Tuesday, 20 November 2018

BEARS: URSIDAE

Bears are one of my favourite mammals. Had they evolved in a slightly different way, we might well have chosen them as pets instead of the dogs so many of us have in our lives today. 

For them and for us, I think things worked out for the best that they enjoy the rugged wild country they call home. 

Bears are carnivoran mammals of the family Ursidae. They are classified as caniforms or doglike carnivorans. Although only eight species of bears are extant, they are widespread, appearing in a wide variety of habitats throughout the Northern Hemisphere and partially in the Southern Hemisphere —  making a home in North America, South America, Europe, and Asia. 

The relatives of our black and brown bears, a dog-bear, entered the fossil record about 20 million years ago. We've found polar bear bones that tell us more about when they split off in the lineage.

DNA from a 110,000–130,000-year-old polar-bear fossil has been successfully sequenced. The genome, from a jawbone found in Svalbard, Norway, in 2004, indicates when polar bears, Ursus maritimus, diverged from their nearest common relative, the brown bear — Ursus arctos.

Because polar bears live on ice and their remains are unlikely to be buried in sediment and preserved, polar-bear fossils are very rare. So the discovery of a jawbone and canine tooth — the entirety of the Svalbard find — is impressive. 

But far more important, is that when molecular biologist Charlotte Lindqvist, then at the University of Oslo's Natural History Museum and now at the University at Buffalo in New York, drilled into the jaw, she was able to collect intact mitochondrial DNA. Yes, a bit Jurassic Park-esque.

Mitochondria — organelles found in animal cells — have their own DNA and can replicate. And because there are many mitochondria per cell, mitochondrial DNA is easier to find in fossils than nuclear DNA. 

Lindqvist wondered whether this mitochondrial DNA could illuminate the evolutionary history of how and when polar bears diverged from brown bears. To find out, she worked with Stephan Schuster, a molecular biologist at Pennsylvania State University in University Park, and a team of colleagues to sequence the genetic material she had collected and was successful.

It is the oldest mammalian mitochondrial genome yet sequenced — about twice the age of the oldest mammoth genome, which dates to around 65,000 years old. From Lindqvist's work, we learned that polar bears split off the lineage from brown bears about 150,000 years ago. They evolved rapidly in the Late Pleistocene, taking advantage of their hunting prowess to become the apex predators of the northern arctic region.

Wednesday, 14 November 2018

ISAAC LAKE: BOWRON CIRCUIT

It is day four of our holiday, with two days driving up from Vancouver to Cache Creek, past the Eocene insect and plant site at McAbee, the well-bedded Permian limestone near Marble Canyon and onto Bowron Provincial Park, a geologic gem near the gold rush town of Barkerville.

The initial draw for me, given that collecting in a provincial park is forbidden and all collecting close at hand outside the park appears to amount to a handful of crushed crinoid bits and a few conodonts, was the gorgeous natural scenery and a broad range of species extant. 

It was also the proposition of padding the Bowron Canoe Circuit, a 149,207-hectare geologic wonderland, where a fortuitous combination of plate tectonics and glacial erosion have carved an unusual 116-kilometre near-continuous rectangular circuit of lakes, streams and rivers bound on all sides by snowcapped mountains. From all descriptions, something like heaven.

The east and south sides of the route are bound by the imposing white peaks of the Cariboo Mountains, the northern boundary of the Interior wet belt, rising up across the Rocky Mountain Trench, and the Isaac Formation, the oldest of seven formations that make up the Cariboo Group (Struik, 1988). 

Some 270 million-plus years ago, had one wanted to buy waterfront property in what is now British Columbia, you’d be looking somewhere between Prince George and the Alberta border. The rest of the province had yet to arrive but would be made up of over twenty major terranes from around the Pacific. The rock that would eventually become the Cariboo Mountains and form the lakes and valleys of Bowron was far out in the Pacific Ocean, down near the equator.

With tectonic shifting, these rocks drifted north-eastward, riding their continental plate, until they collided with and joined the Cordillera in what is now British Columbia. Continued pressure and volcanic activity helped create the tremendous slopes of the Cariboo Range we see today with repeated bouts of glaciation during the Pleistocene carving their final shape.

Thursday, 8 November 2018

ATURIA: OLYMPIC PENINSULA NAUTILOID

Arturia angustata nautiloid, Clallam Formation, WA
This lovely Lower Miocene nautiloid is Aturia angustata collected on the foreshore near Clallam Bay, Olympic Peninsula, northwestern Washington. Aturia is an extinct genus of Paleocene to Miocene nautilids within Aturiidae, a monotypic family, established by Campman in 1857 for Aturia Bronn, 1838, and is included in the superfamily Nautilaceae in Kümmel 1964.

Aturia is characterized by a smooth, highly involute, discoidal shell with a complex suture and subdorsal siphuncle. The shell of Aturia is rounded ventrally and flattened laterally; the dorsum is deeply impressed. The suture is one of the most complex within Nautiloidea. It has a broad flattened ventral saddle, narrow pointed lateral lobes, broad rounded lateral saddles, broad lobes on the dorso-umbilical slopes, and a broad dorsal saddle divided by a deep, narrow median lobe. The siphuncle is moderate in size and located subdorsally in the adapical dorsal flexure of the septum. Based on the feeding and hunting behaviours of living nautiluses, Aturia most likely preyed upon small fish and crustaceans. 

I've found a few of these specimens along the beaches of Clallam Bay and nearby in a local clay quarry. I've also seen calcified beauties of this species collected from river sites within the Olympic Peninsula range.

Thursday, 1 November 2018