Over one hundred arthropod fossil species have been described from the famous Chengjiang Lagerst?tte(South China,Cambrian Stage 3,ca.518 Ma)including a diverse assemblage of radiodonts-a group con-taining Anomalocaris and its relatives.These iconic stem-group euarthropods include some of the largest animals of the time,and some are known from hundreds of specimens.A longstanding conundrum has been the rarity or absence of hurdiids from Cambrian Series 2 Lagerst?tten like Chengjiang.This is because radiodonts are generally common in such deposits and the oldest radiodont ever discovered is a hurdiid.Furthermore,this family displays the widest geographic and temporal ranges of all radiodont families,and the highest diversity.Here we document the first hurdiid frontal appendages from Chengjiang,which display unique features within the family and may provide insights for understanding the character evolution of hurdiid appendages.The palaeoenvironmental distribution of hurdiids sug-gests that the rarity of hurdiids in Chengjiang may be due to a preference for deeper water environments,and the later success of this family from the Wuliuan onwards may relate to their ability to tolerate cooler water temperatures than other radiodont families.The palaeogeographical,palaeoenvironmental,and stratigraphical patterns observed in hurdiids maybe caused in part by the limited distributions of Konservat-Lagerst?tten in the Cambrian as well.

State Key Laboratory of Continental Dynamics,Shaanxi Key Laboratory of Early Life and Environments,and Department of Geology,Northwest University,Xi'an 710069,China;Department of Zoology,University of Cambridge,Downing Street,Cambridge CB2 3EJ,United Kingdom

[1]Yu Wu;Stephen Pates;Jiaxin Ma;Weiliang Lin;Yuheng Wu;Xingliang Zhang;Dongjing Fu-.Addressing the Chengjiang conundrum:A palaeoecological view on the rarity of hurdiid radiodonts in this most diverse early Cambrian Lagerst?tte)[J].地学前缘（英文版）,2022(06):1-15

Chengjiang,palaeoecological,hurdiid,radiodonts,Lagerst,Anomalocaris,euarthropods,hurdiids,radiodont,palaeoenvironmental,Wuliuan,palaeogeographical,stratigraphical,Konservat

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