Early Crinoids Research Articles

Crinoid calyx origin from stem radial echinoderms

AbstractEvidence from the earliest-known crinoids (Tremadocian, Early Ordovician), called protocrinoids, is used to hypothesize initial steps by which elements of the calyx evolved. Protocrinoid calyces are composed of extraxial primary and surrounding secondary plates (both of which have epispires along their sutures) that are unlike those of more crownward fossil and extant crinoids in which equivalent calycinal plating is strongly organized. These reductions inspired several schemes by which to name the plates in these calyces. However, the primary-secondary systems seen in protocrinoids first appeared among Cambrian stem radial echinoderms, with primaries representing centers around which secondaries were sequentially added during ontogeny. Therefore, the protocrinoid calyx represents an intermediate condition between earliest echinoderms and crownward crinoids. Position and ontogeny indicate certain primaries remained as loss of secondaries occurred, resulting in abutting of primaries into the conjoined alternating circlets characteristic of crinoids. This transformative event included suppression of secondary plating and modification or, more commonly, elimination of respiratory structures. These data indicate subradial calyx plate terminology does not correspond with most common usage, but rather, supports an alternative redefinition of these traditional expressions. Extension and adoral growth of fixed rays during calyx ontogeny preceded conjoined primaries in earliest crinoids. Restriction with modification or elimination of calyx respiratory structures also accompanied this modification. Phylogenetic analyses strongly support crinoid origination from early pentaradiate echinoderms, separate from blastozoans. Accordingly, all Tremadocian crinoids express a distinctive aggregate of plesiomorphic and apomorphic commonalities; all branch early within the crinoid clade, separate from traditional subclass-level clades. Nevertheless, each taxon within this assemblage expresses at least one diagnostic apomorphy of camerate, cladid, or disparid clades.

A re‐interpretation of the ambulacral system ofEumorphocystis(Blastozoa, Echinodermata) and its bearing on the evolution of early crinoids

AbstractRecent debates over the evolutionary relationships of early echinoderms have relied heavily on morphological evidence from the feeding ambulacral system.Eumorphocystis, a Late Ordovician diploporitan, has been a focus in these debates because it bears ambulacral features that show strong morphological similarity to early crinoid arms. Undescribed and well‐preserved specimens ofEumorphocystisfrom the Bromide Formation (Oklahoma,USA) provide new data illustrating that composite arms supported by a radial plate that bear a triserial arrangement of axial and extraxial components encasing a coelomic extension can also be found in blastozoans. Previous reports have considered these arm structures to be restricted to crinoids; these combined features have not been previously observed in blastozoan echinoderms. Phylogenetic analyses suggest thatEumorphocystisand crinoids are sister taxa and that shared derived features of these taxa are homologous. The evidence from the arms ofEumorphocystissuggests that crinoid arms were derived from a specialized blastozoan ambulacral system that lost feeding brachioles and strongly suggests that crinoids are nested within blastozoans.

Early phylogeny of crinoids within the pelmatozoan clade

AbstractPhylogenetic relationships among early crinoids are evaluated by maximizing parsimonious‐informative characters that are unordered and unweighted. Primarily Tremadocian–Darriwilian (Early–Middle Ordovician) taxa are analysed. Stratigraphic congruence metrics support the best phylogenetic hypothesis derived using parsimony methods. This study confirms the traditionally recognized lineages of Palaeozoic crinoids and provides new information on the branching order of evolving lineages. Camerates are basal crinoids with progressively more tipward groups (from an Ordovician perspective) being protocrinoids, cladids (paraphyletic), hybocrinids and disparids. The Protocrinoida should be maintained, but the Aethocrinida should be placed within the Cladida. The results of this study identify phylogenetic structure amongst the major early crinoid lineages and delineate the relative positions of crinoid higher taxa along a tree. Each valid higher taxon discussed herein requires a comprehensive treatment to delimit within‐lineage phylogenetic relationships.

