Literature Review: Pleistocene and Holocene

by Carl Strang

Today’s notes are from last year’s literature on the recent ice ages and subsequent prehistoric times. Some are biological in focus, others relevant to past and present climate change.

Coyotes once were bigger and more carnivorous than they are today, according to the following study.

Coyotes once were bigger and more carnivorous than they are today, according to the following study.

Meachen, J.A., A.C. Janowicz, J.E. Avery, and R.W. Sadleir. 2014. Ecological changes in coyotes (Canis latrans) in response to the ice age megafaunal extinctions. PLoS ONE 9(12): e116041. doi:10.1371/journal.pone.0116041 They measured coyote skulls from 29,000 years ago (La Brea tar pits) to present day, and found a transition from features associated with predation specialization to the present-day omnivory. Another study had found in addition a decrease in body size. They interpret this as a change in predator interactions. When the much larger dire wolf was the other dominant canid, and megafauna were abundant, coyotes could make a good living as specialist predators. Megafauna loss, and associated dire wolf extinction, opened the door for gray wolf immigration from Europe. This new, smaller predator was similar ecologically, but at the same time larger than the coyote, forcing a coyote niche shift to a more generalized diet.

Maher, K., and C.P. Chamberlain. 2014. Hydrologic regulation of chemical weathering and the geologic carbon cycle. Science 343:1502-1504. Kerr, Richard A. 2014. How Earth can cool without plunging into a deep freeze. Science 343:1189. The Kerr news article was based on the Maher and Chamberlain paper. The study looked at the mechanism that limits ice age cooling, preventing it from running away to a pole-to-pole glaciation. Volcanoes add carbon dioxide to the atmosphere, warming climate but also dissolving in rainwater, the resultant carbonic acid dissolving rock. The products flow to the sea, are taken up by plankton for skeleton building, and ultimately are buried. This removal process limits carbon dioxide buildup. Most of the dissolved rock is in mountains, and mountain uplift as in the Andes and Himalayas thus is tied to a global thermostat turndown. However, cooling slows the weathering reactions, allowing carbon dioxide to build back up.

Pena, Leopoldo D., and Steven L. Goldstein. 2014. Thermohaline circulation crisis and impacts during the mid-Pleistocene transition. Science 345:318-322. They found evidence for a profound change in oceanic circulation patterns corresponding to the change in glacial cycling from 41-thousand-year to 100-thousand-year durations. They conclude that “North Atlantic ice sheets reached a milestone in size and/or stability” that led to the ocean circulation change, resulting in a greater carbon dioxide drawdown, increased polar glaciation, and setting the pattern for the following 100,00-year cycles.

Guil-Guerrero, J.L., et al. 2014. The fat from frozen mammals reveals sources of essential fatty acids suitable for Paleolithic and Neolithic humans. PLoS ONE 9(1): e84480. doi:10.1371/journal.pone.0084480 They analyzed the fat chemistry of frozen woolly mammoths, horses and bison from Siberia. The fats were judged to be nutritionally good for human hunters of the time (41,000-4400 years ago). Furthermore, the fats of mammoths and horses were like those of hibernating mammals. The authors suggest that the mammoths and horses hibernated in similar fashion to present-day Yakutsk horses, which move little and mainly stand in sleeping positions during the coldest weather. The mammoth fatty acids suggest derivation from certain lichens in the diet.

Willerslev, Eske, et al. 2014. Fifty thousand years of Arctic vegetation and megafaunal diet. Nature 506 (7486): 47. DOI: 10.1038/nature12921 A large, multi-national team went into Pleistocene sediments and mummified gut contents, and used reference DNA from herbarium specimens to characterize vegetational changes over the past 50,000 years. They found that the last ice age caused a significant alteration of northern plant communities, greatly reducing forbs while increasing grasses and woody plants. Many of the megafauna herbivores such as woolly rhinoceros and woolly mammoth depended on the forbs for their protein content, and the authors believe that the failure of forb-rich communities to re-form after the ice receded contributed to or even caused megafaunal extinctions. No mention was made of human hunting in the ScienceDaily article describing the study.

Hoffecker, J. F., S. A. Elias, and D. H. O’Rourke. 2014. Out of Beringia? Science 343 (6174): 979. DOI: 10.1126/science.1250768 They reviewed cores taken from the Bering Sea and found that Beringia was not a barren grassland through the glacial times but had significant areas of tundra shrubs and trees. Animals including elk and moose likely lived there, and the likelihood of long-term human occupation seems good. This could provide a way that the ancestors of Native Americans could have been isolated from Asians for the 10,000 years, between 25,000 and 15,000 years ago, accounting for the genetic differences comparisons show. Beringia was not glaciated, and summers may well have been like those of today, though winters would have been severe. When the glaciers opened a way by melting, the 15,000-year Native American presence in the continent began as the Beringians moved in.

