Sunday, September 30, 2018

Unpacking A Few Layers of an Ichthyosaurus Rostrum ~ The Consequences of Uninformed Bidding at an Auction

This is a post that could have dealt with a renowned fossil hoax or a multi-million dollar illicit fossil deal, but doesn’t.  Instead I here demonstrate that, at least for a specific fossil, I don't know up from down (literally).

Paleontologist Alfred Sherwood Romer (1894 – 1973) asserted many years ago that ichthyosaurs, which first appeared in the Triassic and died out completely late in the Cretaceous, had the honor of being the reptiles “most highly adapted to an aquatic existence.”  (Vertebrate Paleontology, 3rd edition, 1966, p. 117.)  He posited that the ichthyosaur’s niche in the world’s marine ecosystems was now occupied by dolphins and porpoises.  He used a reconstruction of Ichthyosaurus quadriscissus by paleontologist Ernst Freiherr Stromer von Reichenbach (1871 – 1952) to illustrate, in a simplified fashion, the structure and alignment of the bones in an Ichthyosaurus’ skeleton.  (I took the image below from von Stromer’s Textbook of Paleozoology, Volume II:  Vertebrates, Figure 103, 1912, p. 106.)

How ichthyosaurs came to be, he asserted, was a mystery because they appeared in the fossil record nearly fully formed in the Triassic, trailing no transitional forms behind them (p. 120).  Even today, more than half a century after Romer wrote, their origins remain in question, a matter of debate.

I am quite taken with the wonderfully long snouts or rostra many ichthyosaur species sported millions of years ago.  Pictured below is a skull, with its very prominent rostrum, from an Ichthyosaurus sp.  Geologist W. J. Sollas (1849 – 1936) sliced (very carefully) through this skull creating many different cross sections for an analysis in the early 20th century.  (These photographs appear in The Skull of Ichthyosaurus, Studied in Serial Sections, Philosophical Transactions of the Royal Society B, Volume 208, text figure 1, January 1, 1918.)

My interest in ichthyosaurs was rekindled a couple of weeks ago when, during an auction held by a local fossil club, I was sucked into a bidding “war” on two small cross sections of the rostrum from an Ichthyosaurus communis.  According to the label (and I have no reason to doubt it), this rostrum came from the Lower Lias at Lyme Regis, England.  This is a Lower Jurassic geologic unit, roughly 200 to 174 million years old.  I hadn't noticed this specimen prior to the auction and so knew only what the auctioneer chose to share.  Nevertheless, I succumbed to the addictive action of the auction and started putting up my money foolishly and rather blindly.  Ultimately, with some misgivings, I came away with the prize at a price probably well out of line with its value.

As an aside, I have to note that I struggle with the notion of value for such objects; it poses a persistent and unresolvable conundrum for me.  Although ascribing value to such a thing in some clinical, objective way is certainly done all of the time, when it comes to gauging value for me, a critically different factor enters into the equation – the emotional pull of the object in question.  To explain my eagerness to acquire this fossil, one probably need look no farther than its place of discovery – Lyme Regis.  That gives it a nearly irresistible allure.  Lyme Regis on the Dorset coast of England, part of a World Heritage site, is the source of so many breathtaking marine fossils that it occupies a special place on my list of the places where I must hunt fossils at least once in my lifetime.  Integral to its attraction is that this is where the inspired and inspiring Mary Anning worked the cliffs in the early 19th century, establishing herself as a singularly skilled and deeply knowledgeable fossil hunter.  (My post dedicated to Anning appears here.)

And so I carried home the two small pieces of an ichthyosaur rostrum, each piece standing no more than 5 cm tall.

What follows is largely a description of this novice’s attempt to understand, at a very basic level, what he now has in hand.

At the outset, I really had little idea of what I owned; I could not explain what was seen in these cross sections.  It didn’t help that I, for some bizarre and unknown reason (a senior moment, perhaps), became confused about whether, as cross sections, these were transverse or longitudinal sections of the rostrum.  Initially, I labored under the mistaken idea that they were longitudinal in orientation and, as a result, nothing I saw in these sections made any sense.  While digging through the literature I corrected that mistake.

Even resolving that fundamental misunderstanding left my overall understanding of these sections frustratingly limited.  Here are views of two faces of these pieces.  As shown in the picture above, I have labeled the section on the left as “A” (I assume the anterior end of the rostrum overall was somewhere to the left of section A) and the one on the right as “B”.  The two faces (right face of section A and left face of section B) shown below are those created by the cut that separated this portion of rostrum into two pieces.

