Introduction
If you’re a biology student, you must have heard about chordates. Chordates refer to a group of animals that possess a notochord, dorsal nerve cord, pharyngeal slits, and a post-anal tail. The chordates include vertebrates, tunicates, and lancelets. In this article, we’ll discuss the evolution of chordates in Section 33-1.
Chordate Evolution
The evolution of chordates can be divided into three main phases. The first phase is the invertebrate chordates, which lived during the Cambrian period. These invertebrate chordates were marine animals that possessed a notochord, but lacked a backbone. The second phase is the vertebrate chordates, which evolved during the Ordovician period. These animals possessed a backbone made up of cartilage or bone. The third phase is the evolution of modern vertebrates, which includes all the living vertebrates.
Chordate Characteristics
Chordates are characterized by four key features. These features include a notochord, dorsal nerve cord, pharyngeal slits, and a post-anal tail. The notochord is a flexible rod that runs along the length of the body. It provides support and allows for movement. The dorsal nerve cord is a hollow cord that runs along the back of the animal. It develops from a plate of ectodermal cells. The pharyngeal slits are a series of openings in the pharynx that allow water to enter and leave the body. The post-anal tail is a tail that extends beyond the anus.
Invertebrate Chordates
Invertebrate chordates were the first chordates to evolve. They lived during the Cambrian period, which was about 540 million years ago. These animals were marine animals that possessed a notochord, but lacked a backbone. The invertebrate chordates include the lancelets and tunicates.
Vertebrate Chordates
Vertebrate chordates evolved during the Ordovician period, which was about 488 million years ago. These animals possessed a backbone made up of cartilage or bone. The vertebrate chordates include the fish, amphibians, reptiles, birds, and mammals.
Modern Vertebrates
Modern vertebrates include all the living vertebrates. These animals have a backbone made up of bone. They include the fish, amphibians, reptiles, birds, and mammals. Modern vertebrates have adapted to live in a wide range of environments, from the depths of the ocean to the tops of mountains.
Conclusion
In conclusion, chordates are a group of animals that possess a notochord, dorsal nerve cord, pharyngeal slits, and a post-anal tail. The evolution of chordates can be divided into three main phases, including invertebrate chordates, vertebrate chordates, and modern vertebrates. Understanding chordate evolution in Section 33-1 is important for biology students, as it provides insight into the development of modern animals.
