The Horse Series has been a mainstay of the Evolution literature since 1879. Recently, many Creationists have claimed that it is no longer valid. They quote scientists saying things such as
By this I mean that some of the classic cases of darwinian change in the fossil record, such as the evolution of the horse in North America, have had to be discarded or modified as a result of more detailed information - what appeared to be a nice simple progression when relatively few data were available now appears to be much more complex and much less gradualistic.The scientists were not trying to say that the Horse Series is no longer evidence of evolution. They were trying to say that some older books, and some older museum displays, presented a too-simplified view of a very rich history. For example, a more recent quote:David M. Raup, Field Museum of Natural History Bulletin Vol. 50 #1 (January 1979) p. 25
...fossil horses do indeed provide compelling evidence in support of evolutionary theory.Horses, the fossil record, and evolution: a current perspective, MacFadden, B.J., J.D. Bryant and P.A. Mueller, Evolutionary Biology 22:131-158 (1988) page 131