Living vertebrates can be divided into two major clades. Select the appropriate pair. a. the chordates and the tetrapods b. the urochordates and the cephalochordates c. the cyclostomes and the gnathostomes d. the marsupials and the eutherians

Key Concepts

Clades in Vertebrates

Clades are groups of organisms that include a common ancestor and all its descendants. In vertebrates, two major clades are often recognized: the jawless vertebrates (cyclostomes) and the jawed vertebrates (gnathostomes). Understanding these clades is essential for classifying living vertebrates and recognizing their evolutionary relationships.

Cyclostomes and Gnathostomes

Cyclostomes are a group of jawless fish, including lampreys and hagfish, characterized by their round mouths and lack of jaws. In contrast, gnathostomes are jawed vertebrates, which include a vast array of species from fish to mammals. This distinction is crucial for understanding vertebrate evolution and the diversification of species.

Chordates

Chordates are a phylum of animals that share certain key features at some stage of their development, including a notochord, a dorsal nerve cord, and pharyngeal slits. This group encompasses all vertebrates, as well as some invertebrates like tunicates and lancelets. Recognizing the characteristics of chordates helps in understanding the broader classification of living organisms.