Dinosaurs in our garden!

February 27, 2010 at 12:57 pm (science) (, , , )

There are dinosaurs in my garden.  They watch me warily with beady eyes as they hunt for food.  Suddenly, a larger dinosaur appears and the smaller ones scatter in a frenzy of activity; it bites some food which dangles helplessly from its mouth.

Luckily for me, these dinosaurs are not about to break through the window and feast on my flesh.  That is because they are about the same size as a crow, because the one I’m looking at is, in fact, crow.

You may have heard that birds evolved from dinosaurs.  Well, according to scientific nomenclature, that means that birds actually are dinosaurs.  The following evolutionary tree from The Loom illustrates why:

The only groups that it makes (evolutionary) sense to give a name to are mono-phylectic: all descendents from a particular organism.  For example, all dinosaurs have a common ancestor, which is the far left of the figure.  If you look at the bottom of the figure, you’ll see that birds share this common ancestor, and therefore are dinosaurs.

The confusion arises because dinosaurs were discovered before we understood their evolutionary relationship to living organisms.  So we called all of the extinct creatures we found fossilised in rocks by the one name, dinosaur (“terrible lizard”).  Once we discovered that birds were direct descendents from dinosaurs, we were already using the name to mean only the scary lizard type dinosaurs, rather than the winged feathered friends we feed seed to.  So now, the correct term for a “dinosaur” is “non-avian dinosaur” (i.e. all the dinosaurs except the birds).

Similarly, birds are descended from reptiles, so they technically are reptiles.  Again, in everyday language it is useful to talk about all reptiles except the birds.  However, turtles turn out to be less related to crocodiles than birds are, for example, so they all have to be technically called reptiles. (Birds, crocodiles and the extinct dinosaurs are all called archosauria together).

Of course, birds changed a lot since the time of the dinosaurs, so they are really very different.  All this just goes to show that technical language is always going to be at odds with everyday language, even though the technical words (technically speaking…) hold more real information.

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2 Comments

  1. ughsome said,

    Thank for this! 🙂 rushing off to check out the Loom article!

  2. thinkingdan said,

    Welcome! Of course, the loom is the “real” article, mine is just blog noise…

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