Pressing reset

Although you don't tend to hear much about it, the Ordovician Period was a very peculiar time in Earth's history.

From beginning (485 million years ago) to the end (444 million years ago) it experienced two of the biggest global climatic swings the Earth has ever seen.  In the early Ordovician the climate was a sauna -- an intense greenhouse effect caused the highest temperatures the Paleozoic Era would see, and glacial ice all but vanished.  Life was abundant in the shallow seas.  One of the dominant groups were the conodonts:

[Image licensed under the Creative Commons Prehistorica, Panderodus unicostatus, CC BY-SA 4.0]

Those of you who know your fish might guess that conodonts like Panderodus were related to modern lampreys, and you're right.  But it took a really long time to figure that out.  Their soft bodies didn't fossilize well, so about all that we had were the cone-shaped teeth that gave them their name.  In fact, those teeth are the most common fossils in Ordovician sedimentary rocks, so we knew whatever grew them must have been abundant -- but it took a while to determine what kind of animal they came from.

So things were warm, humid, with tropical conditions virtually pole to pole.  Then... something happened.  We're still not entirely sure what.  Part of it was undoubtedly simple plate tectonics; the supercontinent of Gondwana was gradually moving toward the South Pole.  There's some evidence of a large meteorite strike, or possibly more than one.  But whatever the cause, by the end of the Ordovician, glaciers covered much of what is now Africa and South America, resulting in a drastic drop in sea level and a massive extinction that wiped out an estimated sixty percent of life on Earth.  

At this point, life was confined to the oceans. The first terrestrial plants and fungi wouldn't evolve until something like twenty million years after the beginning of the next period, the Silurian, and land animals only followed after that.  As the Ordovician progressed, and more and more ocean water became locked up in the form of glacial ice, much of what had been shallow, temperate seas dried up to form cold, barren deserts.  And that was all there was on land -- thousands of square kilometers of rock, sand, and ice, without a single living thing larger than bacteria to be found anywhere.

Then, the climate reversed again.  The seas flooded back in, and the warmer, sulfur-rich, oxygen-poor water upwelling from the bottom knocked out about twenty percent of the cold-adapted survivors.  By the time the period ended, the Earth had a seriously impoverished biosphere, with something like fifteen percent of the original biota making it through the double-whammy.

But what survived this pair of climate swings was to shape Earth's biological history forever.  Because it included primitive vertebrates with paired jaws -- the gnathostomes -- which became the ancestors of 99% of modern vertebrate animals, including ourselves.

The reason this comes up is some new research out of the Okinawa Institute of Science and Technology that analyzed thousands of fossils from species that made it through the Late Ordovician bottleneck -- and an equal number of those that didn't.  And they found two interesting patterns.  First, the survivors were mostly species that found their way into refugia -- small, isolated pockets of ecosystems with (slightly) more hospitable conditions that allowed them to squeak their way through the worst times.  Second, each of the major extinction pulses was followed by dramatic diversification, as the surviving populations expanded into niches vacated by the ones that weren't so fortunate.

"We pulled together two hundred years of late Ordovician and early Silurian paleontological research," said study lead author Wahei Hagiwara.  "By reconstructing the ecosystems within these refugia, we were able to measure changes in genus-level diversity over time.  Our analysis revealed a steady but striking rise in jawed vertebrate diversity following the extinction.  And the trend is clear -- the mass extinction pulses led directly to increased speciation after several millions of years."

As Ian Malcolm so accurately put it, "Life, uh, finds a way."

A couple of other things strike me about this research, though.

The first is how contingent our existence here is.  Evolutionary biologist Stephen Jay Gould wrote a provocative piece about "replaying the tape of life," coming to the conclusion if you were to start over from the beginning, so much of the path of evolution has rested on chance occurrences that the chances of it turning out exactly the same way is nearly zero.  In a situation like the Late Ordovician Mass Extinction, which assortment of species made it into the few hospitable refugia must have had as much to do with luck as with being well-adapted; had a different set of populations survived, life today almost certainly would look very different.

