Friday, September 29, 2017

Evolution and Historical Contingency ~ A Review of Improbable Destinies


Stephen Jay Gould threw down the gauntlet when he argued in Wonderful Life:  The Burgess Shale and the Nature of History (1989) that, were we able to replay the tape of life – that is, erase the metaphorical tape back to some point in the distant past – then “any [subsequent] replay of the tape would lead evolution down a pathway radically different from the road actually taken.”  (Wonderful Life, p. 51)  Evolution, in Gould’s view, is clearly not deterministic, rather, historical contingency holds sway.  By historical contingency, Gould meant that any particular state (of history, of the evolutionary paths of species) was “dependent, or contingent, upon everything that came before – the unerasable and determining signature of history.” (Wonderful Life, p. 283)

Thirty years later debate over the validity of Gould’s proposition continues.  Are the various constraints on evolution through natural selection such that, regardless of where we re-start the tape, the results shown in the replay eventually would be remarkably similar to what we see around us today, or does contingency play such a powerful role that ending up in the same place is not only improbable but perhaps out of the realm of possibility, dependent as it is upon myriad events occurring in just the right order?

This is the context for evolutionary ecologist and herpetologist Jonathan B. Losos’ new book Improbable Destinies:  Fate, Chance, and the Future of Evolution, a riveting and remarkably accessible exploration of convergent evolution and its import for Gould’s thought experiment.


Convergent evolution is the phenomenon in which different species evolve similar features, that is, they converge on very similar morphological features, say, wings in insects and wings in birds among other vertebrates.  The list of examples of convergent evolution in the natural world is rich and long and growing.  As Improbable Destinies makes clear, anole lizards, an early example and the centerpiece of Losos’ research, have been joined by a host of other instances of convergence involving many different kinds of organisms, ranging from snails to guppies, from bats to stickleback fish.

The wealth of such examples has led some scientists, paleontologist Conway Morris prominent among them, to conclude that (as Losos writes), “evolution is deterministic, predictable, following the same course time after time.  The reason, they argue, is that there are only so many ways to make a living in the world,” and so the tape actually would end up in the same place every time it is replayed.  (p. 5)

At the same time, Losos shows that the list of “evolutionary idiosyncrasies” isn’t short and often features creatures, such as the kiwi or the solendon, that have evolved on isolated land masses such as New Zealand, Australia, and Madagascar.  There’s a diverse richness here.  Losos notes, “Conway Morris and his colleagues have made long lists of examples of convergence, but it would be just as easy to make comparable catalogs of species without counterparts.”  (p. 87)  He argues that these one-offs may appear because “natural selection is either not as predictable or as powerful as some make it out to be.  That is, even when species experience identical environments, they might not evolve in the same way.”  (p. 88)

Losos describes many research projects relevant to our understanding of convergent evolution.  These include observation of convergence in the wild, particularly in settings showcasing natural experiments (principally islands), deliberate experiments in the wild as scientists transfer organisms to different locations and analyze their subsequent evolution (yes, as he makes abundantly clear, evolution need not proceed at the snail’s pace that Darwin would have had it), and finally experiments in the laboratory, often in petri dishes or vials involving microorganisms, such as E. coli.

The highlight of the book for me (and here it’s a page-turning pleasure) is Losos’ account of his research on the Anolis lizard (commonly referred to as the anole lizard) and his field work in the Greater Antilles (Cuba, Hispaniola, Jamaica, and Puerto Rico).  Perhaps their most spectacular feature (reserved in most species to males) is the dewlap, “a flap of skin under their throat,” usually hidden from sight.
But when the lizard has an announcement to make – ‘Get lost, buddy, this is my territory” or “Hey, ladies, come check me out.  I’d make a good baby daddy’ – out comes the dewlap, arching downward from the jaw, forming a semicircle so large that the lizard often has to straighten its legs, pushing its body off the ground, to provide clearance.  (p. 58)
A nice example of the prose that graces the book.  Losos is able to make what is certainly tedious and physically difficult research on these lizards into an exciting narrative, a narrative that shows why the anole lizards are robust examples of convergent evolution.

He found that, although each of the four islands in the Greater Antilles has a different array of anole species, those species generally occupy similar ecological niches (bush, or different parts of trees) across the islands.  Those in each niche have evolved to be so similar from island to island that each of these “habitat specialists” can be mistaken for each other.  Yet all of the species on any of these islands are more closely related to each other than they are to any of the similar habitat specialists across the islands.

There is a great deal to absorb from Losos’ walk through the relevant research from the wild to the laboratory, much of it, particularly those natural and deliberate experiments in the wild, thoroughly engaging.  Yet two aspects of the research covered here are, to me, disquieting.

First, I appreciate what can be learned from projects that involve researchers moving organisms in the wild from one place to another (e.g., guppies from pools with predators to those without, or anoles to islands with no lizards), but, given how complex the array of contingencies is in the natural world, what are the real consequences of this manipulation?  I am reminded of how off putting I found ecologist E.O. Wilson’s research that involved fumigating entire mangrove islands in the Florida Keys to kill off all the arthropods.  Yes, he gained insight into how populations recover and how quickly, but at what cost?  Certainly I’m being overly sensitive about this and I’m sure my concerns would be discounted by those involved.  Still the deliberate interference bothers me.

Second, though much of Losos’ explication of the relevant laboratory research is extremely well done and informative, I had a nagging unease about this research.  It didn’t help that I often lost track of what the various projects were trying to prove and what they did prove.  Perhaps the more substantive part of my discomfort with the laboratory portion of the book has to do with my sense that test tube evolution with microbes is somewhat analogous to running computer programs that seek to replicate evolution:  a limited set of conditions are programmed in, with some random function added to mimic the mutations that natural selection has to work with.  The results can be instructive, yet they are, ultimately, artificial.  The full force of contingency that occurs in the natural world is largely missing in either the lab or the computer program.

None of this is to gainsay the importance of tracking myriad generations of microorganisms in controlled environments in the laboratory, not only to see if identical populations always end up in the same place, but also because, as at least one project was structured, researchers could, literally, replay the tape, taking a population to some previous generation and letting it reproduce from there. The message from such experiments, as I understand it, is that, yes, largely the tape replays exactly as it has run before.  But, and it’s a big but, not always.

Indeed, though most of the research from the field and from the laboratory would appear to support the evolutionary determinist camp – that the replay ends up in the same place – closer examination of the results, often over a longer range of time, shows that isn’t always true.  It’s most likely to be true when the populations begun with are closely related; such relatives are likely to evolve similarly when placed in new environments.  Not so when they are more distantly related.

But I didn’t think that Gould’s thought experiment envisioned the tape replaying exactly as it had before and the only thing in play being how evolution would be affected by random mutations in organisms.  Losos, citing philosopher of science John Beatty, acknowledges as much, positing that Gould actually embraced two concepts of contingency.  The first being that replaying of the tape with nothing changed to see if evolution would or could take a different course.  The second being the replaying of the tape from a specific point with the full panoply of historical contingencies allowed to be at work affecting living organisms.  Though these contingencies may be small events with important or unimportant consequences, they could, as well, be more dramatic things such as a storm wiping out the sole representatives of a species or an asteroid hitting the planet and decimating a host of species.  Each of these specific contingencies cannot be anticipated when we replay the tape – they may or may not occur – and they are likely to make all the difference in the world and we are likely not to end up in the same place with any replay.

In fact, and this needs no spoiler alert given the title of the book, I think Losos comes down largely in the Gould camp though his stance is somewhat nuanced.  As he writes,
So, can we predict evolution?  In the short-term, yes, to some extent.  But the longer the passage of time and the more different the ancestors or conditions, the less likely we are to prognosticate successfully.  (p. 336)
He adds, regarding our species,
If any of a countless number of events had occurred differently in the past, Homo sapiens  wouldn’t have evolved.  We were far from inevitable and are lucky to be here, fortunate that events happened just as they did.  Asteroids, of course, but what other events critically tipped evolution’s path in our favor?  Who knows how slight a difference in the past – a tree falling on great-great-great-to-the-millionth-degree-grandpa Ernie, a forest fire, a mutation – might have snuffed out our future existence?  (p. 335)
As he notes, we weren’t fated to evolve though possibly something like us might have.  Ultimately, no matter the outcomes one might anticipate from evolution, it is highly improbable that any specific one will occur.

