Tuesday, May 6, 2014

Open Nomenclature and Lagodon Fish Teeth ~ Navigating Between Certainty and Uncertainty

Use of open nomenclature is the procedure by which a taxonomist comments upon the identity of a specimen that cannot be readily or securely determined.
                   ~ Peter Bengtson, Open Nomenclature, Palaeontology, 1988, p. 223.

Coming at scientific nomenclature and taxonomy from the land of amateurs, I am always convinced that the fossil specimen I have in hand has a name, I just don’t know it.  It’s a name I need to discover.  But, sometimes, when I do find it, the name carries a sign that the taxonomist, himself or herself, harbored some degree of uncertainty about the name bestowed.  There remains doubt and this post is about such doubt.

The International Code of Zoological Nomenclature, administered by the International Commission on Zoological Nomenclature, is “a uniform system of zoological nomenclature ensuring that every animal has a unique and universally accepted scientific name.”  It is my understanding, that the Code itself provides no way of indicating when a taxonomist may have some degree of doubt about the identification of a specimen.

Open nomenclature, an unofficial facet of scientific nomenclature in zoology and unrecognized by the Code, allows scientists to do just that – alert the community to different levels of ambiguity about an identification.  Paleontologist S.C. Matthews captured well the usefulness of open nomenclature:
By giving taxonomy a means of stretching (in an entirely honest and proper way) the limits of existing knowledge, it [open nomenclature] by itself indicates where improvements are needed and in which direction they might be sought.  It permits us to build any such improvements into nomenclature left open for that purpose, and this without any upset of established names.  (Notes on Open Nomenclature and on Synonymy Lists, Palaeontology, Volume 16, Part 4, 1973, p. 714.)
Open nomenclature involves the use of certain abbreviations and punctuation marks (such as aff., cf., ?, or sp.) in the scientific name given to a specimen as a way of indicating the extent to which the namer harbors doubt or some question about the assignment.  Paleontologist Peter Bengtson’s article (cited in the epigraph) has become a key guide to open nomenclature conventions.  In it, he gave several hypothetical examples to help explain how he believed each of these abbreviations and punctuation marks should be used (p. 226).  Relevant to the discussion which follows in this post are the following:
Agenus cf. aspecies – under Bengtson’s protocol, the “cf. indicates that the identification is provisional.”  In this instance, given the placement of the “cf.” before the species name, it’s the species affiliation that is provisional.  “Cf.” is the abbreviation for the Latin confer meaning “compare to.”
Agenus aspecies? – here, the “?” following the species name indicates that species identification is “uncertain.”  If it had followed the genus name, that would have been uncertain.  According to Bengtson, the “?” signals greater uncertainty than “cf.”
Agenus sp. – the species identification “is impossible or has not been attempted.”
My present adventure in open nomenclature began, as taxonomic issues usually do for me, with some fossil finds that I struggled to identify.  But the full story requires a look back more than a century and half.

Medical doctor and naturalist John Edwards Holbrook (1794-1871) gave the name Lagodon to the extant pinfish genus in his book, Ichthyology of South Carolina, first published in 1855.  He offered no explanation for the name, but was clearly responding to the fish’s teeth.  Lagodon is a combined form of two Greek words –  lago for “hare” and odon for “tooth.”  So, the fish genus is hare’s or rabbit’s tooth.  (For better or worse, Bugs Bunny comes to mind.  The common name, pinfish, apparently refers to its small, first dorsal spine.)

According to the Virginia Institute of Marine Science, the pinfish lives in the Atlantic primarily off the southeastern coast of the United States, as well as in the Gulf of Mexico.  It commonly grows to about 7 inches in length, and is a popular bait fish.

Also, it features distinctive incisors and, thus, offers a small paleontological puzzle which involves open nomenclature.

Pictured below is the beautiful lithograph of L. rhomboides from Holbrook’s 1860 version of the book.  Though the 1855 version features a similar plate, the later one is somewhat more colorful and offers additional, isolated views of the fish’s scales and mouth.

That I have digital access to Holbrook’s 1855 publication through the Internet Archive is a marvelous thing because it is a decidedly rare volume.  Only a few copies of the book had been produced in 1855, when the Artists’ Building in Philadelphia, where the artwork was housed, burned down.  In the fire, Holbrook lost all of the book’s original drawings, lithographic stones, and plates.

