When scientists encounter a new
specimen, part of their research is to observe, describe,
it. In part,
the identification process happens by following an extremely
detailed checklist marking the presence or absence of particular
characters. Examining the patterns of the appearance and
disappearance of characters is the key to figuring out
the relatedness of organisms.
Birds are living dinosaurs.
Research over the last couple
of decades has shown that birds are indeed a kind of theropod
dinosaur. In fact, theropod dinosaurs, like Velociraptor,
are more closely related to modern birds than they are to
almost any other kind of dinosaur you are likely to have
heard of (including Tyrannosaurus, Triceratops, Diplodocus,
and Stegosaurus that is, they share a more recent common
ancestor). Just as we, as humans, are primates and mammals,
chickens, as birds, are theropods, dinosaurs, and reptiles.
What is a theropod?
Theropod dinosaurs are a diverse
group that first appeared over 230 million years ago
and have lived on every continent. The early theropods look
fairly similar to later ones—they were both bipedal
and usually carnivorous. But other than being fearsome creatures,
why are theropod dinosaurs so interesting? This dinosaur
group includes not only spectacular animals like the giant
predators Giganotosaurus, Tyrannosaurus , and Carcharodontosaurus,
but also some of the largest-brained, or smartest, dinosaurs.
Furthermore, the study of theropods has real relevance for
understanding animals that are alive today. We can better
study the evolutionary history of living birds now that we
know they descended from theropods, and ultimately our definitions
of both birds and dinosaurs will change.
and Non-Avian Theropods Compared
Use this illustration
to examine several
skeletal features and make observations
about the characteristics present in a
typical advanced non-avian theropod (Deinonychus)
and a typical modern bird (Gallus).
Which characteristics are the same? Which
characteristics are different?
to the Illustration...