Figure 3. Reconstruction of ancestral patellar states in Tetrapoda, showing the major extant clades.

Reconstruction was performed using Mesquite’s parsimony algorithm and unordered character states, where 0 (black) = absent patella, 1 (yellow) = soft tissue patella/patelloid and 2 (blue) = ossified patella; see “Materials and Methods” for further details. The distribution of the ossified patella among extant clades has been interpreted as three occasions of independent evolution (in Aves, Squamata and Mammalia) (Dye, 1987; Haines, 1940), a conclusion strongly reinforced by specific fossil evidence (absence or equivocality of a patella in all outgroups). Reconstruction within Mammalia is explored in more depth in Figs. 5–7. Mya, millions of years from present.