The ghost forests

I recently read paleontologist Riley Black's lovely book When the Earth Was Green: Plants, Animals, and Evolution's Greatest Romance, which looks at the prehistory of life on Earth through the lens of paleobotany.

While I know the charismatic megafauna like dinosaurs and saber-toothed tigers and giant ground sloths garner most of the attention, I've always found ancient plants equally interesting.  Part of that comes from my ongoing love of both gardening and wild plants, something I've experienced since I was about six and discovered F. Schuyler Mathews's Field Book of American Trees and Shrubs, with its hundreds of pages of descriptions and range maps and wonderful illustrations.  I can't even begin to estimate the amount of time I spent poring over its pages (and I still own my copy of it).

Once I gained a passing knowledge of the trees and shrubs and wildflowers I saw every day, I was shocked to find out that if I were to go back a few million years, I'd find an entirely different assemblage of plant species.  I know, it shouldn't have been a surprise; if the animals had changed, there's no reason the plants wouldn't have as well.  But I still found it astonishing when I found out that (for example) at the moment, there is exactly one extant species of ginkgo (the familiar, and beautiful, Ginkgo biloba), but in the past there had been hundreds, perhaps thousands, of species in the family:

A sampler of now-extinct Jurassic ginkgo species [Image licensed under the Creative Commons Peter R. Crane, Pollyanna von Knorring, Fossil Ginkgoales, CC BY 4.0]

Riley Black does a masterful job of tracing the evolutionary history of plants from their origins to recent times, and her signature lucid writing style makes the subject completely captivating.  One of the chapters deals with an odd period of Earth's history -- the Cretaceous Resinous Interval, a span of about fifty million years during which there was intense diversification amongst gymnosperms, a group that includes not only ginkgos, but the superficially palm-like cycads and the much more familiar conifers.

Anyone who has ever leaned up against a pine or spruce tree knows about their impossibly sticky, golden-brown, aromatic sap.  This glop, so unfortunate for skin and clothing, evolved as a way of sealing wounds and preventing insect damage.  So in a relatively short time, we see the evolution of hundreds of species of plants that produced the stuff -- and, when it met the right conditions, hardening into amber.

Most of the world's amber, whether from Burma or the Baltic region or the highlands of Ecuador and Peru, formed during this time.  Amber has been popular for jewelry-making since the time of the ancient Greeks, and probably before; in fact, an interesting linguistic side-note is that the Greek name for amber, ἤλεκτρον, is where our words electron and electricity come from (due to amber's property of gaining a static charge when rubbed with a silk cloth).  But amber really came into the popular consciousness because of Jurassic Park, wherein some scientists extract dinosaur blood from bloodsucking insects trapped in amber, and use it to clone dinosaurs, with predictable results.

[Nota bene: it's thought that the upper bound for the survival of DNA in amber, even with optimal conditions, is around a million years, not the hundreds of millions required by Jurassic Park.  And even that is likely to be an overestimate.  In 2013, scientists tried -- and failed -- to extract intact DNA from a bee trapped in ten thousand year old copal, an amber precursor.]

That doesn't mean it can't have phenomenal paleontological significance, however, even if we're unlikely to have velociraptors stalking us any time soon.  The reason the topic comes up is a paper that appeared last week in Communications Earth about 112-million-year-old amber unearthed in an Ecuadorean quarry, which contained so many inclusions of insects, pollen, and seeds that it's being called a "Cretaceous time capsule."

A midge from the Ecuadorean amber.  Check out how well preserved those compound eyes and antennae are!  [Image credit: Mónica Solórzano-Kraemer]

The number of insect and arachnid taxa represented, as well as the pollen and other plant fossils discovered, paint a remarkably detailed picture of the ecosystem back then.  The authors write:

The new palaeobotanical evidence suggests the presence of a diverse and humid, low-latitude forest in north-western Gondwana during the early Albian...  The strata in this quarry reveal a vertical evolution of various palaeoenvironments, including proximal braided rivers, lacustrine systems, hyperpycnal [high-density, high-sediment] flows, and distal braided rivers during the Albian...  Pollen and plant macrofossils show abundant ferns and fern-allies that likely grew in the understory and/or near water bodies, in a forest dominated by araucariacean resinous trees.  The overall palynological and plant macrofossil association found in the Genoveva quarry, particularly the high diversity of pteridophytes and the presence of moderately thick coal seams in the stratigraphic sequence, indicates a humid environment, similar to previous reports in other but less studied north-western tropical South American sites.

The presence of relatively abundant chironomid flies and one trichopteran as bioinclusions—both insect groups with aquatic larval stages—further supports the interpretation of predominantly humid conditions during resin production and deposition.

Fascinating to think that if you went back there, in that thriving humid lowland forest, you wouldn't see a single modern plant species.  Not one.  Groups, sure -- we still have araucariacean trees around today (the most familiar being the Norfolk Island pine and the monkey-puzzle tree) -- but our modern forests, even in habitats with similar climates, have no species in common with those that produced the 112-million-year-old Genoveva amber. 

