Exotic Animals

I left off with a discussion of how to define animal groups.  Today I want to talk about mammals and birds, and how to recognize them.

“Recognizing” mammals and birds may sound silly, but it’s not.  After all, if you ask, “What is a bird?” most people will include flight in their definition.  However, not all birds can fly.  So what is a bird?

To start with, all birds have feathers, and front legs that cannot support the body- all birds are obligatory bipeds, walking on two legs is not a choice for them.  Usually, the front limbs are modified as wings, but some birds (penguins) use their wings as flippers, and others (kiwis) lack them entirely.  In addition, all birds have a toothless beak, and a respiratory system that uses air sacs to force air through the lungs in one direction only.  This is connected with birds’ warm-blooded metabolism, since it makes them very efficient at getting oxygen into the bloodstream.  Finally, all birds have a hyper-shortened tail, and reproduce by laying eggs.  You’ll notice that, from this list, only feathers and the air-sac system are unique to birds; other animals have some of these traits, but only birds have them all.

Warm-bloodedness is a trait that birds share with mammals.  Mammals, however, have many more unique traits than birds do.  Fur or hair, mammary glands to produce milk for their young, 3 bones in the inner ear, and a jawbone that connects directly to the skull are the diagnostic characters of mammals.  Bearing live young works for most, but not all, mammal species: the platypus, and two spiny anteater species, all from Australia and New Guinea, lay eggs.

All of this may sound pretty obvious, but remember, a lot of it was not worked out until the 18th and 19th Centuries, when scientists began to rigorously classify the world in a way that we would recognize as modern.  I’ll define more groups later, as this blog grows.  The next couple of posts will be devoted to mammals and birds.

While scrolling through some news today, I found this article:

http://news.yahoo.com/s/livescience/20070412/sc_livescience/trexrelatedtochickens

It is an absolutely fascinating article about the link between dinosaurs and birds.

Now I know I said that I’d write this blog about animals, and I have tried to keep to that, but this was too good to pass up.  I’ve said before that I love birds, but my love of birds grew from my childhood fascination with dinosaurs. That, and my wife had a cockatiel when I met her.  If I loved her, I loved her bird.  Fortunately, the bird liked me, too.  Back to the news…

It seems that a leg bone from a 68 million year old Tyrannosaurus rex (yup, like the one on in Jurassic Park) had intact collagen fibers, whose protein sequence showed unique similarities to the collagen protiens of modern chickens.

This is important.  Protiens are the building blocks of all animal tissues, and are directly coded by the DNA of all animal cells.  If the protien sequences of T. rex and a chicken are similar, that means that the DNA was similar.  And the DNA can only be similar if the pair of animals in question had a common ancestor.

This is a big boost for the avian theory of bird origins.  It is actual evidence that at least some birds share a common ancestor with at least some dinosaurs.  It’ll be very exciting to see where this story leads.

How do we define animal groups?

Well, that depends.  The Kalam people of New Guinea define animal groups primarily by how they use them, and who hunts or gathers them.  Modern biologists use phyical and physiological features.  Little kids sometimes have completely arbitrary definitions.

Since I’ll be using this blog to talk about animals from a lay-scientific standpoint, let’s look at animal groups from a scientific perspective.  In this post, I’ll talk about some of the vertebrates.

We’re all familiar with vertebrates, because we are vertebrates.  If you put your hand between your shoulder blades, just below the nape of your neck, you can feel your backbone; it is made up of a series of small bones called vertebra.  Every vertebrate has a backbone.

There are five main groups of vertebrates: the cold-blooded fish, amphibians, and reptiles, and the warm-blooded mammals and birds.  “Cold-blooded” means that the animal in question does not have a metabolism fast enough to heat its body internally, and must receive heat from its environment.  “Warm-blooded” is the opposite; these animals have a fast-burning metabolism that keeps their bodies at relatively constant temperatures.  We humans are warm-blooded.

Most of the animals we interact with in our daily lives are warm-blooded mammals or birds.  They are all around us.  The sparrows and finches at the bird feeder in the back yard, and the squirrels we chase away from the feeder, and our pet canaries and cats are all warm-blooded animals.  Warm-bloodedness allows birds and mammals to stay active in cold climates, but it also imposes some restrictions.

All warm-blooded animals need to eat, a lot, frequently.  This is especially true when compared with cold-blooded animals of the same weight.  Some birds, for example, eat their own weight in food every day.

To help keep the energy they get from eating, and to improve the efficiency of their metabolism, all warm-blooded animals have insulation.  In birds, it’s feathers; in mammals, it’s hair.  Insulation doesn’t just keep the cold out; it also keeps the heat in.  Remember that, the next time you wear a down-filled jacket.

So what are the actual definitions of vertebrate groups?  Well, I’ll get to that in the next post.