MEETA. 2019 EASTERN PALEONTOLOGIST 3:1–15 S. Fiedel, R. Feranec, T. Marino, and D. Driver A New AMS Radiocarbon Date for the Ivory Pond Mastodon Stuart Fiedel1*, Robert Feranec2, Thomas Marino3, and David “Bud” Driver4 Abstract - The Ivory Pond Mastodon (Mammut americanum) was found in South Egremont, Massachusetts, in 1982. A recent AMS radiocarbon assay on bone collagen yielded an age of 11,885 ± 30 rcbp (UCIAMS 193953), which currently calibrates to 13,580–13,770 cal BP. This date is statistically similar to a much more imprecise date (GX9024-G; 11,440 ± 655 rcbp; 11,500–15,290 cal BP) previously obtained from the specimen. This age is similar to those of other American Mastodon specimens; collectively, these dates imply prior expansion of boreal forest (mastodon habitat) into the region ca. 14,600 cal BP. The location of this specimen east of the Hudson River implies that Late Glacial proglacial lakes that occupied the Hudson River Valley in the past were not a hindrance to megafaunal colonization of New England. The chronology and depositional contexts of this and other mastodon specimens in the region necessitate that human predation be considered as a possible cause of the extinction of this and other megafaunal species in the northeast US. Introduction Mammut americanum (American Mastodon, hereafter, mastodon) is a quintessential species of the Pleistocene epoch; its remains occur in particular abundance in eastern New York. Markedly fewer specimens have been discovered east of the Hudson River in New England. Data regarding the American Mastodon’s distribution and relative abundance are important for understanding ancient habitats, dispersal, and colonization, and the patterns and causes of extinction. Here, we review the discovery and some of the initial findings about the Ivory Pond Mastodon (found in 1982 in South Egremont, MA; Fig. 1). Interestingly, the first published record of a North American fossil vertebrate is Cotton Mather’s description of a mastodon tooth found in Claverack, NY, less than 32 km (20 mi) west of Ivory Pond (Mather 1714). Although early investigations were undertaken on the Ivory Pond specimen, these produced minimal published literature. We present here a review of the context, a new AMS radiocarbon date for the mastodon, and a discussion Figure 1. Map of locations of mammoths and mastodons mentioned in this study. Number- ing as follows: 1, Ivory Pond Mastodon; 2, Claverack Mastodon; 3, Kitchawan Mam- moth; 4, Scarborough Mammoth; 5, Tunka- moose Mastodon; 6, Delaware Mastodon; 7, Farmington Mastodon and New Britain YWCA Mastodon; 8, Merrimack River Mast- odons (two individuals) and Mammoth; 9, Poughkeepsie Mastodon; 10, North Java Mastodon; 11, Hyde Park Mastodon; 12, Grimes Mastodon and Berry Mammoth; 13, Chemung Mastodon; 14, Hiscock Mastodons. Gray-highlighted dots represent the ice-front positions of the Laurentide Ice Sheet about 14,600 cal BP (Ridge, 2019). 1WSP USA, 11 Indian Pipe Lane, Amherst, MA, 01002, USA. 2Research and Collections, New York State Museum, Albany, NY 12230. 3PO Box 187, South Egremont, MA 01258. 47 Beaver Drive, South Deerfield, MA 01373. *Corresponding author - sfiedel@louisberger.com. 1 2019 Eastern Paleontologist No. 3 S. Fiedel, R. Feranec, T. Marino, and D. Driver of its implications regarding mastodon ecology, colonization of New England, and the extinction of this and other megafaunal species at the end of the Pleistocene. Background Discovery and initial examination of the Ivory Pond Mastodon The Ivory Pond Mastodon was accidentally discovered by Thomas Marino in June 1982, during mechanical excavation to create a pond in a muck-filled glacial kettle- hole on his property in South Egremont, MA. Marino troweled and sifted through the backdirt pile of muck and marl, thus recovering bones, teeth, and ivory, as well as cones of Picea glauca (Moench) Voss (White Spruce) and seeds of Najas flexilis (Willd.) Rostk. & Schmidt (Nodding Waternymph). The mastodon remains included parts of the left and right humeri, left tibia, teeth, and tusks. Marino treated most of this material with preservatives (polyethylene glycol, polyvinyl acetate, and Carnuba wax) but set aside some unpreserved bone and cones for possible radiocarbon dating. Marino first received assistance from James Parrish and curatorial staff from the Berkshire Museum (Pittsfield, MA). Although he contacted other institutions to undertake further investigations at the site, the only enthusiastic response came from Roger Moeller, then at the American Indian Archaeological Institute (since renamed as Institute for American Indian Studies, Washington, CT) (Moeller 1984, Parrish et al. 1983). Moeller was particularly excited by the possibility of butchery by Paleoindians, which seemed to be indicated by ostensible cut marks on a distal humerus fragment, and launched a research effort. Screening of the spoil pile