Crinoid ancestry without blastozoans

At present, a debate in the paleontologic literature focuses on whether or not the immediate ancestry of the Crinoidea lies in an unidentified member of the Blastozoa, which includes eocrinoids and an assemblage known variously as the “cystoids”. Those proposing to derive crinoids from within the blastozoans have recently argued for homologies in the construction of the oral region of certain derived taxa from both groups. An opposing viewpoint, outlined here, finds evidence that aside from plesiomorphies, proposed similarities are superficial and homoplastic. We suggest these superficialities represent convergent adaptive strategies. Earliest crinoids express ambulacral traits unlike any blastozoan but that are expressed in the only other pentaradial echinoderms with a known record early enough to be considered in the context of crinoid origins, edrioasteroids and edrioasteroid-like stem echinoderms.

A primitive cladid crinoid from the Jiacun Group, Tibet (Darriwilian, Middle Ordovician)

A collection of numerous crinoid pluricolumnals from the uppermost Darriwilian (Middle Ordovician) of Tibet were derived from one biological species of crinoid. The specimens were collected from well‐lithified, bioclastic shelf limestones of the upper part of the Lower Chiatsun Group, Pygodus serra Biozone; coeval rocks of similar lithology outcrop at the summit of Everest. A new crinoid morphospecies, Segmentocolumnus (col.) hanshessi, is tentatively considered a ‘stem‐group cladid’, perhaps a dendrocrinid. The proxistele is broad and pentagonal in section with a broad, pentagonal axial canal; the mesistele of similar gross morphology is more slender with a regularly heteromorphic column and a similarly wide axial canal; the dististele is a terminal dendritic radice with a pentastellate axial canal. In the mesistele, the meric sutures correspond to the centres of the sides of the column, but in the dististele they occur in the angles. This range of morphologies would have led to their inclusion in at least two morphogenera if they had not been closely associated; as they belong to a single biological species, they have been ‘lumped’ together herein. This is a rare contribution to our knowledge of the early crinoids from a region outside Europe and North America. Copyright © 2012 John Wiley & Sons, Ltd.

Globally significant Early Permian crinoids from the Mount Mark Formation in Strathcona Provincial Park, Vancouver Island, British Columbia — preliminary analysis of a disappearing fauna

Strata of the Mount Mark Formation, Buttle Lake Group, exposed in the vicinity of Marble Peak in Strathcona Provincial Park, central Vancouver Island, contain a diverse Early Permian crinoid fauna. This is the first Permian fauna containing crowns and cups recognized from Wrangellia terrane. The fauna contains representatives of each of the major Paleozoic crinoid subclasses: Camerata, Disparida, and Cladida. Specimens were observed and photographed between 2004 and 2008. No specimens were collected in adherence to regulations of Stratcona Provincial Park. Preliminary identifications recognize several new genera and species within the fauna, but they are not named or described lacking specimens for repository. A minimum of 24 species are judged to be in the fauna, making it the second most diverse Permian fauna known from North America. Identified genera suggest a greater relationship to North American faunas than to Paleotethyan faunas, suggesting Wrangellia was closer to North America than to the Paleotethyan realm during Early Permian time. Exposures of the Mount Mark Formation in the vicinity of Marble Peak are undergoing karstification, and specimens are being lost under the harsh weathering conditions. Observations of individual specimens over a five-year interval found that morphologic details critical for identification are being lost at an alarming rate. It is recommended that sufficient specimens in the fauna should be collected as soon as possible for identification and analysis. These specimens should be preserved for future reference and could form an educational display in the Strathcona Provincial Park headquarters.