The second is the fact that both of the Ordovician climate swings were far slower than what we're currently doing to the environment.  Like, hundreds of times slower.  The second one, in fact -- the warm-up and subsequent melting of polar ice -- was almost certainly a very gradual rebound toward the greenhouse conditions that were to pertain by the mid-Silurian.  We're talking about something on the order of ten million years to go from cool to warm.

What we're doing now has taken only a couple of hundred.

What happened in the Late Ordovician should be a wake-up call for us.  Yet somehow, we arrogant humans think we're immune to the effects of our out-of-control fossil fuel burning.  We have a striking fossil record documenting the terrible effects of rapid climate change in prehistory; at the moment, mostly what we seem to be doing is saying, "Yeah, but it won't happen to us, 'cuz we're special."

So that's our cautionary tale for today.  The climate change deniers are fond of saying, "Earth's climate has changed many times before now," and almost never add, "... and when it did, enormous numbers of species went extinct."  And the difference, too, is that the natural fluctuations (such as those caused by plate movement, asteroid strikes, and changes in insolation) aren't something we could control even if we wanted to, but what we're doing now is entirely voluntary.

And until the people in charge realize that addressing climate change is in all of our best interest, I'm afraid our path forward is not likely to change.

****************************************

Lost and found

I'm currently reading Michael Novacek's fascinating book Dinosaurs of the Flaming Cliffs, which is about the expeditions led by Novacek into the backcountry of the Mongolian Gobi Desert in search of late Cretaceous dinosaur fossils.

And they found 'em.  In abundance.  The remains that Novacek's team unearthed changed our understanding of the evolution of dinosaurs and early mammals in central Asia -- I've already lost count of the number of new species his group found, and I'm only about a third of the way through the book.

What struck me, though, is the combination of physical and personal hardship that the team members were willing to tolerate to achieve their goals.  The Gobi Desert is, even today, largely untraveled and unmapped; the nomadic groups that live in its arid wastes have to keep moving to survive in a climate that is broiling hot in the summer and viciously cold in the winter, has little in the way of drinkable fresh water, and is thin pasturage for domestic animals even at the best of times.  These scientists launched into the arid badlands in old, Soviet-era trucks that broke down every time someone sneezed hard, with carefully-rationed food, water, and gasoline, and exactly zero margin for error.

The fact that they not only survived, but achieved their scientific goals (and then some), is downright astonishing.  And every other page, I've shaken my head and thought, "I would never have the courage to do something like this.  Not in a million years."

Keep in mind, too, that this is coming from someone who did his share of backcountry camping, mostly in the Cascades and Olympics of Washington State.  Being a teacher has its perks -- June, July, and August being top of the list -- and when I was in my twenties I frequently disappeared into the fir-shrouded forests during the summer for weeks at a time.  So I'm no stranger to sleeping outdoors and hiking with a heavy pack.  (Or at least I was.  Now that I am Of A Certain Age, I'm afraid my appreciation of the creature comforts has done nothing but increase.)

But still: I would never have been brave enough to take off into the wilds of Mongolia the way Novacek et al. did (repeatedly).  Which probably would have scotched any intent I might have had to become a paleontologist.

On the other hand, sometimes -- admittedly, it's probably rare -- great paleontological discoveries can come from merely opening the right drawer in a museum.  The reason the topic comes up (besides my current reading-in-progress) is the chance find by paleontologist Georgios Georgalis of the Institute of Systematics and Evolution of Animals of the Polish Academy of Sciences in Krakow, who was doing some research in London's Natural History Museum and stumbled across the bones of a very unusual fossil snake that had been overlooked for forty years.

Dubbed Paradoxophidion richardoweni -- "Richard Owen's paradoxical snake" -- it lived in England during the Eocene Epoch, something like 37 million years ago.  At that point, England was a great deal warmer than it is now.  The world was just exiting the Paleocene-Eocene Thermal Maximum, at eight degrees Celsius higher than today one of the highest global average temperatures ever recorded.  The hot times favored diversification of ectothermic animals -- such as snakes -- in what are now regions with much cooler climates.

