- 745 - WHY MOST OF THE TIMIRIASEVIINAE (OSTRACODA, CRUSTACEA) BECAME EXTINCT by Jean-Pierre COLIN* and Dan L. DANIELOPOL** Abstract Mesozoic and Cenozoic species of Timiriaseviinae, like the recent species have ecological and biological properties defining them as k-strategists. The extinction of most of them could be due to the contraction of their niche during the Cyprididae explosion in the Upper Jurassic-Lower Cretaceous. Their narrow ecological tolerance limits and poor disper- sion abilities made them very vulnerable during major environmental disturbances. Their low rate of sl)eciation during the Tertiary and Quaternary in Europe did not allow to start a new cycle of diversification. This could be due to the change of the reproductive pattern from bisexual to parthenogenetic. R6sum6 Les esp~ces m6sozoittues et c6nozoittues de Timiriaseviinae, comme les esp~ces r6centes,ont des propri6t6s 6cologi- ques et bio~ogiques les d6finissant comme k-strat6gistes. L'extinction de la plupart serait due ~ la contraction de leur niche lors de l'explosion des Cyprididae au Jurassique sup6rieur-Cr6tac~ inf6rieur. Les 6troites limites de tol6rance 6co- logique et leur faible capacit6 de dispersion les ont rendues tr~s vuln6rables aux principales modifications environne- mentales. Leur faible vitesse de sp6ciation, pendant le Tertiaire et le Quaternaire en Europe, ne leur a pas pennis de d6buter un nouveau cycle de diversification. Ceci serait dfi all changement de mode reproductif, de bisexuel ~ parth6- nog~n~tique. Introduction We recently redefined (1) the subfamily Timiriaseviinae MANDELSTAM, 1947 and recognized four groups of genera representing different lineages : Timiriasevia-Metacypris,Kovalevskietla, Theriosynoecum and Afrocythere-Elpi- dium. The oldest representatives occur in the Triassic (2) but they mainly diversified during the Jurassic and the Early Cretaceous and spred over very large areas (fig. 1). During the Upper Cretaceous, they sharply declined with the extinc- tion of the genera Theriosynoecum BRANSON in the Albian and TimMasevia MANDELSTAM in the Paleocene, In the Tertiary, only a small number of species survived mainly in Europe. Recent Timiriaseviinae are represented by 1 or 2 species of Afrocythere KLIE in mosses of streams in Africa, 6 species of Elpidium MULLER in South and Central America (3), 5 species of Kovalevskiella KLEIN in Central and Southern Europe and Turkey (4) and 1 species of Metacypris BRADY & ROBERTSON in Northern and Central Europe (5). * Esso Rep - EPR-E, 213 cours Victor Hugo, 33321 B~gles,France. ** Limnologisches Institut, Berggasse 18, A - 1090, Wien, Austria. G6obios n ° 12- fasc, 5 p. 745 -749, 1 fig., 1 tabl. Lyon, octobre 1979