<Emphasis Type="Italic">Compsaster formosus</Emphasis><Emphasis Type="SmallCaps">Worthen &; Miller</Emphasis> (Asteroidea; Echinodermata): A Carboniferous homeomorph of the post-Paleozoic Asteriidae

All adequately known post-Paleozoic asteroids are either assignable to surviving families or closely related families whereas no Paleozoic species assignable to a surviving order has been recognized. The Mississippian speciesCompsaster formosus is similar enough to various Recent taxa in overall form as well as in the form and arrangement of body wall ossicles to raise the issue of affinities: IsC. formosus nested within a phylogenetic branch hitherto known only from post-Paleozoic strata or is it only homeomorphic?The nature of the ambulacral system is critical to interpretation of echinoderms, and post-Paleozoic asteroids share three fundamental ambulacral characters or character suites: dorsal podial pores, staggered positioning of ambulacrals and adambulacrals, and complex articular structures between these two ossicular types.Calliasterella americana, a Carboniferous asteroid, shares the three ambulacral features, although it is distinctive from post-Paleozoic asteroids in other ways.Compsaster formosus exhibits at least two of the three ambulacral characters, although presence of staggering has not been finally established. LikeC. americana, C. formosus differs from post-Paleozoic species in details of ambulacral anatomy as well as aspects of ventral body surface ossicular arrangement. Although approaching crown-group organization,C. formosus nevertheless represents a branch basal to the crown group.Because asteroids are generalists, understanding of life habits ofCompsaster is sketchy in spite of morphological similarities between it and younger genera.Compsaster probably was epifaunal and its overall form is strongly reminiscent of that of Recent predatory asteriids but it is also similar to small-particle feeding echinasterids.     

New early crown-group asteroids (Echinodermata; Triassic of Germany)

Migmaster angularis n. gen. n. sp. (Trichasteropsiidae, Forcipulatacea, Asteroidea) is described from the German Triassic Lower Muschelkalk of Anisian (Pelsonian) age, and new specimens ofTrichasteropsis bielertorum broaden understanding of this species. Phylogenetic events linking the stem groups, known only from Paleozoic rocks, with the crown group, known only from post-Paleozoic rocks, are problematic; the new fossils partially constrain phylogenetic changes associated with emergence of crown-group asteroids.      

The Asteroidea (Echinodermata) of the Muschelkalk (Middle Triassic of Germany)

Trichasteropsis Eck, from the Muschelkalk of Germany is the only Triassic asteroid known from more than fragmentary material. Most spécimens representT. weissmanni (Münster) whereasT. senfti ECK,T. bielertorum n. sp., andBerckhemeraster charistikos n. gen. et n. sp., are each known from few individuals.Parsimony analysis hère treats the füll Ordovician to Récent history of the Asteroidea using a somasteroid (a pre-asteroid stelleroid) outgroup. Ambulacral évolution is critical in echinoderm history; the ambulacral arrangement of crown-group asteroids first appears in Paleozoic sister groups, and the subclass Ambuloasteroidea n. subcl. is proposed for Paleozoic and younger taxa with critical ambulacral apomorphies. Muschelkalk asteroids are assigned to the family Trichasteropsiidae n. fam., superorder Forcipulatacea. The recently described Triassic genusNoriaster belongs to the extant family Poraniidae, superorder Valvatacea.Trichasteropsis andNoriaster represent separate major phylogenetic branches of the post-Paleozoic infraclass Neoasteroidea, and together they indicate that diversification of modern-type asteroids was under-way during the Triassic, although the Mesozoic marine révolution largely was a Jurassic and later event. Post-Paleozoic asteroids appear to hâve returned to Paleozoic life modes in spite of new morphological expressions. Trichasteropsis is skeletally robust, suggesting protection from wave impact or predators. It is found in sédiments associated with shell banks but not from within the banks.Trichasteropsis senfti commonly occurs with brachiopods whereasT. weissmanni does not, although brachiopods are found in associated strata. Aspects of morphology of both species are similar to those of récent predatory Asteriidae suggesting similar behavior, but feeding habits ofTrichasteropsis are unverified.     

