford. One tooth (Grand Rapids Public Museum, No. 12356), in a gravel pit.

3. Somewhere on Nine Mile Road. "Remains" (Grand Rapids Public Museum, No. 83226).

4. Grand Rapids, 15 miles northeast. Tooth, femur, and other bones. Specimens at the Grand Rapids Junior College.

LENAWEE COUNTY

1. Ridgeway, 1 1/2 miles east. One molar tooth (UMMP 3223), in a gravel pit in 1912. Presented to the University of Michigan by K. A. Easlick.

MACOMB COUNTY

1. "Remains" in Macomb County, locality not known. Tooth, found before 1861 (Lane 1902, 252; Hay 1923, 171).

OAKLAND COUNTY

1. New Hudson, 1 1/2 miles north. Part of a tooth, in a gravel pit. The gravel pit is part of a kame ridge.

SAGINAW COUNTY

1. East Saginaw, near Pere Marquette shaft No. 2. Tooth, found around 1901, three feet below the surface (Lane 1902; Hay 1923).

SHIAWASSEE COUNTY

1. Near Perry, one mile away. Tooth, on dirt from a ditch dredging. Specimen at the Michigan State University Museum, No. 8115.

2. Morrice, 3 miles south. T.5 N., R.2 E. One tooth (UMMP 23607), on the dump of an old drainage ditch. Gift of Roland Schaadt and Alphons Schlicklin.

3. Owosso, in the city limits. Three teeth, found in 1895.

VAN BUREN COUNTY

1. Decatur, a few miles west. One tooth, plowed up in the spring of 1928. Present location is unknown.

2. Mentha, 1 1/2 miles south, in Sec. 1, T.2S., R.13 W. Two upper teeth and tusk fragments.

WASHTENAW COUNTY

1. Chelsea, Sylvan Township, Sec. 13, T.2 S., R.3 E. One half tooth (UMMP 23247). Gift of Virginia Lesser.

RADIOCARBON DATING OF FOSSIL REMAINS

Very few mastodons and mammoths have been collected in the state in recent years, chiefly because of the use of heavy machinery instead of hand labor to dig out muck. When drainage ditches and the like were dug by hand or with oxen or horses, the chances were greater for a bone to be noticed and recovered. Few mastodons and mammoths have become available for radiocarbon ([C.sup.14]) dating since the establishment of the University of Michigan radiocarbon dating laboratory in 1950. The specimens collected before this date were treated with alvar or shellac and are thus worthless for the radiocarbon method (Hibbard and Hinds 1960). It has been found that ivory, because of its compactness, is far better for use in [C.sup.14] dating than bone. Bone often becomes contaminated by the intrusion of small roots and rootlets of recent plants and hence will give an erroneous date.

Part of a mastodon tusk (M-67, Crane 1956) was submitted to the University of Michigan Memorial-Phoenix Project Laboratory for radiocarbon dating. It was partially mineralized. Its source was a gravel pit consisting of Cary outwash in the NE 1/4 Sec. 4, T.3 S., R.4 E., Freedom Township, Washtenaw County, Michigan. The sample from the tusk dated 6100 [+ or -] 400 B.P. from carbon black and 6300 [+ or -] 500 B.P. from a gas sample. It should be noted that acid soluble carbonates from the tusk were used to obtain the samples. The gravels in the exposure are chiefly limestone, and considerable calcium carbonate cementing had occurred in the area in which the tusk was found. The radiocarbon date, therefore, is in error. Dating of the Cary stage (the age of the glacial outwash gravels), is between 13,000 and 15,000 B.P. (Flint 1957; Frye and Willman 1960), which may give a more reliable estimate of the age of the tusk.

The following [C.sup.14] dates for American mastodons were obtained from samples of tusks with one exception, when part of a rib was used. The samples used in dating are given numbers preceded by the letter M, which stands for the University of Michigan radiocarbon dating laboratory. Unfortunately, no dates are available for Jefferson mammoth bones or tusks.
M-347 Tusk (UMMP 37811), taken from muck in Sec. 14, T.7 N., R.10 E.,
 Lapeer County, Michigan (Crane and Griffin 1959)
 5,950 [+ or -] 300
M-280 Inside portion of tusk (UMMP 29276), from Sec. 5, T.8 S., R.2 E.,
 Lenawee County, Michigan (Crane and Griffin 1958)
 7,070 [+ or -] 240
M-281 Outside portion of the above tusk
 7,820 [+ or -] 450
M-490 Rib, from muck near Sheridan, Chautauqua County, New York (Crane
 and Griffin 1959)
 9,200 [+ or -] 500
M-694 Tusk (UMMP 24240), from muck in Elkhart County, Indiana
 9,320 [+ or -] 400
M-39 Tusk fragment, from Nobel County, Indiana (Crane and Griffin
 1958) 12,630 [+ or -] 1,000


EXTINCTION

Hester (1960) states that most of the large Pleistocene herbivores in North America became extinct around 8,000 years ago, as indicated by radiocarbon dates. According to his data, the mammoths apparently died out earlier than the American mastodon. The latter probably survived a little later in isolated areas. According to the above radiocarbon dates, the American mastodon became extinct somewhere after 6,000 years ago. This is approximately the time of the beginning of recorded history.

