Monday, September 27, 2010

Fragility of the Ecphora

It seems a minor miracle to find, amid the shell debris marking the shoreline, an even partial fossil shell from an Ecphora, an extinct sea snail or gastropod.  Paleontologists have used the Ecphora as an index fossil; the presence of specific Ecphora species can be used to date rock and other fossils.  For collectors, of whatever stripe, the Ecphora shells cast a spell by their sheer beauty which is heightened, for me, by the seemingly near impossibility of their survival as intact fossils during that final passage from burial in rock and sand to exposure.  The beaches where I hunt fossils along the Calvert Cliffs formation on the western shore of the Chesapeake are littered with little reddish brown shards of Ecphora shells, a stark reminder of the hazardous life of a fossil.  The fatality rate of these fossils after exposure to the elements must be staggering.

Ecphora are distinguished by the ribs or costae that run like exposed, elevated rails around the exterior of the shell.  The number and shape of those ribs are largely determinative of the specific species of Ecphora that one may have in hand.  The complexity and perceived delicacy of these ribs explains part of their attraction.  Often these shells have an appealing russet color, unusual in a fossilized mollusc, an attribute that also seduces the collector.

Last week, on a hunt in record breaking heat along a Chesapeake Bay beach, I came upon the specimen pictured below.  It sat exposed, wet, upright, and vulnerable amid chunks of clayey material that had fallen from the cliffs.  For seasoned collectors of Ecphora, this isn’t much, a seriously damaged specimen.  For me, it is special, as close as I’ve come to finding a complete specimen of whatever species of Ecphora.

The specimen shown above (1 3/4 inches long, 1 1/8 inches high, and 1 3/8 inches wide) I’ve identified as Ecphora tricostata Martin, an early to mid-Miocene fossil (some 15 to 17 million years ago).  The three prominent costae narrowed the field appreciably as did the location of the find – Calvert Formation.  For confirmation, I relied primarily on Ward and Gilinksy’s article entitled Ecphora (Gastropoda:  Muricidae) from the Chesapeake Group of Maryland and Virginia.  It appeared in the March 15, 1988, edition of The Academy of Natural Sciences of Philadelphia’s journal Notulae Naturae.  It fits in terms of location and its original description:  “body whorl large, with three very prominent elevated revolving ribs with a fourth rudimentary one below it on the largest specimens” (p. 3)  I detected the rudimentary rib on the specimen I found (I think it can be made out in the picture of bottom of the shell).  The other possible Ecphora with three ribs that may be found in the Calvert Formation is E. pamlico Wilson – the location fits but, among other distinguishing attributes, E. pamlico lacks the rudimentary fourth rib and has ribs that are not as prominent as those on my specimen.  (At least, that’s how I'm reading and applying the literature - the two species are clearly closely related.)

The fragility of, and fatality rate among, the Ecphora are not limited to their physical survival but also to their experience of the vicissitudes of the taxonomic process (clearly, not something unique to the Ecphora).  The naming and renaming of Ecphora species is a delightful and ongoing story

The 1980s witnessed a modest taxonomic blossoming of Ecphora species.  In particular, Druid Wilson of the Smithsonian nurtured the process in an article entitled Species of Ecphora, Including the Subgenus Stenomphalus, in the Pungo River Formation (appearing in Geology and Paleontology of the Lee Creek Mine, North Carolina, II, 1987 – full text appears on the Smithsonian website).  In this article, Wilson offered up three new species of Ecphora.

[An aside:  Because it’s germane to a tiny part of my story, the taxonomic name of each individual species given in this posting includes the name of the individual who was the original author of each species’ name.  Following proper nomenclature, if that genus and species combination were modified after initial publication, then the original author’s name is enclosed in parentheses.]

Most important for those collecting Ecphora in Maryland, Wilson stripped the state of the Ecphora quadricostata (Say).  He asserted that “[i]t is now well known that most if not all of the fossils described by [Thomas] Say in 1824 came from Virginia rather than Maryland . . . .” (p. 22)  As a result, he wrote, the “common Ecphora of the St. Marys Miocene of Maryland masquerad[ed] under the name ‘Ecphora quadricostata,’ which properly belongs to the Yorktown species of Virginia.”  (p. 23)  The specific species of Ecphora with four ribs coming from the St. Marys Formation along the Chesapeake that had been misidentified all these years, he renamed as Ecphora gardnerae.  The species name gardnerae is in honor of Julia A. Gardner (1882-1960), a geologist with the U.S. Geological Survey and a specialist in molluscs.

The following year, Ward and Gilinsky went Wilson one better, concluding that there were actually several subspecies of E. gardnerae, so the one Wilson identified was given a subspecies name and is now known as E. gardnerae gardnerae Wilson.  (p. 7)

Adding a fillip to this tale is the fact that, in 1984, the Governor of Maryland had signed legislation naming Ecphora quadricostata (Say) as the official fossil shell for the state.  Now, science had pulled out the rug from under the state.  When legislation correcting the error was enacted in 1994, the state had as its official fossil shell the “Ecphora gardnerae gardnerae (Wilson)” – well, they got it almost right.  Technically Wilson’s name shouldn’t be in parentheses.

The 1999 edition of Miocene Fossils of Maryland, by Harold E. Vokes, et al., published by the Maryland Geological Survey, identifies three Ecphora species as being found in Maryland (missing from this publication is E. pamlico Wilson).  In the illustration below, taken from Miocene Fossils of Maryland, they are #2 – E. gardnerae gardnerae Wilson, #3 – E. meganae Ward and Gilinsky, and #4 –  E. tricostata Martin.  The first shell image (#1) is a reproduction of what is purportedly among the first scientific illustrations of a U.S. fossil, published in the 1770 edition of Martin Lister's Historiae Conchyliorum.  It’s clearly an Ecphora, but which one?  The Maryland Geological Survey suggests that it's E. gardnerae gardnerae.  To others, that's certainly unclear.  Remnant of the masquerade?  (Numbers 5 and 6 are of a species of different genus of gastropod – Siphonalia devexa (Conrad).)  (The Ecphora portion of Miocene Fossils of Maryland is available on the MGS website.)

Maryland in this instance was caught by the crosscurrents coming from a vigorous scientific exploration and reexamination of the Ecphora genus.  Not sure what the excuse is for Maryland choosing, in 2004, something called the "Patuxent River Stone" as its state gem.  This has stirred controversy from the beginning.  Indeed, in 2002, legislation to do this was reported unfavorably from committee.  So, what is this stone really?  A recognized gem or not?  Agate, as its proponents label it, or, perhaps, something much more mundane like iron-stained quartz?  Ah, give me the scientific currents swirling around the beautiful Ecphora any day.

1 comment:

  1. Thank you for your arrival! I just found one of these today at calvert cliffs, 4 ribs and was wondering what it was!


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