Final answer:
Cuvier's four-fold division categorized living things into vertebrata, mollusca, radiate, and articulate, different from a linear nature scale and reflecting distinct groups. Vertebrates, a major chordate group, are known for their backbone, with over 62,000 species. This diversity has been shaped by Darwin's principles of 'natural' classification and common evolutionary ancestry.
Step-by-step explanation:
Cuvier's four-fold division of living things recognized the vertebrata, mollusca, radiate, and articulate (A). This classification system marks a significant historical point in taxonomic efforts, different from the linear scale of nature, and reflects Cuvier's recognition of distinct animal groups based on structural and functional differences.
Vertebrates are a well-known group with over 62,000 identified species and include well-studied extinct members like the dinosaurs. Vertebrates form part of the larger group of chordates, which also includes invertebrate chordates like tunicates and lancelets. Within the vertebrates, traditional classifications, such as those presented by Linnaeus, were further redeemed and refined by the works of Darwin, who tied taxonomy to common evolutionary ancestry and supported the idea of 'natural' classifications over artificial ones.
The phylum Craniata/Vertebrata is characterized by the presence of a backbone and a cranium, while the various traditional classes within this phylum, like Agnatha and Chondrichthyes, showcase the diversity within vertebrates.