REASSESSMENT OF THE GENUS LEANCHOILIA (ARTHROPODA, ARACHNOMORPHA) FROM THE MIDDLE CAMBRIAN BURGESS SHALE, BRITISH COLUMBIA, CANADA

Abstract:  The collection, since 1975, of over 1500 specimens of Leanchoilia Walcott by the Royal Ontario Museum has prompted reassessment of the genus and its species from the Middle Cambrian Burgess Shale. Among new characters in Leanchoilia superlata , the type species, are the presence of two pairs of eyes, a dorsal double carina bracketing the axis of the body segments, segmentation of the gill branch of the appendages, and serration along the body edges from the posterior third of the cephalic shield to the last body segment. Leanchoilia persephone Simonetta, previously synonymized with L. superlata , is also well represented in the Burgess Shale, and is re-established as a valid species, owing to conspicuous differences from the type species. These are the absence of the diagnostic up-curving snout of the cephalic shield, the absence of carina, the shorter 'great appendages', the smooth edges of the body, and its overall shape in dorsal aspect. Leanchoilia superlata and L. persephone may be sexual dimorphs of each other. The ROM collections extend considerably the geographical distribution and stratigraphic range of Leanchoilia in western Canada.     

Bilateral Jaw Elements in Amiskwia sagittiformis Bridge the Morphological Gap between Gnathiferans and Chaetognaths

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Unlocking the early fossil record of the arthropod central nervous system

Extant panarthropods (euarthropods, onychophorans and tardigrades) are hallmarked by stunning morphological and taxonomic diversity, but their central nervous systems (CNS) are relatively conserved. The timing of divergences of the ground pattern CNS organization of the major panarthropod clades has been poorly constrained because of a scarcity of data from their early fossil record. Although the CNS has been documented in three-dimensional detail in insects from Cenozoic ambers, it is widely assumed that these tissues are too prone to decay to withstand other styles of fossilization or geologically older preservation. However, Cambrian Burgess Shale-type compressions have emerged as sources of fossilized brains and nerve cords. CNS in these Cambrian fossils are preserved as carbon films or as iron oxides/hydroxides after pyrite in association with carbon. Experiments with carcasses compacted in fine-grained sediment depict preservation of neural tissue for a more prolonged temporal window than anticipated by decay experiments in other media. CNS and compound eye characters in exceptionally preserved Cambrian fossils predict divergences of the mandibulate and chelicerate ground patterns by Cambrian Stage 3 (ca 518 Ma), a dating that is compatible with molecular estimates for these splits.     

The macro‐ and microfossil record of the Cambrian priapulid Ottoia

The stem‐group priapulid Ottoia Walcott, 1911, is the most abundant worm in the mid‐Cambrian Burgess Shale, but has not been unambiguously demonstrated elsewhere. High‐resolution electron and optical microscopy of macroscopic Burgess Shale specimens reveals the detailed anatomy of its robust hooks, spines and pharyngeal teeth, establishing the presence of two species: Ottoia prolifica Walcott, 1911, and Ottoia tricuspida sp. nov. Direct comparison of these sclerotized elements with a suite of shale‐hosted mid‐to‐late Cambrian microfossils extends the range of ottoiid priapulids throughout the middle to upper Cambrian strata of the Western Canada Sedimentary Basin. Ottoiid priapulids represented an important component of Cambrian ecosystems: they occur in a range of lithologies and thrived in shallow water as well as in the deep‐water setting of the Burgess Shale. A wider survey of Burgess Shale macrofossils reveals specific characters that diagnose priapulid sclerites more generally, establishing the affinity of a wide range of Small Carbonaceous Fossils and demonstrating the prominent role of priapulids in Cambrian seas.     