PERMIAN CRINOIDS FROM THE SAIWAN AND KHUFF FORMATIONS,SOUTHEASTERN OMAN

Early Permian (Sakmarian) crinoids are described from six horizons in the Saiwan Formation of the Huqf area of southeastern Oman. Each horizon yielded only one to three taxa. All specimens lived in a shallow water environment characterized by mixed siliciclastic or siliciclastic-carbonate sedimentation. Disarticulated arm plates of an indeterminate articulate crinoid are described from a tempestite bed in the Khuff Formation (Wordian) of the Haushi area. The Saiwan Sakmarian crinoids are some of the earlier, although not the earliest Permian crinoids known. Representatives of both primitive (sycocrinids) and advanced (scytalocrinids, blothrocrinids, texacrinids, and cromyocrinids) cladids and articulates are present in the Saiwan crinoids that are dominated by advanced dendrocrinids and belong to families previously reported from the Carboniferous or Permian. They show greatest affinity to the late Sakmarian/early Artinskian fauna from the Callytharra Formation of Western Australia. New taxa described herein double the number of genera (three) previously reported from the same area. The diversity of the Saiwan crinoids is relatively low when compared to the large faunas reported from Timor, Western Australia, Russia, and North America. However, they show affinity with each of the larger faunas. New taxa described are Coeliocrinus arenaceous n. sp., Moapacrinus ? omanensis n. sp., Huqficrinus biserialis n. gen. and sp., and Campbellicrinus nodosus n. sp.

Paleogeographic significance of Early Permian crinoids and blastoids from Oman

Early Permian crinoids and blastoids from Oman show relationship with Late Paleozoic Tethyan faunas of Timor and Western Australia and support an Early Permian age for part of the Basleo fauna of Timor. The camerate crinoidPlatycrinites omanensis n. sp. and the blastoidsTimoroblastus andDeltoblastus are reported for the first time from Sakmarian strata of northeastern Oman, doubling the known Permian echinoderms from Oman. The blastoids suggest an offshore lower energy shelf environment of deposition.

A reconnaissance of skeletal crystallography in rhombiferans, diploporans, and paracrinoids

We characterized the skeletal crystallography of representatives of nine rhombiferan, three diploporan, and three paracrinoid species. Crystallographic data from these groups are similar to data from previous studies of crinoids, echinoids, and blastoids in that 1) orientations ofcaxes are consistent within species and within higher taxonomic groups; 2)caxes typically are oriented subparallel to the medial plane of their respective plates; and 3) the inclination of axes within the medial plane varies between taxa. Rhombiferancaxes are oriented normal to plate surfaces whereas diploporancaxes are tangential to plate surfaces. Paracrinoids more closely resemble diploporans in having irregular patterns of thecal plating but theircaxes are approximately perpendicular to plate surfaces as in rhombiferans.In contrast tocaxes,aaxes in all specimens show little regularity and cannot be distinguished from random orientations.The rhombiferanCaryocrinites ornatusdisplays minor differences in the inclinations ofcaxes depending on the location of skeletal elements on the theca. Plates at the base of the theca have slightly aborally inclined axes, whereas distal plates have axes inclined slightly adorally. This pattern matches orientations in some early crinoids, suggesting similarities between rhombiferans and crinoids in development or skeletal construction.Skeletal crystallography in various echinoderms can be compared in light of hypotheses of homology proposed in the Extraxial-Axial Theory (EAT). Skeletal elements homologized under the EAT do not correspond to any particular crystallographic axis orientation, suggesting that the homologies proposed in the EAT encompass significant underlying skeletal variation.

A RECONNAISSANCE OF SKELETAL CRYSTALLOGRAPHY IN RHOMBIFERANS, DIPLOPORANS, AND PARACRINOIDS

We characterized the skeletal crystallography of representatives of nine rhombiferan, three diploporan, and three paracrinoid species. Crystallographic data from these groups are similar to data from previous studies of crinoids, echinoids, and blastoids in that 1) orientations of c axes are consistent within species and within higher taxonomic groups; 2) c axes typically are oriented subparallel to the medial plane of their respective plates; and 3) the inclination of axes within the medial plane varies between taxa. Rhombiferan c axes are oriented normal to plate surfaces whereas diploporan c axes are tangential to plate surfaces. Paracrinoids more closely resemble diploporans in having irregular patterns of thecal plating but their c axes are approximately perpendicular to plate surfaces as in rhombiferans. In contrast to c axes, a axes in all specimens show little regularity and cannot be distinguished from random orientations. The rhombiferan Caryocrinites ornatus displays minor differences in the inclinations of c axes depending on the location of skeletal elements on the theca. Plates at the base of the theca have slightly aborally inclined axes, whereas distal plates have axes inclined slightly adorally. This pattern matches orientations in some early crinoids, suggesting similarities between rhombiferans and crinoids in development or skeletal construction. Skeletal crystallography in various echinoderms can be compared in light of hypotheses of homology proposed in the Extraxial-Axial Theory (EAT). Skeletal elements homologized under the EAT do not correspond to any particular crystallographic axis orientation, suggesting that the homologies proposed in the EAT encompass significant underlying skeletal variation.

