6tol%- HARVARD UNIVERSITY Ernst Mayr Library of the Museum of Comparative Zoology OCCASIONAL PAPERS v.'. of the :r) NATURAL HISTORY MUSEUM The University of Kansas Lawrence, Kansas number 178, pages 1-33 31 july 1996 Paleoecology of Subarctic Faunae Assemblages FROM THE WOODFORDIAN AgE (PlEISTOCENE: Wjsconsinan) Elkader Site, Northeastern Iowa Neal Woodman,' Donald P. Schwert, Terrence J. Frest, AND Allan C. Ashworth Natural Histoiy Museum, The Universit}' of Kansas, Lawrence, Kansas 66045- 2454 (N. W. ); Department of Geology, North Dakota State University, Fargo, North Dakota 58105-5517 (D.P.S., A.C.A.); and Deixis Consultants, 2517 Northeast 65th Street, Seattle, Washington 98115-7125, USA (TJ.F.) ABSTRACT Colluvial, fluvial, and alluvial fan sediments at Elkader, Clayton Co., Iowa, contain one of the most tundra-like biotas known from the Pleistocene of midcontinental North America. Remains of animals recovered from the site include open-ground, arctic/subarctic molluscs, beetles (including Diacheila polita and Pterostichus ventricosus), and mammals (including Spermophilus parryii, Dicrostonyx torquatus, and Microtus cf. miurus). Spruce wood from the fossilifer- ous horizon yielded a radiocarbon age of 20,530 ± 130 yr B.P. (BETA-2748). Analogs to the insect and mammal faunas from Elkader occur today in subarctic parklands near treeline in northwestern North America. We interpret these assem- blages as indicating a subarctic, full-glacial environment at Elkader. Although generally indicative of a cold climate, the molluscan assemblage is more complex in that it includes possible deciduous forest species. This suggests the occurrence of topographically controlled variation in microhabitats at the site. Together, the Elkader assemblages indicate that full-glacial climatic conditions already were well established in northeastern Iowa by 20,500 yr B.P. They confirm the interpretations based on pollen spectra from other Midwestern sites of a tundra-like vegetation and environment in the Upper Mississippi Valley region at this time. Key words: Beetle; Climate; Coleoptera; Insect; Iowa; Mammal; Mollusc; Paleo- ecology; Wisconsinan; Woodfordian. Present address: Department of Biology, Southwestern College, 100 College Street, Winfield, Kansas 67156-2499. © Natural History Museum, The University of Kansas, Lawrence. ISSN:009l-7958 2 UNIV. KANSAS NAT. HIST. MUS. OCC. PAP. No. 178 The environment of the Upper Mississippi Valley region is well docu- mented for some portions of the Wisconsinan glacial stage. Studies of pollen spectra from this region suggest a gradual cooling of the climate from the late Altonian through middle Woodfordian time, although early on the effects of climatic deterioration on the biota may have been limited to more northern parts of the region (Whittecar and Davis, 1982; Baker et al., 1989a,b). During the Farmdalian interstade, about 28,000-25,000 yr B.P., a closed spruce-pine forest covered central and northern Illinois (King, 1979; Whittecar and Davis, 1982; Baker et al., 1989a,b) and eastern Iowa (Mundt and Baker, 1979; Van Zant et al., 1980; Hallberg et al., 1980). Perhaps as early as 26,600 yr B.P., a noticeable shift began to spruce-dominated boreal forest in west-central Illinois (Baker et al.. 1989b); this vegetation was well established by ca. 25,000 yr B.P.. when Woodfordian ice of the Lake Michigan Lobe began to advance into Illinois (Curry, 1990). After about 22,700 yr B.P (Baker et al., 1989a,b), or somewhat later (Garry et al., 1990), tundra-like conditions prevailed in northern and central Illinois. The transition into full-glacial conditions by 21,400 yr B.P. is well represented in a mixed boreal forest/tundra insect and plant assemblage at Wedron, LaSalle Co., Illinois (Garry et al., 1990). Tundra-like conditions also were present in east-central Iowa from at least approximately 18,100-17,200 yr B.P. (Baker et al., 1986). After about 17,200 yr B.P, and at least until 16,700 yr B.P, there was a gradual warming trend, and boreal forest or even mixed forest might have been present in east-central Iowa (Baker et al., 1989b). In central Minnesota, tundra-like vegetation is thought to have persisted from at least 20,500-14,700 yr B.P (Birks, 1976). Interpretations based on pollen spectra are supported at a few sites by plant macrofossils and fossil beetles. However, few dated Wisconsinan faunal sites containing mammalian