From the Field: Searching for Early Life in Churchill, MB

Posted: August 12, 2011 - 12:29 , by royal

July 20

Well, our first full day in the Churchill area doesn’t quite pan out the way we had planned… from splendid weather on the evening of arrival, we shift to a morning of heavy overcast, followed by steady rain driven by gusty easterly winds. No opportunity for field familiarization with the firearms, or for shore work. After an enforced break and some reorganization, we head out to our primary locality for this trip in what we think is an afternoon weather gap, only to retreat from the shoreline outcrop as both wind and rain return with a vengeance. Not a good place to be with bears in the vicinity (earlier in the day we saw – from the vehicle fortunately – a sow and yearling not too far west of that very spot). Same thing happens in early evening, within a few hours of the second low tide of the day: a bit of an opening in the overcast tempts us to head down to the coast with hopes of snagging some of the waning daylight. Fat chance. More rain and bad visibility – a high-risk situation, retreat to the Studies Centre.

Churchill, Manitoba sign

Welcome to rainy Churchill, Manitoba! Home of polar bears and - somewhere out there in the drizzle and fog - Late Ordovician fossils.

Left: A crew member stands on polar bear watch armed with a gun, Right: An image of a polar bear family walking in the distance.

Left - Ed Dobrzanski stands polar bear watch while Debbie Thompson scours Upper Ordovician rocks for evidence of exposed fossils. Right - as seen from our vehicle, a couple of kilometres to the west.

Fossils emerge from the rock bead.

Left - a coiled nautiloid cephalopod; right - a partial trilobite exoskeleton. Both of these are representatives of relatively common types of “shelly” fossils that account for most of the ancient marine biodiversity preserved in these Upper Ordovician sea bed deposits.

But why are we here in the first place, cursing the rains, braving the bugs (more to come on THAT subject), and evading polar bears? Aside from the lure of awesome natural surroundings and Churchill’s fascinating historical background, our primary reason for returning after an absence of 6 years is to resume hunting for the source of some very interesting and important fossils – the remains of creatures harkening back to the Late Ordovician Period about 445 million years ago, when this slice of Canada’s modern-day subarctic lay in subtropical latitudes.

Where ice now grinds against the rocky Hudson Bay coast for 9 months of the year, warm, salty waters once lapped against a coral-lined shore and trilobites scuttled across the muddy sea bed. There were no large, complex life forms on the land’s surface, and animals without backbones still ruled the world’s teeming seas. Most of the fossil record of this interval consists of the enduring “shelly” remains of those animals – such as trilobites and nautiloids – that had hard mineralized body coverings or supporting structures when alive. What we are seeking are the much rarer remains of non-mineralizing or “soft-bodied” animals.

July 21
Better weather today – still cool (11 C) and windy, but the rain has blown through and we’re now looking at a decent short term forecast!

We manage to spend a good part of the two low tides today on one of several important coastal fossil localities we discovered in our previous field seasons in the Churchill area. Some of us are able to find additional specimens of Lunataspis aurora – a rare early fossil horseshoe crab that we first described and named in 2008 – as well as tantalizing fragments of extinct eurypterids (“sea scorpions”) and other bizarre related forms. These are all members of the chelicerate arthropods … a group of joint-legged invertebrates that includes living horseshoe crabs, true scorpions, spiders, and mites.

What makes their fossils so remarkable is that,unlike trilobites (their distant arthropod cousins), ancient chelicerates had no hard mineral matter strengthening their outer body covering (a multi-piece “exoskeleton”). Only under exceptional circumstances could the remains of such non-”shelly” organisms be preserved in ancient sea bed deposits – their resultant rarity as fossils makes unravelling chelicerate evolutionary history (particularly the oldest part) very challenging. Our Churchill fossil sites are of Late Ordovician age – very early in the record of both horseshoe crabs AND eurypterids – so we’re hoping that our new specimens will help us solve some of the outstanding riddles about their origin, ecology, and initial diversification. So far, we only have more questions!

Stay tuned for more!