What's In a Name (Scientific or Otherwise)? Pedigree of a Large Shark Species

For this post, I found myself considering the value and significance of names.  Perhaps inevitably, I turned to Shakespeare's Romeo and Juliet, in which Juliet asks "What's in a name?"  She, in love with Romeo, renounces the family feud that separates them, sorrowfully lamenting:  "''Tis but thy name that is my enemy."  To her, these names - Capulet, Montague, Romeo - are just words, not the essence of the beings bearing them.  In the context of this play, it's a sentiment that resonates with the reader or playgoer, though, in that regard, Juliet is so sweetly and so frightfully naive.  To Capulets and Montagues, their family names have meaning, defining who they are and where they stand.

That latter aspect of names is essentially the thrust of this post:  the various names that a particular fossil shark tooth in my collection bears, depending upon the authority consulted, signals where that species of shark is thought to fit into the broad genealogy of the several very large shark species.  Scientific names are not merely words composed of Latin or Greek phrases; they carry meaning.

My local fossil club recently held a meeting focused on fossils from the Lee Creek Mine in North Carolina.  There is in my collection of fossils, a large, beautiful shark tooth from the mine that I obtained through a club auction.  Lee Creek Mine, a surface extraction phosphate mine and a renowned source for fossil shark teeth, hasn't been open to collectors for many years.  The formations from which the fossils come include the Pungo River (Lower Miocene) and the Yorktown (Early Pliocene).  My specimen is from the Yorktown.

On its longer side, the tooth crown measures 1 3/4 inches (44 mm) on the slant.  The edges of the crown are smooth, with no hint of serrations.  As evident in the picture, the crown angles slightly.   The tip curves inward a bit.

It's a very fine tooth with an auction label identifying it as Isurus xiphodon, a name that bore little significance for me and didn't hint at the prestigious relatives this shark species had and the controversy over that relationship.  Knowing that the identifications cited in club auction labels range from spot-on to very, very wide of the mark, I thought it prudent to double check that ID, a decision that revealed a protracted and intense taxonomic argument, one that involves not only my tooth, but the two most iconic shark species whose teeth are the holy grail to many collectors:  the gigantic, extinct megalodon and the fearsome great white shark.

I have tried to make sense of the ongoing debate but admit defeat.  Each time I think I've grasped the essential positions, I come across still others being advanced.  The following recounts just the initial steps in my taxonomic journey which, nevertheless, do help to elucidate the nature of the debate and the pedigree of my tooth.

I knew I was in trouble as soon as my initial web search for Isurus xiphodon turned up an article by Alexis Rojas on the Florida Museum of Natural History website titled Carcharodon hastalis; the disconnect between the name I searched and the title of the article was just the first hint that I'd stumbled into a morass.  (The article was last updated on February 26, 2015.)

The teeth pictured in Rojas' piece match mine quite closely, and I figured out that my search had landed on this article because Isurus xiphodon is just one of the "alternative scientific names" identified by the author for the species behind this tooth, names that also include Cosmopolitodus hastalis and Cosmopolitodus xiphodon.  The author's preferred name is Carcharodon hastalis.  Lying behind this multiplicity of possible names are various hypotheses about the taxonomic relationship of this shark species to other large toothed sharks, extinct and extant.

To make things a bit easier on me, I will often refer below to the three types of sharks at the center of this discussion by their species names because the battle is joined over their potential genus names.  So, hastalis refers to the kind of shark whose tooth is in my collection, megalodon refers to that super-sized, extinct shark whose teeth can be massive, measuring up to 7 inches or more, and carcharias refers to the great white shark, which, in the post-Jaws era, has come to dominate the popular perception of sharks.

The vigor of the debate has centered, in particular, on the megalodon and carcharias, and is driven in part by the exalted (at least, to collectors) status of those two sharks.  Though it sometimes seems that the shark species with the largest teeth and/or the best PR attracts the most attention in the literature, the taxonomic debate over the relationship of megalodon and carcharias isn't a trivial matter.  In general, how one classifies a particular species or group of species speaks volumes about the perceived evolutionary history of these animals.  The choice of genus names can explicate that history or obscure it.  (See, for example, Kenshu Shimada, et al., A New Elusive Otodontid Shark (Lamniformes:  Otodontidae) From the Lower Miocene, and Comments on the Taxonomy of Otondontid Genera, Including the 'Megatoothed' Clade, Historical Biology, October 2016, p. 8.)

