Mark A. S. McMenamin

The Early Cambrian worm tube Onuphionella from California and Nevada

Two new species of worm tubes referable to the genus Onuphionella occur in Lower Cambrian strata in eastern California and western Nevada. Onuphionella durhami n. sp. is found in the Campito Formation (in pre-trilobite strata, in the Fallotaspis and, possibly, the Nevadella Zones) and O. claytonensis n. sp. occurs in the Middle Member of the Poleta Formation ( Nevadella Zone). The unusual tubes are armored with an imbricated coat of mica flakes, reminiscent of the modern genus Owenia. The lowest occurrence of Onuphionella in western North America corresponds closely with the lowest occurrence of the genus in the Baltic region, indicating that correlations between the two regions are not greatly in error.

Lower Cambrian trilobites, zonation, and correlation of the Puerto Blanco Formation, Sonora, Mexico

-The Lower Cambrian sequence south of the town of Caborca in northwestern Sonora, Mexico, has yielded the trilobites Nevadia ovalis n. sp. and Judomia orbis n. sp., plus an incomplete fallotaspid cephalon. The Nevadella Zone of Fritz (1972) can now be recognized in the Puerto Blanco Formation, and fossils from the middle part of the formation strongly suggest the presence of the Fallotaspis Zone. The new fossils permit improved correlation of the Mexican sequence to sections in the United States and to Lower Cambrian stages of China and the Soviet Union.

TWO NEW SPECIES OF THE CAMBRIAN GENUS MICKWITZIA

ABSTRACr-Mickwitziids are a unique group of brachiopods, known exclusively from the Lower Cambrian. Herein are described the new species Mickwitzia lochmana and M. multipunctata; both species are from southwestern North America. Mickwitzia muralensis Walcott, 1913, the largest mickwitziid, is reported here for the first time from the United States. This paper also discusses the distribution of mickwitziids, their shell structure, and the possible functions of mickwitziid punctae.

Self-organization of the Earth's biosphere-geochemical or geophysiological?

We explore the implications of indicating the biospheres self-organization by the trend over time of the net entropic flow from the Earths surface, the actual physical boundary of virtually all biotic mass. This flow, derived from the radiative surface entropy budget, is approximately inversely related to the surface temperature when the solar incident flux remains constant. In the geophysiological (‘gaian’) interpretation, biospheric self-organization has increased with the progressive colonization of the continents and evolutionary developments in the land biota, as a result of surface cooling arising from biotic enhancement of weathering. The key site for this self-organization is at the interface between land and atmosphere, the soil, where carbon is sequestered by its reaction (as carbonic and organic acids) with calcium magnesium silicates. Along with disequilibrium (steady-state) levels of carbon dioxide in the atmosphere, the occurrence of differentiated soil is the critical material evidence for biospheric self-organization, whether it be geophysiological or geochemical (ie., purely result of inorganic reactions). The computed equilibrium levels of carbon dioxide and corresponding equilibrium temperatures in the past are dramatically different from the steady-state levels. With future solar luminosity increase, the biospheric capacity for climatic regulation will decrease, leading to the ending of self-organization some two billion years from now. The Earths surface will then approach chemical equilibrium with respect to the carbonate-silicate cycle.

Climate, Paleoecology and Abrupt Change During the Late Proterozoic: A Consideration of Causes and Effects

This chapter examines the influence of the biosphere on the initiation, and termination of, the glaciations of the late Proterozoic. Recent considerations suggest that the biosphere controlled the timing of the onset of glaciation and also controlled the timing of the end of glaciation. Massive carbonate accumulation and giant stromatolites of the Late Proterozoic, combined with major blooms of phyto-plankton, led to significant drops in the carbon dioxide content of the atmosphere, and forced climate from greenhouse to icehouse conditions. Cryoconites and hyperscums, each with a distinctively adapted cryophilic microbiota, developed during the Proterozoic ice ages and may have been a factor in melting the ice. The Proterozoic Tindir Group, Alaska provides evidence for such a cryophilic microbiota. Only by invoking the activity of such organisms can we explain the rapidity of deglaciation. A propensity to accumulate massive carbonates was present before the glaciation as well as after the deposition of the cap carbonates. Substrate disturbance by burrowing metazoa after the ice ages disrupted the microbial mat component of Proterozoic carbonate sequestration. Stromatolites after the glaciation tend to have porous, clotted and thrombolitic textures instead of evenly laminated textures and would therefore be less effective at retaining carbon dioxide (as carbonate and organic matter) and keeping it out of marine circulation. Newly emergent, burrowing metazoa of the Late Proterozoic eventually halted the development of ice-age inducing conditions, and may have prevented even worse glaciations by releasing hydrocarbons sequestered in seafloor sediment.

