Some Bits and Bobs of the Taxonomic History of Weltonia ancistrodon

 In which I unravel a bit of the taxonomic foundation for this particular species of cow sharks and get sidetracked by some of the bits and bobs I came across in the process.  I'm easily diverted, particularly since it's the people featured in any taxonomic story that I usually find most interesting.

Among the strangest of shark teeth are those of cow sharks (members of the Hexanchidae family).  Here are a couple fossil teeth of the cow shark Notorynchus primigenius that I found along the Calvert Cliffs.  These likely date from mid-Miocene Epoch, or perhaps roughly 16 to 14 million years ago.

These are all from the lower jaw of the fish with the largest cusp at the anterior end of each tooth.  The larger of the two is 20 mm in length.

The extant species in this family of sharks are distinguished from other sharks principally by the number of pairs of gill slits its members have (either six or seven - other sharks have five pairs) and an array of other attributes often characterized as primitive.  It is assumed that the extinct species with such teeth shared those various morphological attributes.  Perhaps most important for the fossil collector, the species in this family sport distinctive teeth, easily distinguished from all others.  This observation applies principally to teeth from the bottom jaw which, as seen above, are rectangular in shape with a row of several curved cusps headed, for the most part, by a prominent initial one (there may be cusplets in front of it).  Complicating things somewhat is the fact that teeth of any one individual cow shark can vary by its sex and age, and by the precise location in the shark's jaw from which the tooth came.  As a result, precisely ascribing an isolated cow shark tooth to a particular species can be difficult.  (See Bretton W. Kent, Fossil Sharks of the Chesapeake Bay Region, 1994, p. 17.)

As unusual as I find these teeth, those of one species of cow shark - Weltonia ancistrodon (Arambourg, 1952) - are, I think, the most striking of the lot.  The tooth from this species shown below (which may be partially repaired) dates, according to the dealer from whom I purchased it, to the Eocene Epoch (56.0 to 33.9 million years ago) and was found at Khouribga, Morocco.  It is 13 mm in length.

Obviously, the most startling feature of this tooth is the exaggerated first cusp that extends high over the other cusps on the tooth and curves back at its tip.  Remove that and the rest of the tooth bears the typical features of other cow shark teeth.

How did it come to have this scientific name?

Camille Arambourg (1885-1969) was the first to describe this species based on teeth he collected at Khouribga, Morocco.  Arambourg's journey into paleontology was fortuitous.  He trained in agricultural engineering, but, as a young man, while helping his father dig an irrigation system on the family farm in Algeria, he uncovered a trove Miocene fish fossils.  That sparked a life-long interest in the fossils of Africa and a distinguished academic career in geology and paleontology, which culminated in his appointment as professor of paleontology at the Museum of Natural History in Paris (Muséum National d'Histoire Naturelle).  (See entry for Camille Louis Joseph Arambourg at Encyclopedia.com, and Djillali Hadjouis, Camille Arambourg (1885-1969), Historiographie de Préhistoriens et de Protohistoriens Français du XX° Siècle, 2018.)

In Les Vertebres Fossiles des Gisements de Phophates (Maroc-Algerie-Tunisie) (Notes Mem. Serv. Mines Cart Geol. Maroc., 1952), Arambourg described teeth from various cow shark species.  Among the cow shark teeth, one kind was distinctive.  He asserted, "no other fossil form . . . combines similar characteristics.  In order to distinguish it, I therefore propose to name this new fossil:  N. ancistrodon."  (p. 44)  He placed it in the genus Notidanus.  The new species name, he noted, is a combination of Greek roots for "hook" and "tooth."

He also observed that this particular taxon was particularly abundant in strata from the Thanetian and Ypresian Ages.  These straddle the divide between  the Paleocene and Eocene Epochs and are dated 59.2 to 56.0 million years ago and 56.0 to 48.1 million years ago, respectively.  

It's not surprising that Arambourg came to use this species name given that prominent first cusp.  In fact, the word Ancistrodon had already been used taxonomically over the years as the genus name for an array of poisonous snakes:  copperheads, moccasins, and vipers.  Very appropriate for animals with fangs.  (According to the Integrated Taxonomic Information System, this genus name for snakes is no longer valid.  I would note that the scientific name that I believe is now applied to the shark species to which the tooth shown above belongs does not appear at all in the ITIS.)

