"With few exceptions, all animal mitochondrial genomes contain the same 37 genes: two for rRNAs, 13 for proteins and 22 for tRNAs. (...) the comparison of animal mitochondrial gene arrangements has become a very powerful means for inferring ancient evolutionary relationships, since rearrangements appear to be unique, generally rare events that are unlikely to arise independently in separate evolutionary lineages."
Source: Boore (1999) Animal mitochondrial genomes. Nucleic Acids Res. 1999 Apr 15;27(8):1767–1780
Hyperlink: https://pmc.ncbi.nlm.nih.gov/articles/PMC148383/
i.e. mtDNA changes a lot less than our "normal" cell nucleus nDNA