Mastodon herbivory in mid-latitude late-Pleistocene boreal forests of eastern North America

Quaternary Research 78 (2012) 72–81

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Mastodon herbivory in mid-latitude late-Pleistocene boreal forests of eastern North America Chelsea L. Teale a, b,⁎, Norton G. Miller a a b

Biological Survey, Research and Collections, New York State Museum, Albany, NY 12230-0001, USA Department of Geography, 302 Walker Building, The Pennsylvania State University, University Park, PA 16801, USA

a r t i c l e

i n f o

Article history: Received 18 August 2011 Available online 30 May 2012 Keywords: Mastodon herbivory Pleistocene megafaunal extinction Younger Dryas chronozone Vegetation history Taphonomy Alnus Hiscock Site Chemung Site Hyde Park mastodon Northeastern United States

a b s t r a c t Skeletal remains of the extinct American mastodon have often been found with deposits of short, decorticated twigs intermixed with plant fragments presumed to be gastrointestinal or fecal material. If such deposits are digesta, paleobotanical evidence may be used to analyze mastodon foraging strategy, with implications for assessing habitat selection, ecological roles, and response to environmental change. To identify components of mastodon diet in mid-latitude late-Pleistocene boreall forests of eastern North America, plant macrofossils and pollen from a molar socket (Hyde Park site, New York) were compared with dispersed deposits associated with skeletal remains (Hiscock and Chemung sites, New York). Similar macrofossil condition and twig morphology among samples, but difference from a modern boreal fen analog, confirmed the deposits were digesta. Comparison of twigs with material from other paleontological sites and modern elephants suggested dimensions generally indicative of digesta. Picea formed the bulk of each sample but Pinus may have been locally important. Wintertime browsing of Salix and Populus, and springtime consumption of Alnus, were indicated. Evidence for Cyperaceae, Gramineae, and Compositae was ambiguous. If conifers, broadleaf trees, shrubs, and herbs were necessary to fulfill dietary requirements, mastodons would have been nutritionally stressed by rapid late-Pleistocene decrease in vegetational diversity. © 2012 University of Washington. Published by Elsevier Inc. All rights reserved.

Introduction Following deglaciation in mid-latitude eastern North America, boreal forest vegetation and coeval animals dispersed northward and westward from southern and/or coastal plain refugia. Postglacial forests were generally composed of Picea glauca (white spruce), Larix laricina (tamarack), Pinus (pine), and Abies balsamea (balsam fir), with Betula papyrifera (paper birch), Populus balsamifera (balsam poplar), and Salix (willow) often present (Davis, 1983; Williams et al., 2004). Mammut americanum (American mastodon) remains in the Great Lakes region are typically recovered from sediments rich in macrofossils and pollen from these trees, usually in proportions indicative of open Picea forest (Oltz and Kapp, 1963; Dreimanis, 1967; Whitehead et al., 1982; King and Saunders, 1984; Kapp, 1986; Saunders, 1996; Griggs and Kromer, 2008). Detailed investigations into mastodon herbivory are relatively recent but a browsing habit has long been presumed (Warren, 1855; Hartnagel and Bishop, 1922; Saunders, 1996). This conclusion is supported by fossil evidence of forest type, tooth morphology, paleobotanical assemblages found with skeletal remains, and stable isotope analyses of teeth and bones (Kurtén and Anderson, 1980; ⁎ Corresponding author at: Biological Survey, Research and Collections, New York State Museum, Albany, NY 12230-0001, USA. E-mail address: [email protected] (C.L. Teale).

Koch, 1991; Saunders, 1996). Generalizing mastodon feeding strategy, however, is complicated by evidence from additional localities and new analyses that indicate a diverse diet including broadleaf and herbaceous plants (Hartnagel and Bishop, 1922; Lepper et al., 1991; Webb et al., 1992; Gobetz and Bozarth, 2001; Green et al., 2005; Newsom and Mihlbachler, 2006). In order to understand mastodon herbivory—and therefore habitat selection, ecological roles, and response to environmental change—it is necessary to examine all identifiable components of their diet at various periods and regions across North America. The study American mastodon remains have been found from Alaska to central Mexico, including the Atlantic Coastal Plain, which was above sea level during the Wisconsinan glaciation. Most date to the late Pleistocene and are commonly found in peaty or marly sediments that provided water, minerals, forage, and often places to become mired and entombed (Hartnagel and Bishop, 1922; Kurtén and Anderson, 1980; Miller and Nester, 2006). Mastodon fossils are frequently recovered from wetlands and open water environments in the Great Lakes basin and along the Atlantic Coast; with at least 140 known occurrences, New York State is second only to Michigan in number of verified mastodon sites (Thompson et al., 2008). Digesta associated with mastodons found in these areas may reflect browsing

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C.L. Teale, N.G. Miller / Quaternary Research 78 (2012) 72–81

strategy throughout mid-latitude late-Pleistocene boreal forests of eastern North America. Objectives of this study are to describe and compare digesta from three sites in New York State using a combination of plant macrofossil and palynological analyses to identify components of mastodon diet (Fig. 1). Macrofossils can provide direct evidence of plant consumption because they are not easily dispersed, but pollen is more mobile, consumed indirectly, and passes unpredictably through the digestive tract (see Davis, 2006 and works referenced therein). However, pollen can provide supporting evidence when macrofossil identification is constrained and indicate when additional proxy analyses are warranted. The three sites date to the Allerød interstade and Younger Dryas chronozone, and each provides an opportunity to examine mastodon diet during a time of climatic and vegetational instability when most megaherbivores became extinct in North America (Shuman et al., 2002; Barnosky et al., 2004; Fig. 1). There is no evidence for hunting, butchering, or malnutrition at these sites. Macrofossils and twigs were also compared to a modern analog, material from other paleontological sites, and modern elephant dung to evaluate taphonomic differences and identify possible indicator fossils of mastodon digesta.