In closing, I have to explain why I felt compelled to buy and read Improbable Destinies.  I had no choice after reading his interview in Current Biology (August 21, 2017).  He had me from the moment he answers the question:  How did you get started in biology?

Sure, he mentions dinosaurs as a gateway drug, but he goes wonderfully so much further, offering credit to:
a particular episode of Leave it to Beaver, the one in which the Beaver purchases a mail-order baby alligator.
According to the IMDb synopsis of this particular episode (frankly, I don’t remember this one which explains, I guess, why I didn’t become a biologist), Wally and the Beaver acquire a Florida alligator sub rosa and the laughs (such as they are) stem from their efforts to raise an alligator in the house without their parents discovering.  In contrast, Losos, smitten by the idea, was above board in his campaign to be allowed to acquire this kind of reptile.
. . . I knew that local pet stores sold baby caimans, the neotropical relative of alligators. The question was: how to convince my mother to allow a crocodilian in the house. Fortunately, my mom — not liking to say ‘no’ — passed the buck to the local zoo director, a family friend, expecting him to put the kibosh on the idea. To her dismay and my delight, however, he said that having an alligator was how he got his start in herpetology, and the next thing you know, I had a caiman in a kiddie’s wading pool in the basement.
In closing, I must say that my encountering this interview (which in turn prompted me to read and review the book) was contingent on a long, long chain of events that included spotting a turtle in my backyard several years ago and deciding to write a blog post on the turtle shell.  Current Biology had a relevant article and I actually paid for access to it (shows how desperate I was) which got me snared in the publisher's email web which meant the index to this August’s issue reached me.  Then again, even if I hadn’t seen the interview in Current Biology, given what I read I still would have seen reviews of the book and I might very well have ended up in the same place.

Thursday, August 31, 2017

Where Worlds Meet or Perhaps Collide


Several years ago on a whim, I purchased a packet of 100 worldwide stamps that mostly feature dinosaurs.  The Mystic Stamp Company originally assembled and sold this packet.  For reasons not relevant to this post, my philatelic interest from my early teen years has robustly revived and that dinosaur packet (found under a bed after a dusty search) now sits on my desk, the object of some study, offering a sense of two worlds – paleontology and philately – meeting.

Here are a few examples of these stamps.





I’ve concluded that this collection, regardless of how it was brought together, actually constitutes a fairly representative sample of how dinosaurs, and by extension, things paleontological, have been treated on postage stamps.

There are several sites on the web that allow me to make this kind of generalization beyond just my small sample of 100 stamps.  For instance, I consulted with Stamps2Go, a great marketplace for folks selling and those buying postage stamps, which currently has 750 stamps for sale that are nestled under the topic “Animals:  Extinct:  Dinosaurs.”  Admittedly, not all of them are dinosaurs, but most are.  (Later edit:  To be sure, among the 750 stamps are duplicates of the same issue being offered by different sellers.)

Then there’s another website that proves once again that if you can imagine it, it’s probably already on the web.  The Paleophilatelie site is the brainchild of Paleophilatelist in Munich, Germany, who married his interest in fossils with his stamp collecting, creating in the process a beautiful virtual collection of worldwide postage stamps (and related postal items such as first day covers and cancellations) with some relationship to paleontology.  It’s a source of endless fascination (though perhaps that may be true for me just because I’ve been sucked into the black holes of these two interests).  Anyway, I have found it great fun to go through his collection of stamps; one can either browse the full gallery or select stamps from specific countries.

So, based on my sample and what I see at sites like the two just described, I’ve reached the two following conclusions:

  • The artwork and details in these stamps are mostly second rate.  No other way to say it (unless third rate is more appropriate).  Details often seem wrong.  Among the offending aspects are the proportions of various body parts of the animals, the structure of appendages, the animals’ posture, and their general environment.  Even if the details are right, the artwork mostly fails to bring these creatures to life.  Sad stuff.
  • Fossils are missing from the vast majority of these stamps.  In general, postage stamps don’t depict the fossils that underlie our understanding of how extinct ancient animals (and plants) looked and lived.  In my sample of 100 stamps, only one shows a fossil skeleton of a dinosaur.  (I certainly won’t extrapolate from that and suggest that only one percent of postage stamps with dinosaurs or other things paleontological shows fossils.)  The one in my collection was the lowest denomination issue that was part of a five-stamp set released in 1991 to honor that nasty, ill-tempered British paleontologist Sir Richard Owen, a doyen of paleontology in the mid 19th century who coined the word dinosaur.  The stamps feature somewhat stylized portions of skeletons of various dinosaurs, including Iguanodon, the only one of the dinosaurs depicted on these stamps whose fossils Owen actually knew.  (The discussion about these stamps on the Paleophilatelie site is helpful.)






Although some countries do quite nicely with fossils on their stamps, such as Germany, the question remains why fossils are the general exception.  Are fossils harder to illustrate?  Are we (the general public, postage stamp users, or collectors) assumed to be more attracted to depictions of the living creatures or, perhaps, considered likely to be put off by fossilized bones on our stamps?  Maybe fossils are thought to be too static, failing to convey action very well.  Frankly, I don’t think that’s true of fossils, and the inferior artwork used for many dinosaur stamps certainly puts a lie to the notion that illustrating the living animals is necessarily the avenue to attractive, action-filled stamps.

How do U.S. stamps fare in this kind of discussion?  Most of the stamps in my dinosaur packet come from African and Asian nations.  None come from the U.S. though the U.S. has featured illustrations of living dinosaurs on a number of occasions.  For instance, here is a stamp issued in 1970 titled The Age of Reptiles.  (It is in the public domain and downloaded from Wikimedia Commons.)



The artwork on the U.S. stamps I’ve looked at is certainly passable, if generally not memorable.

What of fossils on U.S. stamps?  My search of Arago database of all U.S. stamps on the Smithsonian’s National Postal Museum website turned up exactly one stamp with fossils, featuring a fairly abstract illustration of a trilobite and some ferns.  It was issued in conjunction with the Knoxville World’s Fair in 1982, and bears the title Fossil fuels, one of four stamps in a block with an energy theme (another of the stamps was titled Breeder reactor).  It's telling that that's how fossils came to be on a stamp.  But is that it?  It’s what I could find though I’d be happy to be corrected.

[Well, in this later edit, I will correct myself.  In 1955, the U.S. Postal Service issued a stamp commemorating Charles Willson Peale (1741 - 1827) and his museum.  The gifted Peale was, among other things, an artist, politician, and naturalist, and he turned his massive collection of natural history specimens into a museum.  He painted a portrait of himself lifting the curtain on a view of his museum and this is what the 1955 stamp depicts.  At his feet (on the right side of the stamp) are mastodon fossils.


It was the Paleophilatelist on his Paleophilatelie site in his Milestones Paleontology Related Philatelic Items who led me to this stamp.  Also please see his comment below on this blog post.]

One final note which may relate to a place where the worlds of paleontology and philately do collide, at least in this country.  As I looked at many hundreds of paleontologically oriented postage stamps from across the globe, it was fairly easy to note when the bicentennial of Charles Darwin’s birth occurred (2009) because at roughly that point there was an explosion of Darwin-related stamps from many countries.  The Darwin OnLine website offers a selection of worldwide stamps featuring the great naturalist.  Conspicuously, though not unexpectedly, missing, is the U.S. where I conclude that, even though the published criteria for selection of individuals to be honored on U.S. stamps pose no particular barrier to the British Charles Darwin, the U.S. Postal Service appears to have shied away from offending the religious right.

Sunday, July 30, 2017

Buying a Fossil for its Label

There are myriad reasons for acquiring a fossil from a dealer, but it was a new one for me when the impulse to buy a small gastropod fossil came not from the specimen itself but, rather, from the typewritten paper label that was nestled in the box with the fossil.


The label is 6.3 cm long.

I should make clear that my use of the term “label” in this post is not, I suspect, strictly paleontologically kosher.  For example, the American Museum of Natural History, in its Collections Management site on its Paleontology Portal, defines a label as the numbering that is applied to a fossil specimen itself, not the separate cataloguing record, which is much closer to what in this post I am referring to as a “label.”  That said, the two – numbering on the specimen and the catalogue record – are inextricably (we hope) linked.