"It was my childhood dream to be able to visit the Natural History Museum, let alone do research there," said study lead author Georgalis.  "So, when I saw these very weird vertebrae in the collection and knew that they were something new, it was a fantastic feeling.  It's especially exciting to have described an early diverging caenophidian snake, as there's not that much evidence about how they emerged. Paradoxophidion brings us closer to understanding how this happened."

The snake species, Georgalis said, seems to be related to a group called acrochordids now found only in southeast Asia and Australia -- although more study is needed to be certain.  And it also brought up the tantalizing question of what else might be hiding in museum drawers and cabinets.

"I'm planning to study a variety of snake fossils in the collection, including those originally studied by Richard Owen" Georgalis said.  "These include the remains of the giant aquatic snake Palaeophis, which were first found in England in the nineteenth century.  There are also several bones with differing morphology that haven't been investigated before that I'm interested in looking at.  These might represent new taxa and offer additional clues about snake evolution."

So I guess you don't need to endure sandstorms and blistering heat and terrible food to make significant contributions to the field.

This also highlights the critical importance of museums in the entire scientific enterprise.  I found out yesterday the amazing news that one of our best local museums, the Paleontological Research Institution/Museum of the Earth, has received enough donations to remain open -- funding cuts were looking likely to shutter it permanently.  On the one hand, I'm thrilled that enough people were willing to donate to keep this wonderful place going (and if you're willing, I encourage you to go to their website and do so as well -- even if they met their goal, they can still put every penny to good use).  On the other, though, isn't it sad that we never seem to run out of money for stuff like funding war and paying kickbacks to corporate billionaires, but cutting-edge scientific establishments that are inspirations to thousands basically have to hold a bake sale to stay in business?

[Image licensed under the Creative Commons Matt Wedel, Yale brontosaurus, CC BY 4.0]

In any case, here's another puzzle piece adding to the picture of what the Earth was like tens of millions of years ago, that had been hidden away in a museum cabinet for four decades.  I find the whole thing endlessly fascinating, which probably explains why the topic of paleontology is such a frequent flier here at Skeptophilia. 

But as interested as I am, I still don't think I'd be brave enough to venture into the Gobi Desert to study it.

****************************************

Scattered to the winds

One of the more puzzling aspects of evolutionary theory is the phenomenon of peripheral isolates.

This term refers to widely-separated populations of seemingly closely-related organisms.  One of the first times I ran into this phenomenon came to my attention because of my obsession with birdwatching.  There's a tropical family of birds called trogons, forest-dwelling fruit-eaters that are prized by birdwatchers for their brilliant colors.  There are trogons in three places in the world... Central and South America (27 species), central Africa (3 species), and southern Asia (11 species).

These are very far apart.  But take a look at three representatives from each group -- it doesn't take an ornithologist to see that they've got to be closely related:

The Elegant Trogon (Trogon elegans) of Central America [Image licensed under the Creative Commons dominic sherony, Elegant Trogon, CC BY-SA 2.0]

The Narina Trogon (Apaloderma narina) of central Africa [Image licensed under the Creative Commons Derek Keats from Johannesburg, South Africa, Narina Trogon, Apaloderma narina MALE at Lekgalameetse Provincial Reserve, Limpopo, South Africa (14654439002), CC BY 2.0]

The Red-headed Trogon (Harpactes erythrocephalus) of southeast Asia [Image licensed under the Creative Commons JJ Harrison (jjharrison89@facebook.com), Harpactes erythrocephalus - Khao Yai, CC BY-SA 3.0]

I know, I've gone on and on in previous posts about how misleading morphology/appearance can be in determining relationships, but you have to admit these are some pretty convincing similarities.

The question, of course, is how did this happen?  Where did the group originate, and how did members end up so widely separated?  To add to the puzzle, the fossil record for the group indicates that in the Eocene Epoch, fifty-ish million years ago, there were trogons in Europe -- fossils have been found in Denmark and Germany -- and the earliest fossil trogons from South America come from the Pleistocene Epoch, only two million years ago.

