I Thought He Only Studied Lancelets!

That is the name of his blog anyway. Apparently, though, Martin also studies fossils. National Geographic has the story – and this is the clever part – apparently he didn’t even have to go out into the field:

But Brazeau suspected that in the right circumstances, some bones could withstand time.
So he took a closer look at the well-preserved Ptomacanthus specimen that had been in the literature for 30 years. “Sure enough,” he said, “the specimen had its braincase preserved.”

I’m getting ahead of myself, though, so let me back up.


National Geographic’s article concerns research that will be published in tomorrow’s Nature. The research concerns the braincase of a group known as the acanthodians. This particular specimen dates to near the time of the bony fish/cartilaginous fish split. Here is the cool part:

But data from the new fossil support an emerging idea that the ancient group of fish included a diverse tableau of shapes and characteristics that defy clear-cut categories.

Update 1: The paper is available here. There is also 68 pages of supplementary material

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4 Responses

  1. We like organizing things neatly, with no overlap between groups. Evolution has the distressing habit of letting things slop over. From what I’ve seen I consider it likely that the ancestors of chordates split off from the stem group that later produced the ancestors of arrow worms and conodonts, and then the conodonts split off from the proto arrow worms before that group experienced the great anal-mouth switch that turned a heterostome into a protostome.
    Thus it does not surprise me that acanthodians share features with other groups. You could think of acanthodians as a cusp group, bridging two or more assemblages; much as saurusischians bridge the pelycosaurs and birds.

  2. Actually, I don’t study lancelets at all! It’s just the name of my blog (although there’s a reason behind the name that has very much to do with why I study what I study).
    Thanks for the plug and the link!

  3. Yes, I know, I was just joking. I love results that show that the history of life is more complicated and fascinating than previously thought. Love the supplementary material!

  4. More complicated, yes in the sense that the picture now has more detail. But it’s also greatly simplified. By assuming that Placodermi and Acanthodii were monophyletic, we were forced to assert a lot of ad hoc convergences. We test this assumption by conducting an analysis in which those groups are represented by a selection of individual genera and see if they break apart Acanthodians as a monophyletic group requires too many awkward convergences in order to support that pre-conception. It suggests that it’s masking the real pattern of character distributions and, thus, how we reconstruct evolution in this part of vertebrate history.

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