The tooth from my collection is implicated in this debate and the many "alternative scientific names" that Rojas cites may testify to its intensity.  Consider the graphic below which is based on one that Rojas includes in the Florida Museum of Natural History article cited above.  It shows the author's interpretation of two of the most prominent hypotheses in the literature for the taxonomic relationships among several of the large toothed sharks, megalodon, carcharias, and hastalis in particular.  I have modified it in several ways.  I highlighted in red where my tooth fits taxonomically in the two hypotheses.  Note the difference in genus names.  I circled where the most recent common ancestors would appear under each hypothesis between carcharias and megalodon, and between hastalis and carcharias.  This signals how closely or how distantly related the members of each pair are.  I have also noted which of the various species are extinct or extant.  Finally, I dropped one of the species Rojas include (Lamna nasus) because its relationship to the others is not relevant to the discussion in this post.

Rojas describes the two hypotheses depicted above as follows:

A, traditional hypothesis in which the great white, Carcharodon carcharias is more closely related to the extinct megalodon than it is to mako sharks, genus Isurus.  B, alternative hypothesis, in which the great white, Carcharadon carcharis is more closely related to the extinct species "Isurus" hastalis. (Italics added throughout.)

Rojas notes that Hypothesis B is now favored.  This graphic captures one of the most significant developments in the taxonomic struggles over these sharks, that of, as shown in Hypothesis B, identifying megalodon to be rather distantly, not closely, related to carcharias.  At the same time, it fails to capture many of the alternative interpretations that have been offered over the years regarding the taxonomic status of these megatoothed sharks.  Indeed, Rojas acknowledges that the graphic depiction of Hypothesis B sidesteps at least a couple of ongoing debates.  Some paleontologists contend that, though they are apparently closely related, hastalis and carcharias are from different genera:  they identify the former as Cosmopolitodus hastalis while carcharias remains in the genus Carcharodon.  Also, some argue that there are two kinds of "hastalis" teeth, a broad form and a narrow form, which come from separate species.

The Rojas article may be somewhat dated given that it doesn't mention one of the more significant and contentious recent issues in the debate over megalodon. Shimada et al. in 2016 (see citation above for an article published later than the last updating of Rojas' piece) contend that the characteristics of the new megatoothed species they identify supports moving megalodon to the genus Otodus.  I won't go into the ramifications of this realignment (since I don't understand the complex basis for it), other than to say it's been rather controversial.  For a flavor of the vigor of the debate, I would point to the strong dissenting position expressed in great detail by paleontologist Bretton W. Kent in the chapter titled The Cartilaginous Fishes (Chimeras, Sharks, and Rays) of Calvert Cliffs, Maryland, USA which appears in The Geology and Vertebrate Paleontology of Calvert Cliffs, Maryland, USA (edited by Stephen J. Godfrey, Smithsonian Contributions to Paleobiology, Number 100, 2018, p. 80 et seq.).

At this point, I have decided to cut my losses and accept the position that my tooth is most likely a near ancestor of the great white shark and only distantly related to that monster shark megalodon.  It's still an impressive pedigree.

Stories of the Periodic Table: A Review of The Disappearing Spoon

Sam Kean's The Disappearing Spoon and Other True Tales of Madness, Love, and the History of the World from the Periodic Table of Elements (2011) captures the wonder and power of the periodic table through myriad stories of the elements themselves, as well as stories of the scientists and others whose lives intersected with them.

When I studied it in a college chemistry class, I was fascinated by how the arrangement of the periodic table captured the essence of the different elements and predicted their relationships to each other.

(The version of the table presented above was downloaded from the Los Alamos National Laboratory website.  As the product of a government agency (which I hope will continue to exist), I assume it is in the public domain.)

