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.

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

Old as the hills

In northwestern Australia, there's an administrative region called Pilbara.

Even though on a map, it looks kind of long and narrow, it's big.  The area of Pilbara is just shy of that of California and Nevada put together.  (I suspect that I'm like many non-Australians in consistently forgetting just how big Australia is.  It's the sixth largest country in the world, and is almost the same size as the continental United States.  Flying from Sydney to Perth is comparable to flying from Atlanta to Los Angeles.)

Pilbara is also extremely hot and dry, and very sparsely populated, with only a bit over sixty thousand residents total, most of whom live in the western third of the region.  The northeastern quadrant is part of the aptly-named Great Sandy Desert, one of the most inhospitable places on Earth.  There are only a few Indigenous tribes that somehow eke out a living there, most notably the Martu, but by and large it's uninhabited.

[Image licensed under the Creative Commons Brian Voon Yee Yap, aka Yewenyi, at en.wikipedia]

What brings up the topic, though, is that Pilbara is interesting for another reason than its hostile climate.

It is the home to some of the oldest rocks on Earth.

The Pilbara Craton -- a craton is a contiguous piece of continental crust -- is estimated to be around three and a half billion years old.  For reference, the Earth's crust only solidified 4.4 billion years ago.  Since that time, plate tectonics took over, and as I've described before, tectonic processes excel at recycling crust.  At collisional margins such as trenches and convergent zones, usually one piece slides under the other and is melted as it sinks.  Even in places where two thick, cold continental plates run into each other -- examples are the Alps and the Himalayas -- the rocks are deformed, buried, or eroded.

The result is we have very few really old rocks left.  The only ones even on the same time scale as Pilbara are the Barberton Greenstone Belt of South Africa and the Canadian Shield (and even the latter has been heavily metamorphosed since its formation).

This makes Pilbara a great place to research if you're interested in the conditions of the Precambrian Earth -- as long as you can tolerate lots of sand, temperatures that often exceed 36 C, and a fun kind of grass called Triodia that has leaf margins made of silica.

Better known as glass.

Frolicking in a field of Triodia is like running through a meadow made of Exacto knives.

Be that as it may, geologists and paleontologists have begun a thorough study of this fascinating if forbidding chunk of rock.  The most recent reconstructions suggest that both Pilbara and the aforementioned Barberton Greenstone were once part of an equatorial supercontinent called Vaalbara (which preceded the supercontinent most people think of -- Pangaea -- by a good three billion years).  And those might be the only chunks of that enormous piece of land left intact.

There are two other reasons Pilbara is remarkable.

It contains numerous fossilized stromatolites, which are layered sedimentary structures formed by cyanobacteria, thought to be the earliest photosynthetic life forms.  There are still stromatolites forming today -- probably not coincidentally, in shallow bays in Western Australia.

[Image licensed under the Creative Commons photographer Paul Harrison (Reading UK), March 2005, Stromatolites growing in Hamelin Pool Marine Nature Reserve, Shark Bay in Western Australia.]

As such, the Pilbara stromatolite fossils are the oldest certain traces of life on Earth, dating to 3.48 billion years ago.

The other reason is that it's also home to a massive impact crater dating to 3.47 billion years ago.  Shortly after those earliest, tentative life forms were living and thriving in the warm shallow ocean waters, a huge meteorite struck near what is now the town of Marble Bar, forming a crater and shatter cone between 16 and 45 kilometers in diameter (because of erosion, it's hard even for the geologists to determine where its edges lie).  The resulting Miralga Impact Structure blew tremendous amounts of molten debris up into the air, and some of it landed on that chunk of Vaalbara that would eventually end up in South Africa -- only to be recovered by geologists almost three and a half billion years later.

So there's a place in Australia that gives new meaning to the phrase "old as the hills."  Given its remoteness and inhospitable climate, I'm unlikely ever to visit there, but there's something appealing about the idea.  Walking on rock that is an intact remnant of a continent from over three billion years ago is kind of awe-inspiring.  Even if all the other rock is still here somewhere -- melted and reformed and eroded multiple times -- the idea that this chunk of the Earth has somehow lasted that long more or less intact is mighty impressive.