Labels (as I am defining them here) are the lifeblood of a fossil collection, accomplishing the essential task of linking specimens to the specific places they were found.  Two pieces of information in the label accomplish that:  description of the location and a specimen number.  Yes, more information can be, and usually is, assigned to a specimen through a label, including, among other data, the scientific name of the fossil (the organism from which it came), the name of collector, date of collection, formation where collected, and age of the specimen.  Though in many ways the label shown above is a prime example of a useful label, it has some limitations.

The location description leaves a bit to be desired.  I suspect that this label’s identification of place – “E. of Labelle, Hendry Co., Florida” – meant a very specific location to the collector R.J. Bland, Jr.  Nevertheless, as it comes to me, this probably would not be sufficient for me to find and explore the spot where the fossil was found.

And, of course, absent the same specimen number written on both the fossil and the label, I cannot be absolutely certain that this label was prepared for this specific fossil, but the likelihood is, I think, overwhelming.

Here then is the specimen to which this label was associated – a fairly well preserved example of a fossil Apple Murex which is 4.9 cm long.


Things have changed since this fossil was found and its label prepared.  For instance, Chicoreus pomum is now known as Phyllonotus pomum.  The formation (as written on the label, ‘“Glades” (Unit A)’) is currently designated the Bermont Formation and its age is considered to be Middle Pleistocene, some 1.1 to 1.8 million years ago.  (Primary sources for this information are the World Register of Marine Species (entry for Phyllonotus pomum), and Molluscs:  Bermont Formation (Middle Pleistocene) by Roger W. Portell and B. Alex Kittle, Part 13 of Florida Fossil Invertebrates, a publication of the Florida Paleontological Society, December 2010.)

What hasn’t changed is the name of the collector R. J.  Bland, Jr.  And therein lies one of the most attractive aspects for me of many fossil labels – the link between specimen and collector.  I have, for example, seen labels for specimens in the Smithsonian’s National Museum of Natural History where the collector is identified as John Bell Hatcher, one of my paleontology heroes (see post).  When someone of Hatcher’s stature is directly connected to the specimen before me the feeling is electric.  Though it wasn’t quite the same experience when I spotted the name of the collector of the Apple Murex, there was a spark.  It was a name I knew.

In a post a couple of years ago on state geological surveys and the rocks and minerals (and sometimes fossils) that they put up for sale to the general public, I described the rocks and minerals that the Virginia Department of Mines, Minerals, and Energy (the state’s geological survey) sent me. They were small samples affixed to the inside of a box.  The label described these samples as coming “from the collection of Rudolph J. Bland, Jr.”  No further identification of Bland was provided and I could uncover little additional information on the web.  Yet, through some good fortune, today here in my hands is a gastropod fossil collected in Florida by R.J. Bland, Jr., who, I feel, has to be the same Rudolph J. Bland, Jr., whose rock and mineral collection the Virginia state geological survey is busy dispersing, small specimen by small specimen.  (How the state geological survey came to be doing that is yet another tale waiting to be told.)

Finally, how this fossil shell found its way into the dealer’s collection of wares that he had on sale at a particular gem and mineral show that I attended is a story with a touch of serendipity.  This dealer had very, very few shells for sale amid the myriad fossilized remains of dinosaurs, sharks, marine reptiles, and the like.  Indeed, he admitted that shells are of little interest to him because he felt they’re of little interest to collectors.  This specific specimen with its label came into his possession because of some horse trading he had entered into several years ago with a woman who was trying to clear her basement of an unwanted fossil collection.  He offered her a price for the good stuff (that is, the teeth and bones) and she countered by asking that he name a price that would cover the entire collection, shells included.  He goosed his offer a small bit and both went away happy.

There’s a moral in here somewhere about the fate of collections and collectors, and I wonder if that moral might be stronger if I knew how the woman came in possession of this Apple Murex with its little label in the first place.

Thursday, June 29, 2017

Messing With Patterns


This post features no fossils though my initial intention was otherwise.  Fossil foraminifera shells, the golden ratio, and the logarithmic spiral were among the elements in the mix as I began to draft this post but, sadly, it all spun out of control.  I regrouped and this is what resulted, a piece focused only on composite flowers and the Fibonacci sequence with a salute to Alan Turing at the end.

We are a pattern-detecting species and nature obliges by surrounding us with myriad apparent patterns.  Case in point, the beautiful, flower-heavy stand of coneflowers (Echinacea purpurea) in my front yard.  The many blossoms, white and a few pink, are composite flowers; so not surprisingly the coneflower is a member of the daisy family, or more properly the Asteraceae or Compositae family.  The flower head of the coneflower consists primarily of small disk flowers with small ray flowers along the periphery.  These flower heads, as we perceive them, sport clockwise and counter-clockwise spirals emanating from the flower center.  The first picture below shows a blossom in its natural beauty; the second and third present the clockwise and counter-clockwise spirals I detect in this blossom marked in white.
 



 Such a spiral perceived in the organs (such as leaves and petals) of botanical specimens is called a parastichy; a count of these spirals is referred to as the parastichy number.  Interestingly enough, various definitions of parastichy use the adjectives invisible or hypothetical to describe the spiral patterns, suggesting that the presence of parastichies may well be (in part? mostly?) a function of the predilection of our eyes and brains to join disparate elements into some visual, pattern-filled, coherent whole.

Objects of Wonder, a current exhibit at the Smithsonian's National Museum of Natural History, features unique and seldom-seen treasures from the museum's collections.  A display case promoting the exhibit highlights how scientists find “patterns everywhere," enabling us "to understand the underlying processes that shape our world," part of “a complex and seemingly chaotic universe.”  Among the objects displayed in this case is the flower head of a sunflower (Helianthus annuus); though not one of the museum’s treasures, it is an object of wonder.  The display notes that "[a] sunflower's blossom consists of many small flowers arranged in spirals."  It adds that “[t]his pattern evolved as an efficient way to pack many seeds into a space, keeping them evenly distributed no matter the size of the seed head."

The sunflower, a member of the Asteraceae family and so related to the coneflower, appears prominently in the literature describing mathematical patterns found in living organisms.  So much so, that I consider it a poster child for that concept and particularly for the presence in nature of patterns based on Fibonacci numbers.

Leonardo of Pisa (c. 1170 – 1250), called Fibonacci because he was the son of Bonacci, first presented the series of numbers that Eduoard Lucas (1842 – 1891) named the Fibonacci sequence.  Here is the beginning of the sequence:

1, 1, 2, 3, 5, 8, 13, 21, 34, 55, 89, 144, 233, . . .

The first two numbers (1, 1) are given; from there the pattern dictates that each subsequent number is the sum of the preceding two numbers.  The next number in the sequence above would be 144 + 233, or 377.  It’s an infinite sequence and recursive (that is, it has the attribute that any new number added to the sequence is dependent on earlier numbers).

Connection to sunflowers?  Each sunflower blossom appears to offer a pair of clockwise and counter-clockwise spiral patterns whose parastichy numbers fall on the Fibonacci sequence.  That is an essential attribute of the sunflower that mathematicians and others highlight when they wax enthusiastically about the deep association between mathematics and nature.  As science writer John Bohannon notes (in an article about the sunflower study described below), “Mathematical biologists love sunflowers.  The giant flowers are one of the most obvious – as well as the prettiest – demonstrations of a hidden mathematical rule shaping the patterns of life:  the Fibonacci sequence . . . .”  (Sunflowers Show Complex Fibonacci Sequences, Science, May 17, 2016.)  Mathematicians Peter Tannenbaum and Robert Arnold, in their textbook Excursions in Modern Mathematics (3rd edition, 1998), write (somewhat breathlessly) of the consistency in how Fibonacci numbers appear in some natural objects.  Of the sunflower, they observe, “[T]he seeds in the center of a sunflower spiral in 55 and 89 rows.”  (p. 305)

As to that latter assertion about sunflowers spirals, I must respond, well, that’s not always true.  Indeed, it’s often not true.  In the largest analysis to date (published last year) of parastichy numbers in sunflower blossoms, Jonathan Swinton and his colleagues found that while 74 percent of the 768 parastichy numbers (clockwise or counter-clockwise) included in the study fell precisely on the Fibonacci sequence, the remainder or 26 percent did not.  (Novel Fibonacci and Non-Fibonacci Structure in the Sunflower:  Results of a Citizen Science Experiment, Royal Society Open Science, 2016.)  Yes, 55 and 89 were among the most common Fibonacci numbers appearing in the parastichies, but the rank order for the top four such numbers was 55, 34, 89, 21.  If one were to be generous and include sequences which have “Fibonacci structure” (such as the double Fibonacci sequence, i.e., 2, 4, 6, 10, 16, . . ., or the Lucas sequence, i.e., 1, 3, 4, 7, 11, . . .), another 8 percent of the parastichies in this study might be considered Fibonacci in essence.  That leaves 18 percent of the parastichy numbers outside of the Fibonacci sequence or Fibonacci-structured sequences.  Another 8 percent of the parastichies were non-Fibonacci numbers that were very close to ones in the Fibonacci sequence, differing by only plus or minus 1.  Thus, approximately 10 percent were fully untethered to the Fibonacci sequence or Fibonacci-structured sequences, even being very generous about it.