Undaunted, over the next five years, he had the drawings redone and made some minor edits to the text.  He reissued the book in 1860, at which time, he sought to “recall” all of those copies that had been previously published, offering the new edition in their stead.

For taxonomic purposes, the earlier edition holds sway, no matter the limited number of copies printed and the author’s effort to pull all of that edition from circulation.  As a result, any new name applied by Holbrook in that volume should bear the date of 1855.  So, for example, the Federal Government’s Interagency Taxonomic Information System cites the Lagodon genus as:  Lagodon Holbrook, 1855.

Here’s how Holbrook described the teeth of Lagodon (1855 edition, p. 56):
. . . incisor teeth broad, trenchant, and cleft at their cutting margin; . . . . 
(Based on the various definitions of “trenchant” in the Oxford English Dictionary, I would say Holbrook used the adjective simply to say the tooth had a cutting edge.)  In other words, the apex of the crown spreads out parallel to the jaw line and the crown is split into two cusps.

The paleontological puzzle surrounding Lagodon arises from the appearance in the fossil record, as far back as the Miocene, of teeth that apparently look, for all the world, almost exactly like those in the extant L. rhomboides (the fish pictured above) which is the only species presently assigned to this genus.  (See Lagodon entry in the ITIS Catalogue of Life:  2014 Annual Checklist, Y. Roskov, et al., eds., 2014.)

Here are views (profile and lingual side) of two fossil teeth that I found.  The first was discovered in matrix inside articulated clam shells (Glycymeris parilis) likely eroded from the Calvert Formation along the western shore of the Chesapeake Bay; the second was found in material from the Pungo River Formation in the Lee Creek Mine (North Carolina).  Thus, both of these teeth are early-middle Miocene (roughly 16 million years ago, give or take a few million years).

Certainly there are differences between the two.  The Calvert specimen (top) does not have the split crown of the Pungo River specimen (bottom), and is also appreciably smaller (note that the scale bars in the two pictures differ).

But they share some important similarities.  They both have the scoop-like form on the lingual side, the curved profile, and the same orientation of the oval shape of the hollow root, with the longer axis of the root perpendicular to the apex of the crown.  The Pungo River specimen appears to match Holbrook’s description fairly closely.

Are these from fish of the same genus?  The same species?  Are both or either Lagodon?  What should they be called?

In 1932, paleontologist Charles T. Berry described four fossil fish teeth found in the Calvert Cliffs, specifically the St. Mary’s Formation which, though still Miocene in age, is younger than the material from either the Calvert Formation or the Pungo River Formation.  These teeth, he wrote
are relatively short and stocky, tapering towards the root, while the cutting edge is composed of two chisel-like cusps.  About one-third the way down from the cutting edge there is a slight groove which circumscribes the tooth.  Two-thirds of the tooth is covered with a very hard, black, shiny enamel, while the other rough surfaced third comprises the root – which is hollow in the largest specimen.  The side axis is slightly curved inward.  (Some Miocene Teeth Belonging to the Genus Lagodon, American Journal of Science, Volume XXIV, Number 142, October, 1932, p. 303.  This article resides behind a paywall.)
The maximum length of the specimens he found was 2.7 mm.

Berry noted, that, of extant fish, these teeth most closely resembled those of Lagodon rhomboides, and added, “So far as I have been able to find out this is the first fossil record of this genus.”  (p. 303)

These teeth, as described by Berry and pictured in the article, are a good match for my Pungo River specimen (though I cannot, not matter how I study the tooth, find the groove Berry described).  My Calvert specimen doesn’t pass this test.

