Species Relationships Based on Anatomical Similarity

• Scientists classify species based on shared features. The more features that are shared, the more likely the species are to be closely related in evolution.
• Shared anatomical features, such as the presence of a backbone, are used to study relationships. But some features, such as the presence of wings, make comparisons difficult or confusing.

Lizards and snakes both have backbones and are classified as vertebrates. Anatomy allows physical trait comparisons, but does not allow genetic comparisons.