Change is always the way of things, but still, it strikes me as sad that all those many forms most beautiful and most wonderful (to swipe Darwin's pithy phrase) are gone.  Last week at the Tompkins County Friends of the Library Used Book Sale -- a twice-a-year, three week long, must-attend event for any bibliophiles within driving distance of Ithaca, New York, and which offers a quarter of a million used books each go round -- I picked up a real prize in a lovely illustrated paleobotany text, with drawings and fossil photographs representing over a thousand different species of plants no longer to be found anywhere on Earth.

I think this morning I'll spend some time flipping through its pages, and dream of wandering through the ghostly forests of prehistory.

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A flower in amber

Today's post comes to us purely from the "Okay, This Is Cool" department.

I've been fascinated with plant taxonomy since long before I knew the word.  I couldn't have been more than about seven years old when a friend of the family gave me a lovely old book by the early twentieth-century botanical illustrator F. Schuyler Mathews called Field Book to American Trees and Shrubs.  Not only did I use it to try to identify every tree in my neighborhood, I found out something about how plants are classified -- not by leaf shape (which at the time seemed to me the most logical characteristic to use) but by flower structure.  That's when I learned that beeches, oaks, and chestnuts are in the same family; so are rhododendrons, heather, blueberries, and cranberries; so are birches, alders, and hazelnuts; so, most surprisingly to me, are willows and poplars.

It was also my first introduction to how difficult the classification of organisms actually is, something I learned a great deal more about when I took evolutionary biology in college.  The standout from Mathews's book in that respect is the genus Crataegus, hawthorns, of which he lists (and illustrates with beautiful woodcuts) over a hundred species, many of which looked (and still look) exactly alike to my untrained eye.  Taxonomists argue vehemently over how particular species are to be placed and who is related to whom, although the advent of genetic analysis and cladistics has now provided a more rigorous standard method for classification.

What I didn't know, even after my umpteenth perusal of the Field Book, was that the strange and magical-sounding scientific names of plant families Mathews mentions are barely scratching the surface.  You go elsewhere in the world, all bets are off; you'll run into plants that are in families with no members at all in the United States.  An odd historical filigree is that one of the reasons the British colonizers felt so at home in northeastern North America was that the plants were familiar; oaks, ashes, beeches, birches, willows, maples, pines, and spruces are found in both places (although the exact species vary).  Go to southeast Asia, South America, or pretty much anywhere in Africa, though, and even someone well-versed in the plants of North America and western Europe might well not recognize a single species.  I found that to be the case in Malaysia -- a (very) little bit of reading about the flora of the places I visited gave me at least a name or two, but I'd say 95% of what I saw I couldn't even have ventured a guess about.

One of the many peculiar plants I saw in the rain forests of Malaysia -- I still don't know what it is, but it sure has a cool-looking leaf.

The reason this comes up is an article sent to me by a friend and loyal reader of Skeptophilia about a fossil from Myanmar that was the subject of a recent paper in The Journal of the Botanical Institute of Texas.  Encased in amber, the flower is almost perfectly preserved -- despite being just this side of one hundred million years old, a point at which the dinosaurs would still be in charge of everything for another thirty-four million years.

If it sounds like figuring out the taxonomy of modern plants is a challenge, it gets way worse when you start looking at plant fossils.  Not only do we not have living plants to analyze genetically, often what we're having to judge by is what's left of a leaf or two.  Fortunately, in this case what the researchers have is a preserved flower -- remember that flowering plants are classified by flower structure -- and that was enough to convince them that they were not only looking at a previously unrecorded species, but a previously unrecorded genus -- and possibly a whole new family.

The flower of the newly-named Micropetasos burmensis [Image by George Poinar of Oregon State University)

Most fascinating of all, the researchers aren't even sure how Micropetasos fits into known plant systematics.  The paper says about all we can say so far is that it seems to belong to the clade Pentapetalae -- which doesn't narrow it down much, as that same clade contains such distantly-related plants as roses, asters, cacti, cucumbers, and cabbage.

Long-time readers might recognize the name of the lead author of the paper -- George Poinar.  This isn't the first time he's pulled off this kind of botanical coup.  About a year and a half ago, I wrote about another of Poinar's discoveries in Burmese amber, a little flower called Valviloculus pleristaminis, which also was of uncertain placement amongst known plant families.  Amazing that in bits of fossilized tree sap we can find remnants that allow us to piece together the flora of the Cretaceous Period.

Of course, what it always brings up is the elegiac thought that however many fossils we find, the vast majority of species that have existed on Earth left no traces whatsoever that have survived to today.  If we were to take a time machine back a hundred million years, Micropetasos and Valviloculus we might perhaps recognize from Poinar's work; but there would be thousands more that are completely unfamiliar.  The lion's share of prehistory is unknown -- and unknowable.

But at least we have one more little piece, a tiny flower in amber.  When it was growing, there were triceratopses and T. rexes stomping around, and our closest ancestors were small, rodent-like critters that still had tens of millions of years of evolution before they'd even become primates.  That we can have any sort of lens into that distant, ancient world is astonishing.

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