Restudy On The Early Cretaceous Fossil Triops From Weichang Area,Hebei Province,China

Triopsids are freshwater crustacean,playing an important role in the study of crustacean evolution.Mesozoic triopsids were widely distributed all over the world and found from continental strata commonly.The Weichang area of Northern Hebei is one of fossil sites of Early Cretaceous triopsids in China.All 67 triopsid specimens studied in this paper were collected from the Jiufotang Formation of Early Cretaceous in the Weichang area.According to their morphological and structural characteristics,the studied triopsid specimens are assigned to Weichangiops triangularis Yang et Hong,1980.In the past,some experts thought that some triopsids with supra-anal plate belonged to the cold-water type triopsids living in cold regions of high latitude,but others without supraanal plate were warm-water ones living in warm climate regions.It is noteworthy that the Jiufotang Formation in the Weichang area yields not only some triopsids with supra-anal plate,but also other ones without supra-anal plate.In the past,this phenomenon was interpreted as the ‘mixed existence' of warm-water type and cold-water type of triopsids in the geographic distribution.However,Weichangiops triangularis is distributed only in the Weichang area of Hebei or in North China.Up to now,this species is never found from other regions.Its limited geographic distribution seems hard to support the view of ‘mixed existence'.According to the present study,the following preliminary understandings are obtained.1.The diagnosis of Weichangiops triangularis should be revised.Some experts mistakenly regarded the sensing organ as "a single compound eye" before.In fact,this species develops a pair of compound eyes and a sensing organ on the anterior part of the head.Therefore,the subfamily Weichangiopsinae established by them based on "a single compound eye",is invalid,and its name should be abandoned.2.Among the specimens of Weichangiops triangularis studied in this paper,some specimens clearly have the supra-anal plate,while others have no supra-anal plate.This indicates that this species shows an obvious sexual dimorphism: the male has a supra-anal plate between the furca,while the female has no supraanal plate between the furca.It is of a great scientific value for the study of classification in order to avoid the phenomenon of synonyms in biological classification.