Kean, a widely published science writer, provides enough science for the reader to gain an appreciation of the basis upon which the table functions, though, to some extent, in his hands, that's secondary to the adventures and misadventures of the people he describes.  It's the latter that moves the book along.  He writes

[T]here's a funny, or odd, or chilling tale attached to every element on the periodic table.  At the same time, the table is one of the great intellectual accomplishments of humankind.  It's both a scientific accomplishment and a storybook . . . .  (p. 7)

As Kean notes, an element is "a substance that cannot be broken down or altered by normal, chemical means."  (p. 15)  Further division destroys it.  One simile he uses for the periodic table is a castle.  The overall shape does hint at castle turrets and walls.  Critical to that analogy is that each brick in the structure, representing a discrete element, is crucial to the table, moving or removing any one of them brings down the structure, putting a line to the arrangement.  The other simile Kean employs is that of a map.  Where an element falls on that map "determine[s] nearly everything scientifically interesting about it.  For each element, its geography is its destiny."  (p. 13)  How that map is read is critical.  He stresses that horizontal relationships in the table are perhaps less significant than vertical ones because reading up and down the columns "reveals a rich subtext of relationships among elements, including unexpected rivalries and antagonisms.  (p. 31)

Key to the entire table is the number and arrangements of electrons in each element.  They are located at different energy levels in the atom, and, beyond the two needed to fill the innermost level, each atom will beg, borrow, or steal enough electrons from other atoms to populate its uppermost level with an appropriate number, usually eight.  Kean stresses that the "octet rule" does explain a great deal of the behavior of atoms, particularly how they combine with other atoms.  Elements are placed in the table according to their atomic number, that is, the number of protons in the nucleus, which, in a neutral atom, is also the number of electrons in the atom.

Kean captures the importance of this when he discusses the different bonding behavior of carbon and oxygen.  Oxygen, element number 8, has 8 electrons and, given that 2 of them are in the lowest energy level, the higher has 6.  This means oxygen is impelled to garner two additional electrons (the octet rule) which, he notes, isn't too difficult a task, meaning oxygen can be choosey about which elements it bonds with.  In contrast, carbon at number 6 has 4 electrons in its highest energy level and needs to find another 4 to satisfy the octet rule.  "That's harder to do, and the upshot is that carbon has really low standards for forming bonds.  It latches onto virtually anything."  (p. 35)  This helps explain why life on Earth is carbon-based.  Carbon, ever in search of electrons, bonds into complex chains of atoms and constitutes "the backbone of amino acids, which string together like beads to form proteins."  (p. 34)

Each chapter of the book is organized around a cluster of elements because each cluster provides fertile ground for a linked set of stories, not necessarily because the elements in a group are reflective of relationships shown in the table.  A few of the element groups he creates are:  medicinal elements, elements that have been caught up in "pathological science" (think cold fusion), elements explored at extremely low temperatures, elements with a strong financial facet, elements discovered as part of cold war politics, and elements that in direct or subtle ways poison human beings.  (A minor quibble:  Kean would have done the lay reader a favor by defining each chemical symbol used at the beginning of each chapter.)

The stories in each chapter of the elements and the people somehow linked to them serve to capture science being done methodically and carefully with beautiful results, or science replete with errors or happenstance.  Lives are bathed in glory or disappointment, honors are won and also lost.  Indeed, in these stories, lives may be lost.  It's an amazing panoply of human emotion and action.

Representative of the way Kean approaches his subjects is his description of the source of the book's title.  In the chapter he titles The Galapagos of the Periodic Table, Kean tells stories involving the elements arsenic, gallium, cerium, yttrium, yttrium, erbium, and terbium.  The chapter title highlights the importance of the Swedish hamlet of Ytterby on the island of Resaro to the periodic table.  In Kean's telling, Ytterby is as central to the periodic table as were the Galapagos to the theory of evolution through natural selection put forward by Charles Darwin (1809-1882).  (I will return to this comparison of the periodic table to the theory of natural selection later.)  The last four elements grouped in this chapter are rare-earth elements, all discovered in a mine at Ytterby (as were three others not in this chapter grouping).  Yes, Kean recounts why Ytterby was so rich in these rare-earth elements and how they were discovered, but it's gallium (unrelated to Ytterby) that, to my mind, occupies center stage in this chapter, though it's but one small part of a very busy chapter.  Gallium, element 31, was among the elements whose existence was predicted by Dimitri Mendeleev (1834-1907), the so-called father of the periodic table, using the table he'd constructed.  Later, when a Frenchman, Lecog de Boisbaudran (1838-1912), claimed to have discovered this metal, a debate ensured over who should have credit.  It's unclear from Kean's account who really prevailed in the tussle, though the element has kept the name Lecoq de Boisbaudran assigned it.  It's the predictive power of the Mendeleev's periodic table that's the big take-away from this chapter for me.  But Kean balances that aspect of the gallium story with a bit of humor.  Remarkably, gallium at normal room temperature is a solid, but it turns to liquid at 84 degrees Fahrenheit or higher.  Further, it's one of the rare liquid metals that can be safely touched with a bare hand.  He  writes:

