  A natural similarity in body dimensions of terrestrial animals noticed by
ancient philosophers remains the main key to the problem of mammalian skeletal
evolution with body mass explored in theoretical and experimental biology and
tested by comparative zoologists. We discuss the long-standing problem of
mammalian bone allometry commonly studied in terms of the so-called
''geometric'', ''elastic'', and ''static stress'' similarities by McMahon
(1973, 1975a, 1975b). We revise the fundamental assumptions underlying these
similarities and give new physical insights into geometric-shape and
elastic-force constraints imposed on spatial evolution of mammalian long bones.