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

Mental models and lying stones

Richard Feynman famously said, "The first principle is that you must not fool yourself -- and you are the easiest person to fool."

This insightful statement isn't meant to impugn anyone's honesty or intelligence, but to highlight that everyone -- and I'm sure Feynman was very much including himself in this assessment -- has biases that prevent them from seeing clearly.  We've already got a model, an internal framework by which we interpret what we experience, and that inevitably constrains our understanding.

As science historian James Burke points out, in his brilliant analysis of the scientific endeavor The Day the Universe Changed, it's a trap that's impossible to get out of.  You have to have some mental model for how you think the world works, or all the sensory input you receive would simply be chaos.  "Without a structure, a theory for what's there," Burke says, "you don't see anything."

And once you've settled on a model, it's nearly impossible to compromise with.  You're automatically going to take some things as givens and ignore others as irrelevant, dismiss some pieces of evidence out of hand and accept others without question.  We're always taking what we experience and comparing it to our own mental frameworks, deciding what is important and what isn't.  When my wife finished her most recent art piece -- a stunning image of a raven's face, set against a crimson background -- and I was on social media later that day and saw another piece of art someone had posted with a raven against red -- I shrugged and laughed and said, "Weird coincidence."

Quoth the Raven, pen/ink/watercolor by Carol Bloomgarden (2025) [Image used with permission]

But that's only because I had already decided that odd synchronicities don't mean anything.  If I had a mental model that considered such chance occurrences as spiritually significant omens, I would have interpreted that very, very differently.

Our mental frameworks are essential, but they can lead us astray as often as they land us on the right answer.  Consider, for example, the strange, sad case of Johann Beringer and the "lying stones."

Johann Bartholomeus Adam Beringer was a professor of medicine at the University of Würzburg in the early eighteenth century.  His training was in anatomy and physiology, but he had a deep interest in paleontology, and had a large collection of fossils he'd found during hikes in his native Germany.  He was also a devout Lutheran and a biblical literalist, so he interpreted all the fossil evidence as consistent with biblical events like the six-day creation, the Noachian flood, and so on.

Unfortunately, he also had a reputation for being arrogant, humorless, and difficult to get along with.  This made him several enemies, including two of his coworkers -- Ignace Roderique, a professor of geography and algebra, and Johann Georg von Eckhart, the university librarian.  So Roderique and von Eckhart hatched a plan to knock Beringer down a peg or two.

They found out where he was planning on doing his next fossil hunt, and planted some fake fossils along the way.

These "lying stones" are crudely carved from limestone.  On some of them, you can still see the chisel marks.

More outlandish still, Roderique and von Eckhart carved the word "God" in Hebrew on the backs of some of them.  Making it look like the artisan had signed His name, so to speak.

One colleague -- who was not in on the prank -- looked at the stones, and said to Beringer, "Um... are you sure?  Those look like chisel marks."  Beringer dismissed his objections, and in fact, turned them into evidence for his explanation.  Beringer wrote, "...the figures... are so exactly fitted to the dimensions of the stones, that one would swear that they are the work of a very meticulous sculptor...[and they] seem to bear unmistakable indications of the sculptor's knife."

They were so perfect, Beringer said, that they could only be the work of God.

So as astonishing as it may seem, Beringer fell for the ruse hook, line, and sinker.  Roderique and von Eckhart, buoyed up by their success, repeated their prank multiple times.  Finally Beringer had enough "fossils" that in 1726, he published a scholarly work called Lithographiae Wirceburgensis (The Writing-Stones of Würzburg).  But shortly after the book's publication -- it's unclear how -- Beringer realized he'd been taken for a ride.

He sued Roderique and von Eckhart for defamation -- and won.  Roderique and von Eckhart were both summarily fired, but it was too late; Beringer was a laughingstock in the scientific community.  He tried to recover all of the copies of his book and destroy them, but finally gave up.  His reputation was reduced to rubble, and he died twelve years later in total obscurity.