Pale biological implications of some Upper Ordovician juvenile asteroids (Echinodermata)

Blake, D. B. 1990 10 15: Pale biological implications of some Upper Ordovician juvenile asteroids (Echinodermata). Lethaia , Vol. 23, pp. 347–357. Oslo. ISSN 0024–1164.
Two patterns have been recognized in the early dorsal skeletal development of modern asteroids. The skeleton of well-preserved juveniles of the Late Ordovician species Promopalaeaster finei is similar in fundamental ossiclar arrangement to one of these patterns, suggesting continuity of developmental sequence. Similarities include presence of large terminal ossicles and double rows of marginal ossicles. Ancient and modern juveniles differ in that in P. finei , podial pores leading to the interior of the arms are lacking, thus providing an ontogenetic argument that such pores are phylogenetically derived within the class. An unpaired interbrachial marginal, or axillary, is present distal to the oral frame; positioning supports earlier suggestions that the axillary is the homologue of the odontophore ossicle of modern asteroids. Comparisons between P. finei and another Ordovician species, Macroporaster matutinus , suggest the need for greater mouth frame flexibility contributed to the evolution of the modern odontophore. Axillary development is linked to the common absence of actinal ossicles from Paleozoic species. ▭ Asteroidea, Echinodermata, functional morphology, ontogeny, phylogeny, Ordovician, Paleozoic .     

The Class Asteroidea (Echinodermata): Fossils and the Base of the Crown Group

Because of limited research, a generally accepted hypothesishas not emerged for the phylogeny of the Asteroidea. The fossilrecord is a potential source of needed data, although fossilasteroids are rare, and they tend to be poorly preserved. Emphasis in the taxonomy of both recent and fossil asteroidshas been on characters visible from the exterior, and paleontologistshave sought to fit even the most ancient (i.e., Ordovician)specimens into taxonomic ordinal schemes devised for recentasteroids. Animal form and arrangement of body wall ossiclesof Paleozoic asteroids can be similar to those of younger species,thereby suggesting close affinities, yet ambulacral arrangementsindicate clear separation of Paleozoic stem groups from thecrown group. Traits taken from the ambulacral column that mark crown-groupasteroids include presence of dorsal podial pores (which allowedtransfer of the ampullae to the arm interior), an offset arrangementof ambulacrals on the adambulacrals, and increased complexityof the articulation structures between ambulacrals and adambulacrals.Transfer of ampullae to the arm interior provided protectionand more space for ampullae within the arm, as well as spacewithin the furrow and between the ambulacral and adambulacralossicles for elaboration of the soft tissues that enhance armmotion.     

A new species of Xyloplax (Echinodermata: Asteroidea: Concentricycloidea) from the northeast Pacific: comparative morphology and a reassessment of phylogeny

Abstract. Xyloplax janetae n. sp. is described from the northeast Pacific Ocean. This is the third species recognized for the monogeneric Concentricycloidea. Skeletal structures are elaborated by scanning electron microscopy and compared with those of Xyloplax medusiformis from New Zealand and Xyloplax turnerae from the Bahamas. Critical-point-dried specimens show fibrous connective tissue emerging from openings on the abactinal surface, on the abactinal spine bases, and at broken cross sections of the adambulacral spines. Knob-like structures emerging through the stereom openings of the abactinal spine base are also observed. Tube feet have round, swollen knobs and show few striations relative to other asteroids. Cosmopolitan bathyal–abyssal echinoderm species tend to exhibit few morphological differences over broad geographic ranges; this generalization is true of Xyloplax . The Concentricycloidea is proposed as an infraclass within the Asteroidea, as the sister branch to the Neoasteroidea (the crown-group asteroids) within the subclass Ambuloasteroidea. The hypothesis presented is compatible with recent phylogenetic data supporting affinities between Xyloplax and the Asteroidea. Characters plesiomorphic in basal neoasteroids are consistent with a sister-group relationship to concentricycloids. Actinal plate presence, an important synapomorphy for the Neoasteroidea, is absent from concentricycloids. The substantial morphological departure of Xyloplax is considered to be associated with the post-Paleozoic diversification of crown-group asteroids rather than from modification of an established and conservative morphology.     

