Wednesday, July 31, 2019

An "Aberrant" Path for Sand Dollars

Until now, I would have said, without qualification, that the shells or tests of sand dollars are things of subtle beauty.  In a moment of weakness, I might even be tempted to ascribe some aesthetic purpose to the artistry of the five-pronged stars etched delicately on the obverse of the tests, or to their wonderfully symmetrical disk-like shape.  We are, indeed, attracted to the symmetrical.

But certain fossils recently added to my collection challenge my overall assessment of the charm and beauty of sand dollars.

The echinoderm order Clypeasteroida includes the sand dollar whose rigid test is made up of interlocking plates.  (Of interest, this order’s name comes from the Latin clypeus = shield or medallion, and aster = star.)  The sand dollar, whose calcium carbonate plates readily fossilize, is a relatively recent arrival on the world scene.  The University of California Museum of Paleontology notes that echinoids (which include sea urchins, among other taxa) first appear in the late Ordovician (458 to 444 million years ago), but that the sand dollar shows up only in the Paleocene (66 to 56 million years ago). (Introduction of the Echinoidea, UMCP.)

At a recent gem and mineral show, I came upon a small container sporting the label: “fossil sand dollars.”  At $1 apiece, these small fossils were hard to resist, so I purchased a few.  As seen in the example below, these fossils are quite striking with a shape certainly unlike that of any sand dollar I’ve seen.  (Clearly, my specimens had suffered some breakage.)  Unusual they are, beautiful they are not.


These particular specimens belong to the Rotulidae family whose members exhibit digit-like projections of the test (I refer to them as “digits” below, though they clearly are not fingers).  The Rotulidae first enter the sand dollar family during the Miocene (23 to 5 million years ago).  I have concluded these specimens belong to the genus Heliophora which, according to The Echinoid Directory of the Natural History Museum in London, includes a single species, H. orbicularis.  I am particularly persuaded in my identification by those robust protrusions of the test.  As the NHM puts it for this species, “Posterior of test strongly digitate.”  The NHM also notes that this taxon is first found in the fossil record in the late Pliocene (5 to 3 million years ago) and that it is an extant species found on the west coast of Africa.  So, my specific fossils are, in the scheme of things, remnants of very recent additions to the planet’s fauna.

On my H. orbicularis and on Rotulidae, in general, the digits appear at the posterior of the test.  The dorsal side of the test is somewhat raised (meaning the test is not flat) and shows the star etching, while the ventral or oral side is flat and has two holes in it.  The hole in the center of the oral side is the peristome opening which serves the animal’s mouth, while the second hole, nearer the digits, is the periproct opening which serves the anus.  Though the periproct’s location is variable among sand dollar species, in many it is in the rim of the test.  That’s not the case here, based on my understanding of the Heliophora.

The test’s digits need some explaining.  From my reading to date, I’m not sure there’s a scientific consensus about them.  Two aspects of how sand dollars live (lived) are relevant here.  First, sand dollars are filter feeders, with features (including many spines covering the test; these spines are not preserved in fossils) that act to channel microorganisms such as diatoms into its mouth.  The movement of food occurs not just on the oral side of the test, but also on the dorsal side.  The raised dorsal side with grooves that run down it help to channel food toward the oral side of the organism.

Second, sand dollars live on or in sedimentary beds in moving water.  This introduces consideration of how the shape of the test responds to the hydrodynamic forces of moving water.

I assume that, evolutionarily, there has been an interplay between the demands of securing food and those of "sedimentary" living and coping with moving water.  For the Rotulidae with their test digits, paleontologist Adolf Seilacher’s discussion in Morphodynamics (2015) is relevant.  In this volume, he posited that “lunular notches” in sand dollars – the perforations through the test found in several types of sand dollars; this term includes the digits of the Rotulidae – arose for a constellation of different reasons.  These include aid for digging by allowing sand to move more easily from the oral side to the dorsal side; stability by reducing the lift effect of water moving past the test; and feeding by facilitating the movement of food from the dorsal to the oral side.

In an earlier article, Seilacher noted a possible explanation for the concentration of lunular notches or digits in the posterior edge of the Rotulidae.  Members of this family may increase the effectiveness of these digits for filter feeding by positioning themselves in an upright position in the sediment with the digits exposed to the water currents.  (Constructional Morphology of Sand Dollars, Paleobiology, Volume 5, Number 3, 1979.)

I am struck by how the Rotulidae, those sand dollars with digits, break the connection with the common name for this kind of organism, a name which refers to the test’s similarity in shape to a silver or gold dollar coin.  If the only “sand dollars” we knew were Rotulidae, I doubt they’d have that common name.  Indeed, the H. orbicularis in particular hardly looks like a coin and bears little resemblance to the common names given this group of organisms by other cultures and in other languages.  For instance, H. orbicularis certainly doesn’t bring to mind a cookie, a frequent reference point elsewhere in the world (e.g., sea cookie in New Zealand, galleta de mar in Spanish).  Nor does it evoke a flower (e.g., sea pansy in South Africa).  Yet, the French, it would seem, might have no problem with the unusual shapes of the Rotulidae because, in French, a sand dollar is called (I think) oursin plat, meaning flat sea urchin, a common name which sacrifices metaphor for broadly accurate, though boring, descriptors.

In the end, I fear the H. orbicularis and the other Rotulidae leave me cold.  Their digits make them interesting but also render them much less attractive.  Perhaps the most interesting aspect of the digits is they appear in the Rotulidae which enter the fossil record somewhat later than sand dollars in general and are limited to just three genera.  This, it would appear, is a new evolutionary path for sand dollars, but, at least so far, one that remains very much a minor, restricted “experiment” among the Clypeasteroida.  May it remain so.

Friday, June 14, 2019

David H. Koch Hall of Fossils - Deep Time
~ Come for the Dinosaurs, Absorb the Lessons


On June 8, 2019, after five years of work, $125 million, and, I’m certain, myriad headaches, the Smithsonian’s National Museum of Natural History opened its completely renovated fossil hall, the David H. Koch Hall of Fossils – Deep Time.  This post describes primarily what caught my eye on my first visit to this remarkable hall.  Given that it houses over 700 fossils and presents some 75,000 words on its signage, I clearly missed a great deal and return visits are in order.  At the outset, I would note that, for all intents and purposes, this is a new hall and that’s how I’ll refer to it below.

The prior incarnation of a Smithsonian fossil hall enveloped visitors in darkness that seemed to emanate from the crowded displays, the gloomy worn carpeting, the faint-hearted lighting, and even the outdated science that was referenced in the skeleton poses and the signage.  No natural light, no windows.

This newest hall greets the visitor with grace, space, and, above all (quite literally) light.  (Dear visitors, please embrace these attributes wholeheartedly.)  The picture below – a panorama shot of a  Diplodocus skeleton stretching nearly 90 feet from the tiny tip of its tail (curving off to the left) to its undersized head at the end of a wonderfully long neck – shows some of the new hall in much of its airy glory.


That’s where I have to begin, with the dinosaurs, because that’s where most who come to this hall will naturally first gravitate.  And the child in most of us will find irresistible the tableau in the center of the hall’s long room where a Tyrannosaurus rex and a Triceratops horridus portray a scene that may well mirror many that actually occurred some 66 million or more years ago.


