Physical modeling of the batocrinid anal tube: functional analysis and multiple hypothesis testing

Baumiller, T. K. 1990 10 15: Physical modeling of the batocrinid anal tube: functional analysis and multiple hypothesis testing. Lethaia , VOL 23, pp. 399–408. Oslo. ISSN 0024–1164.
Three hypotheses related to the function of the batocrinid anal tube were tested using physical models: (1) the anal tube served as a 'rudder', allowing the crinoid to passively maintain an effective feeding posture in moving water, (2) the tube served as a splitter 'plate', reducing the drag on the organism while it was in its feeding posture, and (3) the anal tube functioned as a 'chimney' by moving the anus downstream of the arms and thus reducing the risk of the organism ingesting its own wastes and/or gametes. Results of experiments performed in a recirculating flow tank suggested that the tube was well suited for the 'chimney' function: it reduced the concentrations of excreted matter in the proximity of the feeding appendages. Differences in rotational torques between models with a tube versus those without a tube implied that a large tube may have increased the rotational stability of the feeding posture in environments with variable current directions. No differences were detected between drag measurements on models with and without the anal tube; thus the 'splitter-plate' function of the tube was rejected. ▭ Batocrinid anal tube, functional morphology, physical modeling .     

Evolutionary history of regeneration in crinoids (Echinodermata)

The fossil record indicates that crinoids have exhibited remarkable regenerative abilities since their origin in the Ordovician, abilities that they likely inherited from stem-group echinoderms. Regeneration in extant and fossil crinoids is recognized by abrupt differences in the size of abutting plates, aberrant branching patterns, and discontinuities in carbon isotopes. While recovery is common, not all lost body parts can be regenerated; filling plates and overgrowths are evidence of non-regenerative healing. Considering them as a whole, Paleozoic crinoids exhibit the same range of regenerative and non-regenerative healing as Recent crinoids. For example, Paleozoic and extant crinoids show evidence of crown regeneration and stalk regrowth, which can occur only if the entoneural nerve center (chambered organ) remains intact. One group of Paleozoic crinoids, the camerates, may be an exception in that they probably could not regenerate their complex calyx-plating arrangements, including arm facets, but their calyxes could be healed with reparative plates. With that exception, and despite evidence for increases in predation pressure, there is no compelling evidence that crinoids have changed though time in their ability to recover from wounds. Finally, although crinoid appendages may be lost as a consequence of severe abiotic stress and through ontogenetic development, spatiotemporal changes in the intensity and frequency of biotic interactions, especially direct attacks, are the most likely explanation for observed patterns of regeneration and autotomy in crinoids.     

Oral Region Homologies in Paleozoic Crinoids and Other Plesiomorphic Pentaradial Echinoderms

The phylogenetic relationships between major groups of plesiomorphic pentaradial echinoderms, the Paleozoic crinoids, blastozoans, and edrioasteroids, are poorly understood because of a lack of widely recognized homologies. Here, we present newly recognized oral region homologies, based on the Universal Elemental Homology model for skeletal plates, in a wide range of fossil taxa. The oral region of echinoderms is mainly composed of the axial, or ambulacral, skeleton, which apparently evolved more slowly than the extraxial skeleton that forms the majority of the body. Recent phylogenetic hypotheses have focused on characters of the extraxial skeleton, which may have evolved too rapidly to preserve obvious homologies across all these groups. The axial skeleton conserved homologous suites of characters shared between various edrioasteroids and specific blastozoans, and between other blastozoans and crinoids. Although individual plates can be inferred as homologous, no directly overlapping suites of characters are shared between edrioasteroids and crinoids. Six different systems of mouth (peristome) plate organization (Peristomial Border Systems) are defined. These include four different systems based on the arrangement of the interradially-positioned oral plates and their peristomial cover plates, where PBS A1 occurs only in plesiomorphic edrioasteroids, PBS A2 occurs in plesiomorphic edrioasteroids and blastozoans, and PBS A3 and PBS A4 occur in blastozoans and crinoids. The other two systems have radially-positioned uniserial oral frame plates in construction of the mouth frame. PBS B1 has both orals and uniserial oral frame plates and occurs in edrioasterid and possibly edrioblastoid edrioasteroids, whereas PBS B2 has exclusively uniserial oral frame plates and is found in isorophid edrioasteroids and imbricate and gogiid blastozoans. These different types of mouth frame construction offer potential synapomorphies to aid in parsimony-based phylogenetics for exploring branching order among stem groups on the echinoderm tree of life.     

