Classifying the Birds
According to modern taxonomy, every two species have a common
anscestor somewhere in the past, even if that link is hundreds of millions
of years back. The common anscestor for modern day reptiles and dinosaurs
is believed to be the thecodonts (from the triassic period). Near the
middle and late triassic period, thecodonts branched into
what would become the crocodilians, the prosauropods, the theropods,and
the ornithopods (to name a few). Researchers agree that the theropods are the most probable root of the birds,
but after that it gets hazy. Theropods are part of a group called
the Saurischian dinosaurs. They are characterized by their hallow,
thin walled bones; three main fingers on the manus (fourth and fifth
digits are reduced); three main toes on the pes (foot) with first and
fifth digits reduced; sharp, curved teeth used for eating flesh; and claws
at the end of their toes. Some of these characteristics are lost later
on as species evolve. The
theropods can be further divided as the picture below shows.
Birds would best be classified in the clade Ceolurosauria (an
offshoot of Tetanurae). The picture shown sa the Ceolurosaur is an
artist's interpretation
of the well known Archaeopteryx. The
group of Ceolosaurs that are probably the closest relatative of the birds
is the Maniraptora. The California museum of
Paleontology defines the clada Maniraptora as "all dinosaurs closer
to birds than to ornithomimids."
A few chief physical characteristics group the Maniraptora together,
one of which is a bone in the wrist called the semilunate carpal. Along
with other modifications of the forearm, this bone allows for flight.
Maniraptora also have a fused clavicle (collar bone) and a sternum (breast
bone), a pubis that points downward, a short stiffened tail, long arms,
and a large manus (hand).
Warning!
Just to be on the safe side, the end of this page is used for a
general warning. Classifying birds is currently one of the most
contraversial issues in taxonomy. In fact, there are huge gaps in our
knowledge of the evolutionary happenings of the past. To claim that birds
are descendents of Ceoluroaurs is to say that birds are actually reptiles.
(To see some of the similarities between birds and reptiles, click here.) After all, in the subphylum Vertebrata
(kingdom Animalia, phylum Chordata) there are only seven classes: Agnatha
(jawless fish),
Chrondrichthyes (cartilaginous fish), Osteichthyes (bony fish), Amphibia,
Reptilia, Aves, and Mammalia. To take out Aves and put it under reptilia
would be a big change!
So just remember, this page is subject to change at any point it time and
subject to dispute at all points in time.
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