Joseph P. Botting

Ordovician faunas of Burgess Shale type

The renowned soft-bodied faunas of the Cambrian period, which include the Burgess Shale, disappear from the fossil record in the late Middle Cambrian, after which the Palaeozoic fauna dominates. The disappearance of faunas of Burgess Shale type curtails the stratigraphic record of a number of iconic Cambrian taxa. One possible explanation for this loss is a major extinction, but more probably it reflects the absence of preservation of similar soft-bodied faunas in later periods. Here we report the discovery of numerous diverse soft-bodied assemblages in the Lower and Upper Fezouata Formations (Lower Ordovician) of Morocco, which include a range of remarkable stem-group morphologies normally considered characteristic of the Cambrian. It is clear that biotas of Burgess Shale type persisted after the Cambrian and are preserved where suitable facies occur. The Fezouata biota provides a link between the Burgess Shale communities and the early stages of the Great Ordovician Biodiversification Event.

An exceptional Caradoc sponge fauna from the Llanfawr Quarries, central Wales and phylogenetic implications

Synopsis An abundant sponge collection from basal Caradoc mudstones of the Llanfawr Quarries, Llandrindod, Powys is the most diverse fine‐sediment sponge fauna recorded from the British Palaeozoic. It is dominated by reticulosans, but includes some lyssakids and demosponges. Eight new genera and 11 species are erected and one new family proposed: Xylochos palindromica gen. et sp. nov., Pirania llanfawrensis sp. nov., Heminectere minima gen. et sp. nov., Asthenospongia cambria sp. nov. (Asthenospongiidae nov.), Acutipuerilis spinosus gen. et sp. nov., Granulispongia obscura gen. et sp. nov., Hemidiagoniella tenax gen. et sp. nov., H. caseus sp. nov., Solusrectus rosetta gen. et sp. nov., Cyathophycus loydelli sp. nov., and Dilatispongia tumidus gen. et sp. nov. Some specimens are preserved with organic or pyritic films representing soft tissue and most have high‐fidelity preservation of spicule external moulds, although iron oxide spicule replacement obscures details prior to cleaning. D. tumidus shows a thickened wall with specialised dermalia, while retaining some degree of quadruling and represents a lineage that may have given rise to the brachiospongioids. Others, such as S. rosetta, appear close to the ancestral state of the modern Lyssacinosida. The hex‐actinellid taxa are interpreted in a reasoned phylogenetic framework that stresses the importance of root tuft structure, the presence of zero‐order spicules and the number and nature of spicule layers. It also attempts to link extant and Lower Palaeozoic palaeontological classifications. The parallel evolutionary development of thick walls and strong attachment structures is interpreted as being due to an offshore‐onshore expansion, contrary to many other groups.

An Ordovician variation on Burgess Shale-type biotas

The Cambrian Burgess Shale-type biotas form a globally consistent ecosystem, usually dominated by arthropods. Elements of these communities continued into the Early Ordovician at high latitude, but our understanding of ecological changes during the Great Ordovician Biodiversification Event (GOBE) is currently limited by the paucity of Ordovician exceptionally preserved open-marine faunas. Here we clarify the early stages of the GOBE by describing a new open-marine Konservat-Lagerstätte from the Early Ordovician of Wales. The Afon Gam Biota includes many lineages typical of the Cambrian Burgess Shale-type biotas, but the most abundant groups were sponges, algae and worms, with non-trilobite arthropods being unexpectedly rare. Labile tissues occur abundantly in the sponges and are also present in other groups, including brachiopods and hyoliths. Taphonomic biases are considered and rejected as explanations for arthropod rarity; the preserved biota is considered to be an approximation to the original community composition. We note that other exceptionally preserved communities in the Welsh Ordovician are also sponge-dominated, suggesting a regional change in benthic ecology during the early stages of the GOBE.

Llanvirn (Middle Ordovician) echinoderms from Llandegley Rocks, central Wales

A diverse Llanvirn echinoderm fauna is described from nearshore volcanogenic sandstones of Llandegley Rocks, Builth-Llandrindod Inlier, Powys. The fauna comprises six crinoids (including Cefnocrinus samgilmouri gen. et sp. nov., Iocrinus llandegleyi sp. nov.), three asteroids and one cystoid; at least two indeterminate crinoids and one asteroid represent undescribed taxa, but yielded insufficient material for formal description. Two complex radical root structures are among the oldest recorded examples. Preservation occurs as external moulds, often fully articulated, with fine details preserved through early marginal silicification. The high diversity of this site suggests that the significance of echinoderm palaeocommunities from nearshore areas of low preservation potential is underestimated.

Cyathophycus and the origin of demosponges

The relationships between the poriferan classes are currently obscure. Molecular phylogenies appear to be reaching a consensus that the hexactinellids and demosponges are closely related, despite previous attempts to separate the Hexactinellida from other sponges on cytological grounds, but the details of the transition are unknown. Similarities of spicule morphology and structure are used to infer that the transition probably occurred after the onset of silicification, and should therefore be seen in fossils. The similarity between protosponges and early demosponges has been noted previously, based largely on a thin, reticulated wall of simple spicules (monaxons in Leptomitus, stauracts in Protospongia). A close relationship is, however, unlikely, since the protospongiids possessed a precise geometric arrangement of multiple spicule size orders that is lacking in demosponges. A close morphological similarity exists between the skeletons of transitional protosponge-dictyosponge reticulosids, such as Cyathophycus, and the early hazeliid demosponges. The inner spicule layer of primitive dictyosponges consists of a cross-hatched array of fine monaxons, as seen in the wall of some simple hazeliids. Although most described species of hazeliids were morphologically complex, a simple globose species is here recorded from the Caradoc of Wales. The evolutionary link between the classes is suggested to lie within the dictyospongioid and hazeliid lineages. Although the direction of evolution cannot be certainly fixed, it is conceptually much easier to derive the demosponges from the hexactinellids, rather than vice versa.