In 1979, paleontologist David John Ward reconsidered the taxonomy of this species, giving it a new genus name:  Weltonia.  (Addition to the Fish Fauna of the English Palaeogene.  3. A Review of the Hexanchid Sharks with a Description of Four New Species, Tertiary Research, Volume 2, Number 3, 1979.)  Ward selected as the lectotype for this new species, the tooth that Arambourg had shown as figure 65 on plate 1 in his 1952 publication.  (A lectotype is the representative or type specimen for a species when the holotype was not selected by the original author.)  Here is the image of the lectotype tooth from the 1952 publication.  (I believe I have not violated any copyright laws by reproducing a small portion of the original publication and am doing so for educational, noncommercial purposes.)

Ward's professional life has contained the same sort of career change that marked Arambourg's.  He trained and practiced for several years as a veterinary surgeon, but his interest in fossils apparently took over, and he retired as a surgeon to pursue paleontology.  As far as I can tell, he doesn't have an academic degree in the field, though he is the author of many paleontology papers, including the one cited here, and is, at present, a scientific associate at The Natural History Museum, London.

In his description of W. ancistrodon, Ward took Arambourg to task.  First, he stated that Arambourg asserted incorrectly that the teeth with the prominent first cusp were from the shark's upper jaw.  They are, in fact, from the lower.  Further, the teeth Arambourg identified as coming from the species' lower jaw were actually from another cow shark genus altogether.

I am puzzled a bit by Ward's notation about where the teeth Arambourg described were held.  He wrote, "Depository:  (presumably) the Arambourg Collection, Paris Museum."  Presumably suggests that these teeth were, at least then, missing.  Indeed, I could not find them listed in the database of the fish holdings of the Muséum National d'Histoire Naturelle where Arambourg was paleontology chair and whose fish fossil collection he was instrumental in building.  So, it would seem that the identification of this new species rests presently on images reproduced in a 1952 publication, not the actual teeth (wherever they might be).

I am amused by Ward's brief explanation of the origin of the genus name he newly applied to W. ancistrodon.  Actually it's how he explained the origins of several new names he applied in this article that I found most amusing.  For W. ancistrodon, Ward wrote that the genus is "named after the American palaeochondrichthyologist Dr. Bruce Welton."  Full stop.  Nothing more about Dr. Welton.  In contrast, he observed of using Mr. D. Kemp's name for Notorynchus kempi that it was "in recognition of [his] field assistance."  A tad bit more expansive here than he was with the explanation of Weltonia, but not much.

Things become more interesting with Ward's explanation of two other new names.  For Hexanchus collinsonae, a new species in the established genus Hexanchus, Ward said that it was "named after the English palaeobotanist Dr. M. Collison in recognition of field assistance and stimulating conversation."  Hmmm.  For Hexanchus hookeri, another new species in this genus, Wards noted it is "named after the English palaeomammalogist Mr. J. Hooker in recognition of field assistance and lively discussions."

So, apparently, Ward didn't find Welton to be much of a conversationalist, certainly not stimulating or lively, a failing also true, it would seem, for Mr. Kemp.  This looks like a slight to me, whether intended or not.  Though, of course, any sting of the apparent slight to Welton is minimized because his name was given to a genus, a level higher than species in the taxonomic order of things.  Poor Mr. Kemp.

Living Things: A Review of Turning to Stone

 When I began this blog many years ago, my father questioned its title:  Fossils and Other Living Things.

"I don't get it.  Fossils aren't alive," he objected.

I replied that I found that fossils have stories to tell and experiences to share if we are open to communicating with them.  They aren't silent.  I don't think I went much further because his puzzled expression was not encouraging.  At least he'd expressed some interest, even if it was mostly couched in doubt.

I could have gone on and on.  I might have described the multi-hued Miocene shark tooth that lets us know that it came into contact with particular kinds of minerals in its journey to becoming a fossil (e.g., my post titled Colors - Fossils and a Graphic Story About Darwin).  I could have suggested that I love that all fossils carry a living backstory if we choose to explore its taxonomy or its evolutionary history or the people involved in describing that story.  It's an infatuation to which many of the posts in this blog attest, beginning as early as my sixth one titled What's In A Name? Part Un).  Perhaps he would have enjoyed learning that fossils can lie about their history (e.g., the Elvis taxa which I discussed in the post titled Witticisms in the Face of Mass Extinction).  In the end, I don't know that any of this would have made much of an impression.  One needs, I think, to appreciate this understanding of fossils by coming to it with a willingness to challenge the literal, supported by an openness to the poetry and complexity of natural things.

