Taphonomy plays diverse roles in paleobiology. These include assessing sample quality relevant to ecologic, biogeographic, and evolutionary questions, diagnosing the roles of various taphonomic agents, processes and circumstances in generating the sedimentary and fossil records, and reconstructing the dynamics of organic recycling over time as a part of Earth history. Major advances over the past 15 years have occurred in understanding (1) the controls on preservation, especially the ecology and biogeochemistry of soft-tissue preservation, and the dominance of bi- ological versus physical agents in the destruction of remains from all major taxonomic groups (plants, invertebrates, vertebrates); (2) scales of spatial and temporal resolution, particularly the relatively minor role of out-of-habitat transport contrasted with the major effects of time-averaging; (3) quantitative compositional fidelity; that is, the degree to which different types of assemblages reflect the species composition and abundance of source faunas and floras; and (4) large-scale var- iations through time in preservational regimes (megabiases), caused by the evolution of new bod- yplans and behavioral capabilities, and by broad-scale changes in climate, tectonics, and geochem- istry of Earth surface systems. Paleobiological questions regarding major trends in biodiversity, major extinctions and recoveries, timing of cladogenesis and rates of evolution, and the role of environmental forcing in evolution all entail issues appropriate for taphonomic analysis, and a wide range of strategies are being developed to minimize the impact of sample incompleteness and bias. These include taphonomically robust metrics of paleontologic patterns, gap analysis, equal- izing samples via rarefaction, inferences about preservation probability, isotaphonomic compari- sons, taphonomic control taxa, and modeling of artificial fossil assemblages based on modern an- alogues. All of this work is yielding a more quantitative assessment of both the positive and neg- ative aspects of paleobiological samples. Comparisons and syntheses of patterns across major groups and over a wider range of temporal and spatial scales present a challenging and exciting agenda for taphonomy in the coming decades.

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Taphonomy and paleobiology

http://link.springer.com/content/pdf/10.1007/978-3-642-67868-4_4.pdf

Spatial Vision in Arthropods

Mushroom bodies are prominent neuropils found in annelids and in all arthropod groups except crustaceans. First explicitly identified in 1850, the mushroom bodies differ in size and complexity between taxa, as well as between different castes of a single species of social insect. These differences led some early biologists to suggest that the mushroom bodies endow an arthropod with intelligence or the ability to execute voluntary actions, as opposed to innate behaviors. Recent physiological studies and mutant analyses have led to divergent interpretations. One interpretation is that the mushroom bodies conditionally relay to higher protocerebral centers information about sensory stimuli and the context in which they occur. Another interpretation is that they play a central role in learning and memory. Anatomical studies suggest that arthropod mushroom bodies are predominately associated with olfactory pathways except in phylogenetically basal insects. The prominent olfactory input to the mushroom body calyces in more recent insect orders is an acquired character. An overview of the history of research on the mushroom bodies, as well as comparative and evolutionary considerations, provides a conceptual framework for discussing the roles of these neuropils.

/pdf/evolution-discovery-and-interpretations-of-arthropod-2icwz0xkd9.pdf

Evolution, Discovery, and Interpretations of Arthropod Mushroom Bodies

Contents Preface to the Paperback Edition Preface to the First Edition Introduction: The Astrobiology Revolution and the Rare Earth Hypothesis Dead Zones of the Universe Rare Earth Factors 1 Why Life Might Be Widespread in the Universe 2 Habitable Zones of the Universe 3 Building a Habitable Earth 4 Life's First Appearance on Earth 5 How to Build Animals 6 Snowball Earth 7 The Enigma of the Cambrian Explosion 8 Mass Extinctions and the Rare Earth Hypothesis 9 The Surprising Importance of Plate Tectonics 10 The Moon, Jupiter, and Life on Earth 11 Testing the Rare Earth Hypotheses 12 Assessing the Odds 13 Messengers from the Stars References Index