Of note, the skulls of both skeletons shown above are casts because the actual skeletons (housed elsewhere in the museum) would have weighed too much to be posed in such close proximity with each other.  This is described in an article and illustrated map of the new hall that appeared in the Washington Post (Bonnie Berkowitz and Aaron Steckelberg, A New Old Home for the Nation’s Dinosaurs, June 2, 2019).  This is a highly informative piece on the new hall.  Well worth exploring.

Labels throughout the hall clearly identify what’s a cast and what’s not.  Material that fills in incomplete specimens are a different shade allowing the sharp eyed to distinguish real fossil from manufactured material.  I have to say that some of these differences in shading are too subtle for my eyes.

Back to the tableau of a teenage (it is assumed) T. rex beginning to munch on a T. horridus.  It fails to answer a question debated among paleontologists.  Was T. rex a predator or a scavenger?  The display is agnostic on this, though, in all likelihood, T. rex went both ways.  (Hear National Museum of Natural History’s director, Kirk Johnson, discuss this aspect of the T. rex on the NPR show 1A with Joshua Johnson (episode aired on June 11, 2019).  In this episode, Kirk Johnson waxes enthusiastic about many features of the new hall.)

Among other dinosaurs found here is this Camarasaurus skeleton positioned near the Diplodocus.


The Camarasaurus picture highlights one distinguishing feature of the new hall:  there’s no effort to fill spaces with recreated, lifelike foliage from the diverse time periods.  Rather, the vegetation representations are minimalist.  The hall does allow visitors to see the ecosystems of such worlds, depicting them in little “diorama” stands scattered throughout the hall.


Here’s a close-up of the diorama of a grassland scene some 19 million years ago, reconstructed on the basis of fossils found in the Harrison Formation, Nebraska.


How is this new hall organized?  The designers want visitors to enter from the museum's rotunda and, so they are to begin with recent history, not deep time.  Visitors are greeted by bronze statues of a human family being stalked by a saber-toothed tiger.  The former recognizable, the latter striking but still mostly familiar.  Walking from the entrance down the length of the main long gallery, visitors at first move somewhat slowly back in time, only hundreds of thousands of years in those initial steps, but then rather quickly millions of years go by until, angling off to the left from this first gallery, visitors come to the initial emergence of life on the planet.  This organization forces a rethinking of time as, in the process of walking through the exhibits, the familiar or somewhat familiar is replaced by the faintly familiar which in turn is replaced by the truly different, alien even.  Deep time, for sure.

There is a spiral motif that marks some of the hall’s signage which not only represents how Earth’s history reaches far, very far back in time, but also speaks to the connections among all things.  The past is, indeed, prologue.  No “special creations” here.  One such spiral sits high over the entrance to the hall accompanied by a quotation from Charles Darwin’s On The Origin of Species.  That quotation marks one of the recurrent themes that is traced throughout the hall’s displays – the history of life on this planet cannot be understood without a recognition of the fundamental role that evolution played and is still playing.


No shying away in this hall from evolution.  Indeed, a statue of a young Charles Darwin sits near the center of the hall with a Galapagos finch (?) perched on his shoulder.


This message about evolution’s central role in life on Earth is unavoidable as one’s path in the hall moves from the present into deep time.  Among the many exhibits and signage positing and elaborating on this theme, is a large sign featuring Smithsonian paleobiologist Gene Hunt.  An extensive set of quotations from him begins, “Species evolve by natural selection to meet the challenges of the world.”  Accompanying this is a fascinating (at least it was to me) display of two arrays of specimens of the bivalve mollusc Spondylus, commonly, though erroneously, referred to as “spiny oysters.”  The array on the left shows eight Spondylus specimens from a single species that lived in Florida some three million years ago.  Back then specimens of this species exhibited some, relatively marginal variations.  But, as the display notes, “Over time, variations like these can become the building blocks of new species.”  The eight Spondylus specimens on the right are from different species of this genus living in oceans today.


That evolution has had to contend with several major extinction events in deep time is unquestionably also a central element in the hall’s lesson on evolution.  One of the most striking ways this is conveyed comes when one gets back to the end-Permian extinction.  Here is a close-up of the key part of a graphic showing the wealth of diversity among plants and animals that marked the Permian in general (at the left of the event), but which was abruptly curtailed:
Massive volcanic eruptions 252 million years ago released gases that dramatically altered the climate, causing extinctions that rippled through food webs and devastated animal communities.

Emerging from that extinction event, life on Earth was diminished with a tremendous loss of diversity.

Embedded in the text of that sign is another fundamental message of the new hall that is repeated many, many times – Earth’s climate changed frequently in deep time and such changes had fundamental consequences for life on this planet.  Yet, as central as this message is to an understanding of how life as we now know it came to be (yes, the living are all connected in this great spiral of time), what impressed me perhaps most forcefully about the new hall was the way the content of that message is framed for visitors when they begin their journey.  Here is one way that message is delivered early in that journey.


"And humans are the cause."

And another:



One early kiosk loops a video discussing what can be learned about climate change over the past several hundred thousand years by studying ice cores.


Toward the very end of the short video, after it shows the strong correlation discovered between changes in the concentration of carbon dioxide and changes in the Earth’s temperature (more carbon dioxide, higher temperatures), the voice-over narrator says this:
Today CO2 is skyrocketing higher than any time in the past 800,000 years as we burn fossil fuels and cut down forests.  This time, humans are the reason Earth’s temperatures are rising.
Human’s lethal touch on life on Earth is felt in other ways as this display asserts.


To me, that’s the most amazing aspect of the new fossil hall – its robust assertion, clearly backed by science, that today’s climate change has human activities as its root cause and that it poses an existential threat.

Why is this amazing?  Because it shows that a bright line was drawn between David H. Koch, the core financial donor to the remaking of the fossil hall, and the content of the new hall.  David and his brother, Charles, head a multinational corporate empire founded by their father which, among other things, owns oil refineries and pipelines.  Writer Jane Mayer profiled the Koch brothers in a fascinating and detailed article in 2010 that ran in The New Yorker (Covert Operations, August 30, 2010).  In it, Mayer wrote:
The Kochs are longtime libertarians who believe in drastically lower personal and corporate taxes, minimal social services for the needy, and much less oversight of industry—especially environmental regulation.
Their attitude toward climate change?  As quoted by Mayer, a 2010 Koch Industries newsletter asserted that "fluctuations in the earth’s climate predate humanity . . . .  Since we can’t control Mother Nature, let’s figure out how to get along with her changes.”

That's why I think it quite striking that the new hall teaches its lesson about today’s climate change so strongly (stridently even), despite the beliefs of that donor.

I fear I've given the richness of the new hall short shrift because all I've highlighted has been the dinosaurs and the interwoven messages that I hope all visitors absorb.  There are hundreds of fossils on display, most much smaller than those awesome Mesozoic creatures.  I will close with a picture of what is one of the jewels of this new hall (I agree with director Kirk Johnson on this).  The piece of matrix pictured below comes from the Green River Formation (Wyoming) and features the 52-million-year-old, intact, incredibly beautiful skeleton of a tiny early horse, Protorohippus venticolum.  This is the most complete skeleton of this early horse species found to date.  The preserved detail is breath taking.  Given the fossil impressions of several fish in this matrix, evidently this horse died at a lake’s edge, floated out on the water for some distance, and then sank to the bottom.



Friday, May 31, 2019

That Little Rock Tells A Huge Story

This post’s title quotes Caltech entomologist Joseph Parker’s description of the tiny bit of amber, 5.5 mm long and 3.5 mm wide, pictured below.