So it is no wonder that I found structural geologist Marcia Bjornerud's new book Turning to Stone:  Discovering the Subtle Wisdom of Rocks (2024) compelling.  (I do not provide page numbers with the text quoted below given that I read an ebook version.)

It's a marvelous memoir in which she recounts her many different roles:  student, scientist, woman in a male dominated field, academic, wife, mother, and widow.  In the process, she highlights the evolution and growth of the geological sciences over the past several decades, and the maturation of our understanding of the geological processes that make, and have made, the planet.

She tells her story in ten chapters, each highlighting a rock that had significant importance at a different stage of her life:  from the 500 million-year-old sandstone deposited on an ancient oceanside beach that generated the sandy soil marking her childhood in Wisconsin; to the mysterious 700 million-year-old diamictite, a clastic sedimentary rock, she studied in Svalbard as a graduate student; to the 450 million-year-old sedimentary (and, in her telling, boring) dolomite, deposited on an ancient continental shelf, that undergirds the landscape around the Ohio campus where she earned tenure; to the 1.7 billion-year-old granite produced in the cauldron of an ancient continental volcanic arc and now quarried near the Wisconsin university where she thought she'd found a measure of harmony in her life only to experience a period of turmoil.

Given her field of study within the science (structural geology), the stories these rocks have to tell invariably involve some aspect of the upheaval of seismic and volcanic action, the building up and tearing down of mountains, and the movement of tectonic plates and continents.  (On second thought, those are elements in some part of the history of every rock on Earth.)  There's quite a lot of violence in this account, but, as she counsels, much good comes of it.

There are several recurrent themes in this tale, none more important than Bjornerud's relationship with, and attitude toward, rocks.  In the prologue titled Ice, set in Svalbard, a Norwegian archipelago in the Arctic Ocean, she leaves no doubt about a specific perspective that animates the book.  Early in her academic training, she is a graduate student in Norway exploring evidence of tectonic action.  The landscape speaks to her in a way that harkens back to her childhood in Wisconsin when she felt at one with a responsive natural world.

In the sciences, one of the deadliest sins is animism - describing inert entities likes glaciers and mountains as if they were living beings.  And yet, in Svalbard it was undeniable that the austere landscape was alive, its rocks and water, ice and air in constant conversation.  The terrain was animate, sentient, and creative.  It would just take me thirty years to say that out loud.

She states that out loud often in the course of this memoir.  "This book is an invitation into my geocentric worldview in which rocks are raconteurs, companions, mentors, oracles, and sources of existential reassurance."  In her telling, rocks communicate, remember, reveal, wait, are cryptic, are incommunicative or inarticulate, sometimes mumble, . . . .

Embedded in the book are engrossing lessons in geology.  What comes through most clearly to me is how unique Earth is of all the planets.  Bjornerud's treatment of the tectonic forces at work on the planet Earth stands out.  She notes that, of all the planets, ours is the only one that has moving plates.  This continuous movement of plates, in particular the subduction of one plate under another, provides a constant source of communication between the interior of the planet and the exterior, a communication that is critical not only to the structure of the planet as we know it, but to the presence of life here.  The rocks that undergird her story are intimately involved in this repeated construction and destruction of stone.  "The Earth makes no distinction between creation and destruction."

Other themes run throughout the memoir, particularly, that, in the pursuit of short-sighted monetary gain, we have subjected the natural world to wanton destruction and exploited native peoples in that pursuit.  We erroneously believe we are in charge, that we have control.  The rocks know better.  Further, she inveighs against the notion that the Earth we know today was preordained, fated to be what it is.  Reflecting on the history of life from the microbial to the multicellular complex, she notes,

None of these things - though now literally set in stone - were then preordained; given the happenstances of planetary and biological evolution, Earth's story could have unfolded quite differently.

