Why Are Heterotrophs Rare In Proterozoic Rocks

Porter and Knoll (2000) offered two reasons why few, if any, heterotrophs are found in rocks older than 770-800 Ma (when VSMs first appear). The first is that heterotroph diversity may have been low due to limited primary productivity in Mesoproterozoic oceans. Evidence for limited productivity during this interval comes primarily from theoretical arguments. Anbar and Knoll (2002), for example, have argued that if Mesoproterozoic oceans were anoxic and sulfidic below the mixed layer (Canfield,...

Introduction

Paleobiological study of the Phanerozoic and the Precambrian largely developed as separate cultures during the 20th century. This was primarily because the presence of common body fossils with mineralized skeletons S. Xiao and A.J. Kaufman (eds.), Neoproterozoic Geobiology and Paleobiology, 91-114. 2006 Springer. typical of the Phanerozoic allowed certain types of science, such as biostratigraphy and benthic paleoecology, to be done that was not feasible in the Precambrian. However, as fossils...

Planolites Palaeophycus

These are short horizontal or oblique trace fossils without a distinct meandering pattern and represent some of the more widely reported Phanerozoic trace fossils. This type of trace fossil presents problems in terms of interpretation and naming. The morphology is sensitive to preservation, often being preserved as only a small fraction of the original burrow. Many papers have dealt with features by which these two ichnotaxa can be distinguished, mainly with Palaeophycus being lined open...

Conclusions

We utilized the published literature to produce an empirical morphospace to describe the evolutionary history of Proterozoic and Cambrian acritarchs. Mean acritarch vesicle diameter displayed non-directional fluctuation through the Proterozoic and decreased significantly across the Ediacaran-Cambrian boundary. The initial increase of morphological disparity preceded the first taxonomic radiation by approximately 500 million years a pattern similar to that seen in Phanerozoic multi-celled...

Treptichnids

These are trace fossils consisting of repeatedly branching curved elements, representing three-dimensional burrow systems (Fig. 2F). In bedding-plane expression this type of trace fossil may show isolated vertical pipes. All Ediacaran reports of this type of trace fossil are in strata that are close to the Ediacaran-Cambrian boundary. The best-constrained occurrence is in Namibia where treptichnids are ca. 548-545 Ma and occur within the stratigraphic range of Cloudina (Jensen et al., 2000)....

Archaeonassatype trace fossils

These are trace fossils with an upper surface that is either bilobed or consists of prominent marginal raised ridges flanking a central area (Fig. 2A). The nature of the base of the trace typically is not known. Similar Ediacaran trace fossils have been identified as Aulichnites (Fedonkin, 1981 Waggoner, 1998), Archaeonassa (Jensen, 2003), or as Sellaulichnus (Fedonkin and Runnegar, 1992). The assignment to Sellaulichnus for this type of trace is doubtful in view of Zhu's (1997) examination of...

Eukaryotes

The relationships of the major lineages of eukaryotes have become much better known during the last decade as more sequence data have been gathered and analyzed (reviewed in Baldauf et al, 2000 Hedges, 2002 Keeling et al., 2005). Because the relationships of single-celled eukaryotes (protists) are intimately tied to the relationships of multicellular eukaryotes (algae, plants, fungi, animals), it is usually more convenient to discuss this subject in terms of overall (higher-level) eukaryote...

Oxygen and the Cambrian explosion

A simple explanation for the Cambrian Explosion is that it records, in a literal sense, the evolutionary diversification (phylogenetic branching) of animal phyla in the latest Proterozoic and early Cambrian (Gould, 1989 Conway Morris, 2000). Alternatively, if the molecular time estimates showing a deep origin of animal phyla in the Proterozoic (e.g., Fig. 3) are correct, then an explanation is required as to why we see an explosion of fossils in the Cambrian, and almost nothing before that...