It's easy to laugh at Beringer's credulity, but the only reason you're laughing is because if you found such a "fossil," your mental model would immediately make you doubt its veracity.  In his framework -- which included a six-thousand-year-old Earth, a biblical flood, and a God who was perfectly capable of signing his own handiwork -- he didn't even stop to consider it.

The history of science is laden with missteps caused by biased mental models.  In 1790, a report of a fireball over France that strewed meteorites over a large region prompted a scientific paper -- that laughingly dismissed the claim as "impossible."  Pierre Bertholon, editor of the Journal des Sciences Utiles, wrote, "How sad, is it not, to see a whole municipality attempt to certify the truth of folk tales… the philosophical reader will draw his own conclusions regarding this document, which attests to an apparently false fact, a physically impossible phenomenon."  DNA was dismissed as the genetic code for decades, because of the argument that DNA's alphabet only contains four "letters," so the much richer twenty-letter alphabet of proteins (the amino acids) must be the language of the genes.  Even in the twentieth century, geologists didn't bother looking for evidence for continental drift until the 1950s, long after there'd been significant clues that the continents had, in fact, moved, largely because they couldn't imagine a mechanism that could be responsible.

Our mental models work on every level -- all the way down to telling us what questions are worth investigating.

So poor Johann Beringer.  Not to excuse him for being an arrogant prick, but he didn't deserve to be the target of a mean-spirited practical joke, nor does he deserve our derision now.  He was merely operating within his own framework of understanding, same as you and I do.

I wonder what we're missing, simply because we've decided it's irrelevant -- and what we've accepted as axiomatic, and therefore beyond questioning?

Maybe we're not so very far ahead of Beringer ourselves.

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

A light on bias

A woman walks into the kitchen to find her husband on all fours, crawling around peering at the floor.

"What are you doing?" she asks.

"Looking for my contact lens."

"Oh, I'll help."  So the woman gets down on the floor, too, and they spend the next fifteen minutes fruitlessly searching for the missing lens.  Finally, she says, "I just don't see it.  Are you sure you dropped it in here?"

The husband responds, "Oh, no, I dropped it in the living room."

"Then why the hell are you looking for it in the kitchen?" she yells at him.

"Because the lighting is better in here."

While this is an old and much-retold joke, there's an object lesson here for scientists -- which was highlighted by a paper this week out of George Washington University that appeared in Nature Ecology & Evolution.  In it, paleobiologists Andrew Barr and Bernard Wood considered a systematic sampling bias in our study of fossils of ancestral hominid species -- and by extension, every other group of fossils out there.

A large share of what we know of our own early family tree comes from just three sites in Africa, most notably the East African Rift Valley and adjacent regions in Ethiopia, Kenya, and Tanzania.  Clearly that's not the only place early hominids lived; it's just the place that (1) has late Cenozoic-age fossil-bearing strata exposed near the surface, and (2) isn't underneath a city or airport or swamp or rain forest or something.  In fact, the Rift Valley makes up only one percent of Africa's surface area, so searching only there is significantly biasing what we might find.

[Image licensed under the Creative Commons Michal Huniewicz, Great Rift Valley - panoramio, CC BY 3.0]

"Because the evidence of early human evolution comes from a small range of sites, it's important to acknowledge that we don't have a complete picture of what happened across the entire continent," said study co-author Andrew Barr.  "If we can point to the ways in which the fossil record is systematically biased and not a perfect representation of everything, then we can adjust our interpretations by taking this into account."

You can only base your understanding on what evidence you actually have in your hands, of course; besides the areas that might bear fossils but are inaccessible to study for one reason or another, there are parts of Africa where the strata are from a different geological era, or simply don't contain fossils at all (for example, igneous rock).  But you still need to maintain an awareness that what you're seeing is an incomplete picture.

"We must avoid falling into the trap of coming up with what looks like a comprehensive reconstruction of the human story, when we know we don't have all of the relevant evidence," said study co-author Bernard Wood.  "Imagine trying to capture the social and economic complexity of Washington D.C. if you only had access to information from one neighborhood.  It helps if you can get a sense of how much information is missing."