As a result, gallium has been a staple of practical jokes among the chemistry cognoscenti ever since . . . .  One popular trick, since gallium molds easily and looks like aluminum, is to fashion gallium spoons, serve them with tea, and watch as your guests recoil when their Earl Grey "eats" their utensils.  (p.54)

Hence, the "disappearing spoon."

Though I thoroughly enjoyed the book and learned much from it, I dissent from Kean on one important point.  When he discusses Mendeleev's work on constructing his periodic table (Mendeleev didn't create just one, but, over time, many variations, and many more have been designed subsequently), he makes the following assertion:

Overall, Mendeleev's work is comparable to that of Darwin in evolution and Einstein in relativity.  None of those men did all of the work, but they did the most work, and they did it more elegantly than others.  They saw how far the consequences extended, and they backed up their findings with reams of evidence.  (p. 53)

What troubles me about that statement is that I believe that what Mendeleev fashioned, better than anyone had before him, was a table providing a visual display of the elements, capturing the periodicity of characteristics of the elements and depicting very real relationships among them.  There is no denying the power of the table and impact it had on chemistry.  But, as I read Kean, Mendeleev did not understand why the table worked as it did.  Indeed, his organizing principle was not the atomic number of each element (its number of protons), but rather its weight.  For instance, Kean writes

Most of the elements line up on the table in a cattle call of increasing weight.  According to that criterion, nickel should precede cobalt.  Yet to make the elements fit properly - so cobalt sat above cobalt-like elements and nickel above nickel-like elements - chemists had to switch their spots.  No one knew why this was necessary, and it was just one of several annoying cases.  To get around the problem scientists invented the atomic number a a placeholder which underscored that no one knew what the atomic number actually meant.  (p. 99-100)

It took Henry Moseley (1887-1915), in the early 1900s, to discern the basis for the atomic number by firing electron beams at elemental atoms.  He determined that the wave lengths of the emitted X-rays reflected the number of protons in the atom's nucleus.  Thus, he "linked an element's place on the table to a physical characteristic, equating the positive nuclear charge with the atomic number."  (p. 100)

Given the lack of a fundamental understanding of why the periodic table worked as it did when it was initially put forward, I am hesitant to give it equal weight to Darwin's theory of evolution through natural selection.  The periodic law that undergirds the table describes what the reality is for the elements; Darwin's theory of evolution explains why living organisms come in the diversity they do.  I think it's apples and oranges, though I will admit a bias in favor of explanation.

Unanswered Questions About Vacated Osprey Nests

Essayist Margaret Renkl writes in a recent column for The New York Times (July 7, 2025) that the Northern House Wren is "a tiny, feathered terrorist" because of its wanton destruction of the Carolina Chickadee nests (including eggs and young) that graced her backyard.  Nevertheless, that explosion of blood lust failed to dampen her enthusiasm about this spring which was replete with young birds leaving their nests and making their way in the world.  Amid her pleasure in the season, she grappled with myriad questions about the ways of the birds she observed (for instance, "Why did the baby cardinals leave the nest too early, still half bald and flightless?"), questions that brooked no easy, simple answers.  It was this clutch of questions that prompted Renkl to posit that, whereas once she had little tolerance for unanswered questions or ones not answered quickly (e.g., the results of some medical test), "I am older now, and these days not knowing often feels like a gift."