fossils are known from the Upper Mississippi Valley region. Conklin Quany, Johnson Co., Iowa, yielded diverse remains of molluscs, insects, and small mammals, as well as plant macrofossils and pollen, preserved in a swale that filled between about 18,100 and 16,700 yr B.P (Baker et al.. 1986). Moscow Fissure, Iowa Co., Wisconsin, provided a mammalian fauna from approximately 17,000 yr B.P. (Foley, 1984). The Prairieburg site, Linn Co., Iowa, preserved a fauna with a full-glacial aspect, but unfortunately lacks a radiocarbon date (Foley and Raue, 1987). Together, these sites provided preliminary insight into the terrestrial fauna of the Upper Midwest during Woodfordian time. Fossiliferous terrace deposits at Elkader. Clayton Co., Iowa, provide the oldest and most northern, dated Wisconsinan fauna from the Upper Missis- sippi Valley region. They offer a rare opportunity to study molluscs, insects, and small mammals that inhabited the full-glacial environment of north- eastern Iowa about 20,500 yr B.P. SUBARCTIC FAUNAL ASSEMBLAGES FROM ELKADER, IOWA 90 40 — Fig. 1 . Location of Elkader and other selected Wisconsinan sites in the Upper Mississippi Valley region. The shaded and dashed lines represent the approximate position of the Laurentide ice front in the region about 20,000-20,500 yr B.P. (after Fenton et al., 1983; Mickelson et al., 1983; Prest, 1984). SITE DESCRIPTION AND STRATIGRAPHY The Elkader site is within the incorporated hmits of the town of Elkader, Clayton Co., Iowa (SE 1/4, SW 1/4, NE 1/4, Section 23, T. 93 N., R. 5 W.; 42°52"13'N, 9r23"42'W; Fig. 1). The region isoneof comparatively high UNIV. KANSAS NAT. HIST. MUS. OCC. PAP. No. 178 0 m- IHiiipi Dt'l ' (in^ii? I / , jni( / { fiifi stratigraphic units _ 1 2 5 - 10 - .^ ~~T~" 20^0 yr B.P. 4 5 6 7 8 10 Fig. 2. Composite stratigraphy of the west gulley section at Elkader that was sampled for molluscs (Units 6, 7, 9, 10), insects (Unit 10). and vertebrates (Units 9, 10). Spruce wood, radiocarbon-dated at 20,530 ± 130 yr B.P., was recovered from Unit 10. Descriptions of the stratigraphic units are provided in the text. SUBARCTIC FAUNAL ASSEMBLAGES FROM ELKADER, IOWA 5 relief that was last glaciated in pre-Illinoian time (Hallberg et al., 1984). The site is located in a south-trending gully entrenched into high terrace deposits along the east valley wall of the Turkey River. Fossiliferous sediments were collected primarily from the west side of the gully about midway along its length, where 12 m of colluvium and alluvial fan sedi- ments capped by loess or loess-derived colluvium were exposed (Fig. 2). Complete descriptions of stratigraphic sections were presented by Woodman (1982). The basal 3.5 m of the section (Units 9 and 10) consist of dark gray, cobble-rich, silt-dominated colluvium. The silt matrix here and in overly- ing, silt-dominated units probably is reworked loess. The last episode of loess deposition in northeastern Iowa was continuous from about 25,300- 14,000 yr B.P. (Ruhe. 1969); contemporaneous erosion and redeposition of loess-derived sediments is thought to have been rapid, owing in part to the high topographic relief in the area (Leigh and Knox, 1994). Spruce wood {Picea sp.; F. King, in litt.), recovered from approximately 0.5 m above the base of the section (Unit 10), was dated at 20,530 ± 130 yr B.R (BETA- 2748). Overlying the basal units are about 1.5 m of sediments (Units 6-8) transitional between the coUuvial deposits below and alluvial fan deposits upsection. Convolutions up to 0.5 m high in this part of the section (Unit 7) might have resulted from cryoturbation. Interbedded silts and sands in the overlying 6 m of section (Units 3-5) indicate both a fluvial regime and alluvial fan deposition. Southward, toward the terrace escarpment, the deposit grades into fluvial sands and gravels. The section is capped by up to 2.3 m of loess and/or silt-rich colluvium (Units 1 and 2), reworked from upslope loess deposits. METHODS Sediments were sampled separately for molluscs, insects, and verte- brates because of the different techniques involved in recovering speci- mens. Except as noted below, all samples came from the same section. Because of their abundance and wide distribution at the site, molluscs were collected from a number of different units and at one additional site nearby. CoUuvial sediments were sampled in Units 10 (sample MS3; ca. 30 kg) and 9 (MS2; ca. 20 