Now, don't misunderstand me (or them); no one is saying what we have to date is likely to be all wrong.  I absolutely hate when some new fossil is discovered, and the headlines say, "New Find Rewrites Everything We Knew" or "The Textbooks Are Wrong Again" or, worst of all, "Scientists Are Forced Back To The Drawing Board."  For one thing, our models are now solid enough that it's unlikely that anything will force a complete undoing of the known science.  I suppose something like that could occur in newer fields like cosmology and quantum physics, but even there we have tons of evidence and excellent predictive models -- so while there might well be additions or revisions, a complete overturning is almost certainly not gonna happen.  

Second, as astrophysicist Neil deGrasse Tyson put it, "As scientists, we're always at the drawing board.  If you're not at the drawing board, you're not doing science."  We are always exploring what he calls "the perimeter of our ignorance," testing and probing into the realms we have yet to explain fully.  What Barr and Wood are doing for the field of human paleobiology is to define that perimeter more clearly -- to identify where our inevitable sampling biases are, so that we can determine what direction to look next.  Not, like our hapless contact-lens-searchers, to continue to look in the same place just because the lighting happens to be better there.

Biases are unavoidable; everyone's got 'em.  The important thing is to be aware of them; they can't bite you on the ass if you keep your eye on them.  In science -- well, in everything, really -- it's good to remember the iconic line from physicist Richard Feynman: "The first principle is that you must not fool yourself; and you are the easiest person to fool."

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

The migrants

Most people know of at least two reasons that organisms can evolve.  The first, of course, is natural selection; members of the same species with inheritable differences can have different survival rates or reproductive rates, leading to overall shifts in the genetic makeup of the population.  The second is catastrophe; a major external event, such as the eruption of the Siberian Traps or the collision of the Chicxulub Meteorite, can completely destabilize what had been a thriving ecosystem, and cause the selective pressures to go off in a completely different direction.  (The two I mentioned were the dominant factors in the Permian-Triassic and Cretaceous-Tertiary extinctions, respectively.)

Less well-known is the role that plate tectonics can play.  When two land masses split apart, the organisms then go their separate ways evolutionarily, especially once the two pieces drift far enough away from each other to experience significantly different climates.  This is what happened to Australia, which most recently was connected to Antarctica; once they diverged, Australia moved northward and Antarctica southward, resulting in just about everything in Antarctica becoming extinct as the temperatures dropped, and leaving Australia with its unique assemblage of species.

The opposite can happen when two continents run into each other.  This occurred when India separated from Africa and collided with Asia, about fifty million years ago, carrying with it species from the southern supercontinent (Gondwana) and introducing them to the northern one (Laurasia).  But an even more striking example occurred when North and South America got close enough that a bit of the seafloor was pushed above water, creating the Isthmus of Panama.

When this happened, on the order of three million years ago, it opened up an easy avenue of two-way migration between the two continents.  This reconnected land masses that had been separated since the breakup of Pangaea in the early Triassic Period, on the order of two hundred million years ago.  That's a long time for species assemblages to evolve in their own directions, and the result was two entirely different floras and faunas.  Those began to move back and forth across the gap as soon as the isthmus formed.

What is curious -- and still largely unexplained -- is why the survival rates of the northward and southward migrants were so drastically different.  Species went both directions; that much is clear from the fossil record.  But just looking at mammals, South America gained (and still has) various species of cats, wolves, foxes, peccaries, deer, skunks, bears, and mice that it gained from North America, to name only a few of the groups that moved in and thrived.  But going the other direction?

There were only three survivors.  The opossum, the armadillo, and the porcupine are the only mammalian South American imports we still have around today.  Others that attempted the northward trek, including ground sloths, glyptodonts, "terror birds," sparassodonts, notungulates, and litopterns, struggled along for a while but eventually became extinct.

[Image is in the Public Domain]

The surmise is that moving from wet forests where it's warm year-round into cooler, drier temperate deciduous forests or grasslands is harder than the reverse, just from the perspective of resources.  Whatever the reason, though, it altered the ecosystems of South America forever, as the North American species proved to be better competitors (and predators), driving entire families of South American mammals extinct.  Some groups continued to thrive and diversify, of course.  Hummingbirds come to mind; they're a distinctly South American group. increasing in diversity as you head south.  Where I live, there's a grand total of one species of hummingbird (the Ruby-throated Hummingbird).