Re-evaluation of the Devonian family Helianthasteridae Gregory, 1899 (Asteroidea: Echinodermata)

Because of their taxonomic and morphologic diversity, the asteroids of the Lower Devonian Hunsrück Slate of Germany are important to both an understanding of the history of the class Asteroidea and to the interpretation of community evolution during the Paleozoic. Helianthaster Roemer, 1863, a large multiarmed Hunsrück asteroid, is redescribed. The Helianthasteridae Gregory is restricted to Helianthaster and Arkonaster Kesling, 1982 (Middle Devonian, Canada); Lepidasterella Schuchert is similar to the other two genera but known specimens are of poor quality and as a result the status of the genus is uncertain. Helianthaster is noteworthy in part because its size, multiarmed state, and presence of pedicellariae suggest certain crown-group genera, yet aspects of the arrangement of the ambulacral column are characteristic of the Paleozoic asteroid evolutionary grade. Neither Helianthaster nor other Hunsrück asteroids appear closely linked to the crown group; instead, functional patterns apparently re-emerged through time, although identification of specific behavior of ancient asteroids is difficult to impossible.      

Phylogeny of the Zoroasteridae (Zorocallina; Forcipulatida): evolutionary events in deep-sea Asteroidea displaying Palaeozoic features

The Zoroasteridae comprise a small but widespread family of asteroids distributed throughout the deep sea. Although poorly understood, they are often collected in the hundreds, suggesting that they occupy important ecological roles. A phylogenetic analysis including 24 terminal taxa and 70 morphological characters was performed, resulting in a single most-parsimonious tree. The tree separated zoroasterids with open, reticulate skeletons (e.g. Myxoderma ) as more basal than those with more heavily armored, imbricate skeletons (e.g. Zoroaster ), which were more derived. In addition to agreement with established genera, a new genus is supported by the phylogeny as the sister taxon to Myxoderma . The cladistic analysis was performed in conjunction with a revisionary survey of zoroasterid species, resulting in taxonomic changes to species in nearly every genus. Bathymetric and physiographic shifts were observed between the reticulate and imbricate zoroasterid clades. Zoroasterids possess a single marginal plate series, which occurs in basal sister-group neoasteroids (crown-group asteroids). Phylogenetic results suggest that the morphololgical resemblance between zoroasterids and Palaeozoic taxa, such as Calliasterella , is convergent but a paraphyletic Zoroasteride cannot be rejected and remains consistent with basal crown-group affinities. Although the phylogenetic position of the Eocene Zoroaster aff. fulgens was not strongly supported, its presence within a derived cluster of Zoroaster spp. suggests a relatively recent (i.e. Cenozoic) diversification into the deep sea. Taxonomic revisions, and geographical and bathymetric range extensions are also included.  © 2007 The Linnean Society of London, Zoological Journal of the Linnean Society , 2007, 150 , 177–210.     

Paleozoic Foraminifera.

The approximately 300 million years that make up Paleozoic time saw the evolution of eight of the fifteen recognized suborders of Foraminifera. Of the suborders present in the Paleozoic, seven are morphologically relatively simple, slowly evolving, and continued into Mesozoic and Cenozoic times to become the ancestoral lineages from which evolved several additional post-Paleozoic suborders. In contrast, an eighth Paleozoic suborder, the Fusulinina, was an abundant, ecologically dominant group that evolved from simple to highly specialized forms and had a history of rapid evolution with diverse lineages. Fusulinines became extinct at the end of the Paleozoic. Their early representatives may have given rise to three and eventually four post-Paleozoic suborders. A number of suborders in the Paleozoic have similar, supposedly independent, early evolutionary patterns with the following series of morphological steps: (1) single chambers with or without apertures depending on the amount of wall cement; (2) groups of chambers that appear to be buds or aggregations of individuals rather than true chambers; (3) a proloculus followed by a tubular second chamber that is first erect and gradually evolves into enrolled free-living individuals; (4) development of constrictions in the tubular chamber; and finally (5) evolution of true chambers. These morphological steps, which are basic organizational steps with evolutionary significance, appear in lineages with quite different test compositions and, therefore, are considered only distantly related in the present classification.     

The End-Permian mass extinction: What really happened and did it matter?