In most cases the causes of extinction are unknown. It is usually impossible to know exactly why a species of animals could not maintain its numbers. Seldom can a single factor be considered the sole cause. The extinction of the American mastodon and the Jefferson mammoth probably was the result of a number of unfavorable conditions that acted at the same time.

It is known that the Late Pleistocene American Indians of the southwest hunted the now-extinct Columbian mammoth (Wormington 1957), a close relative of the Jefferson mammoth. There is as yet no evidence that early man hunted either the mammoth or mastodon in Michigan.

It is possible that extinction of the American mastodon was partly brought about by the barrier formed by the Great Lakes. Because of this barrier the mastodons might have been unable to follow the northward retreat of the boreal forest environment as the forests followed the retreat of the last glacier. Other barriers were formed by the grasslands and Glacial Lake Agassiz to the northwest. The north outlet to the northeast would offer similar restrictions, since it served as a vast floodway for glacial meltwater.

Recently much work has been done on fossil pollen contained in peat from bogs. The genera of plants represented by the fossil pollen can usually be determined, and radiocarbon dates can be obtained from wood associated with it. From the fossil pollen and its chronology, the type of forest that was present around the bog can be determined for a given time. Two studies from southern Michigan, one from near South Haven, and the other from a bog near Hartford, revealed the following forest changes for these areas (Zumberge and Potzger 1956). A forest consisting chiefly of spruce and some fir was present in southern Michigan 11,000 years ago. This would point to a cool to cold, moist climate. The end of the spruce-fir forest occurred around 8,000 years ago, followed by an increase of pine. The maximum development of pine in southern Michigan was around 6,000 years ago, indicating a warming and drying climate. Associated with the pine was oak and hickory. Approximately 5,000 years ago pine had declined in importance and there was an increase of oak, chestnut, and hickory. The climate at this time was warmer and dryer than at any earlier time in the Late Pleistocene. Since 5,000 years ago, the forest in southern Michigan has consisted mostly of oak, chestnut, hickory, and other broad-leaved species.

Mastodons in Michigan were adapted to life in a mixed coniferous and broad-leaved forest. A mature evergreen forest, composed of large trees with their lowest branches well off the ground, would provide poor browse for these animals and thus cause a decline in their numbers. A mature coniferous forest would have been barren of young seedlings because of the deep shade the large trees produced. Radiocarbon dating indicates that broad-leaved trees became abundant around 5,000 years ago.
TABLE 1. Measurements (in [mm.sup.1]) of Teeth of the American Mastodon

 No. of
 Teeth Range in Size Average

D[p.sub.4], greatest anteroposterior
 length 1 73.9 73.9
D[p.sub.4], greatest width 1 56.0 56.0
[M.sub.1], greatest anteroposterior
 length 6 86.0-99.0 91.6
[M.sub.1], greatest width 6 67.8-76.0 71.5
[M.sub.2], greatest anteroposterior
 length 11 111.0-129.0 120.1
[M.sub.2], greatest width 10 84.6-108.1 98.9
[M.sub.3], greatest anteroposterior
 length 7 184.0-244.3 209.5
[M.sub.3], greatest width 6 96.4-117.8 104.9
D[p.sup.4], greatest anteroposterior
 length 1 70.0 70.0
D[p.sup.4], greatest width 1 61.0 61.0
[M.sup.1], greatest anteroposterior
 length 5 89.3-95.9 92.7
[M.sup.1], greatest width 5 73.8-82.9 77.8
[M.sup.2], greatest anteroposterior
 length 13 108.0-139.2 119.9
[M.sup.2], greatest width 13 87.3-109.9 97.3
[M.sup.3], greatest anteroposterior
 length 10 174.4-223.2 192.1
[M.sup.3], greatest width 10 95.5-114.2 105.3

1. 25.4 millimeters = one inch.


ACKNOWLEDGMENTS

I wish to thank the following persons for granting permission to examine the specimens under their care and for access to the records pertaining to these specimens: Edward Brigham, Kingman Museum, Battle Creek; Frank L. Du Mond, Grand Rapids Public Museum; Rollin H. Baker, Michigan State University Museum; Lester E. Eyer, Alma College; and Lewis B. Kellum, University of Michigan Museum of Paleontology. I especially wish to express my gratitude to Claude W. Hibbard for his advice and criticism during the preparation of this paper, and to John A. Dorr, William S. Benninghoff, and Katharine A. Fellows for reading the manuscript and giving helpful suggestions.

I am also grateful to Edwin H. Colbert, of the American Museum of Natural History, for providing the picture of the Jefferson mammoth skeleton for publication. I also wish to thank Herbert W. Wienert for taking most of the other photographs.

