Global pattern of conodont similarity and faunal constraints during the highstand of the Evae eustatic event(late Floian,Lower Ordovician)

One of the largest Ordovician sea-level rises is the Evae transgression,which occurs in the lower part of the Oepikodus evae Biozone,indicative of a late Floian age.Specifically,the characteristics associated with the highstand of this event included:a higher proportion of specimens of the index species O.evae than other species,a diversity acme in the evae Biozone,and a reduction of biogeographic barriers that resulted in a high proportion of species with cosmopolitan distribution.In the present contribution,the pattern of species similarity among Laurentia,Argentine Precordillera,Baltica,Kazakhstania,South China,and Australia is evaluated with a multiple coefficient analysis including only the sections that recorded the highstand of the Evae transgression.Moreover,the effect of possible terrestrial,latitudinal,physicochemical barriers and palaeogeographic distance on the species distribution is statistically analysed.Our results show a global pattern of conodont species distribution that is highly constrained by the tested palaeoenvironmental factors.This suggests that contrary to what was expected for a prominent transgression,faunal barriers did not decrease significantly during the Evae drowning peak.