Disarticulation patterns in Ordovician crinoids: Implications for the evolutionary history of connective tissue in the Crinoidea

Taphonomic information is examined to evaluate the early history of connective tissues in the Crinoidea. The pattern of stalk segmentation of Middle and Late Ordovician crinoids is consistent with the two-ligament (intercolumnal and through-going ligaments) pattern present in living isocrinid crinoids and interpreted for fossil isocrinids, holocrinids, and Lower Mississippian crinoids. A single rhombiferan was also examined; its taphonomic pattern is also indicative of this style of tissue organization. Furthermore, the taphonomy of all Middle and Late Ordovician crinoids may reflect that they lacked discretely organized muscles between arm brachials, which is consistent with the hypothesis that muscles evolved as a connective tissue between plates only once within the Crinoidea, during the Early Devonian. These data indicate that the two-ligament organization of the stalk is a primitive feature among the Crinoidea and perhaps even among stalked echinoderms. Therefore, the autotomy function of this column-tissue organization among living crinoids is an exaptation. On the other hand, discretely organized muscles as connective tissue in crinoid arms is a derived trait that first appeared during the middle Paleozoic; this adaptation proved very successful for the advanced cladid crinoids.     

Host-specific pit-forming epizoans on Silurian crinoids

Brett, Carlton E. 197807 15: Host-specific pit-forming epizoans on Silurian crinoids. Lethaia , Vol. 11. pp. 217–232. Oslo. ISSN 0024–1164.
Circular-parabolic pits occur commonly on the endoskeletal remains of certain Paleozoic crinoids. Detailed study of several hundred specimens, representing about 30 pelmatozoan species from the Upper Silurian Rochester Shale of New York and Ontario, reveals that such pits occur exclusively in seven species of crinoids. Furthermore, there are consistent differences in the morphology and orientation of holes occurring on the different crinoid species. This suggests that distinct epizoan species settled selectively on given hosts. The relationship between the hole-producing epizoans and crinoid hosts is inferred to have been a form of dependent commensalism. Preliminary surveys of other Paleozoic crinoid assemblages reveal similar host-selectivity by pit-producing epizoans. Crinoidepizoan pairs apparently co-evolved through considerable spans of geologic time as related genera and species of different ages, from Silurian to Pennsylvanian, exhibit similar pits.     

The root of the problem: palaeoecology of distinctive crinoid attachment structures from the Silurian (Wenlock) of Gotland

The holdfast (attachment structure) is the most understudied aspect of the palaeoecology of the endoskeleton of fossil crinoids. A new collection of well-preserved holdfasts from a recently reopened quarry at Hunninge, Gotland, in Homerian (upper Wenlock) strata includes several morphologies. The most common are terminal dendritic radicular holdfasts (TDRHs) that may be derived from the cladid Ennallocrinus d'Orbigny. These have a consistent morphology of five, equally spaced, long radices that spread across the sea floor. These crinoids were gregarious, and TDRHs in a group commonly show the same radice orientations. The radices have a large axial canal compared with those of modern crinoids; each included, at least, nervous tissues. Taken together, these features suggest that, apart from attachment, these distinctive TDRHs may have served a sensory function. Other holdfasts in this assemblage also show monospecific aggregations, perhaps suggesting biochemical attraction such as that shown by certain other sessile invertebrates such as barnacles.     

