Field Notes

Wetland Restoration Uncovers Ancient Ecology

In August, contractors for the Forest Preserve District of DuPage County uncovered prehistoric mastodont remains. The exciting find closely follows the discovery of an ancient lakebed with clues to the mastodont’s prehistoric ecosystem.

While removing drain tiles as part of the 55-acre Brewster Creek Wetland restoration at Pratt’s Wayne Woods in Wayne, Illinois, Daniel Terpstra, an employee of Applied Ecological Services, came upon what he first thought was an elephant tooth, perhaps from a long-gone traveling circus. But Terpstra suspected it might be more. He called Leslie Berns, natural resources supervisor at the Forest Preserve District of DuPage County.

A more intensive investigation found three molars, a partial rib bone, and parts of tusk, which Berns delivered to Jeff Saunders of the Illinois State Museum. Saunders identified the teeth as “the second and third molars from the mastodont’s right upper jaw and another as a third molar from its upper left jaw.” According to Bill Weidner of the Forest Preserve District, “The fully erupted and partially worn third molar indicates that they were from a mature animal.” The remains will be on display at the Danada Forest Preserve in Wheaton.

The American mastodont, or mastodon, which grew as tall as ten feet and weighed an estimated four to seven tons, last lived in Illinois at the end of the recent ice age, about 13,000 years ago.

The last such find in DuPage County was in 1977, when DuPage officials uncovered most of a wooly mammoth at Blackwell Forest Preserve. This region is rich with prehistoric remains — mastodonts, mammoths, giant beaver, and others have turned up in roughly 200 Chicago Wilderness locales. According to district naturalist Jack MacRae, Chicago Wilderness may actually have hosted one of the last healthy mastodont populations on the planet (the label MacRae affixed to the specimens reads “Last Mastodont?”).

Scientists also have been piecing together a picture of the mastodont’s habitat — a practice called “paleoecology” — thanks to discoveries unfolding over the past few years just 100 meters away from the mastodont find. The former wetland had been drained for agriculture, so to find the farmer’s buried drain tiles, conservationists dug exploratory trenches through the muck. Cutting through black soil, peat, and a whitish layer of marl, the trenches soon uncovered ancient snail shells and wood fragments — even a stick chewed at one end by a beaver about 13,000 years ago. Led by Brandon Curry of the Illinois State Geological Survey and Eric Grimm of the Illinois State Museum, researchers pulled core samples from 27 feet down, revealing an ancient glacial lakebed full of accumulated sediment. The cores contained “beautifully preserved” tamarack needles, seeds, and microscopic diatoms, including Fragilariaceae species, a life form often found in the wake of retreating glaciers.

But plant pollen blown onto the lake long ago proved to be the real find. Thanks to improved technology, layers of pollen in the cores revealed in higher resolution than ever before a dynamic procession of prehistoric plants — white spruce giving way to black spruce and fir, with alder and larch becoming more abundant, then pine, oak, and elm — over the course of the roughly 6,000 years for which researchers found records. Identifying by hand the individual pollen grains, the researchers were able to track dry and wet spells that correspond closely to climate records taken around the world. (Eleven thousand years ago, they say, the enormous continental ice sheet just to the north was holding a frontal boundary directly over northern Illinois, causing a 2,000-year wet spell.)

The pollen — very different from that found in another DuPage County deposit — suggests a dynamic ecosystem more reminiscent of Canada, but with species combinations that have no exact match in the present day.

— Judy Nugent

Related Articles:

A Win-Win Restoration, CW, Spring 2000. Early news on Brewster Creek Wetland Initiative.

DuPage FPD to Restore Wetland along Brewster Creek, CW, Spring 2003. DuPage begins work at ancient glacial lake.