The shape of life: how much is written in stone?

Summary Considering the enormous diversity of living organisms, representing mostly untapped resources for studying ecological, ontogenetic and phylogenetic patterns and processes, why should evolutionary biologists concern themselves with the remains of animals and plants that died out tens or even hundreds of millions of years ago? The reason is that important new insights into some of the most vexing evolutionary questions are being revealed at the interfaces of palaeontology, developmental biology and molecular biology. Attempts to synthesise information from these disciplines, however, often encounter their greatest hurdles in considerations of the radiation of the Metazoa. Ongoing challenges relate to the origins of body plans, the relationships of the metazoan phyla and the timing of major evolutionary radiations. Palaeontology not only has its own unique contributions to the study of evolutionary processes, but provides a lynchpin for many of the emerging techniques

A modern assessment of Ordovician chitinozoans from the Shelve and Caradoc areas, Shropshire, and their significance for correlation

New chitinozoan data are presented from the classical section along the Onny River in the type Caradoc area, and from the deeper-water sections in the Shelve area, including the former British candidate GSSP for the base of the Upper Ordovician Series. The rich and well-preserved chitinozoan fauna of the Onny River has been a standard for 40 years, but new data revise some of the identifications. The assemblages are now attributed to biozones that are more readily applicable for international cor relation. The main part of the section can be inter preted as belonging to the originally Baltoscandian Spinachitina cervicornis Biozone, although this is uncertain in the lower part. Within this biozone, the Fungochitina actonica Subzone has been defined. The Onny Formation at the top of the section is equated with the Acanthochitina latebrosa–Ancyrochitina onniensis Biozone; contrary to earlier reports, Acanthochitina barbata is absent. The Lower Wood Brook and Spy Wood Brook section from the Shelve Inlier yielded a great number of moderately to well-preserved chitinozoans, but a low-diversity assemblage. Their ranges have been neatly positioned against the well-known graptolite stratigraphy in the area. A local Eisenackitina rhenana Biozone? has been recognized, allowing us to suggest some international cor relations

Compilation and Network Analyses of Cambrian Food Webs

A rich body of empirically grounded theory has developed about food webs—the networks of feeding relationships among species within habitats. However, detailed food-web data and analyses are lacking for ancient ecosystems, largely because of the low resolution of taxa coupled with uncertain and incomplete information about feeding interactions. These impediments appear insurmountable for most fossil assemblages; however, a few assemblages with excellent soft-body preservation across trophic levels are candidates for food-web data compilation and topological analysis. Here we present plausible, detailed food webs for the Chengjiang and Burgess Shale assemblages from the Cambrian Period. Analyses of degree distributions and other structural network properties, including sensitivity analyses of the effects of uncertainty associated with Cambrian diet designations, suggest that these early Paleozoic communities share remarkably similar topology with modern food webs. Observed regularities reflect a systematic dependence of structure on the numbers of taxa and links in a web. Most aspects of Cambrian food-web structure are well-characterized by a simple “niche model,” which was developed for modern food webs and takes into account this scale dependence. However, a few aspects of topology differ between the ancient and recent webs: longer path lengths between species and more species in feeding loops in the earlier Chengjiang web, and higher variability in the number of links per species for both Cambrian webs. Our results are relatively insensitive to the exclusion of low-certainty or random links. The many similarities between Cambrian and recent food webs point toward surprisingly strong and enduring constraints on the organization of complex feeding interactions among metazoan species. The few differences could reflect a transition to more strongly integrated and constrained trophic organization within ecosystems following the rapid diversification of species, body plans, and trophic roles during the Cambrian radiation. More research is needed to explore the generality of food-web structure through deep time and across habitats, especially to investigate potential mechanisms that could give rise to similar structure, as well as any differences

Late Ordovician trilobites from southern Thailand

Volume: 40Start Page: 397End Page: 44

Morphology and ontogeny of an Early Devonian Phacopid Trilobite with reduced sight from Southern Thailand

International audienc

The best of two worlds - : the Late Ordovician trilobites of the Taimyr Peninsula, Arctic Russia

