Prehistoric Life 6

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.

Silurian Period (438-408 million years ago)

The Silurian Period was named for the Silures (1835), another ancient Welsh tribe. Its fossils were recognized as distinct from those of the preceding Ordovician and following Devonian periods. Its beginning formally is defined by the first appearance of the graptolite species Akidograptus ascensus.

Life on Earth. During the Silurian, the Earth generally showed a warming trend after the ice age that ended the Ordovician. The Silurian reefs, which continued to be based mainly on stromatoporoids and tabulates, were huge. Brachiopods and bryozoans (including a number of colonial, massive stony or sea-fan-like forms) dominated the species count, but corals and echinoderms increased in importance. Nautiloid cephalopods and graptolites largely disappeared by the beginning of the Silurian. Eurypterids (sea scorpions, a group of chelicerate arthropods) appeared in the Silurian, some reaching 10 feet long. Jawless, armored fishes (Agnatha) became more diverse.

A significant step was the appearance of the first vertebrate jaw by the late Silurian, developed from gill arches in the first placoderm fishes and early sharks.  Diversifying early land plants were joined by the first fungi. The first terrestrial chelicerate arthropods (scorpions and eurypterids) had appeared by the end of the Silurian. These were very similar to marine forms of both groups. For instance, Brontoscorpio was an earlier Silurian marine scorpion, very similar to the familiar scorpion shape, which reached 3 feet in length. Genetic studies tie insect origins to crustaceans like today’s fairy shrimp and water fleas, the split occurring near the end of the Silurian. Also, millipedes and centipedes (which evolved in the Devonian) appear to be connected to chelicerate arthropods.

One place where the Niagaran formation is at the surface is at the tip of the Bruce Peninsula in southern Lake Huron.

Local landscape. Our area was a shallow, clear, saltwater sea with abundant dome-shaped reefs. The reefs were part of a barrier reef system surrounding the Michigan Basin. The rock is composed of dolomite, which is a limestone (calcium carbonate) in which magnesium replaces part of the calcium, the replacement possibly having occurred after the limestone was deposited. DuPage County’s bedrock thus is a part of the Silurian layer called the Niagaran formation, which forms a bedrock ring including the western shore of Lake Michigan, the Door peninsula, the southern shore of the U.P., the islands dividing Lake Huron from Georgian Bay, and a zone connecting to Niagara Falls, with large areas curving through Indiana and parts of Ohio. Outliers can be found in eastern Iowa. Our area probably was between the equator and 20° south latitude. The big Thornton Quarry on either side of Interstate 80-294 is mining one of the larger known reefs in this formation.

This structure, referred to as a “flowerpot,” is an isolated pillar of the Niagaran dolomite. It is on an island just off the tip of the Bruce Peninsula.

Local life. Fossils of the Niagaran formation found locally include reef-forming corals (including antler forms and large lumps such as Cladopora reticulata, Halysites catenularia and Favosites niagarensis). Other attached forms include rugose (horn) corals (Asthenophyllum racinensis, Dalmanophyllum wisconsinensis, Pycnostylus guelphensis); bryozoans (Fenestrellina spp., Hallopora ellengantula, Pachydicta crassa); calcareous algae (e.g., the plum-shaped green lump Calathium egerodae); and stromatoporids. Chert nodules are thought to have been derived from the hard parts of sponges (great for arrowheads, lousy for stone crushing machines), but at least one identifiable fossil sponge is known, Calathium sp. The diverse brachiopods include Eospirifer(Spirifer) radiatus, Apopentamerus racinensis, Leptotaena (Leptaena)  rhomboidelis, Rhynchotreta cuneata, Atrypa reticularis niagarensis, Schucheretella subplana, Uncinulus stricklandi, Meristina maria, Conchidium laqueatum, Kikidium, and Wilsonella. There also are several species of crinoids (Crotalocrinites cora, Lampterocrinus infatus, Marsupiocrinus chicagoensis, Siphanocrinus nobilus, Eucalyptocrinus crassus, Periechocrinus infelix), and crinoid-like cystoid echinoderms (Caryocrinites ornatus, Holocystites alternatus)

This diorama is part of the Evolving Planet exhibit at the Field Museum of Natural History. It portrays a Silurian reef.

Mobile life forms include trilobites (Bumastus niagarensis, B. harrisi, B. insignis, Calymene celebra, C. niagarensis, Arctinurus chicagoensis, Dalmanites sp., [=?] Dalmanella platycordata), and mollusks (snails Euomphalopterus halei, Tremanotus alphaeus, T. chicagoensis, Straparollus magnus, Lophospira rotunda, Phanerotrema occidens; pelecypods Mytilarca denticostia, Matheria recta; straight-shelled cephalopods Amphicyrtoceras orcas, Dawsonoceras bridgeportensis, Kionoceras orus, K. cancellatum; and at least one coil-shelled species, Discoceras marshi).

This fossil trilobite is in one of the Silurian dolomite flagstones at Fullersburg Woods, mined from the Lemont Quarry and used by the Civilian Conservation Corps in its construction projects at that forest preserve.

The earlier Alexandrian series, also dolomite, has the brachiopods Platymerella manniensis, Microcardinalia pyriformis, and Pentamerus oblongus.

Vertebrates, i.e., fishes, continued to be relatively uncommon through at least most of the Silurian, and apparently fossils of them have not been found locally.

