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Mid-Pliocene Warm-Period Deposits in the High Arctic Yield Insight Into Camel Evolution

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Mid-Pliocene Warm-Period Deposits in the High Arctic Yield Insight Into Camel Evolution

Natalia Rybczynski et al. Nat Commun.

Abstract

The mid-Pliocene was a global warm period, preceding the onset of Quaternary glaciations. Here we use cosmogenic nuclide dating to show that a fossiliferous terrestrial deposit that includes subfossil trees and the northern-most evidence of Pliocene ice wedge casts in Canada's High Arctic (Ellesmere Island, Nunavut) was deposited during the mid-Pliocene warm period. The age estimates correspond to a general maximum in high latitude mean winter season insolation, consistent with the presence of a rich, boreal-type forest. Moreover, we report that these deposits have yielded the first evidence of a High Arctic camel, identified using collagen fingerprinting of a fragmentary fossil limb bone. Camels originated in North America and dispersed to Eurasia via the Bering Isthmus, an ephemeral land bridge linking Alaska and Russia. The results suggest that the evolutionary history of modern camels can be traced back to a lineage of giant camels that was well established in a forested Arctic.

Figures

Figure 1
Figure 1. Arctic circle and fossil sites.
Locations (white stars) of fossil areas yielding the remains of Arctic giant camels are shown. Location 1. Fyles Leaf Bed (FLB) and Beaver Pond (BP) sites, Strathcona Fiord, Ellesmere Island, Nunavut; Location 2. Old Crow Basin, Yukon Territory. Grey shaded bathymetry indicates <100 m water depth. Yellow shading is current distribution of Beaufort Formation. Schematic stratigraphic columns for the FLB and BP sections showing TCN sample depths and location of the source of the Camelini fossil fragments. St, silt; MS, medium sand; G, gravel.
Figure 2
Figure 2. Geochronology of Ellesmere camel.
(a) 26Al/10Be versus log10Be plot for the five samples collected for burial dating. Black arrow illustrates a simple exposure history (minimum exposure duration indicated by dashed red lines) followed by instantaneous burial (minimum burial durations indicated by solid brown lines). Blue: Beaver Pond Site and Orange: Fyles Leaf Beds Site. The weighted mean age for all four samples of the Beaver Pond Site (shown in inset) is provided in the main graph. This graph assumes no muonic production, as discussed in text (cf. Supplementary Fig. S2). (b) Mean insolation at 78.55 N latitude for winter season (270–0 degrees from vernal) symmetrically smoothed (25 pts) with simple moving window averaging using FFT. The maximum-limiting and minimum-limiting ages with 1 σ total error bars are shown above. MPWP, Mid-Pliocene Warm Period; FFT, Fast Fourier Transform.
Figure 3
Figure 3. Fossil remains of Arctic giant camelines.
(a) Lateral view of right tibia specimen (NUFV 210), from FLB site, Strathcona Fiord (Ellesmere Island), shown within the tibia of an extant camel (Camelus dromedaries, ROM MAM 94191). The modern Camelus tibia has been scaled up 30% to match the size of the fossil tibia. Scale bar, 10 cm. (b,c) Lateral and occlusal view of upper left second molar of Yukon camel (CMN 47895). (d) Medial view of lower right second (?) molar of Yukon giant camel (CMN 47914). (e) Posterior view of first proximal phalanx of Yukon giant camel (CMN 48074).
Figure 4
Figure 4. Collagen spectra of modern and fossil Camelini.
Ellesmere fossil camel (NUFV 210), Yukon fossil camel (CMN 48096), Camelus bactrianus, Camelus dromedarius. ‘α’ denotes homologous peptides (Supplementary Fig. S4), modified in the Bactrian camel (α′); ‘β’ denotes one of the most intense species markers, shared by all camelines analysed here, observed at m/z 2,992 representing the peptide sequence GPSGEAGTAGPOGTOGPQGLLGAOGFLGLOGSR, where O=Hyp and the Q is deamidated (Supplementary Fig. S5). Insets show the isotopic envelopes for peptide ‘β’ (with the monoisotopic peak marked with an asterisk), within which the effect of increased Q deamidation in the ancient peptides can be observed.
Figure 5
Figure 5. FEG-ESEM maps of a cross-section of Ellesmere fossil camel bone.
Maps showing a Haversian canal infilled with mineral precipitates. (a) Back-scattered electron image. X-ray maps are also shown: (b) Fe, (c) O, (d) Ba, (e) S, lighter colours indicate higher concentrations of the element. (Scale bar, 2 μm. Width of all images approximately 50 μm.) Elemental distributions within the canal are consistent with iron oxyhydroxide and barium sulphate precipitation.

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