Order Aves?

So there we were, in the city of Jacksonville on an overcast day.  Our mission was to explore the MOSH, or the Museum of Science and History, and then attend a Jacksonville Suns minor league baseball game -  all the ingredients to having a good day.

The MOSH had several great exhibits including a native plants garden, which contained a pond with the largest alligator snapping turtle, named Tonca, I have ever seen.  But, by far, the most interesting exhibit was their reptile and amphibian exhibit.

I knew something was different when I first walked in, and in the midst of your standard snakes, lizards, and turtles, there was a Blue Jay in a cage.  My first thought was that this bird must be some sort of rescue animal, and that the museum was acting pro bono on the behalf of this feathered creature.  On closer investigation, the sign for the Blue Jay exhibit did not seem to differ from that of all the critters on display, and on even closer investigation I notcied that right after the scientific name of the the Blue Jay, Cyanositta cristata, were the words "Order: Aves"

Now wait just a minute.  I know that it is a class Aves, and that a Blue Jay is considered to be in the "song bird" order Passeriformes.  And, what is also pretty interesting, is that they belong to the crow family - Corvidae.  "Order: Aves" must be a mistake; a typo.


Unless this small reptile exhibit has accepted what many ornithologists have been saying the past few years.  Birds are reptiles. In fact, the first heading in the Sibley Guide to Bird Life and Behavior's section on the origin of birds is entitled "Birds are Reptiles." As I made my way around the rest of the exhibits, my suspicion was confirmed with several large signs describing the various orders of reptiles in which birds were included.  A side note was made on the bird sign which simply read, "formerly Class Aves."

It was nice to see an interpretive exhibit in which informs the public to a new way of looking at reptile taxonomy.  However, not much was presented on why this change in the classic way we look at reptile taxonomy was made.  To really understand that we have to know something about the history of scientific classification itself.

It all started in 1753 with Carl Linnaeus, who came up with the brilliant idea of classifying every living thing into groups.  These groups start out wide in scope, and get more and more selective until each living thing is assigned an individual Latin scientific name.  You know, King Philip Came Over For Great Spaghetti - Kingdom Phylum Class Order Family Genus Species.

When these groups were first formed, living things got lumped together based on morphological characteristics.  For example, Carl Linnaeus noticed that snakes, lizards, turtles, crocodilians, frogs, salamanders, and the like all crept around on the ground in a way that unnerved him a little bit.  All these life forms were creepy and crawly, and back then, that was enough to lump them all together under the zoological study of herpetology.  Herpeton is Greek for creeping thing.  All birds flew, so they were all grouped together under the study of Ornithology.  Ornithos meaning "birds" - makes sense.

Once the idea of evolution came around, scientist started agreeing that living things should be classified based on their evolutionary relatedness to one another, or their phylogeny.  This also brought about the idea of only grouping organisms together if they shared one common ancestor. The groups are called clades, and the graphical depiction of these clades are called cladograms.  But it was not until recently that humans have developed the technological capacity to actually look at a living things' DNA and compare it to other living things.  This allows scientists to quantify the difference of one organism to the next or even compare entire groups of organisms.  Basically, instead of grouping organisms together based on how they look, we can now compare groups of organisms based on how genetically related they are to each other.  Neat.

Now when we look at reptiles and amphibians, we see that they are very different from one another and should be viewed as being in two different classes - Class Amphibia and Class Reptilia.  But just as our current understanding of cladistics allowed us to separate reptiles and amphibians, it has also allowed us to include a group of organisms once thought to be independent of class Reptilia - the birds.

And, if we look at an even finer scale (click on the image for a closer view), we see that birds and crocodiles seem to have shared a common ancestor in the Triassic pried between 208 and 245 million years ago, and that snakes and lizards branched off from the crocodilians even later in the Carboniferous period between 286 to 365 million years ago.

(Thanks to Science Encyclopedia for allowing other folks to use their images)

Briefly, based on the latest information we have, if we consider crocodiles to be reptiles, then we have to consider birds to be reptiles.  And not only should we consider birds to be reptiles, we should also consider them dinosaurs since they appear to be the only surviving member of the group.  Crazy.

But that's the cool thing about science.  Nothing is set in stone, and this whole idea of classifying organisms into neat little groups is, in a sense, just a way to wrap our minds around the immense diversity of life.  There is still much debate as to where to draw these lines, and I doubt that ornithologists and herpetologists will ever join hands, sing "kumbaya," and consider themselves to be one and the same. And we have not even touched upon the question of what would all the orders of birds become if Aves truly becomes its own order instead of a class.  Maybe, just to keep things simple (or would this just make things more confusing) we could consider Aves a class within a class.  For more info about that, check out Animal Diversity Web's short essay on the subject.

I think a truer understanding of it all is that the diversity of life exists on a spectrum of varying degrees of differences and similarities, and it is all a matter of perspective.  Look at things too closely, and you place yourself in the extreme splitter category where the slightest difference between groups is grounds for a new level of classification.  Look at things in too broad a perspective as an extreme lumper, and all the diversity of life becomes one big group, which is not useful at all.

There is a metaphor for life somewhere in there...


Wilson's Plover

Least Tern

1 comment:

  1. Very cool! A well-written explanation of the conversation we had while kayaking. (Brian should read this!)