(Images in this post were clipped from a Caltech video titled Time Capsule from the Cretaceous, available on the Caltech News website.  They are reproduced here with the generous permission of Caltech.)

What flows from this speck of amber is truly an amazing story, one built from a cascading series of logical and highly probable hypotheses and conclusions.  To my mind, it’s a brilliant example of how scientists can identify and make sense of the broader contextual implications of a discovery.  No finding truly exists in a vacuum.

We begin with this Burmese amber that came from a mine in Kachin state, Myanmar.  It is dated at approximately 99 million years old (Early Cretaceous period).  In and of itself, nothing surprising here.  There is an ongoing trade in Burmese amber from this area and the general consensus has been that all such amber is of that age.  Where things become interesting, indeed, the heart of the story, is that this amber contains a minute insect fossil, a beetle, and not just any beetle.

Before I get ahead of myself, I should stress that I have no special knowledge of fossil beetles or Burmese amber.  My entree to all of this was an interesting Caltech News piece titled These Beetles Have Successfully Freeloaded for 100 Million Years, written by Lori Dajose.  From that article, I turned to the peer-reviewed research paper behind it that was written by entomologist Yu-Lingzi Zhou and coauthors, including Joseph Parker.  Titled A Mesozoic Clown Beetle Myrmecophile (Coleoptera:  Histeridae), the paper was recently published in  eLife (April 16, 2019).

Zhou et al. identified the beetle discovered in this amber as a new, extinct species belonging to the Histeridae family of beetles and, more specifically and perhaps more importantly, to the Haeteriinae subfamily.  Histerids are commonly known as clown beetles of which there are over 4,600 extant species described.  The new species has been named Promyrmister kistneri.  Zhou et al marshal a long list of detailed morphological characteristics of this specimen that have direct counterparts in modern haeteriine beetles leading them to place this beetle in this family and subfamily with a great deal of certainty.

So, at this stage, what have we learned?  Some 99 million years ago a species of histerid lived here.  But this is a conclusion with profound ramifications because today’s histerids, particularly including the Haeteriinae subfamily of clown beetles, are myrmecophiles, that is, they live with ants.  The term myrmecophile is derived the Greek root words myrmeco, meaning “ant,” and phil meaning “love” – myrmecophiles are “ant lovers.”

Haeteriine clown beetles are one of two histerid subfamilies that have predominantly evolved the physical characteristics and behaviors necessary to spend much of their lives in ant nests; indeed some extant haeteriine beetles may live out their entire lifecycle in or near an ant colony.  Most are neotropical and live in army ant colonies in ways that differ by genus.  As Parker notes, some are “highly integrated guests” being fed by ant workers.  “The beetles have been observed feeding on the ants’ brood and harvested food, and to run with or phoretically attach to workers during emigrations.”  (A phoretical attachment is one between two different species in which one carries the other.)  This discussion of the haeteriine beetles and myrmecophily draws from Joseph Parker’s fascinating research paper Myrmecophily in Beetles (Coleoptera):  Evolutionary Patterns and Biological Mechanisms (Myrmecological News, February 2016).

Why would these beetles or other myrmecophiles (myrmecophily is an attribute of some 10,000 arthropod species) make the evolutionary transition from free-living to living in ant colonies?  Such colonies offer at least two strong attractions:  they offer an environment rich in nutritional resources and, if their robust lines of defense can be successfully penetrated, they offer protection to the interloper.  But this intimate relationship comes with a potential major cost:  the guest species’ fates are tied to the fates of the ant species they join.  (As will be discussed, histerid beetle species may be particularly able to circumvent this negative consequence.)

Pictured below is a modern clown beetle among its ant hosts.


And from these conclusions about the identity of this specimen, these scientists have taken the logical next step to posit that this new species also lived in an ant colony.  If that is so (and it most likely is), then this clown beetle was probably a symbiont in an ant nest composed of early (stem group) ants which are the kind found so far in Burmese amber.  (Zhou et al. acknowledge that the absence of crown group ants in Burmese amber does not prove that they were not there at this time in the Cretaceous and hosting this clown beetle species.)

The ramifications of the deduction that this beetle species had evolved for life in an ant colony are quite striking.  Entomologists believe that some 99 million years ago, ant social life was first taking shape, which means that, almost from the outset of the evolution of ant social life, clown beetles had evolved to integrate themselves into these urcolonies.  Parker has posited that the Histeridae have “a family-wide predisposition to evolving myrmecophily.”  “Perhaps the majority of histerid genera may be capable to making the evolutionary shift to this lifestyle quite readily, should ecological opportunity permit.”  (Myrmecophily in Beetles.)  That that far back, in the Early Cretaceous, a histerid had already made this evolutionary shift is certainly persuasive evidence of this predisposition.  Further convincing evidence of this predilection comes from the conclusion that this new species of clown beetle lived among early stem ants which have long since gone extinction, yet haeteriines continue to live among the modern counterparts of those early ants.  As Zhou et al. write
Whether haeteriines evolved in stem- or crown-group ant colonies, their original hosts are presumably long-extinct.  The present-day host associations of haeteriines imply that these myrmecophiles have host-switched between many modern ant lineages. . . .  We suggest that it is this capacity for host switching that may explain the great longevity of the clown beetle-ant symbiosis.  Through host switching, the clade as a whole has circumvented potential coextinction with host ant lineages that disappeared from the Cretaceous to the present.  (p. 8)
Indeed, as Parker put it, “That little rock tells a huge story.”

Additional Thoughts

I would note that any Burmese amber with resident fossils may have a dark side, one that is told by science writer Joshua Sokol in Troubled Treasure:  Fossils in Burmese Amber Offer an Exquisite View of Dinosaur Times – and an Ethical Minefield (Science, May 4, 2019).  I certainly am not suggesting that the disturbing aspects of Burmese amber described below necessarily apply to the piece considered in this post, only that Burmese amber in general raises such concerns.

Proceeds from the Burmese amber market are fueling an ongoing war between the Myanmar military and insurgents in the country’s Kachin state.  The recent spate of fossil discoveries from this amber apparently are mostly products of this amber market.  Further, as Sokol describes, because these fossils come to light through a commercial transaction, many important fossils are left in private hands, a situation that professional paleontologists find at least troubling.  That these amber mines are in a conflict area means that the detailed work needed to properly date these pieces of amber (and their fossils) is decidedly difficult to undertake.  The age of the Burmese, set at 99 million years old in a 2012 study, is now under some question with suggestions that it comes from a period of a few million years around that age.  Finally, the amber with fossils makes its way out of Myanmar despite the country’s legal prohibition against exporting fossils because amber is treated as an exportable gemstone.  Paleoentomologist Michael Engel has bemoaned this situation, stating, “It’s like Myanmar’s cultural heritage, paleontological heritage, is just being wholesale ripped out of the ground and distributed around the world.”  (As quoted by Sokol, p. 729.)

Where to draw the line on Burmese amber and paleontology may be clear to some, but not to me.  This amber has provided science with many, truly marvelous finds in recent years, yet it clearly comes at a cost.

