  We report on temperature-dependent size and anisotropy of the Fermi pockets
in graphite revealed by magnetotransport measurements. The magnetoresistances
obtained in fields along the c-axis obey an extended Kohler's rule, with the
carrier density following prediction of a temperature-dependent Fermi energy,
indicating a change in the Fermi pocket size with temperature. The
angle-dependent magnetoresistivities at a given temperature exhibit a scaling
behavior. The scaling factor that reflects the anisotropy of the Fermi surface
is also found to vary with temperature. Our results demonstrate that
temperature-driven changes in Fermi surface can be ubiquitous and need to be
considered in understanding the temperature-dependent carrier density and
magnetoresistance anisotropy in semimetals.
