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