61 thoughts on “Monday morning biology lesson”

  1. Assuming the lineage is valid (and I haven’t studied it) I don’t believe the term “Dinosaur” is intended to imply a monophyletic group including all surviving descendant species.

    1. A modern example, snakes are a monophyletic group inside squamata. Monitors and Snakes have a more recent common ancestor than Monitors and Iguanas.

      While it is proper to refer to both Monitors and Iguanas as Lizards, it is not however proper to refer to a snake as a Lizard, because Lizard is not a monophyletic term.

      It is also quite possible that my sense of humor completely failed me.

      2. It’s perfectly OK to say that snakes are lizards, because evolution happens to be true. Why wouldn’t it be? – membership of more inclusive clades is 100% heritable (like surnames or citizenship, only without exceptions), or you’d have to be able to point to some place on a tree where a lizard-descendant stopped being a lizard. That is logically separate from the problem of identifying the first ‘snake’, so trying to use non-monophyletic group names is just adding useless baggage.

        Interestingly, recent molecular phylogenies put iguanians and monitors nearly equally close to snakes (but still much closer than skinks, geckoes etc.), which doesn’t make sense morphologically and will take a lot of explaining!

    2. This is precisely why birds are now pretty much regarded as the last of the dinosaurs: it makes the dinosaurs a proper clade. One common definition of “dinosaur” is “the last common ancestor of the sparrow and Triceratops, and all its descendants”.

      But it’s more than cladistic nicety – we can project back facts about birds and make useful predictions about ancient dinosaur behaviour.

      1. Why not just consider dinosaurs to be the monophyletic clade before birds branched out them, just like what is done with lizards and snakes? A lizard is a member of squamata that is not a snake (including legless lizards). Lizards are not a monophyletic group but they would be had snakes never evolved.

        I don’t see why there is a reason to redefine what a dinosaur is other than academic mental masturbation. Dinosaurs were known before Carl Linnaeus so there is no reason to expect what we refer to as dinosaurs to be a nice monophyletic clade.

        1. I would suggest that redefining what a dinosaur is only serves to create confusion when reading historical scientific literature.

          Dinosaur is a common term, not a scientific term.

        2. Dinosaurs were defined by Richard Owen in 1842.
          There is more similarity found between birds and their immediate non flying relatives then there is between bats and their non flying relatives. Yet nobody excludes bats from the mammals.
          Where would you draw the line, given such similarity ? Feathers, lots of dinosaurs had feathers. Flight, looks like it evolved more then once. Last common ancestor of modern birds, probably excludes archaeopteryx ,which becomes a flying dinosaur.
          The only reason the division looks clean is that non flying dinosaurs are no longer around to see in the flesh.

          1. Nice catch, but the point still stands.

            Birds were already defined and dinosaur was coined to describe animals that were not birds.

            It would be more appropriate then to call dinosaurs birds than the other way around if following taxonomy naming rules because bird was coined first, no?

            If not following taxonony naming rules than monophyletic doesn’t matter.

  2. One thing I’ve never understood is why do species always split into two. The trees always show a branch splitting into two branches. Is it not possible for a given population to find itself in three locations which then do not interbreed and lead to three new species? I really don’t get this.

    1. Cladistic trees always have a split in two but that does not mean that parent species vanishes when a new species appears (the split), the parent species may survive to split off another new species.

    2. Yes, in principle species could split into more than two descendants. If the range of the ancestor, for instance, is fragmented into several parts, and each of those populations evolves into a new species, one could have a trichotomy rather than a dichotomy. Surely this has happened many times over the history of life, and may account for some recent groups (as in some of my flies) in which one cannot, even using DNA, resolve the phylogeny into a tree with two branches at a time.

    3. It’s an artifact of the limited goal of any given phylogenetic tree. You’re basically starting with two lineages, and tracing backwards to see when they separated.

      It’d be quite a coincidence if you chose three disparate lineages and found they converged at the same point in time.

      A full and complete tree of life would obviously not be a neatly bifurcating chart. It’d be a complete mess.

  3. “Birds aren’t descenden from dinosaurs, they are dinosaurs.”

    I do not dispute this. But then we are a third branch of bony fish. (I don’t have a problem with this. Great to think of ourselves like this!)

    1. “Humans are fish” is not a useful statement from the perspective of birds and dinosaurs, but may be one from the perspective of plants or bacteria.

  5. “They [Birds] are dinosaurs”

    This is a clear statement that evolution never happened.

    Hence Ken Ham, AIG, & the Creation Museum all have it right.

    Remember, you saw it here first.

    1. Oh my….that will be the next thing he’ll have audiences of children laughing about if he hasn’t done it already!

  6. Yes. I like to tell myself that my cat occasionally littering the garden with bloodstained feathers is yet another victorious skirmish in the Great War of Mammals versus Dinosaurs and not just him being a murderous little bastard.

  7. I fully agree, and I often make the joke that my cat wants to finish the job of the big asteroid: exterminating the dinosaurs.