It would appear that, at least for the sunflower, this “hidden mathematical rule shaping the patterns of life” plays out rather untidily in a significant minority of specimens.  There’s no faithful consistency here.  In light of Swinton’s study, Bohannon admits as much when he writes, “The possibility of capturing sunflower development with math just got more realistic – and more complicated.”

I was heartened that Swinton’s study is the culmination of a citizen-science project that was run by the Museum of Science and Industry (Manchester, England) as part of a celebration of the 100th anniversary of mathematician Alan Turing’s birth.  Among his myriad research interests, the brilliant and persecuted Turing toward the end of his life was pondering explanations for why and how the Fibonacci sequence appears in nature.

The photos of the coneflower from my garden that opened this post were prepared following the guidance generated by this citizen-science project.  Interestingly enough, the parastichy pair for that particular blossom (21 and 34) are, in fact, Fibonacci numbers and, better still, adjacent in the Fibonacci sequence.  Other coneflowers that I photographed and for which I generated parastichies reflected how life can get in the way of desired neatness and order.  For instance, the blossom depicted below has a very nice spiral pattern (at least, I perceive it as such) in the clockwise direction (with a parastichy number of 21 that falls on the Fibonacci sequence), but that same blossom features (again, as I perceive it) a rather complex counter-clockwise spiral pattern (third photograph below) whose order breaks down in its left half with partial spirals intersecting ones emanating from the center.  I tried to salvage the counter-clockwise parastichy count for this blossom in a couple of different ways, but I only shifted where the confusion occurred.  In his analysis of the sunflower parastichies produced in the citizen-science project, Swinton notes that in some flowers there may be overlapping or competing parastichy families, sometimes leading to “particularly awkward transitions.”  This may be a coneflower example of that.




 Yes, a bit of a mess as nature prevails over the order some would have it follow.

Tuesday, May 30, 2017

Brooding on Stragglers


I’ve always defined straggler as “someone who falls behind, who fails to keep up.”  So I was intrigued to find that in the literature on periodical cicadas those members of a brood who arrive before or after their expected year of arrival are called stragglers.  Clearly, my definition is much too narrow, missing the essence of what it means to straggle.  The Oxford English Dictionary defines straggler variously, but its first meaning is:  “One who wanders or roves without fixed direction; one who strays from his companions or from the regular route; a gadabout; a camp-follower, a tramp, a vagabond.”  The heart of this as it applies to periodical cicadas is “one who strays from his companions.”  It doesn’t matter whether the straggler arrives early or late, just that the straggler is separated from his or her companions.

In the past several weeks, neighborhoods near me in the Maryland suburbs of Washington, D.C. have seen the emergence of a massive (well, it seems like that) number of periodical cicadas, those of the genus Magicicada.  Lord, what a beautiful name for this genus.  Entomologist William T. Davis named this genus in 1925 but didn’t pause to explain his thinking.  (Cicada Tibicen, A South American Species, With Records and Descriptions of North American Cicadas, Journal of the New York Entomological Society, March, 1925.)  (Periodical cicadas are different from their brethren who emerge annually after relatively brief underground sojourns.)

Streets near me became killing fields with the smashed bodies of cicadas strewn everywhere, testament to the implacable force of the automobile.  Winds deposited in the gutters many, many shells from which the insects had crawled after their extended stay underground sipping on tree sap.  Vertical surfaces, such as trees or telephone poles, were the scenes of amazing transformations as the ghostly cicadas emerged from their shells and, shortly, took on color and substance, before launching into the air in brute-force flight, nothing graceful about it.





Delve into the life history and paleontological history of cicadas and you fall down Alice’s rabbit-hole.  No other insect has a longer total life cycle than the periodical cicadas who have two cycles, one of 13 years and the other of 17 years.  Complicating this story is the fact that there are three “species groups” of periodical cicadas: Decula, Decim, and Cassini.  Each of these groups independently evolved into forms that live under ground for either 13 or 17 years (well, for the most part that’s true, an issue I’ll return to momentarily).  These 13- and 17-year forms have organized themselves into “broods” with different years of emergence and different geographic ranges.  Underlying this developmental (and mathematical) complexity is one astounding attribute, what entomologist Stewart H. Berlocher has described as “the real kicker”:  nearly every brood includes members of the three “species groups.”  (Regularities and Irregularities in Periodical Cicada Evolution, PNAS, April 23, 2013.)

The idea of a “species” seems under some duress here.  Although the Decula, Decim, and Cassini groups interbreed probably rarely enough to be considered separate species, the species designation for the Magicicada, so current thinking goes, drops down one stage to the 13- and the 17-year cohorts of each species group.  This results in the following species of periodical cicadas:  Magicicada tredecim, M. neotredecim, M. tredecassini, M. tredecula, M. septendecim, M. cassini, M. septendecula.  The first four are 13-year species (M. neotredecim came into being recently, evolving from a cohort of M. septendecim, a 17-year species); the last three are 17-year species.  Berlocher notes, “All broods of each of these species have occasionally been proposed as species.”

In Maryland, our periodical cicadas are only members of 17-year broods:  Brood II (last appeared 2013, next expected in 2030), Brood V (in western Maryland – last appeared in 2016, next expected in 2033), Brood X (last appeared in 2004, next expected in 2021), and Brood XIV (lasted appeared in 2008, next expected in 2025).  (17 & 13 Year Cicadas, Cicada Mania website.)  In Maryland, each time one of these broods crawls out of the ground and sets the trees singing, each of the 17-year species, M. septendecim, M. cassini, and M. septendecula, is represented.

Stragglers.  Herein lies another great source of confusion in this already complex life cycle.  The bulk of a brood emerge as expected at the end of their defined 13- and 17-year cycles, but varying numbers of so-called stragglers can emerge before or after their expected arrival year.  Generally, stragglers emerge four years early, one year early, or one year late.  In Maryland, stragglers from Brood X were awaited this year (four years before their 2021 due date) and, apparently, they’ve arrived.  Or, have they?  The verdict is not in.

A bit to my south, in North and South Carolina, and Georgia, Brood VI, a 17-year brood, has emerged on schedule.  Are the periodical cicadas here in Maryland a northern extension of Brood VI?  Entomologist Jonathan Neal raises this question on his blog Living with Insects in the post titled The 2017 Cicada Mystery (May 21, 2017), writing,
Brood VI emerged in NC, TN and GA earlier this year. Brood VI in the past has had heavy emergence in IL, MI and WI. The question cicada sleuths are asking: “Is the current emergence in MD Brood part of Brood X that is emerging 4 years early? Or could the emergence be part of Brood VI. If it is Brood VI, are there factors that cause it to increase its range or cause populations to fluctuate over time? If it is Brood X, what is causing large numbers to emerge early[?”] Many studies and tests will be needed to arrive at a conclusion.
Are they simply stragglers of Brood X arriving four years early?

Or are they the products of the Brood X group that emerged in 2000 (four years before their 2004 due date)?  Biologist Gene Kritsky, on the Mount St. Joseph University’s MSJ Cicada Website, observes that, at least in southwest Ohio, these Brood X stragglers came out in 2000 in numbers that were sufficient to overwhelm predators and allow some of them to mate and reproduce.  It’s those stragglers that he expects to be emerging now.  Are they becoming a separate brood, no longer stragglers from another brood?

