Inertia at Year's End

With my accumulated years, the deepening gloom of late December brings a lassitude, an ebbing of motivation.  Writing a new blog post at year's end seems a daunting challenge.  In his old age, Walt Whitman acknowledged that, even as his heart still beat (hurrah) and the forces long celebrated in his poetry still moved him, he felt a "strange inertia/falling pall-like round me."  (A Carol Closing Sixty-Nine, Sands at Seventy, included in late editions of Leaves of Grass as an "annex.")

Wait . . . that's all much too bleak.  It's not hopeless.  I've found that the effort to put together a post at year's end can be fueled by exploring and learning something new.  And, if that doesn't provide the necessary spark, I can always resort to humor.  That seldom fails and I've turned to it on more than one occasion for a December post.

At the outset, it seemed possible that one of three recent papers might help me get down to business.  Here are brief blurbs about each, suggesting what I felt were some of the likely hooks in them.

#1

I thoroughly enjoyed the recent article by paleontologists Chase Doran Brownstein and Tyler R. Lyson, in which they identify a new species of fish, a giant gar, some 1.5 meters (4.9 feet) long from fossils found in the Fort Union Formation in North Dakota which dates from the Paleocene.  (Giant Gar from Directly Above the Cretaceous-Palaeogene Boundary Suggests Healthy Freshwater Ecosystems Existed within Thousands of Years of the Asteroid Impact, Biology Letters, Volume 18, Issue 6, June 2022.)

At least two aspects of these fossils are striking:  the size of the gar, which makes it one of the largest to have ever lived; and where the fossils were found - in the formation, a mere 18 centimeters (7.1 inches) above the K-Pg boundary (dating from about 66 million years ago) that marks the end Cretaceous extinction event.  Therefore, the authors estimate that this giant fish lived only 1,500 to 2,500 years after the extinction event.

Import of that?  At a very superficial level, I found it reassuring that so soon after the mass extinction, there were animals of this size going about their business.  But, as the authors explain, the implications of this are actually quite profound.  They describe the Lilliput effect (another of the wonderful adjectives used by paleontologist) which, based on the fossil record, shows that average body sizes in different taxa appear to decrease after extinction events.  Brownstein and Lyson note that many species with large bodies went extinct in the end-Cretaceous event.  Here, though, was a very large gar, an animal that could be alive only if there were an existing food chain capable of supporting it.  The authors suggest two possible explanations:  the freshwater environment in which this gar lived survived the extinction, or the local ecosystem rebounded rapidly after the event.  Further, they surmise that, given the size of this gar, under some circumstances the impact of the Lilliput effect could be limited.

I recognized that here were some topics that might be explored in a post.  For example, what other large bodied species are known to have either made it through this or other mass extinction events or that appeared soon after?  What's the background on the Lilliput effect - who first applied it, what extinction event was the focus, what's the dynamic that might be behind it?

#2

The previous post in this blog focused on the fossil record of the fossorial (burrowing) response of some mammals to challenging surface environments, either through hibernation or estivation (the latter a state of torpor to cope with high surface temperatures).  So I was primed for the recent article by paleontologist Calvin So and colleagues that analyzed fossils of a newly identified amphibian found in burrows in the upper Jelm Formation in Wyoming, a formation dating from the beginning of the Late Triassic, about 231 million years ago.  (Fossil Amphibian Offers Insights Into the Interplay Between Monsoons and Amphibian Evolution in Palaeoequatorial Late Triassic Systems, Proceedings of the Royal Society B,Volume 291, 2024.)

The climate in the Late Triassic, particularly in the low latitudes, was brutal, a time of periods of massive monsoons, and dry periods with lethally high temperatures.  So et al. posit that, without behavior adaptations, small animals could not have survived.  After exploring a large collection of these amphibian fossils in their burrows, the authors conclude that this taxon had evolved to burrow into the bottom of riverbeds and estivate in order to survive the hot, arid periods.  This is, they write, "to our knowledge, the first unambiguous evidence of vertebrate behavioral adaptation to extreme seasonality near the early-Late Triassic palaeoequator."  (p. 8)

The fossils of this species exhibit what the authors describe as a "wedge-shaped" skull and short forelimbs.  As a result, they posit that the animal dug its burrows with its head, not with its arms.  Further, they suggest that the fossils found in burrows were of individuals that died during their period of estivation, before the rains returned, ending the dry season.

