anatomy of a dinosaur includes both general and specialized components.
Most of the obvious features of dinosaurs were inherited from their
ancestors, and as such, they often characterize not only dinosaurs
but other animals as well. They also provide clues that scientists
can use to determine how dinosaurs are related to other animals. More
specific anatomical features may characterize only dinosaurs, or only
particular kinds of dinosaurs.
At their most basic level, dinosaurs are multicellular eukaryotes.
This means that dinosaurs were built out of many millions of cells,
each of which had a distinct nucleus containing the dinosaur's genetic
material. Dinosaur reproduction was sexual, in which male and female
gametes combined to create an embryo. Even though we have no fossils
preserving this tiny level of detail, scientists can infer these qualities
of dinosaurs because they are present in all multicellular eukaryotes.
Within eukaryotes, dinosaurs are deuterostomes. Therefore,
like echinoderms, acorn worms, and vertebrates, dinosaurs would
have developed from an embryo according to a certain pattern. Specifically,
the anus would have developed first and the mouth second. A long digestive
tract would have connected the two openings.
Many of the most obvious features of dinosaur anatomy exist because
dinosaurs are chordates and vertebrates. As chordates,
dinosaurs had a tail (defined as the structures following the anus),
heart, and a long, hollow nerve cord that ran down the back. In addition,
they were segmented animals, which would have been reflected in their
musculature. As vertebrates, dinosaurs had an internal
bony skeleton that was constructed around a central chain of segmented
bones, the vertebral column. This chain protected the spinal cord.
Internally, dinosaurs had organs such as the liver and kidneys. Dentine
and enamel were present, forming teeth and scales.