From the Field: Ancient Sea Scorpion Fossil Found

Posted: September 7, 2011 - 08:39 , by David Rudkin

July 23

Clear skies at last! Down to the coast to catch good morning lighting and a fortuitously low tide, so we can see in detail how fossil-bearing Upper Ordovician carbonate deposits (445 million years old) at our main locality “lap” against the elevated flanks of a much more ancient rock mass. This highly resistant Proterozoic (about 2500 million-year-old) quartzite body is the remnant of a small island that formed part of an archipelago in shallow Ordovician subtropical seas.

A rocky shoreline and clear skies are greet the crew as they begin today's dig.

Debbie (right) stands on the Proterozoic quartzite "bump". Although deeply eroded it still retains enough topographic relief to form an island in Hudson Bay, cut off from the mainland at high tide. In the foreground, tilting layers of dolostone represent shoreline sediments deposited along the ancient island margin during Ordovician time; our best fossils have been found in displaced dolostone beds a few metres to the right of this view.

We do a short island walk-about, then each of us hunkers down to the daunting task of scanning countless rock surfaces for elusive chelicerate fossils. It’s a process that requires patience, a sharp eye, and the ability to kneel or squat for hours at a time on cold, damp, sharp-edged dolostone rubble … cold and damp, that is, until an unobscured sun turns our exposed location into a baking, bug-infested dustbowl! Despite the discomforts it’s a successful morning, and by about 1 PM we have a couple of excellent eurypterid (“sea scorpion”) specimens to add to our haul – they are not entire animals, but more complete than anything previously found here.

The team finds a fossil of a sea scorpion.

What we're here for! It may not look like much, but this is a prized find ... nine articulated segments from the rear portion of a eurypterid ("sea scorpion") body. Eurypterid fossils are never common (a consequence of having no mineralized hard-parts), and Ordovician forms - representing the earliest stages of their evolutionary history - are particularly rare.

Left - Debbie completely covers her body and face for protection.  Right - the underbelly of a large tabanid fly.

Left - Debbie, our ace fossil-finder, in full collecting regalia: long sleeves, gloves, sunglasses, scarf, and hat provide protection against both physical and biological hazards. Right - one of the shockingly abundant biological hazards ... a large tabanid fly, known locally as a "bulldog" - capable of chewing through clothing in search of tender flesh!

The afternoon collecting continues to go well, but we have to pack up and head back to the Studies Centre. A crew change is imminent – our colleague Sean Robson arrives on the evening flight from Winnipeg, and Ed departs tomorrow morning. No gradual break-in for Sean – after dinner we’re back out on the coast to look at a section of Lower Silurian rocks. This is a magical time on the tundra and tidal flats, with every little detail thrown into sharp relief by the setting sun.

Shadows cast on the water as the sun sets in Churchill, MB.

long shadows and brown kelp on the tidal flats. Centre - left to right, Sean Robson, Matt Demski, Debbie Thompson, and Graham Young confer on the section. Here, as at many of the places we are studying along this coastline, the most interesting rocks are exposed only at the lowest tides during a short summer season.

The crew stands on the shoreline, a prime location for fossil hunting.

Left to right: Sean Robson, Matt Demski, Debbie Thompson, and Graham Young confer on the section. Here, as at many of the places we are studying along this coastline, the most interesting rocks are exposed only at the lowest tides during a short summer season.

Fossilized shells create a bumpy surface on this rock.

Lower Silurian brachiopod fossils are extremely common at this locality (shells have been dissolved leaving distinctive internal casts).

 

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