Latest Pleistocene paleoecology of Jefferson's ground sloth (Megalonyx jeffersonii) and elk-moose (Cervalces scotti) in northern Illinois

Quaternary Research 61 (2004) 231 – 240 www.elsevier.com/locate/yqres

Latest Pleistocene paleoecology of Jefferson’s ground sloth (Megalonyx jeffersonii) and elk-moose (Cervalces scotti) in northern Illinois Blaine W. Schubert, a,b,* Russell Wm. Graham, c H. Gregory McDonald, d Eric C. Grimm, b and Thomas W. Stafford, Jr. e b

a Environmental Dynamics, 113 Ozark Hall, University of Arkansas, Fayetteville, AR 72701, USA Illinois State Museum, Research and Collections Center, 1011 East Ash Street, Springfield, IL 62703, USA c Denver Museum of Nature & Science, Denver, CO 80205, USA d Geologic Resources Division, National Park Service, Denver, CO 80225, USA e Stafford Research Laboratories, Inc., 5401 Western Avenue, Suite C, Boulder, CO 80301, USA

Received 1 April 2003

Abstract New records of Jefferson’s ground sloth (Megalonyx jeffersonii) and elk-moose (Cervalces scotti) from Lang Farm provide the first precise temporal correlation of these taxa with the specific environments inhabited by them near the time of their extinction. Six AMS 14C measurements establish an age of 11,405 F 50 14C yr B.P. for Lang Farm Cervalces and an age of 11,430 F 60 or 11,485 F 40 14C yr B.P. for the Megalonyx. These measurements represent the youngest 14C dates for these two genera based on direct dating. Comparison of the dates with pollen data from northern Illinois indicates that these species inhabited a nonanalog environment that was transitional from midlatitude tundra to mixed conifer and deciduous woodland. Although spruce (Picea sp.) was dominant, it was less abundant than prior to 12,500 14C yr B.P. The presence of black ash (Fraxinus nigra) and fir (Abies sp.) indicates a wet climate and heavy winter precipitation. This may have been the preferred habitat for Cervalces because of its narrow geographic range. However, this habitat type was only one of many occupied by Megalonyx as indicated by its broad geographic distribution. D 2003 University of Washington. All rights reserved. Keywords: Jefferson’s ground sloth; Megalonyx jeffersonii; Elk-moose; Cervalces scotti; Late Pleistocene; Paleoecology; Extinction

Introduction In 1989 and 1990, while dredging a pond, Mr. Daniel Lang found remains of elk-moose, Cervalces scotti and Jefferson’s ground sloth, Megalonyx jeffersonii on his farm in Bureau County, Illinois. The Lang Farm site (latitude N 41j 32.697V, longitude W 89j 39.768V, elevation 198 m) is located near the area of the western- and southern-most extensions of the Lake Michigan lobe of the late Wisconsin Laurentide Ice Sheet. North-central Illinois is well known for its sequence of glacial fluctuations, with eight major late Wisconsin phases of advance and retreat marked by a series of moraine systems (Wilman and Frye, 1970; Hansel and Johnson, 1992; Hansel et al., 1987). The discovery of * Corresponding author. Environmental Dynamics, 113 Ozark Hall, University of Arkansas, Fayetteville, AR 72701. E-mail address: [email protected] (B.W. Schubert).

remains of these two extinct species in the heart of this glacial sequence offers a unique opportunity for understanding mammal response to these rapidly fluctuating environments. Accelerator mass spectrometer (AMS) radiocarbon dates on highly purified bone collagen from these two taxa place them within an environmental context (ice-sheet margins, physiography, climate, and vegetation) near the time of their extinction. Although the exact stratigraphic location of the elkmoose and sloth specimens is unknown within the dredged pond, the sedimentary sequence was a lower blue clay (marl) with an upper peat layer. The dark brown color of the Cervalces remains suggests that the bones were from the peat layer. The lighter color of the Megalonyx dentary, as well as the fact that small blue clay particles can still be seen on the specimen, suggests that it came from the lower clay layer. Radiocarbon dates on the bone specimens support this stratigraphic reconstruction (see below).