Literature Review: Ice Ages and Climate

by Carl Strang

Today’s literature focus is on two studies from last year that increased our understanding of ice age dynamics and how our changes to the atmosphere may alter them.

Kokechik Bay, Alaska, late winter

Kokechik Bay, Alaska, late winter

Ballantyne, Ashley P., et al. 2013. The amplification of Arctic terrestrial surface temperatures by reduced sea-ice extent during the Pliocene. Palaeogeography, Palaeoclimatology, Palaeoecology, DOI: 10.1016/j.palaeo.2013.05.002  As described in a ScienceDaily article. Recent measures of carbon dioxide in the atmosphere have brought current levels into the range of the Pliocene, which was 3.5-9 degrees F warmer than today. A modeling study indicates that the difference may have been that the Arctic Ocean then was open year-round, a condition toward which we are trending now.

Kerr, Richard A. 2013. How to make a great ice age, again and again and again. Science 341:599. News article describing a study published in Nature that reports an advance in understanding the continental glacier cycle. That cycle corresponds to the 100,000-year stretching and shrinking of the Earth’s orbit around the sun, but that’s too weak to account for ice building and declining. The group led by Ayako Abe-Ouchi modeled in the 23,000-year wobble in the Earth’s spin axis, plus global climate modeling and data on northern ice sheets, which involve changing carbon dioxide levels and the mass of the ice. Simulated ice sheets expanded and contracted in close to the actual pattern. Ice gradually builds over the 100,000-year cycle, but then the 23,000-year cycle corresponds to the warming phase of the longer one, adding summer warmth. By then, crustal depression by the ice mass means that the ice is at a lower, warmer altitude (1 km of depression), and the glacier rapidly melts.

Literature Review: The Cenozoic Era

by Carl Strang

This week we look at some recent studies of the time between the Mesozoic Era and the present day. In recent years there has been much interest in the dynamics of climate change across the ages of the Earth.

A huge amount of carbon today is sequestered in the permafrost soils of the North.

A huge amount of carbon today is sequestered in the permafrost soils of the North.

Robert M. DeConto, et al. Past extreme warming events linked to massive carbon release from thawing permafrost. Nature, 2012; 484 (7392): 87 DOI: 10.1038/nature10929 They combined modeling with the Earth’s orbital dynamics to show the likelihood that in the Paleocene, when the Earth’s orbit became more eccentric and tilt became greater, this resulted in thawing and decomposition of permafrost, releasing huge amounts of carbon dioxide and resulting in a positive feedback loop that produced the Paleocene-Eocene Thermal Maximum.

Pitcher plants, Big Thicket. The following study traces their origin.

Pitcher plants, Big Thicket. The following study traces their origin.

Ellison AM, et al. (2012) Phylogeny and Biogeography of the Carnivorous Plant Family Sarraceniaceae. PLoS ONE 7(6): e39291. doi:10.1371/journal.pone.0039291 They studied nuclear, mitochondrial and plasmid genes to sort out relationships and evolutionary history of the pitcher plants. They conclude that the family appeared in South America 44-53mya (million years ago, Eocene), and by the end of the Eocene was widespread in North and South America.

G. Grellet-Tinner, et al. (2012) The First Occurrence in the Fossil Record of an Aquatic Avian Twig-Nest with Phoenicopteriformes Eggs: Evolutionary Implications. PLoS ONE 7(10): e46972. doi:10.1371/journal.pone.0046972 They found fossils of a basal flamingo in association with eggshells and a floating nest that are like those of modern grebes, in an early Miocene shallow-lake wetland with high evaporation, in Spain. Though they agree that there was an earlier split between the grebes and the flamingos, they mention that fossil flamingos are known from the Oligocene, grebes from the Miocene. Apparently the bones are insufficient to provide much of an understanding of this early flamingo’s appearance.

Zhang Z, Feduccia A, James HF (2012) A Late Miocene Accipitrid (Aves: Accipitriformes) from Nebraska and Its Implications for the Divergence of Old World Vultures. PLoS ONE 7(11): e48842. doi:10.1371/journal.pone.0048842 They describe a fossil bird from Nebraska that links New World hawks and eagles to the Gypaetinae, one of the subfamilies of Old World vultures. This places the timing of that group’s origin in the Miocene, and supports its evolutionary separation from the other Old World vulture subfamily, the Aegypiinae.

Elderfield, H., et al. 2012. Evolution of ocean temperature and ice volume through the mid-Pleistocene climate transition. Science 337:704-709. (Comment by Peter U. Clark on pp. 656-658 in the same issue). They sorted through various isotopic proxies in marine sediments from New Zealand, and found an association between the mysterious change in ice age periodicity around 900,000 years ago (from cycles of 41,000 years to the more recent cycles of 100,000 years, a change not connected to the Earth orbit fluctuations now known to be the underlying cause of ice age cycling generally) and an increase in the volume of ice around Antarctica. They suggest that “an anomalously low Southern Hemisphere summer insolation” failed to melt the Antarctic ice during one interglacial period, and that the ice added during the following ice age was enough to produce the observed period change. The sea level drop during ice ages changed from 70 meters to 120 meters as a result. Their data also argue against a gradual cooling, from changes in atmospheric carbon dioxide, as the primary driver of the periodicity change.

