Shallow Burrows Research Articles

Trace fossil evidence for Ediacaran bilaterian animals with complex behaviors

Distinguishing Ediacaran trace fossils from tubular body fossils can be a challenge, and several Ediacaran fossils previously interpreted as animal traces have been shown to be tubular body fossils. Nonetheless, true Ediacaran trace fossils are present, but they are relatively few and morphologically simple, dominated by horizontal trails and shallow burrows. Such simple morphologies have been taken as evidence for a modest behavioral complexity and limited geobiological impact of animal bioturbators before the Cambrian explosion. Here we report three types of trace fossils—horizontal tunnels, surface tracks/trails, and vertical traces—from the latest Ediacaran Dengying Formation (551–541Ma) in the Yangtze Gorges area of South China. Cross-cutting tunnels and the presence of scratch marks indicate that these traces are unlikely tubular body fossils; instead, these three types of traces likely represent animal activities related to under-mat feeding, epibenthic locomotion, and temporary dwelling, respectively. We show that these three types of traces were constructed by the same bilaterian animals that had moderately complex interactions with microbial mats to exploit nutrients and O2 resources. These animals heralded a new age in ecosystem engineering, animal–sediment interaction, and biogeochemical cycling.

Paleoecology and evolution of Jurassic–Cretaceous corbiculoids from Japan

Corbiculoids are a group of benthic bivalves found in brackish-water environments. Abundant fossil corbiculoids from the Jurassic–Cretaceous strata of Japan are important for interpreting corbiculoid evolution. Most paleontological studies have been concerned with their taxonomy or phylogeny. This study addresses their paleoecology and adaptive strategies to better understand their evolution. Through analyses of fossil assemblages and shell functional morphology, representative corbiculoid species (i.e., Eomiodon lunulatus, E. vulgaris, Costocyrena otsukai, C. radiatostriata, Crenotrapezium kurumense, C. kitakamiense, Myrene tetoriensis, Isodomella shiroiensis, Filosina jusanhamensis, Tetoria sanchuensis, T. yokoyamai, Hayamina naumanni, and H. matsukawai) are interpreted to have been rapid but shallow burrowers, and suspension feeders. This paleoecological interpretation indicates that corbiculoid species were adapted to brackish-water environments. However, to maintain an ecological niche in the environment, organisms must be able to respond to environmental instability. Thus, temporal changes in the stratigraphic and spatial distributions of 23 well-studied corbiculoid species during the Jurassic and Cretaceous were examined. As a result, it is clarified that some corbiculoid species avoided relatively small environmental changes by migration to refugia. On the basis of the occurrence pattern of the corbiculoid species, it is also argued that corbiculoids are polyphyletic, with multiple speciations enabling them to persist from the Jurassic to recent.

Ecological signature of the end-Triassic biotic crisis: what do bivalves have to say?

In order to understand the causes underlying the Triassic–Jurassic (T/J) mass extinction, we tested different bivalve features for extinction selectivity, i.e. shell mineralogy, age at the Rhaetian and three main autoecologic traits (feeding mechanism, tiering and motility/attachment). Also, diversity and turnover rates throughout the Triassic and the Early Jurassic were analysed in detail. The dataset employed for this analysis was a precise database at genus level including data from Induan to Sinemurian times. Results point to a true mass extinction for bivalves around the T/J boundary. This extinction was not age-selective at the boundary. Certain analyses suggested that shell mineralogy was a character significantly increasing survival odds, but this relationship seems to reflect selectivity on autoecologic traits. There was no difference in extinction proportions between both feeding types (i.e. deposit feeders and filter feeders); among the other traits, deep burrowers, epifaunal-motile and endobyssate forms seem to have been favoured, while shallow burrowers (and probably reclined forms) were more heavily affected. This pattern suggests an environmental stress at the boundary with some particular issues affecting the different life modes. Models linking magmatism in the Central Atlantic Magmatic Province with the end-Triassic mass extinction are a plausible scenario for this kind of perturbation.

