The end of the line: competitive exclusion and the extinction of historical entities

Identifying competitive exclusion at the macroevolutionary scale has typically relied on demonstrating a reciprocal, contradictory response by two co-occurring, functionally similar clades. Finding definitive examples of such a response in fossil time series has proven challenging, however, as has controlling for the effects of a changing physical environment. We take a novel approach to this issue by quantifying variation in trait values that capture almost the entirety of function for steam locomotives (SL), a known example of competitive exclusion from material culture, with the goal of identifying patterns suitable for assessing clade replacement in the fossil record. Our analyses find evidence of an immediate, directional response to the first appearance of a direct competitor, with subsequent competitors further reducing the realized niche of SLs, until extinction was the inevitable outcome. These results demonstrate when interspecific competition should lead to extinction and suggest that clade replacement may only occur when niche overlap between an incumbent and its competitors is near absolute and where the incumbent is incapable of transitioning to a new adaptive zone. Our findings provide the basis for a new approach to analyse putative examples of competitive exclusion that is largely free of a priori assumptions

Distinguishing borings and burrows in intraclasts

Hardgrounds are surfaces of synsedimentarily cemented carbonate beds that form at or near the seafloor. They are concentrated in particular periods of the geological record and their presence is closely linked to main climatic and biological events. For example, it has been proposed that early lithification of carbonate sediments facilitated the substantial increase of biodiversity during the Great Ordovician Biodiversification Event. Thus, identification of hardgrounds forms an integral component in documenting both geological and evolutionary events in the early Palaeozoic. Recognition of hardgrounds, including early Palaeozoic examples, is often not straightforward, usually because they lack encrustations and/or bioeroded grains and clasts. Due to the homogeneous texture of micrite, often bioeroded grains and clasts are hard to find and thus cannot be used for hardground identification. Hiatal surfaces, due to omission, are frequently associated with the development of hard substrate. Hiatal surfaces and hardgrounds are often characterised by occurrences of attached organisms, encrustations, truncation and signs of bioerosion. Borings are key evidence in investigations of hardground development. The unequivocal identification of borings is done through identification of the crosscutting relationship between the proposed boring and a hard substrate such as lithoclasts and/or shells. However, morphological criteria are difficult to use when trying to identify borings or burrows in a homogeneous substrate. Bioeroded hardgrounds and burrows with a micrite halo/lining are subjects to fracturing and reworking, resulting in accumulations of intraclasts in flat-pebble conglomerates (FPC). The recognition of borings and broken burrows with a halo can be challenging in FPC. Using trace fossils preserved in situ and in FPC in the late Cambrian carbonates of North China, we established a set of criteria for distinguishing borings from burrows with a halo in FPC. Features such as the relative volume of burrows and borings versus the host pebble and the number of traces per pebble, the cross-cutting relationship with laminae of different colour, and the presence of pyrite or glauconite encrustations can all be used for the recognition of borings. However, examination of the crosscutting relationship and encrustation are not sufficient on their own. Our results suggest caution by defining borings in FPC, particularly as synsedimentary deformation of burrows with a halo in the late Cambrian FPC can create structures similar to borings

The morphological disparity, ecological evolution and palaeobiogeography of Palaeozoic hyoliths

Hyolitha is a group of extinct invertebrates, the most dominant benthic animals within the Cambrian evolutionary fauna and forming a part of the Palaeozoic evolutionary fauna. Hyoliths are generally divided into two groups, Orthothecida and Hyolithida. They originated in the Terreneuvian and experienced a rapid diversification during the Cambrian Explosion but reached a diversity bottleneck during the Cambrian extinction (Sinsk Event). Hyoliths were characterised by low disparity beginning from the Ordovician and got extinct in the Permian. Factors that affected the evolutionary pattern of Palaeozoic hyoliths from the early domination period up to extinction are poorly known. Herein, we collected material on 148 Palaeozoic hyolith genera from around the world and documented their key morphological characters and distributions. Combined with the phylogenetic analysis based on a matrix of morphological characters, the nonmetric multidimensional scaling (NMDS) using the Paleontological Statistics Software Package, and palaeobiogeographical data, we intended to analyse the biodiversity changes during the evolutionary history of hyoliths and uncover the influence of morphological selectivity in different palaeoenvironments, from the Cambrian to the Permian. Our results showed that the Cambrian taxa occupied quite a different morphospace compared to that of the OrdovicianâPermian assemblages. The morphology of the early Cambrian hyoliths was mainly simple, comprising long conical weakly ornamented tubes. They radiated worldwide during the Cambrian âEpoch 2â, reaching high disparity and diversity, but faced a disadvantageous situation after the mid-Cambrian. The younger genera with strong ornamentation usually showed low diversity and provincialism during the Ordovician. The morphological shift from a simple conical tube morphology with weak ornamentation (orthothecids of the early Cambrian) to a complex morphology with distinct venter and dorsal pyramidal conch and strong ornamentation from the late Cambrian up to the Permian reflects ecological evolution of the hyoliths. This was accompanied by a change of their feeding habits from active deposit-feeding to passive suspension/filter feeding and change in conch configuration from rheophilic to non-rheophilic