0033-5894/$ - see front matter D 2003 University of Washington. All rights reserved. doi:10.1016/j.yqres.2003.10.005

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Table 1 Vertebrate fauna (other than Cervalces and Megalonyx) from the Lang Farm site, Bureau County, Illinois Taxon

Vernacular name

Esox sp. Emydidae Castor canadensis Cervidae

Pike or muskellunge One right mandible ISM 492805 Water turtle Plastron fragments ISM 492806 Beaver Femur ISM 492804 Elk-size cervid

Element

Humerus fragment

A

Catalogue No.

ISM 492813

In addition to the elk-moose and ground sloth, the fauna from Lang Farm comprises fish (Esox sp.), turtle (Emydidae), beaver (Castor canadensis), and an unidentified elksize mammal (Table 1). The geologic ages of these additional Lang Farm taxa are unknown. The Esox jaw is stained the same color as the Cervalces cranium and therefore may have come from the peat stratum. The turtle, beaver, and ungulate limb bone specimens are lighter colored. The specimens reported here are curated in the Geology Collections at the Research and Collections Center of the Illinois State Museum (ISM). All measurements on the faunal remains were taken with either digital calipers or sliding metal calipers.

B

Systematic paleontology Class Mammalia Order Xenarthra Family Megalonychidae Megalonyx jeffersonii—Jefferson’s ground sloth Referred material: Anterior portion of left dentary with caniniform (ISM 492815) (Fig. 1); first molariform (ISM 492814a); two undifferentiated molariforms (ISM 492814b and ISM 492814c). Remarks: The genus Megalonyx had one caniniform followed by a diastema and three molariforms or cheek teeth on each dentary. Based on the size of the dentary (Table 2) and that the teeth are parallel sided and not conical, this individual was an adult. The morphology of Megalonyx lower caniniforms is variable. However, one characteristic shared by all Megalonyx caniniforms (upper and lower) is a lingual bulge (McDonald, 1977; McDonald et al., 2000). The Lang Farm specimen has a lingual bulge that is slightly anterior to the mediolateral midline of the tooth (Fig. 1B). The three molariforms all appear to be from the left dentary and match morphological descriptions given by McDonald (1977, p. 79). Molariforms are difficult to differentiate because of their overall similarities and lack of discrete characters. However, the first molariform of the Lang Farm specimen can be identified based on its perfect fit into the alveolus for the first molariform in the dentary. Jefferson’s ground sloth fossils have been recovered from sites in the conterminous United States as well as Alaska, northwestern Canada, and Mexico. The ages of most of the specimens from Beringia are unknown. The Yukon material

Fig. 1. Anterior part of Megalonyx jeffersonii left dentary (ISM 492815) from Lang Farm. (A) Left lateral view. (B) Dorsal view. Scale is 30 mm.

is thought to be Sangamon in age based on its stratigraphic occurrence (McDonald et al., 2000) and there are no dates on other Alaskan or Canadian records. There was a persistent population of Megalonyx south of the ice sheets from the Blancan through the Rancholabrean; M. jeffersonii is Table 2 Measurements (mm) on Megalonyx jeffersonii remains from Lang Farm, Bureau County, Illinois Anatomical dimension Lower left caniniform (ISM 492815) Anterior posterior diameter Greatest width Cheek tooth (ISM 492814a) Anterior posterior diameter Greatest width Cheek tooth (ISM 492814b) Anterior posterior diameter Greatest width Cheek tooth (ISM 492814c) Anterior posterior diameter Greatest width

Measurement (mm) 39.3 17.5 17.5 24.2 f17.8 f26.6

The symbol ‘‘f’’ indicates an approximate dimension.