Here, as elsewhere in the book, she does not shy away from drawing life lessons from the rocks, to wit, "My path into geology felt anything but predestined."  Perhaps most prominently in this vein is the notion that the Earth's sustaining processes of creating and destroying, with the dangers and rewards of the cataclysms involved, are mirrored to some extent in the arc of change in her life where roles and relationships change, sometimes abruptly. 

Perhaps change is the key to this book.  The Earth is vibrant, living, and changing.  Rocks undergo change, sometimes slowly, sometimes violently.  Our understanding of the rocks has changed and deepened over her lifetime.  At one point, while in an academic building's basement, she contemplates an array of neglected crates containing rocks collected years ago.  The rocks have not changed in those relatively few years, whatever their histories before being collected.  She muses,

The rocks have remained as they always were, while our interpretations of them have vacillated and evolved.  The same is true for the events of our lives; the past is immutable, but its meaning changes with time.

This memoir merits and rewards our attention.

Melanistic Eastern Gray Squirrels - Citizen-Science in My Neighborhood

A year ago, I decided to follow in the footsteps of biologist Richard M. Lehtinen, who, over the course of about eight and a half years, took walks through the neighborhoods around The College of Wooster, in Wooster, Ohio, and tallied each black and gray squirrel he spotted.  The data he gathered were then used as part of a study he co-authored about the distribution of the black (melanistic) color morph of the eastern gray squirrel (Sciurus carolinensis) in the Great Lakes region.  (Dispatches From the Neighborhood Watch:  Using Citizen Science and Field Survey Data to Document Color Morph Frequency in Space and Time, Ecology and Evolution, Volume 10, 2020.)  I discussed this and other research on melanistic eastern gray squirrels in a 2023 post.

Lehtinen walked seven set routes daily in his study area - one route was followed for the entire length of the survey period (July 22, 2010 - December 31, 2018), five others were followed for six years, and one was followed for five years.  He recorded a total of 39,966 observations, 66 percent of which were of melanistic individuals.  These data do not provide an unduplicated count of squirrels sighted, given that many of the same individual squirrels were sighted and tallied on more than a single day.  In the aggregate, though, they do gauge the overall melanistic representation among eastern gray squirrels living in the area and along the routes followed.

It's a fairly simple research activity that generated data important for explaining possibly why distribution patterns for the melanistic squirrels are what they are.  Lehtinen et al. found significant differences in the presence of these squirrels among the routes followed, and that these differences changed over time, some consistently in one direction or the other (increase or decrease in melanistic percentage), and others evincing little change.  These walking survey data, coupled with additional population data assembled by the authors, showed the melanistic distribution in Wooster, across much of Ohio, and in the Great Lakes region to be decidedly mosaic in nature.  In essence, different locations showed sometimes substantially different concentrations of black squirrels, a finding true for areas that were geographically close to each other with similar habitats which, the authors posited, exhibited few, if any, obvious distinctions in selective forces that might be in effect (e.g., presence of predators).  Hence, it would appear that something other than natural selection might be driving the ebb and flow of these black squirrel populations:  the authors suggested that chance in the form of genetic drift was at work.

Beginning in November, 2023, and continuing through December 29, 2024, I conducted my own citizen-science project in which I tallied each sighting I made of a black or gray squirrel during my daily walks through my own extended neighborhood.  My primary goal was quite simple:   estimate, as best I could, the overall representation of melanism in the squirrel population in this area.  A secondary objective was to see how the black squirrels were distributed among several localities within the study area.

The area in question is part of Silver Spring, Maryland, a suburb of Washington, D.C..  The study area is shown roughly outlined below in a screenshot from a portion of the map of Silver Spring from Apple Maps.  My walks fell within this area.

My effort differed from Lehtinen's in several significant ways.  The primary and most important one is that mine covered a much shorter time period than his.  I began tallying my squirrel observations on November 5, 2023, and, for this post, used data up through December 29, 2024, a period encompassing 421 days.  I recorded one or more squirrel observations on 269 days or about 64 percent of the days in this period.  Travel, nasty weather, health issues, and an absence of sightings account for the missing days.  In contrast, Lehtinen's survey was conducted for about eight and a half years - from July 22, 2010 to December 31, 2018 - a period of 3,085 days.  During that time period, he made 5,166 surveys, about 1.7 each available day.