On the Morphological History of Proterozoic and Cambrian Acritarchs

JOHN WARREN HUNTLEY, SHUHAI XIAO, and MICHAL KOWALEWSKI Department of Geosciences, Virginia Polytechnic Institute and State University, Blacksburg, VA 24061, USA. 2. Materials and 2.2 Body Size 2.3 Morphological Disparity 2.3.2 Non-metric Multidimensional 3.1 Body 3.2 Morphological 3.2.2 Non-metric Multidimensional 4.1 Comparative Histories of Morphological Disparity and Taxonomic Diversity 39 4.2 Linking Morphological Disparity with Geological and Biological Revolutions 40 4.2.1 Morphological...

Anterior Posterior Patterning and Hox and Para Hox Clusters

The Hox genes play a primary role in body patterning. The multiple genes within what is normally a single cluster among bilaterians (although it is two clusters in Drosophila) pattern the same regions of the body as their order on the chromosome, so that the anterior-most part of the developing larvae is controlled by the genes at the 3' end of the cluster, the middle part is pattern by genes in the middle and posterior regions are controlled by the 5' genes, a pattern described as temporal...

Stratigraphic Distribution and Broader Implications of Ediacaran Trace Fossils

Trace fossils appear towards the end of the Ediacaran and probably are younger than 560 Ma (Martin et al., 2000 Droser et al, 2002b Knoll et al, 2004a). The Ediacaran record is strongly dominated by essentially horizontal unbranched forms such as Helminthoidichnites and Helminthopsis (e.g., Narbonne and Aitken, 1990 Droser et al., 1999). These can be assigned to various ichnogenera but all occupy the same position in the sediment, close to the sediment water interface. Among these are forms...

Head Formation and the Evolution of the Central Nervous System

Formation of the anterior aspect of developing bilaterian embryos is closely linked to the formation of the brain and central nervous system, and the extensive evidence of genetic and regulatory homology implies that substantial components of this system were present in the urbilaterian. Apparently conserved elements include brain patterning, connectivity and neural cell specification, involving a large number of separate regulatory pathways. A related problem is the apparent conservation of a...

Opisthokonts

There are two main opisthokont groups the animals and the fungi. The Proterozoic fossil record of animals is worthy of an extensive review in its own right I will not discuss it here except to note that the earliest well accepted evidence for animals are 580 Ma phosphatized embryos from the Doushantuo Formation, China (Xiao et al., 1998b Xiao and Knoll, 2000 Condon et al., 2005). See papers by Jensen et al. and Bottjer and Clapham, both in this volume, for further information on Proterozoic...

Phylogenetic Framework

Understanding the pattern of developmental and morphological change leading to the diversity of existing animal bodyplans and others documented only from the fossil record requires a well-developed phylogenetic framework. Fortunately, combined molecular and morphological data sets have revolutionized our views of metazoan relationships over the past several decades (see recent reviews by Eernisse and Peterson, 2004 Halanych, 2004 Giribet, 2003 Valentine, 2004). The growing number of workers in...

Body Size Analysis

Maximum vesicle diameters were recorded from species descriptions, when available, for all species occurrences. Figure vesicle diameters were measured from microphotographs of acritarchs. Maximum vesicle diameters were used as a proxy for acritarch body size history and figure vesicle diameters were used as a cross-check. Maximum and figure vesicle diameters were log-transformed. Mean maximum vesicle diameters and mean figure vesicle diameters were calculated for each geochronological bin. To...

Development Of The Urbilateria

For a brief period of a year or so the basis of organismic complexity seemed fairly clear. After the C. elegans genome was released in 1998 (C. elegans sequencing consortium, 1998) with over 19,000 genes, it seemed clear that a substantially more complex organism like Drosophila should have perhaps double the number of genes and humans, near the apex of developmental sophistication, must have near 100,000 genes. This neat story began to crumble in 2000 with the announcement that Drosophila...

Gut and Endoderm Formation

The developmental origin of the mouth and anus is the fundamental divide between the protostomes, where the embryonic blastopore forms the mouth and anus, and the deuterostomes, in which it forms the anus and the mouth arises secondarily. This diference provides little reason to expect underlying similarities in developmental mechanisms of gut and endoderm formation, yet surprising similarities have been identified. GATA transcription factors and forkhead have been identified in endoderm in...