The article had me at the word "fossorial" in its abstract.  Further, a blog post on this article might prompt much more digging into available resources on the origins of the name given the new species:  Ninumbeehan dookoodukah.  The name is in the Shoshone language, which is a way, the authors write "to pay tribute to the Eastern Shoshone people, their language and the land to which they belong."  They note that "the name results from a collaborative partnership between the authors of this publication and the seventh-grade students from the Fort Washakie School."  That partnership begged for exploration.  How did it come about?  What did it consist of?  Is it ongoing?

#3

Geologist Marcia Bjornerud has penned a beautifully poetic essay about, of all subjects, metamorphic rocks.  (Roaming Rocks, Aeon, December 17, 2024.)  The story she tells is captured in the adjective in the essay title, "roaming."  Metamorphic rocks are incredibly well traveled, undergoing profound transformations in the process.  Bjornerud makes the journeys of these rocks mesmerizing.

There seemed to be much in the essay to inspire a blog post.  At a minimum, I might search my collection of rocks and minerals for examples showing some of the transformations.  Even better would be a road trip to nearby places that feature metamorphic rocks with the expectation that I could find very photogenic examples of what Bjornerud describes.  I could delve into the history of what was once thought about the genesis of these rocks and how (and who) offered the actual narrative.

In any post that might come from this, I probably would provide examples of Bjornerud's graceful prose.  For instance, I might draw attention to her graceful description of the metamorphic journey which begins with sediments from eroded rocks, accumulating on the seafloor, being transformed by growing pressure into mudstone and shale.  Then, as she writes:

Millions of years pass. The geography of the world changes with the neverending dance of tectonic plates. One day, the shale finds itself in the vice-like squeeze of colliding continents, folded deep into the interior of a mountain belt. The pressure at such depths is extreme. The fine clay minerals in the shale, now far from the shallow marine waters in which they formed, can no longer hold their shape. Their chemical bonds weaken, their grain boundaries become diffuse, and a remarkable transfiguration begins. The elements within, previously part of a rigid crystal scaffolding, are now free to wander. Atoms of aluminium, silicon, magnesium and iron, surprised at their unaccustomed mobility, form new alliances and reconfigure themselves as minerals comfortable at these depths and temperatures: shiny black biotite, wine-dark garnet, and sky-blue kyanite.

Her language is irresistible.

***

There . . . three possible jumping off points for a new blog post.  Enough to shake me into actually working?

Mulling over which of these pieces seemed most promising, I wandered to my cluttered office.  I sat there for a while.  As I did, my attention drifted to a disorderly pile of materials on the floor; the violet cover of a journal caught my eye.  Improbably, it was the November/December, 1992 issue of The Journal of Irreproducible Results:  The Publication of Record for Overly Stimulating Research and Ideas (Volume 37, Number 6).  (Some of the background and tangled publishing history of the JIR can be found on Wikipedia.  JIR has been cited previously in this blog in a post about scientists as humorists.)  I idly flipped the pages of this issue until I came upon a letter to the editor by P. Finbar Duggan, D.Sc., Ph.D., F.R.S.C., F.I.C.I., M.R.I.A, University College Cork, Cork, Ireland.  I experienced an epiphany of sorts as I read esteemed Professor Duggan's brilliant missive.  In a single, tightly argued paragraph he resolved the dilemma I faced with my pending post.

I quote the letter below in full:

Dear editor:

I became extremely enthusiastic when I saw your call for papers for the special JIR issue on inertia.  I immediately put pen to paper because I have some interest in this topic.  To begin with, I had better explain why I thought it worthwhile to do so.  Even though I am not really interested in inertia in all its facets, nevertheless I would be letting the side down if I did not make a contribution.  For these reasons, therefore, I feel that, reluctantly, I must set out my thoughts even if they are become somewhat unfocused.  I do feel the onus to

The Fossorial Life - Portal to a Better Time?