mportant occurrences of Late Ordovician trilobites of the Taimyr Peninsula, Arctic Russia have been known for nearly 70 years through the work of Balashova (1959/1960) but have been neither well-understood nor revised. A study and revision of 56 Sandbian-Katian species from the Peninsula, including new and previous described material, gives a clear picture of their diversity and distributionfor the first time. The new material is well-preserved and constrained stratigraphically, while the original Balashova specimens are more incomplete and from isolated finds made during mapping in the 1950’s. A new monorakine subgenus and seven new species are recognized in press. Previously thought to be an endemic, Taimyraspisis shown to be an ityophorid close to Effnaspis, Yumenaspis, Ityophorus, and Frognaspis from Laurentia, Baltica and China. The monotypic Goldillaenoides is shown to be close to Failleana. The remopleuridid Pararemopleuridesis recognized for the first time in Taimyr, a genus with other possible occurrences including China, North-eastern Russia and Australia. The genus may be closely related to Robergiella Whittington. Two new species of Robergia prompted a re-investigation of the type species which revealed the presence of a narrow anterior border. This finding suggests that the concepts of Robergia and Pugilator Nikolaisen must be revised. A new species of Dionide is exceptional in having about 30 axial rings on the pygidium. It is found in dark sediments suggestive of a depletion of oxygen at the sea floor, and the high number of segments with accompanied limb pairs and gills may reflect an adaption to such an environment. Eight species of monorakines are described, but while Ceratevenkaspis dominates Monorakos is apparently absent from the Taimyr Peninsula. Seven species of isoteline asaphids are recognized, but with the exception of Homotelus only very fragmentary material is available. Our study clearly distinguishes between two biofacies in the Upper Ordovician. The first is a widespread raphiophorid association found in marginal shelf areas of low latitude Ordovician palaeocontinents. Taxa include Ampyxella, Ampxyina, Failleana, Pararemopleurides, Raymondella, Remopleurides, Robergia, Stygina, Taimyraspis, and Toernquistia. The second biofacies is the shallow shelf monorakine-cheirurid-illaenid association with Carinopyge, Ceratevenkaspis and Evenkaspis, endemic to the Siberian Platform, as well as seven isoteline taxa, Achatella, Ceraurinus¸ Denella?, Whittakerites, and Xylabion otherwise typical of inshore Laurentia. From a biogeographical and palaeogeographic point of view, Taimyr is placed marginally to the Siberian Platform during the later Ordovician

The best of two worlds - : the Late Ordovician trilobites of the Taimyr Peninsula, Arctic Russia

mportant occurrences of Late Ordovician trilobites of the Taimyr Peninsula, Arctic Russia have been known for nearly 70 years through the work of Balashova (1959/1960) but have been neither well-understood nor revised. A study and revision of 56 Sandbian-Katian species from the Peninsula, including new and previous described material, gives a clear picture of their diversity and distributionfor the first time. The new material is well-preserved and constrained stratigraphically, while the original Balashova specimens are more incomplete and from isolated finds made during mapping in the 1950’s. A new monorakine subgenus and seven new species are recognized in press. Previously thought to be an endemic, Taimyraspisis shown to be an ityophorid close to Effnaspis, Yumenaspis, Ityophorus, and Frognaspis from Laurentia, Baltica and China. The monotypic Goldillaenoides is shown to be close to Failleana. The remopleuridid Pararemopleuridesis recognized for the first time in Taimyr, a genus with other possible occurrences including China, North-eastern Russia and Australia. The genus may be closely related to Robergiella Whittington. Two new species of Robergia prompted a re-investigation of the type species which revealed the presence of a narrow anterior border. This finding suggests that the concepts of Robergia and Pugilator Nikolaisen must be revised. A new species of Dionide is exceptional in having about 30 axial rings on the pygidium. It is found in dark sediments suggestive of a depletion of oxygen at the sea floor, and the high number of segments with accompanied limb pairs and gills may reflect an adaption to such an environment. Eight species of monorakines are described, but while Ceratevenkaspis dominates Monorakos is apparently absent from the Taimyr Peninsula. Seven species of isoteline asaphids are recognized, but with the exception of Homotelus only very fragmentary material is available. Our study clearly distinguishes between two biofacies in the Upper Ordovician. The first is a widespread raphiophorid association found in marginal shelf areas of low latitude Ordovician palaeocontinents. Taxa include Ampyxella, Ampxyina, Failleana, Pararemopleurides, Raymondella, Remopleurides, Robergia, Stygina, Taimyraspis, and Toernquistia. The second biofacies is the shallow shelf monorakine-cheirurid-illaenid association with Carinopyge, Ceratevenkaspis and Evenkaspis, endemic to the Siberian Platform, as well as seven isoteline taxa, Achatella, Ceraurinus¸ Denella?, Whittakerites, and Xylabion otherwise typical of inshore Laurentia. From a biogeographical and palaeogeographic point of view, Taimyr is placed marginally to the Siberian Platform during the later Ordovician

Early Ordovician trilobites, Nora Formation, central Australia

Volume: 27Start Page: 315End Page: 36

Extraordinary Ordovician trilobite Fantasticolithus gen. nov. from Peru and its bearing on the trinucleimorph hypothesis

Fantasticolithus isabelae, a new genus and species of trinucleid trilobite from the Lower Ordovician of Peru, developed anterior ventral cephalic ‘props’ that are unique in the Trilobita. Its broad and finely pitted genal prolongations are unlike those of any previously known trinucleid, and closely resemble those invariably present in the unrelated Family Harpetidae, supporting the hypothesis that the two families shared a similar mode of life, as ‘trinucleimorphs’. Fantasticolithus was probably derived from an early trinucleid with a marginal girder, although it resembles younger genera such as Marrolithus in its enlarged anterolateral pits. The new genus provides a natural experiment to test the hypothesis of trinucleimorphs as filter feeders that used a ventral feeding chamber. The role of the pitted marginal fringe as an egress for feeding currents is discussed. Fantasticolithus had an unusual anterior vent that provided a simpler exit mechanism for feeding currents than the pitted fringe. However, the pits were probably important for trinucleids that lacked an anterior arch