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in marly peat and dated to 11,480 ± 50 14C yr BP (Miller and Nester, 2006). Paleoecological analysis of Lozier Pond sediments indicates the animal inhabited an open forest of P. glauca, A. balsamea, and L. laricina (Miller, 2008). The shallow pond and surrounding fen were characterized by emergent aquatic plants, including Carex (sedges), Eleocharis palustris (spikerush), Hippuris vulgaris (mare's tail), Sparganium (bur reed), Scirpus tabernaemontani (bulrush), Najas flexilis (naiad), and Typha (cattail), and rooted floating aquatic plants like Potamogeton (pondweed) and Myriophyllum sibiricum (water milfoil). Other plants along the fen margin included Hypericum virginicum (marsh St. John's wort), Lycopus americanus (water horehound), Ranunculus (crowfoot), and Sagittaria (arrowhead) (Miller, 2008). A small amount of organic matter was removed from a gap between the mastodon's mandible and adjacent m2 and m3 (Fig. 2). By analogy with the process of mesial drift in extant proboscideans—where newly erupted teeth move forward to eventually replace those that have worn out—this gap resulted from natural dissolution and degeneration of the alveolar bone around the exfoliating m2. Food is commonly impacted in such spaces, causing periodontal disease that can promote exfoliation by further degrading tissue (Fagan, D., personal communication, 2012). This sample provides unequivocal evidence of plant consumption.

Study sites Hiscock Site Hyde Park site The Hyde Park site of Dutchess County is a basin (Lozier Pond) located 3 km east of the Hudson River at 68 m asl on the Hyde Park Moraine. Lozier Pond originated as an oxbow of the Fall Kill, existed as a forested wetland prior to excavation, and currently measures 28 by 40 m and ca. 1.8 m deep. Basal cobbles, silt, and clay were overlain by sediment that began to accumulate around 13,000 14C yr BP. Further site analysis is given in Allmon and Nester (2008). While deepening the basin to its current dimensions in 1999, the owners unearthed a single adult male mastodon that likely died as the result of a springtime musth battle (Fisher, 2008). It was found

The Hiscock Site of Genesee County, a 1.9-acre spring-fed wetland at 189 m asl within the Ontario Lowland, was deglaciated around 13,000 14C yr BP. The site has been excavated since 1983 and detailed studies are found in Laub et al. (1988) and Laub (2003a). Palynological data from it and nearby sites indicate regional colonization first by tundra species followed by an open, post-glacial P. glauca forest at ca. 12,000 14C yr BP, with Pinus banksiana (jack pine) and an understory of Shepherdia canadensis (buffaloberry) (Miller, 1988; Miller and Futyma, 2003). Pleistocene fauna, including several mastodons that died in the basin beginning ca. 11,033 ± 40 14C yr BP, may have used the wetland as a mineral lick (Laub, 2003b; McAndrews, 2003;

Figure 1. Site locator map. Hyde Park (41°46.75′N, 73°53.67′W), Hiscock Site (45°5.067′N, 78°4.095′W), Chemung Site (42°15′N, 76°51′W), and Cedar Bridge (43°55.67′N, 73°34.74′W).

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C.L. Teale, N.G. Miller / Quaternary Research 78 (2012) 72–81

Skeletal remains were interspersed with green plant material and gravel, termed the “mastodon matrix,” which lost its color within an hour of exposure to air (Griggs and Kromer, 2008). This layer was thought to have the same origin as the Hiscock Site's FGC and Page– Ladson Site's straw layer, namely a digesta deposit with contributions from several megaherbivores. Griggs and Kromer (2008) identified nearly 1000 twigs from the mastodon matrix, 78% of which were Picea or L. laricina and of similar age as the bones. Another 9% were from Populus or Salix, 8% from Pinus, and 5% from A. balsamea. Cedar Bridge

Figure 2. Lower mandible of the Hyde Park mastodon. Arrow indicates the molar socket. (Image from Fisher, 2008.)

