REINTERPRETATION OF A CONULARIID-LIKE FOSSIL FROM THE VENDIAN OF RUSSIA

Abstract:  Vendoconularia triradiata Ivantsov and Fedonkin, recently described from Vendian (latest Proterozoic) strata of Russia, has been interpreted as a six-sided conulariid cnidarian. However, comparison of published illustrations of V .  triradiata with Palaeozoic conulariids suggests that certain key features of the anatomy of V .  triradiata should be reinterpreted. Specifically, features previously homologized with the corners of conulariid thecae may actually be homologous to the conulariid midlines. Under this new interpretation, the corners of the Vendoconularia theca were sulcate, and the midline of each face was non-sulcate and flanked by a pair of low internal carinae. This alternative set of hypotheses of homology makes the argument for a conulariid affinity for Vendoconularia stronger.     

New data on the morphology of Sphenothallus Hall: implications for its affinities

Van Iten, H., Cox, R. S. & Mapes, R. H. 1992 04 15: New data on the morphology of Sphenothallus Hall: implications for its affinities. Lethaia , Vol. 25, pp. 135–144. Oslo. ISSN 0024–1164.
Recent speculation on the phylogenetic relationships of Sphenothallus Hall, 1847 has focused on two alternatives: (1) affinity with hydrozoan or scyphozoan cnidarians, or (2) affinity with annelids or other 'worms'. We have found that some species of Sphenothallus formed branching clonal colonies, and that others produced a thin transverse wall, similar to the conulariid schott. Sphenothallus tests are composed of carbonate apatite and are built of numerous, extremely thin lamellae (< 1 μm) that parallel the surface of the test. The holdfast, long interpreted as consisting of a pair of nested cups, actually consists of a single closed, broadly conical expansion floored by a thin basal membrane. Many thecate hydrozoan and scyphozoan polyps form branching clonal colonies and produce a thin transverse wall, similar to that produced by Sphenothallus . Further, thecae of coronatid scyphozoans are built of submicron-thick lamellae that parallel the outer surface of the theca, and coronatid thecae possess a closed, broadly conical apical expansion that serves as a holdfast. No such combination of characteristics exists among annelids or other non-cnidarian taxa. The recent discovery of paired tentacles in Sphenofhallus from the Early Devonian Hunsrück Slate by Fauchald et al ., thought to indicate that Sphenorhallus was wormlike, does not militate against a hypothesis of affinity with cnidarians. We therefore favour the hypothesis of a cnidarian affinity for Sphenothallus. * Sphenothallus, vermiform problematica, phylogenetic inference, coloniality, Cnidoria, Hydrozoa, Scyphozoa, Annelida, conulariids, byroniids, Bear Gulch Limestone .     

Pattern Specification and Pattern Regulation in the Embryonic Chick Limb Bud

SYNOPSIS. The embryonic chick limb bud is a growing organ rudimentwhose undifferentiated cells give rise to a precise spatialpattern of differentiated structures. The establishment of positionalvalues of chick limb bud cells (pattern specification) and theresponse of limb bud cells with established positional valuesto experimental perturbations (pattern regulation) are the majortopics considered in this paper. The results of recent experimentswith developing chick limb buds analyzing pattern specificationand pattern regulation are presented. These studies with thechick limb are described in light of the postulates of a modelthat was originally formulated from experiments performed onregenerating amphibian and insect appendages.     

Redescription of Hexaconularia He and Yang, 1986 (Lower Cambrian, South China): implications for the affinities of conulariid-like small shelly fossils

Abstract:  Hexaconularia , a Lower Cambrian small shelly fossil (SSF) that has been allied with conulariids and scyphozoan cnidarians, is redescribed and refigured. A salient feature of this monospecific genus is the presence of distinct apical and abapical regions. The apical region probably represents an embryonic shell that apparently lacked a basal attachment structure. Comparisons of this feature with the apical end of the smallest known conulariids and with conulariids terminating in an apical wall (schott) reveal substantial differences in structure and ornamentation. Differences in apical anatomy between conulariids and Arthrochites , possibly the nearest SSF relative of Hexaconularia , are also apparent. Comparisons of Hexaconularia with Punctatus , an SSF taxon showing distinct apical and abapical regions in both posthatching specimens and prehatching embryos, suggest that the early development of Hexaconularia was direct. These results have important implications for hypotheses of a conulariid/scyphozoan affinity for Hexaconularia and its possible SSF relatives, and they suggest that Hexaconularia -bearing strata may yield prehatching embryos of this genus.     

