Chordates, members of the animal phylum Chordata, which includes all mammals, birds, amphibians, reptiles, and fish. There are about 45,000 species of chordates. They are classified in four subphyla, the largest of which contains the vertebrates. All chordates share three basic characteristics. The first characteristic is a single dorsal nerve cord, which in mammals takes the form of the brain and spinal cord. The second is a flexible rod of cells called a notochord, which in vertebrates takes the form of the backbone. The third is the presence of gill slits at some stage during the development of the animal. All chordates have bilateral symmetry.
Taking a boat trip with your pet can be quite an experience. With the right preparation, a cruise can be lots of fun for both of you. Take this quiz to learn more about preparing for a boat trip with your pet.
Orodromeus is a recently discovered dinosaur and one of the most spectacular. Orodromeus (the name means 'mountain runner') was only about 6 1/2 feet long as an adult. Learn more about the Orodromeus and other Late Cretaceous dinosaurs.