Monday, February 27, 2012

Witticisms in the Face of Mass Extinction

I fear that this posting will be taken as a retelling of an old joke or several jokes from paleontology.  That’s one advantage of being a paleontological amateur of recent standing, these are new to me.  Actually, the term “jokes” misses the mark, these are “witticisms” fashioned by clever paleontologists to describe real phenomena.  I found these all at once, rather than spread out over the decade in which they came into being.  That timing may explain some of my unease about this cluster of witticisms, the focus of this posting.
Earlier this week I spent a dreary morning in the Library of Congress’ Science and Business Reading Room.  The weather outside offered lowering clouds that threatened rain, and a building wind.  This complemented the atmosphere inside with its dim lights, dark wood desks, and a sepulchral echo whenever someone dared to walk the aisles.  All totally appropriate for the texts that lay on my desk, texts recently released from the bowels of the library.  The books were not old themselves – none of the volumes on my desk dated from earlier than the mid-1980s, but the tales they told were ancient – tales of mass extinctions.

(Given these atmospherics, this moment in the drafting of this posting constitutes a fork in the road.  In one direction lies the story I intend to tell, a relatively light-hearted one with a bit of my curmudgeonly attitude attached to it.  In the other direction floats a “ghost” story, perhaps something involving a dusty volume with engravings from which spring long extinct creatures.  Say, for instance, a rash of trilobites breaking the quiet with their skittering across the desks as they flee from the plate volume of Reverend William Buckland’s Geology and Mineralogy Considered with Reference to Natural Theology (1837).

Ah, that would be a ghost story inspired by those magical texts conjured up by Montague (“Monty”) Rhodes James a century ago (such as those he published in Ghost Stories of an Antiquary, 1904).  James, of King's College, Cambridge, wrote ghost stories in the British tradition, stories laced with horror and the macabre, not ghosts, per se.  Part of the horror of my tale would be the prospect of other extinct creatures sliding or thundering from the engravings.  Perhaps some other time, there are paleontological witticisms to explore first.)

Those who study mass extinction events distinguish them from background extinction, that continuous process of winnowing taxa (taxonomic groups), a sort of white noise of extinction.  In contrast, mass extinctions, according to paleontologist Peter D. Ward, “are geologically short intervals of intense species death.”  He notes that, “During the last 530 million years of earth history, the time since the advent of commonly skeletonized creatures on earth, there have been about 15 mass extinctions.  Five of these may have involved as many as 50 percent of the earth’s species.”  He considers three of these to be “major” because they “completely reorganized the ecosystems in the sea and, more relevant to humanity, on land.”  These would be those of the End-Permian (truly, the mother of all extinctions), Late Triassic, and End-Cretaceous.  (Rivers in Time:  The Search for Clues to Earth’s Mass Extinctions, 2000, p. 6.)

It was a morning of contrasts in the LC reading room.  For all of the death that marked mass extinctions and the profound impact these events had on earth’s living organisms, mine, though, was mostly a light-hearted charge.  Critical to analysis of extinction in general, and mass extinction in particular, is determining whether a taxon or taxa have in fact gone extinct.  It’s no simple exercise.  I had been struck by how thoughtful paleontologists have been in identifying the subtle processes that might affect that determination in the fossil record.  Equally striking, though, is how analyses of these situations prompted several paleontologists to engage in clever wordplay to capture their essence, wordplay that, in my mind, may challenge the usual gravitas of the science.  That was my pursuit – the origins of several of the best of those scientific witticisms.  It was really nothing new, very well-trod ground.

Here then are the three bits of wordplay that I explored.

Lazarus Effect

In the early 1980s, paleontologist David Jablonski demonstrated his familiarity with the New Testament when he gave a name to the phenomenon of taxa that disappear from the fossil record in mass extinction intervals only to resurface some time later, apparently not victims, but survivors.  “This disappearance and apparent extinction of taxa that later reappear unscathed can be termed the Lazarus effect.”  (Causes and Consequences of Mass Extinctions:  A Comparative Approach, in Dynamics of Extinction, edited by David K. Elliott, 1986, p. 197.)

It’s a clever and memorable label for such an occurrence.  Perhaps, he suggests, these Lazarus taxa sought refuge elsewhere, riding out the storm, so to speak.

I don’t intend to demean this first term, which I think is a stroke of genius, or the phenomenon it describes.  The Lazarus effect is not just a curiosity.  Jablonski uses it to great advantage, seeing it as “a rough indication of the completeness of the fossil record for the interval in question. . . .  The magnitude of the Lazarus effect is an indication of the distortion suffered by the fossil record in that time interval.”  (p. 197)  Further, “the Lazarus effect, can be used to assess patterns of extinction near mass extinction boundaries:  apparent gradual declines in taxonomic diversity leading to the extinction event can only be accepted as genuine if they exceed the magnitude of the Lazarus effect.”  (p. 211)

Elvis Taxa

In a 1993 piece, paleontologists Douglas H. Erwin and Mary L. Droser consider a related issue – the accurate identification of Lazarus taxa.  (Elvis Taxa, Palaios, Volume 8, Number 6, December, 1993, p. 623-624.)