Homology of posterior interray plates in crinoids: a review and new perspectives from phylogenetics,the fossil record and development

Despite their importance for understanding phylogeny, character evolution and classification, well-constrained homology relationships for posterior plating in crinoids have only recently been attempted. Here, we re-evaluate posterior plate homologies in all major crinoid lineages using development, fossil ontogenies and phylogenetic evidence. Based on these lines of evidence, we change terminology for some posterior plates to correct misnomers and make recommendations for updated terminology of others to better reflect homology. Among pentacrinoids (disparids, hybocrinids, eucladids, flexibles and articulates) the relative position of posterior interray plates, not their topology, reflects homology. From proximal to distal, pentacrinoid posterior plates are the radianal, anal X and right sac plate, regardless of the total number of plates in the adult calyx. Camerate posterior plating contrasts with pentacrinoids, but insufficient data are available to resolve homology relationships between these two clades. More examples of early post-larval ontogeny are needed in camerates and other Palaeozoic crinoids.     

The deflection hypothesis: eyespots on the margins of butterfly wings do not influence predation by lizards

Feeding experiments with lizards are used to examine the function of small eyespot markings found along the wing margins of many butterfly species. Such eyespots are frequently suggested to function by deflecting the attacks of vertebrate predators away from the vulnerable body towards the wing margins, which can tear easily; the eyespots are considered to mislead predators and to act as targets for their attacks. Such misdirected attacks give the butterflies a chance to evade capture, albeit sometimes losing pieces of wing tissue. As a model prey species, we used fruit-feeding individuals of the tropical butterfly Bicyclus anynana that were attacked in a standard way in laboratory cages by the anolis lizard, Anolis carolinensis . We also manipulated the butterflies' wing patterns by pasting eyespots on different parts of the wings to examine the deflection hypothesis in more detail. Our results indicate no influence on the lizard attacks either of the presence of eyespots, or of their position on the wings. The lizards attacked butterflies in a highly stereotyped manner both when the prey were presented on matching or on contrasting backgrounds. We thus found no support for the deflection hypothesis for attacks by insectivorous lizards. Indeed, our only support to date has been obtained for naïve flycatcher birds, but even this requires further corroboration. Although effective deflection may occur rather infrequently, except perhaps under certain ecological conditions such as high-density feeding of butterflies on fallen fruit, it may still be sufficiently consistent over time to have contributed to shaping the evolution of marginal eyespot patterns.  © 2007 The Linnean Society of London, Biological Journal of the Linnean Society , 2007, 92 , 661–667.     

An unusual crinoid-barnacle association in the type area of the Danian (Paleocene), Denmark

The specialization of holopodid crinoids to a sessile habit, by directly cementing the cup to a hard substrate and having short arms that interlock on closure to give a watertight seal, led F.A. Bather to speculate in 1928 that they might once have led an intertidal, barnacle‐like existence in shallow water. Although this remains unproven, holopodid‐barnacle associations from the Danian now provide indirect supporting evidence of their similar environmental preferences at that time. It has long been recognized that the holopodid Cyathidium holopus Steenstrup was encrusted by the verrucomorph Verruca prisca ? Bosquet in Danian submarine caves. This crinoid is now known to occur with abundant plates of the brachylepadomorph barnacle Pycnolepas bruennichi Withers in open sea bed settings, suggesting that they lived together on a substrate now lost due to diagenesis. These were most likely to have been azooxanthellate scleractinian corals (benthic; 100+ m estimated water depth) and/or logs (either on sunken benthic islands (100+ m) or floating as pseudoplankton). If the tight, barnacle‐like closure of the holopodid arms was primarily an anti‐predatory adaptation, suggested as an alternative hypothesis, then it was of limited effectiveness and insufficient to prevent the group having to migrate from shallow into deeper water with the stalked crinoids since the Late Cretaceous.     

