The current open (CC-BY 4.0) zoology text material available here is organized as follows:

Naming and Classifying Animals

Vertebrate Diversity

1. Introduction
2. Cyclostomata
3. Gnathostomata
   1. Chondrichthyes
   2. Euteleostomi
      1. Actinopterygii
      2. Sarcopterygii
         1. Tetrapoda
            1. Amphibia
            2. Amniota
               1. The Diapsid-Synapsid Split
                  1. Diapsida
                     1. Lepidosauria
                     2. Testudines
                     3. Archosaurs
                  2. Synapsida
                     1. Mammalia