Ponomarenko and Telka, 2003). Mastodons contributed 95% of the site's skeletal remains and died without evidence of severe nutritional stress and in different seasons including early winter, late winter/early spring, and summer (Fisher and Fox, 2003). Mastodon remains at the Hiscock Site were found in a layer of “fibrous, gravelly clay” (FGC) above basal cobbles (Laub et al., 1994). Twigs within this layer have also been dated to the late Pleistocene and the matrix interpreted as clay, silt, and gravel mixed with dung and gastrointestinal material left by mastodons wallowing and decomposing in the springs (Laub et al., 1994; McAndrews, 2003). Modern elephant behavior at watering holes supports this theory, and the same conclusion was reached for a similar deposit in a Florida sinkhole (the Page–Ladson Site's “straw layer”) on the basis of plant macrofossil preservation characteristics (Newsom and Mihlbachler, 2006). Previous pollen analysis of the FGC revealed ca. 80% contribution from non-arboreal sources and a higher diversity of herbs and shrubs than in overlying stratigraphic units, where NAP did not exceed 20% (Miller, 1988; Table 1). Contemporaneous sediments in the region also had higher AP:NAP and significantly less Gramineae and insectpollinated Compositae (Miller and Futyma, 2003). Chemung Site The Chemung Site (also referred to as the Watkins Glen, Cornell, or Gilbert Site) of Chemung County is a spring-fed pond approximately 25 km south of Seneca Lake at 290 m asl, just north of the Valley Heads Moraine. Following deglaciation that began ca. 14,400 14C yr BP, the kettle pond gradually became shallow, anoxic, and surrounded by an acidic fen. In 1999 the owners excavated the basin and discovered a nearly complete skeleton of an adult male mastodon and a partial mammoth (Mammuthus sp.) skeleton, as well as bones from a stag-moose (Cervalces scotti) (Griggs and Kromer, 2008). More information is given by Allmon and Nester (2008). The mastodon dated to 10,840 ± 60 14C yr BP, when the Picea forest was open and probably also contained L. laricina, A. balsamea, B. papyrifera, Populus, and Salix (Griggs and Kromer, 2008).

The modern analog is a circumneutral boreal treed fen at 1160 m asl in the Adirondack Mountains of Essex County. The peat did not appear to be associated with animal remains or show evidence of post-depositional modification. Comparison of the fen's stratigraphy with a dated pollen profile from nearby Brandreth Bog indicated the sediment sampled for plant macrofossil analysis was deposited after 1000 14C yr BP (Overpeck, 1985). Although many late-Pleistocene environments consisted of species assemblages not found anywhere today (Overpeck et al., 1992), current conditions at Cedar Bridge may have resembled late-Pleistocene boreal forest and indicator plant species suggest water chemistry similar to Lozier Pond. Therefore, Cedar Bridge serves as a suitable modern analog for evaluating taphonomic aspects of plant macrofossil assemblages from the Hyde Park molar socket, Hiscock Site FGC, and the Chemung Site mastodon matrix. The Sphagnum mat of Cedar Bridge supports Alnus serrulata (hazel alder), Andromeda glaucophylla (bog rosemary), Gaultheria hispidula (creeping snowberry), Ilex verticillata (common winterberry), Kalmia angustifolia (sheep laurel), Kalmia polifolia (bog laurel), Myrica gale (sweetgale), Nemopanthus mucronata (mountain holly), Rhododendron groenlandicum (Labrador tea), Carex trisperma (three-seeded sedge) and other sedges, Eriophorum virginicum (cottongrass), and Chamaedaphne calyculata (leatherleaf). Wetland forest vegetation consists of Picea mariana (black spruce), Thuja occidentalis (eastern white cedar), L. laricina, and Acer rubrum (red maple). Methods Field collection The Hyde Park molar socket contents were removed immediately post-excavation in 2002 at the Paleontological Research Institution, Ithaca, New York, during procedures related to bone stabilization. The 35 mL sample was refrigerated until analyzed for pollen, macrofossil, and twig content in 2005. Three bulk samples of Hiscock Site FGC were obtained in 2002 for macrofossil and twig analysis from excavation pit J3NW (97–111 cm depth: 2.46 L, 102–111 cm depth: 710 mL, 116–125 cm depth: 750 mL). Samples were refrigerated until analysis in 2004. A 100-mL bulk sample of Chemung Site mastodon matrix was collected in 1990 and refrigerated until pollen analysis in 2005 and twig analysis in 2011. Three bulk sediment samples from Cedar Bridge were collected and prepared in 2004 for macrofossil and twig analyses. Samples were taken 20 m inside the peat mat from a 5 by 5 m plot under a P. mariana stand of approximately 15 trees, with a few A. balsamea and one T. occidentalis. Sample 1 (1 L) was taken from 0 to 5 cm, Sample 2 (575 mL) from 5 to 10 cm, and Sample 3 (400 mL) from 20 to 25 cm below the surface. Laboratory analyses Pollen Pollen counts from the Hyde Park and Chemung Site samples were obtained from 2-mL subsamples following standard procedures involving successive treatments in 10% HCl, 10% KOH, and acetolysis solution (Fægri

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Table 1 Late-glacial pollen spectra (percentages) from the Hyde Park molar socket, Hiscock Site fibrous gravelly clay (FGC), and Chemung Site mastodon matrix. Hiscock spectra are from Miller (1988) with depth from surface indicated. Taxon/site Trees Picea Abies Larix Pinus diplox. P. strobus P. undiff. Thuja/Juniperus Populus Quercus Fagus Carpinus/Ostrya Betula Ulmus Acer Carya Fraxinus nigra F. sp. Shrubs Cornus spp. Sambucus pubens Salix spp. Alnus Ericaceae Corylus Myrica Herbs Cyperaceae Gramineae Artemisia Ambrosia Plantago Iva High-spine Compositae Cichorioideae Urticacae Umbelliferae Labiatae Potentilla palustris Other Rosaceae Thalictrum Cruciferae Galium Caryophyllaceae Scrophulariaceae small Scrophulariaceae large Epilobium Sum AP Sum NAP Percentage base A Ferns and allies Lycopodium Ophioglossaceae Polypodiaceae Selaginella selaginoides Aquatics and miscellaneous Myriophyllum Potamogeton Sparganium/Typha Hippurus Pediastrum Conifer stomataa Unidentifiable Unknown Percentage base B a