[Badger] shuffled on in front of them, carrying the light, and they followed him, nudging each other in an anticipating sort of way, down a long, gloomy, and, to tell the truth, decidedly shabby passage, into a sort of a central hall; out of which they could dimly see other long tunnel-like passages branching, passages mysterious and without apparent end. But there were doors in the hall as well—stout oaken comfortable-looking doors. One of these the Badger flung open, and at once they found themselves in all the glow and warmth of a large fire-lit kitchen.

 

Kenneth Grahame, The Wind in The Willows (1908)

At some point, I added the phrase "fossorial life" to a list of interesting words, sayings, and topics for possible blog posts (yes, this list is a catchall).  Writing about this phrase took me from the Badger's comfortable and homey burrow, which offered shelter from a snow storm to the Mole and the Rat, on a journey of discovery, disaster, and speculation.

I've used "fossorial" once in this blog when I suggested that it's possible the turtle's carapace (top shell) originally evolved to further a "fossorial lifestyle."  I like the word for its sibilance and its music - "fa, so, la."  I assume the root word is the Latin foss meaning "trench or ditch" which, in turn, gives rise to the Latin fossul which is a "burrow" and fossor, "a digger."  And, certainly, a related Latin term is fossil defined as "dug up."   (Donald J. Borror, Dictionary of Word Roots and Combining Forms, original copyright 1960.)  The adjective, as all of these Latin words suggest, describes an animal "capable of, or characterized, by digging burrows."  (Oxford English Dictionary (OED).)  I was a bit surprised that it's a fairly recently coined word, first appearing, according to the OED, in 1834.

The fossorial life is one lived, at least in part, underground.  I am intrigued by, and drawn to, such a life in this age of catastrophes, actual and impending, a time marked by climate, social, and political upheaval that threatens all living creatures on the planet.  Its appeal goes beyond metaphorical burrowing or burying one's head in the sand.

Mammals have been burrowing and embracing the fossorial life for millions of years.  In an article on two fairly recently discovered, purportedly fossorial creatures from the Jurassic Period (201 to 145 million years ago (mya)), science writer Riley Black noted that both Docofossor brachydactylus, while not quite a mammal, but close, and Fruitafossor windscheffeli, just slipping in under the wire to qualify as a mammal, sported the hallmarks of the fossorial life among which are truly buff forearms and shovel-shaped forefeet.  These discoveries offer the earliest evidence of burrowing among proto- and early mammals.  (Sciencespeak:  Fossorial, Laelaps, National Geographic, February 16, 2015.)  (I would note that there are other features of mammals that signal a life lived in the soil including small eyes and poor eyesight, little external evidence of ears, and a fusiform or spindle-shaped body.)

Black characterized the Docofossor (living some 160 million years ago) as the "Jurassic equivalent of a mole," though he noted that it's not related to moles and is an evolutionary dead end, as is the Fruitafossor (living some 150 million years ago) which is often described as anteater-like.  Pictured below is the holotype fossil of D. brachydactylus on display at China's National Natural History Museum.  (It is reproduced under the Creative Commons Attribution-Share Alike 4.0 International License and can be found on Wikimedia Commons.)

What I found most compelling about Black's account is his observation that mammals and mammal-like animals have evolved to embrace a fossorial life multiple times.  Clearly, there's a robust and attractive payoff to living this way.

If I cast my net broader to include all vertebrates, the early roots of a fossorial existence go much further back into deep time, perhaps as far back as the Devonian (some 419 to 359 million years ago) or maybe the Carboniferous (about 359 to 299 million years ago), but, most certainly to the Permian (about 299 to 252 million years ago) when "vertebrate burrowing becomes more common and complex."  (Lorenzo Marchetti, et al., Origin and Early Evolution of Vertebrate Burrowing Behaviour, Earth-Science Reviews, Volume 250, 2024.)

What's the pull of going underground?  As paleontologist Marchetti and his colleagues observed, burrowing is used by animals for a host of reasons such as:  acquisition and storage of food, protection from predators, and escape from adverse climate conditions on the surface.  This last may be seasonal when animals hibernate to deal with food scarcity and cold during the winter, or when they aestivate (enter a state of torpor or dormancy) to cope with arid and hot periods above ground.