also yielded a fist-sized cobble and a chert flake, which, though only very loosely associated with the bones, might conceivably have been used as butchering tools. However, the cutmarks subsequently were identified by Pat Shipman (then at Johns Hopkins University, Baltimore, MD) as vascular grooves, not cutmarks. There was no evidence of either machine- or water-induced striations. Moeller (1984) surmised that the bones, derived from massive skeletal elements, must already have been broken at the edge of the bog prior to their submergence; he speculated that predators (probably non-human) had been responsible. It is important to note that an unknown portion of the skeleton may remain unexcavated in the muck, so the representation of skeletal elements cannot be used for comparative taphonomic analysis. Researchers from the New York State Museum (Albany, NY), directed by Robert Funk, and the University of Massachusetts (Amherst, MA), directed by Dena Dincauze, took 2 pollen cores from the vicinity of the bog. Sediment samples were taken at 5.08-cm (2-in) increments for pollen analysis (Lewis 1984:Table 1). The pollen indicated that the deglaciated landscape had first supported a sedge tundra or park-tundra, followed by a boreal forest of spruce, Pinus banksiana Lamb. (jack pine), Betula (birch), and probably Populus spp. (aspen), with Abies sp. (fir) and Larix laricina (Du Roi) K. Koch. (tamarack) increasing over time. Spruce was dominant at the top of this lower sequence (perhaps indicative of Younger Dryas onset at 12,800 cal BP?) followed by a hiatus, after which late-Holocene Castanea sp. (chestnut) pollen was unusually prevalent (Lewis 1984). The location of the cores was estimated as about 45.7 m (50 yards) from the mastodon bones, and the latter (found at an unspecified depth) could not be linked definitively to any section of the pollen sequence. Old and new radiocarbon dates During the early investigations, 2 untreated samples (i.e., white spruce cones, bone) were submitted to Geochron Laboratories (Cambridge, MA) for radiocarbon dating. These 2 2019 Eastern Paleontologist No. 3 S. Fiedel, R. Feranec, T. Marino, and D. Driver samples were treated at the lab using techniques that were standard at the time. As per the 1983 report, the spruce sample was cleaned of exogenous dirt, split into smaller pieces, and treated with hot HCl to remove carbonates, and hot NaOH to remove humic acids. The sample was then combusted and analyzed. The results (Table 2) were reported in January 1983. White spruce cones were dated to 11,630 ± 470 rcbp (GX-9259). This date was not corrected for 13C fractionation. The Mastodon bone was decalcified, washed, boiled in slightly acidic water, and then filtered. The filtrate was evaporated and the collagen was recovered as bone gelatin. This small sample of gelatin was dated to 11,440 ± 655 rcbp (GX-9024-G) and the date was corrected for 13C; the δ13C was reported as -20.6 ‰. Methods Since the time of this initial dating, AMS technology has come into wide use in archaeology and Quaternary environmental research. Direct counting of carbon atoms permits much more precise dating of samples than the old radiometric method. Given the very imprecise nature of the previous date for the animal (ranging from 10,785 to 12,095 rcbp at 1 sigma), and its unique status as the only known Terminal Pleistocene proboscidean in western Massachusetts, we thought it would be important to obtain a more precise AMS date. Following discussions with Fiedel and Driver, Marino provided a sample of untreated bone stored in his collection from the site, and Feranec submitted it to the W.M. Keck Carbon Cycle Accelerator Mass Spectrometry Laboratory at University of California at Irvine (UCI; Irvine, CA). The remaining portion of this sample is curated in the vertebrate paleontology collection of the NY State Museum as NYSM VP-16555. The sample was processed at UCI using standard techniques for bone collagen. Details of sample preparation are available in Beaumont et al. (2010), and on the laboratory’s Table 1. Pollen zones near Ivory Pond (Lewis 1984). Original data are in inches. Depth (cm) Near surface 61 63.5–86 88 101 109 124 % NAP - - [hiatus] - - 33 76 Interpretation (Lewis 1984) 20th-century blight Ca. 3000 rcbp Arboreal data Chestnut decline Chestnut (24%) -- Spruce, fir, tamarack - Spruce dominant Pine dominant Ca. 10,000 rcbp; boreal forest, fir and tamarack increasing Abrupt change from mineral to organic sediments (typical for late spruce pollen zone) - Tundra or park–tundra Table 2. Radiocarbon data for the Ivory Pond Mastodon reported in 1983. Radiocarbon Lab # GX–9259 GX–9024–G Specimen White Spruce cones Ivory Pond Mastodon Fraction ModernA NA NA 14C Age (BP) 11,630 ± 470 11,440 ± 655 2–σ cal age range (cal BP)B 12,650–15,040 11,500–15,290 ANot provided in initial report. BCalibration performed with Calib 7.1 online using the IntCal13 calibration curve (Reimer et al. 2013, Stuiver et al. 2018). 