Tuesday, April 30, 2019

Fossils Magazine ~ Catching Lightning in a Bottle

In early 1976, ads appeared in a host of science-related journals, including the American Zoologist, The American Biology Teacher, and Science News, announcing a new quarterly publication, Fossils Magazine.  A year’s subscription was $12.  Given the readership of the journals in which these ads ran, one can assume that the editor of Fossils Magazine was casting his net broadly, seeking to attract subscribers from a broad spectrum of the scientific community, as well as from those members of the wider public with an interest in science.

The ads described the forthcoming Fossils Magazine as “the world’s first and only magazine for everybody who wants to know more about the 3 ½-billion-year history of life on Earth.”  Best of all, the publication would be “scientific, yet highly readable,” featuring cutting-edge but accessible articles by science professionals.  The ads touted the full color drawings, photographs, and maps that would grace the new magazine.

Some versions of the ads made it clear that the prospective audience for the new magazine would include amateur paleontologists with an interest in collecting fossils.  The magazine, it was stated, would identify precisely where fossils could be collected, and such information would be complemented with guidance from professional paleontologists.

The ads certainly set a high bar (e.g., “scientific, yet highly readable) for the new journal.  I first learned about Fossils Magazine a couple of weeks ago while pursuing one of my interests – postage stamps on which representations of fossils appear.  That initial issue of the magazine included an article titled Fossils On Stamps.  Once I acquired a copy of that first issue and then found those early ads, I decided to write a blog post considering the question:  Did the magazine live up to its advertising “hype?”

Volume One, Issue One of Fossils Magazine appeared in the Spring of 1976, carrying a May, 1976 publication date.  On its first page, editor John Bonnett Wexo welcomed readers, writing:
[T]his magazine is about fossils as objects – where they come from, how they were formed, what they look like, and what they are called, and how you can find them and collect them.
Importantly, he sought to guide those readers who might hunt fossils in the locations profiled in each issue to collect responsibly and to respect private property.  Further, he took great pains in this introduction to stress what I take to be his paramount goal – placing fossils into their scientific context.
We will try in every issue to capture in words and pictures both the excitement of hunting fossils and the equally great excitement of understanding more fully what they mean.
In service of the objective of making the content accessible, Wexo provided a glossary of technical terms in this first issue, a practice that was to be followed in future issues.

Wexo wrote that each issue of the magazine would concentrate on fossils from different organisms – this first had trilobites as its focus – but this would not be to the exclusion of articles touching on other topics.

What was the content of this first issue?  It included the following articles:

Fossils and the Drifting Continents, by Edwin H. Colbert
Ancient & Wonderful Eyes, by Riccardo Levi-Setti
A Portfolio of Trilobites, by Riccardo Levi-Setti
A Fossil for What Ails You, by Chester B. Kennedy
Collecting Trilobites in North America, Part One:  The East, by Niles Eldredge
Localities for Collecting Trilobites in Eastern North America, by Niles Eldredge
Fossils On Stamps, by The Editors
Cambrian Trilobites of the Mohave (A Classic Collecting Locality), by George L. Kennedy
Cretaceous Fossils at Lake Worth (A Classic Collecting Locality), by William R. Pampe
Collecting Fossils in the Old West, Charles H. Sternberg

Quite a stellar array of authors (it even includes the famous Old West collector and long-deceased Charles Sternberg (1850-1943) represented by two chapters of his 1909 autobiography describing some of his fossil collecting exploits).  Four of the authors – Colbert, Levi-Setti, Kennedy, and Eldredge – were profiled in the magazine.

Edwin Colbert, Curator Emeritus of Vertebrate Paleontology at the American Museum of Natural History, penned an insightful piece on the fossil evidence for continental drift (the concept upon which the theory of plate tectonics was built).  He had first hand knowledge of this evidence having undertaken some of the seminal fieldwork that found the fossils showing that the continents had been on the move all through deep time.

Though physicist Riccardo Levi-Setti, author of two of the articles on trilobites, including Ancient & Wonderful Eyes, was not trained as a paleontologist, he pursued trilobites with a passion and in the process became a widely known expert on these animals, particularly their eyes and eyesight.  My own library includes his detailed and beautifully illustrated volume titled Trilobites (1975, 1993).

Chester Kennedy, emeritus professor of American literature and folklore, brought his academic training to bear on the bases for the myriad medical uses to which fossils have been put.  Of the articles in this first issue of the magazine, his appears to be the one most frequently cited in later scholarly articles.

Niles Eldredge, curator at the American Museum of Natural History, extensively studied the evolution of phacopid trilobites. His articles reflected his expertise concerning the animal and also his experience collecting their fossils.  He is perhaps best known (at least to me) for his work with paleontologist Stephen Jay Gould on punctuated equilibrium as a framing construct for the working of evolution.

The articles in this issue were illustrated with a rich collection of beautiful photographs, professional drawings, and detailed maps.

So, do I think this premiere issue of Fossil Magazine lived up to the expectations that were set by the promotional ads?

No question, the ads were right.

Indeed, more than four decades after the magazine came into being, the quality of its writing, illustrations, and photographs remains impressive, certainly meeting, if not exceeding, today’s standards of magazine publication.

Speaking of current standards, I turn to the only contemporary, somewhat comparable publication serving some of the same audience, with which I’m familiar:  Fossil News:  The Journal of Avocational Paleontology.  This magazine began publication in 1995.  I subscribed for several years in the 2000’s when it was edited by Lynne Clos, up until it ceased publication in 2012 (at the time, it was published online every other month, though issues emerged sporadically in the last several years).  Four years later Fossil News was revived by Wendell Ricketts as a print quarterly.  I have read one example of the magazine in this latest incarnation.

Fossils Magazine compares most favorably to Fossil News as it existed when I subscribed and as it is published today.  Indeed, though Fossil News was, and remains, an interesting and informative publication, I think Fossils Magazine managed to attain a higher level of overall quality, particularly with the academic and scientific stature of its contributors.  Further, its potential audience was possibly broader than that of Fossil News because I suspect it may have reached deeper into the community of professional scientists. That said, the editors of both publications recognized the value of first person accounts of fossil collecting, and of the visual aspects of their magazine – superb illustrations and photographs mark both.

Might the Fossils Magazine of 1976 have influenced Fossil News two decades later?  Were the past editors of Fossil News familiar with Fossils Magazine?  They might well have been unaware of the earlier publication for the very simple reason that Fossils Magazine ceased publication after its first issue.  Volume One, Issue One, and . . . done.  Fossils Magazine “went extinct," as the Ventura (California) Gem and Mineral Society’s website states so succinctly.

I find that fact stunning.  Having done so much right, what went wrong?

There’s a hint of at least one problem in that first issue under Acknowledgements.  The ads that appeared early in 1976 described the publication schedule of the new magazine as beginning in April.  So it’s not surprising that, in this first issue that came out a month late in May, the editor would “thank our subscribers, who have waited patiently for this first issue to appear, and have thereby made it possible for us to make this a better magazine than it otherwise would have been.”

Having been a contributor myself to several edited publications, I recognize that it can be hard to get all authors to submit their pieces in a timely fashion.  So, this one month delay in launching the journal is largely understandable.  Was it perhaps exacerbated by the stature of the authors and the rigor of the content they produced?  If so, that might not have augured well for adhering to the publication schedule in the future.

That still wouldn’t explain why a journal that appeared to have so much going for it couldn’t make it beyond its inaugural issue.  Quite possibly, the striking attribute of that one issue – its high quality – rendered the magazine more vulnerable to the economic shoals on which magazines then and now can founder.