Identification of the barrier to gene flow between phylogeographic lineages of the common hamster Cricetus cricetus

In anthropogenically disturbed habitats, natural barriers still exist and have to be recognized, as they are important for conservation measures. Areas of phylogeographic breaks within a species are often stabilized in inhospitable regions which act as natural barriers. An area of contact between phylogeographic lineages of the common hamster (Cricetus cricetus) was found in the Małopolska Upland in Poland. A total of 142 common hamsters were captured between 2005 and 2009. All hamsters were genotyped at 17 microsatellite loci and partial sequences of the mitochondrial (mtDNA) control region were obtained. No mixed populations with mtDNA haplotypes of both lineages were found. The distance between marginal populations was about 20 km; no hamsters were found in the area between. A principal components analysis (PCA) was performed on microsatellite data and the greatest change in PC1 scores was found between marginal samples. To define the habitat components responsible for the phylogeographic break, we compared the habitat composition of sites occupied by hamsters with those from which hamsters were absent. We found that hamsters avoided forested areas and sandy soils. The area of the potential barrier was characterized by a high proportion of woodland and unfavorable soils in comparison with neighboring areas inhabited by hamsters. They cannot settle in this area due to their high winter mortality in shallow burrows and high predation in the fields adjacent to forests.

Neoichnology of Thyonella gemmata: A Case Study for Understanding Holothurian Ichnofossils

While the fossil record of holothurians extends from the Cambrian to the Holocene, adequately evaluating their temporal and spatial distribution is difficult due to their poor preservation potential. Several extant holothurians, however, produce abundant shallow burrows that a have a high preservation potential. Neoichnological experiments allow for the direct observation of burrowing behaviors and the resulting biogenic structures. Data obtained from these experiments are invaluable to the interpretation of ichnofossils lacking associated body fossils. The burrowing behaviors of the holothurian Thyonella gemmata were studied in a laboratory setting under varying environmental conditions. Specimens were exposed to variations in grain size, salinity, and water temperature to assess their behavioral response to environmental change and any resulting biogenic structures. Thyonella gemmata burrows by intruding itself into the sediment using muscular contractions and limited use of tube feet. Thyonella gemmata contracts its body into a U-shape and maintains contact with the sediment surface. The resulting burrow is a wide, U-shaped concentration of disrupted sediment with or without spreite. Sediment size had the greatest effect on burrowing activity and morphology; individuals were able to easily burrow into fine- and medium-grained sand, but experienced difficulty in coarse-grained sand. Altering water temperature yielded no significant results. While increasing salinity had no effect, lowering salinity had an adverse physiological effect on the specimens and inhibited burrowing. Studying the varying burrow morphologies produced in these experiments will aid in the interpretation of potential holothurian ichnofossils and the interpretation of paleoenvironmental conditions.

Systematic revision of the family Kalliapseudidae (Crustacea: Tanaidacea)

Kalliapseudidae is a family of shallow burrow–dwelling and fossorial marine and estuarine tanaidaceans. There are currently 39 known species in 12 genera and three subfamilies. They are distributed throughout the world’s tropical, subtropical, and temperate coastal waters and, with a few known exceptions, are restricted to depths of less than 200 m. The phylogeny of Kalliapseudidae is assessed to test the monophyly of currently accepted subfamilies and genera, based largely on examination of material loaned from various museums and institutions. Multiple exemplars from other apseudomorph families were also included in the ingroup to test the monophyly of the family. Parsimony analyses included 41 terminal taxa and 64 binary and multistate morphological characters. Analyses based on successive weighting resulted in 20 most parsimonious trees. The strict consensus tree of these most parsimonious trees supported Kalliapseudidae, Kalliapseudinae, Tanapseudes, Cristapseudes, and Mesokalliapseudes as monophyletic. The genus Kalliapseudes could not be resolved, but constraining it to be monophyletic resulted in a significantly worse tree. The subfamilies Hemikalliapseudinae and Tanapseudinae were recovered as polyphyletic and paraphyletic, respectively, but without support. Constraining them to be monophyletic did not result in a significantly worse tree. Results indicated high levels of homoplasy in three morphological characteristics traditionally used to differentiate groups. Alokalliapseudes macsweenyi is transferred back to the genus Mesokalliapseudes, rendering Alokalliapseudes a junior subjective synonym. Nine new taxa, including six species of Kalliapseudes and one species of the genus Cristapseudes, and one new genus (Phoxokalliapseudes) and species (P. singaporensis) were discovered and described. Two species of Kalliapseudes (K. gobinae and K. multiarticulus) are transferred to Phoxokalliapseudes n. gen. Neotypes are designated for K. magnus, C. omercooperi and M. schubarti, and a lectotype is designated for K. mauritanicus. Distribution maps, illustrated keys to the subfamilies, genera and species, and preliminary remarks on biogeographic history are also presented.