3 2019 Eastern Paleontologist No. 3 S. Fiedel, R. Feranec, T. Marino, and D. Driver website (https://www.ess.uci.edu/group/ams/files/bone_protocol.pdf). UCI’s procedure is a modified Longin (1971) collagen extraction followed by ultrafiltration (Brown et al. 1988). The bone is first mechanically cleaned, and then decalcified with relatively strong acid. A weak base treatment may be applied if the presence of contaminating humics is suspected. The resulting crude collagen extract is then hydrolyzed to gelatin at 60 °C in weak acid, and the gelatin is ultrafiltered using a Centriprep YM-30 (MilliporeSigma, Burlington, MA; 30,000 molecular weight cutoff) to remove small, contaminating molecules. The purified gelatin extract is then freeze dried in a vacuum centrifuge. Calibrated dates presented in this study were obtained using Calib 7.1 online, based on the IntCal13 calibration curve (Reimer et al. 2013, Stuiver et al. 2018). Stable isotope data were obtained on aliquots of the ultrafiltered bone collagen and measured on a Fisons NA1500NC elemental analyzer (IsoMass Scientific, Inc., Calgary, AB, Canada)/Finnigan Delta Plus isotope ratio mass spectrometer (Select Science, Waltham, MA). Δ13C and δ15N values have a precision of <0.1‰ and <0.2‰, respectively. Results and Discussion UCI provided a new AMS date (Table 3) and carbon and nitrogen isotope measurements for the collagen of the Ivory Pond Mastodon (Table 4). The new date, 11,885 ± 30 rcbp, is obviously much more precise than the radiocarbon date from 1982; with a sigma of only 30 y, this date appears to be the most precise yet reported for any Mastodon. But, is this date more accurate than the previous conventional age? To ensure accuracy, radiocarbon dates should be assessed against some independent chronometer. One way to assess chronological accuracy would be to examine dates on other materi- als, such as plant macrofossils, from the same site. However, the fact that the new AMS date falls within the very broad range of the 1983 date for the spruce cones (470 y at 1σ) is not particularly helpful, as there is no way to ascertain if the animal ingested the cones, or even if they were contemporaneous. The calibrated age range for the spruce cones (12,650– 15,040 cal BP) shows that they could have been deposited about 1000 y either before or after the Ivory Pond Mastodon. At a regional scale, comparison of the dates for the Ivory Pond Mastodon site to other mastodon localities reveals some similarities but also some differences (Table 5). At Hyde Park, NY, 1 spruce bole was dated to 12,548 ± 38 rcbp (14,570–15,120 cal BP), several others from the same context were dated to about 12,400 rcbp (14,150–14,820 cal BP), Table 3. Radiocarbon data for the Ivory Pond Mastodon reported in 2018. Radiocarbon lab # Specimen Fraction Modern 14C Age (BP) 2–σ cal age range (cal BP)A UCIAMS 193953 Ivory Pond 0.2278 ± 0.0008 11,885 ± 30 13,580–13,770 Mastodon ACalibration performed with Calib 7.1 online using the IntCal13 calibration curve (Reimer et al. 2013, Stuiver et al. 2018). Table 4. Stable isotope values for bone collagen of the Ivory Pond Mastodon. Sample Number UCIAMS 193953 GX–9024–G 13C (‰) –20.8 –20.6 15N %C %N C/NA 2.9 41.9 15.0 3.25 NAB NAB NAB NAB AAtomic C/N ratio. BNot provided in initial report. 4 2019 Eastern Paleontologist No. 3 S. Fiedel, R. Feranec, T. Marino, and D. Driver and the most recent was dated to 12,230 ± 80 rcbp (13,830–14,560 cal BP). Like the Ivory Pond specimen, the bone date for the Hyde Park Mastodon, loosely associated with the dated spruce logs (and cones), is much later than and significantly different from the spruce samples: 11,480 ± 50 rcbp (13,210–13,440 cal BP) (Griggs and Kromer 2008). At the North Java, NY site, there appear to be 2 temporally distinct populations of dated spruce: 10 older trees date to between 11,900 rcbp and 12,250 rcbp (13,560–14,500 cal BP), while 2 more recent samples date to about 11,300 rcbp (13,070–13,290 cal BP). The North Java Mastodon has an intermediate date of 11,630 ± 60 rcbp (13,330–13,570 cal BP; Griggs and Kromer 2008). Two pine cones derived from the same zone as the mastodon remains at the Hiscock site, in western New York, dated to about 11,135 and 11,200 rcbp; slightly older than most of the dated bones (ca. 10,500–11,100 rcbp) but younger than 1 of them (11,390 ± 80 rcbp; McAndrews 2003). Compared to those specimens just mentioned, the wood and mastodon bone dates are unusually synchronous at the Chemung, NY site. This finding is less surprising upon further examination, as the spruce and tamarack twigs, a sample of which dated to 10,758 ± 25 rcbp (12,660–12,740 cal BP), are interpreted as mastodon digesta. This date is not statistically different from Table 5. Radiocarbon dates on bone and associated materials from selected proboscidean sites