Results Body Size

Acritarch Morphology Character

The average maximum vesicle diameter of acritarchs displayed non-directional fluctuation through the Proterozoic Fig. 2 . Acritarch body size decreased significantly across the Neoproterozoic-Paleozoic transition, but had increased significantly by the middle late Cambrian though not to the size seen in the late Neoproterozoic . The average figure vesicle diameter of acritarchs displayed a similar pattern, though at smaller sizes Fig. 2 . Average maximum diameter and average figure diameter are...

Ediacaran Trace Fossil Diversity

Trace fossils are given binomial names using the Linnean nomenclature system. No better alternative has been suggested and some form of label is needed for communication. Ichnotaxa have been repeatedly used as a measure in search of evolutionary or ecological trends, such as the colonization of the deep sea Orr, 2001 Uchman, 2003 . It is, however, important to understand what is entailed in an ichnotaxon. There is a broad consensus among trace fossil workers that trace fossil taxa ichnogenera...

Radulichnus

Paired fine ridges, arranged in fans and occasionally associated with Kimberella in South Australia and the White Sea region represent structures analogous to mollusk radula-type grazing Gehling, 1996 Seilacher, 1995, 1997 Fedonkin, 2003 Seilacher et al, 2003, 2005 Gehling et al, 2005 . The animal was located at the apex of the fan from which it appears to have scraped biomats with an extensible proboscis Gehling et al., 2005 . This trace fossil is broadly analogues to the rasping trace fossils...

List Of Ediacaran Trace Fossils

The list of Ediacaran trace fossils presented in Table 1 includes the main reports of Ediacaran trace fossils known to us. We are under no illusion that this constitutes a complete listing of Ediacaran trace fossils and it is certainly weaker in some geographic areas. The list does not include occurrences that have only been reported from abstracts. Taxa that are generally considered body fossils but for which a trace fossil interpretation has been discussed, such as Beltanelliformis and...

Galen P Halverson

Laboratoire des M canismes et Transferts en G ologie, Universit Paul Sabatier, 31400 Toulouse, France. Present Address Geology and Geophysics, School of Earth and Environmental Sciences, The University of Adelaide, Adelaide 5005, South Australia, Australia. 2. Constructing the 2.1 The Neoproterozoic Sedimentary 2.2 The 813C 2.3 Bases for 3. Review of the 3.1 The Tonian 1000-720 Ma 3.2. The Cryogenian 720 -635 Ma .2.1. The Sturtian 3.2.2. The 3.2.3. The Marinoan 3.3. The Ediacaran Period 635-542...

Palaeopascichnustype fossils

Palaeopascichnus and numerous other similar forms are some of the more familiar structures that should be removed from the tally of Ediacaran trace fossils Haines, 1990 Gehling et al., 2000 Jensen, 2003 Seilacher et al., 2003 Shen et al., in press . The exact morphology and affinities of these organisms are still unclear. Gehling et al. 2000 found tantalizing if inconclusive connections to Aspidella, whereas Seilacher et al., 2003 linked them to xenophyophoran protists. Palaeopascichnus...

Neonereites

Neonereites consists of irregular chains, typically uniserial or biserial, of dimples or knobs. It has long been a topic of discussion if it represents a separate ichnogenus or a preservational variant of the ichnogenera Scalarituba, Phyllodicites, Nereites and Helminthoida e.g., Uchman, 1995 . The vast majority of Ediacaran reports of this ichnogenus e.g., Fedonkin, 1981 Chistyakov et al., 1984 are palaeopascichnid-type fossils and therefore not trace fossils Gehling et al., 2000 Jensen, 2003...

Harlaniella

The small rope-like Harlaniella podolica is a candidate for reinterpretation as a body fossil Jensen, 2003 . It is principally known from the Ukraine and Newfoundland and is the name-bearer of a latest Ediacaran trace fossil zone, the Harlaniella podolica Zone Narbonne et al., 1987 . As pointed out by Palij 1976 , Harlaniella is often found together with and appears to grade into Palaeopascichnus. The re-interpretation of Palaeopascichnus casts doubt also on Harlaniella. The common...