Coping between crises: Early Triassic–early Jurassic bivalve diversity dynamics

The Triassic is bounded by two of the most severe biotic crises, but nevertheless this time was, for bivalves, both a recovery and a diversification period, and a moment to fully exploit some of their evolutionary novelties. Just how and when this was achieved is analyzed in this paper, which covers Induan to Sinemurian bivalve diversity, based on a newly compiled database. Taxonomic diversity and ecospace dynamics are examined separately. Diversity and evolutionary rates were assessed, extinction selectivity was tested using a resampling algorithm, and cohort analysis was used to study extinction patterns. During the Early Triassic most bivalve genera were survivors from the Permian and they were mainly cosmopolitan epifaunal and semi-infaunal endobyssate taxa. Reclined, epifaunal and semi-infaunal bivalves increased in diversity during the Triassic, but from Norian on, their diversity declined, and they were strongly affected by the T/J crisis. Although the Triassic/Jurassic extinction strongly impacted bivalve taxonomic diversity, it had little impact on bivalve ecologic diversity. Not a single bivalve life strategy was eliminated at the end of the Triassic. The present study does not support previous conclusions that infaunal bivalves suffered greater extinction than epifaunal ones during the T/J extinction. Not all life strategies were equally affected by the extinction event, being the deep infaunal burrowers positively selected. Bivalves with major energetic requirements seem to have been more affected with negative selectivity on fast shallow burrowers. The ecologic diversity changes of bivalves during the Late Triassic and several adaptations of durophagous predators reflect the effects of increasing predation pressure and support a Late Triassic origin of the Mesozoic Marine Revolution.

Changes in body fluids of the cocooning fossorial frog Cyclorana australis in a seasonally dry environment

We investigated changes in the lymph (equivalent to plasma) and urine of the cocooning frog Cyclorana australis during the dry season in monsoonal northern Australia. Frogs in moist soil for two days were fully hydrated (lymph 220 mOsm kg − 1 , urine 49 mOsm kg − 1 ). From five weeks onwards the soil was dry (matric potential <−8000 kPa). Aestivating frogs at three and five months formed cocoons in shallow (< 20 cm) burrows and retained bladder fluid (25–80% of standard mass). After three months, urine but not lymph osmolality was elevated. After five months, lymph (314 mOsm kg − 1 ) and urine (294 mOsm kg − 1 ) osmolality and urea concentrations were elevated. Urea was a major contributing osmolyte in urine and accumulated in lymph after five months. Lymph sodium concentration did not change with time, whereas potassium increased in urine after five months. Active animals had moderate lymph osmolality (252 mOsm kg − 1 ), but urea concentrations remained low. Urine was highly variable in active frogs, suggesting that they tolerate variation in hydration state. Despite prolonged periods in dry soil, osmolality increase in C. australis was not severe. Aestivation in a cocoon facilitates survival in shallow burrows, but such a strategy may only be effective in environments with seasonally reliable rainfall.

Tremadocian (Lower Ordovician) sea-level changes and biotas on the Avalon microcontinent

The Chesley Drive Group, an Upper Cambrian-Lower Ordovician mudstone-dominated unit, is part of the Ediacaran–Ordovician cover sequence on the North American part of the Avalon microcontinent. The upper Chesley Drive Group on McLeod Brook, Cape Breton Island (previously “McLeod Brook Formation”), has two lithofacies-specific Tremadocian biotas. An older low-diversity benthic assemblage (shallow burrowers,Bathysiphon, phosphatic brachiopods, asaphid trilobites) is in lower upper Tremadocian green-gray mudstone. This wave-influenced, slightly dysoxic facies hasBathysiphon–brachiopod shell lags in ripple troughs. The upper fauna (ca. 483 +/- 1 Ma) is in dysoxic-anoxic (d-a), unburrowed, dark gray-black, upper upper (but not uppermost) Tremadocian mudstone with a “mass kill” of the olenidPeltocare rotundifrons(Matthew)—a provincial trilobite in Avalonian North America that likely tolerated low oxygen bottom waters.Scandodus avalonensisLanding n. sp. andLagenochitinaaff.conifundus(Poumot), probable nektic elements and the first upper Tremadocian conodont and chitinozoan reported from Avalon, occur in diagenetic calcareous nodules in the dark gray-black mudstone. An upper Tremadocian transition from lower greenish to upper black mudstone is not exposed on McLeod Brook, but is comparable to a coeval green-black mudstone transition in Avalonian England. The successions suggest that late late Tremadocian (probable Baltic Hunnebergian Age) sea level was higher in Avalon than is suggested from successions on other paleocontinents. The Tremadocian sea-level history of Avalon was a shoaling-deepening-shoaling sequence from d-a black mudstone (lower Tremadocian), to dysoxic green mudstone (lower upper Tremadocian), and back to black mudstone (upper upper Tremadocian).ScandodusLindström is emended, with the early speciesS. avalonensisLanding n. sp. assigned to the emended Family Protopanderodontidae.TriangulodusVan Wamel is considered a junior synonym ofScandodus. Peltocare rotundifronsis emended on the basis of complete specimens.