Still, for a brief moment, John Bonnett Wexo caught lightning in a bottle.  Sadly, he could not hold it.

That said, he went on to other successful publication ventures, including the Zoobooks series of which 100 million copies have gone into print.  His legacy is being supported by the John Bonnett Wexo Foundation (A Voice for Wildlife Education and the Arts).

Without a doubt, given its great promise, the demise of Fossils Magazine was a loss, particularly to our community of amateur paleontologists.

Sunday, March 31, 2019

When Glossopteris Missed the Spring

Late in the Permian Period, springtime had clearly changed in what is now the Sydney Basin (New South Wales, Australia).  No longer did forests of Glossopteris trees greet the changing of the seasons with new leaves.  The collapse of this Glossopteris flora in the Basin’s ecology occurred some 370,000 years before the mass extinction of marine life on the planet which happened roughly 251.9 million years ago as part of the End-Permian-Extinction (EPE).  This is the picture that geologist Christopher R. Fielding and his colleagues paint in a new study drawing on careful study of geologic formations in the Sydney Basin that allow for fine tracking of changes in flora from the late Permian through the EPE, and into the first half of the Triassic.  (Fielding, et al., Age and Pattern of the Southern High-Latitude Continental End-Permian Extinction Constrained by Multiproxy Analysis, Nature Communications, January 23, 2019.)

The glossopterids were large, very likely deciduous gymnosperms with trunk diameters that could reach 80 centimeters (over 2.6 feet) and heights of up to 30 meters (over 98 feet).  They lived in water-soaked environments, creating “moderately dense mire forests.”  (For an excellent article on the Glossopteris, see Stephen McLoughlin’s Glossopteris – Insights Into the Architecture and Relationships of an Iconic Permian Gondwanan Plant, Journal of the Botanical Society of Bengal, 2011.)

Pictured below are my sole Glossopteris fossils - multiple impressions of Glossopteris sp. leaves stained red-orange with hematite (iron oxide) during the fossilizing process.  They stand out dramatically from the cream colored matrix of claystone, a sedimentary clastic (composed of rock fragments).  These were found near the town of Dunedoo in New South Wales, on the northwestern edge of the Sydney Basin.


The demise of glossopterids in the Sydney Basin was a change with probably profound implications for that location at that time,and possibly for us today.  In the Late Permian, the Glossopteris was under threat across the mid to high latitudes of the Southern Hemisphere.  Until then, these trees had been so abundant and widespread in the southern expanses of the world that paleontologists refer to the vegetation found fossilized in Permian alluvial settings of the Southern Hemisphere as “Glossopteris flora.”  Indeed, the Glossopteris is an index fossil used to identify Permian strata.

Fielding et al. attribute the demise of the glossopterids in the Basin to a relatively short period of climate change.  Temperatures rose.  As they put it, there was “a brief perturbation to warmer, more humid climate conditions.”  The largely complete disappearance of the Glossopteris in the Sydney Basin was a piece of a much more widespread vanishing of this plant across the southern latitudes prompted by subsequent changes in climate.  As paleontologist Stephen McLoughlin has written (see article cited above), “it is clear that the demise of the Glossopteris flora in most regions is intimately associated with the global environmental changes and biotic crisis at the close of the Permian.”  (p. 10)  The plant did not go extinct in the EPE, but, instead, hung on into the Triassic for awhile in the colder climates found in higher latitudes further south.

Significantly, Field et al. find no evidence in the Basin of an “exceptional erosional event or catastrophic physical degradation of the landscape” coincident with the EPE.  The damage to the glossopterids had been done hundreds of thousands of years earlier.

Geologist Robert A. Gastaldo, in an article that considers this work on the Sydney Basin, observes that Fielding et al. delineate a “scenario for how vegetation might respond to current global warming.”  (Ancient Plants Escaped the End-Permian Mass Extinction, Nature News and Views, March 1, 2019.  More on that title later.)  The experience of plants, such as the Glossopteris, so clearly sensitive to relatively small changes in the average temperature in the climate, “might be a harbinger of the plant group’s ultimate extinction.”  And it’s that related aspect of the research on this once amazingly abundant tree that intrigues and worries me.

It’s now very evident that spring is here in the Northeast United States, though for several weeks many subtle signs had been there to see.  In the 1930s, botanist and nature writer Donald Culross Peattie (1898 – 1964) noted in An Almanac for Moderns (1935) (written, I believe, when Peattie lived in the D.C. area and had a nature column in the Washington Star newspaper) that it was in the last week or so of March that one could say that spring had, in fact, arrived.  That was not too early, he thought, though “poets and musicians” tended to announce its coming in late April and early May when, he noted sarcastically, no fool could miss the signs.

Peattie wrote in his Almanac entry for March 24th:
So does our spring begin, in a slow flowering on the leafless wood of the bough of hazel and alder and poplar and willow, a hardy business, a spawning upon the air, like the spawning in the ponds, a flowering so primitive that it carries us back to ancient geologic times, when trees that are now fossils sowed the wind like these, their descendants – an epoch when the world, too, was in its naked springtime. (The Norton Book of Nature Writing, edited by Robert Finch and John Elder, 1990 p. 452.)
“Naked springtime” is a wonderful phrase for that very brief period when the woods are still airy and filled with myriad shafts of light, even as buds open and leaves unfurl.  Without the Glossopteris in the Sydney Basin, the nakedness was probably much more pronounced and long lasting.

Peattie’s observation for March 24th about the “spawning upon the air” describes a phenomenon with which we are very familiar, to wit, car windshields thickly coated in sticky yellow-green pollen.  But that pollen-based covering of cars is only just in its early stages here in the waning days of March.  Is this late for us?  Were we vigorously cleaning our windshields last year at this time or the year before?  I don’t remember, but I seriously doubt that spring typically arrived for Peattie earlier in the 1930s than it does for us today.

In fact, with the relentless climate change we’ve set in motion for the planet, spring is arriving earlier and earlier in many places.  Data from the citizen-science project, USA National Phenology Network, show that around the country, spring, or, at least, certain harbingers of spring have been arriving on average several days earlier in recent years compared to prior decades.  A recent study, based on USA-NPN data for the four major migratory bird flyways and for the National Wildlife Refuge System, finds that in those areas:
the onset of spring is now earlier in 76% of all wildlife refuges and extremely early (i.e., exceeding 95% of historical conditions) in 49% of refuges. . . .  This differential rate of advance in spring onset is most pronounced in the Atlantic flyway, presumably because of a “warming hole” in the southeastern US.  (Erik K. Waller, et al., Differential Changes in the Onset of Spring Across US National Wildlife Refuges and North American Migratory Bird Flyways, PLOS One, September 12, 2018, abstract.)
Some do argue that earlier plant growth in the early spring will lead to greater absorption by plants of carbon dioxide with an ameliorating impact on the warming climate, but recent research seriously challenges that contention, showing that early spring growth comes at a cost.  Water is absorbed from the soil earlier in the year and the plants are unable to sustain their growth spurt throughout the summer leading to increased drought conditions and early death of the plants.  Indeed, climate change modeling apparently assumes some degree of increased absorption of carbon dioxide which this research asserts is overestimated.  (See, for example, Marlene Cimons’ blog post titled With Shorter Winters, Plants Bloom Early and Die Young, National Geographic Blog, October 19, 2018.)