Presumed postlarval pentacrinoids from the Lower Devonian Hunsrück Slate,Germany

Several tiny crinoids with crowns as small as 1 mm, or less, in width are newly recognized from the Hunsrück Slate of southwestern Germany. The presence of erect arms above an amorphous calyx in some specimens can be inferred. Based on comparison with the size and gross morphology of developmental stages in living crinoids, these tiny Hunsrück crinoids are judged to be at an early postlarval stage that is analogous to the pentacrinoid stage just after development from the stalked, but armless, smaller cystidean larval stage found in both living comatulids and isocrinids. Some of these tiny crinoids have a stalk up to 4 mm long attached to a now pyritized former substrate. Their clustered occurrence suggests gregarious settlement of larvae. Taxonomic identification of these presumed pentacrinoids is not possible, even to the sub‐class level, although they are preserved with larger juveniles of the cladids Propoteriocrinus and Lasiocrinus. These larger juveniles exhibit 3‐D pyritized calcite plates, whereas the probable pentacrinoids appear to be preserved as flattened, micro‐crystalline pyritized dermal tissues that enclosed lightly calcified, porous ossicles. The pentacrinoids were likely buried within weeks or months of hatching, based on developmental stages in similar‐sized living crinoids. These tiny crinoids, presumably pentacrinoids, are a further example of the extraordinarily detailed preservation of delicate tissues in pyrite from the Hunsrück Slate. They are most likely the pentacrinoid stage from one or more of the crinoid taxa (30 genera) present in the Hunsrück Slate. Assuming these are not microcrinoids, they are the first report of pentacrinoids from the fossil record and document that a Palaeozoic sister group to modern crinoids had similar developmental stages.     

Epizoan encrustation on Marsupites testudinarius – additional argument favoring an epifaunal mode of life of uintacrinoids?

Uintacrinoids (Uintacrinoidea Zittel) are among the best-known Late Cretaceous crinoids, but owing to their unusual morphology and widespread distribution their mode of life has become a subject of much discussion. Of several competing hypotheses, nektonic, pseudoplanktonic, hemipelagic, semi-infaunal and epibenthic lifestyles have been suggested. Recent study synthesizing and extending previous data has shown that these crinoids were epibenthic, holding their arms vertically for feeding. However, evidence supporting a rheophilic epibenthic model over an alternative rheophobic semi-infaunal model is still limited. Here we report epizoans, mostly represented by serpulids and bryozoans, encrusting thecal plates of Marsupites testudinarius from the Lägerdorf in Germany. Although a definitive interpretation whether recorded infestations occurred syn vivo or post mortem is not certain, it is remarkable that all epizoans (or their traces) are attached to the convex side (latera) of well-preserved isolated plates displaying no signs of reworking. Furthermore, a bryozoan colony crossing plate boundaries has been also found on the surface of a sub-articulated theca suggesting that it may have been colonised syn vivo. Recorded epibiotic associations, whether syn vivo or post-mortem, must have developed prior to burial of the specimens, above the surface of sea floor, and thus provide another argument against rheophobic semi-infaunal mode of life of uintacrinoids.     

Rapid laboratory evolution of adult wing area in Drosophila melanogaster in response to humidity

Abstract We examined the evolutionary response of wing area (a trait highly correlated with other measures of body size) to relative humidity (RH), temperature, and their interaction in Drosophila melanogaster , using replicated lines that had been allowed to evolve at low or high humidity at 18°C or at 25°C. We found that after 20 weeks of selection (5–10 generations), low RH lines had significantly greater wing areas than high RH lines in both sexes. This evolutionary response may have resulted from selection of larger flies with a smaller surface area for water loss relative to their weight, or as a correlated response to selection on some other unidentified trait. There were no evolutionary effects of temperature on wing area or cell density. This may have been due to the short duration of the selection experiment, and/or counteracting selection pressures on body size at warm temperature.     

