The following quote appears in at least one Creationist book:
"I fully agree with your comments on the lack of direct illustration of evolutionary transitions in my book. If I knew of any, fossil or living, I would certainly have included them. . .I will lay it on the line, There is not one such fossil for which one might make a watertight argument."
-- Dr. Colin Patterson, senior paleontologist at the British Museum of Natural History.
This quote is from a letter from Dr. Patterson to creationist Luther D. Sunderland. The next few sentences are:
"... a watertight argument. The reason is that statements about ancestry and descent are not applicable in the fossil record. Is Archaeopteryx the ancestor of all birds? Perhaps yes, perhaps no: there is no way of answering the question. It is easy enough to make up stories of how one form gave rise to another, and to find reasons why the stages should be favoured by natural selection. But such stories are not part of science, for there is no way to put them to the test."
So, what Patterson is saying is that perhaps modern birds descended from the species Archaeopteryx, or perhaps they descended from a cousin species. He just doesn't know how to prove which is the case. Therefore, he refuses to make a claim he can't fully back up.
Dr. Patterson does believe that there are transitional fossils, as witness this quote from the book in question:
"In several animal and plant groups, enough fossils are known to bridge the wide gaps between existing types. In mammals, for example, the gap between horses, asses and zebras (genus Equus) and their closest living relatives, the rhinoceroses and tapirs, is filled by an extensive series of fossils extending back sixty-million years to a small animal, Hyracotherium, which can only be distinguished from the rhinoceros-tapir group by one or two horse-like details of the skull. There are many other examples of fossil 'missing links', such as Archaeopteryx, the Jurassic bird which links birds with dinosaurs (Fig. 45), and Ichthyostega, the late Devonian amphibian which links land vertebrates and the extinct choanate (having internal nostrils) fishes ..."I personally have a low opinion of Dr. Patterson's objection. A claim about history most certainly can be scientific. There are fossil series where a "watertight argument" can be made. In the case of Archaeopteryx, the problem is not that the questions can never be decided. The problem is that we have not yet found enough relevant fossils.
Evolution 1978, Routledge & Kegan Paul Ltd. pp. 131-133