Marine communities of the Paleozoic differ markedly from those of the post-Paleozoic, a dichotomy long recognized as the most fundamental change between the Cambrian metazoan radiation and the present. The end-Permian mass extinction of about 54% of marine families eliminated many of the groups that dominated Paleozoic communities. Correlative changes occurred in terrestrial vertebrate and plant communities, but there is no clear evidence that these changes are related to the marine extinction. The marine extinction occurred during a period of physical change, and a variety of extinction mechanisms have been proposed, most related to a major Late Permian marine regression or to climatic changes. Unfortunately, the regression has made it difficult to gather data on the rate, timing and pattern of extinction, and the available data exclude only a few hypotheses. Thus the largest mass extinction, and the one with the greatest evolutionary importance, is also the most poorly understood.     

Hettangian Asteriidae (Echinodermata: Asteroidea) from southern Germany: taxonomy,phylogeny and life habits

Germanasterias amplipapularia andHystrixasterias hettangiurnus are new genera and species of Asteriidae (Asteroidea: Forcipulatida) described from the Hettangian (lowest Jurassic) of southern Germany. They are among the oldest known relatively complete asteroids assignable to surviving families, yet they are remarkably similar to certain living species. Modern asteriids are efficient predators of sessile and slow-moving stoutly-armored mullusks, however much asteriid morphology is suggested to have originated with suspension-feeding habits. The lineage leading to the modern Forcipulatacea might have separated from that of the remainder of the modern asteroids as early as the Carboniferous.     

MICROGAMETOPHYTE DEVELOPMENT IN THE PALEOZOIC SEED FERN FAMILY CALLISTOPHYTACEAE

Well-preserved stages of microgametophyte development are described from pollen produced by the Paleozoic seed fern family Callistophytaceae. Microgametophyte development in both the Middle Pennsylvanian pollen organ Idanothekion and Upper Pennsylvanian Callandrium involved the initial production of an axial row of at least three small prothallial cells proximally and a large embryonal cell distally. The arrangement and form of these cells is like that present in some extant genera of the Pinaceae. The prothallial cells were relatively large in comparison with extant gymnosperms, occupying the entire region of the cap-pus, and were apparently all primary. Evidence is presented that in Callandrium further development involved an anticlinal division of the large distal cell (antheridial initial) into a small generative cell contained within a larger tube cell. Previously described microgametophytes of the late Paleozoic order Cordaitales are reinterpreted and are shown to consist of an embryonal cell and three to four discoidal prothallial cells in an axial row like that of the Callistophytaceae. Microgametophytes thus far described from the Paleozoic are remarkably modern in appearance and provide no evidence to support the generally held view that the seed plant microgametophyte is an extremely reduced sexual phase that has arisen through the loss of almost all of the vegetative cells and the sterile outer cells of the antheridium. Evidence to support or refute this view will depend upon the discovery of microgametophytes from older groups of seed plants than those for which they are now known.     

Paleobiology of the oldest known articulate crinoid

The evolutionary and ecological recovery of benthic marine invertebrate faunas from the devastating Permian-Triassic mass extinction is poorly understood. In particular. Paleozoic crinoids were decimated, creating an evolutionary bottleneck, so that Early Triassic (Scythian) and Anisian representatives of the genus Holocrinus may be considered the stem group for the monophyletic crinoid subclass Articulata, which includes all post-Paleozoic crinoids. Crinoid ossicles in limestones of the Scythian (Spathian) Virgin Limestone Member (Moenkopi Formation) of southern Nevada and southwestern Utah, identified as Holocrinus? smithi, respresent the oldest known Holocrinus. Limestone units of the virgin were deposited in nearshore and inner shelf environments of an arid epeiric seaway. Although these crinoids are generally completely disarticulated and occur commonly in storm-generated deposits. they are interpreted to have been deposited near their living sites in ‘disturbed neighborhood’ assemblages. Counts of ossicles in bulk samples indicate a relatively low number of individuals, suggesting that populations of H.? smithi occurred in scattered clumps or as isolated individuals. attached to hardgrounds or shell beds. Bivalves are the most common associates, and are commonly more numerous than the estimated number of crinoid individuals, although bivalve species richness is never greater than three. Virgin Limestone fossil assemblages probably represent the first redevelopment of relatively complex tiered epifiaunal communities in the Mesozoic. *Echinodermata, mass extinction, Early Triassic, paleoecology, Crinoida, Articulata.     