When lingulid brachiopods became infaunal(?) – perspectives from the morphological and anatomical information

Morphology usually serves as an effective proxy for functional ecology, and the evaluation of morphological, anatomical, and ecological changes allows for a deeper understanding of the nature of diversification and macroevolution. Lingulid (Order Lingulida) brachiopods were diverse and abundant during the early Palaeozoic, but decreased in diversity over time, with only a few genera of linguloids and discinoids present in modern marine ecosystems, frequently referred to as âliving fossilsâ. The dynamics that drove this decline remain unclear and it has not been determined if there is an associated decline in morphological and ecological diversity. We applied geometric morphometrics to reconstruct global morphospace occupied by lingulid brachiopods through the Phanerozoic, with results showing that maximum morphospace occupation was reached in the Early Ordovician. At this time of peak diversity, linguloids with sub-rectangular shells already possessed several evolutionary features common to all modern infaunal forms such as the rearrangement of mantle canals and reduction of the pseudointerarea. The end-Ordovician mass extinction had a differential effect on linguloids, disproportionally wiping out those with rounded shells whilst forms with sub-rectangular shells survived both the end-Ordovician and the PermianâTriassic mass extinctions, with post-extinction faunas predominantly composed of infaunal forms. For discinoids, both morphospace occupation and epi-benthic life strategies remain consistent through the Phanerozoic. Analysis of the morphospace occupation of lingulids over time, taking into account their body size, anatomical features and ecological changes, suggests that the reduced morphological and ecological diversity observed in modern lingulid brachiopods reflects evolutionary contingency rather than deterministic processes

Foraminiferal fauna and biotopes of a barrier estuary system : St Georges Basin, New South Wales, Australia

A 66-sample study of estuarine foraminifera within St Georges Basin identified 30 species from three biotopes that are divided almost equally in diversity between calcareous and agglutinated forms. The latter, however, are twice as abundant as the former, and the species Amnwhaculites exiguus, Portatrochammina sorosa, Rhumblerella subconica, and Ammonia aoteana represent 78% of the fauna. The main driver of biotope distribution is water depth or factors related to it. Faunal composition and biotope distribution are similar to those found in other estuaries in the region, suggesting the possibility of a "standard fauna" for Australian estuaries with limited connections to the open ocean.14 page(s

Spatial patterns and diversity of foraminifera from an intermittently closed and open lagoon, Smiths Lake, Australia

Foraminifera represent an important tool for assessing and monitoring the past, present and future relative health of marine systems, but this is only possible where baseline assemblage characteristics have been previously established. This type of baseline data is currently lacking for intermittently closed and open lakes or lagoons (ICOLL). ICOLLs are estuarine environments that are isolated from the open ocean for much of the time, but are subject to distinct periods of tidal exchange and large fluctuations in hydrodynamic factors when the barrier that isolates the ICOLL is opened to the sea. This study provides new data on diversity and distribution of foraminifera from Smiths Lake, an ICOLL on the Australian eastern coastline. Environmental parameters were measured to identify potential abiotic controls on the distribution and relative abundance of assemblages and individual taxa. Results indicate that, whilst the Smiths Lake assemblage is largely similar to foraminifera assemblages found in estuaries consistently open to the sea, it can be differentiated based upon lower species richness and a lack of calcareous taxa, even in the seaward parts of the lagoon. Parameters associated with depth, including sediment grain size and nutrient supply, are identified as significant controls on both assemblage distribution and the relative abundance of common taxa in Smiths Lake. ICOLLs are considered extremely sensitive to anthropogenic activities and these results represent an important potential tool in ICOLL management.13 page(s

Reply to Aze et al. : distinguishing speciation modes based on multiple lines of evidence

1 page(s

Assessing the role of cladogenesis in macroevolution by integrating fossil and molecular evidence

Assessing the extent to which population subdivision during cladogenesis is necessary for long-term phenotypic evolution is of fundamental importance in a broad range of biological disciplines. Differentiating cladogenesis from anagenesis, defined as evolution within a species, has generally been hampered by dating precision, insufficient fossil data, and difficulties in establishing a direct link between morphological changes detectable in the fossil record and biological species. Here we quantify the relative frequencies of cladogenesis and anagenesis for macroperforate planktic Foraminifera, which arguably have the most complete fossil record currently available, to address this question. Analyzing this record in light of molecular evidence, while taking into account the precision of fossil dating techniques, we estimate that the fraction of speciation events attributable to anagenesis is <19% during the Cenozoic era (last 65 Myr) and <10% during the Neogene period (last 23 Myr). Our central conclusion-that cladogenesis is the predominant mode by which new planktic Foraminifera taxa become established at macroevolutionary time scales-differs markedly from the conclusion reached in a recent study based solely on fossil data. These disparate findings demonstrate that interpretations of macroevolutionary dynamics in the fossil record can be fundamentally altered in light of genetic evidence.6 page(s