Hyde Park molar socket

Hiscock Site FGC 149 cm

Hiscock Site FGC 164 cm

Hiscock Site FGC 174 cm

Chemung Site mastodon matrix

4.4 – – – – 1.3 – – 0.5 – – 5.3 – – – – –

10 – – 0.5 – 2.5 0.3 – – – – 0.6 0.1 0.1 0.1 – –

9 – – 0.5 – 2.5 0.4 0.1 – – 0.5 0.6 – – – – –

15.5 – – 2 – 2 0.4 – 0.3 – 0.5 0.6 – – – – –

19 0.6 0.2 7 0.8 9 – – 2 0.3 2 0.6 0.5 0.2 – 0.6 0.5

– – 1.1 80.9 0.1 0.1 1.1

0.6 – 0.5 – – – –

1 – 0.5 – – – –

0.2 – 0.5 0.1 0.1 – 0.1

0.8 0.3 11 0.2 – – –

2.6 1 0.5 – – – 0.6 – – – – – – 0.1 – 0.1 – – – – 12 88 797

27 30 0.8 0.4 0.6 – 20 0.1 – – 0.5 2.5 2 0.1 0.1 – 0.2 0.2 0.1 1.2 13 87 1561

32 27 0.8 0.9 1 – 15 – – 0.2 0.4 2.5 1.5 – – – 0.2 1.3 – 0.5 15 85 1285

50.5 21.5 0.7 0.3 1 – 3 0.2 – – 0.5 0.3 0.5 – – – – 0.2 – 0.4 20 80 760

25 10 0.6 0.5 – 0.2 4 – 0.2 1.3 – – 1.1 0.2 1.1 0.2 – – – – 43 57 621

– – 0.5 –

– 0.2 0.3 –

– 0.3 0.1 –

– 1 0.3 –

0.1 0.1 0.3 0.1

0.1 – – – 0.1 0.4 0.1 4.5 806

– – – – – – 4 0.3 1640

– – – – – – 5.2 3 1368

– – – – – – 3 1 803

0.4 1.5 0.6 0.1 0.1 5.1 4 2 720

Solitary or in linear groups with other epidermal cells.

and Iversen, 1975). Prior to acetolysis, larger plant fragments were removed by sieving through a 125-μm screen. Samples were then washed through a 10-μm nylon mesh and the residue recaptured, cleaned, and

mounted in 2000-cs silicone oil from tertiary butyl alcohol. Counts were performed at 400× magnification. Pollen data for the Hiscock Site were previously reported by Miller (1988).

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Macrofossils After pollen analysis, the remainder of the Hyde Park sample (33 mL) was used for macrofossil and twig counts. The three Hiscock Site FGC bulk samples were analyzed for twigs and 140-mL subsamples from each were analyzed for macrofossils. Macrofossil analysis of the Chemung Site matrix is the subject of an ongoing project through Cornell University and the Paleontological Research Institution. Four subsamples of 100 mL each were taken from the Cedar Bridge bulk samples for macrofossil analysis, and three subsamples of 500 mL and one of 400 mL were used for twig counts. Macrofossil samples were disaggregated in warm water and small particles eliminated by water washes through a 250-μm screen. Sample residues were examined under a dissecting microscope and plant fragments were separated, identified, and placed in vials with 70% ethyl alcohol for storage in the New York State Museum's Quaternary Paleobotany Collection. Identification was aided using the Museum's Fruit, Seed, and Plant Fragment Collection, derived from voucher specimens in the Museum's Vascular Plant Herbarium and other sources. Twigs at least 1 mm in diameter from each site were measured and recorded. Narrower twigs were too numerous to count and often indiscernible from other plant fibers.

Results Hyde Park molar socket The Hyde Park molar socket primarily contained degraded Picea needle fragments, branch cortex with sterigmata, bud scales, and buds (Table 2). P. balsamifera (branch fragments), Betula/Alnus (eroded achenes), and Salix (buds and bark) were also represented by abundant macrofossils. N. flexilis (seed coat fragments), Viola (violet; seeds), M. sibiricum (leaf fragments and fruits), and charophyte (an alga) oogonia were identified. Non-arboreal pollen contributed almost 90% of the total, with Betula (5%), Picea (4%), and Pinus (1%) as representative tree genera (Table 1). Herbaceous plants contributed 5%, more than half that amount from Cyperaceae, and others 1% or less. Alnus comprised 81% of total pollen, in contrast to 15% in surrounding Lozier Pond sediment. This high percentage indicates that the Betula/Alnus achenes (over thirty) were probably Alnus, though Betula cannot be ruled out. Most Alnus pollen (77% of 274 Alnus grains) was the Alnus rugosa type (Richard, 1970; McAndrews et al., 1973; Mayle et al., 1993), which includes the following species: Alnus incana subsp. rugosa (DuRoi) R. T. Clausen, A. serrulata (Aiton) Willdenow, and Alnus maritima (Marshall) Muhlenberg (Furlow, 1997). Twenty percent of the sample was obscured or too poorly preserved to be identified, and the remaining 3% Alnus viridis subsp. crispa (Aiton) Turrell. Alnus sheds pollen in spring, confirming the season of death previously determined by analysis of tusk growth patterns (Fisher, 2008).

