  "What is the difference between space and time?" is an ancient question that
remains a matter of intense debate. In Newtonian mechanics time is absolute,
while in Einstein's theory of relativity time and space combine into Minkowski
spacetime. Here, we firstly propose Minkowski fermions in 2+1 dimensional
Minkowski spacetime which have two space-like and one time-like momentum axes.
These quasiparticles can be further classified as Klein-Gordon fermions and
Dirac-Minkowski fermions according to the linearly and quadratically dispersing
excitations. Realization of Dirac-Minkowski quasiparticles requires systems
with particular topological nodal-line band degeneracies, such as hyperbolic
nodal lines or coplanar band crossings. With the help of first-principles
calculations we find that novel massless Dirac-Minkowski fermions are realized
in a metastable bulk boron allotrope, Pnnm-B16.