So are these the remnants of what was a much larger and more widespread group, whose northern members perhaps succumbed due to one of the ice ages?  Did they start in one of their homelands and move from there?

And if that's true, why are there no examples of trogons from all the places in between?

Another example of this is the order of mammals we belong to (Primata).  Primates pretty clearly originated in Africa and spread from there; the earliest clear primates were in the Paleocene Epoch, on the order of sixty million years ago, but the ancestor of all primates was probably at least twenty million years before that, preceding the Cretaceous Extinction by fourteen million years.  From their start in east Africa they seem to have spread both east and west, reaching southeast Asia around fifty million years ago.  Some of the earliest members to split were the lorises and tarsiers, along with the lemurs of Madagascar.

But the next group to diverge -- and the reason the whole topic of peripheral isolates came up -- are the "New World monkeys," the "platyrhines" of Central and South America.  It looks like this split happened during the Oligocene Epoch, around thirty million years ago... but how?

At that point, Africa was separated from South America by nine hundred miles of ocean -- narrower than the Atlantic is today, but still a formidable barrier.  But a paper in Science describes recently-discovered evidence from Peru of some fossilized primate teeth from right around the time the New World/Old World monkey split happened.

What this discovery suggests is staggering; all of the New World monkeys, from the spider monkey to the black howler monkey to the Amazonian pygmy marmoset, are descended from a single group that survived a crossing of the Atlantic, probably on a vegetation raft torn loose in a storm, only a little over thirty million years ago.

"This is a completely unique discovery," said Erik Seiffert, the study's lead author and Professor of Clinical Integrative Anatomical Sciences at Keck School of Medicine of the University of Southern California, in an interview with Science Daily.  "We're suggesting that this group might have made it over to South America right around what we call the Eocene-Oligocene Boundary, a time period between two geological epochs, when the Antarctic ice sheet started to build up and the sea level fell.  That might have played a role in making it a bit easier for these primates to actually get across the Atlantic Ocean."

So here we have a possible explanation for one of the long-standing puzzles of evolutionary biology.  Note that these puzzles aren't a weakness of the theory; saying "we still have some things left to explain" isn't the same as saying "the theory can't explain this."  There will always be pieces to add and odd bits of data to account for, but I have one hundred percent confidence that the evolutionary model is up to the task.

Now, I wish it could just come with an explanation for the trogons, because for some reason that really bothers me.

****************************************

Footprints in the boneyard

The difficulty with paleontology is its inherent limitations.

There are, of course, things it's very good at.  In the hands of a skilled expert, fossils can tell you a great deal -- not only direct information about the parts that are preserved, but indirect information (from spaces, gaps, muscle attachment points, and so on) about the parts that were not.  I'm currently reading the wonderful book by Jack Horner and Edwin Dobb, Dinosaur Lives: Unearthing an Evolutionary Saga, and was astonished to find out that many paleontologists now believe that the quintessential Big Scary Dinosaur, Tyrannosaurus rex, was primarily a scavenger and not a hunter -- based upon the fact that the interior of the skull shows that its brain had an enormous olfactory lobe and a correspondingly small visual cortex, similar to hyenas and vultures.

Even so, there's a lot that fossils have a harder time telling us.  Other than a few fortuitous exceptionally-preserved feathers, we know next to nothing about colors and markings; art featuring prehistoric animals is almost entirely basing those features on guesswork using the patterns we see in modern animals.  In addition, how ancient organisms fit into the bigger ecological picture is like trying to figure out the pattern in a thousand-piece puzzle when you only have a handful of pieces. Given that a very small percentage of the biological remains left behind ever become fossils, chances are there are tens of thousands of prehistoric species we know absolutely nothing about because they left no traces behind after the last of their kind died.