The little country of Ecuador has 132.

The reason all this comes up is the discovery of the complete skeleton of an extinct species of porcupine in Florida, dating to 2.5 million years ago -- and therefore, one of those early migrants northward from its ancestral homeland.  It's related to the modern North American species, but definitely not the same; the extinct species, for example, had a prehensile tail, similar to modern South American species (and which our North American porcupines lack).  It's still unknown, however, if the Florida species is ancestral to our current North American porcupines, or if they're cousins; further study of the skeleton may help to resolve that question.

It's fascinating, though, to see the fingerprints of this mass migration that was to change so radically two different continents.  The process of plate movement continues; Australia will eventually collide with Asia, for example, with similar results, mixing together two sets of species that have been isolated for millions of years.  Change is inevitable in the natural world; it can happen quickly or slowly, and sometimes occurs in ways we're just beginning to understand.

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

Lords of the air

Ever since I was a kid, my favorite group of dinosaurs has been the pterosaurs.

These are one of the six groups of animals that independently evolved flight, or at least significant capacity for gliding (the others are insects, birds, bats, flying squirrels, sugar gliders, and colugos).  They had incredible diversity at their height, during the Jurassic and Cretaceous Periods, from the pint-sized Sordes pilosus (with a sixty-centimeter wingspan) to the almost unimaginably huge Quetzalcoatlus northropi (with a ten-meter wingspan, as big as a light plane).

Most of them were probably clumsy on the ground -- it's hard to imagine how Quetzalcoatlus got off the ground -- but in the air, they were nimble, maneuverable, and fast.  The smaller ones were probably insect-eaters; the larger ones likely fed on fish, although a terrestrial diet of small reptiles and mammals is also possible. 

What brings all this up is the discovery of a new species of pterosaur, one of dozens that have been identified from the Jehol Biota, a stupendous fossil deposit in northeastern China near Huludao.  This fossil bed has produced not only pterosaurs but incredibly well-preserved species of prehistoric birds and other vertebrates -- it's like a tapestry of late Cretaceous animal life.

"Pterosaurs comprise an important and enigmatic group of Mesozoic flying reptiles that first evolved active flight among vertebrates, and have filled all aerial environmental niches for almost 160 million years," said Xiaolin Wang, of the Institute of Vertebrate Paleontology and Paleoanthropology at the Chinese Academy of Sciences, who co-authored the paper describing the discovery.  "Despite being a totally extinct group, they have achieved a wide diversity of forms in a window of time spanning from the Late Triassic to the end of the Cretaceous period.  Notwithstanding being found on every continent, China stands out by furnishing several new specimens that revealed not only different species, but also entire new clades."

This includes the newly-discovered Meilifeilong youhao, belonging to the family Chaoyangopteridae, which is represented at the site by two other species that have been found nowhere else.

Meilifeilong looked like something out of a nightmare, if the artist's reconstruction is accurate (and probably even if it isn't):

[Image courtesy of artist Maurilio Oliveira]

The name means "beautiful flying dragon," which I doubt is what I'd say if I saw one, but what I'd say is borderline unprintable so we'll leave it at that.

It's astonishing to think of how long these creatures ruled the skies -- from the late Triassic until the very end of the Cretaceous, a time span of around 160 million years.  Had change not come in the form of the Chicxulub Meteorite collision, they might well still be here, soaring on thermals above our forests and lakes and oceans, the undisputed lords of the air.  And even if we now know them only from fossils, they still can't help but impress.

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

Birds down under

I've been an avid birdwatcher for many years, and have been fortunate enough to travel to some amazingly cool places in search of avifauna.  Besides exploring my own country, I've been to Canada (several times), Belize (twice), Ecuador (twice), Iceland (twice), England (twice), Scotland, Sweden, Finland, Denmark, Russia, Spain, Portugal, and Malaysia.

One place I've never been, though, is Australia, which is a shame because it's got some incredible animals.  And despite a pretty well-deserved reputation for having far more than their fair share of wildlife that's actively trying to kill you, most tourists come back from trips to Australia alive and with all their limbs still attached in the right places.