Jeremy D. Shakun, et al. Global warming preceded by increasing carbon dioxide concentrations during the last deglaciation. Nature, 2012; 484 (7392): 49 DOI: 10.1038/nature10915 From an article in ScienceDaily: “Here is what the researchers think happened.

“Small changes in Earth’s orbit around the sun affected the amount of sunlight striking the northern hemisphere, melting ice sheets that covered Canada and Europe. That fresh water flowed off of the continent into the Atlantic Ocean, where it formed a lid over the sinking end of the Atlantic Meridional Overturning Circulation — a part of a global network of currents that brings warm water up from the tropics and today keeps Europe temperate despite its high latitudes.

“The ocean circulation warms the northern hemisphere at the expense of the south, the researchers say, but when the fresh water draining off the continent at the end of the last Ice Age entered the North Atlantic, it essentially put the brakes on the current and disrupted the delivery of heat to the northern latitudes.

“ʻWhen the heat transport stops, it cools the north and heat builds up in the Southern Hemisphere,ʼ Shakun said. ʻThe Antarctic would have warmed rapidly, much faster than the time it takes to get CO2 out of the deep sea, where it was likely stored.

“ʻThe warming of the Southern Ocean may have shifted the winds as well as melted sea ice, and eventually drawn the CO2 out of the deep water, and released it into the atmosphere,ʼ Shakun said. ʻThat, in turn, would have amplified warming on a global scale.ʼ”

The study was a global review of the timing of temperature and atmospheric carbon dioxide changes at the end of the last period of continental glaciation.

Lessons from Travels: Caribou

by Carl Strang

Travel offers many comparisons to the home landscape. Sometimes you can go back in time. I felt that way during my trip to Newfoundland in 2002, when my first day’s drive brought me to a herd of caribou.

The irregular southeastern peninsula of this island province in Canada offers the rare opportunity to encounter caribou along a paved road.

The irregular southeastern peninsula of this island province in Canada offers the rare opportunity to encounter caribou along a paved road.

A curious calf detached itself from the group and approached my stopped car.

My clicking shutter sent him back to the herd.

My clicking shutter sent him back to the herd.

Thousands of years before paved roads, as the glacier retreated from northeast Illinois, caribou followed with the tundra and stunted early trees as they trailed the ice edge.

Lessons from Travels: Turtle Range Gap

by Carl Strang

There are many sorts of comparisons that can be made between our region at the southern end of Lake Michigan and other parts of the world. Today’s focus is on a puzzling absence. I loved turtles as a child, and enjoyed encountering eastern box turtles and ornate box turtles in the woodlands of north central Indiana where I grew up.

The eastern box turtle (shown) is a forest dweller. The ornate box turtle is a prairie species that has become rare in Indiana.

The eastern box turtle (shown) is a forest dweller. The ornate box turtle is a prairie species that has become rare in Indiana.

When I lived in south central Pennsylvania I got the opportunity to conduct an ecological study of eastern box turtles and wood turtles, whose ecological differences I summarized in an earlier post.

The wood turtle, like the eastern box turtle, lives in forests.

The wood turtle, like the eastern box turtle, lives in forests.

When I moved to northeast Illinois, I was disappointed and somewhat puzzled to learn that none of these three semi-terrestrial species lives here. After pondering this absence off and on for some years, I feel ready to pose a hypothesis. In the case of the box turtles, I think it has to do with our soil. Box turtles bury themselves in upland places to hibernate for the winter.

A box turtle emerges from its sandy-soil hibernaculum in spring.

A box turtle emerges from its sandy-soil hibernaculum in spring.

Our northeast Illinois soil is derived from a clay parent material, ground up New Albany shale which the Lake Michigan lobe of the last continental glacier left behind as part of its legacy. Bricks are made of clay. It’s a difficult material to dig in, whether for gardening or for hibernating, and I suspect this is what is blockading the eastern box turtles, which live east and south of us, and the ornate box turtles, which live west and south of us.

As for the lack of wood turtles, that is perhaps a simpler puzzle to solve. Wood turtles live in forests, and our region historically was prairie punctuated by more open, drier woodlands. Here the wood turtles appear to be replaced by Blanding’s turtles, which live in prairies and their adjacent wetlands in much the same way that wood turtles made their living in the lowland eastern forests, spending some of their time (and hibernating) in the marshes, ponds and streams, but emerging frequently to forage on drier prairie land. Perhaps I am influenced by my childhood experience here as well. Most of our local landscape in Indiana historically was a mix of prairie and dry to mesic woodlands on sandy soil. We had eastern box turtles, ornate box turtles, and Blanding’s turtles, but no wood turtles.

