Engineering the Cambrian explosion: the earliest bioturbators as ecosystem engineers

By applying modern biological criteria to trace fossil types and assessing burrow morphology, complexity, depth, potential burrow function and the likelihood of bioirrigation, we assign ecosystem engineering impact (EEI) values to the key ichnotaxa in the lowermost Cambrian (Fortunian). Surface traces such as Monomorphichnus have minimal impact on sediment properties and have very low EEI values; quasi-infaunal traces of organisms that were surficial modifiers or biodiffusors, such as Planolites, have moderate EEI values; and deeper infaunal, gallery biodiffusive or upward-conveying/downward-conveying traces, such as Teichichnus and Gyrolithes, have the highest EEI values. The key Cambrian ichnotaxon Treptichnus pedum has a moderate to high EEI value, depending on its functional interpretation. Most of the major functional groups of modern bioturbators are found to have evolved during the earliest Cambrian, including burrow types that are highly likely to have been bioirrigated. In fine-grained (or microbially bound) sedimentary environments, trace-makers of bioirrigated burrows would have had a particularly significant impact, generating advective fluid flow within the sediment for the first time, in marked contrast with the otherwise diffusive porewater systems of the Proterozoic. This innovation is likely to have created significant ecospace and engineered fundamentally new infaunal environments for macrobiotic and microbiotic organisms alike

Maps of complex motion selectivity in the superior temporal cortex of the alert macaque monkey: a double-label 2-deoxyglucose study

The superior temporal sulcus (STS) of the macaque monkey contains multiple visual areas. Many neurons within these regions respond selectively to motion direction and to more complex motion patterns, such as expansion, contraction and rotation. Single-unit recording and optical recording studies in MT/MST suggest that cells with similar tuning properties are clustered into columns extending through multiple cortical layers. In this study, we used a double-label 2-deoxyglucose technique in awake, behaving macaque monkeys to clarify this functional organization. This technique allowed us to label, in a single animal, two populations of neurons responding to two different visual stimuli. In one monkey we compared expansion with contraction; in a second monkey we compared expansion with clockwise rotation. Within the STS we found a patchy arrangement of cortical columns with alternating stimulus selectivity: columns of neurons preferring expansion versus contraction were more widely separated than those selective for expansion versus rotation. This mosaic of interdigitating columns on the floor and posterior bank of the STS included area MT and some neighboring regions of cortex, perhaps including area MST

Late time tails from momentarily stationary, compact initial data in Schwarzschild spacetimes

An L-pole perturbation in Schwarzschild spacetime generally falls off at late times t as t^{-2L-3}. It has recently been pointed out by Karkowski, Swierczynski and Malec, that for initial data that is of compact support, and is initially momentarily static, the late-time behavior is different, going as t^{-2L-4}. By considering the Laplace transforms of the fields, we show here why the momentarily stationary case is exceptional. We also explain, using a time-domain description, the special features of the time development in this exceptional case.Comment: 7 pages, 5 figure