18.5 24.2

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considered to be the only Rancholabrean (late Pleistocene) species (Kurte´n and Anderson, 1980). M. jeffersonii is known from over 150 sites in the United States (McDonald, unpublished data). These sites include peat bogs, gravel deposits, caves, fissures, sinkholes, and tar pits. However, very few of these sites can be assigned to specific temporal intervals (Fig. 2). The wide geographic distribution of M. jeffersonii, combined with the diversity of depositional environments where fossils are recovered, makes it difficult to determine preferred habitats for this species (McDonald and Anderson, 1983). The Lang Farm M. jeffersonii is the only specimen of its taxon that has been directly dated by radiocarbon methods and is from a context that provides a well-defined paleoenviromental record. This is the seventh record for this species from Illinois. Order Artiodactyla Family Cervidae Cervalces scotti—elk-moose Referred material: Posterior portion of cranium or braincase (ISM 495763) (Fig. 3), fragmentary scapula (ISM 492816); distal condyle of metapodial (ISM 492812); left navicular-cuboid/cuneiform (ISM 492810); phalanx I (ISM 492807); phalanx I (492808); phalanx II (492811a); phalanx II (492811b). Remarks: Cervalces is a Rancholabrean taxon that occurred as two distinct populations in North America during the late Pleistocene—one population immediately south of the Laurentide ice sheet, and the second in Beringia. It is unresolved if these two populations represent different species (Churcher and Pinsof, 1987); however, the type

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specimen of C. scotti (Lydekker, 1898) is from the southern population. The greatest concentration of Cervalces localities for the southern population is in the upper midwestern United States where fossils commonly occur in bog deposits (Faunmap Working Group, 1994) (Fig. 4). The elk-moose remains from Lang Farm represent the tenth Cervalces specimen reported from Illinois. The Lang Farm cranium (Fig. 3) was compared to six modern moose (Alces alces) specimens (ISM 688314; 689179; 688040; 683611; 692610a; 692610b). The lack of a distinct notch on the supraoccipital at the edge of the foramen magnum (Fig. 3B) of the Lang Farm specimen is the most diagnostic feature for its identification as Cervalces. The absence of a prominent knob (located between the pedicles in males) on the midline of the frontal bone (Fig. 3A) is another important character. Both Alces and Cervalces have an oval depression on the anterior part of the frontal bone (Scott, 1885). Of the six A. alces specimens, all had much deeper and more pronounced depressions than the Lang Farm specimen. Measurements on the Cervalces cranium from Lang Farm are shown in Table 3. McDonald (1989) compared differences between the braincases of a modern A. alces and the late Wisconsin Cervalces (OSU 14925) from Wild Cat Swamp, Ohio. There is considerable individual variation in some of these comparative features. For example, while the Ohio specimen had pedicles with a round cross section, the pedicles on the Lang Farm individual are elliptical with the long axis oriented posterodorsal to anteroventral (Fig. 3D); this orientation is similar to that described for Alces by McDonald (1989). The maximum length of the ellipse along this axis is

Fig. 2. Full and late-glacial records of Megalonyx jeffersonii (data from Faunmap Working Group, 1994; Graham and Lundelius, unpublished data).

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Fig. 3. Cervalces scotti braincase (ISM 495763) from Lang Farm. (A) Dorsal view. (B) Posterior view. (C) Ventral view. (D) Right lateral view. Scale is 30 mm.

75.5 and 76.8 mm on the left and right pedicles, respectively, for the Lang Farm cranium. The diameter perpendicular to the long axis is 54.2 mm (incomplete) and 58.5 mm on the left and right pedicles, respectively. McDonald (1989) thought morphological differences in the tubercles for the attachment of the M. rectus capitus ventralis minor and M. rectus capitalis ventralis major

muscles might reflect differences between the genera. These muscle scars are paired and located on the ventral surface of the cranium, with one on either side of the midline (Fig. 3C). The M. r. c. v. minor tubercles are located on the posterior end of the basioccipital bone, whereas, the M. r. c. v. major extends from the anterior end of the basioccipital onto the basisphenoid. McDonald (1989) described these in

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Fig. 4. Full and late-glacial records of Cervalces scotti (data from Faunmap Working Group, 1994; Graham and Lundelius, unpublished data).

detail but inadvertently reversed their positions. As in the Wild Cat Swamp specimen, the Lang Farm tubercles for the M. r. c. v. minor are more equadimensional in orientation than the same tubercles in Alces, which are narrow and have expanded lateral edges that are more pronounced. This character was analyzed on four modern Alces in the ISM collection and matches McDonald’s (1989) description, therefore further supporting the utility of this character in distinguishing the two taxa. The insertion area for the M. r. c. v. major may be shared with the insertion of another muscle (e.g., M. longus capitis; Smuts and Bezuidenhout, 1987, p. 66), which would contribute to the morphology of the same tubercles. These tubercles are variable in Alces and may have been equally variable in Cervalces. On the Lang Farm specimen (Fig. 3C) these tubercles are rugose and asymmetrical. McDonald (1989) also noted differences in the prominent ridge that runs down the midline of the basioccipital in the Wild Cat Swamp Cervalces and the Alces specimen he

