Problematic Taxa Research Articles

Alberto M. Simonetta and Simon Conway Morris (eds.)., The Early Evolution of Metazoa and the Significance of Problematic Taxa

Alberto M. Simonetta and Simon Conway Morris (eds.)., The Early Evolution of Metazoa and the Significance of Problematic Taxa

The Early Evolution of Metazoa and the Significance of Problematic Taxa.

The Early Evolution of Metazoa and the Significance of Problematic Taxa.

Bizarre and Extinct The Early Evolution of Metazoa and the Significance of Problematic Taxa A. M. Simonetta S. C. Morris

Bizarre and Extinct The Early Evolution of Metazoa and the Significance of Problematic Taxa A. M. Simonetta S. C. Morris

Morphological Disparity in the Cambrian

An analysis of the range of morphology among arthropods demonstrates that disparity among living arthropods is similar to that in Cambrian arthropods. The range of morphological design resulting from the Cambrian "explosion" has been overestimated, reflecting a tendency to separate as "problematic" taxa that cannot be accommodated in the classification on the basis of the living biota. Problematic taxa are largely an artifact of an inadequate taxonomy. Special evolutionary processes may not be necessary to explain the early radiation of the metazoans.

The Sirius Passet Fauna, an Early Cambrian Lagerstätte from North Greenland

The Sirius Passet Fauna of North Greenland is one of the oldest Cambrian lagerstätten from the North American continent. It is known from a single locality in Peary Land (83°N, 40°W), on the shores of the Arctic Ocean, where outer shelf mudstones from the lower part of the Buen Formation (Early Cambrian) yield a rich assemblage of mainly poorly skeletised organisms with preserved soft parts. The steeply-dipping fossiliferous mudstones occur in close proximity to horizontally-bedded platform carbonates of the underlying Portfjeld Formation (Early Cambrian) in a structurally complex terrane. The boundary between the fossiliferous mudstones and the platform carbonates apparently defines the original northern margin of the carbonate platform and is not, as previously suggested, a structural feature, although some minor tectonic modification can not be excluded. Thus, the fossiliferous mudstones were apparently deposited in a transitional slope setting basinward of the shelf edge.As currently known, the Sirius Passet Fauna comprises about 40 species, based on a collection of almost 5,000 slabs collected during brief visits to the isolated locality in 1989 and 1991. Arthropods dominate, with bivalved bradoriids and the trilobite Buenellus higginsi Blaker, 1988 being the numerically most abundant taxa. Weakly skeletised Naraoia-like and Sidneyia-like arthropods often preserve limbs and gills, as do bivalved arthropods similar to Waptia. Choia is the most common of several sponges. Worms include both priapulids and polychaetes, with a large palaeoscolecidan being conspicuous.Fully articulated specimens of halkieriid worms, clad in an armour of hundreds of individual sclerites, are most notable amongst several problematic taxa. Rare specimens of possible onychophorans are also present, while brachiopods, hyoliths and other shelly fossils are rare or absent.The Sirius Passet Fauna seems to show little taxonomic similarity to the Middle Cambrian Burgess Shale of western Canada or the Chengjiang Fauna from the Lower Cambrian of China at the generic level. Together with the latter fauna, however, it confirms both the general picture of Cambrian life presented by the Burgess Shale, and the existence of this great diversity of weakly skeletised arthropods already in the Early Cambrian.

Shelf-facies microfossils from the Uluksan Group (Proterozoic Bylot Supergroup), Baffin Island, Canada

Coccoid and filamentous microfossils in the Borden Rift Basin on northwestern Baffin Island and western Bylot Island are reported from 14 localities at six general stratigraphic levels in the Society Cliffs Formation, and one in the Victor Bay Formation. At least seven of 12 fossiliferous Society Cliffs samples, and one of two Victor Bay samples, are from cherty dolostones formed in shallow restricted, peritidal evaporitic environments. The remaining six fossiliferous samples accumulated in somewhat deeper, less restricted waters. The assemblage is preserved in black chert nodules and layers and comprises 30 taxa, including the filamentous formsArchaeotrichion? sp.,Tenuofilum septatum, Eomycetopsis robusta, Siphonophycus inornatum, S. kestron, Rhicnonema antiquum, Brachypleganonsp.,Eomicrocoleussp.,Uluksanella baffinensisn. gen. and sp.,Talakania? sp., the coccoid taxaEosynechococcus medius, E. grandis, Archaeoellipsoides obesus, Sphaerophycus parvum, S. medium, Myxococcoides minor, M. grandis, Melasmatosphaeraspp.,Phanerosphaerops capitaneus, Palaeoanacystissp.,Tetraphycus hebeiensis, Eogloeocapsa bella, Gloeodiniopsis magna, G.sp. 1,G. mikros, Polybessurus bipartitus, Cymatiosphaera? sp., the fusiformEupoikilofusa? sp., and rare specimens of two unidentified and problematic taxa.

Relationships of the Osmeroid Fishes and the Use of Reductive Characters in Phylogenetic Analysis

The phylogenetic relationships of the osmeroid fishes are examined in the context of character congruence. The Osmeroidei is monophyletic, and its sister taxon is the monophyletic Argentinoidei. The division of osmeroids into Northern and Southern Hemisphere groups is largely corroborated. Two problematic taxa, the neotenic Salangidae and the monotypic Lepidogalaxias salamandroides, are hypothesized to be members of the Southern Hemisphere clade, in which reductive evolution has been common

The ultrastructure of fossil gymnosperm pollen

SummaryThe ultrastructure of fossil gymnosperm pollen is reviewed based on studies of in situ grains. The following groups contain taxa that have been investigated at the ultrastructural level: Lyginopteridales, Medullosales, Callistophytales, Corystospermales, Caytoniales, Cordaitales, Voltziales, Coniferales, Cycadeoidales, Pentoxylales and problematic taxa that cannot clearly be classified (incertae sedis). Details of pollen wall ultrastructure in these groups are discussed, as well as information on the progymnosperm groups Aneurophytales and Archaeopteridales. Since many groups are known from a study of only one taxon, it is not currently possible to homologize wall layers in pollen from different taxonomic categories. However, within major clades there is some uniformity in the infrastructure of the pollen wall. The implications of developmental information from fossil pollen, as well as data on saccus evolution are discussed.

