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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The forest primeval

One of the reasons I'm so fascinated with paleontology is that it induces me to picture what the Earth looked like a loooooooong time ago -- and to consider a planet that was nothing at all like it is now.

I remember when I first realized something about the three earliest periods of Earth's history -- the Precambrian, Cambrian, and Ordovician -- from a kids' book on prehistory, when I was maybe ten years old.  There was a casual statement that during these periods, there was no life on land.  Every living thing there was lived in the water.

And I thought, "Wait, that can't mean what it sounds like."

But it does.  During those three periods -- which together comprise 90% of the history of the Earth -- the land masses were completely barren.  Rock, sand, dust, dirt (with no organic matter whatsoever), stretching over entire continents.

You think the Sahara is a vast wasteland.  Every square kilometer of the early Earth looked like that, without even the occasional palm tree or camel to break the monotony.

Strange to think of an Earth so unlike what we see around us today.  Even after life colonized the land -- starting with plants living around the margins of bodies of water, in the early Silurian -- it would still have looked pretty foreign, and I'm not just talking about dinosaurs, here.  During the Carboniferous Period there were dragonflies with three-foot wingspans, and centipedes almost big enough to ride.  The Devonian, one step earlier, had some fish called placoderms that look like they're wearing poorly-fitting plate armor.

[Image licensed under the Creative Commons, Nobu Tamura (http://spinops.blogspot.com), Dunkleosteus BW, CC BY 3.0]

In fact, it was a discovery dating to the Devonian that spurred me to write this post.  Last week a paper appeared in Current Biology about a fossilized forest in Xinhang, China that spreads over 250,000 square meters.

Quite a significant find.

Don't, however, picture your typical forest here.  These weren't oaks and maples and pines, they were lycopsids, a group now represented only by club mosses, small and generally unassuming plants you'll find in moist forest understories.  But in the Devonian, they got big.  The largest were over seven meters tall, or about the size of your average dogwood or crabapple tree.

But they didn't look anything like modern trees.  More like something Doctor Seuss would have drawn.

[Image licensed under the Creative Commons Tim Bertelink, Lepidodendron, CC BY-SA 4.0]

Imagine a whole forest of these short, skinny trees and you've got the idea.

"The large density as well as the small size of the trees could make the Xinhang forest very similar to a sugarcane field, although the plants in Xinhang forest are distributed in patches," said Deming Wang, a professor in the School of Earth and Space Sciences at Beijing University, who co-authored the study.  "It might also be that the Xinhang lycopsid forest was much like the mangroves along the coast, since they occur in a similar environment and play comparable ecologic roles."

So our picture of this odd world, when fish were the dominant life-form and the only land animals were primitive amphibians, insects, and arachnids, is becoming more complete.  Think about that next time you go for a walk in the woods.  You might not only ponder what the land you're walking on looked like 400 million years ago, but how different it might look like 400 million years from now -- during which evolution will have had plenty of time to generate, as Darwin put it, "endless forms most beautiful and most wonderful."

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This week's Skeptophilia book recommendation is sheer brilliance -- Jenny Lawson's autobiographical Let's Pretend This Never Happened.  It's an account of her struggles with depression and anxiety, and far from being a downer, it's one of the funniest books I've ever read.  Lawson -- best known from her brilliant blog The Blogess -- has a brutally honest, rather frenetic style of writing, and her book is sometimes poignant and often hilarious.  She draws a clear picture of what it's like to live with crippling social anxiety, an illness that has landed Lawson (as a professional author) in some pretty awkward situations.  She looks at her own difficulties (and those of her long-suffering husband) through the lens of humor, and you'll come away with a better understanding of those of us who deal day-to-day with mental illness, and also with a bellyache from laughing.

[Note: If you purchase this book using the image/link below, part of the proceeds goes to support Skeptophilia!]