kg). Smaller samples of local alluvium were collected from Unit 6 (MS4; ca. 15 kg) and a 3-cm, probably fluvial, sand at the base of Unit 7 (MS5; ca. 5 kg). Fluvial sand and gravel lag from a small lens (MS6; ca. 2 kg) downslope contained the richest concentration of molluscs of any of the Elkader units. A 25-kg sample of upland loess was bulk-quarried from a 1-m interval above the basal loess paleosol (MSI). Because the predominantly south-facing exposure here was unusual for fossiliferous loess sites, a 15-kg sample was collected from a nearby east 6 UNIV. KANSAS NAT. HIST. MUS. OCC. PAP. No. 178 and north-facing, calcareous, upland basal loess section (Elkader North: center, NW 1/4, SW 1/4, Sec. 15, R. 5 W., T. 93 N.). Age of the basal loess at Elkader and Elkader North should be comparable. All samples were wet- sieved through a standard series (to 425 jim). Insect analyses were based on 102 kg of sediment sampled from Unit 10. Because stratigraphic sampling of this unit was inhibited by the presence of large, angular clasts and by the disrupted layering of the colluvium, efforts were concentrated on sampling the thin, organic, laminated silt lenses in the unit instead. Beetles and other insect remains were recovered and prepared for identification using standard procedures (Elias, 1994). Nearly 4000 kg of matrix were bulk-quarried for vertebrate remains along a 2-m vertical section from approximately 120 cm below the top of Unit 9 to the base of the section. An additional 450 kg of matrix were collected from mottled, olive-gray silts on the gully's east side that coire- late with Unit 8 in the west section (Woodman, 1982). All sediments were water-screened on 1.6-mm screen and the residues picked for vertebrate remains. Specimens are reposited in the collections of the Quaternary Entomol- ogy Laboratory, North Dakota State University (insects); and the Reposi- tory, Department of Geology, The University of Iowa (molluscs and mam- mals). PALEONTOLOGY We consider the fossils collected from the Elkader site to be entirely autochthonous. The site is located in a small tributary basin approximately a township section (2.59 km^) in size. Some specimens show wear that may be the result of transport, but the upland borders of the drainage basin are less than 650 m distant horizontally; it is unlikely that animal remains were moved fluvially or colluvially farther than this distance, and there is no evidence of transport by predators. In addition, many of the invertebrate species concur ecologically with the depositional environments interpreted for the sediments in which they occur. MOLLUSCA A complete list of the molluscs recovered from Elkader is presented in Table 1 . Sample sizes for all units, with the possible exception of Elkader North, likely are large enough to approximate original diversities (Tables 1 and 2). Preservation at Elkader generally is good, and it is noticeably better in alluvial and colluvial samples, in which full ontogenies are present for abundant taxa. Specimens from fluvial samples are somewhat eroded. 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No. 178 cies recovered from Elkader were provided by Frest and Dickson (1986). Modern di.stributions are based on Pilsbry (1939-1948) and Hubricht (1985). Wisconsinan distributions are based on various sources. Unusual taxa are discussed below. Vertigo hanuai This extinct pupillid has an Illinoian-to- Wisconsinan geological distri- bution. It has been reported from a few Woodfordian sites in Kansas, Iowa, Illinois, and Indiana (Baker et al., 1986:fig. 3). In western Iowa, the species occurs only in sites transitional between the Pleistocene Midwest and Taiga Biomes of Frest and Fay (1980; also Frest and Dickson, 1986:140). The Taiga Biome is hypothesized to have been an irregular band of boreal, coniferous forest with some open parkland that extended from Kansas through Ohio. The Midwest Biome is based on a widespread nonanalogous fauna (sensu Semken, 1988) of molluscs that is typified by a number of endemic species. The biome is believed to have occurred south of the Taiga Biome in northern Missouri, parts of central and southern Illinois, and southern Indiana. The vegetation associated with the Midwest Biome is interpreted to have included a few tree species from both the taiga and mixed coniferous forest-deciduous forest, and the environment is thought to resemble the modern