Effects of infaunal bivalve density and flow speed on clearance rates and near-bed hydrodynamics

The influence of bed density (from 0 to 1000 ind. m − 2 ) and flow speed (2, 5, and 15 cm s − 1 , i.e. “low”, “medium” and “high”, respectively) on clearance rates (CR) of an infaunal suspension-feeding bivalve ( Austrovenus stutchburyi) and boundary layer dynamics were investigated in annular flumes. Near-bed flow speeds decreased and bed shear stresses increased with bivalve density due to the bed roughness generated by the shallow burrowers. At low densities (< 500 ind. m − 2 ) there was no detectable effect of feeding currents on bed shear stress, but at high densities (1000 ind. m − 2 ) and at the low flow speed bed shear stress was almost 80% higher when Austrovenus were feeding (0.0016 N m − 2 ), compared to when they were not feeding (0.0009 N m − 2 ). These results suggest that bed roughness generated by Austrovenus and their feeding currents are capable of influencing food supply to the bed. Individual CR were significantly ( p < 0.01) greater at the high flow speed (0.88 L h − 1 ind. − 1 ), compared to the medium and low flow speeds (0.34 to 0.54 L h − 1 ind. − 1 ). With increasing bed density, individual CR was significantly ( p < 0.001) reduced; at low densities CR ranged from 0.6 to 1.4 L h − 1 ind. − 1 , but at high densities they were 0.1 to 0.8 L h − 1 ind. − 1 . Bed CR (L h − 1 m − 2 ) did not scale proportionally with density, initially increasing up to 500 ind. m − 2 but remaining relatively constant thereafter. This was in part due to the negative effect of density on individual CR but also because the proportion of bivalves feeding decreased with increasing density. Our results demonstrate that recording the number of bivalves feeding is necessary to interpret the effect of density on bed CR. Moreover, if the effects of both bivalve density and flow speed are not considered, then scaling up individual CR obtained using animals at low densities will over estimate population filtration capacity. As high (but equivalent to in situ) densities reduced both the number of animals feeding and individual CR other factors may offset this negative interaction, such as protection from wave disturbance or enhanced resuspension of benthic microalgae.

Wind-Powered Wheel Locomotion, Initiated by Leaping Somersaults, in Larvae of the Southeastern Beach Tiger Beetle (Cicindela dorsalis media)

Rapid movement is challenging for elongate, soft-bodied animals with short or no legs. Leaping is known for only a few animals with this “worm-like” morphology. Wheel locomotion, in which the animal's entire body rolls forward along a central axis, has been reported for only a handful of animals worldwide. Here we present the first documented case of wind-powered wheel locomotion, in larvae of the coastal tiger beetle Cicindela dorsalis media. When removed from their shallow burrows, larvae easily can be induced to enter a behavioral sequence that starts with leaping; while airborne, larvae loop their body into a rotating wheel and usually either “hit the ground rolling” or leap again. The direction larvae wheel is closely related to the direction in which winds are blowing; thus, all our larvae wheeled up-slope, as winds at our study site consistently blew from sea to land. Stronger winds increased both the proportion of larvae wheeling, and the distance traveled, exceeding 60 m in some cases. In addition, the proportion of larvae that wheel and the distance traveled by wheeling larvae are significantly greater on smooth sandy beaches than on beach surfaces made rough and irregular by pedestrian, equestrian, and vehicular traffic. Like other coastal species of tiger beetles, C. dorsalis media has suffered major declines in recent years that are clearly correlated with increased human impacts. The present study suggests that the negative effects of beach traffic may be indirect, preventing larvae from escaping from predators using wheel locomotion by disrupting the flat, hard surface necessary for efficient wheeling.