Hiscock Site fibrous, gravelly clay Like the Hyde Park molar socket contents, the Hiscock Site FGC was characterized by degraded Picea needle fragments (tips, bases, cuticle, cushions, vascular bundles), cone scales, bud/twig scales, and detached branch cortex with sterigmata (Table 2). Very few intact needles were recovered. Other arboreal material included L. laricina (possible cone scale fragments) and P. banksiana (possible seed with wing and a cone scale). Miller (1988) reported AP:NAP as 1:9, with high herb and shrub diversity, and Cyperaceae, Ranunculus, and Potentilla (cinquefoil) were also represented by macrofossils. A fruit stone of Rubus (blackberry or dewberry), two leaf fragments of Dryas integrifolia (mountain avens), and three unidentified angiosperm leaf fragments and one petiole were also found (Table 2).

Table 2 Plant macrofossils from the Hyde Park molar socket, Hiscock Site fibrous gravelly clay (FGC), and Cedar Bridge fen analog. Macrofossil analysis of Chemung Site mastodon matrix is ongoing through Cornell University and the Paleontological Research Institution. Values are fossil number per 100 mL and represent counts per sample rounded to nearest whole number, but if less than 1, rounded up to 1. Macrofossil type/site name Trees and shrubs Picea Whole needles Needle tips Needle bases Needle vascular bundles Detached needle cushions Branch cortex with attached sterigmata Buds Bud/twig scales Cones Cone scales Seed wings Microsporangia Microsporangial bracts Microsporangial cones Larix laricina Whole needles Needle tips Needle bases Cones Cone scales Short shoots Abies balsamea Whole needles Needle tips Cone fragments Pinus strobus Needle fragments Needle tips cf. Pinus banksiana Seed Cone scale Populus balsamifera Branch fragments Salix Buds Bud scales Bark Betula/Alnus Bract Fruits Upland taxa Ranunculus Achene Rubus Fruit stone cf. Dryas integrifolia Leaf fragments Aquatic, wetland, and damp-ground Myriophyllum sibericum Fruits Turion leaf fragments Viola Seeds Najas flexilis Seed coat fragments Potentilla Fruits Cyperaceae Achenes Perigynium and achene Eriophorum virginicum Achenes Receptacle

Hyde Park molar socket

Hiscock Site FGC

Cedar Bridge fen analog

9 80 40 6 0 80

15 376 159 234 575 642

124 50 28 0 0 0

3 6 0 0 0 1 1 0

0 51 0 12 0 0 0 0

0 1 1 1 1 1 0 1

0 0 0 0 0 0

0 0 0 0 9 1

30 19 17 1 0 2

0 0 0

0 0 0

1 2 1

0 0

0 0

1 1

0 0

1 1

0 0

14

0

0

1 0 20

0 1 0

0 0 0

0 34

0 0

1 1

0

1

0

0

1

0

3

2

0

6 11

0 0

0 0

3

0

0

11

0

0

0

2

0

0 0

13 0

2 1

0 0

0 0

2 1

taxa

C.L. Teale, N.G. Miller / Quaternary Research 78 (2012) 72–81

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Table 2 (continued) Macrofossil type/site name

Hyde Park molar socket

Hiscock Site FGC

Cedar Bridge fen analog

0 0

0 0

1 1

0

0

1

0

0

1

0

0

1

0

0

1

0

0

1

Miscellaneous and unidentified Charophyte oogonia Angiosperm leaf fragments Angiosperm leaf petiole base Angiosperm leaf petioles Unidentified seeds/fruits

9 0 1 0 0

0 3 0 1 1

0 0 0 0 0

Twigs (≥1 mm diameter) Total number Corticated Decorticated

151 0 151

231 0 231

22 17 5

Chamaedaphne calyculata Fruit Leaf fragments cf. Ilex verticillata Seed Rhododendron groenlandicum Leaf fragments Andromeda glaucophylla Leaf fragment Vaccinium sp. Leaf fragment Myrica gale Leaf fragment