What I find most fascinating about Berry and his treatment of these teeth is what he did not do. He was remarkably candid in the article about his own internal debate about what to claim taxonomically for these teeth.
With only four teeth to work with it would be unscientific to be categorical regarding the genus, but I think there can be no doubt that these teeth are distinctive enough to prove that they belong to a fish closely related to the modern Lagodon rhomboides.  (p. 305)
Nevertheless, he did place the fish of these fossil teeth in the Lagodon genus (the title of his article made that clear).  Though he came right to the edge of taking the next step, naming a new species, he backed off.  I was surprised at that, given the seductive appeal of naming a new species.  Berry laid out the justification for making such a move and, then, trashed the whole idea as very inappropriate.
It is hardly likely that the existing species goes back unchanged to the middle Miocene, but there is no reason for supposing that the genus Lagodon may not have been in existence at that time.  Although, therefore these Miocene teeth probably belonged to a distinct species of Lagodon, it would be highly improper, despite distinguished precedent, to give them a specific name.  (p. 303, emphasis added.)
I’m not such what really gave him pause.  As he noted, naming a new species on such evidence wouldn’t have been at odds with past practice (or perhaps even his own practice - see below).  Was he more inclined to believe the extant species could have gone back so many millions of years than he let on, so these teeth should be assigned to L. rhomboides?  Were four teeth really too few for him?  I have another paper of his in which he named a new species of Miocene "dog" based solely on two associated molars found along the Calvert Cliffs; his reasoning in that article doesn't appear (to this amateur) to be any more persuasive than the evidence presented regarding Lagodon (A Miocene Dog From Maryland, Proceedings of the United States National Museum, Volume 85, Number 3035, 1938).  I wish I knew more about Charles T. Berry, but the web has been startlingly unforthcoming with background on him.

Several years later, ichthyologist David K. Caldwell in his monograph on the pinfish (The Biology and Systematics of the Pinfish, Lagodon rhomboides (Linnaeus), Bulletin of the Florida State Museum, Volume 2, Number 6, 1957), applauded Berry’s restraint.  He noted that, though Berry expressed doubt that the existing species would be the same as the Miocene species of fish to which the fossil teeth belonged, “he admirably does not elect to assign a specific name to this form merely on the basis of the few teeth.”  (p. 151)

Caldwell also described two fossil teeth found in a site in Florida that are extremely similar to those of the extant L. rhomboides.  This is a Pliocene site (5.3 to 2.6 million years old).  He “tentatively ascribed” his teeth to that existing species and he did so by using the conventions of open nomenclature (yes, I finally did get back to it).  He identified the fossil species as Lagodon cf. L. rhomboides.

As described earlier, the element from open nomenclature here is the abbreviation “cf.” which Caldwell inserted following the genus name.  But, this identification was made in 1957, well before Bengtson’s piece on open nomenclature, so it’s not clear how Caldwell was actually using the abbreviation “cf.”  Bengtson noted that, in the past, paleontologists had been accustomed to use this abbreviation either to convey uncertainty or to make a “provisional” identification.  (A distinction without a difference?)

Parenthetically, Caldwell’s format for the name doesn’t adhere to Bengtson’s suggested protocol because it repeats the genus name (the initial “L.”) following the inserted abbreviation “cf.”  That repetition, according to Bengtson, is unnecessary and introduces a note of ambiguity.

That name has stuck (as has the potentially confusing initial for the genus).  In 2001, when paleontologist Robert W. Purdy, et al., described the fish found at the Lee Creek Mine, they included Lagodon cf. L. rhomboides.  (The Neogene Sharks, Rays, and Bony Fishes From Lee Creek Mine, Aurora, North Carolina, appearing in the Geology and Paleontology of the Lee Creek Mine, North Carolina, III, Smithsonian Contributions to Paleobiology, 2001, p. 173.)

My Pungo River specimen is, I’ve decided, Lagodon cf. L. rhomboides.  (I wonder if I am at liberty to drop the “L.”)  The tooth from the Calvert Formation remains a challenge.  I’ve considered labeling it in my collection, using open nomenclature conventions, as Lagodon? sp.  Or, perhaps I should follow the lead of elasmo.com, the excellent website on Lee Creek and related fauna, when it dealt with a similar (e.g., no dual cusps in the crown), though much larger, tooth.  It bumped the identification up to the Lagodon’s family – Sparidae (the porgies) (link here), and described it as a porgy of “undetermined genus.”  Either way, it would signal that I am still in search of a name.  The tooth needs a name.

I am reminded of a poem by Billy Collins titled Osprey in which the poet, while out canoeing, encounters a large bird.  Addressing the bird, he says he will, posthaste, work his way back home to his guide to North American birds.  He concludes (with what I thought was a somewhat misplaced certainty, though perhaps not in this instance) –
. . . I promise I will learn what you are called.

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