Earlier springs can have dire consequences for some species as dependent relationships that have built up over millennia are broken.  Mismatches between feeders and food sources are increasing.  For instance, research has shown that some migratory songbird species are arriving at their springtime destinations too late for their offspring to be sustained on caterpillars and other insects because those insects have long since emerged in order to feed on the plant leaves that have come out early.  Ecologist Stephen J. Mayor, as quoted in a Washington Post article on this research, observed, “The rate at which birds are falling out of sync with their environment is almost certainly unsustainable.”  He added, “We can end up with these increasingly quiet springs.”  (Ben Guarino, Experts Fear ‘Quiet Springs’ as Songbirds Can’t Keep Up With Climate Change, Washington Post, May 16, 2017.)

Peattie’s naked springtimes may become also very quiet springtimes.

I find it worrying that a dominant tree like the Glossopteris could be undone by relatively small increases in temperature in the Sydney Basin in the Late Permian, well before the severe changes in climate that marked the EPE elsewhere on the planet.  On point (and fueling my anxiety) is a recent study of the distribution today of 86 tree species in the Eastern U.S. that found that among important factors influencing the distribution of tree species, climate change had a significant (though not sole) impact, possibly driving some species northward to cooler climates and some species westward to areas of greater precipitation.  (Songlin Fei, et al., Divergence of Species Responses to Climate Change, Science Advances, May 17, 2017.)  Ecologist Fei and his colleagues, focusing on data covering a 30-year period that describe the geographical abundance of different tree species, found that 73 percent of the 86 species experienced a westward shift (mean shift per decade was 9.6 miles) and 62 percent of the 86 species moved poleward (per decade mean shift of 6.8 miles).  Clearly, some species moved both westward and poleward.  The angiosperms in the study group were more likely to more westward, most of the gymnosperms moved north (ah, there go the Glossopteris trees in the Late Permian).  The authors raised the possibility that this divergence might be related to the fact that most gymnosperms are pollinated by the wind, while angiosperms are pollinated by animals.  Nevertheless, trees are on the move today, a phenomenon with potentially profound affects.  Fei et al. write:
The reduction or replacement of certain species in a community can be consequential, because species can have substantially different effects on ecosystem structure, function, and services, and the impacts can cascade through a broad range of ecosystem processes.
Almost a no brainer to suggest that the interdependence of organisms in ecosystems means that the loss of any taxon (through extinction or movement to more hospitable environments) may have adverse consequences for other organisms in those systems.

As noted earlier, Robert Gastaldo's article has what would appear to be a rather contradictory title – Ancient Plants Escaped the End-Permian Mass Extinction – given its coverage of the research findings by Fielding et al. just described.  But Gastaldo reviewed not just Fielding’s work but also a study by Hendrik Nowak et al. of a database on the plant fossil record across the Permian-Triassic boundary.  Nowak and his colleagues found that the evidence of substantial plant extinction cross this boundary was largely a function of biases in the fossil record.  In fact, they found that diversity of plant genera was largely unchanged, even though species diversity declined in this period.  Gastaldo observes, “In contrast to prevailing wisdom, Nowak and colleagues demonstrate that land plants did not experience widespread extinction during Earth’s most severe biological crises.”  This finding, Gastaldo asserts, is supported by Fielding and his coauthors because they posit that, at the EPE, the environment in the Sydney Basin was not marked by any dramatic change or decimation of flora.

But I would caution that, though the analysis by Nowak and his colleagues does cast doubt on a significant extirpation of plants at the EPE, their work should not be read as evidence that all was well for plants at that point and that, more generally, plants have been able to skate largely unscathed through those events across deep time that decimate the ranks of marine organisms and land animals.  Changes in flora occur at these dramatic junctures in deep time, something that even Nowak et al. do acknowledge:
[T]he compositions of floras changed repeatedly throughout the history of land plants.  By all accounts, their dominance structures were also drastically altered during the Permian-Triassic transition both on the short term and long term.  (No Mass Extinction for Land Plants at the Permian-Triassic Transition, Nature Communications, 2019, p. 6.)
Further, Nowak and his colleagues observe that plants that rely in some fashion on the activities of animals are particularly susceptible during periods of mass extinction because animals are generally more at risk during periods of rapid environmental change.

Most troubling to me is the note of optimism (seemingly directed to those of us who worry about the impact of climate change) that Nowak et al. strike at the very end of their analysis for those plants that do not partner up with animals:
[O]ther major plant groups that rely on abiotic vectors have a comfortable chance of survival.  (p. 6)
Frankly, I found their conclusion puzzling and offering only cold comfort.  “Abiotic vectors” are those nonliving elements in the environment – light, temperature, atmospheric gases, pollution, geography, etc.  If the Glossopteris would be included in the abiotic plant groups then clearly there is something to worry about with changes in climate.  And, now revealing my ignorance and bias toward a belief that all living creatures are interdependent, I must ask, Are there really significant plant taxa reliant solely on abiotic vectors, that is, independent of any animal partners?

Even if there are, all other plants that clearly survive and flourish in partnership with animals are at risk and the consequences of the loss of such plants – think, for example, food crops – would be profound.  I conclude that, whether or not plants generally managed to make a transition across the Permian-Triassic boundary without the same level of extinction that marine organisms or land animals experienced, the earlier blinking out of Glossopteris in the Sydney Basin means something troubling for us today in this 2019 springtime.

Wednesday, February 27, 2019

George Washington Wilson ~ His Photographs a Century and a Half Later

One of my favorite photographers is George Washington Wilson (1823 – 1893) who described himself as an artist and a photographer, always in that order.  Though this post features no fossils, there is geology (eventually) and natural history (broadly speaking).

At the outset, a note about sources is in order.  Various sources are cited throughout this post, but special attention should be directed to Roger Taylor’s richly detailed and accessible biography titled George Washington Wilson:  Artist & Photographer (1823~1893), published in 1981.  I’ve relied on Taylor’s work for details of Wilson’s life and for an understanding of the photographic processes of the time.  Unless otherwise noted, please assume that Taylor is my source.

I know George Washington Wilson from his incredibly broad portfolio of beautiful stereoviews which he published in the latter half of the 19th century from establishments in Aberdeen, Scotland.  Shown below is an example of one of his stereoviews, featuring side-by-side photographs of a rowboat on the Loch of Park, Aberdeenshire, at sunset.  I believe Wilson photographed this scene sometime in the late 1850s.


A stereoview is a card on which are pasted two printed photographs of the same subject taken from very slightly different perspectives.  When the card is viewed through a stereoscope, a three- dimensional image is created.  Stereoviews are discussed in several posts on this blog, including this one.

The card presented above includes images that I find particularly striking both for their artistic composition, as well as for the technical mastery they reflect.  As to the latter, if one considers the photographic processes and equipment in use at the time (more on those later) and the challenge of capturing clear images of objects that cannot be posed, including, in this instance, the water, the clouds, and the rowboat with its occupants, the photographs are even more amazing.  Photographs of objects in motion, labeled “Instantaneous,” were difficult to obtain and highly prized.

Son of a tenant farmer, Wilson trained as a painter and specialized in portrait miniatures, finding success with his paintings in Aberdeen during the late 1840s and early 1850s.  This was also a time of striking technological developments in photography which led to the creation of a new, burgeoning business category in Europe, Great Britain, the United States, and elsewhere – the professional photographer.  In the 1850s, Wilson expanded his business to include photographic portraits.  Shortly, he fully committed to photography, a move certainly fueled by his success in fulfilling a commission from Prince Albert to photograph the construction of Queen Victoria’s Balmoral Castle.  From his ongoing relationship with the Queen and her family, Wilson would identify himself as Photographer to Her Majesty in Scotland.  Seen below is a photograph by Wilson of the Castle; it was not part of his commissioned construction series.