Kayak at Last

by Carl Strang

I was beginning to wonder if I would get the opportunity to put a paddle in the water this year, but circumstances allowed me to run my dragonfly monitoring route on the Des Plaines River at Waterfall Glen Forest Preserve this past weekend. Of course, in the context of this blog the monitoring is the main thing, but on a personal level it’s been hard to go almost a year without paddling. My sea kayak has taken me through north Georgian Bay.

It’s given me sights like this, Devil’s Island in the Apostles of Lake Superior.

On Sunday afternoon the sea kayak Water Strider was my vehicle yet again. I found no new species, but was interested to find that the counts for various species fell between the values for last year’s August 2 and September 3 counts, despite other measures of phenology generally placing this year earlier than last. Common whitetail and eastern amberwing dragonflies were closer to the August 2 count, though both exceeded any of last year’s counts for those species. Powdered dancers and stream bluets fell between the counts of last year’s dates. Familiar bluets were closer to the September 3 count. Many, like those in the following photo, were ovipositing.

Skimming bluets showed a significant increase, with 10 counted on this trip against 1 for the entire 2009 season. In contrast, jade clubtails were missing this time, and orange bluets were few. I wonder if their seasons are done for this year.

Bear Circuit

by Carl Strang

Recently a half-day symposium took place at the Brookfield Zoo, providing an overview of mountain lions and their potential appearance in the Chicago area. This was prompted by the animal that was killed in the city two Aprils ago. That lion, the third to appear in Illinois in the past decade, previously had been sighted several times in south-central Wisconsin (details available here). The Wisconsin cat had cut its foot at one of the sighting locations. Genetic analysis of the blood and the dead animal allowed the connection to be made.

That string of sightings, and the long journey the mountain lion made from its probable origin in the Black Hills of western South Dakota, reminded me of a black bear I observed a few years ago. I was on the next-to-last day of my sea kayak trip across northern Georgian Bay, on the Canadian side of Lake Huron.

As I approached the mile-wide crossing to Dokis Island where I intended to make my 7th and final camp, I saw a bear.

It had swum the channel between a tiny, bare islet and a somewhat larger one, pulling out of the water just before I had my camera ready. The big bear angled up the shore heading southwest. It paused before disappearing into the woods.

I paddled over to Dokis, and found a campsite on a rocky point. You can tell where people have camped before by the circles of rocks used to hold down tent corners. The soil in this scoured, Canadian Shield country seldom provides good tent anchorage, at least near the water’s edge.

I had looked for bear sign, failed to find any, hung my bear bag, set the tent, had lunch, and went exploring. Only then did I find the fresh bear scats (and no, they were not in the woods; they were on an open point).

Soon thereafter I found a bear’s trail, the tracks as fresh as the scats and pointed straight toward them.

Later in the afternoon some people walked past. They were cottagers, their home on the other side of Dokis Island. They mentioned that they had a visit from a bear the previous night, and that this was uncommon. As I continued to explore I found that though there were a few other bear scats, these were few, and by their age had been deposited at intervals of weeks. Looking at my map, I found that the locations of the cottage, the bear’s trail, the fresh scats, the tiny islet where I first saw the bear, and the point at which the animal entered the woods, all were in a straight line and followed an ordered sequence.

Though I don’t have the genetic evidence to back it up, I believe that all those observations were of the same animal. If so, in that relatively nutrient poor country, the bear was following a huge circuit over an enormous area to make its living. Occasionally it had to swim channels a mile or more wide. This bear may come through the Camp 7 area only 3-4 times a season, and I had the good fortune to see it. My fortune was even greater, perhaps, that the bear departed before encountering the temptation of my bear bag.

Goodbye, Old Friend

by Carl Strang

My friends know that I’m a hopeless nature nerd. If you know me only through this blog, that has been evident enough. But I have my emotional side, and I can get sentimental about what to others might seem to be ridiculous things. The time has come to say goodbye to my old Saturn station wagon, and I’m sad about it. The car made a cameo appearance in the early days of this blog, when I described my pilgrimage  to trace the route of the Lake Michigan lobe of the latest continental glacier.

Watershed sign 2b

That was the last significant adventure the Saturn and I shared. It was not, however, the greatest. That trip would have to be my journey to Newfoundland in 2002. Newfoundland is, of course, an island province. The car made the crossing in the hold of a ferry much like this one.

Newfoundland ferry b

I drove all around Newfoundland. This photo of a caribou calf I took through the car’s window.

Caribou peekaboo b

In that car I went as far south as Mobile, Alabama, and as far west as the southwest corner of Kansas. I drove all around lakes Superior and Huron in 2004, scouting for good kayaking possibilities that set up my crossing of northern Georgian Bay in 2006. Here the car and kayak sit in the Ontario town of Killarney as I feast on the evening before starting that adventure.

04b Car in Killarney

Of course there were innumerable shorter trips. Here is my campsite at Wisconsin’s Wyalusing State Park, where I discovered a new northern range limit for the broad-winged tree cricket.

Wyalusing 4b

But, as my arthritis increasingly reminds me, all things wear out and ultimately must end. That car made it past 190,000 miles and 11 years, but was completely worn out and no longer reliable. I no longer could trust it for longer trips or for carrying my boats. At the end of May it broke down so significantly that I could not justify the cost of repairing it. So now I feel the sadness of saying goodbye to an old friend. Thank you, Saturn, for carrying me all those miles. And thank you, readers, for indulging me in this cathartic posting.

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