So we’re left with a big unknown.  Absent data on the numbers of periodical cicadas that emerged in 2000 in Maryland, it’s hard to know which of these possibilities – stragglers from Brood X, range extenders from Brood VI, or products of the stragglers that emerged in 2000 – is the case here.

Other aspects of these life cycles have attracted lots of scientific interest.  The hypotheses about why these periodical cicadas have so synchronized their life cycles that all three species groups nearly always emerge in enormous numbers at the same time tend to center on safety in numbers.  Predators are overwhelmed, so many individual cicadas survive to reproduce.  That evolution has moved to 13 and 17, prime numbers, is often explained by reference to the challenge those periods pose to predators trying to harmonize their own shorter life cycles to those of their prey.  It has also been suggested that these periods ensure that cicadas breeding on different cycles will very seldom emerge at the same time, avoiding the prospect of crossbreeding that would doom the offspring.  (See Susan Milius, Mystery in Synchrony:  Cicadas’ Odd Life Cycle Poses Evolutionary Conundrums, Science News, July 13, 2013.)

Further, straggling is a longstanding phenomenon.  Some periodical cicadas are always early or late to the party.  Opinion about the current straggling raises the prospect that climate change has had an impact with warmer conditions prompting faster growth and earlier emergence.  As writer Scott Dance describes it, “[S]cientists say there are always some subsets of the 17-year cicada broods that don’t wait the full cycle before emerging.  These experts think cicadas ‘count’ in fours, and if they are big enough after 13 years, some crawl out sooner.”  (This Isn’t a Cicada Year, So Why Are They Now Showing Up Across the Mid-Atlantic?, Washington Post, May 20, 2017.)  But research by entomologist Richard Karban shows that the members of any specific brood do not develop in lockstep, some complete certain stages before their compatriots, but, in general, the early finishers, as science writer Susan Milius puts it, “end up waiting for the signal to emerge, giving the laggards time to catch up.”  (Mystery in Synchrony citing research by Richard Karban.)

Apparently, these 13- and 17-year cycles are relatively recent phenomenon in geological and paleontological terms.  Based on genetic studies, biologist Teiji Sota and his colleagues, conclude that the three species groups (Decula, Decim, and Cassini) separated some 3.9 million years ago, during the Pliocene Epoch.  They posit that this speciation process occurred when populations of their common ancestor became geographically isolated and evolved into separate species groups (allopatric speciation) and then, later, came back together to evolve their synchronized life cycles.  (Independent Divergence of 13- and 17-Y Life Cycles Among Three Periodical Cicada Lineages, PNAS, Volume 110, No. 17, April 23, 2013.)

Does the work by Sota et al. mean that no cicadas before, say, 3.9 million years ago had such long life cycles?  I don’t know.  They suggest that because these species have shown repeated shifting between 13- and 17-year cycles during their existence, there is probably a genetic basis for these life cycles that predates the separation into the three species groups.  Was it manifest before that point?  Again, I don’t know.  Cicadas, themselves, (not necessarily periodical ones) do go back, far earlier than the Pliocene.  The wonderful fossil cicada (unidentified as to genus and species) shown below is from the Eocene Florissant site in Colorado.  It's some 34 million years old.


(This picture is reproduced from the National Park Service’s Florissant website.)

Apparently the earliest cicada fossil that has garnered general agreement that it is, in fact, that of a cicada dates from the Early Cretaceous (more than roughly 100 million years ago).  (George Poinar, Jr., and Gene Kritsky, Morphological conservatism in the foreleg structure of cicada hatchlings, Novicicada burmanica n. gen., n. sp. in Burmese amber, N. youngi n. gen., n. sp. in Dominican amber and the extant Magicicada septendecim (Fisher) (Hemiptera: Cicadidae), 2012, accepted manuscript subsequently published in Historical Biology, Volume 24, Issue 5, 2012.)  But Poinar and Kritsky believe that the cicadid group goes back much farther, perhaps to the Permian Period.

I’ll close with some wonderful speculation (I assume that's what it is, speculation) by entomologist Scott Richard Shaw in his book Planet of the Bugs (reviewed previously in this blog).  He posits that insects played an essential role in the development of dinosaur diversity by being the source of protein for smaller, herbivorous dinosaurs which, in turn, were a source of protein, along with other insect-eating animals, for carnivorous dinosaurs.  Efforts in the insect world to deal with dinosaurs' incessant munching on its denizens prompted, Shaw observes, various kinds of avoidance strategies among insects.  Some turned to “behavioral escape mechanisms” in which case, writes Shaw, 
[I]t’s certainly possible that mayflies’ and cicadas’ mass synchronized emergences adapted and were fine-tuned in response to intense dinosaur predation.  (p. 121)
A neat thought.

Sunday, April 30, 2017

Sexual Dimorphism ~ Another Challenging Variable


This post was prompted by the recent publication of a fascinating article by paleontologist Jordan C. Mallon about our ability or, more specifically, our inability to distinguish between males and females in the available fossils for several prominent dinosaur taxa.  (Recognizing Sexual Dimorphism in the Fossil Record:  Lessons from Nonavian Dinosaurs, Paleobiology, 2017.)

Sexual dimorphism is present when characteristics of the males and the females of a given species differ.  These differences may be reflected in male and female morphology including such features as body shape (e.g., display features such as crests), body size, or coloring, and may also be found in variations in behavior.  Sexual dimorphism is an important attribute that is central to evolutionary biology, particularly as it relates to sexual selection.

With extant animals, some aspects of sexual dimorphism may be obvious as with the African lion species (Panthera leo) whose males sport a distinctive mane and may be somewhat larger than the females.  Pictured below are mounted specimens on display in the Hall of Mammals at the Smithsonian’s National Museum of Natural History.



A word of caution.  Having living animals available for study offers no certainty that we will, in fact, accurately identify sexually dimorphic traits.  The lions in the Hall of Mammal, as posed, promote the widely accepted canard that the female lions do all of the hunting for the pride and the males just lounge around.  It was only in this decade that careful tracking of male and female lions in Kruger National Park (South Africa) using GPS and other technology showed that females hunt in open areas while males do their hunting in denser vegetation shielded from observation.  (Scott R. Loarie, et al., Lion Hunting Behaviour and Vegetation Structure in an African Savanna, Animal Behaviour, Volume 85, 2013.)

Certain patterns of sexual dimorphism have been detected in extant animals.  For example, with respect to size and morphology, biologists Ehab Abouheif and Daphne J. Fairbairn observe, “In most species of animals, females attain larger body sizes than do males (e.g., most spiders, insects, fish, amphibians, reptiles), whereas in most birds and mammals, males are the larger sex.”  (A Comparative Analysis of Allometry for Sexual Size Dimorphism:  Assessing Rensch’s Rule, The American Naturalist, Volume 149, Number. 3, March, 1997, p. 540, references omitted.)

But all bets are off with extinct animals known from the fossil record.  Mallon is not alone in positing that the barriers to identifying the sex of extinct species are particularly high.  Armed only with fossils, we find ourselves without much of what might help to distinguish males from females including gender-specific behavior as well as some morphological attributes such as sex organs and coloring.  Without the information that observation of living animals provides, paleontologists face a daunting challenge.  As evolutionary ecologist Robert J. Knell and his colleagues have written,
Identifying sexual dimorphism in animals known only as fossils is often difficult; specimens of a particular species are sometimes rare, unique, or unavailable, and reliably identifying sex in fossils is often difficult or impossible.”  (Robert J. Knell, et al., Sexual Selection in Prehistoric Animals:  Detection and Implications, Trends in Ecology and Evolution, 2012.)
On the one hand, if the sex-related differences preserved in the fossil record are slight, then, as Knell et al. note, one must work with large samples (IF such sample sizes are actually available).  Apparently, it hasn’t been unprecedented for claims to be made about the sexes of dinosaur fossils based on bones from just two specimens (which is clearly an inadequate sample size).  At times, it may be differences in the sizes of features that distinguish males from females, not the presence or absence of such features in either of the genders.

On the other hand, “when dimorphism is strong, there is a risk that different sexes will be described as different species.”  (Knell, et al.)  That is, relying on morphology to identify species, as is a common and necessary practice in paleontology, poses the risk that significant differences in fossils, possibly related to sexual dimorphism, might be treated as indications of the presence of different species, not the two sexes of the same species.

