Turtles all the way down!

By Razib Khan | April 29, 2013 2:46 am

Nature Genetics (2013) doi:10.1038/ng.2615

No time to comment extensively, but check out The draft genomes of soft-shell turtle and green sea turtle yield insights into the development and evolution of the turtle-specific body plan (open access). The paper and the ScienceDaily press release allude to some phylogenetic confusion as to the relationship of turtles to other reptilian lineages, but my own superficial knowledge of this area left me rather unsurprised by this tree. What am I missing? Though reading the Wikipedia entry it seems that spotty marker coverage has produced a lot of controversy. What’s more striking to me is that so many terrestrial vertebrate lineage seem to have emerged over a relatively short period of time. Though presumably this may simply be an artifact of the reality that most lineages go extinct so we’re only left with relatively deep branching patterns. Someone who knows fossils can chime in.

CATEGORIZED UNDER: Evolution
MORE ABOUT: Evolution
  • http://www.facebook.com/karl.zimmerman Karl Zimmerman

    The phylogenic position of Turtles has been the subject of some discord for awhile. The three basic hypotheses were.

    1. They were anapsids related to Procolonophonids or Pareiasaurs. This has fallen out of favor in more recent years, as the lack of fenestra in their skulls may be secondary.

    2. They were Diapsids, but along the “lizard-line” Lepidosauromorpha. This was considered more likely in recent years, because the oldest turtle, Odontochelys, seems to show some similarities to Sauropterygia – marine reptiles thought to be “lizard line”

    3. The third argument is the Archosaur/Archosauromorph hypothesis, which has had excellent genetic evidence, but some paleontologists don’t trust, because cladistic analyses of skeletal traits don’t support it.

    More generally, the Permian extinction is a bitch. To show how deep time is, and how severe it was, consider that it’s possible that no more than seven species which crossed the Permian-Triassic boundary form the origin of all extant modern tetrapods. The minimum number of species is four, presuming Turtles didn’t split off until the Triassic, and modern amphibians only had one common ancestor, and not three, at that time.

    • Felis

      Those numbers are based on large living clades, but we know more than seven tetrapod species survived because many now-extinct clades crossed the boundary too (like temnospondyls, dicynodonts and other stem-mammals, various stem-archosaurs). Background extinction has reduced the number of surviving lineages as much as any single mass extinction event.

      • http://www.facebook.com/karl.zimmerman Karl Zimmerman

        I did say extant, which by definition excludes extinct lineages. I also made a reference to deep time.

  • http://twitter.com/Jhangora Dinesh Mohan Raturi

    There is something wrong. The hyperlink for the latest post, on the homepage and the links for the previous and the next post on this page, just above the title of this post – point to the homepage of the blog. I think you need to hire a web-designer in order to prevent page-views and visitors being lost.

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This blog is about evolution, genetics, genomics and their interstices. Please beware that comments are aggressively moderated. Uncivil or churlish comments will likely get you banned immediately, so make any contribution count!

About Razib Khan

I have degrees in biology and biochemistry, a passion for genetics, history, and philosophy, and shrimp is my favorite food. In relation to nationality I'm a American Northwesterner, in politics I'm a reactionary, and as for religion I have none (I'm an atheist). If you want to know more, see the links at http://www.razib.com

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