References

A., 1999, Marine Red Algae of the Hawaiian Islands, Bishop Museum Press, Honolulu, Hawaii. Anbar, A. D., and Knoll, A. H., 2002, Proterozoic ocean chemistry and evolution A bioinorganic bridge Science 297 1137-1142. Bengtson, S., and Yue, Z., 1992, Predatorial borings in late Precambrian mineralized exoskeletons, Science 257 367-369. Berger, S., and Kaever, M. J., 1992, Dasycladales An Illustrated Monograph of a Fascinating Algal Order, Georg Thieme Verlag, Stuttgart. Bi, Z., Wang,...

Ediacara Nama Assemblage

Namacalathus

The youngest Ediacara fossils are known from Namibia, where they range through the last 7 million years of the Ediacaran to just below the base of the Cambrian. The Nama Assemblage occurs primarily in very shallow marine delta plain to distributary mouth bar environments Saylor et al, 1995 Grazhdankin and Seilacher, 2002 Grazhdankin, 2004 and is preserved, often transported, as three-dimensional casts within event beds typical Nama-style preservation Narbonne, 2005 . Compared to the earlier...

Bilinichnus

Bilinichnus consists of two parallel ridges on bed soles, and was interpreted as marginal imprints of a creeping organism Fedonkin, 1981 . There have also been reports of Bilinichnus in the Cambrian e.g., Fedonkin et al., 1985 Paczesna, 1996 , but these appear to be different. The biogenicity of the type material of Bilinichnus has been questioned by Runnegar 1992 , who labelled it a pseudofossil, and doubts were raised also by Keighley and Pickerill 1996 and Buatois et al. 1998 .

Cnidarian Development

In contrast to the situation with sponges, there is a wealth of new developmental data on cnidarians and this greatly aids in defining the patterns of metazoan innovation. Four taxa have received the bulk of the attention from developmental biologists the sea anemone Nematostella vectensis the coral Acropora millepora the freshwater hydrozoan Hydra for which there is the least information and the colonial marine hydroid Podocoryne carnea see Ball et al., 2004 for discussion of all four model...

T g

Cochlichnus Isp

C T ITreptichnus isp, not figured t c T Treptichnusisp Jensen etal. '00 g e - Pseudofossil Seilacher etal. '00 Horizontal back-fill burrow Knotted burrow Meandering feeding trail Problematic fossil Shallow branching burrow Sinuous to meandering trails Germs '72 Germs '72 Glaessner '69 Glaessner '69 Glaessner '69 Glaessner '69 Glaessner '69 Glaessner '69 Namibia, Nudaus Fm. Namibia, Huns Mbr. South Australia, Ediacara Mbr. South Australia, Ediacara Mbr. South Australia, Ediacara Mbr. South...

Evolutionary Paleoecology of Ediacaran Benthic Marine Animals

CLAPHAM Department of Earth Sciences, University of Southern California, Los Angeles, CA 900890740, USA. 2. A Mat-Based 3. Nature of the 3.1 Geology and 3.4 Molecular Clock 4. Evolutionary 4.1 Doushantuo Fauna 600-570 Mya 4.2 Ediacara Avalon Assemblage 575-560 4.3 Ediacara White Sea Assemblage 560-550 4.4 Ediacara Nama Assemblage 549-542

Torrowangea

Torrowangea rosei is a sinuous to meandering trace fossil with regularly spaced constrictions, which may reflect peristalsis Narbonne and Aitken, 1990 . The type material from the Lintiss Vale Beds Webby, 1970 is of disputed terminal Ediacaran-earliest Cambrian age see above . Ediacaran material has been figured by among others Narbonne and Aitken 1990 . Several other reported occurrences Linan and Palacios, 1987 Lin et al., 1986 do not show these constrictions and are better assigned to other...

Eukaryotic Tree

Eukaryotic Tree

After much flux, we seem to be converging on a stable phylogeny for eukaryotic organisms Fig. 1 Baldauf, 2003 Simpson and Roger, 2002 Keeling, 2004 Nikolaev et al. 2004 Simpson and Roger, 2004 although see, e.g., Philip et al., 2005 . Most eukaryotes fall into one of six major clades 1 the opisthokonts, containing the animals and fungi and a few unicellular groups 2 the amoebozoans, containing the lobose amoebae both naked and testate and the slime molds 3 the plants, containing the red and...