From his analysis, Mallon concludes that, with the dinosaur fossils at hand, paleontologists, for the most part, cannot tell whether an individual dinosaur was male or female.  In this vein, I would add that one must ignore the nicknames given some of the iconic dinosaur fossil skeletons such as the Field Museum’s Tyrannosaurus rex which is known as “Sue,” the Triceratops horridus cast on display in the Last American Dinosaurs exhibit at the Smithsonian’s National Museum of Natural History which is fondly called “Hatcher” and its companion T. rex cast in the same exhibit carrying the nickname “Stan.”  (The National Museum has Hatcher's fossil bones, while its Stan is just one of many casts that can be found worldwide.  Stan's original fossil bones are in the Black Hills Institute.)  These nicknames honor the collectors who found the original fossils – Sue Hendrickson, John Bell Hatcher and Stan Sacrison.  In all fairness, the Field Museum’s T. rex was nicknamed Sue by Peter Larson because he believes this specimen was, in fact, female.  (See, Jacqueline Ronson, Sue the Tyrannosaurus Has a Sexual Identity Crisis, Inverse Science, December 1, 2016.)

Yes, there are some dinosaur fossils that can be identified as female because they carry eggs or have a medullary bone which, in contemporary birds, supplies the calcium used to fashion egg shells.  Mallon concludes that, for the taxa he studied (nine prominent species including Tyrannosaurus rex, Allosaurus fragilis, a couple of Stegosaurus species, and Protoceratops andrewsi), the available evidence offers “no support for sexual dimorphism.”  Mallon takes pains to make it clear he is not saying that such dinosaurs were not sexually dimorphic, simply that, in his considered view, the fossil record is inadequate to make such a claim.

This is certainly a thought-provoking, revisionist conclusion and it’s not just relevant for dinosaurs.  Mallon lays out the conditions under which sexual dimorphism might be successfully detected in different fossil taxa.

For me personally, his article brought me up short.  I have to admit that for the years that I’ve collected vertebrate fossils (principally shark teeth), I have never pondered the gender of the animals and how that might be reflected in the fossils I have at hand.  So much for my intellectual curiosity and my efforts at taxonomy.

Considering just fossil shark teeth, several of the most important variables that might account for differences in the teeth under study are:

  • natural variation among individuals within the same species (hey, this variability is the material that natural selection work with),
  • chronological age of the specimens (not only might teeth from younger sharks be smaller, they might also differ in terms of shape),
  • position of the teeth in the jaws (most shark families are heterodonts, that is, teeth vary by location in the jaws; depending upon the shark, teeth from the upper jaws can differ from those in the lower jaw, and/or they can vary by location within a specific jaw),
  • differential influence of the environment on the health and development of individuals from the same species,
  • taphonomic processes (i.e., what happens to an organism in death) which may introduce variability in the fossils that emerge millions of years later, and
  • sexual dimorphism.

This list is based primarily on paleontologist Bretton W. Kent’s Fossil Sharks of the Chesapeake Bay Region (1994, p. 2).  Though he does include sexual dimorphism as a factor behind some variation in fossil shark teeth, as far as I can tell, it’s only in a very few species that sexual dimorphism has been identified.  He cites it in just two fossil shark species found in the Chesapeake Bay region – Hexanchus (cow sharks), and Rhizopriondon (sharpnose sharks).

Ultimately, it’s somewhat ironic that, despite his warnings and the unlikelihood of detecting sexual dimorphism in most of my collected fossils, Mallon’s piece has prompted me to be sensitive to that possibility.

Thursday, March 23, 2017

A Point With Multiple Dimensions


I manage to confine my collecting to a few, discrete interests, though the temptation is always there to add another.  I admit I felt a tug as I read novelist Gary Shteyngart’s account of his obsession with expensive, mechanical wristwatches, sparked by Donald Trump’s rise to power over the course of 2016.  Yes, it seemed to him that the time is out of joint.

How almost irresistible when he writes lovingly about his four-thousand-dollar Nomos Minimatik Champagner watch with its “exhibition-case back” revealing its inner mechanics:
[It] is a riot of sunburst decoration, tempered blue screws, and a small constellation of rubies.  A tiny golden balance wheel spins back and forth, regulating the time . . . , and this action gives the watch the appearance of being alive.  It is not uncommon for some watch enthusiasts to call this part of the watch its “heart,” or even its “soul.”  (Shteyngart, 2017, p. 38.  Full citations to all reference are provided in the Sources section at the end of this post.)
But, no, collecting mechanical watches would be far too expensive and possibly smack of affectation.  Even the few interests I’m feeding are too many.

Nevertheless, there is a virtue to multiple interests because, at some rare moments, my interests intersect, suggesting there may be some sort of logic to my collecting mania, not simply a psychological need.  So it is with a recent purchase, a rather small Native American projectile point with a broken tip from New York.  Though certainly not of high quality nor expensive, this point is profoundly appealing because in it are met three of my collecting passions – points, minerals, and fossils.
This is a triangular Madison Point, an identification based on William A. Ritchie’s A Typology and Nomenclature for New York Projectile Points (1961, p. 33-34), which squares with what the seller asserted.  According to Noel D. Justice, Madison Points were part of many “cultural phases across eastern North America” during the Late Woodland period, probably dating from 800 to perhaps as late as 1350 CE (Justice, 1987, p. 224, 227).  Ritchie describes Madison Points as “very finely chipped by pressure flaking” (p. 34), though I assume that the artisan who fashioned this point used some direct percussion flaking initially to shape it.  Ritchie also notes, “Among the northern Iroquois the principal material employed was Onondaga flint from the exposures of central New York and the Ontario Peninsula.”  (p. 34)  Absent any provenience (beyond the geographic state in which it was recovered), I won’t make any such claims for this particular point.

Nevertheless, my point is manufactured from Onondaga chert.  This gray chert is often referred to as flint, though, as I have learned, geologists apply the term chert to all of those rocks that artifact and rock collectors tag with such terms as flint or jasper based on differences in color.  As Prothero and Lavin write, “The color differences are not only superficial, but frequently misleading, especially since heat treatment may change the color range of a particular chert.”  (Prothero and Lavin, 1990, p. 561.)

Chert has a geological life story understood in general, but apparently not in its smallest details.  It is a hard sedimentary rock composed of silica (silicon dioxide) in the form of very tiny crystals, either only discernable under a microscope (microcrystalline) or not even then (cryptocrystalline).  This material comes into being through what has been characterized as “an obscure chemical process”  (Roberts, 1996, p. 24) involving the precipitation of silica from solution.  Chert can be found as nodules, lenses, or beds depending upon the environment within which it forms.  Given its fine crystalline composition, chert fractures conchoidally, that is, “fracture faces have smooth, curved surfaces” with sharp edges (Ostrom and Peters, 2012, p. 12) which makes it ideal for fashioning projectile points, scrappers, and knives.

Assuming the chert in this point was found as a nodule, which is likely given its origin in the Onondaga Formation dating from the Devonian Period, it is also highly likely that the source of its silica was the hard silicon elements (spicules) that sponges secrete to give themselves structure and a means of protection.  (Maliva et al., 1989, p. 523)

From their analysis of thin slices of the chert from different sites in the northeastern U.S., Prothero and Lavin find that the chert in Native American implements can often be easily identified as to its place of origin.  I found their description of chert from western New York State particularly applicable.  They write, in part, of this chert:  “Small (0.1 mm in diameter) dolomite rhombs are abundant, but there are few large rhombs.  Fossils and pyrite are common . . . .”  (Prothero and Lavin, p. 570)

Two elements of that description ring very true for the point I have in hand.  First, there are the dolomite rhombs which are the rhomboidal crystals or impressions of those crystals left by some dolomite caught up in the geological process creating the chert.  The mineral dolomite is a calcium magnesium carbonate and is the primary component of dolomite, a biogenetic sedimentary rock.  Pictured below is a close-up (30x) of a small portion of one face of my point.  This chert, under magnification, appears less strongly colored than a more removed view would have it since the color is, I surmise, often the cumulative effect of impurities in the mineral.  I have marked several of the rhomboidal shapes that appear on the surface of this section of the point; these are, I assume, dolomite rhombs.