Ordovician Paracrinoids from the Baltic: Key Problems of Comparative Morphology of Pelmatozoan Echinoderms

The erect feeding appendages of paracrinoids, brachioles of typical blastozoans and arms of crinoids are morphologically similar in their terminal growth, biserial cover plates, and pinnulation. This is attributed to the inducing effect of the radial ambulacral canal on their growth mode. The uniserial brachioles of Laurentian paracrinoids are homologous to the biserial brachioles of the Baltic Achradocystites and Heckerites, and those of other blastozoans. Based on this assumption, the two Baltic genera, which have a brachiole system plesiomorphic for paracrinoids, and a similar morphology of the theca, are assigned to this class. Brachiolars in brachioles are a new development, homologous to the flooring plates of the food groove and, where present, are the continuations of these plates beyond the theca. The uniserial brachioles of Laurentian paracrinoids evolved from the biserial brachioles as a result of a gradual shift of brachiolars in the neighboring rows and their subsequent fusion in pairs. Brachials in crinoidal arms are a new development that evolved as distal serial growth of radial plates under the induced influence of the incipient radial canals emerging from the closed vestibular cavity, which was an ontogenetic innovation in crinoids. The transformation of a nonorganized small-plated theca into a large-plated, and completely or partly symmetrized theca, or vice versa is possible and results from accelerated or retarded growth of some plate generation in relation to the growth rate of the theca.     

Osteogenesis,homology, and function of the intercostal plates in ornithischian dinosaurs (Tetrapoda,Sauropsida)

Intercostal plates are bony structures positioned lateral to the anterior dorsal ribs in some ornithischian dinosaurs. Some propose these plates are homologous, or functionally analogous, with the uncinate processes of extant avian dinosaurs that assist in breathing, while others suggest they served a defensive function. To elucidate their osteogenesis, homology, and function, a histological survey of intercostal plates from three taxa (Hypsilophodon, Talenkauen, and Thescelosaurus) was undertaken. This study reveals that osteogenesis of intercostal plates closely resembles that of secondary centers of ossification in endochondral bone, typically present in the epiphyses of mammalian long bones. In contrast, ossification of avian uncinate processes begins at a primary ossification center via the development of a bony collar around a cartilaginous model. Based on these data, intercostal plates and avian uncinate processes are likely not evolutionary homologs. Dense packets of obliquely oriented Sharpey’s fibers within the parallel-fibered bone of somatically mature intercostal plates indicate these plates were positioned medial to at least a portion of the hypaxial musculature, which does not support their use as bony armor. Rather, we propose that intercostal plates performed some biomechanical function, either assisting in breathing in a way analogous to avian uncinate processes, or working together with the sternal ribs and sternal plates of these ornithischian taxa to provide increased rigidity to the anterior portion of the ribcage.     

Functional ecological implications of intraspecific differences in wing melanization in Colias butterflies

Variation in the degree of insect wing melanin affects thermoregulation, and is expected to be adapted to local environmental conditions, for example over an elevational gradient. The effects of melanization on flight activity and egg maturation rate were assessed in the closely related butterflies Colias philodice eriphyle and C. eurytheme using experimental manipulation of wing darkness and transplant experiments between high and low elevation sites. Experimental manipulation of wing darkness in C. p. eriphyle demonstrated that light males had reduced flight activity at high elevations, and darkened males had reduced flight activity at low elevations. In contrast, the transplant experiments revealed asymmetrical adaptation for male C. p. eriphyle . At high elevations darker, high-elevation males had higher flight activity than lighter, low-elevation males, but there was no difference between the two groups at low elevation. For females, melanization had no effect on flight activity. However, an increase in female C. eurytheme wing darkness led to a significantly higher egg maturation rate at cold ambient temperatures, which may increase female reproductive output under natural conditions. Therefore, dispersers moving down in elevation may be more successful than those moving up.  © 2004 The Linnean Society of London, Biological Journal of the Linnean Society , 2004, 82 , 79–87.     

