Friday, February 13, 2009

DINOSAUR ANATOMY part1


Because dinosaurs are also craniates (within vertebrates), they have a specialized head at the front of the body.
This head contains the brain, an enlarged nerve organ at the front of the spinal cord that encompasses three sensory capsules. These capsules detect light, smell, and sound, relaying this information to the brain.
The skull of a dinosaur, like your own, contains specific regions to house each of these sensory functions.
Dinosaurs also had specific organs associated with each sensory capsule: eyes for sight, ears for hearing, and a nose for olfaction. Specialized nerves led out from the brain to various parts of the body, the paths of which can sometimes be seen in dinosaur skull bones.
As gnathostomes, dinosaurs had hinged jaws that could open and close the mouth.
The scapula or shoulder bone of the forelimb was connected by muscles to the rib cage, but the pelvis or hip bone of the hind limb was firmly attached to the backbone. Semicircular canals in the inner ear helped the animal to maintain its balance.
Dinosaurs also had dermal bones (such as armor, as well as the outer skull bones), another gnathostome characteristic.
Because dinosaurs are tetrapods, their limbs had feet and hands.
The forelimb was suspended on the ribcage, but the pelvis was firmly attached to the vertebral column. Among tetrapods, dinosaurs are amniotes.
Thus they produced hard-shelled eggs with gas-permeable shells, which had to be laid on land. They did not have gills at any stage in their lives, and their skin was probably dry and scaly rather than moist and permeable.
As diapsid reptiles, dinosaurs had two openings in the skull behind the eye, one near the skull roof and another near the jawline.
As archosaurs, they had an extra opening in the skull between the nose and eye, and another in the lower jaw.

DINOSAUR ANATOMY part1



The 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.