Then there are the fossils in Onondaga chert which is where another of my collecting interests finds play in this point.  Pictured below is the full point (minus, of course, its tip) with an inset showing a closer look at a small hole in its surface – a fossil mold.
Given the common occurrence of fossils in Onondaga chert, it isn’t at all that surprising that Native American stone artifacts fashioned from this material would, sometimes, contain a fossil or two.  Source of the mold in my point?  The seller suggested coral and he may well be right.  But, the impression in the point strongly reminds me of columnals from some types of crinoids.  These animals, also known as sea lilies, create long structures of “stems” topped with long branch-like appendages for food gathering.  Secreted calcium carbonate pieces (ossicles) provide crinoids with structure and protection; in the stem, the stacked individual ossicles are known as columnals.  Crinoids are still with us, but their fossil record goes back well before the Devonian Period, which means that, yes, they were around when and (based on my reading) where the Onondaga Formation was laid down.

Pictured below is a bit of a Devonian crinoid fossil (first image) I found at a site in Maryland exposing Needmore Shale (which has been stratigraphically correlated to the Onondaga Formation in the Devonian’s Eifelian Age, about 393 – 388 million years ago).  The arrow points to where some columnals remain (the grooves to the left of the head of the arrow are where columnals have been lost).  The columnal in the second image, the first one remaining in the stem, appears to match nicely the mold left in my point.



Sure, not conclusive evidence, but wonderfully suggestive.

Shteyngart’s New Yorker essay is, ultimately, quite dark.  As the presidential campaign unfolds in 2016, his need to buy watches spirals out of control; he is “in deep.”  I may be contorting his message, but when he writes of how people cope and coped in Putin-era and Soviet-era Russia (e.g., collecting deluxe shaving equipment or compulsively doing mental math problems), I read him as saying that, in a society out of joint, we turn to find refuge and security in “the particular and microscopic” because they are “the only things that could still prove reliable.”

He may have a point.


Sources

Noel D. Justice, Stone Age Spear and Arrow Points of the Midcontinental and Eastern United States, 1987.

Robert G. Maliva et al., Secular Changes in Chert Distribution:  A Reflection of Evolving Biological Participation in the Silica Cycle, PALAIOS, Volume 4, Number 6, December 1989.

Meredith E. Ostrom and Roger M. Peters, Wisconsin Rocks and Minerals, Wisconsin Geological and Natural History Survey, ES046, 2012.

Donald R. Prothero and Lucianne Lavin, Chert Petrography and Its Potential as an Analytical Tool in Archaeology, in N.P. Lasca and J. Donahue, editors, Archaeological Geology of North America, Geological Society of America, Centennial Special Volume 4, 1990.

William A. Ritchie, A Typology and Nomenclature for New York Projectile Points, New York State Museum and Science Service, Bulletin Number 384, April 1961.

David C. Roberts, A Field Guide to Geology:  Eastern North America, 1996.

Gary Shteyngart, Time Out:  Confessions of a Watch Geek, The New Yorker, March 20, 2017.

Tuesday, February 28, 2017

Lost in Another Taxonomic Adventure

You are in a maze of twisty little passages, all alike.
~ Will Crowther’s Colossal Cave Adventure

The classic, late 1970s text-based computer game, the Colossal Cave Adventure (also carrying various other names, including Adventure or ADVENT), begins:
You are standing at the end of a road before a small brick building.
With patience, you can explore the building, follow the nearby stream to a locked grate, and enter a colossal multi-chambered cave.  With even greater patience, you can explore the myriad passages and chambers of the cavern, accumulating treasures, avoiding, in the process, such threats as axe-throwing dwarves.

The game was a source of endless frustration for me because, when I was lost in the cave’s passages, I didn’t have the large reservoir of patience needed to map their layout (though I knew an option was dropping items as I went).  That’s why it’s an appropriate analogy (at least, for me) to the process of identifying particular fossil specimens.  All too often, in this effort at retracing steps taken by taxonomists, I end up lost in a maze.
In a stream in woods near the town of Caledonia, Alabama, a Paleocene strata outcrops.  With commitment and patience, you may discover that the stream yields a fossil-rich matrix, abounding in two kinds of microfossils – ostracodes and foraminifera.
So might begin my present adventure in navigating through a taxonomic "cavern."

Both fauna from this geologic strata have been described in some detail in separate treatises; in both cases, well over half a century ago.  For his master’s thesis, Gordon C. Munsey, Jr., studied the ostracodes collected here.  (An ostracode is a microscopic crustacean living inside the two calcium carbonate shells it secretes.)  The paper he wrote based on the thesis is titled A Paleocene Ostracode Fauna From the Coal Bluff Marl Member of the Naheola Formation of Alabama (Munsey, 1953; a highlighted author's name links to the publication in question, and full citations to all publications cited are provided in the Sources section at the end of this post).  He was following in the footsteps (quite literally) of the preeminent foraminifera expert Joseph A. Cushman who, in 1944, had published A Paleocene Foraminiferal Fauna From the Coal Bluff Marl Member of the Naheola Formation of Alabama (Cushman, 1944).  (A foraminifera, or foram, is a unicellular organism, a protist, that, in most species, secretes a calcium carbonate shell that it adds to as it grows.)

Taxonomy is the science of arranging or classifying.  The two-part scientific names (binomen), drawn from Greek and Latin, that species bear are the work of taxonomists.  The first part is the specimen’s genus (italicized and capitalized); the second is the species name (italicized and lower case).  (Taxonomy has been treated previously in this blog, such as in this post,)  When done well, taxonomy reflects the careful application of encyclopedic knowledge of the taxon being analyzed, attention to detail, and consideration of a taxon’s evolutionary relationship to other taxa.  As paleontologist Donald R. Prothero has described it:
[T]axonomy is not just naming species, because species and higher taxa reflect evolution.  Taxonomists do much more than label dusty jars in a museum.  They are interested in comparing different species and deciding how they are related and ultimately in deciphering their evolution history. . . .  In short, they look at the total pattern of natural diversity and try to understand how it came to be.  (Prothero, 1998, p. 43.)
My favorite characterization of the science (though I’m not sure exactly what it means) is:  “Taxonomy is an art and we are all painters.”  (McCartney and Harwood, 1992, p. 819.)  To be honest, it frequently seems that it’s the same canvas being painted from different vantage points at different times by different painters.  A maze, indeed.

Given a small sample of material from the Alabama stream site, I was foolhardy enough to begin picking through it, crosschecking my finds against Munsey’s and Cushman’s papers.  It was an effort that drew me immediately into a taxonomic muddle that, from the outset, mirrored the Colossal Cave Adventure.  And, frankly, I don’t think my getting lost was always my fault (as the saga that follows might show).

An example of the very first type of ostracode that I tried to identify is pictured below.  Shown is a right valve – exterior (left image) and interior (right).  (As will become clear, I think it important to note that I have found several specimens like this one.)


Here is my description of this kind of ostracode (some of these aspects are visible in the pictures, some are not due to the limits of my microscope and photographic equipment).  It has the following attributes (with a few of the preferred taxonomic adjectives in parentheses and italicized):
  • a spiny (spinose) surface;
  • a rounded anterior and a pointed (acuminate) posterior with a narrowed (compressed) upper half;
  • perhaps two rows of small spines that follow and accentuate the anterior marginal rim;
  • large, blunt spines marking the lower half of the posterior marginal rim;
  • dorsal and ventral margins lined with spines;
  • several nodes (perhaps tight clusters of spines), mostly on the central portion of the shell, with the most prominent one about a third back from the anterior end;
  • a net-like (reticulate) pattern on the surface of the shell where not obscured by the spines;
  • internal ventral and dorsal margins that are mostly straight; and
  • hinges that involve balls (right valve) and sockets (left valves) straddling a straight bar.
This description was a productive exercise because it helped me wend my way through some of the taxonomic maze.

Here then are the highlights (or something) of my adventure with this species.  Described below are the major guideposts that I found; as is clear, this was a trip with some time travel elements.  The heading for each section below provides the year of publication of a relevant paper and the species name assigned in that paper which I thought applied to my specimens.  (I consulted other publications, but the ones cited are those that moved me along - to where was not always clear.)