https://physicstoday.scitation.org/doi/pdf/10.1063/1.1325239

Rare Earth: Why Complex Life is Uncommon in the Universe

The faunal criteria for the recognition of the relative separation of old continents are: 1, the contrast between shallow- (not deep-) water faunas off opposite shorelines; 2, the recognition of deeper-water facies surrounding the edges of continents; and 3, the recognition of the disposition of ancient climatic belts. These criteria are defined and used to assess the relative position of the various parts of what is now Britain in the Palaeozoic. The Iapetus Ocean is well characterized by faunal differences from the Cambrian until the lower Ordovician, but from Caradoc times onwards these differences dwindle, until by the latest Silurian only the distribution of the ostracods separates the two sides of the ocean on faunal grounds. In the early Ordovician, S British faunas are comparable with those from Bohemia, France and elsewhere to the S, indicating connection with Gondwanaland, and these faunas differ from those in the Baltic area, a distribution which we attribute to a true ocean, Tornquist9s Sea, between N and S Europe. Tornquist9s Sea probably closed in the upper Ordovician, and from Ashgill times onwards the S British and Baltic faunas remained similar. During the middle and late Silurian there is evidence of increasing faunal distinction between Britain, the Baltic area and North America on the one hand and southern Europe and Gondwanaland on the other, indicating an opening Rheic Ocean which appears to have persisted until late Carboniferous times.

Faunal evidence for oceanic separations in the Palaeozoic of Britain

Isolated specimens of the appendage Anomalocaris canadensis have long been known; a single incomplete specimen of an animal having a pair of these appendages attached anteriorly is described. Seven dorsoventrally compressed, partly complete individuals of a similar animal that had a different pair of appendages (‘F’ of Briggs 1979) attached anteriorly are described, together with two obliquely compressed individuals that are thought to be conspecific. Surrounding the mouth of this latter species is a circlet of plates identical with the supposed medusoid coelenterate Peytoia nathorsti ; this species is referred to Anomalocaris; Laggania is a junior synonym. As now understood, Anomalocaris was an animal that reached a length of 0.5 m, the elongate body having a head region bearing one pair of large, lateral eye lobes, each borne on a short stalk, the single pair of appendages attached at the ventral, anterior margin. The 13 segments of the appendage in A. canadensis bore paired spines on the inner side, short spines on the outer side, and there was a terminal, spinose 14th segment. The appendage in A. nathorsti consisted of 11 segments, the 2nd to 10th bearing on the inner side a graduated series of spinose blades, and spines on the lateral and outer sides, the terminal 11th segment ending in a group of spines. The circlet of plates surrounding the mouth was situated ventrally on the head region immediately behind the appendages; the plates bore teeth and the circlet constituted a jaw mechanism; additional groups of spines were present in the buccal cavity. Beneath the head region, behind the mouth, were three pairs of semicircular flaps, strongly overlapping: on the tapering trunk were 11 pairs of triangular lateral lobes, widest at the mid-length of the trunk, reduced progressively in size backward. These lobes were strongly overlapping in the same sense as the flaps on the head, and attached low on the sides. The trunk termination was short and blunt, without any projecting spine or lobe. Attached to the side of the body, above each flap and lateral lobe, was a multi-lamellar structure, apparently a gill. A thin cuticle covered the head region dorsally, and ventrally around the appendages and jaw circlet, behind this becoming a lateral strip that narrowed backward. It is suggested that a thin cuticle covered the trunk region dorsally and hung down beside the gills; this covering may have been continuous, but possibly was divided into tergites. Irregular patches of apatite, and some matrix, occur in the trace of the alimentary canal, which extended to the tip of the trunk. Mineralized patches occur in association with the gills, and as transverse strips, presumed traces of some internal organ or structure. The cuticle of the appendages and jaw circlet was presumably stout, hence these parts of the body were more resistant to decay and so were preserved in isolation. The thin cuticle of the lateral lobes shows rays which were presumably thicker and strengthening in function. We suggest that this animal, the largest known from Cambrian rocks, swam by using the series of closely spaced lateral lobes essentially as a lateral fin along which waves of motion were propagated. If the waves were moved in either the same, or opposite, sense on each side, considerable manoeuvrability would have resulted. The anterior pair of appendages, and jaw mechanism, would have made Anomalocaris a formidable predator, particularly on soft-bodied benthos including the abundant arthropods without a mineralized exoskeleton. No fragments of hard parts have been observed in the gut, but there is evidence that it may have inflicted wounds on trilobites. Anomalocaris was a metameric animal, and had one pair of jointed appendages and a unique circlet of jaw plates. We do not consider it an arthropod, but the representative of a hitherto unknown phylum. It is best known from A. nathorsti , the single specimen of A. canadensis having a different appendage but the rest of the body similar, probably including the jaw circlet. The evidence is insufficient to reach any conclusion on whether or not these two 9species9 may be sexual dimorphs of a single species. The single specimen of Amiella ornata is redescribed. It shows what may be lateral lobes like those of Anomalcris, but other features unlike it. We conclude that this specimen is not an example of Sidneyia inexpectans , and is too incomplete for its relationship to be determined.