Originally published in Papers of the Michigan Academy of Science, Arts, and Letters Pt. 1 (1962): 101-33.

LITERATURE CITED

BLUMENBACH, JOHANN FRIEDRICH. 1799. Handbuch der Naturgeschichte, ed. 6, 708 pp., 2 plates.

CASE, E. C., ET. AL. 1935. Discovery of Elephas primigenius americanus in the Bed of Glacial Lake Mogodore, in Cass County, Michigan. PMASAL, 20: 449-54, 2 figures.

CASE, E. C., AND GEORGE M. STANLEY. 1935. The Bloomfield Hills Mastodon. Cranbrook Inst. Sci., Bull. 4: 1-8, 3 pls., 2 figures.

CRANE, H. R. 1956. University of Michigan Radiocarbon Dates I. Science, 124: 664-72.

CRANE, H. R., AND J. B. GRIFFIN. 1958. University of Michigan Radiocarbon Dates II. Science, 127: 1098-1105.

_____. 1959. University of Michigan Radiocarbon Dates IV. Am. Jour. Sci. Radiocarbon Supplement 1: 173-98.

DICE, L. R. 1920. The Mammals of Warren Woods, Berrien County, Michigan. Univ. Mich. Mus. Zool., Occ. Pap. (86): 1-20, 2 pls., 1 figure.

FARRAND, W. R. 1961. Frozen Mammoths and Modern Geology. Science, 133 (3455): 729-35, 3 figures.

FELIX, JOHANNES. 1912. Das Mammuth von Borna. Veroff. Stadt. Mus. Volkerkunde, 4: 1-52, 8 tab., 9 figures.

FLINT, R. F. 1956. New Radiocarbon Dates and Late Pleistocene Stratigraphy. Am. Jour. Sci., 254: 265-87, 1 plate., 1 figure.

FRYE, JOHN C., AND H. B. WILLMAN. 1960. Classification of the Wisconsinan Stage in the Lake Michigan Glacial Lobe. III. State Geol. Surv. Circ. 285: 1-16, 1 figure.

HAY, O. P. 1914. The Pleistocene Mammals of Iowa. Iowa Geol. Surv., 23 (Ann. Rep., 1912): 1-662, 75 pls., 142 figures.

_____. 1923. The Pleistocene of North America and its Vertebrated Animals from the States East of the Mississippi River and from the Canadian Provinces East of Longitude 95[degrees]. Carnegie Inst. Wash. Publ., No. 322: 1-499, 41 pls., 25 figures.

HEINTZ, A. 1955. The Mammoth Teeth from Norway. Norsk. Geogr. Tidsskr. b. 34, h. 2-4: 73-104, 2 plates, 7 figures.

HESTER, J. J. 1960. Pleistocene Extinction and Radiocarbon Dating. Am. Antiquity, 26 (1): 58-77, 1 figure.

HIBBARD, C. W. 1951. Animal Life in Michigan During the Ice Age. Mich. Alumnus Quart. Rev., 57 (18): 200-8, 4 figures.

HIBBARD, C. W., AND F. J. HINDS. 1960. A Radiocarbon Date for a Woodland Musk Ox in Michigan. PMASAL, 65: 103-8, 2 pls., 1 figure.

JEPSEN, G. L. 1960. A New Jersey Mastodon. New Jersey State Mus., Bull. No. 6: 1-20, illus.

LANE, A. C. 1902. Report of the State Board of Geological Survey of Michigan for the Year 1901, 252-3.

LUCAS, F. A. 1939. Animals of the Past. Am. Mus. Nat. Hist. Handbook Series No.4, 7th ed., 1-221, 24 pls., 18 figures.

MACALPIN, A. 1940. A Census of Mastodon Remains in Michigan. PMASAL, 25: 481-90, 1 figure.

OSBORN, H. F. 1936. Proboscidea. Am. Mus. Nat. Hist., 1: 1-802, 12 pls., 680 figures.

_____. 1936. Proboscidea. Am. Mus. Nat. Hist., 2: 805-1675, 18 pls., 563 figures.

PALMER, T. S. 1904. North American Fauna. U. S. Dept. Agr., Wash., (23): 1-984.

SHERZER, W. H. 1927. A New Find of the Woolly Elephant in Michigan. Science, 65 (1695): 616.

WARREN, JOHN C. 1852. The Mastodon Giganteus of North America. Boston: 1-219, 26 plates.

WORMINGTON, H. M. 1957. Ancient Man in North America. Denver Mus. Nat. Hist. Pop. Ser. No.4: 1-322, 72 figures.

ZUMBERGE, J. H., AND J. E. POTZGER. 1956. Late Wisconsin Chronology of the Lake Michigan Basin Correlated with Pollen Studies. Bull. Geol. Soc. Am., 67 (5): 271-88, 1 pl., 6 figures.

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MARGARET ANNE SKEELS

University of Michigan
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