in the Northeast. CMam = Chemung Mammoth, HM = Hiscock Mastodon, HPM = Hyde Park Mastodon, NJM = North Java Mastodon, SM = Scarborough Mammoth, TM = Tunkamoose Mastodon. Site Kitchawan Mammoth Scarborough Mammoth SM SM Tunkamoose Mastodon TM Delaware Mastodon Farmington Mastodon Merrimack River Mastodon Poughkeepsie Mastodon North Java Mastodon NJM NJM NJM NJM NJM NJM NJM NJM NJM Material sampled Bone Tusk Tooth Bone Tusk Tusk Bone Tusk Tooth Bone Bone Spruce bole Tamarack bole Spruce bole Spruce bole Tamarack bole Spruce bole Spruce bole Spruce bole Spruce bole 14C Age (BP) 12,950 ±100 12,720 ± 250 12,200 ± 55 12,160 ± 50 12,300 ± 45 12,350 ± 65 12,360 ± 120 12,430 ± 40 12,300 ± 130 12,060 ± 40 11,630 ± 60 12,254±60 12,064±44 12,092±32 12,049±27 11,966±25 12,056±29 11,970±80 11,969±30 11,902±51 Cal BP (IntCal 13) 15,070–16,330 13,960–14,200B Lab # OS–97775 AA–8215A OS–5636 CAMS–54733 OS–78282 OS–78281 AA–84998 Beta–[NA] OS–487 UCIAMS–169202 Beta–176928 Hd–22780 Hd–22596 Hd–22585 Hd–24121 Hd–24123 Hd–24122 Beta–168586 Hd–25622 Hd–23065 5 B B 14,060–14,540 B 13,930–15,010 14,200–14,900 13,860–14,940 13,770–14,060 13,310–13,670 13,970–14,500 13,770–14,060 13,800–14,090 13,770–14,020 13,730–13,970 13,770–14,030 13,580–14,030 13,730–13,970 13,560–13,930 B 2019 Eastern Paleontologist S. Fiedel, R. Feranec, T. Marino, and D. Driver No. 3 Table 5 (Continued). Site NJM NJM NJM NJM NJM Hyde Park Mastodon HPM HPM HPM HPM HPM Merrimack River Mastodon New Britain YWCA Mastodon Merrimack River Mammoth Grimes Mastodon Berry Mammoth Chemung Mastodon Chemung Mammoth CMam CMam CMam Hiscock Mastodons HM HM HM HM HM HM HM HM HM HM HM HM ASplit sample. BCalibrated range from pooled mean of multiple dates from Material sampled Spruce bole Spruce bole Spruce bole Spruce bole Spruce bole Bone Spruce bole Spruce bole Spruce bole Spruce bole Spruce bole Bone Bone (bioapatite) Tooth root Tooth Tooth Bone Bone Spruce/tamarack twigs 14C Age (BP) 11,969±19 12,046±74 12,030±45 11,328±61 11,296±44 11,480 ± 50 12,548 ± 38 12,416 ± 31 12,416 ± 33 12,396 ± 53 12,230 ± 80 11,570 ± 60 11,160 ± 130 11,202 ± 88 11,070 ± 130 10,930 ± 315 10,840 ± 60 10,890 ± 50 10,758 ± 25 Cal BP (IntCal 13,730–13,970 13,740–14,100 13,750–14,030 13,080–13,290 13,070–13,250 13,210–13,440 14,570–15,120 14,210–14,790 14,200–14,800 14,150–14,820 13,830–14,560 13,480–13,310 12,894–13,100 12,830–13,250 12,690–13,170 12,110–13,430 12,590–12,890 12,680–12,840 12,660–12,740 13,990–14,610 14,090–14,840 13,110–13,410 - 12,760–13,030B - 12,600–12,850 12,550–12,850 12,400–12,700 12,050–12,650 12,750–13,170 12,820–13,260 11,400–12,420 12,800–13,380 12,440–12,740 a particular specimen. 13) Lab # Hd–24119 Hd–22597 Hd–22782 Hd–22598 Hd–22586 Beta–141061 Hd–22395 Hd–22583 Hd–22687 Hd–22595 Beta–168585 Beta–371886 UGAMS–17668 AA106431b AA–1506 AA–1505 Beta–176930 Beta–176929 Hd–26603 Hd–20780 Hd–20795 AA–6977 CAMS–30528 CAMS–30529 GX–22038 CAMS–62560 CAMS–27143 CAMS–17407 Beta–24412 Beta–28829 Beta–28830 NZA–1107 Beta–16736 AA–6968 Spruce root Spruce root bone tusk 12,269 ± 66 12,365 ± 75 11,390 ± 80 11,100 ± 80A 11,070 ± 70A 10,930 ± 70A 10,810 ± 50 10,790 ± 70 10,630 ± 80 10,515 ± 120 11,135 ± 100 11,200 ± 100 10,240 ± 120 11,250 ± 140 10,705 ± 80 tusk tusk bone bone bone bone Jack pine cone Jack pine cone conifer twigs Fir or juniper 6 2019 Eastern Paleontologist No. 3 S. Fiedel, R. Feranec, T. Marino, and D. Driver a bone date of 10,840 ± 60 rcbp (12,660–12,830 cal BP) for the Chemung Mastodon (Griggs and Kromer 2008). Dates on digesta and the individual would be expected to be the same. Another concern for this and other studies focused on AMS dating of Ice Age faunal remains is the relative credibility of radiocarbon dates on collagen derived from different pre-treatment methods. Pleistocene-age samples treated recently either by ultra-filtration, XAD resin, or separation of the hydroxyproline fraction have yielded ages that are hundreds or thousands of years older than previous gelatin-based ages for the same specimens (e.g., Higham 2011, Marom et al. 2012, McCullagh et al. 2010, Nalawade- Chavan et al. 2014, Waters et al. 2015). An extreme position is that all collagen-based dates produced by any other methods are likely to be inaccurate, probably too young because of incomplete removal of exogenous humic acids (e.g., Higham 2011, Waters et al. 2015). Other specialists contend that the new methods are not a panacea; e.g., the filters may introduce old carbon, as happened at the Oxford AMS laboratory before 2004 (Bronk Ramsey et al. 2004, Fülöp et al. 2013). In a test of pretreatment protocols, Fiedel et al. (2013) compared the dates produced by 4 laboratories (including UCI) for bones of the Miesenheim Elk (moose), for which the overlying Laacher See tephra (11,060 rcbp or ca. 13,000 cal BP) provided a terminus ante quem. Only Oxford’s hydroxyproline date of 11,100 rcbp was in the expected range; the