A simple evolutionary tree for the craniates showing where simple lattices and superlattices have been found. Data from Luther et al. (1996), Luther and Squire (2014), and Ma et al. (2019). Particularly large families are the teleosts, where all muscles studied so far have simple lattices, and the tetrapods (mammals, amphibians, reptiles, and birds), which until now have generally shown superlattice structures. The work of Ma et al. (2019) has now found the simple lattice structure in rat SOL muscles, which consist predominantly of slow fibers.