FREE ESSAY ON DINOSAURS AND BIRDS

DINOSAURS AND BIRDS

Dinosaurs and Birds
Nat 305
Christopher Meadows
11-2-00
Are birds really dinosaurs or are they simply related? That is a question that has gained
new life in recent years due to the overwhelming facts the are pouring in from newly
found fossils and studies from fossils that have been found in the past. Two groups have
formed in the study of this question: those who believe birds are a direct result of
dinosaurs and those who feel dinosaurs and birds must have had a common ancestor.
Determining which view is correct is a matter of opinion based on fact. The main problem
involves the use of cladistics or phylogenetic systematics to group organisms according
to characteristics they share. When one looks at dinosaur fossils, he or she may feel
that certain characteristics are used for something entirely different than someone else
who has looked at the same fossil. 
One cannot talk about dinosaur and bird lineage without mentioning Archaeopteryx. Most
paleontologists agree that Archaeopteryx was the first bird. Archaeopteryx thus
represents what paleontologists would call a "transitional form" between two major groups
of animals, the reptiles (dinosaurs) and birds. The main difference between the theropods
and Archaeopteryx were the long arms of the Archaeopteryx, adapted as wings, the
feathers, and the presence of a wishbone that the theropods did not have. All of these
features tie it to birds and its other characteristics tie it to theropods. One might say
it was the "missing link" between the two. Opponents of this idea say that the
similarities between Archaeopteryx and theropods were due to convergence, with the
birdlike dinosaurs appearing in the Cretaceous some 75 million years after Archaeopteryx.
Also, support is gaining that Archaeopteryx was not in fact the first bird, but instead a
descendent of an earlier bird ancestor that had developed along a different pathway and
actually represents an evolutionary dead end.
Two opponents of the "birds are dinosaurs theory" are Alan Feduccia of the University of
North Carolina and Larry Martin of the University of Kansas. They believe that birds
evolved from some unknown reptile from a time before dinosaurs came to be. One point they
make is that flight must have begun from tree climbing or an arboreal ancestor but that
all the proposed dinosaurian ancestors were ground dwellers or cursorial On the other
side, supporters for the "birds are dinosaurs theory" feel there is an unknown dinosaur
bird that was arboreal, or simply that birds evolved flight from the ground by chasing
after insects.
In recent years other fossil finds have stirred the argument even more. One of these is
the fossil named Sinosauroptyrex found in China. It appears to be an important link
between birds and dinosaurs. Sinosauropteryx appears to be a feathered dinosaur having a
mane of feathers along its neck, back, and tail-a feature until then seen only in birds.
Sinosauroptyrex appears before Archaeopteryx and gives a substantial link between the
theropods and birds. One opponent of this find is Martin who feels the structures that
are considered to be feathers are simply frayed collagenous fibers beneath the
skin-having nothing to do with birds. Another find involves a fossil that was found in
Madagascar in 1995. The fossil was identified as a bird because its arm bones contained
knobs where feathers would have been attached. It also has a reversed first toe, a
characteristic of birds unknown in any other type of theropod dinosaur, according to
Catherine Foster of the State University of New York at Stony Brook and discoverer of the
fossil. The real link between the Madagascan bird and dinosaurs is the retractable claw
on its second toe, which does not appear on any other birds. This is, according to some,
direct proof showing a link between birds and theropods. Opponents like Martin feel the
creature is actually a dinosaur and not a bird at all. 
One of the main problems in deciding this argument is the time scale in which the fossils
are found. Feduccia feels that one of the biggest problems is the "time paradox," meaning
that the so-called birdlike dinosaurs came too late to address avian evolution.
Supporters of the theory feel they will eventually find the fossils they need to prove
the "birds are dinosaurs theory" but it takes time to fill the gaps in the geologic
fossil record and discover the "missing links."