The main reason for Australia's unique ecosystems is that it's been isolated for a very long time.  During the breakup of Pangaea, the northern part (Laurasia, made up of what is now Europe, North America, and most of Asia) separated from the southern part (Gondwanaland, made up of what is now Africa, South America, Antarctica, Australia, and India), something on the order of 180 million years ago.  The other pieces gradually pulled apart as rifting occured, but Australia remained attached to Antarctica until around thirty million years ago.  At that point, the whole thing had a fairly temperate climate, but when the Tasman Gateway opened up during the Oligocene Period, it allowed the formation of the Antarctic Circumpolar Current, isolating and cooling Antarctica and resulting in the extinction of nearly all of its native species.  Australia, now separate, began to drift northward, gradually warming as it went, and carrying with it a completely unique suite of animals and plants.

The reason all this comes up is a sharp-eyed Australian loyal reader of Skeptophilia, who sent me a link to a news story about a recent discovery by a dedicated amateur fossil hunter and birdwatcher, Melissa Lowery, who was looking for fossils on the Bass Coast of Victoria and stumbled upon something extraordinary -- some 125 million year old bird footprints.

Lowery's bird footprints [Image by photographer Rob French, Museums Victoria]

At that point, the separation of Australia and Antarctica was some 65 million years in the future, the sauropod dinosaurs were still the dominant animal group, and Victoria itself was somewhere near the South Pole.  Lowery's find led to a full-scale scientific investigation of the area, and uncovered a great many more bird tracks, including some with ten-centimeter-long toes.  Also in the area were the footprints of dozens of kinds of non-avian dinosaurs.

"Most of the bird tracks and body fossils dating back to the Early Cretaceous are from the Northern Hemisphere, particularly from Asia," said Anthony Martin, of Emory University, who led the study.  "Our discovery shows that there were many birds, and a variety of them, near the South Pole about 125 million years ago."

Of course, being a birdwatcher, I'm intensely curious as to what these birds looked like, but there's only so much you can tell from a footprint, or even fossilized bones.  It's simultaneously intriguing and frustrating to think about the fact that these animals -- and all the other animals and plants that lived alongside them -- had every bit of the diversity, all the curious and wonderful and beautiful adaptations and behaviors, that our modern wildlife does.

Imagine what it would be like to transport yourself back to Australia in the early Cretaceous, and witness all of that with your own eyes and ears.  (With, of course, a guarantee of coming back alive and with all your limbs still attached in the right places.  Back then, Australia was a rougher place than it is now.)

So thanks to the reader who sent me the link -- it's renewed my desire to visit Australia.  If I can't see the amazing birds they had 125 million years ago, at least I can have a look through my binoculars at some of the ones they have today.

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

All in the family

Archaeologists and paleontologists are up against the same problem; bones and other fossils only get you so far.

There are cases where fossil evidence can give you some hints about behavior -- patterns of tracks, for example, or the rare case where the positions of the fossils themselves give you a picture of what was going on, like the recent discovery of an opossum-sized mammal, Repenomamus, attacking a much larger dinosaur, Psittacosaurus.  The pair of fossil skeletons were preserved, locked in a battle to the death -- the death of both, as it turned out, because they were both engulfed mid-fight in a mudslide.

But such lucky finds are rare, and inferences of behavior from fossils are usually sketchy at best.  This is why the study of a group of Neolithic human skeletons found near Gurgy-les-Noisats, France, 150 kilometers southeast of Paris, was so extraordinary.

The level of DNA analysis now possible allowed the analysis of the genomes of 94 of the 128 individuals buried at the site, to the level that the researchers not only were able to construct a seven-generation family tree for them, but make a guess as to what each individual looked like.

The analysis found that the bodies were buried in family groups -- the more closely two people were related, the closer together they were buried -- and that women who were not descendants of the original couple were mostly completely unrelated, suggesting they'd come into the family from another community.  Just about all the males at the burial site, on the other hand, were related, leading the researchers to conclude that men in this community tended to stay put, and at least some women did not.