Table 3 Measurements (mm) on the Cervalces scotti cranium from Lang Farm, Bureau County, Illinois (Dimensions after Driesch, 1976) Anatomical dimension

Measurement (mm)

Circumference of the distal end of the left pedicel Circumference of the distal end of the right pedicel Least frontal breadth Greatest breadth of occipital condyles Greatest breadth of foramen magnum Greatest width between pedicels (ventral side)* Greatest width between pedicels (dorsal side)*

217.2 219.4 117.5 103.6 36.6 224.3 205.5

* Indicates new measurements by BWS.

examined. In contrast to the Wild Cat Swamp braincase, the Lang Farm specimen has a ridge that extends anteriorly to the middle of the tubercles of the M. r. c. v. major and ends just before the basisphenoid which is flat (Fig. 3C). Three ISM Alces specimens show a wide range of variation in the morphology of this ridge; consequently, the utility of this character is diminished. Finally, McDonald noted that Alces has a prominent sulcus beginning at the dorsal portion of the lateral margin of the occipital condyle. This sulcus extends to the condylar foramen. The Wild Cat swamp Cervalces lacks a welldeveloped sulcus (McDonald, 1989). The Lang Farm individual has a sulcus and it does not differ greatly from Alces in this character. We identified an additional character that may be useful in distinguishing the braincases of Alces and Cervalces—the orientation of the dorsal end of the condyle. In the ISM Alces specimens, there is a more constricted and deeper depression adjacent to the dorsal portion of the medial margin of the occipital condyle when compared to Cervalces. Additional Cervalces specimens will need to be analyzed to confirm this character. The postcranial remains are probably from the same individual; however, this interpretation is not definitive. The Cervalces postcranial elements have the same physical preservation and color as the cranium (ISM 495763). Measurements on these specimens are shown in Table 4. The referred navicular-cuboid (ISM 492810) is fused to the cuneiform. Scott (1885) noted this feature in the specimen he described and used this character in his diagnosis of Cervalces. However, this feature probably reflects the advanced age of the individual as indicated by skull morphology discussed below and is not taxonomically valid as a

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Table 4 Measurements (mm) on Cervalces scotti postcranial remains from Lang Farm, Bureau County, Illinois (Dimensions after Driesch, 1976) Anatomical dimension Navicular-cuboid (left) (ISM 492810) Greatest breadth Phalanx I (ISM 492807) Greatest length Greatest breadth of proximal end Smallest breadth of diaphysis Greatest breadth of distal end Phalanx I (ISM 492808) Greatest length Greatest breadth of proximal end Smallest breadth of diaphysis Greatest breadth of distal end Phalanx II (ISM 492811a) Greatest length Greatest breadth of proximal end Smallest breadth of diaphysis Greatest breadth of distal end Phalanx II (ISM 492811b) Greatest length Greatest breadth of proximal end Smallest breadth of diaphysis Greatest breadth of distal end

Measurement (mm)

cervids (Kitchener, 1987) and almost certainly occurred among extinct taxa. Because the puncture on the Lang Farm cranium shows no sign of healing, we believe the carnivore puncture is more plausible.