Drill holes in Australian Cainozoic brachiopods

The fossil record of drill holes in marine invertebrates has received a considerable amount of interest from paleontologists, primarily due to its importance for reconstructing the history of interactions between drilling predators and their prey. Such drill holes have been described in numerous studies of Paleozoic brachiopods but rarely in those focusing on brachiopods of the post-Paleozoic, a striking pattern given that in the late Mesozoic and Cainozoic drilling gastropods diversified and frequencies of drilled molluscs increased dramatically. During the past several years, however, drilled brachiopods were reported in several studies of the Mesozoic and Cainozoic, suggesting that this phenomenon may be more common than has been previously assumed. Here we report on 10 genera of brachiopods from four Cainozoic basins in Australia of which 7 shows evidence of having been drilled by predators. Of 298 specimens examined, 38 contain a single complete hole. Drilled specimens were identified in all 4 basins and in all stratigraphic units. When considered in the context of recent reports of drilled Cainozoic brachiopods, these Australian brachiopods further imply that drilling predation on these invertebrates was geographically, taxonomically and temporally widespread.     

Some peculiarities in the behavioral reactions of the lophophore and the trophic structuring of the colonies of the post-Paleozoic Stenolaemata (bryozoa)

Some peculiarities in the behavioral reactions of the lophophore, a feeding apparatus of the living marine bryozoans, are discussed. In bryozoans of the class Stenolaemata the position of the lophophore is regulated by the autozooidal peristome. In post-Paleozoic Stenolaemata the individual and collective activities of the lophophores are determined by the peculiarities in the trophic structuring of colonies, which are established based on the individual or group arrangement of autozooidal apertures. Two main types of the trophic structuring are distinguished: individual and group structuring. The adaptive significance of the trophic structuring consists in the effective extracting of food particles from water currents. In combination with the peculiarities of the colonial organization of post-Paleozoic Stenolaemata, the types of trophic structuring of colonies can be used when characterizing taxa of different levels.     

Appendicular skeletal morphology in minute salamanders,genus Thorius (amphibia: Plethodontidae): Growth regulation,adult size determination,and natural variation

Patterns of growth and variation of the appendicular skeleton were examined in Thorius, a speciose genus of minute terrestrial plethodontid salamanders from southern Mexico. Observations were based primarily on ontogenetic series of each of five species that collectively span the range of adult body size in the genus; samples of adults of each of seven additional species provided supplemental estimates of the full range of variation of limb skeletal morphology. Limbs are generally reduced, i.e., pedomorphic, in both overall size and development, and they are characterized by a pattern of extreme variation in the composition of the limb skeleton, especially mesopodial elements, both within and between species. Fifteen different combinations of fused carpal or tarsal elements are variably present in the genus, producing at least 18 different overall carpal or tarsal arrangements, many of which occur in no other plethodontid genus. As many as four carpal or tarsal arrangements were observed in single population samples of each of several; five tarsal arrangements were observed in one population of T. minutissimus. Left-right asymmetry of mesopodial arrangement in a given specimen is also common. In contrast, several unique, nonpedomorphic features of the limb skeleton, including ossification of the typically cartilaginous adult mesopodial elements and ontogenetic increase in the degree of ossification of long bones, are characteristic of all species and distinguish Thorius from most related genera. They form part of a mechanism of determinate skeletal growth that restricts skeletal growth after sexual maturity. Interspecific differences in the timing of the processes of appendicular skeletal maturation relative to body size are well correlated with interspecific differences in mean adult size and size at sexual maturity, suggesting that shifts in the timing of skeletal maturation provide a mechanism of achieving adult size differentiation among species. Processes of skeletal maturation that confer determinate skeletal growth in Thorius are analogous to those typical of most amniotes – both groups exhibit ontogenetic reduction and eventual disappearance of the complex of stratified layers of proliferating and maturing cartilage in long bone epiphyses – but, unlike most amniotes, Thorius lacks secondary ossification centers. Thus, the presence of secondary ossification centers cannot be used as a criterion for establishing determinate skeletal growth in all vertebrates.     