Behavior, too, is often a puzzle.  It was Jack Horner (the same Jack Horner who co-wrote Dinosaur Lives) who made the discovery of the nesting and parental care behavior in the duckbilled dinosaur Maiasaura (the name means "good mother lizard"), based upon a group of fifteen fossilized juveniles and one adult that had been killed simultaneously in a volcanic ashfall.  But despite what Jurassic Park would have you believe, we really know very little about the behavior of prehistoric animals.  (Dilophosaurus, for example, almost certainly didn't have a retractable frill and poisonous spit.  Spit rarely fossilizes.)

The reason the topic comes up, actually, is because of a different volcanic eruption that left behind a treasure trove of fossils; a "supereruption" of the Yellowstone volcanic system twelve million years ago that smothered (and preserved) a huge herd of the prehistoric North American rhinoceros species Teleoceras.  The site -- in what is now northeastern Nebraska -- has been nicknamed "the rhino Pompeii."

"The eruption was so massive that ash would have fallen like snow 1,600 kilometers from the eruption site in Idaho," said Ashley Poust, a curator of vertebrate paleontology at the University of Nebraska State Museum, who gave a talk on the find last week at the annual meeting of the Society for Vertebrate Paleontology.  "This would have darkened the skies, buried plant life and water sources, and been a real hazard to anything with a delicate respiratory system."

A paleontologist working on unearthing Teleoceras fossils in the Ashfall Fossil Beds [Image credit: Ashley Poust]

What's most amazing about this find, though, is that the study also uncovered footprints in the ash -- the traces of two species of "bone-crushing dogs," Aelurodon taxoides and Epicyon saevus, which apparently somehow escaped being suffocated themselves and afterward made use of the huge amounts of free meat from the dead rhinos.  Aelurodon and Epicyon seem to have occupied the same niche as modern hyenas, but were a lot bigger; these prints were about eight centimeters long and seven centimeters wide.

Reconstruction of Epicyon [Image licensed under the Creative Commons Jarrod Amoore from Sydney, Australia, Epicyon, CC BY 2.0]

"There is some evidence that they may have scavenged among the animals who didn't survive, using the buried rhinos as a food cache," Poust said.  "But since we haven't found the bones of these meat eaters, we aren't sure yet whether this was enough to see them through to better times, or whether they eventually had to depart to seek their fortunes elsewhere in the massive disaster zone that covered much of North America."

It's also uncertain how they survived.  Volcanic ash is nasty stuff.  Not only does it clog airways if inhaled, it's made of sharp slivers of something very much like glass.  Even walking through a recent ashfall would raise enough dust to cause significant health risk, much less living through it while it was actively falling out of the sky.  Interesting that there haven't been any fossils of the dogs found at the site -- although research is ongoing, and it's anyone's guess about what's left there to discover.

So here's another case where we can made at least some tentative inferences about behavior from twelve million year old fossils.  Although the sad truth is that we still have access to information about only a tiny percent of the life that has ever existed on Earth, sometimes a chance discovery will give us a startling window into the past -- in this case about packs of scavengers that may have taken advantage of a catastrophic disaster.

****************************************

Resurrection

The environmentalists tell us "extinction is forever," and that certainly seems unarguable.  Once a species is lost, evolution will never recreate it.  You may get something that looks like it; there are numerous examples of Elvis taxa, species that evolved to fit vacated niches and underwent convergent evolution resulting in a similarity to some extinct form.  (The name comes from the huge numbers of Elvis impersonators that have popped up since the original's death in 1977.)  But the sad truth is that the original is gone forever.

The issue, though, can be making certain the species actually is extinct.  There are ongoing efforts to find relic populations of a number of presumed-extinct species (two of the best known are the ivory-billed woodpecker and the thylacine).  Naysayers have criticized the efforts to find these species as nothing more than wishful thinking, but it bears keeping in mind that there is a long list of organisms thought to be extinct that have turned out to be very much alive.

