David Raup has stated:

"The evidence we find in the geologic record is not nearly as compatible with darwinian natural selection as we would like it to be. Darwin was completely aware of this. He was embarrassed by the fossil record because it didn't look the way he predicted it would and, as a result, he devoted a long section of his Origin of Species to an attempt to explain and rationalize the differences. There were several problems, but the principle one was that the geologic record did not then and still does not yield a finely graduated chain of slow and progressive evolution." (pp 22-23)

Page 24:

"And as I have already noted, different species usually appear and disappear from the record without showing the transitions that Darwin postulated."

Page 25:

"Well, we are now about 120 years after Darwin and the knowledge of the fossil record has been greatly expanded. We now have a quarter of a million fossil species but the situation hasn't changed much. The record of evolution is still surprisingly jerky and, ironically, we have even fewer examples of evolutionary transitions than we had in Darwin's time. 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."

"Conflicts Between Darwin and Paleontology," Bulletin, Field Museum of Natural History, January 1979,50:22- 29.