ecotone between those two biomes. Frest and Fay (1980) hypothesized that a more equable climate, with reduced tempera- ture extremes and more available moisture than at present, permitted the coexistence of Midwest Biome species. Vertigo occulta This species is typical of the Midwest Biome and has a pre-Illinoian-to- Wisconsinan fossil range. Currently, Vertigo occulta is a relict species known from six sites in the Paleozoic Plateau in Iowa and Wisconsin. It has been recovered from a few Woodfordian sites in Iowa and western Illinois. Reexamination of specimens identified as V. occulta from other fossil sites indicates that some are large Vertigo nylanderi Sterki, a related species. Only records confirmed by T. Frest are plotted in Figure 3. Vertigo modesta parietalis This taxon has a limited modern distribution within the range of Vertigo modesta modesta (Say) in the Northern Province in Canada (Pilsbry, 1948). There is only one previous record from Peoria Loess (Woodfordian) in western Iowa (Frest and Dickson, 1986). Examination of large numbers of Woodfordian specimens of the V. modesta complex from Iowa, Illinois, and Nebraska yielded additional V. m. parietalis (Fig. 3), all from sites in the Taiga Biome. Fig. 3 (opposite). Distributions by county of selected Elkader molluscs. Dots indicate living (relict) records; filled counties are late Wisconsinan (Woodfordian) sites. SUBARCTIC FAUNAL ASSEMBLAGES FROM ELKADER, IOWA 1 3 Vertigo occulta Vertigo modesta parietalis ifi't" i-T-if .JT Sc^ ^-C\ tft^^ffl \ I 1 1 ^1 — 1 1 ( 1 "^ XTJ VtH^TT) trUrV-^LiJl /* .^W 1^ 1 iiY- -'- II ,7] r^Wri WvR-flJjr —T'^tVl iS2K-" -J 4$^s vP^ffib^y-'-^av -- "-^ "W 'l iyl Z\- ■mt--5-H i-TT _a-T>-i^-/ xi'V^V-HSI i-[a ' ' ,tVi rWvttfVS A-HixiSr _^h7t^^ Htt\ I 1 Lr :7-r±Ul Wrc _n+Yrpp /Yl -dTWWd -VAV'"T\?r, ,-1 ; M^^pWA: i^H^J^^ T = = ^-=§3SffiffiT^ r rrtr lTO?TOim-^IW:tZXj V--- ^t?i"ti L-l/yHA -glplffit^^^ zejtt* — ~ — r ^^m -;:|g|i| ^ JzfxS-L-T --:::--© TO^^^^^^^^Ri! K, I'l i' ini'i'il Rvv-i M >vrn ^3^^ f^ra-lWirVT-D-l-n Discus macclintocki 14 UNIV. KANSAS NAT. HIST. MUS. OCC. PAP. No. 178 Succinea pleistocenica This taxon was reported as Succinea sp. at Conklin Quarry (Baker et al., 1986). The Pleistocene fossil record for this extinct species is poorly known, in part because of confusion with Succinea chittenangoensis (Pilsbry) and an undescribed relict species from Minnesota and Iowa. Discus macclintocki Discus macclintocki also typifies the Midwest Biome. The fossil record of this species ranges from pre-Illinoian to Holocene, and late Woodfordian loess records are known from Nebraska, Iowa, Missouri, Illinois, and Ohio. Twenty-eight small relict colonies are known in the Paleozoic Plateau in Iowa and Illinois (Fig. 3). Fossaria (Bakehlymnciea) dalli Today, Fossaria dalli is uncommon in Iowa, where it occurs in perma- nent lakes and ponds, marshes, and small streams. It occupies similar habitats in southern Ontario and the southern Prairie Province in Canada (Clarke, 1981). Fossaria (Fossaria) exigua In Canada, this small, aquatic snail inhabits mud substrates "in protected parts of lakes and ponds, in backwater areas of rivers, in swamps, and in subarctic muskeg pools" (Clarke, 1981:100). Fossaria (Fossaria) parva This amphibious species is common in eastern Iowa, and is known to occur in marshes, wet mud flats, and near the water's edge on lake shores and river banks south of tree line in Canada (Clarke, 1981). Discussion. — The interpretations of sedimentological units at Elkader as representing fluvial, alluvial, colluvial, and eolian upland environments based on geomorphic and pedological evidence (Woodman, 1982; Hallberg and Bettis, 1985) are supported by their molluscan faunas. This is espe- cially striking because (with the exception of the upland loess sample I MSI J and the Elkader North site) mollusc samples were collected from within an area no more than 1 50 m long. The upland and basal slope faunas are distinct, as are the two upland slope exposures. None of the units has a mollusc assemblage with a modern analog (Tables 2, 3), and no Interior Province endemics (i.e., much of the Elkader area's current land snail fauna) are present. All assemblages have major Rocky Mountain and Northern Province taxa; most include trace Midwest Biome species, and all have significant numbers of extinct taxa. SUBARCTIC FAUNAL ASSEMBLAGES FROM ELKADER, IOWA 15 Table 3. Provincial