Nest use by western pygmy-possums (Cercartetus concinnus) (Marsupialia:Burramyidae) at Innes National Park, South Australia

We examined the nest use of 15 radio-tracked western pygmy-possums (Cercartetus concinnus) throughout one year for up to nine nights each at Innes National Park, South Australia. At least one pygmy-possum was followed in each of 12 months. Nest type and nest fidelity varied greatly; shallow burrows under debris were the most frequently used. Nest preferences of females with young remain unknown. The ability of C. concinnus to use a diversity of nest types over relatively short periods is likely to be an important survival strategy.

Northeast Pacific Upper Cretaceous and Paleocene Glycymeridid Bivalves

The Late Cretaceous to late Paleocene record of glycymeridid bivalves in the region extending from the Alaska Peninsula, southward to Baja California, Mexico is studied in detail for the first time.Glycymeris pacifica(Anderson, 1902), of late Cenomanian to late Turonian age, is the earliest known glycymeridid in the study area. Very locally, it is found with the middle to late TuronianGlycymeris yoloensisn. sp. The latter apparently represents some intermediate state between genusGlycymerisda Costa, 1778 and genusGlycymeritaFinlay and Marwick, 1937. In the study area,Glycymeritais represented byGlycymerita veatchii(Gabb, 1864), middle to late Turonian to late Campanian;Glycymerita banosensis(Anderson, 1958) new combination, late Campanian to latest Maastrichtian;Glycymerita aleutan. sp., known only from Alaska and of early Maastrichtian age; andGlycymerita major(Stanton, 1896) new combination, Selandian to Thanetian. All the studied species lived in warm-temperate, shallow-marine waters and were shallow burrowers in fine-grained siliciclastic sediments. Variability in morphology is common in sizeable populations of the various species, especiallyGlycymerita veatchii, which increased nearly fivefold in size during its 19.5 million-year-long range and culminated in shells up to 84 mm in length.

Bivalves from the Triassic-Jurassic transition in Northern Spain (Asturias and Western Basque-Cantabrian Basin)

Bivalve mollusks from the Triassic-Jurassic transition collected in eight localities in Asturias and the western Basque-Cantabrian Basin (Palencia province) are systematically revised. Preservation is poor at all localities. The dominant Rhaetian bivalves are Isocyprina concentrica (Moore) and Bakevellia (Bakevelloides) praecursor (Quenstedt). These species, together with Isocyprina cf. ewaldi (Bornemann), Pteromya cf. crowcombeia (Moore), Pseudoplacunopsis alpina (Winkler), and Modiolus? sp. (cf. minimus J. Sowerby), with a specimen of Arcestidae (?), belong to an assemblage similar to that found in the Westbury and Lilstock formations (Penarth Group) in the late Rhaetian of southern England. The most abundant Hettangian species is Isocyprina (Eotrapezium) germari (Dunker). Others are referred to Cuneigervillia rhombica (Cossmann), Sphaeriola? sp., Eomiodon? sp. and Pteromya cf. tatei (Richardson and Tutcher). All Hettangian shell beds examined are monotypic or have very low diversity, a biological indication that they may belong to a restricted marine environment, with high environmental stress levels. Even the more diverse assemblage (Pteromya-Cuneigervillia-Eomiodon) was probably also salinity controlled. The fauna analyzed here clearly belongs to the same facies and environment as those described from Aquitaine (France) and the Pyrenees and is different from coeval bivalve assemblages from other European Hettangian localities. The Triassic-Jurassic boundary cannot be precisely located at the studied sections on the basis of the bivalve faunas alone, but these indicate that the transition beds in Asturias were deposited in a marginal marine environment and the benthic fauna was dominated by shallow burrowing, suspensivorous bivalves.