At this point in the essay, she shifts from unanswered questions involving nature on a small scale or her own personal well being, to the more fundamental question of what will happen in the long term environmentally to the planet, with those in charge evincing little regard for the consequences of their actions.  It's in the not knowing the outcome that she finds hope; the dire expectations haven't been realized yet, so, in the space between the now and the future, action might be taken.  "I am grateful for the way that not knowing allows room for a future that is different from the one I fear."

I'm not grappling in this post with the long term environmental consequences of how people currently in power are intent on sacrificing the future for some short term payoff in the present.  Rather, I want to share a couple of Renkl-like questions that have left me stumped.  Over the past three years, I have been monitoring a small number of Ospreys each summer on the North Fork of Long Island.  It wasn't until July of this year that I returned to my summer cottage and found that, of seven nests that were active in July and August of 2023 and 2024, three are vacant.  By "active," I mean these were nests where, as best I could determine, short of climbing up to peer into the cavity, female birds were incubating eggs and the Osprey couple was subsequently feeding and tending to young.  Nests I deemed "vacant" this year were ones without any Ospreys in or on them.  Significantly, none appears to be damaged.  I admit that I do not know if these nests were the scene of some nesting activity earlier in the season, and were subsequently abandoned before I started observing at the beginning of July.

In a post in 2023 I described an active nest very near my summer cottage that, despite the commotion visited on the it and its occupants by the passage of daily commuter trains, boasted healthy parents and robust, demanding young.  It was also active in 2024.

Now it stands empty.

My first question was:  What happened to the pairs that once raised young in this nest and the other two?  My second was an attempt to place the experience of my nests into context:  What's the expected year-to-year vacancy rate for Osprey nests?

I am unable to answer the first question with any certainty.  Though Renkl suggests she has a willingness not to have an immediate answer to her nature questions, she did pursue some with a bit of determination.  That's the case here.  I do want to know the fate of my pairs, though, as I explain below, not having an answer leaves some room for hope.

The starting point, I guess, is that, as with nearly every kind of bird, the nest during the breeding season is the focal point of the Osprey's activity.  The breeding pair becomes singularly attached to its nest, not only dedicating great time and energy to its construction, but, often, returning year after year to the same nest, repairing and adding to it.  (See, for example, Alan F. Poole, Ospreys:  The Revival of a Global Raptor, 2019, p. 80.)  Which makes it puzzling why so many of the nests I'd observed over the past three years now are vacant, some even with vegetation now growing in them.

The factors that can influence why any single nest might be occupied one year and not the next are many.  The most dire, of course, is that one or both of the birds that dedicated upwards of six months to it, perished on the several thousand mile long migration the Ospreys took to and from their wintering ground in the southern hemisphere.  Alan Poole in his 1989 work on ospreys describes various ways of estimating the raptor's mortality rate.  (Ospreys:  A Natural and Unnatural History, 1989.)  For large banded populations this may be a relatively straight forward calculation.  He writes that preliminary data for two such populations offer estimated annual mortality rates of between 10 and 17 percent.  (1989, p. 142)  As I noted in my previous post on Ospreys, mortality in the earliest years of the bird's life is quite high:  "Fewer than half of the birds that fledged will survive to breed."  (For similar data, see, Hinterland Who's Who:  Osprey, Minister of the Environment, Canada, 1993, p. 4.)  The most dangerous periods in the bird's life are during the long migrations to and from the wintering grounds, and the wintering period itself.  It's also the case that mortality rates are relatively low in early adulthood through late adulthood.  (Federico De Pascalis, et al., Shift in Proximate Causes of Mortality for Six Large Migratory Raptors Over a Century, Biological Conservation, volume 251, 2020.)  The percentage of absent breeding pairs in the seven nests is higher (at 43 percent) than the estimated mortality rates among adults just cited.  This does make me question whether mortality, alone or at all, might account for these vacant nests.

Of particular relevance to my concern is Poole's observation:

Because most Ospreys are faithful to breeding sites, one can reasonably assume that any established breeder failing to return to its nesting territory (or nearby) at the start of the season has died.  (1989, p. 142)

Though the import of his comment is profoundly negative (no bird returning to the site equals a dead bird), he does hint at a more benign outcome for my birds.  One or more of these osprey pairs that, in past years, used the now vacated nests might have found some other nearby location more to its liking.

