Environmental change and seasonal behavior of mastodons in the Great Lakes region inferred from stable isotope analysis

Abstract

We investigate seasonal variations in the diet and drinking water of four Great Lakes mastodon (Mammut americanum) specimens using stable isotope analysis of serially sampled inner-enamel bioapatite structural carbonate (δ 13 C sc , δ 18 O sc ), and previously published bulk analyses. Isotopic analyses and thin section measurements showed that mastodon tooth enamel extension rates (~12-4 mm/yr, decreasing toward the cervix) were lower than those of mammoths or modern elephants. Mastodons had distinct and highly regular seasonal variations in δ 13 C sc and δ 18 O sc , which we interpret in the context of local glacial history and vegetation changes. Seasonal variations in δ 18 O were large but variations in δ 13 C were small, and may have been obscured if coarser sampling methods than our inner-enamel sampling approach were used. Thus, our approach may be particularly useful for understanding relatively small seasonal changes in δ 13 C within C 3 environments. The seasonal patterns, though not entirely conclusive, suggest that the Ontario mastodons did not migrate over very long distances. Rather, the climate and seasonal dietary patterns of mastodons within the region changed over time, from 12,400 to 10,400 14 C yr BP (~15,000 -12,000 cal yr BP). Insights gained using these methods can contribute to a better understanding of megafaunal extinctions and Paleoamerican lifeways.

Taxonomy, location of origin and health status of proboscideans from Western Canada investigated using stable isotope analysis

“…Recent research supports the idea that the environmental niches of various proboscidean taxa were broader than traditionally envisaged (Saunders et al ., ; Metcalfe and Longstaffe, ; Baumann and Crowley, ). The example of AB12 (P96.12.1) demonstrates that mammoths in Alberta occupied a range of environments, and suggests that taxonomic designations based on stable isotope analyses should ideally be attempted for specimens from known locations and time periods, where baseline isotopic compositions for the taxa in question have already been determined.…”

“…To minimize bias, we sampled pieces of enamel that represented the entire enamel thickness (∼1–2 mm) and typically ∼10 mm or greater of tooth height, homogenizing the samples for each individual. Growth rate estimates for both mammoth and mastodon molar enamel indicate that more than 1 year is required for the full thickness of the enamel to develop (Metcalfe and Longstaffe, , ). Growth in the occlusal–basal direction of mammoth and modern elephant teeth occurs at a rate of 13–22 mm a −1 , with the faster rates only occurring near the occlusal surface (Dirks et al ., ; Metcalfe and Longstaffe, ; Uno et al ., ).…”

“…Growth in the occlusal–basal direction of mammoth and modern elephant teeth occurs at a rate of 13–22 mm a −1 , with the faster rates only occurring near the occlusal surface (Dirks et al ., ; Metcalfe and Longstaffe, ; Uno et al ., ). Occlusal–basal growth rates for mastodon enamel are slower, with a maximum rate of 12 mm a −1 near the occlusal surface and a minimum of 2 mm a −1 near the cervix (Metcalfe and Longstaffe, ). Thus, our enamel sampling method averaged seasonal variations in both directions of tooth growth.…”

“…Mastodon remains are typically associated with relatively wet, forested regions, such as that present in the Great Lakes region during the terminal Pleistocene (Dreimanis, , ; McAndrews and Jackson, ; Haynes, ; Saunders, ; Newsom and Mihlbachler, ; Yansa and Adams, ). Studies of mastodon tooth enamel isotopic compositions, microwear and gut/faecal contents support a browsing adaptation (Lepper et al ., ; MacFadden and Cerling, ; Koch et al ., ; Green et al ., ; Newsom and Mihlbachler, ), although mastodon diets did include some grasses (Koch et al ., ; Gobetz and Bozarth, ) and mastodons were able to adapt to significant temporal changes in vegetation within the Great Lakes region (Metcalfe and Longstaffe, ). Woolly mammoths ( Mammuthus primigenius ) were associated with open steppe–tundra environments (Haynes, ; Guthrie, ) and their southern cousins, the Columbian mammoths ( Mammuthus columbi ), were most common in temperate grasslands (Agenbroad, ).…”

Pleistocene Overkill and North American Mammalian Extinctions

“…And yet, as studies in historic biogeography have shown, "understanding the structure of assemblages of species requires that the history of each species in that assemblage be studied on its own" (Grayson 2007, p. 194). That means developing highresolution records of the "biogeographic histories of individual species in relation to paleoclimatic, paleoecological, and archaeological data" (Faith 2014a, p. 5,434) that lead up to the times of extinctions so as to show how changes on the landscape-possibly including the arrival of humansmight have affected them (Grayson & Meltzer 2015, Lorenzen et al 2011, Meltzer 2009, Metcalfe & Longstaffe 2014, Orlando & Cooper 2014.…”