The improbability of a muscular crinoid column

Donovan, Stephen K. 1989 07 15: The improbability of a muscular crirroid column. Lethaia , Vol. 22, pp. 307–315. Oslo. ISSN 0024–1164.
It has sometimes been assumed that the stems of ancient crinoids were muscular. However, the only contractile fibres found in the stems of extant crinoids are in the cirri of isocrinids and comatulids. On uniformitarian grounds, it is improbable that any ancient crinoid had tissues in the stem that would have aided active orientation, apart from the non-muscular catch connective tissue. This conclusion is supported by a detailed functional analysis of the various forms of column and cirrus articulation. The axial canal has been seen as the probable site of any column musculature, but this is functionally impossible with symplexial and synostosial articulations, both of which are poorly adapted for muscular flexure. Columns that articulate synarthrially are much more flexible, but modern bourgueticrinids lack any stem musculature, despite having such stalks. The only crinoid columns that were functionally adapted to utilize contractile fibres were those of certain coiled-stemmed taxa, where the axial canal was not in the plane of the synarthrial fulcra. However, it is unlikely that such stems, even if muscular, possessed any advantage over a non-muscular column. The only pelmatozoans with a probable muscular column were not crinoids, but the glyptocystitid rhombiferans. * Crinoids, stem, columnal, cirrus, catch connective tissue, contractile fibres, functional morphology .     

Contribution of DNA repair and cell cycle checkpoint arrest to the maintenance of genomic stability

DNA damage response mechanisms encompass pathways of DNA repair, cell cycle checkpoint arrest and apoptosis. Together, these mechanisms function to maintain genomic stability in the face of exogenous and endogenous DNA damage. ATM is activated in response to double strand breaks and initiates cell cycle checkpoint arrest. Recent studies in human fibroblasts have shown that ATM also regulates a mechanism of end-processing that is required for a component of double strand break repair. Human fibroblasts rarely undergo apoptosis after ionising radiation and, therefore, apoptosis is not considered in our review. The dual function of ATM raises the question as to how the two processes, DNA repair and checkpoint arrest, interplay to maintain genomic stability. In this review, we consider the impact of ATM's repair and checkpoint functions to the maintenance of genomic stability following irradiation in G2. We discuss evidence that ATM's repair function plays little role in the maintenance of genomic stability following exposure to ionising radiation. ATM's checkpoint function has a bigger impact on genomic stability but strikingly the two damage response pathways co-operate in a more than additive manner. In contrast, ATM's repair function is important for survival post irradiation.     