This image and all others appearing below in this post were selected from stereoviews.

Wilson was also an entrepreneur with a keen eye on the bottom line.  He saw the potential for photographs to generate substantial income.  In 1854, the carte de visite had made its appearance, featuring a posed photographic portrait of one or more individuals mounted on a small (2 ½ x 4 inch) card.  Due to its relatively low cost and ease of exchange, the carte de visite offered a much broader swathe of the general public the opportunity to have and share images of loved ones. Wilson lost no time in focusing on this photographic technique and format, a move which proved financially successful.  But, quite quickly, he felt compelled to push beyond the subject matter and technical limits of the carte de visite, taking his cameras into the wider world to capture landscape images, as he clearly had done in creating the photographs for the stereoview of the Loch of Park presented earlier.

To take photography on the road was no mean feat because Wilson was using the wet-collodion technology to capture his images.  When a scene was to be photographed, the photographer first had to create a light sensitive plate.  Roger Taylor describes the process as follows:
The collodion solution was, for the most part, commercially prepared by dissolved gun cotton in ether.  The photographer then used this viscous mass to coat a glass plate which had been carefully cleaned and degreased.  After an even coating had been applied, the ether present in the solution evaporated, leaving a moist absorbent film adhering to the plate.  This was then made sensitive to light by dipping it into a bath of silver salts which were readily taken up by the collodion film.  After the excess solution was drained off, the still moist plate was secured in a light-tight plate holder so that it could be taken into the light and to the camera for exposure.  (p. 194)
This whole process had to be undertaken in near total darkness.

To develop the image that had been taken up by the film on the glass plate, the photographer carefully followed another series of complex and sensitive steps.  This involved submerging the plate with the captured image in pyrogallic and acetic acid, a step requiring the photographer to judge when the image was correctly developed.  The image was then fixed on the plate using a solution of the highly poisonous hypo or potassium cyanide.  Again, the photographer worked in near darkness.

Wilson outfitted a wagon with the requisite hardware and chemicals and, accompanied by an assistant, undertook journeys throughout Britain taking photographs.  The image below, which features a view of the Pass at Ballater (in Aberdeenshire, near the River Dee, Scotland) may include in the left foreground Wilson’s own horse-drawn wagon, his darkroom on wheels.  The wagon is also an example of how Wilson often included something in his photographs to provide a sense of scale.  On occasion he used a wagon, more often it was one or more people.


The degree to which Wilson found financial triumph as a photographer cannot be overestimated.  His firm also printed photographs in larger, single-image formats.  In due course, Wilson became “the world’s largest publisher of photographs,” and, fulfilling the demand for his images, must have taxed his establishment.  (John Jones, Wonders of the Stereoscope, 1976, p. 54.)  In the 1870s, G.W. Wilson & Company had some 45,000 glass negatives from which it produced photographs for sale.  The average daily production of prints was estimated by Wilson’s son Alexander at 3,000; thus, potentially a million prints were produced annually.  (Beaumont Newhall, The History of Photography From 1839 to the Present, 1982, p. 105.)

It was no accident that the success of his enterprise coincided with the explosion of tourism.  Presumably rising incomes coupled with the expansion of rail lines in Great Britain turned travelers into sightseers and tourists.  Tourists, of course, sought mementos of the places visited, and photographs quite nicely satisfied that need.

Regardless of the commercial success Wilson enjoyed, it’s the beauty of the photographs that are the heart of his claim to fame.  He brought an inspired artist’s eye to his work, his photographs reflect careful creative intention.  They are typically tightly composed images that, to my mind, merit the label art.

Though landscapes may have been a predominant subject of his photographs, he also created many stunning images of other subjects.  These included, perhaps most prominently, the interiors and exteriors of cathedrals throughout Britain.  Seen below is one example:  the nave of Gloucester Cathedral in England.


He also photographically explored the ruins of abbeys and other religious structures.  Pictured below is a view of Melrose Abbey in Scotland.


Wilson has been called one of the two “giants among British stereographers” and the one “who had no peer in scenic photography.”  (William C. Darrah, The World of Stereographs, 1997, p 104.)

There are among Wilson’s landscape photographs, a small handful to which I am powerfully drawn, not just for the artistry expressed in the image, but, primarily, for the stories of natural history (interpreting that term broadly) that are told in the images.  Here are three of those.

Fingal’s Cave, Staffa

The first shows the entrance to a geological structure known as Fingal’s Cave on the Isle of Staffa, in Scotland’s Inner Hebrides.


It’s a remarkable photograph of a remarkable geological structure, the enormity of which becomes clear when one spots the two (perhaps three) men standing to the right of the mouth of the cave.  The cave, which acquired its name from the hero of an epic poem by the Scottish poet James Macpherson, has walls that stand about 72 feet tall and the opening extends some 269 feet.  These awe-inspiring hexagonal basalt columns are products of a lava flow some 60 million years ago.  Such geometrically symmetrical columns are relatively common features of basalt structures because, as lava solidifies and cools, the stresses from temperature change and pressure can generate vertical fractures, or columnar joints, at the surface of the basalt.  These then spread into the interior of the basalt.  Those at the surface begin as tetragonal joint networks, developing into hexagonal joints as they journey inward.  (Atilla Aydin and James M. DeGraff, Evolution of Polygonal Fracture Patterns in Lava Flows, Science, January 29, 1988.)

That’s a stab at a scientific explanation for these columns.  Folklore would have it that the cave is one end of a bridge that stretches to the geologically similar Giant’s Causeway in Ireland.  Purportedly, an Irish giant created the bridge in order to travel to Scotland to defeat a rival.  The basalt columns on Staffa are indeed geologically linked to the Giant’s Causeway.

It’s not surprising that Wilson’s portfolio included photographs of the basalt columns on Staffa.  The island became a tourist attraction beginning in the late 18th century, attracting such luminaries as Queen Victoria, William Wordsworth, John Keats, Jules Verne, and Sir Walter Scott.  In addition, the cave has inspired musicians from Felix Mendelssohn to Pink Floyd.  (Jeff Wallenfeldt, Fingal’s Cave, Encyclopaedia Britannica.)

Cheesewring

I love this photograph of the “Cheesewring” structure near Liskeard in Cornwall in part because it looks for all the world as though it’s about to fall on the poor person seated at its base.  An example of Wilson’s sense of humor, I suspect.


The Cheesewring (still standing) is a granite tor; a tor is a stack of stone blocks that forms naturally through differential weathering and erosion of rocks.  According to the novelist Wilkie Collins, the name of this tor supposedly comes from its resemblance to a Cornish cheese press, also called a “wring.”  (Rambles Beyond Railways; or Notes in Cornwall, 1851, p. 58.)

The Cheesewring stands amid a landscape punctuated by other standing rock or fallen tors.  Collins described it with some literary flourishes:  “The whole plain appeared like the site of an ancient city of palaces, overthrown and crumbled like atoms by an earthquake.”  (p. 61)  He offered two explanations of the Cheesewring.  Either it was built by Druids or it was the result of geological forces.  He opted for the latter, though his explanation of the way in which those forces conspired to stacks these rocks leaves something to be desired.  (Admittedly, the same criticism applies to the explanation I provided above.  I haven't found a satisfactory one, though, clearly, I, too, opt for one grounded in geology.)