A large new leanchoiliid from the Burgess Shale and the influence of inapplicable states on stem arthropod phylogeny

Characterized by atypical frontalmost appendages, leanchoiliids are early arthropods whose phylogenetic placement has been much debated. Morphological interpretations have differed, some of which concern critical characters such as the number of eyes and head appendages, but methodological approaches also have diverged. Here, we describe a new leanchoiliid, Yawunik kootenayi gen. et sp. nov., based on 42 specimens from the newly discovered Marble Canyon locality of the Burgess Shale (Kootenay National Park, British Columbia; middle Cambrian). This new morphotype demonstrates the presence of a four‐segmented head in leanchoiliids, along with two small antero‐median eyes in addition to lateral eyes. Yawunik is characterized by a 12‐segmented trunk and a carinate, lanceolate telson adorned with minute spines. The ‘great appendages’ of the animal bear teeth on their two distal rami, which would have enhanced their ability to grasp prey. Attitudes of specimens, resulting from burial at multiple aspects of bedding, suggest the ‘great appendages’ were flexible and capable of antero‐posterior rotation. We also discuss the nature of intersegmental tissues and filaments present within the ‘great appendages’. Our phylogenetic analyses extend the monophyly of leanchoiliids to include Haikoucaris and Yohoia in a new clade, the Cheiromorpha nom. nov. (within Heptopodomera nom. nov.). Other nodes are poorly resolved unless implied weights are used, and in this case, the topology is critically sensitive to the coding prerogative of inapplicable states (NAs). Both the traditional ‘Arachnomorpha’ hypothesis (NAs as additional states) and the more recently favoured ‘Artiopoda + Crustacea’ (NAs as uncertainties) were obtained using the same data set and outgroup. This result stresses, first, the historical importance of polarization over data content in scenarios of early arthropod evolution, and second, a pressing need to investigate the impacts of coding inapplicables, especially given the inflating effect of implied weights.     

Using Soil Amendments to Increase Bermuda Grass Growth in Soil Contaminated with Hydraulic Fracturing Drilling Fluid

Hydraulic fracturing is the process of injecting solutions at high pressure to break apart rock formations and increase efficiency of natural gas extraction. The solutions are recovered and have been land-applied as a disposal technique. The objective of this greenhouse study was to evaluate the effects of inorganic fertilizer, broiler litter, or Milorganite®, and soil depth interval on the growth of Bermuda grass [Cynodon dactylon (L.) Pers] in soil from a site that had been contaminated with fracturing fluid and was devoid of vegetation. In soil from 0–15 cm depth, initial electrical conductivity (ECe), Na, and Cl levels were 14.5 dS/m, 2994 mg/kg, and 5603 mg/kg, respectively. For the 0–30 cm depth, initial ECe, Na, and Cl levels were 14.1 dS/m, 2550 mg/kg, and 5020 mg/kg, respectively. Bermuda grass was sprigged and harvested after nine weeks. Addition of inorganic fertilizer, broiler litter, or Milorganite® resulted in 290, 241, and 172%, respectively, greater shoot biomass compared to unamended soil. Plants grown in the 0–30 cm depth soil had greater root biomass (95%), length (67%), volume (61%), and surface area (65%) compared to those grown in soil from the 0–15 cm depth. Fertilization and cultivation may be useful in revegetating sites contaminated with fracturing fluid.     

The Machaeridian Lepidocoleus Sarlei Clarke, 1896, from the Rochester Shale (Silurian) of New York State

Eight new specimens and the holotype of Lepidocoleus sarlei Clarke, 1896 from Lagersta¨tten deposits within the Rochester Shale (Silurian, Wenlock) of New York are described to elucidate the morphology, function and construction of the scleritome. The material exhibits an unusual type of dorsal hinge with a pronounced antero-posterior displacement between the two sides. Two specimens have an aberrant sclerite on the right side of segment eleven. One tightly enrolled specimen may demonstrate a method of defence with the stronger protected dorsal side oriented outwards. The presence of a segmented body plan is suggested, based on requirements for a functional spiral enrolment. Distinct anterior and posterior morphologies together with the pattern of rugae provide valuable help in reconstructing disarticulated lepidocoleids.     