Among other differences in the two neighborhood surveys is the larger area covered by mine.  His routes traversed an area of 0.33 square kilometers or 0.13 square miles.  My routes fell within an area of very roughly 0.73 square kilometers or 0.28 square miles.

In contrast to his effort, I did not have precisely prescribed routes.  As described below, I traversed some streets, avenues, and parks in the neighborhood much more frequently than others.  To minimize double counting of individual squirrels in any one day, the daily circuits I followed through my study area were nearly all loops.  In the event my path did cover any of the ground twice on a particular day, only tallies that exceeded those from the initial passage were included.

Finally, I would stress that the topographical nature of the area being studied in each of these projects may differ.  My study area included several relatively quiet, tree-lined residential roads, and three busy and noisy thoroughfares, among them, one undergoing substantial reconstruction in this period.  Included in my study area were two large parks, one abutting a small woods and one bordered by woods and a creek, and one small, partly treed, park bounded by neighborhood roads.  Lehtinen did not describe his study area beyond noting that "each of [his] routes followed streets in residential neighborhoods adjacent to the College of Wooster campus and Cornerstone Elementary School and are situated along parallel or perpendicular streets."  (p. 1529)  After looking at a satellite view of the presumed area in which he gathered his data, I believe his to be more consistently residential than mine if his routes lay only along an axis running directly from the College of Wooster to Cornerstone Elementary School.  In that case, his study area, unlike mine, featured few, if any, natural or manmade barriers to squirrel movement among the routes.

The additional important issue of identifying color morphs should be addressed.  As I noted in the previous post on these squirrels, analyses by biologist Helen R. McRobie of the genetic basis of the color morphs in the eastern gray squirrel found three distinct such morphs:  gray, black, and brown-black.  The genetic source of the last is a heterozygous version of the allele controlling color.  (Helen Rebecca McRobie, The Genetic and Molecular Basis of Melanism in the Grey Squirrel (Sciurus carolinensis), Anglia Ruskin University, Doctoral thesis, September 2014; and Helen R. McRobie, et al, The Genetic Basis of Melanism in the Gray Squirrel (Sciurus carolinensis), Journal of Heredity,Volume 100, Number 6, 2009.)  To my untrained eye, there is some fluidity in the color variations sported by individual eastern gray squirrels, fluidity that goes beyond the three distinctions McRobie identified.  (See, for example, the discussion of several other color variations "in the vicinity of Washington, D.C.," by zoologists Richard W. Thorington, Jr., and Katie Ferrell in Squirrels:  The Animal Answer Guide, 2006.)  Nevertheless, despite detecting some slight variations in the coloring of a very few of the squirrels I observed, I had no issue distinguishing black from gray individuals in my study area.  All my observations fell into of those two categories.  Lehtinen et al. did not indicate that such color distinctions were an issue for them.

The data provided below are based on tallies of observations on days on which I actually walked the neighborhood and spotted at least one squirrel, whether gray or black.  This means that the few days on which I walked but failed to spot a single squirrel are missing from these data.  The aggregate data provided below regarding the overall representation of gray and black squirrels, as well as the data used to determine differences in melanistic presence in the several specific subsets of neighborhoods I covered (see below), are based on the entire data set of days when squirrels were tallied.

Aggregate Observations

Over the course of the entire study period, I recorded 1,565 observations of squirrels in my neighborhood.  Of this total, 1,152 or 73.6% were of gray squirrels and 413 or 26.4% were sightings of melanistic individuals.

I have no prior baseline data for this or nearby areas with which to compare this melanistic representation in my neighborhood population.  I take with the proverbial grain of salt the unsubstantiated and vague estimate offered up in a recent article in The Washington Post by freelance writer Ashley Stimpson.  She stated that black squirrels make up "as much as half of the District's squirrel population."  (Why We Celebrate Black Squirrels, But Think of Gray Ones as Pests, The Washington Post, October 8, 2024.)  As a source for this estimate, she linked to a CBC News article which posited that "about half of Washington's squirrel population" is melanistic.  This article offered no source for its estimate.  (Matt Kwong, White House, Black Squirrels:  How 8 'Desirous' Canadian Rodents Ended Up Overrunning Washington, CBC News, July 12, 2018.)

