Functional morphology of synarthrial articulations in the crinoid stem

Synarthrial fulcral ridges are found in crinoid columnals from the mid-Ordovician to the present and in all four subclasses. Similar articulations did not become common in the cirri until the Mesozoic. Synarthrial stem articulations fall into two broad groups. Type I articulations have a fulcral ridge in the centre of the articular facet. In elliptical ossicles this ridge corresponds to either the long (IA) or short (IB) axis of the facet. Although both are functionally similar, Type IA ossicles are more common. Type II articulations have an excentric fulcral ridge, parallel to either the long (IIA) or short (IIB) axis of the articular facet. Type IIA articulations are found in crinoid stems capable of coiling. Type II articulations are particularly common in the cirri of articulates and are well adapted for attachment to hard and soft substrates. Columnals with Type I articulations often have divergent fulcra, giving the stem flexibility in all directions, but this feature is not seen in cirri or in coiled stems, where it would impair normal functions. Only the cirri of isocrinids and comatulids are muscular, so the movement of columns with fulcra must be passive.     

Phylogenetic implications of the Protocrinoida: Blastozoans are not ancestral to crinoids

A traditional, widely cited hypothesis for over a century posits the origin of the crinoids from blastozoans. The blastozoan hypothesis is contradicted by the discovery of a new crinoid order, the Protocrinoida. Protocrinoids exhibit many traits that are consistent with a basal crinoid phylogenetic position, but inconsistent with a blastozoan ancestry. Protocrinoids are among the oldest crinoids and are therefore stratigraphically correctly placed. The blastozoan hypothesis in contrast, relies on putative homologies between blastozoans and crinoids taken from taxonomically and stratigraphically disparate representatives of both groups; these disparities indicate homoplasy rather than propinquity of descent. Data supporting these ideas are reviewed here. These findings reinforce insightful observations made by Georges Ubaghs decades ago with less data.     

A crinoid concentration Lagerstätte in the Turonian (Late Cretaceous) Conulus Bed (Miechów-Wolbrom area, Poland)

More than one hundred centrodorsals of the comatulid crinoid Glenotremites paradoxus have been found in Turonian deposits (Upper Cretaceous) in the Miechów-Wolbrom area (southern Poland). This is the first dense occurrence of the genus Glenotremites in the Upper Cretaceous of Poland. Furthermore, so many individuals of this species in one level (the so-called Conulus Bed) forming a crinoid Konzentrat-Lagerstätte are very surprising because only disarticulated remains (cirrals and brachials) are encountered in the older (Cenomanian and earliest Turonian) and younger (late Turonian) deposits. The Glenotremites individuals are accompanied by isocrinids, which prove that stalked forms remained in shallow-water settings for some time after the initiation of the Mesozoic marine revolution.     

Lower Middle Devonian,Eifelian, crinoids from central Guangxi,South China

The extensive Devonian marine deposits of South China have yielded few articulated crinoid cups or theca. Two Eifelian specimens, from the Gupa Member, are the first ones reported from the Yingtang Formation, Eifelian, from the Ma’anshan section, Guangxi, South China. The new taxon Guangxicrinus xiangzhouensis n. gen. n. sp. is the first report of a marsupiocrinid in China, extending the paleogeographic range of the family into the Paleotethys and the stratigraphic range of the family upward from the upper Silurian into the lower Middle Devonian, Eifelian. The occurrence of Halocrinites sp. is the third occurrence of a cupressocrinitid in China and extends the paleogeographic range from Yunnan to Guangxi.     

New data on crinoid assemblages from the oldest sedimentary rocks of the Polish Outer Carpathians (Jurassic-Cretaceous)

Crinoids (Crinoidea) preserved in the so-called Cieszyn Beds (Tithonian-Hauterivian; southern Poland) are relatively numerous, especially in some levels, but not highly diversified. They are absent in the Lower Cieszyn Shale (Tithonian) and the Upper Cieszyn Shale (Valanginian-Hauterivian). The Lower Cieszyn Limestone (Tithonian) yielded crinoid remains classified as Isocrinus cf. amblyscalaris (Thurmann) and Isocrinida indet. In the Upper Cieszyn Limestone (Berriasian) crinoids are much more numerous and diversified. The following taxa are recorded: Isocrinus? annulatus (Roemer), Balanocrinus subteres (Münster), B. cf. smithi Hess and Gale, and Hemicrinus sp. The presence of specimens resembling Isocrinus amblyscalaris (Thurmann) in the Tithonian strata is surprising since the last occurrence of this taxon was reported from the Kimmeridgian. The Lower Cieszyn Limestone crinoidal assemblage is dominated by isocrinids (Isocrinida). This probably reflects the much shallower sedimentary environment of these sediments compared to that of the Upper Cieszyn Limestone, where excepting isocrinids, hemicrinids (Hemicrinidae, Cyrtocrinida) typical for deep marine environments were found. It is consistent with the analytical results from the foraminiferal assemblages, among which the benthic forms known from shelfal and paralic epicontinental environments first dominated, and then were supplanted by deep-sea taxa at the turn of the Jurassic and Cretaceous.     

