共查询到20条相似文献,搜索用时 15 毫秒
1.
刺细胞动物是一类具有刺细胞的水生无脊椎动物,分布在世界各地的海洋和淡水中.作为后生动物最早分化出的一支,刺细胞动物对研究后生动物的起源和早期演化具有极其重要的意义,也为研究后生动物系统发育、地层对比和古地理恢复等方面提供了重要的科研线索.本文简要介绍了刺细胞动物早期(埃迪卡拉纪至寒武纪苗岭世)的化石记录和研究现状,将刺... 相似文献
2.
新元古代奇异叠层石和凝块石中可疑的动物活动证据 总被引:6,自引:0,他引:6
在湖北保康马桥地区,新元古代神农架群石家冲组产出一套奇异的叠层石,凝块石和叠层石-凝块石联合体。其中叠层石具类似于食草和钻孔动物破坏的疤痕,通过对上述构造形态和特征分析,这些构造可能与后生动物的活动有关,但也不排除它们是非生物成因的可能。这些后生动物似乎已显示高度发育的行为。当前的资料表明,在凝块石构造与食草和钻孔动物生态效应之间似乎存在着一种紧密的联系,在生物进化史上,寒武纪生命大爆发似乎仅是一 相似文献
3.
《Biological reviews of the Cambridge Philosophical Society》2018,93(2):914-932
Rocks of the Ediacaran System (635–541 Ma) preserve fossil evidence of some of the earliest complex macroscopic organisms, many of which have been interpreted as animals. However, the unusual morphologies of some of these organisms have made it difficult to resolve their biological relationships to modern metazoan groups. Alternative competing phylogenetic interpretations have been proposed for Ediacaran taxa, including algae, fungi, lichens, rhizoid protists, and even an extinct higher‐order group (Vendobionta). If a metazoan affinity can be demonstrated for these organisms, as advocated by many researchers, they could prove informative in debates concerning the evolution of the metazoan body axis, the making and breaking of axial symmetries, and the appearance of a metameric body plan. Attempts to decipher members of the enigmatic Ediacaran macrobiota have largely involved study of morphology: comparative analysis of their developmental phases has received little attention. Here we present what is known of ontogeny across the three iconic Ediacaran taxa Charnia masoni, Dickinsonia costata and Pteridinium simplex, together with new ontogenetic data and insights. We use these data and interpretations to re‐evaluate the phylogenetic position of the broader Ediacaran morphogroups to which these taxa are considered to belong (rangeomorphs, dickinsoniomorphs and erniettomorphs). We conclude, based on the available evidence, that the affinities of the rangeomorphs and the dickinsoniomorphs lie within Metazoa. 相似文献
4.
Duncan J. E. Murdock 《Biological reviews of the Cambridge Philosophical Society》2020,95(5):1372-1392
Biomineralized skeletons are widespread in animals, and their origins can be traced to the latest Ediacaran or early Cambrian fossil record, in virtually all animal groups. The origin of animal skeletons is inextricably linked with the diversification of animal body plans and the dramatic changes in ecology and geosphere–biosphere interactions across the Ediacaran–Cambrian transition. This apparent independent acquisition of skeletons across diverse animal clades has been proposed to have been driven by co‐option of a conserved ancestral genetic toolkit in different lineages at the same time. This ‘biomineralization toolkit’ hypothesis makes predictions of the early evolution of the skeleton, predictions tested herein through a critical review of the evidence from both the fossil record and development of skeletons in extant organisms. Furthermore, the distribution of skeletons is here plotted against a time‐calibrated animal phylogeny, and the nature of the deep ancestors of biomineralizing animals interpolated using ancestral state reconstruction. All these lines of evidence point towards multiple instances of the evolution of biomineralization through the co‐option of an inherited organic skeleton and genetic toolkit followed by the stepwise acquisition of more complex skeletal tissues under tighter biological control. This not only supports the ‘biomineralization toolkit’ hypothesis but also provides a model for describing the evolution of complex biological systems across the Ediacaran–Cambrian transition. 相似文献
5.