    1. Mordanicus,

      Unfortunately, it is not a joke. Cats (both feral and house cats-allowed-to-roam), kill enormous numbers of songbirds nationwide. Far too many cat owners ignore their responsibility to keep their cats indoors where they cannot slaughter birds indiscriminately. I am a cat lover but also a bird lover.

  8. Pedantic, I know, but I hate when the specific epithet is not represented correctly…

    Falco peregrinus, not…
    Falco Peregrinus

    …italics and/or underlining not shown !

      1. Well Ant, until I read Michael’s response, I would have pointed you to the only time the species name is actually mentioned in the illustration ! Read what Michael stated for the (to me) correction..

        Thanks Michael.

        1. Well, I was going to the same place, only more obliquely and less humorously… 

          It does annoy me how often “serious” websites get the format of binomials wrong (almost as much as folks drawing the Union Jack/Flag incorrectly).

          /@

          1. No, I did determine your remark may have been an oblique seconding, but I went with you were asking me straight – it seemed the more likely of the dichotomous choices !

            And, yes, I seem to have an eye for these little things too. Shoot us down dead ! Take care.

    2. The International Code of Zoological Nomenclature has an exemption for cartoons ~ where the use of upper case throughout takes priority

      BTW did you get a kick out of the punchline in red?:- “This is a good world”

      So true

      Regards ~ the liar pedant

    3. Yes, that sort of thing bothers me, too; but not here. It’s all in caps because that is the cartoon font itself–no lowercase letters anywhere. And it looks to me like Randall did try to put it in an italic-like slant, at least as much as his space limitation allowed.

      1. Definitely slanted relative to the rest of the paragraph, and note that the F is taller than any of the other letters. Randall knows what he’s doing, and gets it right.

  9. Thank you….just now fighting to make my students (high school, conservative community),understand the relationship between birds and other Dino’s. Graphic is superb!

    3. Great Horned Owls have been reported to take the occasional cat. I wouldn’t put it past some of the other large raptors as well.

  11. I frequently greet my zebra finch with “hello my little dinosaur!”

    He’s a better singer than most other dinosaurs so I put him at the top of the chart.

  12. Great things are afoot.
    But I didn’t imagine just how great, when I mailed Jerry earlier this morning to ask whether he would care to drop a line about today’s xkcd.

    Today’s xkcd is # 1211.

    There is a website named Qirina that has set itself the mission “to ascertain what sites are about based on an analysis of the text content on the front page,” i.e., to determine a site’s niche.
    Qirina accessed xkcd.org’s front page at 12:24 UTC on February 10, 2011. “The source was comprised of 8337 characters, of which 7126 are code, leaving an organic character count of 1211“.

    After a careful analysis of the text, Qirina’s algorithm concluded:

    We’ve identified the niche as finds jesus.

    As indeed predicted on the xkcd front page!

    Laddies and yentlmen, we have it all:
    – Evolution;
    – Dinosaurs;
    – Numerology;
    – Prophecy (self-fulfilling);
    – Jesus!

    Now, if you please, I’ll have that Templeton prize y’all have been dissuading Sean Carroll from accepting.

  13. In Boulder, Colorado there was some program a while back to inspect the nests of local birds of prey (I think it was eagles, but I’m not sure). Anyway, when they climbed up to the nests they found loads of collars from local pets (cats and small dogs). So I guess the predator/prey thing goes both ways.

    2. That would probably have been golden eagle or bald eagle nests. I don’t think there’s another raptor in the US that’s big enough to regularly prey on cats and small dogs like that- with the possible exception of great horned owls, and they generally go for smaller targets.

  14. However Stegosaurus and T. rex are both still dinosaurs, and sparrows are still birds.

    1. Birds are also still dinosaurs, because they never stopped being dinosaurs.

  15. Ok, the main topic here has been the statement that birds ARE dinosaurs. Could someone write me a teacher-ly, concise explanation of why this is true? You could post it here, or send it to me at emerose@gmail.com. I’m thinking, if you’re wondering, pitch it at about the same level that Jerry’s book, WEIT, is pitched at.

    1. 1. If you add birds, then dinosaurs form a proper clade, and that’s nice and elegant.

      2. Reconstructions of feathered theropod dinosaurs come out very birdlike. If you saw these things, you would think “weird bird with teeth”, not “weird lizard with feathers”.

      3. Thinking of birds as dinosaurs has predictive value for learning about dinosaurs, and (I forget the examples, but) this has, I believe, worked out.

  16. When doing phylogenies, we try to avoid “unresolved polychotomies”. One of Hennig’s simplifying assumptions is that a speciation event is an extinction event for the ancestral species. Never mind that one of the new species looks very much like the ancestral species. And, of course, all ancestors, nodes of the tree, are hypothetical

  17. I’m curious. If we use the same analysis, can we then say we are fishes without upsetting taxonomists?

    Say, that lungfish are more closely related to humans (or sparrows) than to sharks. Or that adding tetrapods makes fishes a proper clade.

  18. Osteicthtyes without tetrapods is a paraphyletic group. We prefer monophyletic groups which include the unique common ancestor and all its descendants.

    I once carefully explained to a colleague why we are osteichtyes. She responded, “That is the stupidest thing I have ever heard!”:-(

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