71.9 95.0 38.7 26.9 35.1 90.8 38.1 27.4 32.6 70.7 35.8 22.5 27.4 70.2 35.2 23.9 28.4

character. For example, one mature Alces specimen (ISM 692607) has this same tarsal fusion, although it is not as extreme as that noted in the Lang Farm specimen. Based on the intact antler pedicles, the braincase is that of a male. The terminal ends of the pedicles are porous, indicating that the antlers were shed prior to death. In A. alces, the antlers are normally cast in the early winter (December – January) and the new antlers do not start growing until early spring (April– May) (Van Ballenberghe, 1983). If Cervalces had a similar pattern, it would suggest that the Lang Farm Cervalces died during the winter (February – March). The cranial sutures are well fused; therefore, the cranium is that of a mature animal. The parietal and frontal bones display a series of gouges and grooves that were made by the metal blade of the dredging equipment (excavation cut marks in Fig. 3A). A puncture showing no sign of healing is apparent on the dorsal braincase just left of the parietal’s anteroposterior midline. Similar damage occurs on a modern male A. alces (ISM 688314) at the same location on the cranium. The morphology of these marks is similar to depressed fractures or punctures (Hill, 1980, p. 139) caused by carnivore teeth (Hill, 1989, p. 175, Fig. 8). Carnivore punctures are typical features on artiodactyl bones found in the wild. One of us (R.W.G.) has observed numerous examples of these punctures on caribou that were scavenged by wolves (Canis lupus). This is not the first example of possible carnivore activity on Cervalces remains. Farlow et al. (1986) noted carnivore chewing on the attached antlers of a Cervalces cranium from Indiana. These punctures may also result from wounds received from combat between battling males. Such fighting occurs during the rutting season among modern

Geochronology—AMS

14

C dating

Bone samples were removed from the Cervalces cranium (ISM 495763) and the Megalonyx lower jaw (ISM 492815) for AMS 14C dating. Different chemical fractions were dated to assess the amount of foreign carbon contamination and monitor the purification process. AMS 14C ages were measured on two chemical fractions of collagen: (1) gelatin isolated from KOH-purified decalcified collagen and (2) the XAD-resin-purified hydrolyzate of the gelatin. Chemical methods were those cited in Stafford et al. (1991) and Stafford (1998). Because the XAD-purified hydrolyzate is the most chemically pure of any fraction of bone collagen, the 14C dates on XAD-purified fractions are considered to be the most accurate. Dates were calibrated with CALIB 4.3 (Stuiver and Reimer, 1993; Stuiver et al., 1998). The radiocarbon results are summarized in Table 5 and Table 6. The 14C ages on gelatin were younger than on XAD fractions for the elk-moose, and older than XAD dates for the sloth. The XAD fractions for the elk-moose and sloth dated within one standard deviation; the two XAD fractions for the sloth (CAMS-33974 and CAMS-82933) were within one standard deviation for the same bone dated by identical methods, first in 1997 and again in 2002. Humates often date less (younger) than the bone because these secondary compounds are often pedogenic and incorporated into bone mineral and its organic matter during burial. However, humates can have older apparent 14C ages if stratigraphically lower (older) humates contaminate the fossil. Humates older than the fossil are incorporated by either of two processes—the bone sinks into lower and older sediments during its burial or groundwater circulation in the deposit moves older dissolved carbon compounds into stratigraph-

Table 5 AMS Radiocarbon measurements on different chemical fractions of bone collagen from the Lang Farm Megalonyx jeffersonii (ISM 492815) Chemical fraction dated

14

C yr B.P. F 1 SD

14

cal yr B.P. (2 SD)

Gelatin from KOH-extracted collagen Gelatin from KOH-extracted collagen XAD-purified KOH-gelatin XAD-purified KOH-gelatin

11,530 F 70

CAMS-10224

13,171 – 13,825

11,710 F 80

CAMS-13033

13,447 – 14,012

11,430 F 60

CAMS-33974

13,157 – 13,790

11,485 F 40

CAMS-82933

13,170 – 13,803

C Lab No.

The XAD-purified chemical fraction dates are considered to be the most accurate.

B.W. Schubert et al. / Quaternary Research 61 (2004) 231–240 Table 6 AMS Radiocarbon measurements on different chemical fractions of bone collagen from the Lang Farm Cervalces scotti (ISM 495763) Chemical fraction dated

14

C yr B.P. F 1 SD

14

Gelatin from KOH-extracted collagen XAD-purified KOH-gelatin

11,260 F 70

CAMS-09476 13,007 – 13,755

11,405 F 50

CAMS-82932 13,154 – 13,783

C Lab No.

cal yr B.P. (2 SD)

The XAD-purified chemical fraction date is considered to be the most accurate.