Not all written in stone: interdisciplinary syntheses in echinoderm paleontology

The fossil record of the Echinodermata is relatively complete, and is represented by specimens retaining an abundance of features comparable to that found in extant forms. This yields a half-billion-year record of evolutionary novelties unmatched in any other major group, making the Echinodermata a primary target for studies of biological change. Not all of this change can be understood by studying the rocks alone, leading to synthetic research programs. Study of literature from the past 20 years indicates that over 1400 papers on echinoderm paleontology appeared in that time, and that overall productivity has remained almost constant. Analysis of papers appearing since 1990 shows that research is driven by new finds including, but not restricted to, possible Precambrian echinoderms, bizarre new edrioasteroids, early crinoids, exquisitely preserved homalozoans, echinoids at the K-T boundary, and Antarctic echinoids, stelleroids, and crinoids. New interpretations of echinoderm body wall homologies, broad-scale syntheses of embryological information, the study of developmental trajectories through molecular markers, and the large-scale ecological and phenotypic shifts being explored through morphometry and analyses of large data sets are integrated with study of the fossils themselves. Therefore, recent advances reveal a remarkable and continuing synergistic expansion in our understanding of echinoderm evolutionary history.

Earliest crinoids: New evidence for the origin of the dominant Paleozoic echinoderms

The oldest crinoids have been discovered in Early Ordovician strata of the western United States. A set of emergent crinoid traits based on these and other early crinoids enables reinterpretation of crinoid origins and early history. The new fossils retain primitive echinoderm characteristics, including ambulacral floor plates and largely unorganized cup plating, a first for crinoids. They lack shared derived characteristics linking them to other stalked echinoderms, including blastozoans. Contrary to current widespread opinion, crinoids originated as an independent group during the Cambrian, apparently from an edrioasteroid ancestor. All four major Paleozoic crinoid clades had evolved by the early Ibexian (Tremadocian), and this initial diversification slightly preceded those of most other Paleozoic evolutionary fauna components. These earliest crinoids attached to carbonate hardgrounds developed on sponge-algal mounds, intraformational conglomerates, and grainstones.

Reinterpretation of thecal plate homology and phylogeny in the Class Crinoidea

Since the Class Crinoidea was erected in 1821 there has been a consistent failure to resolve the phylogeny of this major group on even the coarsest scale. Reinterpretation of crinoid thecal plate homology, using the orientation of the stem rather than the position of the arms as a reference point for the theca, indicates that two-circlet (monocyclic) crinoids may be derived from three-circlet (dicyclic) taxa by the loss of any one of the three plate circlets in the theca rather than just the lowest circlet as has been assumed previously. Cladistic analysis utilizing this new homology, which is supported by evidence from ontogeny and from the position of other plates in the theca, suggests that Aethocrinus is sister group to all other crinoids and that the Cladida are primitive sister group to both the Disparida and Camerata. The Disparida, Hybocrinida and Perittocrinidae together represent a monophyletic clade. The Camerata also are monophyletic, but the orders Monobathrida and Diplobathrida can no longer be considered to represent natural taxa, with two-circlet camerates probably having evolved more than once. This reinterpretation of thecal plate homology sheds new light on the relationships between the major crinoid groups and the pattern of early crinoid evolution. □Echinodermata, Crinoidea, homology, phylogeny.