Literature Review: Pleistocene

by Carl Strang

The following notes complete my review of last year’s scientific literature. These studies looked at the most recent epoch, the Pleistocene, and focus on the megafauna, the large mammals.

Mastodon fossil, an iconic megafaunal species

Edwards, Ceiridwen J., et al. Ancient Hybridization and an Irish Origin for the Modern Polar Bear Matriline. Current Biology, 07 July 2011 DOI: 10.1016/j.cub.2011.05.058     As described in a ScienceDaily article. This new mitochondrial DNA study places the female ancestor of all current polar bears in Ireland 50,000 years ago, at the peak of the last ice age. Brown and polar bears once were both circumpolar, or nearly so, and the ebb and flow of the glaciers brought them in and out of contact, providing hybridization opportunities. The authors mention that this continues today, with the retreat of polar ice bringing the two species more into contact, and several recent hybrid individuals are known. The researchers indicate that this process needs to be taken into consideration both in understanding the nature of these species and in conservation planning.

Long, Charles A., and Christopher J. Yahnke. 2011. End of the Pleistocene: elk-moose (Cervalces) and caribou (Rangifer) in Wisconsin. J. Mammal. 92:1127-1135. They describe the northernmost caribou fossils found to date in Wisconsin, from Marathon County. The Cervalces (also known as stag moose) from the same site is the first for the state, and northernmost for the species. The study location was at the boundary between the glacier’s Green Bay Lobe and the driftless area. The age of the caribou antler is placed at 11,260-11,170 years ago. The elk-moose was from 12,920-12,790 years ago. The caribou probably was of the more southern woodland caribou species. The older elk-moose fossil was found in a sediment layer suggesting it lived close to the edge of the glacier, in more of a tundra environment.

Eline D. Lorenzen, et al. Species-specific responses of Late Quaternary megafauna to climate and humans. Nature, 2011; DOI: 10.1038/nature10574     As described in a ScienceDaily article. They looked at a range of genetic, archeological and other evidence, and found that the megafauna that went extinct and those that survived in the northern hemisphere represent a complex picture. All had survived previous glacial cycles by finding refugia in warm periods, with populations just large enough to continue. Some were able to do so again after the most recent glacial retreat, for instance caribou and musk oxen in the far north and bison in the North American plains, and survive to this day. Others did not, and in at least most of these cases humans are implicated, either by preventing retreat to refugia or by decimating the reduced populations.

Waters, Michael R., et al. 2011. Pre-Clovis mastodon hunting 13,800 years ago at the Manis site, Washington. Science 334:351-353. (also interpreted in a news article on p. 302 of the same issue). They found a spear point made of mastodon bone, imbedded in the rib of an adult male mastodon. It is dated to several hundred years before the Clovis culture. The location near the coast in Washington State is consistent with a coastal spread of people from Beringia, where bone spear points also were used. This also supports an extended period of megafauna hunting, further pointing toward human hunting as a factor in extinctions (a long period of hunting, even if it only removes animals slightly faster than they can reproduce, increases the importance of that mortality factor).

Lessons from Travels: Alpine Tundra

by Carl Strang

Before I experienced high-altitude tundra for the first time, I was inclined to dismiss it. After all, I had lived in what I regarded as the real thing, when I conducted my thesis research in western Alaska. To my way of thinking, any tundra south of the great treeline of the North could not be anything but a pretender. When the time came in 1984 to visit alpine tundra in Rocky Mountain National Park, however, I was forced to change my tune.

In the mountains the treeline makes clear where the tundra begins.

Part of my conversion was visual. High in the Rockies it just plain looks like tundra.

The treeless terrain, still holding snow patches at the height of summer, reminded me of scenes from western Alaska, though of course with much greater topographic relief.

Up close the plants were of different species, but their colors, attitude and arrangement were very familiar.

Some of the plants clearly belonged to the same genera as species I’d encountered in Alaskan upland tundra areas.

What won me over in the end was that it simply felt like tundra. The clarity of the air, the smell and edge to the atmosphere, the light and sky and configuration of the land, all fit together in the same way. The feeling I had in Alaska when stepping out into that ever-present edged wind was the same, and I had to acknowledge that I had been wrong to dismiss alpine tundra.

That’s not to say that it was the same in every way. There were no pikas on my Alaskan study area.

Though they look like big mice, pikas are more closely related to rabbits.

They were cute and industrious, gathering plants to cure for the long wintry season.

Here one transports a big mouthful.

Pikas never have been in northeast Illinois or northwest Indiana, but tundra was here in the not-so-distant past. People hunted big game in our local tundra 15,000 years ago as the last glacier’s edge melted its way back north.