They acknowledge the importance of the Lazarus effect for its utility in characterizing the quality of the fossil record, and, based on the length of time between the disappearance and reappearance of the Lazarus taxa, its contribution to an understanding of some aspect of the recovery of the environment after the extinction event.  But they stress that its usefulness depends upon correctly identifying the Lazarus taxa.  They note, “Extensive homoplasy and morphologic simplicity may confound recognition of Lazarus taxa.”

As I understand it, homoplasy describes the situation where unrelated taxa share very similar or identical morphological traits.  (See, for example, Homoplasy, A Good Thread to Pull to Understand the Evolutionary Ball of Yarn, ScienceDaily, February 24, 2011.)  As a result, finding such a taxon may lead to the conclusion that its look-alike had risen from the grave when it hadn’t.  “These apparent Lazarus taxa are a taxonomic artifact.”  Erwin and Droser “suggest that such [ersatz Lazarus] taxa should be known as Elvis taxa, in recognition of the many Elvis impersonators who have appeared since the death of The King.”

They then argue for the positive contribution of such taxa for our understanding of possible limits to the amount of “play” in evolution.
Elvis taxa, properly recognized, illustrate the pervasiveness of homoplasy but also the constraints on morphological evolution and community construction.  If Elvis taxa are as common as Lazarus taxa they may indicate that morphology may be more highly constrained than commonly believed, or that particular roles require particular morphologies.
I have to admit that this particular label strikes me as a bit too playful.  Even Erwin and Droser appear to be sensitive on this score.  They acknowledge,
New terms should be proposed with caution, when they describe a particularly important phenomenon, and never in jest.  In addition, terms should be short and memorable if they are to achieve any currency.
Hmmm, . . . Elvis taxa . . . memorable, sure, but I have to think these two paleontologists had a laugh, or several, when they coined the name.  They explicitly reject following in Jablonski’s biblical footsteps, aspiring to what they characterize as “a more topical approach.”

Zombie Effect

In Dinosaur Extinction and the End of an Era:  What the Fossils Say (1996), paleontologist J. David Archibald waxes enthusiastic about the fossil record despite its limitations.
The spotty nature of the geological record is not unique to natural history.  All histories bear this burden.  There is, however, no cause for despair.  The information that has been preserved in the rock and retrieved by human effort is truly a wondrous précis of past life. (p. 64)
But he strikes a serious cautionary note, “The difficulty comes when we must determine whether our record is accurately portraying the biological past.”  (p. 64)

He focuses his concern for the accuracy of the record on the implications of several different phenomena, including the Lazarus effect.  He introduces a new term, the Zombie effect, for a potentially misleading artifact of the fossil record resulting from the reworking of fossils from older rocks to younger ones, leading to the erroneous conclusion that some taxon was alive after it had actually gone extinct.  These reworked fossils, Archibald writes, “lurk in later sediments like the living dead.”  (p. 68)

He describes organic (e.g., burrowing) and mechanical (e.g., changes in streams) processes leading to the Zombie effect.  And then reinforces his initial cautionary warning,
I argue that the Zombie effect is far more common that we paleontologists would like to believe.  Basically, we should be suspect of any fossil bone that is not articulated with a good bit of the rest of the skeleton.  (p. 70)
Surely Archibald has fun with this term, making sure he works in phrases like “the living dead” and “exhumed remains of organisms that lived earlier” to describe the Zombie effect.  I suppose once the literature sports terms like Lazarus effect and Elvis taxa, Zombie effect doesn’t seem so far out of line.

Still, even though I particularly like the Lazarus effect (I suspect it was not offered in jest), I would suggest that these very real, very important phenomena are somewhat devalued and robbed of some their deserved gravitas by the cumulative effect of these witticisms.  Restraint is in order.  But, after reading a column by Edward Willett (Guess How Some Fossils Are a Lot Like Elvis, Regina Leader-Post, February 1, 2007), I have to wonder whether that's possible.  Some two decades after Archibald brought forth the Zombie Effect, Willett mentions that some would describe “so-far-undiscovered bones that must be hidden somewhere” as a Jimmy Hoffa taxon.  May it stay buried.

Perhaps this turned out to be a ghost story after all.


  1. very interesting!

    can you coin a suitable witticism for pseudo-extinction? that is another pattern that may be at play during mass extinctions.. -

  2. Thanks for the comment. Afraid I'd try to be too cute were I to try to coin some new term. I enjoyed the posting on your blog re: Red Queen. It's thoughtful and challenging. The different relationship you write about between species-age and extinction of species in mass extinctions, as compared to other time periods, brings to mind Jablonski's work. Focusing at higher levels of aggregation than the species, he shows that the range of factors enhancing survival by taxa of mass extinction are different from those at play regarding background extinction (e.g., Mass Extinctions and Macroevolution, Paleobiology, Volume 31, Number 2, 2005; Background and Mass Extinctions, Science, January 10, 1986) Among the differences -- genera's species-richness is a factor enhancing chances of surviving background extinction but not mass extinction. Fascinating and, for me, very complicated stuff (except for the Jimmy Hoffa taxon which I have to think is purely a joke). Tony

  3. yes, Jablonski and the Chicago school of palaeontology have contributed much to our understanding of macroevolutionary patterns.


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