The Largest Cambrian Animal, Anomalocaris, Burgess Shale, British Columbia

Lists of families and genera of trilobites from the stratigraphical series of the Ordovician have been compiled, using information considered adequate from various areas in the world. Dissimilarities between these faunas have been assessed at both generic and family level, using Simpson's index. These indices have been analysed by a non-metric multidimensional scaling technique, and the groupings revealed are interpreted as indicating faunal provinces. Four provinces are recognized in the Lower Ordovician, the faunal characteristics and geographical extent of three of them (the Bathyurid, Asaphid and Selenopeltis provinces) being as previously described. A fourth province, here named the Asaphopsis province, is proposed for South American and Australian faunas in the Arenig and Llanvirn; the affinities of faunas from southeast Asia are indeterminate. In the Caradoc, faunas from areas occupied earlier by Bathyurid, Asaphid and Asaphopsis faunas, together with trilobites from south-east Asia, constitute a single province, here named the Remopleuridid. The Selenopeltis province persists in southern Europe and North Africa. These two provinces are recognizable only by a generic analysis in the Ashgill, and the latest faunas of that series are world-wide. It is assumed that a faunal province originally extended over parts of a single continental mass (cf. Wilson 1966), and that migration between provinces is inhibited by width of seas or temperature differences. An assemblage of continental masses consistent with these assumptions, and with palaeomagnetic data, is proposed to give four palaeogeographical maps for the Ordovician period. The position of the proto-Atlantic ocean proposed by Wilson (1966), and Gondwanaland of McElhinney & Luck (1970), are accepted; the remainder of Eurasia is divided into four blocks. The maps suggest relative movements between continental blocks that may have removed barriers to migration and resulted in progressive merging of the faunal provinces. They are models to be tested against distributions of other animal groups, new palaeomagnetic and palaeoclimatic evidence, and theories on lithosphere plates. The geographical reconstructions imply that the faunas of South America, southern Europe and North Africa inhabited cool waters, those of North America, northern Europe, north-east Asia, south-east Asia and Australia, warm waters. Cooler water faunas appear to have been less diverse. Decreasing provinciality of faunas during the Ordovician appears to have been accompanied by a reduction in total diversity; supposed climatic deterioration does not seem to have resulted in increased diversity. The differences between contemporaneous faunas within the Bathyurid and Remopleuridid provinces are investigated, and are shown to reflect differences in environment and evolution and diversification of groups of trilobites which took place in these environments.