What about mountains? For that possibility we have to look much farther back in time, 1-1.5 billion years, during the Proterozoic Eon when North America was being hammered together through the collision of smaller continental plates. Just as we see in the Himalayas of today where India is slamming into Asia, such collisions can pile up significant mountain ranges. However, in that time when our bit of North America may indeed have been mountainous, land plants had not yet evolved, so there would have been no alpine tundra here then. Our area has seen tundra, and it probably has seen mountains, but never at the same time.

Prehistoric Life 19

by Carl Strang

This year’s winter series has been a review of the prehistoric life and geologic history of northeast Illinois. Each chapter has summarized current understanding, gleaned from the literature, of what was going on with life on Earth in a particular span of time, what we know about the local landscape, and what we can say about local life. I include some references, particularly to papers published in the journal Science which commonly is available at public libraries. Contact me if you need sources for other items. The Earth is so old that every imaginable environment was here at some point, from ocean depths to mountaintops, from equatorial tropics to tundra, and from wetlands to desert. Today’s chapter concludes the series.

At last we reach the most recent times. This mastodon and its kind lived in our area in the recent past.

Pleistocene Epoch (1.64 million years ago to the present day)

The Pleistocene Epoch (named 1839), literally “most recent,” marks the latest series of continental glacial times. We are in an interglacial interval, regarded as part of the Pleistocene by some, by others named separately the Holocene (1885) or Recent (1833) Epoch.

Life on Earth. This is the time when our human species Homo sapiens evolved, along with the rest of the modern species. Our species originated in Africa around 200,000 years ago as it separated from its earlier hominid precursors, then began to migrate out of Africa around 100,000 years ago, fanning out into Europe, Asia, Polynesia-Australia and ultimately North America. Homo erectus earlier (1.5 million to 770,000 years ago) ranged from Kenya to China (Science 323:1197, 1419). Shaped tools and red ochre use suggest modern-like behavior had begun to appear by 164,000 years ago (Science 318:777). Genetic studies indicate that the Neandertals were a separate species, though they shared with us a gene for speech communication (Science 318:546). Skin color may have diversified in our species much more recently, with pale skins in some races developing only within the past 5300-12,000 years (Science 316:364).

Reconstructed giant ground sloth, Mastodon State Historic Site, Missouri.

There were new arrivals in North America from South America: 2 sloth genera (Nothrotheriops and Eremotherium), opossum, anteaters. And, from Eurasia, mammoths, bison, saiga, musk oxen, and humans. The polar bear evolved away from brown bear ancestors of the southeast Alaska area around 150,000 years ago. Many large birds and mammals became extinct, in many areas (including North America) because of human hunting (Science 300:885; 306:70).

Local landscape. This was a time of ice ages, more than 20 periods of continental glaciation alternating with periods when the glaciers retreated (only 4 of these reached as far as the Mississippi River drainage basin). The dominant theory ties the growth and ebbing of glaciers to regular cycles in the Earth’s orbit, tilt, and precession. Up until 1 million years ago, the glacial cycles were 41,000 years long, corresponding to the cycling of the Earth’s tilt. For the past million years the cycle has become 100,000 years long, for reasons that are unexplained but may be connected to a change in atmospheric carbon dioxide.

Rotten or weathered rock had formed at the surface; most of this was removed by Pleistocene glaciers. Glaciers don’t remove much thickness of bedrock, however, carrying mostly fractured pieces. In the DuPage County area, the glaciers scoured the Silurian dolomite bedrock clean of any sediments, except for the Devonian or Mississippian marine clays in cracks on the upper surface (this is why there are no pre-Pleistocene terrestrial fossils in much of northeast Illinois).

If we could clear the glacial deposits from our bedrock we might see something like this, grooves scratched on the surface by the glacier as it pushed southwest out of the Lake Michigan basin. Rock Point, Ontario.

Dolomite bedrock escarpments such as the one tracing the western and southern boundary of the Lake Michigan basin, and other highlands such as the northern Wisconsin Arch, played a significant role in channeling glacial flow. Lake Michigan started as a south-flowing stream. The sequence and timing of events: the Nebraskan glacial advance 1.8mya (million years ago), then the Aftonian interglacial stage, then the Kansan advance 900-600kya (thousand years ago), then the Yarmouthian interglacial, then the Illinoian advance 400-300kya, then the Sangamon interglacial, then the Wisconsinan glacial advance began 100kya and ended 18kya. Within the Wisconsinan there was an Altonian advance 70-30kya that reached northeast Illinois, a retreat 30-22kya called Farmdalian time, and the largest final advance 22-18kya called the Woodfordian.

A continental glacier was not a single body, but rather several rivers of ice, or lobes, flowing side by side. The Silurian escarpment divided the Lake Michigan lobe from the Green Bay lobe. Kettle Moraine in Wisconsin is a glacial deposit left between those lobes. The Lake Michigan Lobe had to climb (be pushed) several hundred feet to overtop the escarpment and enter northeast Illinois.

