The Falsity of Living Fossils

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Today’s tadpole shrimp, or notostracans, have a shield-shaped body, ending in a forked pair of filaments—a shape that makes them almost indistinguishable from their ancestors in the Triassic period some 265 million years ago. This outward constancy has earned them the description of “living fossils”—a term referring to species with no close living relatives, which seem to have gone unchanged for long spans of time.


But according to a genetic analysis of notostracans published today in PeerJ, these animals have by no means stopped evolving. Indeed, researchers are coming to realize that the term “living fossil” is a misnomer. One by one, the classic examples—horseshoe crabs, coelacanths, cycads, and more—have turned out to be very different from the fossils that they apparently resemble, either at a genetic level or through subtle physical changes. Their recognizable nature is a red herring—these creatures simply did not exist in their current form millions of years ago.

“I would favor retiring the term ‘living fossil’ altogether as it is generally misleading,” said Africa Gomez at the University of Hull who led the study.

In the latest study to disprove the concept of a living fossil, Thomas Mathers, Gomez’s student from the University of Hull, sequenced several genes from 270 tadpole shrimp, and built a family tree charting their evolutionary relationships. Although taxonomists recognize 11 species of tadpole shrimp, based on DNA evidence, Mathers suspects that there are actually 38 distinct species alive. These fall within two living genera—Triops and Lepidurus—which diverged from one another 184 million years ago, during the Jurassic period. The diversification of species within these genera arose around 73 million years ago.  “Our work shows that organisms with conservative body plans are constantly radiating, and presumably, adapting to novel conditions,” said Gomez.

“The article provided more proof, if more were needed, that the term "living fossil" is both poorly defined and misleading,” said Patrick Laurenti, an evolutionary biologist from the CNRS in France. “Calling a given species a living fossil suggests that it has crossed time without evolving—a hypothesis that is in sharp contrast with evolutionary genetics principles.”

Written By: Ed Yong
continue to source article at the-scientist.com

7 COMMENTS

  1. I’m bound to say I’m not very impressed. It would indeed be surprising if MOLECULAR evolution had not proceeded at approximately the same rate in the lineages leading to “living fossils”. For that not to be true, the whole – rather successful – principle of the molecular clock would have to be wrong. But anatomically it seems to be legitimate to point to animals, such as Lingula and Limulus, which have changed rather little since remote ancestral times, and call them living fossils.

    • In reply to #1 by Richard Dawkins:

      I’m bound to say I’m not very impressed. It would indeed be surprising if MOLECULAR evolution had not proceeded at approximately the same rate in the lineages leading to “living fossils”. For that not to be true, the whole – rather successful – principle of the molecular clock would have to be wrong. But anatomically it seems to be legitimate to point to animals, such as Lingula and Limulus, which have changed rather little since remote ancestral times, and call them living fossils.

      I think they are focusing on the “rather little” and trying to make it seem “rather a lot” or, at least, “significant enough”. With all of the variables and opportunity for evolution to occur, I would find it difficult to imagine that any species could last as long as the ones mentioned and not undergo some evolutionary change. The sport of rugby has undergone “rather little” change but it is still called rugby and pretty much the same game. For instance, I can’t get away with punching someone anymore.

    • In reply to #1 by Richard Dawkins:

      I’m bound to say I’m not very impressed. It would indeed be surprising if MOLECULAR evolution had not proceeded at approximately the same rate in the lineages leading to “living fossils”. For that not to be true, the whole – rather successful – principle of the molecular clock would have to be wrong. But anatomically it seems to be legitimate to point to animals, such as Lingula and Limulus, which have changed rather little since remote ancestral times, and call them living fossils.

      I have to say I was thinking the same thing, except somewhat less technically. :-)

      Call me cynical if you like, but I think this is part of a growing trend in science to make results seem more controversial than they are, probably to try and boost citations. They are after all, the bread and butter of science.

    • In reply to #1 by Richard Dawkins:

      I’m bound to say I’m not very impressed. It would indeed be surprising if MOLECULAR evolution had not proceeded at approximately the same rate in the lineages leading to “living fossils”. For that not to be true, the whole – rather successful – principle of the molecular clock would have to be wrong. But anatomically it seems to be legitimate to point to animals, such as Lingula and Limulus, which have changed rather little since remote ancestral times, and call them living fossils.

      i think it’s ok too but can see where people with poor understanding of evolution can get confused by it. mostly because ‘changed little’ and ‘remote ancestral times’ can be somewhat subjective terms. explaining humans exist and did not evolve from chimps but human and chimp ancestors were chimp-like is a tricky one i find. is a chimp a living fossil or is there an agreed minimum time-frame in which to remain similar looking?

  2. I see living fossils as convergent evolution over the time dimension rather than the species dimension. There is no particular reason why convergent evolution over attributes w and x (say shape and size), should correlate with factors y and z (reproduction and breathing). Compare dolphins and sharks.

    • In reply to #4 by God fearing Atheist:

      I see living fossils as convergent evolution over the time dimension rather than the species dimension. There is no particular reason why convergent evolution over attributes w and x (say shape and size), should correlate with factors y and z (reproduction and breathing). Compare dolphins and sharks.

      I don’t see this. Ordinary convergent evolution is where genetically and morphologically distinct species come to resemble one another under the influence of selective pressure, like dolphins and sharks under the influence of water. In living fossils the species are of course from the same family, so their genes and form are the same from the start.

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