Chemung Site mastodon matrix Griggs and Kromer (2008) identified 967 twigs from the mastodon matrix, including 758 Picea and/or L. laricina. Picea contributed 19% and L. laricina 0.2% of total pollen (Table 1), though Larix pollen is not widely dispersed and twigs could have been transported in the gut for some distance. However, P. glauca cones were also found in the matrix and during this investigation cone scale fragments were observed. Smaller numbers of twigs were from Pinus and Abies, which respectively contributed approximately 17% and 0.6% of total pollen. Nearly 100 twigs were either Populus or Salix, but no pollen was identified as Populus while 11% was Salix. Non-arboreal plants contributed over half of total pollen, though 25% was from Cyperaceae; Gramineae provided 10%, high-spine Compositae 4%, and other herbs 0.1–1.3% of the total (Table 1). Cedar Bridge The Cedar Bridge analog macrofossil assemblage consisted mainly of intact P. mariana and L. laricina needles, as well as A. balsamea, T. occidentalis, and Pinus strobus tangled in a matrix of Sphagnum (Table 2). Twigs of P. mariana were abundant. Few needle fragments and minimal detached cuticle, cortex, or sterigmata were recovered. Seeds, fruits, and achenes were identified as B. papyrifera, Cyperaceae, C. calyculata, E. virginicum, and I. verticillata. Leaf fragments of Vaccinium (probably blueberry or cranberry), R. groenlandicum, M. gale, C. calyculata, and B. papyrifera were also identified. Plants of these species are currently found at the fen-mat surface, indicating little vegetational change during peat accumulation. Twigs Twigs found in the Hyde Park molar socket were decorticated, with ends sheared cleanly, and broken into lengths that ranged from 0.2 to 6.0 cm (n= 95, average = 1 cm, median= 0.7 cm). The majority of twigs from the Hiscock Site FGC was similar in condition and many were split or crushed, also between 0.2 and 6.0 cm (n= 830, average = 1.4 cm, median= 1.3 cm). Twigs from the Chemung Site mastodon matrix were identical and ranged in length from 0.2 to 5.4 cm (n= 180, average = 0.96 cm, median = 0.8 cm). Conversely,

Figure 3. Statistical comparison of twig length. Boxes encompass the interquartile range (IQR), horizontal lines are median lengths, circles represent means, the upper whisker is median plus IQR × 1.5, the lower whisker extends to the minimum value measured, and solid squares indicate outliers.

Cedar Bridge contained twigs that were nearly all cylindrical, with bark and sterigmata attached, ranging from 0.3 to 11.5 cm (n= 419, average = 2.0 cm, median= 1.5 cm). Figure 3 summarizes these measurements. Because none of the twig-length distributions is normal, the nonparametric two-sample Kolmogorov–Smirnov (K–S) test was chosen to compare twig lengths from each sample (H0: twig lengths in each dataset are drawn from the same distribution). The K–S test uses a D statistic (maximum deviation between cumulative frequency distributions) to calculate p, which in all comparisons indicated significant differences between datasets (all p-values are at zero except Hyde Park vs. Chemung Site, where p = 0.003). The null hypothesis was therefore rejected for each comparison, suggesting that although there was a significant difference between lengths of naturally deposited twigs and those associated with mastodons, digesta samples were also dissimilar. This may be due to the accumulation of allochthonous material in the Hiscock and Chemung basins. Although none of the twig samples were statistically identical, the Hyde Park, Hiscock, and Chemung samples had shorter ranges and average lengths than the Cedar Bridge analog (Fig. 3). The analog also had the highest mean length and greatest range of lengths when compared to twigs and fibers measured from other mastodon digesta and modern elephant dung (Table 3). Twig condition was qualitatively similar among the three digesta samples analyzed here (Fig. 4) and compared favorably to those from other mastodon sites, particularly the Page–Ladson Site of north Florida. There, Newsom and Mihlbachler (2006) were able to exclude several other megaherbivores as the source of a digesta deposit comprised mainly of decorticated Taxodium (cypress) twigs less than 3 yr old. Other mastodons in New York have also found with digesta containing similar twigs, which are described in Warren (1855) and Hartnagel and Bishop (1922) and summarized in Laub et al. (1994).

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Table 3 Twig lengths (cm) reported from mastodon sites, modern elephants, and Cedar Bridge fen analog. Values are as reported in published articles or through personal communications with authors, and listed in order of increasing maximum length. Location

Source

Min length

Max length

Mean length

Range

SD

N

Latvis–Simpson site, FL Burning Tree site, OH Page–Ladson Site, FL (FS 28C) Goshen, NY Loxodonta (Amboseli) Jamestown, NY Chemung Site, NY Loxodonta (North Kenya) Hiscock Site, NY Hyde Park molar socket, NY Elephant “Lulu” Elephant “Surapa” Page–Ladson Site, FL (FS 24C) Page–Ladson Site, FL (FS 131) Cedar Bridge fen analog, NY

Mihlbachler (1998) Lepper (pers. comm. 2008) Newsom and Mihlbachler (2006) Warren (1855) Newsom and Mihlbachler (2006) Hartnagel and Bishop (1922) This study Newsom and Mihlbachler (2006) this study this study Laub et al. (1994) Laub et al. (1994) Newsom and Mihlbachler (2006) Newsom and Mihlbachler (2006) This study

0.6 1.5 0.3 2.54a 0.2 1.27a 0.2 0.5 0.2 0.5 1.0 1.0 0.4 0.1 0.5

1.2 2.58 3.5 3.81a 5.0 5.0a 5.4 5.6 6.0 6.0 6.2 7.0 8.9 9.9 11.5

– 2.0 1.3 – 1.03 – 0.96 1.24 1.4 1.0 1.89 1.74 1.26 1.07 2.1

0.6 1.08 3.2 – 4.8 – 5.2 5.1 5.5 5.5 5.2 6.0 8.5 9.8 11.0

– 0.6 0.47 – 0.59 – 0.62 0.66 0.77 0.9 0.87 0.77 0.85 0.54 1.7

– 14 612 – 672 – 180 329 1068 98 – – 209 788 419

a

Converted to centimeters from inches.