As the glacier advanced, the Straits of Mackinac outlet became blocked, and Lake Michigan drained south through the Chicago and Des Plaines Rivers. The Glenwood phase of Glacial Lake Chicago, as it is called, was followed by alternating advances and retreats that blocked and opened the Mackinac Straits and further eroded the Des Plaines valley. Because the weight of the glacier had depressed the crust, for a time after the last glacial retreat the river through the Straits lowered Lake Michigan (in that incarnation called Lake Chippewa) to the point where it was much smaller and occupied only part of its current area. Crustal rebound later raised the northern end of the lake to the point where the current basin filled. When the Upper Peninsula of Michigan, Lake Huron and part of Lake Superior were cleared of retreating glacial ice but other outlets still were blocked, the Des Plaines became the major drainage for all three lakes.

In 2007-2008 Mastodon Camp, a partnership between the Forest Preserve District of DuPage County and the Field Museum of Natural History, gave high school teachers and students an opportunity to participate in a dig. Bits of mastodon bone and tusk, as well as buried black spruce trees and cones, were the main physical product from the site at Pratts Wayne Woods Forest Preserve.

During the latest, Wisconsin glaciation, the permafrost (tundra) zone was 50-120 miles wide beyond the glacial margin, and the mean annual temperature was about 5 degrees C cooler than today. Most of our familiar prairie and forest species were restricted to rather small refuges in the South during the glacial maximum, though oaks and hickories occupied a large part of the southern U.S. Species occurred in unfamiliar combinations, which changed as environmental conditions shifted (i.e., distributed themselves according to individual species tolerances rather than in community clusters of species).

According to recent work with cores from Nelson Lake in Kane County and Brewster Creek in DuPage, our landscape originated 18,000 years ago as the Wisconsin glacier melted away. By 17,000 years ago the glacier locally had shrunk back to the Lake Michigan basin. Open sedge tundra with some spruce trees invaded the zone nearest the glacier (18,000-16,000 years ago), then white spruces filled in to form a recognizable northern coniferous forest until around 15,000 years ago. The climate was dry and windy, piling a layer of loess (silty material) on top of the glacial till and outwash. The wind diminished and the climate became wet around 15,000 years ago because of the collision of warm air from the Gulf with polar air from the glacier north of us. White spruce declined, with black spruce becoming important in low wet areas, and black ash and fir along with a variety of deciduous trees invading the uplands. The glacier retreated to Canada by 13,000 years ago, then advanced in a new cool period as far as northern Wisconsin and the U.P. of Michigan (this may have been a Northern-Hemisphere-only cooling: Science 318:86), and began its final retreat 11,650 years ago. Then alder, birch, jack pine, ironwoods and elms increased locally, and additional trees invaded until a mix of deciduous species, including lots of oaks, was achieved. Beginning around 10,000 years ago there was a drying period, which led to the spread of prairie through our area. The prairie then retreated a little, so that by 6200 years ago our area became a prairie with islands of woodlands.

Local life. After the Wisconsin glacier retreated, first there was tundra, home of woolly mammoths (grazers), musk oxen, caribou, collared lemmings and other animals now extinct or found only in arctic Canada and Alaska. People arrived at this time, hunting with spears (one of the earliest human sites in North America, with butchered mammoth bones dated at 12,500 years ago, has been discovered just north of here near Kenosha; Science 305:590). As the forest filled in the warming landscape, additional mammals included moose, stag moose, scimitar cats, dire wolves, giant beavers, snowshoe hares, Jefferson’s ground sloths and mastodons (unlike mammoths these were browsers which also ate walnuts, spruce cones and other seeds; some species such as Kentucky coffee tree and osage orange are thought to be relatively uncommon today because they have lost mastodons and other large herbivores as seed dispersers). During the time of deciduous forest, local mammals included mountain lion, bobcat, red wolf, elk, white-tailed deer, raccoon, gray fox, porcupine, black bear, flying squirrel and gray squirrel. The prairie and mixed prairie savanna of historical times included today’s familiar animals, along with black bears, badgers, mountain lions, red wolves, elk and bison.

Imagined Paleoindians, Mastodon State Historic Site, Missouri.

Clovis points have been found in DuPage County, indicating that some of those early big animal hunters (known as Paleoindians) were here. The largest animals became extinct, thanks in large part to the Paleoindians’ killing them faster than they could reproduce (Science 326: 1100). Subsequent human cultures wandered less, and shifted to more of a hunting-gathering economy in the several thousands of years of the Archaic Period. Thrust spears and spear-throwers did not give way to bow and arrow in North America until later, during the Woodland Period that began with early signs of agriculture about 2000 years ago. Agriculture did not become an important part of the local economy until the most recent 1500-1000 years. The Woodland people were even more sedentary than Archaic people, and used pottery. Mississippian and Oneota cultural influences, centered in west central Illinois and Wisconsin, respectively, were characterized by increasing social-political complexity made possible by corn-based agriculture. Ultimately the familiar tribes emerged, in northeastern Illinois the Miami followed by the Potawatomi.