Melanism Representation in Several Distinct Localities of the Study Area

Although I did not follow fixed routes during my survey, there are at least five distinct portions of the study area in which I frequently walked.  Some of these localities, though often adjacent to one another, have features potentially posing some physical boundaries (e.g., busy roads) that separate them.  I describe each locality below.

Locality 1:  Two tree-lined, relatively quiet residential roads whose houses share backyards.  The roads are connected by a grassy walkway.  This locality is separated from the others by a busy road, though squirrels do cross it, sometimes unsuccessfully (see data below on squirrels killed by traffic).

Locality 2:  The open and partially wooded area of a park with several ball fields, separated from Locality 1 by a busy street.  Part of the park abuts Localities 4 and 5.

Locality 3:  The broad lawn with mature oak trees along the side of a church, bounded by a very busy road undergoing construction, the parking lot of a small cluster of stores, and a small apartment building.  It seems quite isolated from the rest of the study area.

Locality 4:  A triangular area bounded by tree-lined, relatively quiet residential roads, encompassing a small park with a soccer field and tennis court, partly contiguous to Localities 2 and 5.

Locality 5:  Two, tree-lined, relatively quiet residential roads, that cross each other, partly contiguous to Localities 2 and 4.

My walks took me to each of these localities with varying frequencies.   Of the 269 days on which I recorded any observations, 49.4 percent included observations made in Locality 1, 33.5 percent in Locality 2, 11.5 percent in Locality 3, 26.4% in Locality 4, and 19.7% in Locality 5.  Nearly all of my daily walks ventured into more than one of these localities.   I made observations in each locality in all seasons of the year.

The table below shows the aggregate counts of gray and black squirrel observations in each locality, and the percentage of the total observations in each locality that were of melanistic individuals.

Locality 1 may well have had an outsized influence on the aggregate counts reported earlier.  This can be attributed to the high frequency with which daily observations came from this locality (almost 50 percent), the large number of aggregate observations from this locality (453 or 28.9 percent of aggregate observations across my study), and the healthy representation of melanistic squirrels living in that area (more than 42 percent of Locality 1 observations were melanistic and those accounted for 46.5 percent of all melanistic sightings in my study).

I would note that the data Lehtinen et al. provided in a supplementary data table to their study ("wooster_summary_route_year") show that Lehtinen's Route 1 contributed significantly more data to his survey data than did his other routes.  Approximately 44.0 percent of the total observations from his entire walking survey were accounted for by Route 1 and 46.9 percent of all melanistic observations came from that same route.  No other route he followed came close.  The nearest was Route 2 with 17.0 percent of total observations and 15.7 percent of melanistic observations.  Nevertheless, given the high representation of melanistic squirrels across all  of his routes (the range was from about 49 percent to over 73 percent with a median of approximately 69 percent and a mean of about 66 percent), the aggregate data he reported were not disproportionately influenced by his Route 1.

It would appear that my study showed melanistic squirrels to be distributed across these nearby localities in a mosaic pattern with some substantial differences, often much larger than those from Lehtinen's walking survey data.  Even those localities abutting each other without physical barriers (Localities 2, 4, and 5) showed sizable differences.

It may be that, due to the physical barriers demarcating some of my localities, my findings are somewhat more reflective of the mosaic pattern that Lehtinen et al. found in the separate surveys they conducted of 55 urban areas in Ohio.  The frequencies of melanistic squirrels across these urban areas was "extremely broad."  (p.1534)

I don't know whether the habitats of my localities were similar in the selective forces that might be at work in each.  A few observations are in order.  Several of these localities are bounded by high-traffic roads presenting a threat to squirrels seeking passage across them (particularly Localities 1 and 3).  Over the course of my survey, I counted five dead gray individuals on the road separating Localities 1 and 2.  (I observed one other dead squirrel in this period, a melanistic squirrel inside Locality 1.)  Locality 3 is effectively isolated by the road barriers.  Human traffic and activities, including dog walking, were evident in all of these localities.  Locality 2 also featured well-attended organized sports in the spring and fall.  With regard to natural predators, there are hawks in the area and several were observed or heard in Localities 1, 2, 4, and 5 at various times in the year.

Although more limited in its duration and less structured in its execution than the walking survey by Lehtinen, I believe that the results of my citizen-science effort are not without their utility, offering some support for the findings Lehtinen et al. described in their 2020 study of melanistic gray squirrels in the Great Lakes region.