Proximal–distal ichnofabric changes in a siliciclastic shelf, Early Pliocene, Guadalquivir Basin, southwest Spain

The lower Pliocene deposits, cropping out along the Atlantic coast of Cadiz, in the Conil–Cabo Roche area, formed on a shelf gently deepening towards the W–NW. Up to five types of facies can be recognized, distributed in belts from proximal to distal parts of the shelf: 1) Coarse-grained sandstone with trough cross-stratification facies on the most proximal parts of the shelf (inner-shelf deposits). 2) Medium-grained sandstone with low-angle planar cross-stratification facies deposited in a more distal position due to storm currents transporting sediment offshore. This facies intercalates with the previous trough cross-bedded sandstone. 3) Massive fine-grained sandstone and siltstone facies laterally and vertically related with the previous facies type and representing sediments formed in the middle shelf close to the storm wave-base. 4) Tabular sandstone bed facies corresponding to storm-bed deposits intercalated within the two previous facies. 5) Greenish–bluish shale facies accumulated on the outer shelf below storm wave-base. Three ichnofabrics associated with these facies are recognized: 1) The two cross-bedded facies are dominated by a Macaronichnus ichnofabric, characterized by Macaronichnus and Bichordites traces that represent colonization of a shifting sandy substrate by polychaetes ( Macaronichnus tracemakers) and by sea urchins ( Bichordites producers). 2) A Rosselia ichnofabric, consisting of vertical traces of Rosselia cross-cutting Macaronichnus, characterizes the interval of massive fine-grained sandstone and silt facies and interbedded tabular sandstones. This ichnofabric formed under high sedimentation rates with Rosselia traces exhibiting stacked patterns that indicate vertical readjustment following deposition. 3) Massive fine-grained sandstone and silt facies are distinguished by a Cylindrichnus ichnofabric. This fabric was produced by the activity of a moderately diverse community dominated by sessile, burrow-dwelling, probably superficial-detritus-feeding polychaetes ( Rosselia and Cylindrichnus tracemakers) and vagile, deposit-feeding polychaetes ( Planolites producers). In addition, infaunal deposit/detritus-feeders producing spreiten structures ( Teichichnus) are found in distal areas. Pervasive indistinct mottling of the sediment of this facies was probably due to the activity of very shallow burrowers in the uppermost sediment tiers. This proximal–distal replacement of ichnofabrics reflects the change of benthic communities across the shelf. This distribution does not fit the traditional Seilacherian ichnofacies model for soft-ground shallow-marine settings, in which proximal, vertical-dwelling burrows of the Skolithos ichnofacies dominate high-energy environments. In the Pliocene of Cadiz, shallow-tier burrows of deposit/detritus-feeders characterize the high-energy facies instead, which fit better with the Cruziana ichnofacies. This deviation can be related with the particular palaeoenvironmental conditions. Thus, vagile, opportunistic deposit-feeders colonized the dune foreset when the dunes were stable, and the progradation of the structure favored the preservation of the traces.

Resistance of crayfish (Procambarus spp.) populations to wetland drying depends on species and substrate

Wetland or stream drying can be a severe disturbance for aquatic animals, but the severity of a drying disturbance is context dependent. We used a controlled drying experiment to investigate the resistance of populations of 2 crayfish species (Procambarus fallax and Procambarus alleni) found in south Florida wetlands in 3 sediment types (sand, marl, and peat). The species had different putative burrowing abilities, and we tested the hypothesis that the severity of drying disturbance for populations of burrowing crayfish would be species and substrate dependent. Observations of initial burrowing success indicated that the species could burrow equally well in peat, whereas P. alleni burrowed more effectively than P. fallax in marl and sand. No P. fallax burrowed in the dense sand substrate. The number of crayfish surviving 2 mo underground was a function of particular combinations of species and substrate. Survival of both species was high in peat (∼66%) and similarly high for P. alleni in marl. Survival of P. fallax in marl was considerably lower (31%), and no P. fallax survived in sand. Despite their initial burrowing success, only a few P. alleni survived in the sand in shallow burrows. Survivors of both species showed some loss of body mass from initial conditions, but P. fallax lost relatively more mass. The substrate-specific survival of P. fallax helps explain their persistence at relatively high densities in peat-dominated wetlands that dry every 1 to 3 y and their small populations in marl-dominated marshes with similar drying frequencies. Attempts to explain or forecast the net effects of wetland drying for crayfish populations and other burrowing animals should consider that resistance to drying disturbances will depend on characteristics of both species and substrate types. These considerations have important implications for hydrological restoration of aquatic ecosystems that have pronounced gradients of hydrology and substrates.

