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Laryngeal echolocation in bats

Two years ago, “the most primitive bat known” was reported in Nature. It was not primitive in its wings and body, but “the morphology of the ear region suggests that it could not echolocate, making it a possible intermediate link between bats and their non-flying, non-echolocating mammalian ancestors”. At the time, the find was suggested to settle the question as to which came first: flight or echolocation? The answer was a definite flight first.

“The problem of understanding bat evolution dates back at least to Charles Darwin, who in The Origin of Species enumerated a list of difficulties he saw with the theory of evolution by natural selection. The example often discussed is the origin of the eye. But Darwin also mentioned the vexed issue of how bats had arisen from terrestrial ancestors.” (Speakman 2008).

This assessment of the fossil must now be reappraised. New work on modern-day bats has revealed another mechanism of echolocation. One of the authors described the work thus:

“We borrowed 35 specimens from the Royal Ontario Museum in Toronto and performed micro-computed tomography on them. This imaging technique allowed us to see the fine details of the bats’ ear and throat regions: the larynges, stylohyals and tympanic bones. Previous work had relied on dissecting these bones, a challenge in animals as small as bats. We found that the fusion or connection of two bone structures – the stylohyal bone in a bat’s throat and the tympanic bone in the ear region of its skull – was a feature of all laryngeally echolocating bat species we studied.”

This finding is new and unexpected. It means that previous conclusions need to be reappraised. This is exactly what is happening with the “most primitive fossil bat”.

“The relatively small cochleae and lack of paddle-like expansions on the cranial tips of the stylohyal bones have been interpreted as evidence that O. finneyi lacked laryngeal echolocation, which supports the hypothesis that flight evolved before echolocation. However, we find that articulation between the stylohyal and tympanic bones is a better predictor of laryngeal echolocation ability than the shape of the stylohyal bone, at least among extant bats. If the stylohyal bones articulated with the tympanic bones in O. finneyi, then we propose that this species had the capacity for laryngeal echolocation. Our results thus reopen basic questions about the timing of the appearance of echolocation and flight in the evolution of bats.”

There are several lessons to be learned here – and one of these is to always be prepared to hold judgment on the word “primitive” – even if it is said to be the “most primitive”!

The new Nature paper is “A bony connection signals laryngeal echolocation in bats”
For the full reference and abstract, go here.

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6 Responses to Laryngeal echolocation in bats

  1. It should be noted that the “most primitive” bat fossil is not the oldest fossil:

    Bats – An Example of Sudden Origins in the Fossil Record:
    Excerpt: Onychonycteris (the bat talked about in the article) was a contemporary with the more advanced bats Icaronycteris and Palaeochiropteryx, and it is actually predated by the bat from Queensland Australia.
    http://www.jesusbelievesinevol.....ossils.htm

    I believe, correct me if I’m wrong, The oldest bat fossil ever found goes to Australonycteris clarkae at 54.6 million years:

    http://www.jstor.org/pss/4523576

    And the Ear bones of Australonycteris show that it could navigate using echolocation.
    http://australianmuseum.net.au.....is-clarkae

  2. this is precisely why most evolutionary biologists long ago gave up the terms “primitive” and “advanced” (which necessarily include a value judgement) in favor of “ancestral” and “derived”. “Ancestral” traits in a member of a particular taxon are similar to (i.e. relatively unchanged from) those found in the phylogenetic ancestor(s) of that taxon. “Derived” traits in a member of a particular taxon, by contrast, are different from (i.e. significantly changed from) those found in the phylogenetic ancestor(s) of that taxon. These distinctions provide the basis for cladistic analysis, which forms the core of modern evolutionary systematics/taxonomy. Furthermore, it is an almost universal rule that every organism has both ancestral and derived traits, and that the rates of change of derived traits vary (i.e. speeding up and slowing down) in ways that are not necessarily correlated.

  3. Ergo, finding “ancestral” traits alongside “derived” traits in the same organism in no way violates current evolutionary theory. Indeed, it validates its basic premises.

  4. Allen,

    Thanks for the reminder of the circular nature of evolutionary theory.

    By the way, who were the ancestors of bats?

    If you don’t know the ancestors, how do you determine which traits are the ancestral traits?

    Is it the ones which are the most primitive?

    There’s nothing wrong with the term primitive. It doesn’t necessarily include any value judgment. Why evolutionists would think it does is a mystery.

    primitive – primary – that which came first.

  5. First the fossil record cannot tell us anything about when what trait arrived.

    So by looking at the fossil record we cannot use it to time an arrival of a trait.

    The best we can do is if we find a fossil with trait X is say that trait X existed in this organism at this speculated time.

    Cladistics takes shared traits and depending upon the number of shared traits creates sister groups- groups more closely relateed to each other more so than to any other group.

    All based on the number of shared characteristics.

    The problem with that is convergence can explain shared characteristics as can Common Design.

    So to rid themselves of convergence scientists use many traits because they say that too many traits are impossible/ too improbable for convergence to hit upon.

    And to rid themselves of Common Design they just refuse to allow such a notion.

  6. Thank you for the interesting comments.

    bornagain77 @ 1
    I believe, correct me if I’m wrong, The oldest bat fossil ever found goes to Australonycteris clarkae at 54.6 million years.
    You are correct to say that this is the oldest reported bat fossil – albeit in fragments. The dating is not without its problems. Suzanne Hand with co-authors addressed this in a paper in PLoS ONE (2008; 3(3): e1858. | doi: 10.1371/journal.pone.0001858) – see the supporting text S1. It appears to me that this has not settled concerns about the dating. In an article on Onychonycteris, Nancy Simmons (Scientific American, December 2008) wrote: “Until recently, the oldest and most primitive bat on record was the 52.5-million-year-old Icaronycteris index“.

    Allen_MacNeill @ 2
    this is precisely why most evolutionary biologists long ago gave up the terms “primitive” and “advanced” (which necessarily include a value judgement) in favor of “ancestral” and “derived”.

    All I note is that the term “primitive” has appeared in a very pronounced way in these discussions of fossil bats – used by the researchers, those commenting on the findings and in the Editor’s summary. One of the authors even used the term “missing link” in the Scientific American article cited above: “In retrospect, Icaronycteris was never much of a “missing link.” But another fossil bat from the Green River Formation would turn out to fit that description nicely. Enter Onychonycteris.” Cladistics has some major unresolved methodological problems. Joseph @ 5 is on target.

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