Ordovician geography and faunal provinces deduced from trilobite distribution

Fifteen specimens of A.pedunculata have been prepared, photographed, and drawn to show how each specimen is interpreted and how portions preserved only in part or counterpart are related to the whole. The body was elongate, sub-cylindrical, bearing one pair of conical, branched anterior appendages inserted in the lateral wall, and ten pairs of short, uniramous limbs; anteriorly no distinct head region, posteriorly the body merged into the bases of the last pair of limbs. The cuticle was unmineralized, flexible, the body wall, anterior appendage and limbs, annulated. On the trunk the evenly spaced annulations were high, sharp-crested dorsally, changing to low and rounded laterally and faint or absent ventrally; dorsally the annulations appear to have borne a row of seven tubercles, each tubercle sharp and possibly spinose apically. One annulation opposite midline of anterior appendage and limbs 1-9, three in the space intervening between these limbs, five between anterior appendage and first limb; posteriorly annulations of trunk formed a continuous series with those of last pair of limbs. This arrangement implies that the body consisted of at least 12 somites. Annulations of the anterior appendage were sharp-crested, uniform in height; branches of the appendage were long, slim, pointed, three at the tip and three along the anterior side, each branch slightly flexible and movable about its base. About ten annulations on each limb, uniform in height, the cross-section varied from low, rounded, to high, sharp-crested, as the limb was extended, contracted or flexed. The tip of the limb was bluntly rounded, on the posterior wall of limbs 1-8, and the anterior wall of limbs 9, 10, was a group of seven curved claws. On limbs 2-8 a forwardly directed spine on the seventh annulation and a shorter spine on the distal annulation, on limbs 9 and 10 a prominent, backwardly directed spine. In front of the anterior appendage the one or two annulations were faint, the anterior end of the body bluntly rounded, the mouth, surrounded by a ring of six or so slim papillae, situated medially on the anterior wall. The alimentary canal is not preserved as a sediment fill, but as a reflective strip, widest adjacent to the mouth, extending back to end between the bases of the last pair of limbs. Sagittal length 1 to 6 cm, smallest similar to largest specimen. Aysheaia pedunculata is one of the rarer animals in the Burgess Shale, occurring in association with arthropods and worms, and to an exceptional extent with sponge fragments. It was not a burrowing, mud-ingesting animal, and the soft body would seemingly make it vulnerable to predatory arthropods. It may have been protected by living amid sponge colonies, the claws having facilitated clinging to the sponge, the anterior appendage holding the suctorial mouth in position to feed on the soft parts. While it shows resemblances to both Onychophora and Tardigrada, it is not placed in either group, nor in any taxon of higher rank than Family Aysheaiidae. It may be regarded as the sole known example of the types of lobopod animals from which the arthropod phylum Uniramia, and the Tardigrada, may have been derived.

The Lobopod Animal Aysheaia pedunculata Walcott, Middle Cambrian, Burgess Shale, British Columbia

Ten almost complete specimens have been studied in detail; nine coming from C. D. Walcott’s original collection, one from the recent re-investigation. The cuticle is preserved as a thin, dark layer; the external surface was apparently smooth, except for striations on the frontal process and adjacent to the mouth. Dorsally on the short cephalon were five eyes, thought to have been compound, the inner and outer pairs pedunculate, the median not stalked. From the anteroventral slope of the cephalon arose a long, flexible frontal process, divisible into a longer, cylindrical proximal portion, and a shorter, broad distal portion. The latter was divided longitudinally, each half bearing a group of long spines, directed inward and forward. The process probably contained a median, fluid-filled canal. The mouth was situated on the vertical, posteroventral wall of the cephalon, the alimentary canal U-shaped. The cylindrical axial region of the trunk tapered slightly backward, the alimentary canal situated ventrally and extending to the tip. The trunk was divided into a main portion of 15 segments, subequal in length, and a short posterior portion lacking segmentation. The junctions between segments gave a limited flexibility to the body. Each segment of the main portion of the trunk bore a pair of thin lateral lobes, directed downward and outward, overlapping, of maximum width medially, the lobes progressively more strongly prolonged backward. Dorsal to lobes 2-15, a paddle-shaped gill was attached near the base of the lobe. The ventral surface of the gill was flat, the outer, dorsal surface bearing imbricated, thin lamellae. The gills lay between adjacent, overlapping lateral lobes. Internally, in the main portion of the trunk what may have been diverticula of the gut are preserved, extending into the proximal portions of the lateral lobes. The posterior portion of the trunk bore three pairs of thin, lobate blades, directed upward and outward, overlapping in the opposite sense to the lateral lobes, the entire structure forming a tail fan. The dorsal margin of the tip of the axial region of the fan appears to have borne a pair of spines. The body is preserved with thin layers of rock between such parts as left and right eyes of a pair, adjacent lateral lobes, between gills and lobes, and between gill lamellae. The parts of the bodies are shown to have been entombed at varied angles to the horizontal bedding planes, and are greatly compressed. It is therefore considered that individuals were trapped in a cloud of sediment in suspension, moving along the sea bottom, and buried as it settled out. If so, the animal was benthonic in habit. Opabinia regalis may have ploughed shallowly in the bottom mud, propelled by movement of the lateral lobes. The eyes are presumed to have been capable of detecting movements in the surrounding waters, and the frontal process to have been used to explore the mud for food and bring it to the backward-facing mouth. The posterior region of the trunk may have aided in producing water currents over the dorsal surface of the body, or have aided in steering if the animal was capable of swimming. No structures that appear to have been antennae, and no other jointed appendages, have been observed, and the gills are not trilobite-like. O. regalis is not considered to have been a trilobitomorph arthiopod, nor is it regarded as an annelid. It may be descended from segmented animals from which arthropod phyla and/or annelids were derived.

