Left Behind

23 December 2008

img_0773Much of the chatter around the Latimeria tank at the newly revamped California Academy of Sciences concerned the health of the specimen, as in, “is that thing alive?” Of course, the putative “living fossil” was, in fact very dead–although a certain fish expert I know with quite a bit of aquarium experience predicts live, captive coelacanths the near future.

Vitality deduced, many passers-by voiced familiarity with “the greatest fish 51rlmlqpq4l_sl500_aa280_story ever told.” In fact, a few even recalled recent news about the discovery1 of a second living species of coelacanth in an Indonesian fish market.  Now, perhaps the San Francisco museum-going crowd is more hip to these things than most, but it’s impossible to deny that Latimeria has become something of a pop-culture icon , making cameo apperances in commercials, video games, and swan-songs of American primitivists.The Earth is a museum.” The hope that creatures long thought extinct might lurk in hidden corners of the world runs from popular cryptozoology to King Kong to the fiction of Arthur Conan Doyle and Jules Verne to Thomas Jefferson telling Lewis and Clark to be on the look out for mastodon and giant ground sloth back even to the original Enlightenment debates about whether God could even allow any portion of his perfect creation to disappear.

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It was seventy years ago today (well in my time-zone still at least) that Marjorie Courtenay-Latimer, curator of a small museum outside Cape Town, noticed an unusual blue fin poking out from amongst a pile of sharks.  After pulling it out of the pile, Courtenay-Latimer was face to face with a coleacanth–a group fishes known well from fossils but previously thought to have gone extinct along with the (non-avian) dinosaurs at the end of the Mesozoic.

Astonishingly, while Latimer didn’t immediately know what she had discovered, she was able to recognize that it was something very significant.  She threw the five-foot (1.5 m) fish carcass into her taxi (apparently against the objections of the driver) and brought it back to the museum.   Latimer made a quick annotated sketch of the fish (shown above) and sent it to a fish-expert/chemist named J. L. B. Smith.  After a week’s delay (Smith was on holiday), Courtenay-Latimer recieived a telegram from Smith: “MOST IMPORTANT PRESERVE SKELETON AND GILLS = FISH DESCRIBED.”

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Within weeks the discovery, the coelacanth, became a global sensation.  Newspapers ran the story on their front page and thousands flocked to the tiny natural history museum to see the specimen.  Although similar to fossil coelacanths, the new fish was  distinctive enough to merit its own genus, named appropriately enough Latimeria.

Metasequoia

Latimeria belongs to a curious league of organisms known first as fossils and later discovered as living, respiring beings.  Perhaps the next most famous example is the deciduous conifer Metasequoia discovered living in an isolated region of Sichuan province, China just a few years after Latimeria.  Unlike Latimeria, the “Dawn Redwood” does have living relatives: the Giant Sequoia (Sequoiadendron) and Coast Redwood (Sequoia) of western North America.  These three highly endemic trees are relicts of a subfamily that was once an important component of conifer forests across the Northern Hemisphere going back to the late Mesozoic at least.

While not nearly as famous as Latimeria, Metasequoia is considerably easier to observe in a living state.  Most decent-sized tree collections in North America have a specimen, and they are even widely availabe for purchase.  Pictured above is one of several Metasequoia in the UC Davis arboretum in full autumn flair

GingkoesTo my knowledge, there is no established term for this phenomenon.  Latimeria and Metasequoia are often called “living fossils.” But this term is more broadly applied to various taxa that appear to have changed little, at least anatomically, over long periods of geologic time. Gingko (right) and the Australian lungfish Neoceratodus (below), distant relatives of Metasequoia and Latimeria respectively, are outwardly similar to fossils known from the Mesozoic.  Plenty of other supposed living fossils, for instance sharks or crocodilians, simply aren’t by any stretch of the definition.

img_0789The vaguely religious epithets “lazarus taxon” and “relict” are also frequently trotted out to describe Latimeria and Metasequoia. These terms are not exclusive to living organisms first known as fossils however.  “Lazarus taxa” are organisms which reappear in the fossil record after an extended hiatus. Imposter Lazarus taxa which merely appear to be the same as older fossils are known as Elvis taxa, while reworked fossils that wander after they are dead into younger rocks are Zombie taxa.  “Relicts” are generally any isolated taxonomic or biogeographic fragments inferred to be holdovers from previously more diverse or widespread group (although they need not have a fossil record at all).

So what shall we call Latimeria and Metasequoia, along with Neopilina, Laonastes, Catagonus? Lost in the past, hidden in plain sight only to suddenly reappear  one day without warning.  I suppose we should stick with the religious theme…

Mahdi taxa? Occult Taxa? the nonraptured?

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1 – Throughout this post I use “discover” to mean “discovered by Western science.” In many, if not all cases however the plants and animals were well-known to peoples who live among and even exploited them.

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