THE EARLY RADIATION AND PHYLOGENY OF ECHINODERMS

1. Living echinoderms are characterized by an extensive water vascular system developed from the larval left hydrocoel, a complex, multi-plated endoskeleton with stereom structure, and pentamery. Fossil evidence shows that stereom evolved before pentamery, but both were acquired during the Lower Cambrian. 2. Cladistic analysis of Lower Cambrian genera reveals very few characters in common between carpoids and true echinoderms, and that the split between them was the first fundamental evolutionary dichotomy within the Dexiothetica. 3. Helicoplacoids are stem group echinoderms with spiral plating and three ambulacra arranged radially around a lateral mouth. They are the most primitive echinoderms and the first to show a radial arrangement of the water vascular and ambulacral systems. Unlike later echinoderms, their skeleton shows no dorsal/ventral (aboral/oral) differentiation. They were probably sedentary suspension feeders. 4. Camptostroma is the most primitive known pentaradiate echinoderm and, in our view, possibly a common ancestor of all living groups. It had a short conical dorsal (aboral) surface with imbricate plating, a ridged lateral wall and a slightly domed ventral (oral) surface with five curved ambulacra in a 2-1-2 arrangement inherited from the triradiate pattern of the helicoplacoids. Interambulacral areas bore epispires and the CD interambulacrum contained the anus, hydropore and/or gonopore. All parts of the theca had plates in at least two layers. 5. All other echinoderms belong to one of two monophyletic subphyla, the Pelmatozoa and the Eleutherozoa. 6. Stromatocystites is the earliest known eleutherozoan and differs from Camptostroma in having a test with only one layer of plates and having lost the dorsal elongation. In Stromatocystites the dorsal surface is flat and the plating tesselate. Stromatocystites was an unattached, low-level suspension feeder. 7. The lepidocystoids are the earliest known pelmatozoans. They differ from Camptostroma in having an attached dorsal stalk which retained the primitive imbricate plating, and by developing erect feeding structures along the ambulacra. In Kinzercystis, the ambulacra are confined to the thecal surface and erect, biserial brachioles arise alternately on either side. Lepidocystis has a similar arrangement except that, the distal part of each ambulacrum extends beyond the edge of the theca as a free arm. 8. Pelmatozoans diverged more or less immediately into crinoids, with multiple free arms composed of uniserial plates, and cystoids sensu lato, which retained brachioles. Gogia (Lower to Middle Cambrian) is the most primitive known cystoid and differs from Kinzercystis principally in having all plating tesselate, while Echmatocrinus (Middle Cambrian) is the most primitive known crinoid and differs from Lepidocystis in lacking brachioles and in having more than five free arms with uniserial plates. 9. Post Lower Cambrian differentiation of pelmatozoan groups proceeded rapidly, exploiting the primitive suspension-feeding mode of life. Maximum morphological diversity was reached in the Ordovician, but thereafter crinoids progressively displaced cystoid groups and reached their peak diversity during the Carboniferous. The eleutherozoans were slower to diversify, but by the Arenig the earliest ‘sea-stars’ (in reality, advanced members of the eleutherozoan stem group) had reversed their living orientation and had begun to exploit a deposit-feeding mode of life. These in turn led to the ophiuroids, echinoids and holothuroids. 10. The basic echinoderm ambulacrum was already present in the helicoplacoids. It had biserial, alternate flooring plates and complexly plated sheets of cover plates on either side. The radial water vessel lay in the floor of the ambulacrum, external to the body cavity, and gave rise ventrally to short, lateral branches (fore-runners of tube feet) that were used to open the cover plate sheets, and dorsally was connected to internal compensation sacs which acted as fluid reservoirs (and were preadapted for a role in gaseous exchange). Plating on the cover plate sheets was organized and reflected the positions of the lateral branches from the radial water vessel. In Camptostroma, the cover plate sheets had biserially aligned rows of cover plates associated with the lateral branches. 11. Brachioles arose by extension of the lateral branches of the radial water vessel and associated serially aligned cover plates found in Camptostroma. They bear a single alternate series of cover plates. In Lepidocystis the ambulacra extended beyond the edge of the oral surface as true arms. Brachial plates of arms are homologues of primary ambulacral flooring plates, and arms bear multiple series of cover plates. Uniserial ambulacral plating is a derived condition and evolved independently in crinoids, paracrinoids and isorophid edrioasteroids. Pinnules in crinoids arose independently in inadunates and camerates by a progressively more unequal branching of the arms. Thus all parts of the subvective system in crinoids are internally homologous, whereas in cystoids, brachioles and arms (or ambulacra) are not homologous structures. 12. The position of the hydropore is the best reference point in orientating echinoderms. Carpenter's system of identifying ambulacra by letters, arranged clock-wise in oral view with the A ambulacrum opposite the hydropore, is consistent in all echinoderm classes. In all Lower Cambrian pentaradiate echinoderms the anus, gonopore and hydropore lie in the CD interambulacrum and this is accepted as the primitive arrangement. In helicoplacoids we tentatively suggest that the A ambulacrum spiralled down from the mouth while the two ambulacra that spiralled up represent the B + C and D + E ambulacra combined. 13. The pelmatozoan stem arose from a polyplated stalk, via a meric stem to a true column with holomeric (single piece) columnals. This happened independently in the crinoids and the cystoids. 14. Our analysis of echinoderm phylogeny leads us to recommend the following changes to the higher level classification of echinoderms: The phylum Echinodermata includes only those groups with radial symmetry superimposed upon a fundamental larval asymmetry. It has a stem group that contains the triradiate helicoplacoids and a crown group to which all other (pentaradiate) echinoderms belong. The crown group contains two monophyletic subphyla, the Pelmatozoa and the Eleutherozoa, and the Pelmatozoa contains two superclasses, the Crinoidea which are extant and the Cystoidea, which are extinct.     

