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  • Underwhelming Fossil Fish of the Month: May

    By Mark Carnall, on 28 May 2013

    It was inevitable I guess. A mere six months into this wonderful voyage through the underwhelming fossil fish of the Grant Museum I’m throwing in the grass roots, voice-of-the-internet, fighting for the underdog, black and white film with a subtitles nature of these posts. In short, this month is when underwhelming fossil fish of the month is selling out.

    I want to apologise to the loyal fans of this series and thank you for your support but pressure from the sponsors has meant that my hand has been forced and I’ve no alternative but to go for the mass appeal fossil fish. The fossil fish that sell ideas. The fossil fish that make it into TIME magazine and all those rich lists. You’ve got to have chops to cut it in this hyper competitive ruthless world of blogs about fossil fish. So with a heavy heart let’s have a look at this lovely large specimen of a shark, no less, Cladoselache. I know, I know, you’ve all heard of it. Just cherish the memories of when the fossil fish were underwhelming and not as Hollywood as this genus of Devonian chondrichthyan.

    LDUCZ-V1416 Cladoselache. Underwhelming fossil fish trivia fans will be keen to know that this is the biggest fossil fish so far

    LDUCZ-V1456 Cladoselache. Underwhelming fossil fish trivia fans will be keen to know that this is the biggest fossil fish so far

    Cladoselache is a genus of extinct shark and the specimen we have here is a nice chunk of the pectoral girdle- so in the orientation pictured above, the head would have been below the chunk preserved and the tail would have been above it. We’re looking down on the paired fins and inside the body of the animal. Here’s an expertly created reconstruction by an up and coming undiscovered palaeontological illustrator.

    This guy has some serious talent

    Illustration to marginally improve the understanding of what this fossil shows.

    As if this specimen wasn’t already too Hollywood this fossil fish is one from D.M.S. Watson‘s fossil fish collection and was collected from the Cleveland Shales in Buffalo in the United States of America. The Cleveland shales are a relatively well known rock series precisely because of beautifully preserved fossils like this one making sharks in the genus Cladoselache one of the best known of the early sharks. The fossils found within these rocks provide a really clear picture of the fauna between 350 and 380 million years ago, including family favourite Dunkleosteus often depicted chasing down a poor Cladoselache. Fossils from this area are so well preserved that soft tissue and stomach contents can be discerned. I’m constantly amazed at how far back we can look in time and be able to reconstruct how animals like this lived, what they ate, how their physiology worked and how organisms have changed since then.

    Preservation Considering the age of this fossil, even at a distance, you can discern the shape of the fins. Specimens from this locality have been found with soft tissue preserved including what has been interpreted to be organs, skin as well as stomach contents. I’ve run this specimen under both a microscope and under the skilled eye our resident shark expert and there’s a few bumps, lumps, patterns and nodules that look to be skin and possibly muscle. Have a look and see what you think of these bumpy bits.

    Micrograph of Cladoselache skin? muscle? nothing?

    Micrograph of Cladoselache at 30 times magnification. Skin? muscle? nothing?

    Research Cladoselache  is often mentioned in the palaeontological literature because of specimens like this one. The fossil record of sharks before and after fossils of this age is very patchy so fish like Cladoselache get a nod every now and then as shorthand for ‘this is what sharks in general were up to in the Devonian’. Articles specifically on Cladoselache aren’t nearly as common. In 1894 Bashford Dean seems to have written the reference on Cladoselache from specimens similar to this one and since then numerous other references have pointed in the direction of this one. Interestingly, Dean describes denticles (small toothlike projections) covering the skin, however subsequent authors claim that Cladoselache was a very weird shark because it lacked denticles over the whole body. Essentially, a naked shark. Another fun fact is that from the fossils of Cladoselache studied so far this group of animals appear to lack the pelvic claspers that males of many other cartilaginous fish possess. These claspers function much like docking bays between spaceships, helping to anchor onto females and channeling sperm, rather than the away team, to the cloaca. This has been speculated to suggest that perhaps Cladoselache had a different way of mating to most other sharks.

    In Society Despite the build up introduction to this post, Cladoselache is well known to anyone who has picked up a text book on the history of life on Earth as it’s one of the earliest vertebrates that has a good fossil record. It’s not quite up there with the A list fossil fish like Dunkelosteus or Megalodon but any chunky encyclopedia of prehistoric animals for the young palaeogeek will feature Cladoselache. I’m fairly confident that this is also the first UFFoTM that you can find a plastic toy of, Wild Republic produced an excellent extinct shark set that includes a Cladoselache. We all know that representation in action figure form is the true measure of fame and fortune.

    Cladoselache sp. 

    Preservation 9
    Research 6
    In Society 3 <—- AKA SELLING OUT FACTOR
    Underwhelmingness 5

    References

    Dean, Bashford, 1894, Contributions to the morphology of Cladoselache (Cladodus): Journal of Morphology, v. 9, p. 87–114.

    Mark Carnall is the Curator of the Grant Museum of Zoology

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