No. 20: Mar-Apr 1982
"Under the very best circumstances, however, morphological and stratigraphically graded transitions between classes and subclasses have been found. At the level of phyla and higher categories, any information on transitions as far as the fossil record is concerned is essentially nonexistent."
(Olson, Everett C.; "The Problem of Missing Links; Today and Yesterday," Quarterly Review of Biology, 56:405, 1981.)