CRYPTIC AND SIBLING SPECIES AMONG THE DECAPOD CRUSTACEA

are those which are difficult to recognize using traditional systematic methods. Among the decapod Crustacea, there are probably many unrecognized complexes of cryptic because of dependence on preserved material. Electrophoretic and mating studies have been very useful in determining whether individuals that differ in ecology, behavior, life history, or color can potentially interbreed. Color pattern of living specimens is a particularly useful character, since it is easy to assess and appears to differentiate morphologically similar in a number of decapod groups. Examples include of Uca and various symbionts of coral reef organisms (e.g., in the genera Trapezia and Alpheus and the subfamily Pontoniinae). Although nonmorphological characters cannot be scored in most museum specimens, statistical analysis of morphometric data first collected for individuals of known identity can subsequently be used to identify preserved material. Electrophoretic analyses, such as those done for complexes of Uca, Trapezia, and Alpheus, have also shown that cryptic pairs may or may not be more closely related to each other than morphologically distinct congeners. For this reason the term should be reserved for those which have been shown to be very closely related using biochemical techniques. Various speciation patterns, including possible examples of host race speciation and speciation facilitated by sexual selection, occur within decapod complexes. Decapod crustaceans, like most species, are primarily described and identified by morphological characters which can be studied in preserved specimens (McLaughlin et al., 1982). Although this procedure effectively delineates many species, clusters of morphologically similar but reproductively isolated taxa cannot easily be resolved using such techniques. These problematic taxa are variously called cryptic or species. The term sibling species has traditionally been used for sets of which are difficult to distinguish using traditional morphological characters (Mayr, 1963). Cryptic when used taxonomically (as opposed to ecologically) is another frequently used term for the same concept. The latter is etymologically preferable (Henry, 1985), since implies a particularly close relationship, a feature which Mayr (1963) asserted did not differentiate from other congeneric species. More recent studies have shown, however, that which are difficult to tell apart morphologically may or may not be as distantly related to each other, on the basis of biochemical characters, as are morphologically distinct congeners (Ayala, 1975; Henry, 1985). For this reason, I will refer to all morphologically similar as cryptic species, unless biochemical data exist to indicate that they are in fact siblings as well. Numerous nonmorphological characters have been used to distinguish cryptic species, depending on the group involved (Mayr, 1963). They include karyology, hybridization experiments to detect postzygotic incompatibility, distribution patterns, resource use, breeding season, life history and development, mating behavior (including visual, acoustical, and chemical signals), color pattern, and various biochemical characters (especially soluble proteins studied by gel electrophoresis). Those which directly assess either the presence of hybrids (e.g., allozyme or chromosome studies) or the potential for hybridization (e.g., mating experi

Shelf-facies microbiotas from the Odjick and Rocknest formations (Epworth Group; 1.89 Ga), northwestern Canada

Moderately well preserved microfossils are reported from two formations of the Epworth Group in the Wopmay Orogen. An assemblage in a stromatolitic unit in the uppermost part of the Odjick Formation contains the microfossils Huroniospora spp., Gunflintia sp., and Frutexites sp. This assemblage, which is remarkable for its preservation in a carbonate matrix, is similar to one found in a stromatolitic chert facies in the Gunflint Iron Formation of Ontario. Taxa in four members of the overlying Rocknest Formation are preserved in cherty dolomites of inner-shelf shallowing-upward cycles capped by small digitate stromatolites. These assemblages comprise the spheroidal taxa Huroniospora spp., Melasmatosphaera magna, Sphaerophycus sp., and Palaeoanacystis sp., the filamentous taxa Archaeotrichion sp., Eomycetopsis sp., Siphonophycus sp., Brevitrichoides sp., Biocatenoides incrustata, Gunflintia? sp., and Archaeonema sp., the acritarch Eomicrhystridium sp., and rare specimens of two unidentified and problematic taxa.

The taxonomy of Synura (Chrysophyceae) in Ontario with special reference to taste and odour in water supplies

Electron microscopy of silica scales was used in the identification of 13 taxa of the colonial chrysophyte Synura found in Ontario lakes and ponds, one of which has not been reported previously from North America (Synura spinosa f. longispina Petersen & Hansen). Two other taxa found in Ontario (Synura splendida Korshikov and Synura petersenii f. praefracta Asmund) have previously been reported only once from North America. One new combination is proposed (Synura leptorrhabda (Asmund) Nicholls) which provides for more consistent taxonomy of species in the Synura echinulata group (S. echinulata Korshikov, Synura mammillosa Takahashi, Synura multidentata (Balonov & Kuzmin) Péterfi & Momeu, and S. leptorrhabda). The systematics of other problematic taxa, including the related genus Chrysodidymus, are discussed. Samples containing Synura spp., previously implicated in 11 recent cases of "fishy" taste and odour in Ontario lakes, were reexamined by electron microscopy and found to be dominated by S. petersenii Korshikov. All affected sites were lakes of the Precambrian Shield (pH 5.7 – 7.5; alkalinity < 1 – 45 mg CaCO3/L). No evidence of obnoxious tastes or odours from other Synura species has been found.