Systematics

Birds are such a diverse assemblage that some order must be found among them so that we can better understand their relationships. Modern bird taxonomists have developed methods for looking at the relationships of birds. In the past, most of these methods were based on morphological features, whereas today a lot of work is being done on an examination of the molecular similarities between birds.

For modern birds there are a few prominent features that stick out that have been used to differentiate them from one another. The primary two are the palette and the ankle bones. The first big division in birds is in the Neornithes: a separation of the Neognathae and the Paleognathae

The Paleognathae are represented by large (mostly) flightless birds such as the Moa, Emu, Cassowary, and other ratites. These birds have a paleognathan palette, and premolars that are connected to the braincase.

The Neognathae represent the rest of the modern birds. Their palette is much smaller and their ankles have, instead of a process on the astragalus, it’s the calcaneum that has the process.

Biogeography:
Why is it important to study the relationships of birds? Probably the best use of bird phylogeny or cladistics is to answer larger questions, such as those posed by biogeography. How might a group of birds have gotten from one continent to another? Why this distribution instead of others? If you look at one group, the Paleognathae, we can examine the possible uses.

The Ratites, are Paleognathan birds that are usually fairly large and flightless. The Cassowary of Australia and New Guinea is more closely related to the Emu of Australia than it is to the Ostrich. The Ostrich is fairly closely related to the Rheas of South America. We know now that Africa and South America were at one time connected. The study of these birds helped shed light on the dilemma of continental drift.

So how do you relate birds to one another? Cladistics is one common way. Cladistics uses shared, derived characters to determine the overall relatedness of each. For a detailed report on how cladistics are used see the Introduction to Cladistics

Biochemical systematics

In addition to morphological traits there are a few different types of molecular or biochemical techniques used to show the relationships of birds.

• Protein electrophoresis
• Restriction-fragment-length polymorphisms. (RFLP’s): take restriction enzymes and cut the mitochondrial DNA’s into base-pair specific sets.
  o Take the mDNA and put a bunch of enzymes in it.
  o Then you run them through an electrophoresis.
  o The more similar the fragment lengths the better.
• DNA hybridization
  o Two strands held together by chemical bonds.
  o Within the same molecule the bonding is very strong.
  o But if you split the DNA from one and mix it with those of another taxa.
  o If you heat them up you can measure the point in which they start to dissociate. The the higher the temperature needed, the closer related they are to each other.
• Sequence Data:
  o Takes a chunk of DNA and sequences this.
  o It has a few approaches: One would be a few individuals with long sequences and another, many individuals with shorter sequences.
  o Apapane from Maui; or Apapane from Kaui.
  o In this sequence, there is only one difference from the two islands. WOW.
  o Yet, if you look at the apapane to amakihi’s they are more different.
  o Considered to be the most powerful way of doing systematics; also the most expensive.
  o Sequence long regions of less rapidly evolving sequences, with more rapidly evolving sequences.

Bird Phylogeny
The process of determining relatedness in birds is a very complex process. Part of the reason for this is that birds are very similar. If you take a horse and a dog, both of which are mammals, there are significant differences between their skeletal make-up. If however, you do the same thing with the skeleton of a chicken and a parrot, you won’t find those differences. The complexities of the skull, pelvis, pectoral girdle, and foot are almost entirely the same!

If you look at a chicken you see the same thing. You can learn avian systematics by looking at any part of the bird. You could take any two orders of bird and their skull would be nearly identical. A horse and dog would be very different, but not with birds. This is part of the reason systematics is so difficult. The body plan has very little morphological differences in them!

BIRD SYSTEMATICS LINKS

• Introduction to AVES

By Rob Nelson

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