For a time in recent years, a group of researchers attempted to make the case that a comet or other extraterrestrial object exploded over North America, causing a climatic cooling (the Younger Dryas time), ending the Clovis culture and resulting in the extinction of the North American megafauna. By the end of 2010 a number of studies had invalidated the supposed evidence for this idea and shown that the Younger Dryas was the result of a sudden influx of cold, fresh glacial meltwater into the northern oceans that for a time shut down the Gulf Stream current.

Prehistoric Life 9

by Carl Strang

This year’s winter series is a review of the prehistoric life and geologic history of northeast Illinois. Each chapter will summarize current understanding, gleaned from the literature, of what was going on with life on Earth in a particular span of time, what we know about the local landscape, and what we can say about local life. I include some references, particularly to papers published in the journal Science which commonly is available at public libraries. Contact me if you need sources for other items. The Earth is so old that every imaginable environment was here at some point, from ocean depths to mountaintops, from equatorial tropics to tundra, and from wetlands to desert.

Pennsylvanian Period (320-286 million years ago)

The Pennsylvanian Period is named for the state of Pennsylvania (1891). This North American subdivision of the European Carboniferous Period is distinguished by many cyclic repeated advances and retreats of the sea, as indicated by alternating rock layers.

Life on Earth. This was the time of the coal forests, when the growing land area provided the home for forests of lycopsids (club mosses, the most abundant trees), sphenopsids (the group containing today’s scouring rush, horsetails and other members of genus Equisetum), ferns (including tree ferns), and seed ferns. There were early conifers as well. These were vascular but not flowering plants. Most coal was produced during this period because fungi, critical to decomposition, had not yet developed that ability to a significant extent. Dead plant tissue piled up without breaking down, ultimately was buried and fossilized into coal. As a result, oxygen built in the atmosphere to an all time high of 30% (Science 316:557).

You can see a life-sized reconstruction of a Pennsylvanian forest at the Field Museum in Chicago. Here are some model sphenopsids.

The earliest Amniota (the terrestrial egg-bearing group ultimately including reptiles, birds and mammals) appeared and diverged in the Pennsylvanian, producing the cotylosaurs (and other anapsid reptiles, a group represented by turtles and tortoises today; fossil cotylosaurs have been found as close to Illinois as Nova Scotia), synapsids (also known from N.S. and the group from which mammals ultimately evolved; the basal synapsids are referred to as pelycosaurs), and the diapsids, a reptile group that evolved into lizards, snakes, dinosaurs, birds and crocodiles.

Winged insects (including the first mayflies and enormous primitive dragonflies) first appeared in the Pennsylvanian, as did cockroaches, grasshoppers and crickets. The earliest beetle was reported from Illinois fossil material in 2009 (J. Paleont. 83:931). Some invertebrates, such as the dragonflies and certain millipedes, reached giant sizes (thanks at least in part to the elevated oxygen levels).

Local landscape. In Illinois, the sea continued its advance and retreat cycling, so that our area alternated between marine and land, often low and swampy. Our area remained just south of the equator, and the climate was warm and humid.  It is thought that alternating periods of glaciers forming and thawing on the southern Gondwana supercontinent (at that time drifting over the South Pole) caused the rises and falls of sea level that produced the local advances and retreats of the sea. Over geologic time, glacial episodes typically are associated with a continental mass at one of the poles (Antarctica in recent times).

Tree ferns still exist today. This one in Tasmania had a thick stem more than 10 feet tall.

The North American continent was beginning to collide with Europe and Africa as the sea that had begun to appear between them closed, forming the northern supercontinent of Laurasia. This event is what lifted our part of the world above the sea for good.

The nearest Pennsylvanian bedrock to Chicago is the Mazon Creek area (much of Illinois’ bedrock is Pennsylvanian), except for some bits in the Des Plaines Disturbance.

Local life. Coal forests dominated Illinois during the Pennsylvanian. Not only was coal left (itself fossil plant material), but remains of a variety of plant and animal fossils can be found just a little south of us in the world-famous Mazon Creek deposits of Middle Pennsylvanian age, just a little southwest of Joliet. Seed-fern leaves such as Medullosa, Neuropteris inflata, N. scheuchzeri, N. ovata and N. rarinerus are especially abundant (note: names of these plants are confusing, because different names are given to different parts such as leaves, stems and reproductive parts). There also were the giant sphenopsid Calamites, the smaller weedy horsetail Sphenophyllum, the tree fern Psaronius, small ferns (Pecopteris, Sphenopteris, Alloiopteris), the conifer relative Cordaites, giant club moss relatives Cyperites, Lepidodendron, Lepidophloios, and Sigillaria (up to 6 feet in diameter!), and other, smaller club mosses (Lycopodites, Bothrodendron).

