". . .Fossils may tell us many things, but one thing they can never disclose is whether they were ancestors of anything else." It is actually this statement which is the key to interpreting the Sunderland quote correctly; it is not possible to say for certain whether a fossil is in the direct ancestral line of a species group. Archaeopteryx, for example, is not necessarily directly ancestral to birds. It may have been a species on a side-branch. However, that in no way disqualifies it as a transitional form, or as evidence for evolution. Evolution predicts that such fossils will exist, and if there was no link between reptiles and birds then Archaeopteryx would not exist, whether it is directly ancestral or not. What Patterson was saying to Sunderland was that, of the transitional forms that are known, he could not make a watertight argument for any being directly ancestral to living species groups.
Of course Patterson, as the curator, could never agree with the fledgling (at the time) intelligent design gang, but he was intellectually honest enough not to make the blatantly false assertion that most of him comrades do.
What he did do, is a common debate tactic that shows his erudition. In logic this is called the infinite regress, often analogized as a "lengthening of the shadow". The arguement was ended by chasing a "rabbit" into a hole no one could follow. Smart guy, intent on not being ridiculed as a fool, unlike many of his compatriots.