ically higher sediments. Because the Cervalces specimens were apparently from the upper, peaty sediments, and the Megalonyx was from the lower, marly sediments, the humate geochemistry of the two sediments was apparently different, based on how the gelatin and XAD chemical fractions dated. We conclude from the AMS 14C data that the best age determination for the elk-moose is 11,405 F 50 14C yr B.P. (CAMS-82932). The most accurate ages for the sloth are 11,430 F 60 14C yr B.P. (CAMS-33974) and 11,485F40 (CAMS-82933). Because of fluctuations in atmospheric D14C, the calibrated dates fall into two possible age ranges: f13,800 –13,660 cal yr B.P. and f13,500 – 13,170 cal yr B.P. The calibrated age ranges fall within Greenland Interstade 1c, which is a warmer phase of Greenland Interstade 1 (Bjo¨rck et al., 1998), widely known as the Allerød (Dansgaard et al., 1971; Mangerud et al., 1974; Stuiver et al., 1995). The 14C measurements reported here on Megalonyx represent the first reported AMS radiocarbon dates for this taxon. Until now, only two Cervalces specimens have been radiocarbon dated from the population south of the Laurentide ice sheet (Churcher and Pinsof, 1987). Of these two specimens, only one (from Kendallville, Noble County, Indiana) was dated using AMS technology. The Kendallville specimen dates to 11,420 F 70 14C yr B.P. (CAMS14809) using the gelatin fraction discussed above (Farlow and McClain, 1996). The XAD date for this specimen (not reported by Farlow and McClain, 1996) is 11,620 F 70 14C yr B.P. (CAMS-17128). Our recent 14C dating of the Lang Farm C. scotti specimen (Table 6) is only the second time that C. scotti has been AMS radiocarbon dated directly. Both the Lang Farm and Kendallville specimens were dated by TWS using the same laboratory procedures (Stafford et al., 1991). Based upon the Kendallville and Lang Farm dates for Cervalces, and the dates reported here for Megalonyx, it appears that these two taxa may have gone extinct in the upper midwest by 11,400 14C yr B.P.

Paleoecology of Cervalces and Megalonyx The late Pleistocene environments of northern Illinois were quite dynamic, as exemplified by rapidly fluctuating

237

ice fronts and vegetational communities. King (1981) reconstructed the late Quaternary vegetational history for northern Illinois based upon records from Volo Bog, which is about 170 km northeast of Lang Farm, and Chatsworth Bog, which is about 90 km to the southeast. The chronologies of these sites are based on conventional, decaycounting radiocarbon dates on bulk sediment. Consequently the ages of these late-glacial sections are imprecise. The base of the Volo Bog sequence contains the late-glacial spruce (Picea) zone and probably postdates Lang Farm. Chatsworth Bog was not cored to its base; therefore, the incomplete record for the bog precludes making absolute temporal comparisons with Lang Farm. A new pollen profile (Fig. 5) from Nelson Lake, 111 km northeast of Lang Farm, is well dated by AMS techniques (Grimm and Maher, unpublished data). Picea forests predominated from about 17,000 to the beginning of the Bølling, when spruce declined. A mixed conifer-deciduous forest characterized the Bølling-Allerød period from 14,700 to 12,900 cal yr B.P. The calibrated age range for the Lang Farm specimens is within the Allerød (Fig. 5). Spruce (Picea) and fir (Abies) were common conifers, but together they account for <35% of the pollen. Black ash (Fraxinus nigra) was abundant (f25% of the pollen). Other deciduous trees common in the vegetation included aspen (Populus), hornbeam (Ostrya/Carpinus), and oak (Quercus). Elm (Ulmus) was also present, as were thermophillous trees such as sugar maple (Acer saccharum), hickory (Carya), walnut (Juglans), and hackberry (Celtis). This interpreted assemblage of conifers and deciduous trees has no modern analog and represents one example of the nonanalog plant communities dominant throughout the Midwestern United States during the late glacial period. Consequently, reconstructing the late glacial climate from the vegetation record is problematic (Jacobson et al., 1987; Overpeck et al., 1992; Williams et al., 2001). Based on the ecological requirements of the dominant tree species, summers are interpreted as fairly cool based on the presence of Picea and Abies, but with winters warm enough to support deciduous taxa propagation. Climate must have been wet. F. nigra typically grows in swamps and on poorly drained soils. Abies is another indicator of abundant precipitation (Webb et al., 1983; Prentice et al., 1991; Thompson et al., 2000). Summers were probably cooler than in Illinois today, but the conifers and deciduous trees that dominated the vegetation do occur together in Wisconsin, although not in the same quantitative abundances. Picea can become more abundant at warmer temperatures if precipitation and soil moisture are high (Webb et al., 1983). We conclude that high precipitation characterized the climate during the time of the Lang Farm fauna’s accumulation. M. jeffersonii and C. scotti remains have been recovered from marl deposits in Darke County, west central Ohio (Mills, 1975; Mills and Guilday, 1972). The stratigraphy of this site is similar to Lang Farm with marl deposits overlain by peat and the site was located at the edge of the Shelby-