Here are some giant club mosses in the Field Museum exhibit.

Most bizarre among the diverse aquatic animals was the Tully monster (Tullimonstrum gregarium), first found by amateur fossil collector Francis Tully, Illinois’ state fossil, and only known from this area. There were horseshoe crabs (Palaeolimulus, Euproops), freshwater fish (Rhabdoderma oxiguum, Conchopoma edesi, Elonichthyes peltigerus, Platysomus circularis), and mollusks, as well as a lamprey-like fish, Actinopterygian fishes (Elonichthys pettigerus, Platysomus circularis), polychaete worms (Astreptoscolex anasillosus, Escorites zelus, and others), shrimps (Belotelson sp., Kallidecthes richardsoni, Acanthotelson stimsoni, and others), a sea cucumber (Achistrum sp.), a nematode (Nemavermes mackeei), a chiton (Glaphurochiton concinnus), ribbon or priapulid worms (Archisymplectes rhothon, Priapulites konecniorum), the arrow worm Paucijaculum samamithion, the spoonworm (phylum Echiura) Coprinoscolex ellogimus, jellyfish (Essexella asherae, Octomedusa pieckorum, Anthracomedusa turnbullii), cephalopods, brachiopods (Lingula sp.), the scallop Aviculopectin mazonensis, as well as several “mystery animals” of unknown affinities. 

The Field Museum model forest includes a millipede you could put a saddle on!

Land animals included centipedes, millipedes (the giant millipede Arthropleura cristata was a flat species, 16” wide and more than 6 feet long), scorpions, cockroaches (Platymylacris paucineruis) and their relatives (Gerarus danielsi, G. vetus), and spider-like arachnids. There were amphibians (Amphibamus grandiceps, A. yelli).

The upland trees, less well known, were different from those in the swamps, and included the genera Megalopteris and Lesleya. An upland animal was the scorpion Labriscorpio alliedensis.

Green Bay Lobe

by Carl Strang

A second goal of my trip to Michigan’s Upper Peninsula last week was to investigate further the stones left by the most recent continental glacier. As I outlined in an earlier series of posts, my vacation trip last year was a pilgrimage into Canada to trace the route  of the Lake Michigan lobe of that glacier, which is responsible for the deposits which cover the land in the northeast corner of Illinois. The turquoise line in the map below follows the route I think that lobe followed.

Glacial lobe map b

I studied the various categories of bedrock northeast of Lake Superior, chunks of which were picked up by the glacier and now reside where that powerful river of ice left them when it melted away. I found that there appeared to be commonalities in the stones left as drift along the Lake Michigan lobe’s route in Canada, on the Upper Peninsula of Michigan, and in northeast Illinois. Stones northwest of that route in Canada seemed different, and I was curious to see if those differences might hold farther south along the route of the Green Bay lobe, which is the one immediately west of the Lake Michigan lobe. I chose to visit Muskallonge Lake State Park, on the U.P.’s north shore, approximately in the center of the Green Bay lobe’s route, so that I could compare the beach stones there to those at Whitefish Point, at the U.P.’s tip, which was on the route of the Lake Michigan lobe.

Muskallonge Lake sign b

It was a foggy day, but a few people were there. Some were gathering stones, a practice which might bias the results.

Muskallonge Lake beach 5b

For instance, it seemed to me that beach stones at Canada’s Agawa Bay, along the Green Bay route, included an unusual number of red granites and greenstones. If these are selectively removed by visitors, the remaining stones might not represent what had been there originally. I certainly found greenstones, and in the following photo two appear.

Muskallonge Lake beach 10b

However, there were very few compared to Agawa Bay. Here is a typical aggregation of Muskallonge stones, representing the Green Bay lobe.

Muskallonge Lake beach 1b

Here is a corresponding photo for Whitefish Point, along the Lake Michigan lobe’s route.

Whitefish Point 9b

While to my eye there did seem to be more reds and a few more greens at Muskallonge, and a few more grays and browns at Whitefish point, I don’t think the differences would hold up in a proper sampling procedure and statistical analysis. Furthermore, when I bring in a photo from Illinois Beach State Park (below), I am hard pressed to say that it is closer to one U.P. site or the other.

Illinois Beach 2b cropped

Nevertheless, the two years’ travel and study were enjoyable, and I learned a lot especially from studying the Canadian bedrock. The glacial drift may not provide additional support for the route map shown above, but the scratches on bedrock indicated by the little arrows in the geologists’ original map certainly are consistent with the turquoise line I added after last year’s trip.

Incidentally, there were places at Muskallonge Lake where there were deposits of black sands, I suspect composed of hematite like I found at Lake Maxinkuckee last winter.

Muskallonge Lake beach 4b

The next installation from this trip will be more biological.

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