Information about osteological changes in the groups of reptiles that
gave rise to mammals is preserved in the fossil record, but the
musculature of these reptiles has been lost forever. Nevertheless, a
reasonably accurate picture of the morphology and the spatial
relationships of the muscles of many of these extinct vertebrates can
be inferred by studying the scars or other marks delimiting the origins
and insertions of muscles on the skeletons of the fossils and by
studying the anatomy of Recent genera.