K. C.  Nixon and Davis, J. I., ?Polymorphic taxa, missing values and cladistic analysis?, Cladistics, vol. 7, pp. 233-241, 1992.

K. C.  Nixon and Davis, J. I., ?Polymorphic taxa, missing values and cladistic analysis?, Cladistics, vol. 7, pp. 233-241, 1993.

K. C.  Nixon and Wheeler, Q. D., ?Extinction and the origin of species?, in Extinction and Phylogeny, M. J.  Novacek and Wheeler, Q. D., Eds. New York: Columbia University Press, 1992, pp. 119-143.

M. A.  Gandolfo, Nixon, K. C., and Crepet, W. L., ?Moncotyledons and their fossil record: a review?, in Monocots II Abstracts, K.  Wilson, Ed. Sydney: RBG, 1998, p. 21.