Another curious thing was that the study detected no half-sibling relationships.  All of the sibling groups were from the same mother and father.  In this family group, at least, monogamous relationships were the norm.

Of course, there's a lot we still don't know; while this is a stunning accomplishment, it still leaves a great many questions unanswered.  For example, were the "outsider" women brought in because of a custom of outbreeding, or by conquest/capture?  What were the religious practices and beliefs that led these people to bury family members near each other?  Was the monogamy shown in this family universal in this culture, or was this grouping an exception for some reason?

It's an intriguing piece of research.  "This type of work really breathes new life into our understanding of ancient peoples," said Kendra Sirak, an ancient-DNA specialist at Harvard Medical School in Boston, Massachusetts, who was not involved in the study.  "I'm especially curious about the man at the root of the family tree.  I would love to know what made this person so important."

And given that a significant percentage of my ancestry comes from central and western France, I have to wonder if anyone in this family tree is a direct ancestor of mine.  There's no way to find out, of course, but the thought did cross my mind.  It's kind of eerie to think when I look at those facial reconstructions, one of those faces looking back at me might be my great-great (etc.) grandparent.

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

Mysterious network

Back in 1850, Italian paleontologist Giuseppe Meneghini found a peculiar fossil in the early Cambrian rocks of Sardinia.  It had a very distinctive appearance -- a set of what appeared to be tubes arranged in a network of perfect hexagons, regular as a honeycomb -- and Meneghini named it Paleodictyon, which means "early net."

The problem was, no one could quite figure out what it was.  There was speculation that it was the skeleton of a sea sponge, that it was some kind of filter-feeding trap laid down by peculiar giant single-celled organisms called xenophyophores, or that it was the tunnel network of some burrowing creature like a tube worm.  None of these hypotheses had much in the way of direct evidence in their favor, and all had significant arguments against.

Then Paleodictyon was found in Devonian rocks.  Then Carboniferous rocks.  Then Triassic rocks.  Always in sedimentary strata associated with deep marine environments -- and never with the slightest evidence of who might have created it.

So it went into the catalogues as a "trace fossil" -- a remnant of some unidentified organism.  This didn't mean the paleontologists were giving up, however; the origins of other trace fossils have been solved, most notably the incredibly common conodonts, small, spiky fossils found in oceanic sedimentary rocks up through the Triassic Period, and which were finally determined to be the teeth of primitive fish a little like today's lampreys.

But Paleodictyon proved more difficult, despite the fact that pretty much everywhere -- and everywhen -- you look in deep-ocean sedimentary rocks, you find it.  Here's a specimen from the Miocene Epoch:

[Image licensed under the Creative Commons Hectonichus, Palaeodictyon, CC BY-SA 4.0]

Then a survey of the seafloor near volcanic vents on the Mid-Atlantic Ridge -- in very recent sediments -- came across a series of regularly-spaced holes.  Curious, the oceanographers studying the area devised what amounted to a giant water gun to blow away the sediment and see what was beneath the mud, and hopefully, what might be creating the holes.

And underneath...

... was Paleodictyon.

Here, though, there was an additional clue; at each of the nodes in the network was a small upward-facing tube.  It was the openings of the tubes, poking above the sediment, that had attracted the attention of the scientists.  Naturally, they took samples (not to mention a closer look) to see what was in there.

Nothing was.

Detailed DNA analysis was performed on the samples, looking for anything that might give a clue as to what had made the network.  All three of the most commonly-held hypotheses -- sponges, xenophyophores, and tube worms -- came up negative.  There were traces of DNA present, but all of it seemed to be from bacteria and protists living in the tubes, not the creature that made the tubes.

To cut to the punch line: we still have no idea what Paleodictyon is, or who made it.

But whatever it is has been around for a very, very long time -- at least 540 million years -- substantially unchanged.  It's true that there are lots of things in nature exhibiting hexagonal tiling; it's the simplest way to tile a two-dimensional surface, and is seen in everything from quartz crystals to the symmetrical cooling cracks in the Giant's Causeway in Ireland.  But the fact that this trace fossil is only found in deep-sea sedimentary rocks is certainly suggestive that its origin is biological.