The enigmatic animal Opabinia regalis, middle Cambrian, Burgess Shale, British Columbia

The type species of the genus, N. compacta, is described from new preparations and measurements of over 100 specimens from C. D. Walcott's original collection, and 5 from the recent re-investigation. Photographs and explanatory drawings provide the basis for considerations of mode of preservation, and lead to a new reconstruction. The dorsal exoskeleton was divided by a single articulation into two shields, each moderately convex with a raised axial region, the subcircular anterior shield over-lapping for a short distance the longer posterior shield; narrow reflexed doublure on both shields. Dorsal surfaces of shields smooth, without transverse furrows, eyes absent. Axial region of anterior shield widest posteriorly, extending forward to three-quarters length of shield, labrum may have been present under anterior portion. Axial region of posterior shield tapered back, reaching close to posterior margin of shield. Alimentary canal may be preserved filled with sediment, and was probably U-shaped anteriorly, broadest beneath anterior portion of axial region, tapering back to tip of posterior shield. Two types of alimentary diverticula preserved as reflective bands on anterior shield; single trunk of lateral diverticula ran transversely at midlength and ramified beneath lateral region of shield; three pairs of axial diverticula, one per segment, originated behind main trunk of lateral diverticula and ramified in posterior part of axial region. Axial diverticula, one per segment and not ramifying, appear to have been present beneath the axial region of the posterior shield. Paired areas of muscle attachment, preserved as reflective or pyritous areas, are segmentally arranged along the axial region, one pair close together at the anterior extremity. One pair of long, uniramous, multi-jointed antennae was attached beside anterior extremity of axial region, followed by a maximum of 19 pairs of similar biramous appendages, three pairs on the posterior part of the anterior shield, remainder beneath posterior shield. Large triangular coxa strongly spinose on adaxial margin; inner, leg branch of five podomeres and terminal, thorn-like spine; large, spinose endite on proximal podomere. Outer branch arose from abaxial, dorsal margin of coxa, and consisted of slim, tapering shaft with terminal lobe, dorsal margin of shaft bore many long, thin, upward and backwardly directed lamellae. Specimens range in length from 9 to 40 mm, some 40% of the sample being cast dorsal exoskeletons, the remainder whole animals. About one-fifth of the sample bore a posterolateral spine on the anterior shield, rather than having a rounded angle. This difference was recently used to erect two new species, Naraoia halia and N. pammon; here it is taken as the sole evidence of dimorphism in the single species N. compacta. A second species, N. spinifer, is recognized from two poorly-preserved specimens, characterized by seven pairs of lateral spines and a median posterior spine on the margins of the posterior shield; the axial region is poorly defined and appendages virtually unknown. N. compacta is considered to have been a benthonic predator and scavenger, walking, digging and raking in search of food much as did the trilobite Olenoides serratus, and to have had poor swimming powers. The lamellate outer branch of the appendage is regarded as a gill branch, aerated by currents produced when walking and swimming or drifting. There is no evidence of an abdomen or telson, so that N. compacta is a trilobite-like animal lacking the articulated thorax; it is regarded as representing a separate order of class Trilobita.

Harry Blackmore Whittington

Papers

The Largest Cambrian Animal, Anomalocaris, Burgess Shale, British Columbia

Ordovician geography and faunal provinces deduced from trilobite distribution

The Lobopod Animal Aysheaia pedunculata Walcott, Middle Cambrian, Burgess Shale, British Columbia

The enigmatic animal Opabinia regalis, middle Cambrian, Burgess Shale, British Columbia

The Middle Cambrian Trilobite Naraoia, Burgess Shale, British Columbia