Comparison of geochemical and distinctive mineralogical features associated with the Kinzers and Burgess Shale formations and their associated units

This paper compares two North American occurrences of fossils that exhibit Burgess Shale-type preservation (BST): the Middle Cambrian Burgess Shale Formation of southeastern British Columbia, and the Lower to Middle Cambrian Kinzers Fm of southeastern Pennsylvania. Redox-sensitive trace elements (Mo, Ni/Co, V/Sc) indicate that palaeo-oxygenation conditions varied with respect to faunal assemblage and location. Ogygopsis-bearing fauna in both the Burgess Shale and Kinzers formations are associated with a dysoxic metal signature. Burgess Shale-type preservation in the Kinzers Fm was deposited in a fluctuating oxycline, whereas the BST-fossil beds of Fossil Ridge and Mt Stephen (Burgess Shale Fm) yield a geochemical signature that consistently indicates oxic conditions. Thus, sustained low-oxygen conditions do not correlate with higher quality of fossil preservation at these sites. Ogygopsis is associated with dysoxic conditions in both localities, and may therefore be a faunal indicator of such environments in Middle Cambrian strata. Carbonate units associated with both the Burgess Shale and Kinzers formations contain large, generally concordant, near-surface cavities that contain herringbone calcite cements that show no significant enrichment in the potential calcite inhibitor ions such as reduced Fe, Sr, S, Pb, and Zn. The abundance of micro-inclusions of dolomite suggests that Mg may have been the calcite inhibitor ion responsible for herringbone cement in these Cambrian occurrences. Another distinctive mineralogical feature is the presence of doubly-terminated, euhedral, zoned, authigenic quartz as a conspicuous part of a carbonate host-rock replacement assemblage. The association of both herringbone calcite and zoned quartz crystals in units associated with the Burgess Shale and Kinzers formations suggest a common feature in the depositional and diagenetic environment of these two regions in which Burgess Shale-type fossil preservation occur; syn-depositional brine flow is the likely cause of these distinct mineralogical features. Brine seeps in the depositional environment may have provided nutrients for stable high-abundance faunal communities in a slope setting, thereby accounting for the abundance of fossil material. Furthermore, high-salinity brine in the pore waters of carcass-bearing Cambrian muds may have further limited shallow burrowing, scavenging, and decomposition rates, accounting for the exceptional preservation in these two localities.

Thermal Biology, Torpor, and Activity in Free‐Living Mulgaras in Arid Zone Australia during the Winter Reproductive Season

Little is known about the energy conservation strategies of free-ranging marsupials living in resource-poor Australian deserts. We studied activity patterns and torpor of free-living mulgaras (Dasycercus blythi) in arid central Australia during the winter of 2006. Mulgaras are small (approximately 75 g), nocturnal, insectivorous marsupials, with a patchy distribution in hummock grasslands. Mulgaras (six males, three females) were implanted intraperitoneally with temperature-sensitive transmitters and monitored for 6-55 d. Temperature profiles for different microhabitats and the thermal properties of soil and a number of burrows were also measured. Air temperature ranged from -3 degrees C at night to 30 degrees C during the day. Although burrows buffered temperature extremes, the thermal diffusivity of the sandy soil was high, and many burrows were shallow. Hence, soil and burrow temperatures averaged about 15 degrees C. The activity of mulgaras was often restricted to a few hours after sunset, before they retired into their burrows. Mulgaras employed torpor frequently, often entering torpor during the night and arousing around midday, with arousals occurring later on cooler days. Shallow burrows allowed cooling below mean T(soil). Consequently, body temperatures as low as 10.8 degrees C were observed. The longest torpor bout was 20.8 h. Torpor patterns changed seasonally and differed between males and females. From June to August, females entered torpor almost daily despite mating and gestation, but from the end of the gestation period onward, they remained normothermic. In contrast, males showed only shallow and short torpor during the mating season, but from mid-July, a transition to more frequent and deeper torpor resembling that of females was observed. Apparently, in both sexes, the reproductive effort entails energetic costs, but torpor, as an energy-saving mechanism, and reproduction are not exclusive in mulgaras. In a resource-poor environment during the least productive part of the year, frequent torpor seems to provide the means to compensate for the increased energetic costs associated with reproduction.