I then considered what might influence that decision.  Is the relatively substantial human activity in the area around some of the nests I've been tracking discouraging Ospreys from returning?  Likely not.  Ospreys adapt readily to urbanized locations.  A very interesting study on the factors that influence the success (not the presence) of Osprey nests in an urbanized Florida location found that it was principally the timing of the nesting activity which affected success rates (earlier nests fared better than later), not urbanization.  Results from this study are affected by the fact Florida hosts migratory and non-migratory Osprey populations; the latter may nest earlier than the former.  (Elizabeth A. Forys, et al., Predictors of Osprey Nest Success in a Highly Urbanized Environment, Journal of Raptor Research , Volume 55, Number 4, 2021.)  The authors found no significant effect on nest success from the location factors they measured, including the nature of the land surrounding the nests - forests, grassy tracts, parks and ball fields, and "urban cover."  They write:

In conclusion, this study provides further evidence that Ospreys can be productive in highly urban environments and this might be particularly true for areas like Pinellas County that are surrounded by water.  (p. 493)

That conclusion rings true with my local populations.  There is substantial human activity in this environment (e.g., repeated passage of commuter trains) which has not deterred Ospreys from nesting and nesting successfully in the area in the past, and there's been no obvious change this year in that activity.  I would note that, after the 2023, breeding season, the local power company added a platform to the utility pole seen in the photographs above.  That change to the pole in one year didn't preclude nesting in the following.  Might this modification, nevertheless, have rendered the site sufficiently less attractive so the pair this year looked elsewhere?  Perhaps.

It is possible that some threat to an Osprey nest is now present in the neighborhood, say a Great Horned Owl, though there's no evidence of that, and it's not clear why all three of the vacated nests were affected.  As already noted, none of the nests appeared damaged, ruling out that potential deterrent to reoccupying a nest.

So, this first question remains unanswered.

As for the second, I tried to determine if the vacancy rate of my nests is unusual.  It certainly appeared so to this uninformed observer.  My journey through the research has not been very productive.  Much of the research on Osprey nesting is focused on the success of the nesting activity (as is the one just cited for Florida).  In contrast, if one asks the question regarding year-to-year use of a nest, there appears to be little data readily at hand.  I've tried to tease out the answer to that question from data provided in various published sources, data not focused on the vacancy issue.  I turned particularly to state projects monitoring Osprey nests, but, so far (the search continues), I have found only one with reported figures even tangentially speaking to my concern.

The Connecticut Audubon Society, in its 2024 report on the observations recorded by its Osprey Nation (a network of citizen scientists dedicated to monitoring and reporting on the state's Osprey population), noted that, in that year, there were "105 vacant platforms or comparable sites previously used."  (Osprey Nation 2024 Season Report, November 8, 2024, p. 6.)  If I read that description correctly, that's potentially the numerator I need - nests used previously, now vacant. But, what's the denominator?

Based on the data reported by the Society, the aggregate total number of nests observed in 2024 was 945.  This includes 726 active nests, 31 nests that were removed or somehow destroyed, 83 abandoned nests, and the 105 vacant nests.  That's not the appropriate denominator since the count of active nests includes ones newly observed that year, and some of the removed, destroyed, or abandoned nests might not have been used in prior years.  ("Active" is defined as nests in which observers saw birds in the incubation posture or young not ready to fly.)

Recognizing that it's not wholly defensible, I turned to the prior year's count of active nests - 688 - and added it to the 105 vacant nests from 2024, to calculate a potential denominator of 793.  That generated a vacancy rate in Connecticut in 2024 of approximately 13 percent.

If this is at all close to a reasonable year-to-year vacancy rate in my locality, then the 43 percent (3 of 7 nests) vacancy rate of my nests is dramatically higher.  I recognize, though, that it's folly to draw any conclusions from data based on such an absurdly small sample.  So, I will leave off, for the moment, the search for an answer to that and my initial question.

