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).


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.


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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