A quadrupling of Famennian pelmatozoan diversity: New Late Devonian blastoids and crinoids from northwest China

Abstract

A new diverse Famennian echinoderm fauna (∼600 specimens representing 33 genera and 47 species) dominated by blastoids and cladid, small-calyx camerate, and flexible crinoids is reported from the Hongguleleng Formation, Junggar Basin, Xinjiang-Uygar Autonomous Region, China. Two stratigraphically distinct pelmatozoan faunas were collected: one from the lower member of the Hongguleleng Formation (crepidaZone tomarginiferaZone) and one from the upper member of the Hongguleleng Formation (praesulcataZone). Both faunas are distinctively “Carboniferous” in aspect. The older fauna is dominated by cladids and small-calyx camerates, whereas the younger fauna is dominated by blastoids.Discovery of these two faunas has more than doubled the number of Famennian echinoderm specimens known in the world and more than quadrupled the number of known taxa. Latest Devonian (Famennian) and earliest Carboniferous stemmed-echinoderm (pelmatozoan) faunas traditionally have been considered to be very low diversity relative to earlier Frasnian and later Early Carboniferous faunas. Furthermore, Carboniferous pelmatozoan faunas seemingly arose suddenly, with unclear ancestral ties to Devonian taxa. The Hongguleleng faunas are critical in understanding pelmatozoan biogeography and evolution in the aftermath of Devonian extinction event(s) prior to the Carboniferous echinoderm diversification, as they indicate that diversification and re-radiation of stemmed echinoderms already were well underway before the close of the Famennian.Collections from field excursions in 1993 and 1995 include seven new taxa of blastoids and nine new taxa of crinoids among the twenty-four total taxa reported. New blastoid taxa areEmuhablastus planus, Tripoblastus plicatus, Breimeriblastus pyramidalis, B. gracilis, Conoblastus invaginatus, Sinopetaloblastus grabaui, andHyperoblastus emuhaensis. Together with collections from 1991, we have amassed 333 blastoid specimens, representing 13 genera and 15 species.Emuhablastus planus, new genus and species, is the oldest genus of the Family Codasteridae, extending the familial record back from the Viséan to the Famennian. The hyperoblastid genera,Breimeriblastus, new genus, andConoblastus, new genus, apparently represent transitional genera between aPentremitidea-like ancestor and aPentremites-like descendant. These taxa imply that the fissiculate-spiraculate transition may have occurred in a mosaic fashion during the Middle to Upper Devonian.Hyperoblastus emuhaensis, new species, is the first report of the genus from rocks of Famennian age or from Asia.New crinoid taxa includeAthabascocrinus orientale, Hexacrinites pinnulata, Abactinocrinus devonicus, Euonychocrinus websteri,?Parisocrinus nodosus,?P. conicus, Bridgerocrinus discus, Julieticrinus romeo, andSostronocrinus quadribrachiatus. In addition, we propose several other taxonomic reassignments based on new collections.Uperocrinus zhaoaeis reassigned to the genusActinocrinusbased on the presence of pentagonal or hexagonal primibrachials in the cup, even though the primibrachials have a pseudo-quadrate appearance.Bridgerocrinus delicatulusis reassigned toLogocrinusbased on the presence of three, rather than two, primibrachials. Sostronocrinidae, new family, is erected for genera with 20 arms that otherwise might be placed in the Family Scytalocrinidae. Genera included within the Sostronocrinidae, new family, areSostronocrinus, Hertocrinus, Tundracrinus, andAmadeusicrinusnew genus.Bridgerocrinus minutusis reassigned to the genusSostronocrinus. Pachylocrinus subpentagonalisis reassigned toAmadeusicrinusnew genus. “Decadocrinus” xinjiangensisis reassigned toGrabauicrinusnew genus, which is erected for decadocrinids with 10 arms, all of which branch on the second primibrachial.