They're called Lazarus taxa, after the biblical character Jesus raised from the dead.  Some of them are astonishing.  The one that always comes to mind for most people is the coelacanth, a crossopterygian fish that was only known from fossils preceding the Cretaceous Extinction sixty-six million years ago, which was discovered living in the Indian Ocean in 1938.  But that's only one of many.  Here's a sampler of Lazarus taxa:

• The South American bush dog (now split into three separate species in the genus Speothos) was only known from some Pleistocene-age bones found in a Brazilian cave, but is now known to have a range from southern Central America all the way to northern Paraguay.  Its reclusive habits and rarity still make it the least-studied canid in the world.

A Brazilian bush dog [Image licensed under the Creative Commons Xerini, Waldhund, CC BY-SA 3.0]

• The nightcap oak (Eidothea hardeniana and E. zoexylocarya), which aren't oaks at all but a member of the Protea family (Proteaceae), were known only from fifteen-million-year-old fossils -- and then a stand of them were discovered growing in a remote part of Australia.  The Royal Botanical Gardens in Sydney has a cultivation program for the two species, which are threatened because the seeds are frequently eaten by introduced mice.

Eidothea hardeniana [Image is in the Public Domain]

• The monito del monte, or colocolo opossum (Dromiciops gliroides), was not only thought to have gone extinct eleven million years ago, it was believed that its entire order (Microbiotheria) was gone as well.  It was found -- alive -- in the temperate bamboo forests of the southern Andes Mountains in 1894, and has no near relatives anywhere in the world.  (The closest are the Australian marsupials, but even those are very distant cousins.)

[Image licensed under the Creative Commons José Luis Bartheld from Valdivia, Chile, Monito del Monte ps6, CC BY 2.0]

• In 1898 a fish was discovered that was a near perfect match to Oligocene-age fossils on the order of twenty-eight million years old.  It's Lignobrycon myersi, and is only known from the Rio Braço and Rio Contas in east-central Brazil.  Somehow, it alone of its genus survived through all of those years and made it down to the present day.

[Image licensed under the Creative Commons Alexandre dos Santos Rodrigues et. al., Lignobrycon myersi specimens (9382613) (cropped), CC BY 4.0]

• The monoplacophorans were a group of mollusks common during the Silurian and Devonian Periods, but were last seen in the fossil record in the mid- to late-Devonian, around 375 million years ago.  After that -- nothing.  Reasonably, biologists thought they'd gone extinct, until live monoplacophorans were discovered in deep water off the west coast of Costa Rica.  Further surveys have found no fewer than thirty-seven different species in deep water across the Pacific.

A live specimen of Neopilina filmed off the coast of Samoa by the 2017 Okeanos Explorer mission [Image is in the Public Domain courtesy of NOAA]

• Even the monoplacophorans don't hold the survival record, though.  That honor goes to Rhabdopleura, which is a graptolite -- a (very) distant relative of chordates known mainly through Cambrian-age fossils.  The last Rhabodopleura was thought to have gone extinct in the mid-Cambrian, five hundred million years ago (and the rest of the group didn't make it past the mid-Carboniferous).  In 1869 they were discovered living in the deep water of the Pacific, and since that time nine living species have been identified.

A drawing of Rhabdopleura normani [Image is in the Public Domain]

While the general rule still applies -- extinction is forever -- it's worth keeping in mind that sometimes we find ourselves in a situation a little like Mark Twain did, resulting in his quip, "Rumors of my death were great exaggerations."  The Earth is a big place, and there are still plenty of poorly-explored regions where we might well have lots of surprises in store.

All of which should be encouraging to the folks out there chasing the ivory-billed woodpecker and thylacine.  Don't give up hope.  If Rhabdopleura could survive for five hundred million years unobserved, surely these two could manage a century or so.

****************************************

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.

****************************************

The skull in the cave

"If humans came from monkeys, why are there still monkeys?"

If there is one phrase that makes me want to throw a chair across the room, it's that one.  (Oh, that and, "The Big Bang means that nothing exploded and became everything.")  Despite the fact that a quick read of any of a number of reputable sites about evolution would make it clear that the question is ridiculous, I still see it asked in such a way that the person evidently thinks they've scored some serious points in the debate.  My usual response is, "My ancestors came from France.  Why are there still French people?"  But the equivalence of the two seems to go so far over their heads that it doesn't even ruffle their hair.