affinities and diversities of molluscan faunas from Elkader and Conklin Quarry. Figures are numbers of species. Figures in parentheses are percentages. Abbreviations and symbols as in Tables 1 and 2. Molluscan faunal 1 province Total Locality C RM N MW I no. of species Loess: Conklin Quarry 4 (23.5) 3 (17.6) 3 (17.6) 6 (35.2) 1 (5.8) 17 Elkader North 1 (11.1) 3 (33.3) 2 (22.2) 3 (33.3) — 9 MSI 1 (20.0) 2 (40.0) 2 (40.0) — 5 Colluvium: MS2 1 (10.0) 2 (20.0) 4 (40.0) 3 (30.0) 10 MS3 2 (15.4) 2 (15.4) 4 (30.8) 5 (38.5) 13 Alluvium: MS4 2 (20.0) 4 (40.0) 4 (40.0) 10 Fluvium: MS5 2 (15.4) 2 (15.4) 4 (30.8) 5 (38.5) 13 MS6 2 (14.3) 2 (14.3) 4 (28.6) 6 (42.9) — 14 The Elkader upland loess assemblage (MSI) has an unusually low diversity, perhaps because of the southern exposure of the site. The assem- blage from nearby east- and north-facing Elkader North has almost twice the diversity, and the assemblage from the Conklin Quarry site contains more than three times the diversity of the upland loess site (Table 2). Most individuals in the upland loess assemblage are extinct and relict succineids; slugs and small pupillids together account for only about 23% of the fauna (Table 1 ). The presence of slugs and the abundance of succineids suggests an open, cold, but not intensely xeric, environment. If the interpretation of 16 UNIV. KANSAS NAT. HIST. MUS. OCC. PAP. No. 178 the Conklin Quarry upland and swale sites as a partly open, tundra-treeline analog is correct (Baker et al., 1986), the upland at Elkader probably was a still more open and tundra-like habitat. The basal colluvial slope assemblages (MS2, MS3) contrast sharply with that of the upland loess. Diversity is more than double that of the upland sample (Tables 1, 2), and the presence of small numbers of the Midwest Biome species Hendersonia occulta. Vertigo occulta, and Discus macclintocki is noteworthy. Elkader is the most northerly Wisconsinan site for these taxa. Experiments by Frest indicated that the surviving Midwest Biome taxa are stenothermal, glacially adapted calciphiles. Vertigo occulta and Discus macclintocki feed almost exclusively on deciduous leaf litter, particularly leaves of birch (Betula), but also of maple (Acer) and ash {Fra.xi?uis). Their presence suggests the limited persistence of stands of deciduous trees in protected lowlands relatively near the Wisconsinan glacial margin. Slope-base, fluvial deposits (MS5, MS6) have comparatively high di- versities, with the additional taxa being mostly aquatic snails of the genus Fossaria. These assemblages closely resemble that from Conklin Quarry (Baker et al., 1986), except for the inclusion of Midwest Biome taxa. The local alluvial assemblage (MS4) has a diversity and species compo- sition comparable to those of the colluvial sites (MS2, MS3). Collectively, the Elkader molluscs suggest a well-differentiated glacial environment consisting of a mosaic of microhabitats, although it was tundra-like overall. Excluding extinct and relict components, the assem- blages are most closely analogous to those of subarctic parkland near the boreal forest-tundra ecotone. However, the limited persistence of taxa that typify the Midwest Biome suggests the local presence of warmer microcli- mates. The environment at Elkader probably resembled that interpreted for Conklin Quarry, but with colder uplands and a slightly more extensive deciduous component in topographically protected situations. The results from Elkader contrast with previous interpretations from upland loess showing a more regionally homogeneous pattern of recurrent land-snail assemblages within more or less consistent biomes (Leonard and Frye, 1960; Frest and Fay, 1980). The Elkader molluscs more closely resemble a situation hypothesized by Rhodes (1984) to explain non-analo- gous assemblages of small vertebrates associated with alluvial fills in the Loess Hills of western Iowa. Insects Insect remains at Elkader are sparse relative to those of other late Wisconsinan sites, and most are worn and fragmented. A complete list of the taxa identified from Elkader is provided in Table 4. Beetles dominate the assemblage, and ground beetles (Carabidae) are particularly well repre- SUBARCTIC FAUNAL ASSEMBLAGES FROM ELKADER, IOWA 17 Table 4. Coleoptera and other insect fossils from Elkader. Numbers in parenthe- ses refer to the number of indeterminate species within a taxon. Abbreviations for si