Terminal addition, the Cambrian radiation and the Phanerozoic evolution of bilaterian form (original) (raw)
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Molecular Phylogenetics and Evolution, 2002
The study of metazoan evolution has fascinated biologists for centuries, and it will certainly keep doing so. Recent interest on the origin of metazoan body plans, early metazoan evolution, genetic mechanisms generating disparity and diversity, molecular clock information, paleontology, and biogeochemistry is contributing to a better understanding of the current phyletic diversity. Unfortunately, the pattern of the metazoan tree of life still shows some important gaps in knowledge. It is the aim of this article to review some of the most important issues related to the inference of the metazoan tree, and point towards possible ways of solving certain obscure aspects in the history of animal evolution. A new hypothesis of the metazoan diversification during the Cambrian explosion is proposed by synthesizing ideas from phylogenetics, molecular evolution, paleontology, and developmental biology. Ó
The problem of early bilaterian evolution.
In: Ruiz-Omeñaca, J. I., Piñuela, L. & García-Ramos, J. C. (eds.) Libro de Resúmenes. XXIV Jornadas de la Sociedad Española de Paleontología. Museo del Jurásico de Asturias (MUJA), Colunga, 15-18 de octubre de 2008. MUJA, Colunga, 227-228. ISBN: 978-84-691-6581-2., 2008
From Vendian to Cambrian: the beginning of morphological disparity of modern metazoan phyla
Russian Journal of Developmental Biology, 2010
Continuity of the transition from Precambrian to the Phanerozoic metazoan fauna at the phylum level is analyzed. The discrete traces of feeding on bacterial mats by Dickinsonia and similar organisms are explained by extracorporeal digestion, characteristic of a placozoan level of organization, as in the extant Trichoplax. The absence of a morphologically developed anterior end of the body, of food-gathering
The cambrian evolutionary ?explosion? recalibrated
BioEssays, 1997
The sudden appearance in the fossil record of the major animal phyla apparently records a phase of unparalleled, rapid evolution at the base of the Cambrian period, 545 Myr ago. This has become known as the Cambrian evolutionary 'explosion', and has fuelled speculation about unique evolutionary processes operating at that time. The acceptance of the palaeontological evidence as a true reflection of the evolutionary narrative has been criticised in two ways: from a reappraisal of the phylogenetic relationships of the early fossils, and from predictions of molecular divergence times, based on six appropriate metazoan genes. Phylogenetic analysis of the arthropods implies an earlier, Precambrian history for most clades, and hence an extensive period of cladogenesis unrecorded by fossils. A similar argument can be applied to molluscs, lophophorates and deuterostomes. Molecular evidence implies divergence between clades to at least 1000 Myr ago. The apparent paradox between the sudden appearance of recognisable metazoans and their extended evolutionary history might be explained by a sudden Cambrian increase in body size, which was accompanied by skeletisation. A new paradigm suggests that the 'explosion' Accepted in the record may have been decoupled from the evolutionary innovation.
Paleotorus: The Laws of Morphogenetic Evolution
2009
This book aims to address the deficiencies of contemporary evolution studies by evaluating Multi-Torus or Morphogenetic Torus Theory using the fossil record. The book begins with description of and discussion of one of most recently recognized members of the Ediacaran biota, a fossil that looks astonishingly like a fossilized morphogenetic torus. This is followed by evaluation a newly discovered giant trilobite with characteristics that appear to support toroidal morphogenesis theory. The book then looks at an application of the model to scleritome theory (i.e., the theory of shell evolution) and to the Cambrian origin of mollusks and brachiopods, and as a result will develop a new and powerful dual application of torus scleritome theory. Next follows focus on the early development of cephalopods and a new variant of the torus called hypertorus. Finally, the book considers a counterexample to toroidal morphogenesis in the growth of marine microbes known as foraminifera. Using a newly discovered foraminiferal microbiota (that turns out to be exactly contemporary with the new giant trilobite), the book explores the metacellular/chambering style of morphogenesis that stands in direct contrast to toroidal morphogenesis as a parallel morphogenetic system.
Small bilaterian fossils from 40 to 55 million years before the cambrian
Science (New York, N.Y.), 2004
Ten phosphatized specimens of a small (<180 micrometers) animal displaying clear bilaterian features have been recovered from the Doushantuo Formation, China, dating from 40 to 55 million years before the Cambrian. Seen in sections, this animal (Vernanimalcula guizhouena gen. et sp. nov.) had paired coeloms extending the length of the gut; paired external pits that could be sense organs; bilateral, anterior-posterior organization; a ventrally directed anterior mouth with thick walled pharynx; and a triploblastic structure. The structural complexity is that of an adult rather than a larval form. These fossils provide the first evidence confirming the phylogenetic inference that Bilateria arose well before the Cambrian.
Proceedings of the National Academy of Sciences, 2002
The trace fossil record is important in determining the timing of the appearance of bilaterian animals. A conservative estimate puts this time at Ϸ555 million years ago. The preservational potential of traces made close to the sediment-water interface is crucial to detecting early benthic activity. Our studies on earliest Cambrian sediments suggest that shallow tiers were preserved to a greater extent than typical for most of the Phanerozoic, which can be attributed both directly and indirectly to the low levels of sediment mixing. The low levels of sediment mixing meant that thin event beds were preserved. The shallow depth of sediment mixing also meant that muddy sediments were firm close to the sediment-water interface, increasing the likelihood of recording shallow-tier trace fossils in muddy sediments. Overall, trace fossils can provide a sound record of the onset of bilaterian benthic activity.