Exceptionally preserved conulariids and an edrioasteroid from the Hunsrück Slate (Lower Devonian,SW Germany)

Abstract: Nineteen partial specimens of Conularia sp., together with an articulated agelacrinitid edrioasteroid and several discinid brachiopods, occur in close association with a probable biological substrate on a small slab of silty Hunsrück Slate (Lower Devonian, Emsian) from Bundenbach, Germany. Most of the conulariids occur in V‐like pairs or in a single cluster of 12 specimens arranged in a fan‐like radial pattern. Together with the edrioasteroid and (possibly) brachiopods, the conulariids probably were attached to the substrate in life and then were buried and possibly killed by a single influx of silty mud. The apertural end of many of the conulariids is partially covered by inwardly folded short lappets, which may have closed in response to rapid (but gentle) burial. Rock matrix in the apertural region of the peridermal cavity of nearly all of the conulariids exhibits irregular, variably dense concentrations of pyrite. The concentrations occur almost exclusively within the conulariids, where they probably formed as a result of the decay of retracted conulariid soft parts. Although the concentrations lack clearly defined anatomical features that can be unambiguously homologized with particular anatomical structures of any extant taxon, their form and distribution within the conulariids are consistent with the hypothesis that conulariids were polypoid scyphozoans.     

Life mode of in situ Conularia in a Middle Devonian epibole

Abstract: Exceptionally abundant specimens of Conularia aff. desiderata Hall occur in multiple marine obrution deposits, in a single sixth‐order parasequence composed of argillaceous and silty very fine sandstone, in the Otsego Member of the Mount Marion Formation (Middle Devonian, Givetian) in eastern New York State, USA. Associated fossils consist mostly of rhynchonelliform brachiopods but also include bivalve molluscs, orthoconic nautiloids, linguliform brachiopods and gastropods. Many of the brachiopods, bivalve molluscs and conulariids have been buried in situ. Conulariids buried in situ are oriented with their aperture facing obliquely upward and with their long axis inclined at up to 87 degree to bedding. Most specimens are solitary, but some occur in V‐like pairs or in radial clusters consisting of three specimens, with the component specimens being about equally long or (less frequently) substantially different in length. The compacted apical end of Conularia buried in situ generally rests upon argillaceous sandstone. With one possible exception, none of the examined specimens terminates in a schott (apical wall), and internal schotts appear to be absent. The apical ends of specimens in V‐like pairs and radial clusters show no direct evidence of interconnection of their periderms. The apical, middle or apertural region of some inclined specimens abuts or is in close lateral proximity to a recumbent conulariid or to one or more spiriferid brachiopods, some of which have been buried in their original life orientation. The azimuthal bearings of Conularia and nautiloid long axes and the directions in which conulariids open are nonrandom, with conulariids being preferentially aligned between 350 and 50 degree and with their apertural end facing north‐east, and nautiloids being preferentially aligned between 30 and 70 degree. Otsego Member Conularia were erect or semi‐erect, epifaunal or partially infaunal animals, the apical end of which rested upon very fine bottom sediment. The origin of V‐like pairs and radial clusters remains enigmatic, but it is probable that production of schotts was not a regular feature of this animal’s life history. Finally, conulariids and associated fauna were occasionally smothered by distal storm deposits, under the influence of relatively weak bottom currents.     

Evidence of clonal budding in a radial cluster of Paraconularia crustula (White) (Pennsylvanian: ?Cnidaria)

Monospecific conulariid clusters have been interpreted as products of gregarious behavior or as clonal colonies, with members of a colony originally inclined at a high angle to the substrate and connected to each other at their apices. However. individuals in all previously documented clusters are preserved parallel, or nearly parallel, to bedding, and their apices are not preserved. We describe a cluster of three Paraconularia crustula (White) (Pennsylvanian of Missouri, USA) in which the individual specimens exhibit an original steeply inclined orientation. The individuals in this cluster converge adapically on an extremely thin. crumpled sheet of apatitic material that is similar to conulariid test material. The conulariids and associated sheet bear a striking resemblance to regenerated, clonal colonies of polypoid coronatid scyphozoans. Such colonies arise from a thin, periderm-covered sheet of non-differentiated soft tissue, produced following severance of a single parent polyp. We suggest that the conulariid cluster originated through a similar process. Should this interpretation be corroborated by the discovery of better preserved conulariid clusters, it would provide strong additional evidence for the hypothesis of a scyphoroan affinity for conulariids