To end on a bit more of an upbeat note:  even with nearby vacant nests, I have still been enjoying the piercing calls of Ospreys soaring high overhead while I work in the yard of my summer cottage or walk around the neighborhood, down to the beach, and along the road that abuts the marshy, reedy extension of the bay.  There are Ospreys here and in number, some with nests that have escaped my detection.  I have seen the raptors with plump, glistening fish in their talons, taking a meal to mates and fledglings in nests somewhere nearby.  I hope my previous tenants are among them.

Another bit of good news.  At some distance from my cottage, in the heart of the town of Riverhead, I found an Osprey nest new to me.  What a beautiful sight, even with the unintended product placement.

The Enigmatic Scaphopoda Reflect the Downside of Distinctiveness

I find the members of the Scaphopoda Class of mollusks to be beautiful and quite distinctive.  This post is partly about how that distinctiveness may work against them in paleontological terms.

My interest in these animals was sparked by several fossil shells (shown below) from Dentalium attenuatum Say 1824, an extinct member of this class.  These were a gift from a friend who collected them at Windmill Point on the St. Marys River.  The formation shedding fossil shells at this location is considered Upper Miocene, deposited about 11.6-5.6 million years ago.

Marine biologist Helen Scales, when describing the various classes of mollusks, had this to say of the members of the Scaphopoda Class:

Scaphopods or tusk shells are fairly self-explanatory:  they look like little tusks.  Often they live buried in the seabed, head down, with the tips of their shells poking out.  (Spirals in Time:  The Secret Life and Curious Afterlife of Seashells, 2015, p. 27.)

In a wonderful aside in her discussion of the changing thinking about the relationships among different taxa of the mollusk family, she wrote of Scaphopoda:

The scaphopods continue to be a pain in the neck to identify; we simply don't know enough about them to be sure where exactly they fit in.  (Scales, p. 35.)

Though there is uncertainty about the kinship of scaphopods with all of the other mollusk taxa, there is no doubt that they belong in the mollusca phylum.  (Scales, p. 28.)  Further, we also know that they are the newest of mollusk classes to show up in the fossil record, appearing perhaps as early as the Mississippian in the Carboniferous Period, about 362.5 million years ago.  (Patrick D. Reynolds, The Scaphopoda, Advances in Marine Biology, Volume 42, 2002, p. 139.)

To elaborate on Helen Scales' brief description, each of the extinct and extant scaphopods generally positions itself in sea bottom sediment with its larger opening (the aperture) buried and its narrower opening (the apex) exposed.  The aperture houses the animal's "creeping" foot and its mouth.  Water is drawn in through the exposed apex and waste is excreted from the same opening.  (See descriptions of tusk shells in:   National Audubon Society Field Guide to North American Seashells by Harald A. Rehder, 1981, p. 655; and Invertebrate Fossils by Raymond C. Moore, et al., 1952, p. 273-275.)

I think it undeniable that the Scaphopoda Class, as a whole, is distinctive:   shells of all members share the same morphology, one which readily distinguishes them from other mollusks.  At the same time, it may be challenging to differentiate among species within the class.  That morphological sameness has long been noted as a potential issue.  For example, when the D. attenuatum shells were first described in 1824 by conchologist and entomologist Thomas Say (1787-1834), he noted of the Dentalium genera as a whole:

The species of this genus are very closely allied to each other, and at the same time they exhibit so few characters, that it is with difficulty that some of them are determined.  (An Account of Some of the Fossil Shells of Maryland, Journal of the Academy of Natural Sciences of Philadelphia, Volume IV, Part 1, 1824, p. 155.)

They exhibit so few characters:  from a taxonomic perspective, that's a fairly damning statement.  Later, paleontologist Raymond Moore et al., in Invertebrate Fossils (cited above), characterized the Scaphopoda as being "simple tapered tubular shells [exhibiting] few sorts of difference other than size and surface markings."  (Moore, p. 275)  The authors,  prompted by the general sameness of the various species in this class, concluded that these shells "are not very useful as index fossils."  (Moore, p. 275)

Hmmm.  Though their dismissal of the shells of scaphopoda as potential index fossils seems to have been sparked solely by the relative uniformity of the morphology of the individual species in the class, Moore et al. may not have been wrong about the possible utility of these shells as index fossils.  I turned to Hervey Woodburn Shimer and Robert Rakes Shrock, who, in their Index Fossils of North America (1944), defined an index fossil as:

one which identifies and dates the strata or succession of strata in which it lies.  The ideal index species has narrow or restricted stratigraphic range and broad, even worldwide geographic distribution. . . .  A genus which has narrow stratigraphic range and rather broad geographic distribution is now considered an index fossil.  (Shimer and Shrock, p. 1.)