Sheltering from adverse surface conditions can be singularly important for the survival of species.  Marchetti et al. looked closely at the appearance of fossorial vertebrates in the fossil record and mapped that information to events in deep time.  What is striking is how often climate change (e.g., transition in the early Permian from an ice age to a greenhouse climate) and specific extinction events (e.g., end-Permian mass extinction) appear to be associated with an increase and proliferation of fossoriality.  They concluded, "In some instances, burrowing can be viewed as a potential survivor's gate through a mass extinction." (p. 32)

A gate or portal to a better time.  What a wonderful image.

Paleontologist Elsa Panciroli, in her masterful book Beasts Before Us:  The Untold Story of Mammal Origins and Evolution (2021, subject of a previous post in this blog) began her chapter on the end-Cretaceous mass extinction by recreating the experience of one, small, burrowing mammal the day the asteroid slammed into the Earth.  Reminiscent of The Wind in the Willows, the chapter opens with:

In a nest furnished with moss, a small circle of fur twitches.  Nose tucked against warm belly.  Whiskers flickering.  The sleeper is thrilled by memories of herbal scents and squirts of crushed bug.  Senseless dreams of scampering curl its minute toes.  The burrow is Goldilocks warm, just big enough to turn around and tuck in your tail.  It is mushroom dark, filled with musk.  The Earth clasps this sleeping body in her hand.

The little sleeper barely stirs as a rumble reaches it from another continent.  (p. 273)

When this insectivore finally leaves its burrow, it enters into a dark and devastated landscape, littered with decaying carcasses, which actually serves the animal well.  In Panciroli's telling, the animal survives and procreates, giving rise to generations more of these burrowing creatures.

Panciroli asserted:

From a mammal's point of view, the epic end-Cretaceous catastrophe might be nothing more than a harsh season to weather.  It's not that mammals were unaffected - like most animals they suffered catastrophic casualties.  Many lineages became extinct.  But we all know our own creation mythology:  our ancestors rose like a phoenix from dinosaurian ashes.  (p. 274)

The thought of those days, months, and many, many years when the environment was lethal or, at least, extremely difficult for myriad animals is actually quite terrifying.  I find some solace in the scene that Panciroli described: a warm burrow in the soil, hidden away from the devastation, a way for an animal and its species to survive.

Clearly, little mammal insectivores were not the only type of animal to pass through the portal.  For an analysis of which general types of animals could have survived the immediate aftermath of the asteroid's impact, I recommend a paper by earth scientist Douglas S. Robertson and his colleagues titled Survival in the First Hours of the Cenozoic (Geological Society of America Bulletin, May/June, 2004).  Perhaps no surprise that they found the vertebrate animal groups that did make it from the Cretaceous into the new era were much more likely to be those whose members had a life that involved sheltering in water or burrows.

It's appealing in some way to consider the advantages of a fossorial life as a way to endure climate change and make it through to the other side (assuming there is an other side), but it's not for us.  We haven't evolved to live that way, regardless of its advantages.  So, it's interesting, but idle speculation.  Yet there are those who take seriously the idea of a fundamental change in our existence as a means to survival.  As mentioned above, hibernation is a feature that some burrowing mammals experience as a way to deal with challenges on the surface (cold and food scarcity).  Vladyslav Vyazovskiy, a sleep physiology professor at the University of Oxford, has penned a provocative essay titled Could Humans Hibernate?  (Aeon Newsletter, November 18, 2024).  The takeaway is that, no, we cannot hibernate (yet), though perhaps our earliest ancestors did.  The attraction of it as a solution to a host of problem resonates with me.  Vyazovskiy wrote:

The revival of interest in hibernation in general, and human hibernation in particular, comes at the right time. The genre of science fiction is about imagining and predicting practical solutions for real-life problems when they cannot be solved with existing means. When the world is facing acute problems at a planetary scale, including climate change, technogenic disasters, wars, incurable disease, pandemics and mental health crises, and we are grappling with perennial questions, such as how to attain immortality (or at least extend high-quality life considerably), solve the mystery of consciousness or reach the far corners of the Universe, hibernation emerges as a potential opportunity, if not the only hope.