Unpacking these cross sections required carefully study of their faces and some close comparison to some images of rostral cross sections I found in the literature – yes, they differ in detail, but overall they are clearly like those in the literature.  For instance, rostral cross sections typically exhibit a fairly significant degree of horizontal and vertical symmetry, paired upper and lower elements that flow into bulbous structures in the middle of each cross section, and isolated circular and fusiform (spindle-like) structures.  Consider the drawing (below) of the somewhat distorted elements a fragment of a rostrum found encased in a chert cobble.  This cross sectional view appears in an article by paleontologist Charles Lewis Camp (1893 – 1975) (Ichthyosaur Rostra from Central California, Journal of Paleontology, Volume 16, Number 3, Figure 1, p. 363, May, 1942.)

(I cropped this image from Camp's article and reproduce it here, assuming this is covered by the fair use doctrine.)

Or consider the cross section (below) of an anterior portion of a rostrum of an ichthyosaur from Lyme Regis that appears in Sollas' article cited earlier (text figure 16 A, p. 119).

Though the pictures above of my sections suggest that I know up from down, that is, the top from the bottom of these sections with some certainty, I really do not.  Identifying the dorsal and ventral sides of rostral ichthyosaur cross sections may not be all that easy in general and has proven problematic for me and this specimen.  It provides me with some solace that Camp noted that one of the features distinguishing  ichthyosaurs from other marine reptiles is “the unusual similarity of the upper and lower jaws” (p. 363).  Nevertheless, in these pictures, I have chosen the thicker and somewhat broader portion of these sections as the dorsal side (see the photograph above of the two sections standing together).  This attribute seems to apply to many of the ichthyosaur rostra images in the literature.  If the orientation I've chosen is correct, then the dentary bone is at the bottom of these sections and the premaxilla is at the top.

Delving a bit deeper, when I magnified portions of these faces I detected distinctive patterns in the large structures in each quadrant (what I take to be bones of the premaxilla and dentary), a feature missing from the various isolated circular and fusiform elements in each face.  This strongly suggested to me that the latter are other than bone and most likely teeth.  The first image below shows the right face of section A with a portion highlighted.  The second image is a close up of that highlighted area.

Bone (or what I take to be bone) with its distinctive patterning is clearly evident in this photograph as is the smoother texture of the purported teeth.  The larger structure that lies in the middle of this closeup is, I believe, a tooth that was cut longitudinally when the cross section was made.  The lighter coloring at its upper point may be enamel.

To clarify my thinking, I outlined the gross structures of the lower right quadrant of the right face of section A (this is an area larger than that shown in the closeup above).  That work is shown below - bone is outlined in black, tooth in red.

To be clear, I think the different configurations of the purported teeth are a function of how they were oriented in the jaw as fossilized.  Those in a vertical position are fusiform.  In other words, they were cut longitudinally by the cross sectioning.  Those teeth at or approaching a right angle to the cross section appear more or less circular, the result of being cut transversely.  I assume that the hollow center of some of these fossilized teeth is the pulp cavity.

At this juncture, I have managed to acquire some slight sense of what is displayed in these cross sections.  Understanding them still further (beginning with distinguishing dorsal from ventral sides) will require some real work, so, I have decided to draw my work and this post to a close, at least for the moment.

That said, I ventured, albeit briefly, into an area I’m often drawn to – the backstories of the people related in some fashion with a fossil – without intending to write about them now.  How much more remarkable could those stories be than my confusion over knowing up from down with these rostral sections?

Well, probably a great deal more exciting, given that they may involve fossil fraud and illicit fossil dealing.  Some have posited that W.J. Sollas (author of the article cited earlier) was a party to the Piltdown man hoax, that grand fossil fraud perpetrated in England in the early 20th century.  (Richard Harter, Piltdown Man:  The Bogus Bones Caper, The TalkOrigins Archive.)  Then there’s what turned up when I explored the provenance of these ichthyosaur rostrum sections.  One of the labels associated with them indicates that, at some point, these sections were purchased from a dealer named Christopher Moore with an address in Charmouth, a village near Lyme Regis.  This is, I believe, the same Christopher Moore who was implicated in a multi-million dollar case involving dinosaur fossils stolen from Mongolia.  (Alex Hannaford, The Trade in Stolen Dinosaur Fossils, The Telegraph, October 30, 2013.)  It was quite a splashy crime.  Perhaps for another day.

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