Trochosa sepulchralis, a senior synonym of Trochosa acompa, and the restoration of Trochosa abdita (Araneae, Lycosidae)

Trochosa sepulchralis (Montgomery 1902) is recognized as the senior synonym of Trochosa acompa (Chamberlin 1924) based upon careful examination of critical morphological characteristics. In addition, Trochosa abdita (Gertsch 1934), once considered a junior synonym of T. acompa, is now recognized as a valid species. Trochosa sepulchralais and T. abdita are fully illustrated and described, and essential information regarding species identification, morphological dimensions, and geographic distribution is included. Spiders of the lycosid genus Trochosa are small to medium sized wolf spiders (5.8-13.0 mm) that are largely Holarctic in distribution. They are often found at the edge of woods and in woodland habitats. In this paper, we clarify the relationship of two Nearctic species in this genus: Trochosa sepulchralis (Montgomery 1902) and T. abdita (Gertsch 1934). Previously T. sepulchralis and T. acompa (Chamberlin 1924) were recognized as separate species (Platnick 2007), but are in fact one with T. sepulchralis as the senior synonym. Roewer (1955) placed T. sepulchralis in Geolycosa, despite the fact that it lacks characteristic features of this genus, such as a very high cephalothorax, darkened forelegs, and obligate burrowing behavior. Trochosa abdita was considered a junior synonym of T. acompa by Wallace (1947), but it is a distinct species. Both species have genitalic and morphological characters consistent with those of Trochosa. Lycosa sepulchralis was first described by Montgomery (1902) from Philadelphia, Pennsylvania and has received little attention since that time. When Lycosa acompa was described by Chamberlin (1924) from a single female individual collected from New Orleans, he apparently was unaware of the great similarities between these two popula- tions. As a result, they have been recognized as two separate species up to this point. This research began as an investigation into the relationship between T. abdita and T. acompa. We discovered drawings by Brady during the 1970's of the L. sepulchralis holotype that bore a striking similarity to T. acompa. The holotypes were then compared and it was concluded that they represent the same species, and hence the new synonymy. Gertsch (1934) described L. abdita based upon a single female specimen. For reasons that were not made clear, Wallace (1947) synonomized it with L. acompa. The two species were grouped together and locality records for these two species from Florida, Texas, and Georgia were consoli- dated. Barnes (1953) did not recognize Wallace's synonymy when he included T. abdita in a list of spiders from North Carolina, nor did Roewer (1955). Trochosa abdita and T. acompa, both originally described in Lycosa, were not included in Brady's revision of the genus Trochosa (Brady 1979), but their placement in this group is now considered valid. A thorough examination of the holotypes and many additional specimens of both species collected during the past 50 years have allowed us to clarify the distribution of and relationship between T. abdita and T. sepulchralis. Differences in size, geographic distribution, and the morphology of somatic and reproductive structures in these two species became readily apparent, and the existence of two distinct species is now recognized. Trochosa abdita occurs in peninsular Florida and north along the eastern seaboard to North Carolina, while T. sepulchralis is found from the Florida panhandle east throughout Texas. Specimens from Pennsylvania and New York extend the range of the latter species into New England (Fig. 21). Little is known of the natural history of these two species other than that inferred through collection methods and locations, and the scant information found with the original descriptions. Wallace (1947) reported T. abdita collected from ''leaf mould of mesophytic hammocks in northcentral Florida.'' He also noted that T. abdita ''is usually found close to its retreat which is most often a shallow burrow in the ground beneath the leaf mould.'' Whether or not T. sepulchralis shares these specific behavioral characteristics needs to be ascertained. It is hoped that this paper will stimulate further investigations of these interesting woodland wolf spiders. METHODS

Living in a shallow burrow under a rock: Gas exchange and water loss in an Australian scorpion

The scorpion, Urodacus manicatus (Scorpionida: Urodacidae), inhabits temperate sclerophyll woodland in south-eastern Australia and excavates a shallow burrow into soil beneath a rock. Mean minimum and maximum temperatures within a burrow were respectively higher and lower than outside measurements, and relative humidity within a burrow remained higher than outside the burrow at all times. Using flow-through respirometry, VCO 2 and water loss were measured at three ecologically relevant temperatures (10, 20 and 30 °C) to assess patterns of gas exchange and the temperature dependence of VCO 2 and water loss rates. Daytime VCO 2 corresponds to a lower metabolic rate than reported for the closely related, but more arid region inhabiting species Urodacus armatus and Urodacus yaschenkoi. CO 2 output is continuous at 10 °C; however, at 20 °C scattered sharp depressions are observed and these become more frequent and periodic at 30 °C. Total water loss in U. manicatus is nearly double that in U. armatus, indicative of lessened selective pressure for water conservation within a mesic rather than xeric environment.