Daniel W. McShea 《Evolution; international journal of organic evolution》1996,50(2):477-492
The notion that complexity increases in evolution is widely accepted, but the best-known evidence is highly impressionistic. Here I propose a scheme for understanding complexity that provides a conceptual basis for objective measurement. The scheme also shows complexity to be a broad term covering four independent types. For each type, I describe some of the measures that have been devised and review the evidence for trends in the maximum and mean. In metazoans as a whole, there is good evidence only for an early-Phanerozoic trend, and only in one type of complexity. For each of the other types, some trends have been documented, but only in a small number of metazoan subgroups. 相似文献
6.
Budd GE 《Philosophical transactions of the Royal Society of London. Series B, Biological sciences》2008,363(1496):1425-1434
The fossil record of the earliest animals has been enlivened in recent years by a series of spectacular discoveries, including embryos, from the Ediacaran to the Cambrian, but many issues, not least of dating and interpretation, remain controversial. In particular, aspects of taphonomy of the earliest fossils require careful consideration before pronouncements about their affinities. Nevertheless, a reasonable case can now be made for the extension of the fossil record of at least basal animals (sponges and perhaps cnidarians) to a period of time significantly before the beginning of the Cambrian. The Cambrian explosion itself still seems to represent the arrival of the bilaterians, and many new fossils in recent years have added significant data on the origin of the three major bilaterian clades. Why animals appear so late in the fossil record is still unclear, but the recent trend to embrace rising oxygen levels as being the proximate cause remains unproven and may even involve a degree of circularity. 相似文献
7.
In this study we compare patterns of mandibular integration between mice and baboons using both phenotypic and quantitative genetic data. Specifically, we test how well each species fits with the mosaic model of mandibular integration suggested by Atchley and Hall (Biol Rev Camb Philos Soc 66:101–157, 1991) based on developmental modules. We hypothesize that patterns of integration will be similar for mice and baboons and that both species will show strong integration within developmental modules and weaker integration between modules. Corresponding landmark data were collected from the hemi-mandibles of an advanced intercross mouse sample (N = 1239) and mandibles from a baboon sample of known pedigree from the Southwest Foundation for Biomedical Research (N = 430). We used four methods of analysis to quantify and compare the degree of mandibular integration between species including two methods based on a priori assumptions, and two a posteriori analyses. We found that patterns of integration are broadly similar for baboon and mouse mandibles, with both species displaying a modular pattern of integration. While there is a general trend of similarity in integration patterns between species, there were some marked differences. Mice are strongly correlated among distances within the coronoid process and the incisive alveolar region, whereas baboons are strongly integrated within the condylar process. We discuss the potential evolutionary implications of the similar patterns of integration between these species with an emphasis on the role of modularity. Electronic supplementary material The online version of this article (doi:) contains supplementary material, which is available to authorized users. 相似文献
8.
Charles R. Marshall James W. Valentine 《Evolution; international journal of organic evolution》2010,64(5):1189-1201
The genomes of taxa whose stem lineages branched early in metazoan history, and of allied protistan groups, provide a tantalizing outline of the morphological and genomic changes that accompanied the origin and early diversifications of animals. Genome comparisons show that the early clades increasingly contain genes that mediate development of complex features only seen in later metazoan branches. Peak additions of protein‐coding regulatory genes occurred deep in the metazoan tree, evidently within stem groups of metazoans and eumetazoans. However, the bodyplans of these early‐branching clades are relatively simple. The existence of major elements of the bilaterian developmental toolkit in these simpler organisms implies that these components evolved for functions other than the production of complex morphology, preadapting the genome for the morphological differentiation that occurred higher in metazoan phylogeny. Stem lineages of the bilaterian phyla apparently required few additional genes beyond their diploblastic ancestors. As disparate bodyplans appeared and diversified during the Cambrian explosion, increasing complexity was accommodated largely through changes in cis‐regulatory networks, accompanied by some additional gene novelties. Subsequently, protein‐coding genic richness appears to have essentially plateaued. Some genomic evidence suggests that similar stages of genomic evolution may have accompanied the rise of land plants. 相似文献
9.
