Development of a phylogenetic classification has been a primary pursuit of crinoid paleontologists during the 20th century. Wachsmuth and Springer and Bather vigorously debated crinoid classification during the waning years of the 19th century, and although tremendous progress has been made a comprehensive phylogenetic classification is still the primary objective for crinoid research during the early 21st century. Twentieth century crinoid studies are divisible into four periods. The direct influence of Frank Springer and Francis Bather continued until approximately 1925. Descriptive studies dominated the period of 1926–1943 and culminated in a comprehensive classification of Paleozoic crinoids that was a combination of the ideas of Wachsmuth and Springer and Bather. The end of the third period, 1944–1978, was marked by publication of the Treatise on Invertebrate Paleontology. The Treatise compilation brought together classification ideas for the entire class into a truly comprehensive classification, although problems remained with the phylogenetic underpinnings of the Treatise classification. During the third period, pioneering work on crinoid paleobiology laid the foundation for significant paleobiology advances for the fourth, 1979–1999, period. This last period also witnessed significant advances in the taxonomy of crinoid faunas at critical intervals, the taxonomy of crinoids from new geographic areas, and working toward the solution to the origin and early evolution of the Crinoidea.
Continued work on crinoids in the 21st century promises to provide significant advances both for understanding the evolutionary history of crinoids and for understanding the history of epifaunal benthic communities through time. Immediate challenges include completion of a comprehensive phylogenetic classification, which will open the door for evolutionary paleoecologic and paleobiologic studies; utilization of computerized morphometric techniques in the analysis of functional morphology; systematic studies of new faunas in critical intervals; discovery of faunas in new geographic areas to better constrain knowledge of crinoid biogeography; and modern systematic revision of classic North American and European faunas.