Discussion Evidence for mastodon diet from mid-latitude, late-Pleistocene eastern boreal forests The contents of the Hyde Park molar socket were interpreted as intentionally ingested and masticated plant material. Consumption of Picea was clearly indicated by large amounts of degraded macrofossils, and the relatively low percentage of Picea and Betula pollen resulted from overwhelming contribution by Alnus. Although the 34 achenes could have been from Betula, the corresponding high amount of Alnus pollen indicates recent browsing of alder catkins. Alnus is highly nutritious but toxic in winter, becoming more palatable and digestible in spring (Bryant and Kuropat, 1980). Betula and Alnus could have become important components of mastodon diet during the Younger Dryas when they increased in abundance in the Northeast (Mayle et al., 1993; Williams et al., 2004). Consumption of other broadleaf plants was indicated by fragments of P. balsamifera branches and Salix bark, but the lack of fruits and pollen suggests that woody tissue was consumed earlier in the spring or possibly during the winter. Young wood and buds of P. balsamifera contain resins toxic to monogastric

herbivores, but mature trees are relatively undefended—perhaps why only branch fragments, suggesting an older tree, were identified (Bryant and Kuropat, 1980). Salix provides few nutrients in winter but wood and buds do offer calories and are less resinous. Like the Hyde Park sample, the Hiscock Site FGC was dominated by Picea macrofossils while pollen from herbaceous taxa (primarily Gramineae and Compositae) was relatively more abundant than from trees—even when excluding Cyperaceae, which also provided a large amount of macrofossils. However, modern elephants typically clear woody vegetation from around watering holes and mineral licks and herbaceous plants would have been locally common (Laub, 2003a). Larix cone scales and a possible P. banksiana seed and scale could have entered the basin through mastodon activity, but a general lack of macrofossil evidence for plants other than Picea and Cyperaceae makes further speculation difficult. Likewise, over half of total pollen in the Chemung Site mastodon matrix was from non-arboreal plants, mostly Cyperaceae and Gramineae. Relatively high amounts of Pinus and Salix pollen and twigs in the mastodon matrix indicated they were browsed along with Picea. Pinus (and Abies, also a twig contributor) began to increase in forests around the Chemung Site early on and could have substituted

Figure 4. Visual comparison of twigs. A) all twigs from Hyde Park molar socket (35 mL); B) subsample of twigs from Hiscock Site (35 mL); C) all twigs from Chemung Site (100 mL); D) subsample from Cedar Bridge fen analog (300 mL).

C.L. Teale, N.G. Miller / Quaternary Research 78 (2012) 72–81

for spruce in some locations (Williams et al., 2004). It is noteworthy that the Hiscock Site FGC accumulated during periods both of regional Picea dominance and localized Pinus increase, but samples contained minimal pine pollen and macrofossils. King and Saunders (1984) proposed physiological adaptations to Pinus in the Midwest but it does not appear to have been an ideal food. Picea also characterized the Cedar Bridge macrofossil and twig assemblages but material was better preserved than those of the digesta samples, indicating that fossils in digesta were subject to different taphonomic processes. Conifer material was presumably concentrated in digesta as a result of selective consumption, and eroded through mastication, digestion, and trampling. Specifically, needles were broken and cortex and sterigmata detached from twigs. The analog and digesta samples compared favorably, however, in that broadleaf and herbaceous material was more completely decomposed—and therefore more difficult to identify—compared to conifer fossils. This indicates the need to include additional proxies (e.g., phytoliths, cuticle analysis) in paleoenvironmental and paleodiet analyses. Twig appearance and dimensions were also different in naturally deposited sediments and digesta. Twigs at Cedar Bridge were more intact and showed a greater range of length than twigs found in the Hyde Park molar socket, Hiscock Site FGC, Chemung Site mastodon matrix, digesta of other mastodons, and modern elephants (Table 3). Our data show that anomalously large quantities of decorticated twigs less than ca. 10 cm and averaging 1–2 cm in length, in association with skeletal remains, are indicators of mastodon digesta. This conclusion holds true for twigs of any species, because this and other studies confirm consumption of broadleaf trees and shrubs by American mastodons. Implications for mastodon herbivory and extinction in North America Extinction of 15 of 35 North American megafauna species was roughly contemporaneous with Clovis arrival and the Younger Dryas chronozone (Barnosky et al., 2004). Megafaunal extinction at the end of the Pleistocene has therefore been attributed to overkill by humans, environmental change, or a combination of both. Identifying components of mastodon diet is central to understanding which factors contributed to their extinction. Late-Pleistocene vegetational reorganization was rapid in much of North America (Williams et al., 2004) and may have led to regional extirpation caused by decreased extent of coniferous forests (King and Saunders, 1984), less-diverse plant assemblages (Guthrie, 1984), and possibly “co-evolutionary disequilibrium” between plant and animal communities (Graham and Lundelius, 1984). The ecological roles of megaherbivores in plant dispersal and maintaining open forests are also in question (Owen-Smith, 1987; Newsom and Mihlbachler, 2006; Johnson, 2009). The contents of the Hyde Park, Hiscock, and Chemung samples complement descriptions of digesta elsewhere—most obviously small, decorticated twigs of uniform size (Warren, 1855; Bishop, 1921; Hartnagel and Bishop, 1922; Lepper et al., 1991; Webb et al., 1992; Laub et al., 1994; Mihlbachler, 1998; Newsom and Mihlbachler, 2006; Griggs and Kromer, 2008). These twigs have been identified as Picea or Larix in the Great Lakes region, whereas Taxodium formed the bulk of digesta in Florida (Newsom and Mihlbachler, 2006). Mastodons in west-central North America have been recovered from locations rich in Pinus (Mead et al., 1979; King and Saunders, 1984; Miller, 1987), but analyses of digesta in those regions are lacking. The presence of Pinus at the Chemung Site suggests it may have also been a food source in the east, at least in areas where Picea was becoming less abundant. This and other studies suggest conifers provided the bulk of mastodon browse, but there is evidence for a more diverse diet and taphonomic bias in fossil preservation. Plant macrofossils in digesta from Florida were primarily from deciduous trees and shrubs, Cucurbita pepo (gourd), Vitis (wild grape), and herbaceous plants (Webb et al., 1992; Mihlbachler, 1998; Newsom and Mihlbachler, 2006). Patterns of