Whoa!

A "Magical" Experience Identifying Fossils

Old Lodge Skins (after lying down and waiting to die, is aroused by rain):  Am I still in this world?

Jack Crabb:  Yes, Grandfather.

Old Lodge Skins:  I was afraid of that.  Well, sometimes the magic works.  Sometimes it doesn't.

From the movie Little Big Man (1970)

I recently worked to identify the genus and species of two fossilized shells in my collection.  I thought that keeping close track of the steps I followed in this process would make it more directed, less random than it usually is for me.  I was wrong.  This post is an account of the path I followed.

I believe the two macro attributes of any fossil probably most important for identification are (1) shape and (2) geological provenience (that is, where the fossil was found).  Both of these attributes may feed into each other repeatedly during the identification process.

Here are the two fossils I sought to identify.  The dorsal views of these shells (first picture) are labelled 1a and 2a; the ventral views (second picture showing the apertures) are 1b and 2b.  These specimens are referred to below as #1 and #2.

Pictured below is shell #2 labelled with some of the general conchology terminology used in the literature.  For this illustration of terms, I have relied on Percy A. Morris' A Field Guide to Shells of the Atlantic and Gulf Coasts and the West Indies (third edition, original copyright of 1947, renewed 1975, endpapers).

I knew from the outset these two specimens were gastropod or snail shells because of their shape and form.  To deconstruct this recognition, which occurred instantaneously, I would say that my decision tree branched from animal (not plant) to shell (not tooth or bone) to gastropod (not a mollusk bivalve or other type of mollusk).

To take the decision tree down to the level of genus and species of the gastropods at hand, I had to address a second main attribute - geological provenience.  These specimens came to me as part of a small clutch of fossil shells collected by a friend on the western shore of the Chesapeake Bay in Maryland.  This is a site where, I believe, fossils from the Windmill Point member of the St. Marys Formation can be found.  These particular fossil shells, therefore, are likely to have come from a geological strata which is dated from roughly 11.6 to 7.2 million years ago in the Late/Upper Miocene epoch.  (See Paleobiology Database entry for Busycotypus.)  A study of the stratigraphy of the site posited that back in the Miocene, this was "a warm-temperate marine environment" with, some "subtropical influences."  (Lauck W. Ward and George W. Andres,  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. 51.)

At this stage in the identification process, I turned to the literature on the fossils of the St. Marys Formation, including the Windmill Point member.  Paleontologists have identified many members of the molluscan assemblage that populated that location during the Miocene.  The literature I consulted included:  

• Timothy Abbott Conrad, Monograph of the Genus Fulgur:  Notes on Shells, Proceedings of the Academy of Natural Sciences of Philadelphia, Vol. 6 (1852 - 1853), 1853
• George C. Martin, gastropoda discussion in Miocene, Maryland Geological Survey, 1904, and Miocene Plates, Maryland Geological Survey, 1904
• Harold E. Vokes, et al., Miocene Fossils of Maryland, Bulletin 20, Maryland Geological Survey, 1999
• Lauck W. Ward, Molluscan Biostratigraphy of the Miocene, Middle Atlantic Coastal Plain of North America, Virginia Museum of Natural History Memoir Number 2, 1992

Based, primarily on perusal of the illustrations in these sources, I found two likely candidate species:  Busycotypus coronatum and B. rugosum.  These names are those provided by Ward in Molluscan Biostratigraphy.  There have been changes in these names over time (e.g., Busycotypus coronatum began its taxonomic life as Fulgur coronatus).  Except in direct quotations from these sources, I usually refer below to each of these species as B. coronatum or B. rugosum, regardless of the name actually used by the author.

I must stress that I certainly did not exhaust the available taxonomic literature on these species.  So, any conclusion reached in this post, should be weighed against the possibility that a full sweep of the literature would have led me elsewhere in the identification process.

