Re-investigation of the Mesozoic cycad genus Chilinia: fossil record, diversity, spatio-temporal distribution, and palaeoclimate implications

Chilinia is an extinct genus of cycads, established by Li and Ye in 1964 based on leaf fossils from the Lower Cretaceous in Jilin Province, China. Morphologically, the genus Chilinia closely resembles Ctenis, another cycad foliage genus, in having pinnately divided leaves with laterally inserted pinnae on the rachis and reticulate venation but differs mainly from the latter in having toothed or irregularly lobed rather than entire-margined pinnae. Fossil records show that up to now, nine species of Chilinia have been reported worldwide, representing an index fossil plant in the Jurassic to Early Cretaceous. In this study, we present a comprehensive overview of all reported Chilinia fossils from a systematic palaeobotanical perspective. Fossil records indicate that Chilinia mainly occurred in the middle–high latitudes of the northern and southern hemispheres in Pangea from the Middle Jurassic to mid-Cretaceous. Combined evidence from the morphology of Chilinia and its floral patterns suggests that the genus probably lived in humid warm-temperate palaeoclimatic conditions with brief seasonal variations.