29.6: Mammals Last updated Mar 6, 2021 Save as PDF 29.5B: Evolution of Birds 29.6A: Characteristics of Mammals Page ID13935 BoundlessBoundless ( \newcommand{\kernel}{\mathrm{null}\,}\) Topic hierarchy29.6A: Characteristics of Mammals29.6B: Evolution of Mammals29.6C: Living MammalsLiving mammals can be classified in three subclasses: eutherian, metatherians and monotremes.