Of course, not all the blame lies with the creationists and their ilk.  How many times have you seen, in otherwise accurate sources, human evolution depicted with an illustration like this?

It sure as hell looks like each successive form completely replaced the one before it, so laypeople are perhaps to be excused for coming away with the impression that this is always the way evolution works.  In fact, cladogenesis (branching evolution) is far and away the more common pattern, where species split over and over again, with different branches evolving at different rates or in different directions, and some of them becoming extinct.

If you're curious, this is the current best model we have for the evolution of hominins:

The cladogenesis of the hominin lineage; the vertical axis is time in millions of years before present  [Image licensed under the Creative Commons Dbachmann, Hominini lineage, CC BY-SA 4.0]

The problem also lies with the word species, which is far and away the mushiest definition in all of biological science.  As my evolutionary biology professor put it, "The only reason we came up with the idea of species as being these little impermeable containers is that we have no near relatives."  In fact, we now know that many morphologically distinct populations, such as the Neanderthals and Denisovans, freely interbred with "modern" Homo sapiens.  Most people of European descent have Neanderthal markers in their DNA; when I had my DNA sequenced a few years ago, I was pleased to find out I was above average in that regard, which is undoubtedly why I like my steaks medium-rare and generally run around half-naked when the weather is warm.  Likewise, many people of East Asian, Indigenous Australian, Native American, and Polynesian ancestry have Denisovan ancestry, evidence that those hard-and-fast "containers" aren't so water-tight after all.

The reason all this comes up is because of a new study of the "Petralona Skull," a hominin skull found covered in dripstone (calcium carbonate) in a cave near Thessaloniki, Greece.  The skull has been successfully dated to somewhere between 277,000 and 539,000 years ago -- the uncertainty is because of estimates in the rate of formation of the calcite layers.

The Petralona Skull  [Image licensed under the Creative Commons Nadina / CC BY-SA 3.0]

Even with the uncertainty, this range puts it outside of the realm of possibility that it's a modern human skull.  Morphologically, it seems considerably more primitive than typical Neanderthal skulls, too.  So it appears that there was a distinct population of hominins living in southern Europe and coexisting with early Neanderthals -- one about which paleontologists know next to nothing.

Petralona Cave, where the skull was discovered [Image licensed under the Creative Commons Carlstaffanholmer / CC BY-SA 3.0]

So our family tree turns out to be even more complicated than we'd realized -- and there might well be an additional branch, not in Africa (where most of the diversification in hominins occurred) but in Europe.  

You have to wonder what life was like back then.  This would have been during the Hoxnian (Mindel-Riss) Interglacial, a period of warm, wet conditions, when much of Europe was covered with dense forests.  Fauna would have included at least five species of mammoths and other elephant relatives, the woolly rhinoceros, the cave lion, cave lynx, cave bear, "Irish elk" (which, as the quip goes, was neither), and the "hypercarnivorous" giant dog Xenocyon.  

Among many others.

So as usual, the mischaracterization of science by anti-science types misses the reality by a mile, and worse, misses how incredibly cool that reality is.  The more we find out about our own species's past, the richer it becomes.

I guess if someone wants to dismiss it all with a sneering "why are there still monkeys?", that's up to them.  But me, I'd rather keep learning.  And for that, I'm listening to what the scientists themselves have to say.

****************************************

Life, not as we know it

I've written here before about unusual paleontological discoveries -- illustrations of the fact that Darwin's lovely phrase "many forms most beautiful and most wonderful" has applied throughout Earth's biological history.

We could also add the words "... and most weird."  Some of the fossils paleontologists have uncovered look like something from a fever dream.  A while back I wrote about the absolutely bizarre "Tully Monster" (Tullimonstrum spp.) that is so different from all other life forms studied that biologists can't even figure out whether it was a vertebrate or an invertebrate.  But Tully is far from the only creature that has defied classification.  Here are a few more examples of peculiar organisms whose placement on the Tree of Life is very much up for debate.