In the end, we're left with a mystery, and are honestly no closer to figuring Paleodictyon out now than we were when Giuseppe Meneghini first discovered it over 170 years ago.  So we'll continue looking -- and trying to determine the origin of one of the most persistent and widespread fossils ever found.

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

A new view of the "eye lizard"

I am forever astonished at the level of detail we can infer from fossils that are hundreds of millions of years old.

The most recent example of this came from analysis of a fossil of Stenopterygius, an ichthyosaur that lived during the Jurassic Period (this particular fossil has been dated to about 180 million years ago).  We usually think of fossils as preserving bones and teeth, and occasionally impressions of scales or skin or feathers -- but this one was so finely preserved that researchers have been able to make some shrewd inferences about color, metabolism, and the structure of soft tissues.

Artist's conception of Stenopterygius [Image licensed under the Creative Commons Nobu Tamura (http://spinops.blogspot.com), Stenopterygius BW, CC BY-SA 3.0]

We've known for a long time that ichthyosaurs are bizarre animals. They were streamlined predators that look remarkably like dolphins, although they are only distantly related (making the two groups a great example of convergent evolution).  A number of them had an even stranger feature, which is the largest eye-diameter-to-body-size ratio of any animal known -- the well-named Ophthalmosaurus (Greek for "eye lizard") was six meters long and had eyes the size of basketballs.

Stenopterygius was a bit smaller, with an average adult size of four meters.  But up until recently, all we've been able to do is speculate on what it might have looked like, and how it behaved.  A discovery in Germany, described in a paper in Nature called "Soft-Tissue Evidence for Homeothermy and Crypsis in a Jurassic Ichthyosaur" and authored by no fewer than 23 scientists, has given us incredibly detailed information on these oddball dinosaurs.

The authors write:

Ichthyosaurs are extinct marine reptiles that display a notable external similarity to modern toothed whales.  Here we show that this resemblance is more than skin deep.  We apply a multidisciplinary experimental approach to characterize the cellular and molecular composition of integumental tissues in an exceptionally preserved specimen of the Early Jurassic ichthyosaur Stenopterygius.  Our analyses recovered still-flexible remnants of the original scaleless skin, which comprises morphologically distinct epidermal and dermal layers.  These are underlain by insulating blubber that would have augmented streamlining, buoyancy and homeothermy.  Additionally, we identify endogenous proteinaceous and lipid constituents, together with keratinocytes and branched melanophores that contain eumelanin pigment.  Distributional variation of melanophores across the body suggests countershading, possibly enhanced by physiological adjustments of colour to enable photoprotection, concealment and/or thermoregulation.  Convergence of ichthyosaurs with extant marine amniotes thus extends to the ultrastructural and molecular levels, reflecting the omnipresent constraints of their shared adaptation to pelagic life.

So from a 180-million-year-old fossil, we now know that Stenopterygius (1) was a homeotherm (colloquially called "warm-blooded"), (2) had a blubber layer much like modern dolphins and whales, and (3) were countershaded -- dark on top and light underneath, to aid camouflage -- similar to dozens of species of modern fish.

This level of preservation is extremely unusual.  "Both the contour of the body and the remains of internal organs are clearly visible," said paleontologist Johan Lindgren of the University of Lund, who co-authored the paper.  "Surprisingly, the fossil is so well preserved that it is possible to observe individual cell layers inside the skin."

"This is the first direct chemical evidence of warm blood in an ichthyosaur, because a subcutaneous fat layer is a characteristic of warm-blooded animals," said Mary Schweitzer of North Carolina State University, also a co-author.  "Ichthyosaurs are interesting because they have many features in common with dolphins, but they are not related at all to these mammals that inhabit the sea.  But the enigma does not stop there...  They have many characteristics in common with living marine reptiles, such as sea turtles; but we know from the fossil record that they gave live birth to their young...  This study reveals some of those biological mysteries."

Which is pretty astonishing.  I've always had a fascination for the prehistoric world, and have spent more time than I like to admit wondering what it might have been like to live in the Jurassic world. This research gives us one more piece of information -- about a fierce prehistoric predator that shared some amazing similarities to creatures that still swim in our oceans.

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