Stratigraphic and Paleoenvironmental Reconstruction of a Mid-Pliocene Fossil Site in the High Arctic (Ellesmere Island, Nunavut): Evidence of an Ancient Peatland with Beaver Activity + Online Appendix Figures S1 and S2 (See Article Tools)
Abstract:ABSTRACT. Neogene terrestrial deposits of sand and gravel with preserved wood and peat accumulations occur in many areas of the High Arctic. The Pliocene-aged Beaver Pond fossil site (Ellesmere Island, NU) is one such site that differs from other sites in the great thickness of its peat layer and the presence of a rich vertebrate faunal assemblage, along with numerous beaver-cut sticks. Although the site has been the subject of intense paleontological investigations for over two decades, there has not been a r… Show more
“…abstrusus , including Empetrum nigrum (crowberry), Vaccinium sp. (e.g., blueberry, lingonberry), Rubus idaeus (raspberry) 69 , and their abundance may have been enhanced following forest fires, which is evident at this site 33 . Therefore berries may have constituted a component of the Beaver Pond bear’s diet, particularly during the peak seasons, and their high sugar and acid contents could have resulted in the observed pronounced dental caries.…”
Section: Discussionmentioning
confidence: 74%
“…Abundant beaver-cut branches and cut saplings of larch trees suggest that the peat growth may have been promoted by beaver activity. Further supporting this view are the skeletal remains of multiple beaver individuals, and two clusters of beaver-cut branches found within the peat unit, at least one of which was interpreted to be the core of a dam 32 , 33 . Using terrestrial cosmogenic nuclide (TCN) burial dating 34 , four samples of quartz-rich coarse sand from above the peat unit yielded a weighted mean date of >3.4 + 0.6/−0.4 Ma, suggesting the peat accumulation was formed during a mid-Pliocene warm phase 31 .…”
The skeletal remains of a small bear (Protarctos abstrusus) were collected at the Beaver Pond fossil site in the High Arctic (Ellesmere I., Nunavut). This mid-Pliocene deposit has also yielded 12 other mammals and the remains of a boreal-forest community. Phylogenetic analysis reveals this bear to be basal to modern bears. It appears to represent an immigration event from Asia, leaving no living North American descendants. The dentition shows only modest specialization for herbivory, consistent with its basal position within Ursinae. However, the appearance of dental caries suggest a diet high in fermentable-carbohydrates. Fossil plants remains, including diverse berries, suggests that, like modern northern black bears, P. abstrusus may have exploited a high-sugar diet in the fall to promote fat accumulation and facilitate hibernation. A tendency toward a sugar-rich diet appears to have arisen early in Ursinae, and may have played a role in allowing ursine lineages to occupy cold habitats.
“…abstrusus , including Empetrum nigrum (crowberry), Vaccinium sp. (e.g., blueberry, lingonberry), Rubus idaeus (raspberry) 69 , and their abundance may have been enhanced following forest fires, which is evident at this site 33 . Therefore berries may have constituted a component of the Beaver Pond bear’s diet, particularly during the peak seasons, and their high sugar and acid contents could have resulted in the observed pronounced dental caries.…”
Section: Discussionmentioning
confidence: 74%
“…Abundant beaver-cut branches and cut saplings of larch trees suggest that the peat growth may have been promoted by beaver activity. Further supporting this view are the skeletal remains of multiple beaver individuals, and two clusters of beaver-cut branches found within the peat unit, at least one of which was interpreted to be the core of a dam 32 , 33 . Using terrestrial cosmogenic nuclide (TCN) burial dating 34 , four samples of quartz-rich coarse sand from above the peat unit yielded a weighted mean date of >3.4 + 0.6/−0.4 Ma, suggesting the peat accumulation was formed during a mid-Pliocene warm phase 31 .…”
The skeletal remains of a small bear (Protarctos abstrusus) were collected at the Beaver Pond fossil site in the High Arctic (Ellesmere I., Nunavut). This mid-Pliocene deposit has also yielded 12 other mammals and the remains of a boreal-forest community. Phylogenetic analysis reveals this bear to be basal to modern bears. It appears to represent an immigration event from Asia, leaving no living North American descendants. The dentition shows only modest specialization for herbivory, consistent with its basal position within Ursinae. However, the appearance of dental caries suggest a diet high in fermentable-carbohydrates. Fossil plants remains, including diverse berries, suggests that, like modern northern black bears, P. abstrusus may have exploited a high-sugar diet in the fall to promote fat accumulation and facilitate hibernation. A tendency toward a sugar-rich diet appears to have arisen early in Ursinae, and may have played a role in allowing ursine lineages to occupy cold habitats.
