Sheltered preservation of cyrtocrinid crinoids from the Lower Cretaceous of Madagascar and their palaeogeographic significance

Sheltered preservation,in which organisms are trapped within shells of cephalopods,is a wellknown phenomenon.This preservational style constitutes an important source of paleontological data.Here,we report the first crinoid preserved inside the early Albian ammonite Cleoniceras besairiei Collignon from Madagascar.This crinoid is assigned to the aspidocrinid phyllocrinid(Apsidocrinus,Phyllocrinidae),and constitutes the first phyllocrinid from the African continent,the second from the southern margin of the Tethys(after New Zealand),and also from the southern hemisphere.This specimen represents the youngest occurrence of a phyllocrinid in the world as well,and constitutes one of the youngest occurrences of cyrtocrinids from shallow sea environments,before predation-induced migration of the stalked crinoids to the deep sea refugia due to the so-called Mesozoic Marine Revolution.This finding highlights that ammonite shells may also be a convenient material for studying echinoderms.

The Discovery of a Crinoid Community in the LateTriassic Zhuganpo Formation of Guizhou Provinceand Its Geological Significance

: Recently a rich and well—preserved crinoid community including Traumatocrinus and Encrinus has been found in the Late Triassic Zhuganpo Formation in Guanling and Xingyi, Guizhou province, China. Among the fossils Traumatocrinus is the richest, and most of it occurs as clusters, with each cluster containing 3–42 crinoid branches. Study of the stem and calyx of Traumatocrinus shows that the number of stem-joints (columnals) is equal to the total stem length × K (5.85 per cm × stem—diameter). There are about 376 first- and second—order columnals on the whole stem. This number seems to coincide with the number of days in a year at that time. According to the present study of the palaeoecological environment of the crinoid community, it is considered that the reproduction and preservation of the crinoid community were controlled by the Late Triassic regression and the restricted bay of an interior sea behind the S—shaped shoal zone.

Copernicrinus zamorae gen.et sp.nov.,the oldest thiolliericrinid crinoid(Crinoidea,Echinodermata) from the Bajocian strata of Algeria,Africa

The thiolliericrinids(Thiolliericrinidae) are comatulids(Comatulida),which retained their stalks as adults.Here,we report a centrodorsal from the Bajocian strata(Middle Jurassic) of the Djebel Kérdacha area,northwestern Algeria(Africa).It is the first thiolliericrinid report from outside of Europe and also the oldest representative of the Thiolliericrinidae whose first occurrence is from the Oxfordian.The crinoid is assigned to Copernicrinus zamorae gen.et sp.nov.The reported new taxon shows strong similarities with the stemless ‘true’comatulids,Solanocrinites;the only difference is the presence of a facet to the stem in Copernicrinus.The closest comparable thiolliericrinid to Copernicrinus is the Oxfordian Thiolliericrinus,interpreted as a descendant of the latter.The origin and overview of all thiolliericrinid representatives are also discussed herein.

The unexpected occurrence of enigmatic'percevalicrinids'(Echinodermata,Crinoidea)in the Lower Jurassic strata of North Africa—Implications for their stratigraphic and palaeogeographic distribution and discussion on their belonging to the subfamily Balanocrininae

The marl and limestone alternations of the Lower Jurassic Ain Ouarka and Ain Rhezala formations(Pliensbachian-Toarcian)in the western Saharan Atlas,Northwest Algeria,yield a diverse micro-and mac-rofauna,including moderately numerous crinoids,which are represented by remains of isocrinids,i.e.,Bal-anocrinus ticinensis Hess and columnals of the genus Percevalicrinus.So far,the latter genus has been observed from the Upper Jurassic-Lower Cretaceous strata of Eurasia,North America,and the African continent.Thus,the present find is the oldest record of this crinoid genus,and the second one from the southern Tethyan margin.In this paper,it is shown that Percevalicrinus,which is traditionally regarded as a representative of the subfamily Balanocrininae,displays several features of the subfamily Isocrininae.The crinoid assemblage and associated facies and invertebrate fauna are typical of a low-energy deep outer shelf/ramp(below the storm wave-base)setting.