other dates, averaging about 10,700 rcbp, were clearly too young, although the suspected contaminant could not be determined. In a follow-up experiment involving 5 laboratories, most of the conventionally prepared bone samples yielded expected ages (averaging 11,092 ± 19 rcbp), but 2 paired ultra-filtration– derived dates from the University of Arizona AMS laboratory appeared to be about 130 radiocarbon-y too old (Kuzmin et al. 2018). Similarly, Widga et al. (2017) recently reported a large suite of new AMS dates for Late Glacial mastodons and mammoths from the northern Midwest. These samples were processed at the University of Arizona AMS laboratory using the standard acid-base-acid (ABA) technique to yield purified collagen for dating. Nine samples that might produce terminal ages for proboscideans were subjected to additional analyses. The ABA-extracted gelatin was ultra-filtered (UF) and the UF fraction also was dated. In all cases, the UF fraction radiocarbon age was the same as the ABA fraction radiocarbon age at 2 sigma. Six of the 9 paired ABA and UF measurements overlapped at 1 sigma. Widga et al. (2017) recommended that critical dates (e.g., terminal dates for Ice Age megafauna) be subjected to replicate dating in different labs using various techniques to better certify an age for the specimen or event. Our conclusion from these findings is that the new Ivory Pond AMS date, in the context of the initially obtained dates from the mastodon bone and white spruce, is probably accurate but, we acknowledge that this current calibrated age might well be several centuries younger (or less likely, older) than the true age of the bones. In the future, with improved pretreatment techniques, analytical methodologies, and calibrations, the Ivory Pond Mastodon’s age may be further refined. Regional context and implications Although the Mastodon might be somewhat older than the new date indicates, a likely terminus post quem is provided by regional environmental data. Mastodons appear to have expanded into New York and New England in tandem with the boreal forest. The expansion of boreal forest into southeastern New York apparently was underway by 12,548 ± 38 rcbp, as indicated by the oldest of the dated spruce boles from Hyde Park. Interestingly, this date calibrates from 14,570 cal BP to 15,120. Much of the calibrated age range for this date 7 2019 Eastern Paleontologist No. 3 S. Fiedel, R. Feranec, T. Marino, and D. Driver precedes the abrupt Bølling-Allerød warming seen in Greenland ice cores at 14,650 cal BP. This interpretation would be problematic, as the warmer Bølling climate was the evident precondition for the northward forest expansion. Several other dates for spruce boles from the same context are about 12,400 rcbp; they currently calibrate to as recent as 14,200– 14,400 cal BP, but again, they could be as old as ca. 14,800 cal BP. Similar dates have been obtained for the oldest spruce remains at the Chemung (or Gilbert, or Watkins Glen) and North Java sites in western New York (Griggs and Kromer 2008). It would appear then that the boreal forest biome had spread to the latitude of, at least, Hyde Park, NY, just after the initiation of Bølling warming. The oldest dated mastodon specimen in New York is the Tunkamoose Mastodon from Orange County, NY, with 2 dates: 12,300 ± 45 and 12,350 ± 65 rcbp (Feranec and Kozlowski 2012, 2016). A calibrated date on the pooled mean of the Tunkamoose Mastodon (12,316 ± 37 rcbp) is 14,080–14,560 cal BP. A mastodon of the same age was found in Delaware, in southern ON, Canada; dentin from this specimen has been dated to 12,360 ± 120 rcbp (Metcalfe 2011). These dates calibrate to about 14,450 cal BP, but could instead be centuries older, ca. 14,700 cal BP, due to rapid radiocarbon excursions (Adolphi et al. 2017). In either case, these dates for mastodon imply that their colonization of previously glaciated areas of New York and northward closely coincided with the onset of Bølling warming and northward boreal forest expansion. The location of the Ivory Pond Mastodon is geographically interesting in that it high- lights the dispersal abilities of these ancient proboscideans. Evidently, neither glacial lakes Albany and Vermont, nor the paleo-river in the now-submerged Hudson Shelf Valley, posed an impassable obstacle for Late Glacial proboscideans. Perhaps they crossed the lakes in the winter when they were frozen. In any case, proboscideans were living east of the present Hudson River even before the Bølling warming began. First came the mammoths. The Kitchawan, NY, Mammoth has been dated to 12,950 ± 100 rcbp (15,170–15,800 cal BP) (Feranec and Kozlowski 2018). At that date, the recently deglaciated region would have been a nearly treeless tundra (as indicated by the lowest pollen zone at Ivory Pond). The Scarborough Mammoth, found on the coast of Maine, yielded 3 radiocarbon dates: 12,160 ± 50, 