A new fossil wood from the highly diverse early Eocene equatorial forest of Gujarat (western India)

During the early Eocene (～55–52 Ma), when the Indian subcontinent relished equatorial climatic conditions, lignite was deposited along its north western margin. Lignite mines of northwestern India have proved to be an outstanding resource for palaeoenvironmental information. The Vastan lignite mine of the early Eocene age situated near Surat district (Gujarat) is one of the well-dated and fossiliferous lignite mines in western India. A fossil wood, retrieved from this mine, is systematically described and shows a strong resemblance to the modern genus Chisocheton of the family Meliaceae. Plant fossils are the best source to reconstruct the palaeoenvironment of any region, and here a luxurious, highly diverse tropical evergreen forest is interpreted in and around the fossil locality in contrast to the tropical thorn forest of the present day. This early Eocene highly diverse equatorial forest, once covered a significant portion of the Indian subcontinent, is now restricted in fringes known as Western Ghats in south India attesting to changes in climate.     

Probable predation on Upper Cambrian trilobites and its relevance for the extinction of soft-bodied Burgess Shale-type animals

The lower Rabbitkettle Formation of northwestern Canada is a monofacial Upper Cambrian unit of variably calcareous, argillaceous siltstone and fine-grained sandstone with rare bioclastic grainstone, deposited on a gentle slope below fair-weather wave base with no discernible fluctuation in water depth. The trilobite fauna is a mixture of pandemic agnostoids and Laurentian polymeroids, including protaspides and meraspides, and individuals are disarticulated, non-abraded and mostly oriented convex-upward. Bioclasts are interpreted as in situ elements affected only by weak bottom currents and storm-induced turbulence. A major proportion of the larger (≥5 mm across) polymeroid cranidia and pygidia in the lower part (Marjuman) of the formation are broken; large thoracic segments are often broken at the axial furrow and some broken free cheeks occur, but essentially no broken agnostoids or hypostomes were observed. Trilobites are not broken in upper beds (Steptoean), above the base of the Glyptagnostus retculatus Zone. Physical breakage cannot be dismissed entirely, but most damage is interpreted to be due to size-selective predation, possibly through lethal blows similar to those delivered by some extant stomatopod crustaceans. A possible culprit may be an animal akin to Yohoia , known from the Middle Cambrian Burgess Shale. The distribution of attacked trilobites serves as a proxy for the presence and disappearance of soft-bodied carnivores. In the Rabbitkettle Formation, it suggests that Burgess Shale-type animals may have persisted into the Late Cambrian but suffered extinction at the Marjuman-Steptoean 'biomere' event when most trilobite species vanished.     

Arthrophycus as a mimic of crinoid column impressions in the lower Silurian of central Kentucky,USA

Unusual specimens of an ichnofossil, herein ascribed to Arthrophycus, are described from siltstone tempestites in the lower Silurian (Llandovery, Telychian) Estill Shale near Irvine, Estill County, central Kentucky, USA. The specimens display closely spaced, uncurved transverse annulations, but lack the medial ridge, rectangular cross‐sectional shape and dense branching typical of common Silurian Arthrophycus ichnospecies. This combination of features, coupled with the straightness of burrows and alignment parallel to inorganic tool marks, closely approximates the appearance of moulds of partially articulated crinoid columns (= pluricolumnals) that were impressed into firm mud and cast by storm‐deposited sediment. That these structures do not represent the external moulds of body fossils is suggested by minor width variations along the long axis of specimens, possible bioglyphs and the total absence of skeletal material, including isolated crinoid columnals, in this and other tempestites from this interval. More convincingly, the presence of very sparse branching indicates a trace fossil origin for these structures. These fossils are best interpreted as the products of preferential mining of inorganically generated tool marks by deposit feeders, owing to exposure of more organic‐rich muds by erosional scouring. Thus, this occurrence represents a rare instance in which trace fossils display a strong alignment parallel to inorganic sedimentary structures.