The forest primeval

A couple of days ago my friend and fellow writer Andrew Butters sent me a link about a new fossil discovery.  He hastened to point out that he'd thought of me because he knows I'm interested in paleontology, not because my name comes to mind when he thinks about antiquated relics.  There may have been a touch of local pride involved as well, because the discovery was made in his home province of New Brunswick, Canada.

There's no doubt that it was a remarkable find.  The fossil was unearthed in a quarry near the town of Norton, where there is a layer of 350-million-year-old sandstone deposited when Atlantic Canada was a tropical swamp.  This was near the beginning of the Carboniferous Period, a time when the Earth was significantly warmer and wetter than it is now.  The high temperatures and carbon dioxide levels boosted plant growth, causing the oxygen levels to rise to an estimated 35% (compared to today's 21%).  This had the effect of allowing animals that had previously been held back by their inefficient respiratory systems, especially arthropods, to become huge, leading to millipedes 2.5 meters long and dragonflies with 75-centimeter wingspans.

The plants, though, were also pretty different from what we've got around now; by far the most common ones today are flowering plants, which make their first unequivocal appearance in the fossil record about 130 million years ago, in the early Cretaceous Period.  So when the New Brunswick sandstone was being deposited, the first flowering plants were still 220 million years in the future.

The dominant plants back then were distantly related to today's ferns, horsetails, and club mosses, although as you'll see we don't have anything left that looks much like what you'd see in a typical Carboniferous forest.  But the fossil discovered in the Canadian quarry was bizarre even compared to a lot of the strange vegetation from that time -- and has drawn comparisons to something you might see in a book by Dr. Seuss.

"What it really does look like is one of those truffula trees from The Lorax," said Olivia King, of St. Mary's University in Halifax, who was part of the team that discovered the fossils.  The most remarkable thing about the fossil, though, is its amazing state of preservation.  It's thought to have been entombed in an upright position when a landslide caused part of the bank of a lake to collapse.  The entire tree was dragged down to the bottom of the lake and buried in sediment, where it's lain for 350 million years -- and now has been excavated carefully to reveal what it looked like when it was alive.  Dubbed Sanfordiacaulis densifolia, after quarry owner Laurie Sanford who has been instrumental in allowing the investigation to progress, it had a mop of spiky leaves topping a spindly trunk:

A reconstruction of Sanfordiacaulis densifolia [Image credit: artist Tim Stonesifer]

With the acceleration of plant growth during that time period, there was extreme competition to access light, leading to dramatic increases in plant height and canopy size.  Eventually, there were club mosses (genus Lepidodendron) fifty meters tall -- taller than the oaks and maples in an average hardwood forest.

A sampler of ancient trees, from Robert Gastaldo et al., Current Biology.  [Note: "Mississippian" and "Pennsylvanian" are two divisions of time usually lumped together as the Carboniferous Period.]

Of course, the good times -- at least if you were a weird club moss tree or a 2.5-meter-long millipede -- couldn't last forever.  Around 305 million years ago, the climate turned from hot and humid to cool and arid, probably because by that time the plants had locked up so much atmospheric carbon dioxide underground -- what would eventually become our coal deposits -- that the greenhouse effect decreased and the temperature fell.  In essence, the plants sowed the seeds of their own destruction, and in the Carboniferous rain forest collapse that followed, the enormous forests and many of the animals that depended upon them became extinct.

It also set the fuse for the largest mass extinction ever.  All that organic matter sequestered underground was tinder just waiting to burn, and when the Siberian Traps erupted 252 million years ago, the lava ripped through a huge chunk of the Carboniferous coal and peat, using up oxygen (dropping it to an estimated 12%) and dumping that excess carbon dioxide back into the atmosphere.  The temperature spiked, the oceans became anoxic, and something like 95% of life on Earth became extinct.

But at the point that the Sanfordiacaulis tree was growing in what would become New Brunswick, that cataclysmic event was still a hundred million years in the future.  Think about what a thrill it'd be to get to wander amongst those bizarre forests, so unlike anything we have today.

Even if it meant dodging enormous dragonflies.

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