12,200 ± 55, and 12,720 ± 250 rcbp (Hoyle et al. 2004). These dates are not statistically different and have a pooled mean of 12,190 ± 37 rcbp (13,960–14,200 cal BP). It appears that the first mastodons arrived very soon after the conifers colonized New England. A specimen found in Farmington, CT, in 1913, has been dated recently to 12,430 ± 40 rcbp (14,210–14,870 cal BP) (Boulanger and Jones 2015). A mastodon tooth recovered 3 miles (~5 km) offshore the Merrimack River in the Gulf of Maine was dated to 12,300 ± 130 rcbp (13,860–14,940 cal BP; OS-487) (Claesson et al. 2017). Once established east of the Hudson Valley, both mastodons and mammoths persisted until the onset of the Younger Dryas. A mastodon found in 1854 near Poughkeepsie, NY, has been dated recently to 12,060 ± 40 rcbp (13,770–14,050 cal BP) (Feranec and Kozlowski 2018). The Hyde Park Mastodon was dated to 11,480 ± 60 rcbp (13,210–13,440 cal BP). The New Britain YWCA Mastodon has been dated to 11,160 ± 130 rcbp (12,750–13,260 cal BP; Boulanger 2014). A mammoth molar dredged up from the paleodelta of the Merrimack River in 2013 has been dated to 11,202 ± 88 rcbp (12,830–13,250 cal BP). A mastodon mandible found about 8 km to the south of the mammoth tooth was dated to 11,570 ± 60 rcbp (13,280–13,540 cal BP; δ13C: -19.4 ‰, δ15N: 3.0 ‰) (Claesson et al. 2017). Among the many other proboscidean teeth previously found offshore are the Berry Mammoth tooth (10,930 ± 315 rcbp, 12,000–13,450 cal BP, AA-1505) and the Grimes Mastodon tooth 8 2019 Eastern Paleontologist No. 3 S. Fiedel, R. Feranec, T. Marino, and D. Driver (11,070 ± 130 rcbp, 12,710–13,140 cal BP, AA-1506); both were dredged up from ca. 50 m below the present ocean surface in Massachusetts Bay off Salem (Oldale 1987). Mastodon diets The recently acquired δ13C of the Ivory Pond sample (-20.8‰) agrees closely with the value of -20.6‰ reported for the 1983 sample (Table 4). It also falls precisely within the established range for bones of Late Glacial mastodons in Ontario and western New York; the mean is -20.9 ‰ with a standard deviation of 0.6 (Metcalfe 2011:Table 6.2). These values imply consumption of C3 plants with a δ13C value of about -26‰, which are expected for a boreal forest environment. The δ15N of the Ivory Pond sample is 2.9‰. This value is slightly higher than was normal for the bone collagen of the Ontario and western New York mastodons (2.3 ± 0.3‰) (Metcalfe 2011:11, Metcalfe et al. 2013), but it is a little lower than the typical values reported for Michigan, Ohio, Indiana, and southern New York (3.9 ± 1.0‰) (Koch 1991). These low values, contrasting with the high values seen in mammoths, have been attributed to occupation of a recently deglaciated landscape with young soils, consumption of nitrogen-fixing plant taxa (e.g., alder or lichens), or consumption of spruce (Metcalfe et al. 2013). These very low δ15N values also may reflect the mastodons’ occupation of open spruce forests (Metcalfe 2011:177; Metcalfe et al. 2013). The nitrogen content of the forest floor is much higher around spruce trees than other tree species (Vesterdal et al. 2008). The plants growing in that soil would have low δ15N values (Amundson et al. 2003). In modern Alaska, spruce needles have significantly lower δ15N values than the shrubs and grass leaves growing underneath the trees (mean δ15N = -7.7 [spruce], -4.3 [shrub], and 0.9‰ [grass]) (Schulze et al. 1994). The approximately contemporaneous spruce cones, as well as the pollen core, show that the Ivory Pond animal was living among spruce trees, although it has not been demonstrated that it was consuming their twigs or needles. It is noteworthy that White Spruce cones have been recovered previously from the vicinity of several other mastodons (Dreimanis 1968:Table 3). It is widely assumed that the preferred diet of mastodons consisted of spruce twigs, needles, and bark (e.g., Dreimanis 1968:Table 2; Griggs and Kromer 2008; McAndrews 2003; Teale and Miller 2012; Yansa and Adams 2012). They may have been able to digest spruce twigs, with their toxic terpenes and resins, by ingesting silts and clays, which could act as laxatives and detoxifiers (McAndrews 2003). However, some presumed mastodon gut contents or feces indicate a very different diet including sedges, grasses, weeds, pond plants, mosses, and twigs and leaves of deciduous trees including Ulmus (elm), Quercus (oak), and Fraxinus (ash) (e.g., the Burning Tree, OH, specimen excavated by Lepper et al. [1991] and re-analyzed recently by Birks et al. [2018]). Yansa and Adams (2012) dismissed this mastodon as a late-surviving (11,390 ± 80 rcbp, 13,397–13,085 cal BP), stressed individual forced to broaden its diet due to loss of its favored habitat. However, given the extensive range of this species, they seem to have had very flexible diets. At the Page–Ladson site in Florida, mastodon dung yielded remnants of more than 27 