The La Voulte Lagerstätte (Callovian): Evidence for a deep water setting from sponge and crinoid communities

The siliceous sponges and crinoids from the Chénier Ravine (France, Lower Callovian) are used here as biological markers to characterize the palaeoenvironment of the adjacent and contemporaneous La Voulte Lagerstätte that is remarkable for its unique soft-bodied fauna (e.g. worms, cirrate octopods, vampire squids). Sponges are abundant with dominant hexactinellids (80%) and lithistids (20%). Four lines of fossil evidence, supported by Recent analogues, indicate that this sponge community inhabited deep-water setting under dysphotic or aphotic conditions: (1) the dominance of hexactinellids; (2) the prevalence of cone-shaped and erect morphologies that usually characterize Recent bathyal sponges; (3) the close similarities with Recent hexactinellids from the continental slope and; (4) the lack of encrustation by photophilic organisms. Attachments of sponges on hard substrate (e.g. crystalline basement) and their preservation in soft sediments (e.g. muds) indicate heterogeneous bottom conditions. The Chénier fauna also contains small stalked, asymmetric cyrtocrinid crinoids that are known to live on hard substrates in bathyal environments such as the SW Pacific steep seamounts. Convergent palaeoenvironmental clues obtained from both crinoids and siliceous sponges support the notion that the La Voulte area, including the La Voulte Lagerstätte, was situated in the upper part of the bathyal zone near the slope-basin transition with a water depth most probably exceeding 200 m. Supporting evidence from heterogeneous substrates and complex fault systems indicate a depositional environment along the external part of the slope where steep topographies and blocks usually favour the settlement of cyrtocrinid crinoids and hexactinellid sponges. La Voulte may therefore be one of the rare and extremely precious Mesozoic Lagerstätten to have fossilized a deep marine environment.     

AERODYNAMICS,THERMOREGULATION, AND THE EVOLUTION OF INSECT WINGS: DIFFERENTIAL SCALING AND EVOLUTIONARY CHANGE

We examine several aerodynamic and thermoregulatory hypotheses about possible adaptive factors in the evolution of wings from small winglets in insects. Using physical models of Paleozoic insects in a wind tunnel, we explore the potential effects of wings for increasing gliding distance, increasing dispersal distance during parachuting, improving attitude control or stability, and elevating body temperatures during thermoregulation. The effects of body size and shape, wing length, number, and venation, and meteorological conditions are considered. Hypotheses consistent with both fixed and moveable wing articulations are examined. Short wings have no significant effects on any of the aerodynamic characteristics, relative to wingless models, while large wings do have significant effects. In contrast, short wings have large thermoregulatory effects relative to wingless models, but further increases in wing length do not significantly affect thermoregulatory performance. At any body size, there is a wing length below which there are significant thermoregulatory effects of increasing wing length, and above which there are significant aerodynamic effects of increasing wing length. The relative wing length at which this transition occurs decreases with increasing body size. These results suggest that there could be no effective selection for increasing wing length in wingless or short-winged insects in relation to increased aerodynamic capacity. Our results are consistent with the hypothesis that insect wings initially served a thermoregulatory function and were used for aerodynamic functions only at larger wing lengths and/or body sizes. Thus, we propose that thermoregulation was the primary adaptive factor in the early evolution of wings that preadapted them for the subsequent evolution of flight. Our results illustrate an evolutionary mechanism in which a purely isometric change in body size may produce a qualitative change in the function of a given structure. We propose a hypothesis in which the transition from thermoregulatory to aerodynamic function for wings involved only isometric changes in body size and argue that changes in body form were not a prerequisite for this major evolutionary change in function.