The role of pyroclastic volcanism in Ordovician diversification

Abstract Pyroclastic volcanism has been tentatively correlated with Ordovician faunal diversification, but it is unclear whether the volcanism itself or associated tectonic effects were more influential. Elevated nutrient flux from uplifted areas has been widely discussed, but the link between enhanced productivity and diversification is unclear. Ecosystem compartmentalization due to irregular topography was probably significant, but it is debatable whether this was sufficient to explain the entire diversification. This paper introduces a further volcanic process, which may have been more significant than these established hypotheses, although it is emphasized that all relevant factors acted in combination. Recent studies of the local ecological effects of ash-fall have revealed dramatic post-depositional plankton and benthic blooms associated with overturning of a stratified water mass. The data are consistent through all studied sections from the Builth Inlier, Central Wales, while deeper-water sediments showed plankton blooms only. Repeated bloom events over localized dysaerobic shelf areas may have produced temporary benthic ‘islands’, enhanced genetic heterogeneity within affected regions, and increased speciation rates. In order to maximize bloom intensity (and possible effects on evolution), this process requires widespread pyroclastic volcanism combined with extensive shelf areas with well-developed stratification. The hypothesis potentially allows explanation of the differential rates of evolution between different groups, particularly the decoupled planktic-benthic patterns. A preliminary test using Welsh Basin ostracodes is presented, with predictions for the global database results.

Growth patterns of Lower Palaeozoic sponges

Detailed studies of the growth patterns of modern siliceous sponges are restricted to demosponges and theoretical models. It is generally assumed that sponge growth is essentially incremental, with completion of one arbitrary unit being followed by external addition. All recent species are thick-walled, but Lower Palaeozoic sponges are dominated by thin-walled hexactinellids, with most Cambrian taxa consisting of a single spicule layer. Large populations of a primitive dictyospongiid have allowed the reconstruction of the growth patterns of their spicules and body morphology. The results indicate that growth occurred through continuous expansion of the globose body, accompanied by continuous enlargement of existing spicules, with a spicule size limit being reached only during the lifetime of a few individuals. It is noted that this skeletal growth pattern is otherwise restricted to deuterostomes. Consecutive appearance of successive spicule size orders appears to have maintained a maximum inhalant pore area. Comparisons with more limited data from two acanthose hexactinellids and a hazeliid demosponge indicate that an identical growth pattern operated in these species. The subsequent evolution of growth patterns is discussed, with various mechanisms producing the later thick-walled morphologies of hexactinellids and demosponges. The implications of these observations are discussed with reference to identification and systematics, since spicule size and arrangement are shown to vary during growth.

First post-Cambrian records of the reticulosan sponges Valospongia and Hintzespongia from the late Tremadocian of North Wales

A new sponge fauna has been discovered in silty mudstone of the early Migneintian (late Tremadocian, Ordovician) of North Wales. The assemblage is dominated by reticulosan hexactinellids, including several species bearing parietal gaps; this feature is common among Cambrian hexactinellids, but is rare in Ordovician faunas. Of particular significance is Valospongia bufo sp. nov., representing the first record of the genus outside the Middle Cambrian of Utah, USA. A single specimen assigned to Hintzespongia? sp. is also described, and also represents the first occurrence outside the Laurentian Burgess Shale-type faunas. This fauna indicates that deeper-water hexactinellids from the Burgess Shale-type faunas survived in places into at least the Early Ordovician, in addition to the Cambrian-type protomonaxonid assemblage seen in the Fezouata Biota.

A Lower Carboniferous sipunculan from the Granton Shrimp Bed, Edinburgh

Synopsis Sipunculans are sedentary marine worms, believed to represent either an early coelomate grade or a later offshoot of the annelids, but are unmineralized and extremely rare in the fossil record. Here we describe an example from the Granton Shrimp Bed, a Lower Carboniferous Konservat-Lagerstätte. This is the third known occurrence of Palaeozoic sipunculans, although they may have been previously overlooked. The recognition of fossil sipunculans is discussed, based partly on cuticle deformation due to the underlying muscle arrangement.

Graptolite faunas and monaxonid demosponges of the Cyrtograptus lundgreni event (late Wenlock, Silurian) interval from the Orange district, New South Wales

Muir, L.A. & Botting, J.P., December, 2007. Graptolite faunas and monaxonid demosponges of the Cyrtograptus lundgreni event (late Wenlock, Silurian) interval from the Orange district, New South Wales. Alcheringa 31, 375-395. ISSN 0311-5518. Three monograptid and five retiolitid graptoloids, and one species of sponge, are described from late Wenlock sections (Cyr. lundgreni and Co. ludensis biozones) at Spring Creek and Wallace Creek, near Orange, New South Wales, Australia. The sponge Janussenia orangense gen. et sp. nov. is the first monaxonid demosponge to be described from the Australian Silurian. An object containing broken Testograptus testis, and interpreted as the faecal pellet of a predator or scavenger on graptoloids, is described. Lucy A. Muir [l.muir@nhm.ac.uk], Department of Palaeontology, Natural History Museum, Cromwell Road, London SW7 5BD, UK. Joseph P. Botting [joe@asoldasthehills.org], 2C Roslyn Close, Mitcham CR4 3BB, UK. Received 28.4.2006; Revised 10.10.2006.