The species' descriptions in the literature I did consult proved singularly challenging with inconsistencies, widely varying levels of detail, and conflicting assertions.  Further, the illustrations accompanying these descriptions often failed to capture, at least for me, the differences purportedly distinguishing the two species.

The original identifier of many of the mollusks found in the Windmill Point member, including the gastropod genera and species listed above, was paleontologist Timothy Abbott Conrad (1803-1877), a prolific discoverer and namer of species.  (See Ward and Andres, p. 50-51.)  So, I thought it would most appropriate to consider first what he wrote about these two species in the report listed above.  (In addition, the text written by paleontologist George Martin (also cited above) includes excerpts from several of the many early to mid-19th century descriptions Conrad penned.)

According to Conrad (1853), the shell attributed to B. coronatum is shaped liked a spindle ("fusiform") and swollen ("ventricose"), in contrast B. rugosum is pear-shaped ("pyriform").  B. coronatum has fine lines circling the shell while B. rugosum's shell is marked by coarse lines.  The spire in the former is "short," while that of the latter is "prominent."  The nodes on B. coronatum are "elevated, compressed," while those of B. rugosum are "obtuse."  Their sizes differ markedly.  Conrad stated that B. coronatum's maximum length (the conchology literature often identifies this measurement as "height") is six inches while the length of B. rugosum is just three inches.  (p. 317)

Did Conrad's descriptions of these two species help me?  Less than I hoped.  Some of his observations suggested to me that #1 might be B. coronatum and #2 B. rugosum (e.g., #1 appears to be more spindle-like and #2 perhaps more pear-like; the spire of #1 appears shorter than that of #2).  But the size measurements he gave pointed in the opposite direction.  Of my two specimens, #2 clearly has a greater length than #1, consistent with an identification of B. coronatum.  To further complicate the identification, the differences in some of the attributes he highlighted aren't clear from language he used, particularly regarding the nodes.  And, in their present condition, elements such as the lines circling the body of the shells aren't clear enough to help in the identification process.  Fossil wear is a factor that can thwart an effort to identify the genus and species of a fossil.

Consideration of another paleontologist's comparison of these two species also highlighted the difficulties I faced.  Here is an excerpt from the publication by Harold Vokes (1999) in which he briefly contrasted these species.  He used the genus name Busycon for both and, significantly, considered B. rugosum to be a variety of B. coronatum (that is, not a separate species and at a taxonomic level lower than the species).

The large short-spired shells of Busycon coronatum (Conrad) ... are common in the St. Marys fauna associated with the variety rugosum (Conrad) . . . which differs in having coarser spiral ornamentation and more numerous and heavier elongated nodes on the shoulder of the whorl.  (p. 25)

The everyday adjectives in this description are a bit unclear to me.  Consider "large short-spired."  Is there a comma missing?  I assumed he was characterizing the shell as "large" and the spire as "short."  But that didn't get me very far.  Is B. coronatum bigger than B. rugosum?  Or is it simply, in the scheme of things, "large," though B. rugosum might be bigger still or possibly smaller?  Unfortunately, Vokes provided no measurements for these species.  I concluded that he thought the spire of B. coronatum to be shorter than that of B. rugosum.  Conrad would agree with this characterization of the B. coronatum spire.

To help address my confusion regarding Vokes' treatment of overall shell size and tallness of spire, I turned to his illustrations.  I discovered that his illustrations of these two species are actually from the earlier Maryland Geological Survey publication by George Martin, specifically, plate XLVI (Miocene Plates).  From that plate, Vokes chose to use just the illustration of the dorsal side of B. coronatum and only that of the ventral side of B. rugosum.  Why?  I don't know.  I thought the full plate from Martin (see below), showing dorsal and ventral views of both shells, would be potentially more informative.  The two views at the top of the plate (1a and 1b) are of B. coronatum and those at the bottom of the plate (2a and 2b) are B. rugosum (which, as noted, Vokes considered a variety of B. coronatum).