plant genera, including very numerous Taxodium (cypress) twigs and cones, nuts, fleshy fruits, gourds, and wetland herbs (Newsom and Mihlbachler 2006). Both mammoths and mastodons in northern Illinois occupied Late Glacial woodlands that were dominated by Fraxinus nigra Marsh. (black ash), not spruce (Saunders et al. 2010). For the northern mastodons, low-quality spruce twigs might have been a near-starvation food, consumed mainly in winter. As Dreimanis (1968:267) succinctly observed, “Even if mastodons lived 9 2019 Eastern Paleontologist No. 3 S. Fiedel, R. Feranec, T. Marino, and D. Driver in spruce forests, the spruce branches were not necessarily their main food. They may have preferred other plants growing in spruce forests”. Implications of the depositional context With rare exceptions, mastodons in the Northeast, including the Ivory Pond animal, have been found in ponds. It is obvious that these settings were unusually propitious for bone preservation by alkaline marl. However, it is not so obvious how the giant carcasses ended up in these ponds. Mastodons, like their modern elephant cousins, were long-lived and probably very intelligent animals (Haynes 1991); they did not blunder into muck-filled ponds through sheer stupidity. Fisher (2009:63) recognized mastodon trackways along lake and pond margins at the Brennan and Heisler sites; these “suggest that mastodon behavior was characterized by an appropriate avoidance of the soft, yielding substrates encountered within the pond itself”. Fisher (2009) identified 24 out of a sample of 34 Late Glacial mastodons as males. Based on their tusk growth, he inferred that most of these males were young adults that died in autumn, probably due to predation. A minority died in the mid- to late spring; Fisher interpreted these as animals that died as a result of musth (rutting) battles. In contrast, Haynes (1991:105) speculated that male rutting battles would have occurred in early winter. Proboscideans require a lot of water. Thirst alone might have impelled mastodons to frequent pond edges, but in that case, we would expect them to have ventured into the muck, or onto thin ice, either in summer or winter, not autumn and spring when water should have been more available. Haynes (1991:281) suggested that some damage observed in mammoth tusks may have been caused by the animals’ fighting for access to late-winter water sources. The closest living analogue to the mastodon, at least with respect to habitat and diet, although not social behavior, may be the Alces alces L. (moose) (an Early Holocene immigrant into northeastern North America [Hundertmark et al. 2002]). Haynes (1991:103) observed that “In northern ranges, where predation accounts for the greatest proportion of carcasses, many moose die in low-lying areas because moose spend a great deal of time feeding there. Many also die on iced-over lakes, ponds, and sloughs, where they are chased by wolves or are ambushed while feeding”. On Isle Royale, where most moose died due to Canis lupus L. (gray wolf) predation, “Calves were found primarily near shorelines, where the most effective means of escape from wolves was to enter the water”. Before the gray wolves became established on the island, “Moose carcasses and skeletons apparently were not uncommon sights, especially near salt licks, bogs, and lakes, the results of deaths caused by winterkill, disease, or accident” (Haynes 1991:104). Using data from Isle Royale as an analogue, Fox-Dobbs et al. (2007) interpreted carbon and nitrogen isotope data from the La Brea tar pits as indicating that dire wolves may have obtained as much as 21% of their meat by hunting or scavenging mastodons. Saber-toothed cats (particularly Homotherium) evidently could hunt immature proboscideans and drag them back to their dens, as indicated by the undated remains from Friesenhahn Cave, TX (Evans 1961). Homotherium were ranging close to the ice front in Minnesota ca. 26,000 cal BP (Widga et al. 2012), and they were still prowling about the southern end of the ice-free corridor in Alberta ca. 12,700 cal BP (10,740 ± 40 rcbp) (Ewald et al. 2017). However, neither dire wolves nor saber-toothed cats have yet been found in the Northeast. In fact, the ostensible absence of any tooth marks of large carnivores on the bones of Late Glacial proboscideans in the Midwest led Widga et al. (2017) to hypothesize that those predators were already extinct or regionally extirpated. 