First, we have the strange Tribrachidium heraldicum, a creature of uncertain relationships to all species at the time or afterward.  It had threefold symmetry -- itself pretty odd -- and its species name heraldicum comes from the striking resemblance to the triskelion design on the coat of arms of the Isle of Man:

Tribrachidium fossil from near Arkhangelsk, Russia [Image licensed under the Creative Commons Aleksey Nagovitsyn (User:Alnagov), Tribrachidium, CC BY-SA 3.0]

Despite superficial similarities to modern cnidarians (such as jellyfish) or echinoderms (such as sea urchins and starfish), Tribrachidium seems to be neither.  It -- along with a great many of the Ediacaran assemblage, organisms that dominated the seas during the late Precambrian Era, between 635 and 538 million years ago -- is a mystery.

The Ediacaran is hardly the only time we have strange and unclassifiable life forms.  From much later, during the Carboniferous Period (on the order of three hundred million years ago), the Mazon Creek Formation in Illinois has brought to light some really peculiar fossils.  One of the most baffling is Etacystis communis, nicknamed the "H-animal":

Reconstruction of Etacystis [Image is in the Public Domain]

It's an invertebrate, but otherwise we're still at the "but what the hell is it?" stage with this one.  Best guess is it might be a distant relative of hemichordates ("acorn worms"), but that's speculative at best.

Next we have Nectocaris.  The name means "swimming shrimp," but a shrimp it definitely was not.  It next was thought to be some kind of primitive cephalopod, perhaps related to cuttlefish or squid, but that didn't hold water, either.  They had a long fin down each side that they probably used for propulsion, and a feeding tube shaped like a funnel (that you can see folded to the left in the photograph below):

Photograph of a Nectocaris fossil from the Burgess Shale Formation, British Columbia [Image is in the Public Domain]

All of the Nectocaris fossils known come from the early Cambrian.  It's possible that they were a cousin of modern chaetognaths ("arrow worms"), but once again, no one is really sure.

Another Cambrian animal that has so far defied classification is Allonnia, which was initially thought to be related to modern sponges, but their microstructure is so different they're now placed in their own order, Chancelloriidae.  You can see why the paleontologists were fooled for a while:

Reconstruction of Allonnia from fossils recovered from the Chengjiang Formation, Yunnan Province, China [Image licensed under the Creative Commons, Yun et al. 2024 f05 (preprint), CC BY 4.0]

At the moment, Allonnia and the other chancelloriids are thought to represent an independent branch of Kingdom Animalia that went extinct in the mid Cambrian Era and left no descendants -- or even near relatives.

Last, we have the bizarre Namacalathus hermanestes, which has been found in (very) late Precambrian shales in such widely-separated sites as Namibia, Canada, Paraguay, Oman, and Russia.  Check out the reconstruction of this beast:

[Image credit Zhuravlev, Wood, and Penny, Proceedings of the Royal Society B, November 2015]

It's been tentatively connected to lophophorates (which include the much more familiar brachiopods), but if so, it must be a distant relationship, because they look a great deal more like something H. P. Lovecraft might have dreamed up:

Unlike the, um, "Yuggothians," though, Namacalathus was quite real.  And, apparently, widespread.

The early Cambrian seas must have contained plenty of nightmare fuel.

And those are just five examples of organisms that would have certainly impelled Dr. McCoy to say, "It's life, Jim, but not as we know it."  Given how infrequently organisms fossilize -- the vast majority die, decay away, and leave no traces, and the vagaries of geological upheaval often destroy the fossil-bearing strata that did form -- you have to wonder what we're missing.  Chances are, for every one species we know about, there are hundreds more we don't.

What even more bizarre life forms might we see if we actually went back there into the far distant past?

I guess we'll have to wait until someone invents a time machine to find out.

****************************************