Depth-related ecological zonation of a carboniferous carbonate ramp: Upper Viséan of Béchar Basin,Western Algeria

Summary Following the demise of the stromatoporoid-coral reef community in Late Frasnian time, Lower Carboniferous carbonate shelf profiles possessed a ramp geometry, with major organic buildups represented by mud-rich mounds. Microfacies petrography of the exceptionally well-preserved Upper Viséan (Lower Carboniferous) carbonate ramp of the Béchar Basin, Algerian Sahara, may well contribute significantly to our understanding of the paleoecological zonation of Carboniferous non-rimmed platforms, and of the still enigmatic mounds commonly referred to as Waulsortian banks or mounds. Facies are grouped into two broad groups: (a) a mound facies group which comprises sponge wackestone-bafflestone, sponge-fenestellid bafflestone-wackestone, crinoid wackestone-packstone, and bedded flanks of intraclastic wackestone-packstone, all four facies composing the actual mud-rich mounds, and (b) a supramound facies group composed of coral-microbial framestone, crinoid packstone-grainstone, algal-foraminiferal grainstone and oolite grainstone. Calcareous algae are important bathymetric indicators and are used to delineate three bathymetric zones based on light penetration: the aphotic zone, which contains no calcareous algae; the dysphotic zone, where there is little ambient light, and which is characterized by the presence of red algae (Fasciella, Ungdarella, Stacheia, Epistacheoides) and absence of green algae; and the euphotic zone, which receives the full spectrum of sunlight, and is characterized by the occurrence of both green algae (Koninckopora, Kamaenella, Kamaena, Palaeoberesella, Calcisphaera, Anthracoporellopsis, Issinella, Exvotarisella) and red algae. Integration of algal zonation, distribution of the other biota, and recurrence of distinct assemblages, enable recognition of seven depth-related benthic assemblages. Together with the physical properties of the facies, the benthic assemblages were used to define seven bathymetric zones, from upper to lower ramp: (1) algal assemblage (upper ramp); (2) crinoid-ramose bryozoan assemblage (mid-ramp); and (3) productid brachiopod assemblage, (4) colonial rugose coral-microbial encruster assemblage, (5) crinoid-fenestellid assemblage, (6) sponge-fenestellid, and (7) sponge assemblage (lower ramp). The vertical zonation of the mud-rich mounds and associated facies differ from that reported from the classical Upper Tournaisian-Lower Viséan Waulsortian mound-bearing successions.     

A radicle solution: morphology and biomechanics of the Eucalyptocrinites ‘root’ system

Eucalyptocrinites is one the most common and familiar mid‐Palaeozoic crinoids and is the exemplar of a form with dendritic radicular holdfasts. American museums have hundreds of specimens of Eucalyptocrinites holdfasts from the Silurian Waldron Shale of Indiana and Kentucky, USA. The radix (‘root’) system of Eucalyptocrinites can be described as comprised of links (branches) that meet at nodes. Measured values include the x‐ and y‐coordinates of the nodes, the distances of the nodes from the stem, the angles between branches, branch length and branch width. Rose diagrams show clearly that the root systems are not isotropic but have preferred orientations. Branch angles are highly variable, but cluster around 60 degrees. Branch lengths and distal branch widths are relatively constant, but branch width increases variably towards the column. The branching pattern can be modelled as a self‐similar (‘fractal’) structure. Several specimens labelled as Eucalyptocrinites show a distinct fivefold symmetry without branching and very likely represent a different taxon. The Eucalyptocrinites radix system, along with the probably stiff dististele, most likely functioned as a rigid plate that resisted rotational forces due to currents acting on the crown. Upstream radicles experienced tension, whereas downstream roots were compressed. This force distribution may explain the observed anisotropies in radix morphology. The ‘roots’ of Eucalyptocrinites and other crinoids have long been compared with the root systems of plants. Although there are superficial similarities, there are fundamental differences.     

The northern most Emsian crinoids known, a Devonian fauna from the Chuluun Formation, Shine Jinst area, Southern Mongolia

The most northerly known Emsian crinoids were located at approximately 45° to 50° N latitude. They are the first Devonian crinoid cups discovered in Mongolia. Specimens are reported from excellent exposures of the informally designated crinoidal beds in the upper part of the stratotype section of the Chuluun Formation, between N44° 22.119', E99° 27.130' and N44° 22.201', E99° 26.906', near the Tsakhir Well, in the foothills south of Tsagaan Khaalga Mountain, Shine Jinst area, southern Mongolia. All specimens are crushed, altered by low-grade metamorphism, and ossicles flake as they weather. Five genera are present including a new genus of the Periechocrinidae, two indeterminant camerates, an undesignated new species of Cyathocrinites, and one indeterminant crinoid. These genera agree with a middle Emsian age previously assigned to the upper part of the Chuluun Formation on the basis of brachiopods and conodonts. They show affinity to European and North American Emsian faunas.