MASTODONS (MAMMUT AMERICANUM) AND THE LATE-GLACIAL VEGETATION OF THE EASTERN USA

Climate change and associated vegetation and dietary changes have been implicated in the extinction of mastodons. Numerous studies of tooth plaques and remains of gut contents have confirmed that mastodon diet was composed of woody browse species, forbs, nuts, and fruits. However, fossil gut contents also suggest that mastodon diet included significant amounts of spruce, even though spruce is a low-quality, chemically-defended food. Most extant large mammals only browse on spruce when all other food sources are exhausted, and mastodon tusk growth increments indicates that mastodons were not food limited as they moved toward extinction. Here we review the vegetation associated with mastodon habitat from the Great Lakes to the Gulf Coast, USA, over the period 20-10ka BP.

Interpretation of the compositional structure of mastodon habitat is complicated; Late Glacial vegetation assemblages lack modern analogs and the degree to which pollen abundance represents species abundance is the focus of great debate. To evaluate the species composition of mastodon habitat we compiled pollen assemblage data from 29 sites located near proboscidean fossil remains from the Gulf Coast to the Great Lakes using the Neotoma database and the Landscape Reconstruction Algorithm of Sugita (2004). Although spruce was the dominant conifer from the Gulf Coast to the vicinity of the ice margin in the Great Lakes Region until ca. 10 ka BP, deciduous species such as, ash, oak, and elm comprised 50% or more of the vegetation assemblages even at the earliest and northernmost sites, and remained at similar levels until mastodon extinction. Many of these species have been found in mastodon gut contents. These vegetation assemblage reconstructions support the suggestion that mastodons were not food limited as they neared extinction. Moreover, these analyses of landscapes surrounding mastodon sites strongly suggest that the contemporaneous forest, composed of large amounts of spruce intermixed with ash, elm, and oak, was unlike that found in much of eastern North America today.