1953 – Cythereis reticulodacyi

Based on photographs in Munsey’s 1953 paper (Plate 4, figures 1 and 16), I tentatively identified my specimens of this ostracode as Cythereis reticulodacyi Swain 1948.  I had only the pictures in this paper to go on because Munsey provided no description.  The images do resemble the specimens I have.  He noted that it’s “common” in the Coal Bluff Marl, and that adult specimens have a “heavily spinose surface.”

1948 – Cythereis reticulodacyi

Munsey’s main contribution to my effort was offering a path to follow; he cited the publication in which this species was first described by paleontologist Frederick M. Swain (Swain, 1948).

Swain, working with Eocene material from a well drilled in the Eastern Shore of Maryland, had identified a new species of ostracode (p. 202).  His description largely jibed with mine.  We agreed on the general shape and ornamentation of the anterior and posterior margins, though, among other differences, he asserted that the anterior had three (not two) rows of fine spines and the posterior had two.  We were in relative agreement regarding the surface, which he described as “reticulately ornamented with a pattern of ridges, at the junction of which there are blunt spinelike projects.”  He also noted that there was a grouping of nodes.

Rather disturbing for me was his admission when he described the hinge elements of this species, that he could only write about the configuration of the hinge of the left valve because he had found just one specimen, a single left valve.

I suppose it was naive to find it stunning that, from just one shell, Swain had identified a new species.  Perhaps I should have just shrugged my shoulders because such an action is not unprecedented in taxonomy.  Still, I think it would have made more sense for him to have considered ascribing it to a genus (the one he presumably felt was evident) without taking the next step to apply a new species name (clearly, he didn’t think his sole specimen belonged to any previously identified species).

There were more distressing twists in the trail at this juncture.  When I looked at the two photographs of this specimen, which the paper identified as figures 13 and 14 of Plate XIII, it became apparent quickly that those figures in that plate weren't what he described.  It turned out that the plate with these photographs had been misnumbered; Plates XIII and XIV were transposed.  After resolving that issue, the disappointments continued to multiply because the images (in the digital version that I had available to me) were somewhat light-struck and out-of-focus.  Also, his sole specimen bore only a somewhat limited resemblance to my specimens.  His photographs (exterior and interior views) are shown below.  (Hopefully not erroneously, I have treated Swain's paper, which appeared in a publication from the State of Maryland, as a public document, carrying no copyright restrictions on my use of these images.)


Where was I at this juncture in this adventure?  Was my specimen actually C. reticulodacyi?  No, apparently not.

1957 – Trachyleberis ? spinosissima

In 1957, geologist and paleontologist Willem Aaldert van den Bold identified some Paleocene ostracode specimens as Trachyleberis ? spinosissima (van den Bold, 1957, p. 9.)  (The question mark in his identification indicated that he was uncertain about the genus of these ostracodes.)  Subsumed under this new identification are Cythereis reticulodacyi.  (His citation to this species reads: “? Cythereis reticulodacyi Swain” which is puzzling since Swain didn’t use a question mark.)  Significantly, van den Bold also indicated that he applied the T. ? spinosissima name to the specimens that Munsey had identified as C. reticulodacyi.

Losing the Cythereis genus name wasn’t too surprising because, over the years, that genus had become a “dumping ground” for myriad genera and their species (Puri, 1956, p. 274).  At least as early as the mid-1950s, taxonomists were at work, trying to clarify matters by reassigning many of the species  to genera in the Trachlyeberidinae subfamily.

But I was uncomfortable at stopping the journey here.  Not only was van den Bold uncertain about the genus, his specimens were so abraded that his drawings of T. ? spinosissima lacked spines, one of the defining attribute of my specimens.  I delved deeper into the taxonomic history of Trachyleberis spinosissima to see if it might reveal whether or not this was actually the species I had in hand.

1889 – Cythereis spinosissima and Cythereis spiniferrima

The taxonomic history for T. spinosissima stretches back to the late 19th century when T. Rupert Jones and C. Davies Sherborn first identified Cythereis spinosissima.

I cannot find a copy of the publication in which that description appeared, but, the authors later renamed C. spinosissima as C. spiniferrima in an 1889 publication which I do have.  (Jones and Sherborn, 1889, p. 34-35.)    (According to the 1889 publication, the name originally given was C. spinossissma, not C. spinosissima as it’s spelled in van den Bold and everywhere else I’ve seen it.  I’m not sure who’s in error.)

Turns out Jones and Sherborn worked with just two specimens (sigh) – a right and left valve – from the Eocene London Clay.  Still their description dovetails fairly nicely with mine as does the drawing they provided.  Pictured below is the woodcut of the right valve.  I have turned this image so it’s oriented horizontally.


I wasn’t comfortable leaving van den Bold with the last word, given his uncertainty, so I ventured forth once more, this time in search of Trachyleberis spinosissima to see if van den Bold's doubt had been resolved later.

1965 – Trachyleberis spinosissima

In a search for more recent taxonomic treatments of Trachyleberis spinosissima, I found just one (I’ve ignored passing mentions of this species).  In 1965, William Kenneth Pooser described specimens he identified as T. spinosissima as follows:
Characterized by a strongly rimmed anterior margin bearing double row of short stout spines, strongly compressed and triangular posterior, and coarsely reticulate carapace with numerous spines arising from junctions of the reticulations.  (Pooser, 1965, p. 55)
Ah, a concise description, and mostly in sync with mine.  The external view of a right valve that Pooser published (shown below) matches my specimens rather well.


(This image, used with permission, is from The University of Kansas Paleontological Contributions, Article 8, Biostratigraphy of Cenozoic Ostracoda from South Carolina, William Kenneth Pooser © 1965, The University of Kansas Paleontological Institute.)

And, thankfully, in Pooser's work van den Bold's T. ? spinosissima is subsumed under T. spinosissima as are Jones and Sherborn's Cythereis species names (C. spinosissima and C. spiniferra).

At this stage, somewhat exhausted, I have settled down in the Trachyleberis spinosissima chamber of this cave, where I remain (at least for the moment).

Closing

In closing, I must mention the wonderful YouTube video series The Brain Scoop at The Field Museum hosted by Emily Graslie which had an episode (March 24, 2016) devoted to taxonomy.  In it, Graslie asked several taxonomic experts how one might classify an array of different kinds of candies.  The discussion is informative, despite some of the distractions that candy brought to it.  On a serious note, regarding the science of taxonomy, The Field Museum’s Oliver Rieppel, curator of fossil reptiles, asked,
Is it us who brings order to the world or is the world coming to us in an ordered way?  And probably it’s the first way around.
And sometimes the order someone tries to bring may leave us lost in a maze of twisty little passages.


Sources

Joseph A. Cushman, A Paleocene Foraminiferal Fauna From  the Coal Bluff Marl Member of the Naheola Formation of Alabama, Contributions from the Cushman Laboratory for Foraminiferal Research, Volume 20, Part 2, No. 255, June, 1944.

T. Rupert Jones and C. Davies Sherborn, A Supplementary Monograph of the Tertiary Entomostraca of England, Printed for The Palaeontographical Society, 1889.

Kevin McCartney and David M. Harwood, Silicoflagellates From Leg 120 on The Kerguelen Plateau, Southeast Indian Ocean, in S.W. Wise, Jr., et al., Proceedings of the Ocean Drilling Program, Scientific Results, Volume 120, 1992.

Gordon C. Munsey, Jr., A Paleocene Ostracode Fauna From the Coal Bluff Marl Member of the Naheola Formation of Alabama, Journal of Paleontology, Volume 27, Number 1, January, 1953.

William Kenneth Pooser, Biostratigraphy of Cenozoic Ostracoda From South Carolina, Arthropoda, The University of Kansas, Paleontological Contributions Article 8, January 15, 1965.

Donald R. Prothero, Bringing Fossils to Life:  An Introduction to Paleobiology, 1998.

Harbans S. Puri, Two New Tertiary Ostracode Genera From Florida, Journal of Paleontology, Volume 30, No. 2, March 1956.

Frederick M. Swain, Ostracoda From the Hammond Well, in Cretaceous and Tertiary Subsurface Geology, State of Maryland Board of Natural Resources, 1948.

Willem Aaldert van den Bold, Ostracoda From the Paleocene of Trinidad, Micropaleontology, Volume 3, No. 1, January, 1957.

 
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