There's nothing in that definition about whether the difficulty of distinguishing one species from another might affect what could be considered an index fossil, though that could be the case.  The actual focus of Shimer and Shrock's definition is on the temporal and geographic distribution of a species:

Is it found in a short and well defined interval in the stratigraphic column and, so, could it be used to identify and date the interval?

Is it distributed widely enough that it could be useful for correlating formations across a broad geographic range?

I wondered what we do know of the distribution of the scaphopods in the Maryland Miocene formations.   Of this class of animal here, paleontologist Harold E. Vokes et al., in their useful Miocene Fossils of Maryland (Maryland Geological Survey, second edition 1999), wrote that the scaphopods "occur throughout the [Maryland] Miocene deposits."  (Vokes, p. 18.)  I became hung up over that "throughout."  Undoubtedly, this does not mean that each species in this class is found everywhere in the stratigraphic column.  So what does it mean?

The seminal work on the Maryland Miocene published by the Maryland Geological Survey in 1904 is somewhat helpful in teasing this out.  (Miocene, Text, Maryland Geological Survey, 1904, p. eviii-evix.)  Five scaphopod species are identified in that publication.  (I think it interesting that there is no statement in this volume regarding any particular difficulty in distinguishing among these species.)  Data presented on the distribution of these five species among the Maryland Miocene formations show they may be widely, though unevenly, distributed in these formations.  The distribution of these species across the three formations covered in the report is this:  three of the species had been collected in localities in all three formations, two of the species were collected in only one formation (a different one for each).  Does that pattern offer any support to using scaphopod species as index fossils or militate against such an application?  Frankly, I don't think the data from this particular publication are sufficient to inform such a decision.

A better sense of the adequacy, or, rather, inadequacy, of the scaphopods as potential index fossils may be gained from their complete absence in the stratigraphic work on the mid-Atlantic coastal Miocene formations by paleontologist Lauck W. Ward.  In Molluscan Biostratigraphy of the Miocene, Middle Atlantic Coastal Plain of North America (Virginia Museum of Natural History, Memoir Number 2, 1992), he proposed stratigraphic zones for these formations based on the distribution of various mollusk taxa, defining the boundaries of zones in his schema by the first appearance of a mollusk taxon in the stratigraphic column.  For instance, the zone from which the D. attenuatum shells in my collection came is the Chesapecten/Glossus fraterna Interval-zone, which begins where fossil shells of the species Chesapecten santamaria first appear, and ends where fossil shells of Glossus fraterna enter the fossil record here.  None of Ward's zones in this work involve scaphopods.  (There is also no mention of scaphopods in Ward's later work with George W. Andrews titled Stratigraphy of the Calvert, Choptank, and St. Marys Formations (Miocene) in the Chesapeake Bay Area, Maryland and Virginia (Virginia Museum of Natural History, Memoir Number 9, 2008, p. 48).)

Ward characterized the mollusk species that he used in setting the boundaries for the zones as "well represented."  Further, confidence in appropriateness of these taxa to mark zone boundaries was heightened

because of the relatively complete phyletic record of the aforementioned taxa and because this record is found over a wide geographic area.  (Ward, Molluscan Biostratigraphy, p. 9.)

The scaphopoda species are missing because they, in general, did not meet these index standards.  (Ward indicated as much in a private communication.)  I would note that, for each molluscan zone, he also listed mollusk species restricted to that zone, as well as, various mollusk species common in, but not restricted to, that zone.  Scaphopods are excluded from those lists as well.

In sum, it would appear that our knowledge of scaphophod fossils is limited, here in Maryland and elsewhere.  Further, biologist Patrick D. Reynolds has argued that the morphological sameness of the scaphopods, coupled with the taxon's uncertain phylogeny in the mollusk family tree, "renders the scaphopods an enigmatic group."  (Reynolds, p. 139, emphasis added.)  Indeed.