Distribution of vinculin in the Z-disk of striated muscle: analysis by laser scanning confocal microscopy

Vinculin is a major cytoskeletal component in striated muscle, where it has been reported to form a rib-like structure between the cell membrane and the Z-disk termed a costamere. This arrangement of vinculin has been purported to be involved in the alignment of the myofibrils. However, the three-dimensional arrangement of vinculin in relation to the Z-disk of the myofibril was not known. In the present study, we examined the distribution of vinculin in striated muscle with monospecific antibodies using immunofluorescence and laser scanning confocal microscopy. Isolated cardiac and skeletal muscle cells from a variety of species, tissue sections, and neonatal myocytes with developing myofibrils were examined. Optical sectioning in the X-Y and X-Z planes demonstrated that vinculin immunoreactivity was heaviest at the periphery of the cell; however, the immunoreactivity was also distributed within the Z-disk although at a relatively reduced level. This distribution is potentially significant in understanding the physiological significance of vinculin in striated muscle function and in myofibrillogenesis.     

Spatial competition among clonal organisms in extant and selected paleozoic reef communities

Summary Occurrences of densely packed benthic organisms in extant reefs are of two types: 1) live-live interactions, where two living organisms interact, and 2) live-dead associations, where only one is alive and uses the other as a substrate. The latter are common in reef deposits due to biostratinomic feedback, i.e. dense skeletal accumulations provide hard substrates for clonal recruitment, thus facilitating greater frequency of live-dead encounters than in lower biomass level-bottom communities dominated by solitary organisms. Differentiating between these two types in ancient reefs is difficult, often impossible. Most live-live interactions among clones in extant reef communities involve competition for space. Clonal spatial competition is divisible into four types: 1) direct-aggressive: encrusting overgrowth; 2) indirect-passive: depriving neighbors of resources, chiefly sunlight, by growth above them; 3) stand-off: avoidance of competition by organisms adopting positions that avoid or minimize direct polyp/zooid contact; and 4) overwhelming: one clone/ species volumetrically or numerically overwhelms the other, meeting minimal resistance. Despite class-order level differences in taxa, our results indicate that extant analogs, based on the arrangement and distortion of skeletons, are valuable for recognizing live-live interactions in Silurian and Carboniferous reefs and interpreting the types of spatial competition represented. Comparison of overhead (plan) views of live-live coral competition in Polynesian reefs with vertical sections of Silurian and Carboniferous sponge-dominated reefs and biostromes suggests that direct-aggressive competition is more common among extant than among Paleozoic reef-builders. Stand-offs showing clone margin distortion and overwhelming with minor skeletal distortion are most common in our fossil examples and probably relate to the dominance of these reefs by sponges. Success by extant sponges in spatial competition is largely due to allelochemical deterrence which may explain the predominance of stand-off and overwhelming confrontations in fossil sponges rather than tentacle-mesentery based direct aggression among extant corals and bryozoans.     

Randomness or order in the occurrence and preservation of shallow-marine carbonate facies? Holocene, South Florida

This paper re-examines unsolved problems concerning the relationships between skeletal benthic communities, the skeletal carbonate sediments they produce and how these are preserved in the subsurface. Recent work based on shelf-wide datasets of modern shallow-marine carbonate sediments of South Florida suggest that the boundaries between facies occur randomly and that facies occurrence bears little relation to water depth. This is at variance with earlier work from the region that indicated facies occurrence related to different environments and which helped establish the basis for palaeoenvironmental analysis of ancient limestones.A windward-facing depositional margin of a carbonate mound in the back-reef area of the Florida Keys is used as a small-scale, case study to examine whether surface peritidal facies occur in an ordered or random fashion and whether they are depth related. Lateral facies transition analysis along transects from the shoreline to the shallow subtidal indicates that peritidal facies occur in a very well-ordered (i.e. non-random) arrangement of zones and patches. Surface facies are generally well-preserved and recognisable in the shallow subsurface and in cores through the Holocene carbonates and shoreline mangrove peats. Analysis of upward facies transitions in cores also indicates common facies trends reflecting the evolution of the sediment mound in response to rising Holocene sea level. However, even though the modern facies occur in an ordered and depth-related pattern, subsurface facies do not show a simple relation to the known sea-level curve in the area. Rather, they relate to a complex of different rates of sea-level rise, sea-floor topography, carbonate production rates, wave/storm energy input, and bioturbation.