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Fig. 5. Summary pollen diagram from Nelson Lake. The shaded bar shows the range of the calibrated Lang Farm radiocarbon dates, which falls during the Bølling-Allerød period, dominated by Fraxinus nigra-type (black ash) and Picea (spruce).

ville moraine. Again, the remains were found by dredging a topographic depression, but at the Darke County site, the bones were clearly encased in marl deposits. The depression is located about 3 km southwest of the Bloomer end moraine and 8 km northeast of the Union City end moraine. Both of these moraines, like those in Bureau County, Illinois, are part of the ‘‘Shelbyville’’ complex. The bones have not been radiocarbon dated; however, spruce wood from the marl dated 12,190 F 215 14C yr B.P. (Mills, 1975, p. 148). Although this date is not directly on bone, it is evidence that the sloth and elk-moose remains could be contemporaneous with those from Lang Farm. Shane (1976, 1980) analyzed a radiocarbon-dated pollen profile from this site and described a double spruce peak that generally characterizes Bølling-Allerød/Younger Dryas climate fluctuations. If the Megalonyx and Cervalces from Darke County dates ca. 12,000 14C yr B.P., these taxa would have inhabited an environment transitional from a mixed hardwood forest to a spruce forest. This transitional environment is the same one as suggested at Lang Farm. Similar to the Lang Farm situation, disturbance of the Kendallville site in northeastern Indiana prohibited specific identification of the stratum from which the Cervalces specimen was recovered and development of a pollen spectrum. However, sediments around the specimen consisted of gray, mollusc-rich marl (Farlow and McClain, 1996). Plant macrofossils, pollen, and molluscs were found

in the marl sediments in the immediate vicinity of the Cervalces cranium (Farlow and McClain, 1996, p. 325). Although it is uncertain, it appears that the Kendallville Cervalces inhabited an environment similar to that at Lang Farm during the terminal Pleistocene. Comparing the date for the Kendallville Cervalces with well-dated pollen sequences from the surrounding area would evaluate this reconstruction. A pollen sequence associated with mastodon (Mammut americanum) and caribou (Rangifer tarandus) from Christiansen Bog (Graham et al., 1983) in central Indiana dates from ca. 14,000 to ca. 12,000 14C yr B.P. The bog has similar environmental successions (spruce parkland changing to mixed coniferous and deciduous woodland and finally into a hardwood forest) as those at Nelson Lake. Similarly, pollen and plant macrofossils from the Kolarik Mastodon site in Starke County, Indiana, indicate that the environment in northern Indiana at 11,000 to 12,000 14C yr B.P. was open, spruce-dominated forest or woodland (Jackson et al., 1986). These environmental reconstructions are consistent with those for the elk-moose sites reviewed here.

Acknowledgments We thank the late Daniel Lang and his family for graciously donating the Lang Farm specimens to the Illinois

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State Museum and Randy Nyboer for bringing the specimen to the attention of the Museum. We thank the following for loaning their expertise: Julie Snider fabricated casts of the megafaunal specimens for the landowner, Mona Colburn identified the fish dentary, Wayne Luzardi and Alan Fuhrmann assisted in the field work, Gary Andrashko photographed the specimens, and Alan Gillespie, C.R. Harington, and an anonymous reviewer provided suggestions and comments that improved this paper.

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