Rediscovery of the type specimen of Jehol flying squirrel(Sciuropterus wulungshanensis Mori,1939)and its significance for the taxonomy of PteromysOA

In mammals,the litter size is approximately half the number of mammae,known as the‘one-half rule’,which has been recognized since the time of Aristotle in ancient Greece(Aristotle,1937)and applies to many species(Gilbert,1986;Diamond,1987).In contrast,arboreal squirrels,including flying squirrels,notably diverge from this norm by producing fewer offspring(Gilbert,1986).However,the reasons underlying this smaller litter size in arboreal squirrels have long remained elusive.