10 2019 Eastern Paleontologist No. 3 S. Fiedel, R. Feranec, T. Marino, and D. Driver Without top-down control by the big carnivores, proboscidean populations increased unchecked until they crashed ca. 12,500 cal BP, and the result was their extinction (Widga et al. 2017). Even if dire wolves and big cats were present in the Northeast, they may not have been able to bring down a full-grown proboscidean, although perhaps they might have harassed some animals to the point where they sought refuge in ponds. If not carnivores, perhaps the mastodons were fleeing from humans. Fisher (2009) has interpreted nearly all mastodons in ponds as animals killed, butchered and then stored in cold water by human hunters. This explanation must be seriously considered given the peculiar representation of skeletal elements in ponds (e.g., sometimes only the head is present), as well as the current wide acceptance of several claims of pre-Clovis hunt- ing of proboscideans. Evidence to support these claims include: the Manis Mastodon in Washington State at ca. 13,800 cal BP (11,960 ± 17 rcbp) (Waters et al. 2011); the lithic artifacts lying dispersed in mastodon dung at the Page Ladson site in Florida at ca. 14,300 cal BP (Halligan et al. 2016); and the Schaefer and Hebior mammoths, both with a few associated lithic artifacts and both dated to ca. 14,300 cal BP (Joyce 2006, 2013). While Fisher thought humans stored mastodon meat in cold ponds, Gramly (2017) added the possibilities of bone and ivory treatment for tool production, as well as some ritual behav- iors. It is pertinent to note that Pitulko et al. (2015) described storage of mammoth skulls in stagnant, relatively warm, slow-moving creek water at the Yana RHS site in Siberia, ca. 32,000 cal BP, in order to remove tusks from alveoli. In Arctic Siberia, the ivory was a necessary substitute for wood, a circumstance that would not have prevailed in the bo- real forest of Late Glacial New England. Although the lithic assemblage at Yana is not as impressive as the ivory and bone tools, there are stone tools; it is primarily the absence of associated chipped stone tools and debitage that undercuts Fisher’s and Gramly’s theories about the mastodon sites. Regardless of the behaviors that may have resulted in the fortuitous preservation of mastodons in ponds across the Northeast, the small number of these accidentally preserved skeletons east of the Hudson creates a misleading impression of the original density of living proboscideans on the Late Glacial landscape. Fisher (2009:71) noted that the tusks of the Hyde Park Mastodon indicated both atypically late maturation (at 15 years of age) and annual musth battles from the age of 23 until his death at 36, “implying a dense local population of adult male adversaries”. As stated above, the date for this animal is 11,480 ± 50 rcbp. Widga et al. (2017) observed a peak occurrence of dated proboscideans in the northern Midwest between 14,000 cal BP and 12,800 cal BP. Similarly, Boulanger and Lyman (2014) observed an equivalent peak in the Northeast (including New England) between 13,600 cal BP and 12,700 cal BP. But, while Widga et al. (2017) interpreted this maximum as evidence of a booming predator-free population, Boulanger and Lyman (2014), regarded it instead as indicating the accelerating mortality rate of a declining regional population. Despite their contradictory interpretations of the Allerød maximum of proboscidean deaths, both studies converged in their denial that the abrupt extinction by ca. 12,500 cal BP could have anything to do with the well-documented arrival of fluted point-using humans around 13,000 cal BP (Lothrop et al. 2016). We will not wade into the debate about the causes of extinction here as this has been dealt with in detail elsewhere (e.g., Barnosky et al. 2004, Prescott et al. 2012, Stuart 2015). We only note that: (1) the new Ivory Pond date fits comfortably near the start of the 14,000 cal BP to 12,800 cal BP peak; and (2) this Allerød maximum of dated proboscideans contradicts the inference of the “functional extinction” of megaherbivores around 13,800 cal BP based upon the sharply reduced relative frequency of Sporormiella fungal spores (Feranec and Kozlowski 2016, 2018; Feranec et al. 2011; Fiedel 2018; Gill et al. 2009). 11 2019 Eastern Paleontologist No. 3 S. Fiedel, R. Feranec, T. Marino, and D. Driver Conclusions The Ivory Pond Mastodon, from South Egremont, MA, has yielded a precise AMS radiocarbon date of 11,885 ± 30 rcbp (13,580–13,770 cal BP). This date is similar to those of other mastodon specimens from New York and New England and corresponds to a period when boreal forest prevailed in the region. These dates collectively indicate that mastodons were thriving in the Northeast during the Allerød, and contradict the inference from coprophilic fungal-spore abundance that their population was approaching extinction ca. 13,800 cal BP. No convincing explanation has yet been advanced for the discovery of so many specimens of this period, including the Ivory Pond Mastodon, within small ponds. We suggest that attempted evasion of predators, possibly including humans, may have driven animals into the water. Human manipulation and/or storage of carcasses, though unproven in the absence of lithic artifacts, cannot be precluded. 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