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enamel scarring on 76 mastodon teeth from the same region also indicated heavy bark and fruit consumption (Green et al., 2005). Pollen from a tooth in Washington was mainly contributed by Pinus, Salix, Shepherdia canadensis, Rosaceae, Compositae, Cyperaceae, and Gramineae (Petersen et al., 1983). Phytoliths from the teeth of four Kansas mastodons indicated consumption of Gramineae, Celtis (hackberry), and some deciduous trees (Gobetz and Bozarth, 2001). Stomach contents of an Ohio mastodon living in a forest of Picea, Pinus, and Abies contained aquatic species and Amaranthus (pigweed) but no conifer twigs (Lepper et al., 1991). Over half (62%) of the pollen recovered from its teeth was from Cyperaceae, Gramineae, and aquatic plants. An 1874 report of digesta from western New York similarly listed only material from riparian herbaceous species and mosses (Stodder, 1875; Hartnagel and Bishop, 1922: 58). A mass of “half-masticated reeds, twigs, and grass or leaves” was also found with a Virginia mastodon (Warren, 1855). In addition, seasonal and location-specific diets have been suggested by isotope ratios. Reliance on C3 plants is indicated by δ13C measurements from Florida, Michigan, Ohio, Indiana, Illinois, New York, and the Atlantic Coastal Plain (Koch, 1991; Koch et al., 1998; Saunders et al., 2010). However, the δ13C of one Illinois mastodon was higher than others nearby, likely because it was found in a calcareous wetland complex and would have grazed on aquatic vegetation when available (Saunders et al., 2010). Similarly, seasonal consumption of Cyperaceae could be indicated by fluctuating δ13C levels in Hiscock Site mastodons (Fisher and Fox, 2003). Strontium ratios also provide evidence for late-Pleistocene mastodon migration in the Southeast, which was not detected in older specimens and could have been environmentally triggered (Hoppe and Koch, 2007). Mastodon foraging strategy might be clarified through comparison with extant ruminant and monogastric herbivores. Ruminants have been observed to balance consumption of instantaneous energy sources (usually larger plants that satiate quickly, but are often difficult to digest) and daily energy sources (typically smaller plants that take longer to locate and consume but are more digestible and nutritious) (Babin et al., 2011). The staples of monogastric diet are typically nutrient-poor but chemically undefended, and are therefore consumed in large quantities; supplements are more nutritious but eaten only when toxin levels are low (Guthrie, 1984). Mastodons probably employed a similar foraging strategy: low-quality but digestible conifers constituted the bulk of their diet, but broadleaf and herbaceous species provided supplemental nutrients when toxin levels decreased (usually seasonally).

Conclusion The contents of the Hyde Park mastodon's molar socket provided a unique opportunity to examine direct paleobotanical evidence of diet at a known time of year. This study is the first to compare such evidence to material from other deposits and a modern analog in order to propose a general indicator fossil of mastodon digesta. Plant macrofossil and palynological evidence from the Hyde Park, Hiscock, and Chemung sites confirmed that large amounts of Picea were indeed consumed by mastodons in mid-latitude, late-Pleistocene boreal forests of eastern North America, but Pinus may have been important in some areas. However, a diet that varied at least seasonally is indicated by macrofossils and pollen of Salix, Populus, Alnus, and Betula. High amounts of Cyperaceae, Gramineae, and Compositae pollen could be derived from the wetlands themselves or localized clearings, and taphonomic biases against broadleaf and herbaceous macrofossils warrant multi-proxy analyses of digesta. Rapid changes in plant associations and patterns during the late Pleistocene could have restricted access to both the physical bulk and nutritional substance of mastodon diet.

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Acknowledgments Bradley Lepper is thanked for sharing data on the Burning Tree Site. Access to the Hiscock Site was given by the Buffalo Museum of Science (Richard Laub). The Paleontological Research Institution (Warren Allmon, Peter Nester, and James Sherpa) provided access to the Hyde Park mastodon skeleton, the molar socket contents, and a sample of digesta from the Chemung Site. David Fagan (Coyler Institute) provided insight into the origin of the molar socket and its contents. Robert Ferancec (New York State Museum) and reviewers Richard Laub and Anthony Barnosky provided helpful comments on earlier drafts of the manuscript.

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