Dickinsonid trace fossils

One of the most remarkable recent additions to the record of Ediacaran trace fossils is the discovery of serial foot prints in direct continuation with Dickinsonia and Yorgia in the White Sea area and South Australia Ivantsov and Malakhovskaya, 2002 Fedonkin, 2003 Gehling et al, 2005 . The producer is preserved in negative relief on the bed sole with sharply defined imprints of the body. The associated trace fossils have the general size and outline of the producer but are preserved in low...

Narrative Description

Narrative Description

Although many carbonaceous compressions have functional morphologies generally consistent with algal interpretation, their exact phylogenetic affinities are poorly resolved because of pervasive morphological convergence among algae. Possible exceptions include Miaohephyton bifurcatum and Beltanelliformis brunsae from the Doushantuo Formation these have been compared, respectively, with fucalean brown algae and the coenocytic green alga Derbesia Xiao et al, 1998a Xiao et al., 2002 . In addition,...

Lagersttten

Because almost all of the fossils in the Ediacaran do not have a mineralized skeleton, paleobiologists rely upon the presence of Lagerst tten Bottjer et al., 2002 to understand faunas from this time. Thus, it is only from Lagerst tten that we can view the Doushantuo biota and its microscopic world and the Ediacara biota and its macroscopic world. Taphonomy, although not the focus of this contribution but see Bottjer et al., 2002 , is paramount. There are different types of preservational...

Rhizarians

Rhizarians include three major groups, foraminifers, cercozoans, and radiolarians. The last of these is polyphyletic recent phylogenies suggest that phaeodareans, traditionally grouped with the other radiolarian classes, polycystineans and acantharians, are derived from within cercozoans Nikolaev et al., 2004 . With a few exceptions e.g., Paulinella, chlorarachniophytes , all rhizarians are obligate heterotrophs. Radiolarians are not known from Precambrian rocks. The earliest fossil evidence...

The C Record

Fig. 1A presents an up-to-date version of the Neoproterozoic composite 513C record, modified from Halverson et al. 2005 . This record includes new data from the Little Dal Group Mackenzie Mountain Supergroup , northwest Canada, and incorporates new radiometric ages, most importantly, two U-Pb dates from the basal Doushantuo Formation the cap carbonate sequence to the Marinoan-aged Nantuo glacials in south China Condon et al., 2005 and ages on the Sturtian glaciation that suggest an age closer...

Tubular Organisms

The three-dimensional preservation of relatively large tubular organisms of uncertain affinities has been a common source of mistaken identification of trace fossils. Examples of such structures have been discussed by Runnegar 1994 and Droser et al. 2005 . Scalloped margins in strongly curved portions and varying degree of sand-fill along the length of the tubes suggest that these were tubular organisms that were deformed and filled with sediment during transport and entombment in sand. Some of...

Didymaulichnus

Didymaulichnus is a trace fossil with a bilobed lower surface without obvious ornamentation. It occurs widely in the lower Cambrian, including Didymaulichnus miettensis, a large form restricted to the lower Cambrian characterized by prominent lateral bevels e.g., Walter et al., 1989 . The Ediacaran record of Didymaulichnus is dubious. Most occurrences e.g., Poire et al., 1984 are in sections stratigraphically close to the Cambrian and with few geochronological constraints. The type material of...

Problems In The Interpretation Of Ediacaran Trace Fossils

Ediacaran Images

General principles on which to distinguish trace fossils from body fossils and structures of inorganic origin have been discussed by Ekdale et al. 1988 . Jensen et al. 2005a and, in particular, Droser et al. 2005 , discuss the identification and preservation of Ediacaran trace fossils. For example, signs of sediment displacement, such as raised levees, provide convincing evidence for a trace fossil origin. Sediment-filled shrinkage cracks Fig. 1A are the inorganic structures most commonly...

