Comparative anatomy is the study of similarities and differences in the anatomy of different species. The fundamental similarity in the basic skeletal structure of most vertebrates—specifically, the presence of a skull, vertebral column, and paired girdles (pectoral and pelvic)—points to shared evolutionary origins, making it a key piece of evidence for evolution based on comparative anatomy. These shared structures, despite variations in specific shape and function (e.g., a human arm versus a bat wing), are known as homologous structures, indicating descent from a common ancestor.

A. Molecular records refers to evidence from DNA and protein sequences, which also provides strong evidence for evolution, but the specific observation of the physical skeletal plan falls under anatomy.

B. Fossil records provide physical evidence of extinct organisms and show transitional forms over geological time, illustrating the historical sequence of evolutionary changes. While the fossil record shows the development of this body plan over time, the direct comparison of the current common structure across living species is comparative anatomy.

D. Embryology is the study of embryonic development. Similarities in the early developmental stages of different vertebrates (e.g., gill slits and tails in early embryos) offer evidence of common ancestry, but the final, common adult skeletal plan is an anatomical observation.