“…For example, taxa at the Meighen Island sites that are known for their role as pioneers include Alnus alnobetula, A. incana, and Betula populifolia, none of which were found at BP, which was likely stable for the duration of peat deposition estimated at 49,000 years (Mitchell et al, 2016). Thus, the stage of the vegetation post-disturbance, and any time averaging of the assemblages may also impact the composition.…”
Section: Reconciling Similar Climates and Dissimilar Communitiesmentioning
A recurring goal in ecological and paleoclimatic studies is to either forecast how ecosystems will respond to future climate or hindcast climate from past ecosystem assemblages. The Pliocene is a useful deep-time laboratory for understanding an equilibrium climate state under modern atmospheric CO 2 , and has been a focus for climate modelers. Accurate estimates of proxy data-model mismatch are hindered by the scarcity of well-constrained observations from well-dated sites in the High Arctic. Using a recently developed community-based approach (Climate Reconstruction Analysis using Coexistence Likelihood Estimation: CRACLE) compared with an established method (The Coexistence Approach: CA), and applied to extraordinary, permafrost-driven preservation of floras, we explore the climate and community assemblages at five Pliocene sites in the Canadian Arctic Archipelago. The results suggest that climatic differences at this scale do not simply correlate to differences in community assemblage between sites. The threshold temperature for tree line is one important component, but other factors in the environment (e.g., soil characteristics) may drive dissimilarity of communities where the taxa could share the same climate space. Estimates from CRACLE agree with previous estimates where available, and generally fall within the ranges of CA. Mean annual temperatures were ∼22 • C hotter (ranging from 0.8 to 6.2 • C by species across sites) and mean annual precipitation ∼500 mm wetter (ranging from 530 to 860 mm by species across sites) during the Early to "mid"-Pliocene (∼3.6 Ma) when compared with modern climate station data in the Canadian Arctic Archipelago. Comparison of estimates for three levels of taxonomic input suggest judicious interpretation is needed when generic level identifications are used, especially in the Polar Regions. The results herein are a reminder of the large impact of non-climatic abiotic and biotic factors to be accounted for when predicting future ranges of communities under different climate conditions from the present, and when hindcasting climate from past ecosystem assemblages.
“…2 ). Rybczynski and Harington 16 , Matthews and Fyles 17 , Hutchison and Harington 18 , Tedford and Harington 10 , Dawson and Harington 19 , Murray et al 20 , Mitchell et al 21 , Gosse et al 22 , and Wang et al 23 provide detailed descriptions of Pliocene terrestrial flora and faunal assemblages associated with the Beaver Pond site. Figure 2 ( A ) An in-situ macrofossil cone within the Beaver Pond fossiliferous peat deposit.…”
Here, we present stable carbon and nitrogen isotope data for Pliocene-age (i) plant macrofossils and (ii) bone collagen from High Arctic Dipoides sp. subfossil remains. The specimens originate from a peat deposit at the Beaver Pond fossil site, located on Ellesmere Island (locally known as Umingmak Nuna, meaning "land of muskoxen"), situated within the Canadian Arctic Archipelago (78° 33′ N, 82° 25′ W) (Fig. 1). We reconstruct High Arctic Dipoides sp. palaeodiet within the context of coeval terrestrial and freshwater plant macrofossil remains excavated from the same ~ 4 Ma old peat layer. The Beaver Pond site provides a very rare opportunity for such a palaeodiet reconstruction using coeval herbivore and plant remains.
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