Amoebozoans

Amoeba Invagination

Amoebozoans comprise two major groups the slime molds and the lobose amoebae. Slime molds have a very poor fossil record there are only two occurrences of fossilized slime molds from Phanerozoic rocks, both in Baltic amber Eocene in age Dorfelt et al., 2003, and references therein . Eosaccharomyces ramosus, an unusual organic-walled fossil from 1000 Ma shales of the Lakhanda Formation, Siberia, consists of open, web-like colonies of cells, a structure reminiscent of the aggregating cells of...

Critical Look at the Ediacaran Trace Fossil Record

DROSER and JAMES G. GEHLING rea de Paleontolog a, Facultad de Ciencias, Universidad de Extremadura, E-06071 Badajoz, Spain Department of Earth Sciences, University of California, Riverside, CA 92521, USA South Australian Museum, South Terrace, 5000 South Australia, Australia. 2. Problems in the Interpretation of Ediacaran Trace 2.1. Tubular 2.2. Palaeopascichnus-type 3. List of Ediacaran Trace 4.1. True and False Ediacaran Trace 4.1.1 Archaeonassa-type trace 4.1.2...

Starshaped trace fossils

By this we refer to trace fossils that consist of elements that radiate from a central area. This is clearly a heterogeneous group with a problematic Ediacaran record. One possible source of confusion is with algal rhizoids. These are known from the Doushantou Formation Steiner, 1994 Xiao et al., 2002 , and likely are present also in younger Ediacaran rocks. However, the most common source of confusion is with Ediacara-type fossils with prominent radial elements. For example, Hiemalora and...

Evolutionary Paleoecology

The nature of Ediacara biota preservation, recording soft-bodied fossils instantaneously buried underneath or within events beds tempestites or ashfalls , is ideal for paleoecological studies as the fossil assemblages are often preserved as census assemblages of in situ organisms. The soft-bodied nature of the Ediacara biota precludes time-averaging and there is no sedimentary or taphonomic evidence for transport in most localities. Namibian localities and Nama-style preservation in general ,...

Matbased World

Much Phanerozoic benthic paleoecology has focused on the effects of bioturbation and the nature of substrates. One of the biggest differences between Phanerozoic and Proterozoic benthic ecosystems is that while vertical bioturbation and all its effects upon seafloor characteristics are nearly ubiquitous in the Phanerozoic, only limited horizontal bioturbation was present in the Ediacaran Seilacher, 1999 Bottjer et al., 2000 . Thus, a distinguishing feature of the Ediacaran is that it was a time...

Synopsis Of Proterozoic Macroalgal Fossils

Chuaria Tawuia

Most Proterozoic macroalgae are preserved as carbonaceous compressions. Relatively few macroalgae are preserved in the permineralization windows i.e., silicification and phosphatization , which are widely open for Proterozoic microorganisms Schopf, 1968 Knoll, 1985 it is worth mentioning in passing that the contrast between the compression and permineralization windows may represent some major taphonomic biases or environmental heterogeneity. Recently, it has been recognized that some Ediacaran...

Doushantuo Fauna

Embryon Doushantuo

The Doushantuo phosphorites of southwestern China, constrained between 635 and 551 Ma Condon et al, 2005 but probably 600-570 Ma in age Barfod et al., 2002 Condon et al, 2005 , are famous for phosphatized eggs and embryos Fig. 2A Xiao et al., 1998 Xiao and Knoll, 2000 . Other reported animal fossils include tiny adult sponges Fig. 2C Li et al, 1998 , stem cnidarians Fig. 2D Xiao et al, 2000 Chen et al, 2002 and a tiny bilaterian Fig. 2B Chen et al, 2004 Bottjer, 2005 . These fossil occurrences...

Skolithos

Skolithos consists of vertical or inclined unbranched burrows that are typically cylindrical. Skolithos-type trace fossils may represent a range of behaviors and widely different producers. They may be a structure built by a mobile organism of small dimension relative to the tube or a protective dwelling structure closely corresponding to the animal's size. A further possibility, which in particular applies to short vertical knobs, is that they may represent an anchoring structure of an...