A Triassic giant amphipod from Nevada, USA

A giant fossil amphipod Rosagammarus minichiellus n. gen., n. sp. occurs in a Triassic limestone (Luning Formation, west-central Nevada) in association with ichthyosaurs (Shonisaurus sp.) and the deep-water trace fossil Protopaleodictyon ichnosp. Fossil pereion and pereiopod morphology suggest affinities with Acanthogammaridae, a freshwater amphipod family largely endemic to Lake Baikal. The large size (17 cm) of the Triassic amphipod shows that supergiant, deep marine amphipods comparable to modern Alicella gigantea Chevreux, 1899 were extant during the early Mesozoic. By analogy with A. gigantea, R. minichiellus was likely a necrophagous, benthopelagic scavenger that fed on ichthyosaur and other sea floor carcasses. Rosagammarus minichiellus appears to be the oldest known fossil amphipod, extending the known geological range of Amphipoda by at least 170 million years.

Origin and Early Evolution of Predators

Our current knowledge on the origin and early evolution of large predators is summarized by Simon Conway Morris (1999, 153–154) as follows: ...for many years it was claimed that Cambrian marine communities were almost entirely free of predators… the seas were [thought to be] full of suspension-feeders gently swaying in the sea water and deposit feeders calmly digging their way through the sediment. This view is now seen to be far too idyllic, but the story of the rise of predators is still quite tentative. It does appear, however, that in contrast to Cambrian communities those of the Ediacaran were largely free of predators.

Origin of the vertebrate body plan via mechanically biased conservation of regular geometrical patterns in the structure of the blastula.

We present a plausible account of the origin of the archetypal vertebrate bauplan. We offer a theoretical reconstruction of the geometrically regular structure of the blastula resulting from the sequential subdivision of the egg, followed by mechanical deformations of the blastula in subsequent stages of gastrulation. We suggest that the formation of the vertebrate bauplan during development, as well as fixation of its variants over the course of evolution, have been constrained and guided by global mechanical biases. Arguably, the role of such biases in directing morphology-though all but neglected in previous accounts of both development and macroevolution-is critical to any substantive explanation for the origin of the archetypal vertebrate bauplan. We surmise that the blastula inherently preserves the underlying geometry of the cuboidal array of eight cells produced by the first three cleavages that ultimately define the medial-lateral, dorsal-ventral, and anterior-posterior axes of the future body plan. Through graphical depictions, we demonstrate the formation of principal structures of the vertebrate body via mechanical deformation of predictable geometrical patterns during gastrulation. The descriptive rigor of our model is supported through comparisons with previous characterizations of the embryonic and adult vertebrate bauplane. Though speculative, the model addresses the poignant absence in the literature of any plausible account of the origin of vertebrate morphology. A robust solution to the problem of morphogenesis-currently an elusive goal-will only emerge from consideration of both top-down (e.g., the mechanical constraints and geometric properties considered here) and bottom-up (e.g., molecular and mechano-chemical) influences.

Epilogue to the tale of the Triassic amphipod: Rosagammarus McMenamin, Zapata and Hussey, 2013 is a decapod tail (Luning Formation, Nevada, USA)

M. A. S. McMenamin and colleagues described a unique crustacean fossil from the Triassic Luning Formation in west-central Nevada as a new genus and species of amphipod, Rosagammarus minichiellus McMenamin, Zapata and Hussey, 2013. The amphipod identity caused an over-150-million-year ghost range connecting R. minichiellus with the next-oldest fossil amphipods in Eocene amber. The amphipod identity nevertheless failed to stand up to closer scrutiny. Additional preparation of the fossil, coupled with examination using polarized light and electron microscopy revealed that many podomere boundaries of the original interpretation were either artifacts of incomplete exposure of the fossil, or they represented places where the fossil arthropod cuticle had flaked off. The polarized light showed the weathered remnants of the cuticle to be more extensive than originally realized. Examination with a scanning electron microscope and energy-dispersive X-ray analysis showed the cuticle to be at least partially replaced with silica in stark contrast to the calcium carbonate matrix. Elemental mapping revealed that some supposed boundaries between adjacent legs actually had a strong silica signal, suggesting that the silica-replaced cuticle continues beneath the matrix connecting the two legs laterally. The amphipod identity for R. minichiellus is therefore rejected. The fossil is instead proposed to represent the right half of a tail belonging to a lobster-like decapod, with two broad, flat, uropods preserved. Other decapods are known from the Luning Formation, but none with enough detail to meaningfully compare with R. minichiellus . The relatively broad ecological distribution of decapods does not shed any new light on the unique paleoecology of the Luning Formation.

Ammonite fossil portrayed on an ancient Greek countermarked coin

The image on a Greek coin of the second-first century BC is identified as an ammonite fossil and linked to the eponymous Ammon, the Egyptian ram-headed god.