Looking at the shells depicted in Plate XLVI and assuming they are drawn to scale (a significant assumption), it seemed obvious to me that B. coronatum (1a and 1b), as illustrated, is larger than B. rugosum (2a and 2b), certainly consistent with Conrad's description given above and presumably Voke's as well.  Yet, according to Martin's own text describing these species, that understanding would be incorrect.  In his description of B. coronatum, he provided these measurements:  length, 130 mm (5.1 inches); diameter, 75 mm (3.0 inches).  (Presumably the distance across the widest part of the last or body whorl is the diameter.) For B. rugosum, he cited these:  length, 170 mm (6.7 inches); diameter, 90 mm (3.5 inches).  So, despite the illustrations, B. coronatum, according to the text, is smaller than B. rugosum.  I noted also how different Martin's measurements are from those given by Conrad (see above).

So, at this juncture, I wondered whether I assume that Martin got the measurements wrong, inadvertently flipping them between species.  Ultimately, though, I concluded that size, with respect to my specimens, might be a red herring.  Martin included a quotation from an 1843 report by Conrad that reminded me of a serious issue that should be addressed in the identification process.  Conrad noted that the shell of B. rugosum is shorter and more swollen than that of B. coronatum "when adult."  (As quoted in Martin, p. 182.)  This is an important consideration in the identification process:  is the fossil in question from an adult organism or some younger version of that species?  Size differences between specimens may reflect different maturation stages of the same species.  Frankly, given that neither of my specimens comes very close to the measurements Martin provided, I concluded that neither is from an adult and, therefore, size in this case probably wasn't dispositive.

There were still other aspects of Vokes' comparison between these species that I needed to consider.  What about the height of the spires on the specimens illustrated in Plate XLVI?  I thought the spire of B. rugosum as illustrated appeared to be shorter than that of B. coronatum, contradicting Vokes.  As already noted, I thought my specimen #1 had a shorter spire, suggesting that #1 might be B. coronatum and #2 B. rugosum.  Still hardly persuasive as to identification.

Vokes was as confounding as Conrad on the nodes of these shells.  Vokes stated that B. coronatum had more nodes than B. rugosum, and that its were "heavier."  I found the adjective "heavier" unclear.  So, I turned to considering the number of nodes, a feature that seemed likely to be fairly easy to assess.  Hmmm, not likely.  Examination of Plate XLVI suggested to me that B. rugosum as depicted had more nodes, which didn't fit with Vokes' description.  When I examined my fossils (#1 and #2 in the first photos in this post), I found it nearly impossible to count those on one of these (#1) because the specimen is worn.  As already noted, wear and tear on a fossil constitutes an important aspect of fossils that may confound their identification.

Finally, one of the discussions of these two species raised an additional and rather fundamental factor that should be considered in the identification process.  Similar fossils might not be different species at all, but, instead, reflections of naturally occurring variation, or a fossil might be a transitional stage in the evolution from one species to another.  These possibilities may make drawing sharp distinctions among fossils a fool's errand.  Indeed, B. coronatum and B. rugosum are, as Lauck Ward observed, "related."  He wrote:

Busycotypus coronatum first is differentiated from the parent stock (B. rugosum) in the Little Cove Point beds of the St. Marys Formation.  (p. 132)

I understood Ward (with the phrase "parent stock") to be positing that B. coronatum evolved from B. rugosum, which is consistent with the former appearing after the latter in the fossil record.  But that perplexed me because, as already discussed, Martin and Vokes thought rugosum to be a variety of B. coronatum.  Doesn't that suggest B. coronatum was the predecessor?  Maybe I've misunderstood "variety" all these years.

At that stage, I considered whether, from the outset, my effort to distinguish between the worn fossils of apparently immature and evolutionarily related animals that lived at the same time had been doomed to failure.  To salvage something from this taxonomic journey, I took refuge in what might be considered a cop-out, though I thought it a safe harbor.  I concluded that both specimens are from the genus Busycotypus, but couldn't go any further than that.  I applied the following taxonomic label to both:  Busycotypus sp.

Not a very happy conclusion.  Though it's one that paleontologist George Martin presumably would have understood.  Considering B. rugosum to be a variety of B. coronatum, he noted that it is "sometimes difficult" to separate the two, and, curiously, he added, "it is not essential that it should be done."  (p. 181)

Amen to that.