  An intrinsic physical mechanism, based on the doping evolution of the Fermi
surface (FS), is explored to reconcile the contradictory experimental results
on the superconducting (SC) pairing symmetry in electron-doped cuprates. It is
argued that the FS pocket around $(\pi/2,\pi/2)$ has not yet formed until
doping reaches about the optimal value. Therefore, in the underdoped regime,
even if the SC order parameter is $d$ wave which vanishes along the line
$k_x=k_y$, the quasiparticle excitation gap is still finite and looks
s-wave-like due to the absence of the FS across that line. This makes it
possible, with d-wave SC pairing, to understand those experiments which
evidenced the s-wave quasiparticle excitation. An explicit theory with
consideration of both antiferromagnetic and SC orders is implemented to exhibit
the FS evolution from underdoping to overdoping and associated with it the
variations of the quasiparticle property, electronic density of states, and low
temperature dependences of the physical quantities heat capacity and superfluid
density.