I do really enjoy Collins’ characterization of the Cheesewring itself:  “If a man dreamt of a great pile of stones in a nightmare, he would dream of such a pile as the Cheese-Wring.  All of the heaviest and largest of the seven thick slabs of which it is composed are at the top; all the lightest and smallest at the bottom. . . .  When you first see the Cheese-Wring, you instinctively shrink from walking under it.”  (p. 65)

Stonehenge

There’s a certain logic in moving from Cheesewring to Stonehenge given the association of both in the popular imagination with Druids.  Wilson visited Stonehenge possibly in 1860 and took several pictures of it from different vantage points.  The image below shows the megalithic structure from the East.


Stonehenge was the product of intense labor by neolithic peoples, an effort that stretched over millennia, beginning 5,000 years ago as a circular ditch dug into the dirt.  The area was graced at some later point with wooden posts; said posts were replaced with large stones beginning in roughly 2,600 BCE.  The amount of labor required to quarry the multi-ton stone slabs, move them from the quarry to the site on the Salisbury Plain, and then erect them is almost unfathomable given the technology available at the time.  Current thinking about the purpose of Stonehenge includes two primary hypotheses, one astronomical in nature (functioning as an observatory), the other religious (possibly focused on ancestor worship).  (James Owens, Stonehenge, National Geographic.)

The image above that Wilson took of Stonehenge from the East is curious.  It’s almost as though he wanted to have the viewer first believe that the stones erected on the plain are relatively small.  He took the photograph from such a distance, including a broad expanse of grass, that puts the circle of stones into the deep middle ground.  It’s not until the sheep in the scene, the man leaning against one of the center pillars, and the wagon on the right all come into focus, that the impressive size of the structure comes clear.

I’ll close by observing that, more than 150 years after George Washington Wilson traveled across Great Britain photographing the landscape, his images are still speaking.

Wednesday, January 30, 2019

Interpreting Fossil Tableaus Frozen in Time

No, this post isn’t about the polar vortex.

I’ve come to the conclusion that one of paleontology’s core missions is the reconstruction of ancient communities of plants and animals.  At the heart of this effort is the challenge of deciphering and understanding what the fossil record says about the biological communities of organisms that lived and interacted in specific places in deep time.

One key to meeting this challenge is the field of taphonomy, first defined by paleontologist J.A. Efremov as:  “. . . the study of the transition (in all its details) of animal remains from the biosphere into the lithosphere . . . .”  In essence, analysis of how organic remains become rock.  (Taphonomy:  New Branch of Paleontology, Pan-American Geologist, September 1940.)  The utility of this field of study is how it enables us to determine, as paleontologist Anna K. Behrensmeyer and her colleagues have written, “how faithfully biological history has been recorded” in the fossil record.  (Taphonomy and Paleobiology, Paleobiology, January 2000.)

Not surprisingly, it turns out we must approach the fossil record with great care because what we see in the fossils from any specific site may not provide a reliable picture of the biological reality at that time in that place.

The particular interest that prompts this post is quite narrow and, as it often true of this blog, idiosyncratic.  I am wrestling with a few of the basic questions that might be asked of fossils that offer the remains of organisms affixed to each other, in other words, specimens and moments frozen in a fossil tableau.  Two such are pictured below.



The first picture shows the exterior and interior of a shell from the scallop Chesapecten nefrens.  This shell measures roughly 4.5 inches vertically and was found at the Scientists’ Cliffs portion (Choptank Formation) of the Calvert Cliffs on the western shore of the Chesapeake Bay.  Roughly 12 to 16 million years old, the scallop sports the remains of a number of barnacles, including remnants of the basal edges of several barnacle shells.  I won’t hazard an opinion on the species (one or more) of barnacle that encrusts this scallop.

The second photo shows two views of a 3.25 inch tall shell of the gastropod Ecphora gardnerae germonae.  An amazing gift from a friend, this specimen comes from the St. Mary’s Formation, further south along the Calvert Cliffs than the scallop, and is approximately 8 to 10 million years old.  The basal edges of barnacle shells abound on this Ecphora specimen.  Again, I’ve made no effort to identify the species of encrusting barnacle.

And here’s my rather simplistic set of questions.  For fossil specimens like those shown above, what can we say about the interaction of the different species that, through fossilization, are fixed in this kind of direct relationship with each other?  Did these individual specimens live at the exact same time in the same place?  Were the hosts alive when their “guests” took up residence?

My assumption has been that, in most cases, the best we can do is draw from modern analogs of the interaction of similar kinds of organisms and only offer educated suppositions about what these tableaus from deep time are telling us.  But I should have realized that brilliant people find brilliant ways to tease out greater meaning than the rest of us are resigned to.

An article that only recently came my way offers a kind of direct response to my assumption.  The renowned evolutionary biologist Geerat Vermeij has coauthored a fascinating piece on a specific species of Miocene barnacle, Chesaconcavus chesapeakensis, and its interactions with the gastropod Conradconfusus parilis and the scallop Chesapecten santamaria.  (Vermeij and Sara K. Ruch, Barnacles, Their Molluscan Hosts, and Comparative Ecology in the St. Mary’s Formation (Late Miocene) of Maryland, USA, Journal of Paleontology, Volume 92, Number 2, 2018.)  These species lived during the Tortonian age of the Miocene epoch, between 7 and 12 million years ago.

Working with a collection of these fossil species, Vermeij and Ruch concluded that representatives of this barnacle species came to be anchored on a high percentage of the fossil specimens of C. parilis and C. santamaria they had for analysis, and did so only when those gastropods and scallops were alive.  No question in their minds that these barnacles settled on the snail and mollusc shells when the hosts were definitely going about their daily business.

How can these scientists know that these hosts were alive, carrying living barnacles on their shells?

Their logic is simple and, to me, persuasive.  Consider, first, the barnacles and gastropods.  Vermeij and Ruch found that, of the gastropod specimens in their study collection that sported barnacles, none had barnacles encroaching on their hosts' apertures.  Had the barnacles done so, they would have interfered markedly with their hosts’ ability to survive.  No barnacles were found to have taken up residence on the interior of the gastropod shells.  Further, and, to my mind, quite telling, the shape of many of the barnacles was curved toward the growing edge of the gastropod shells signaling that they were growing even as their hosts, themselves, grew.

As for the barnacles on the scallops, they, too, refrained from overlapping the outer edges of the shells, so did not impede the normal opening and closing of the articulated valves.  Also, in no case, did barnacles inhabit the interiors.

Accepting the logic of this analysis, one obvious takeaway is that clearly the species under study lived at precisely the same time and in the same place.  That is, they were members of the same community, interacting as members of biological communities do.  Quite beautiful I think.

But I hesitate to take too much inspiration from the work of Vermeij and Ruch because that might mean I’d have to consider approaching the specimens depicted in the tableaus presented earlier with their analysis in mind.  My fossils are, after all, single samples, not part of a broader representative collection of Chesapecten or Ecphora that might be subjected to the methodology these scientists brought to bear.  Further, there are many basic pieces of information I’m missing (e.g., what species of barnacles are these?).  I’m smart enough to know my limits and am content just to enjoy the Vermeij and Ruch tour de force.

 
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