  Rank--frequency distributions of nucleotide sequences in mitochondrial DNA
are defined in a way analogous to the linguistic approach, with the
highest-frequent nucleobase serving as a whitespace. For such sequences,
entropy and mean length are calculated. These parameters are shown to
discriminate the species of the <I>Felidae</I> (cats) and <I>Ursidae</I>
(bears) families. From purely numerical values we are able to see in particular
that giant pandas are bears while koalas are not. The observed linear relation
between the parameters is explained using a simple probabilistic model. The
approach based on the nonadditive generalization of the Bose-distribution is
used to analyze the frequency spectra of the nucleotide sequences. In this
case, the separation of families is not very sharp. Nevertheless, the
distributions for <I>Felidae</I> have on average longer tails comparing to
<I>Ursidae</I>.