Heyo Van Iten Antonio C. Marques Juliana de Moraes Leme Mirian L. A. Forancelli Pacheco Marcello Guimaraes Simões 《Palaeontology》2014,57(4):677-690
Diploblastic eumetazoans of the phylum Cnidaria originated during the Neoproterozoic Era, possibly during the Cryogenian Period. The oldest known fossil cnidarians occur in strata of Ediacaran age and consist of polypoid forms that were either nonbiomineralizing or weakly so. The oldest possible anthozoans, including the genus Ramitubus, may be related to tabulate corals and occur in the Doushantuo Lagerstätte (upper Doushantuo Formation, South China), the age of which is poorly constrained (approximately 585 Ma?). Conulariid scyphozoans may first appear as early as 635–577 Ma (Lantian Formation, South China). A definite conulariid, most similar to Palaeozoic species assigned to the genus Paraconularia, occurs in association with the possible scyphozoan, Corumbella werneri, in the latest Ediacaran (c. 543 Ma) Tamengo Formation of Brazil. Basal Cambrian (c. 540 Ma) phosphorites in the upper Kuanchuanpu Formation (South China) yield solitary polyps of the oldest probable anthozoan (Eolympia pediculata), which appears to have been a stem hexacorallian. This same formation contains fossils interpreted by some authors as pentaradial cubozoan polyps; however, both the oldest known cubozoans and the oldest hydrozoans, all medusae, may actually occur in the Cambrian (Series 3, c. 505 Ma) Marjum Formation (Utah, USA). Although these recently published palaeontological data tend to corroborate the hypothesis that Cnidaria has a relatively deep Neoproterozoic history, the timing of major internal branching events remains poorly constrained, with, for example, the results of some molecular clock analyses indicating that the two cnidarian subphyla (Anthozoaria and Medusozoa) may have originated as many as one billion years ago. Further progress towards elucidating the evolution and early fossil record of cnidarians may accrue from: (1) an intensive search for phosphatized soft parts in possible anthozoans from the Ediacaran Doushantuo Formation; (2) an expanded search for Ediacaran conulariids; and (3) additional detailed analyses of the taphonomy and preservation of Ediacaran and Cambrian cnidarians, including possible pentaradial cubozoan polyps from the Fortunian upper Kuanchuanpu Formation. 相似文献
10.
11.
12.
Colony age and size can be poorly related in scleractinian corals if colonies undergo fission to form smaller independent
patches of living tissue (i.e., ramets), but the implications of this life-history characteristic are unclear. This study
explored the ecological consequences of the potential discrepancy between size and age for a massive scleractinian, first
by testing the effect of colony origin on the growth of small colonies, and second by quantifying the contribution of ramets
to population structure. Using Siderastrea siderea in St. John (US Virgin Islands) as an experimental system, the analyses demonstrated that the growth of small colonies derived
from sexual reproduction was 2.5-fold greater than that of small ramets which were estimated to be ≈100 years older based
on the age of the parent colonies from which they split. Although fission can generate discrete colonies, which in the case
of the study reef accounted for 42% of all colonies, it may depress colony success and reef accretion through lowered colony
growth rates. 相似文献
13.
Paul M. Magwene 《Evolutionary biology》2008,35(3):191-198
Characterizing and comparing the covariance or correlation structure of phenotypic traits lies at the heart of studies concerned
with multivariate evolution. I describe an approach that represents the geometric structure of a correlation matrix as a type
of proximity graph called a Correlation Proximity graph. Correlation Proximity graphs provide a compact representation of
the geometric relationships inherent in correlation matrices, and these graphs have simple and intuitive properties. I demonstrate
how this framework can be used to study patterns of phenotypic integration by employing this approach to compare phenotypic
and additive genetic correlation matrices within and between species. I also outline a graph-based method for testing whether
an inferred correlation proximity graph is one of a number of possible models that are consistent with a “soft” biological
hypothesis. 相似文献
14.
Numerous macro-organisms of the Doushantuo macrobiota, which were found in the black carbonaceous mudstone of the upper Neoproterozoic Ediacraan Doushan-tuo Formation in Jiangkou County, Guizhou Province, China, are considered to live on sea floor by their holdfasts. The appearance and preserved forms of the macroalgal holdfasts may provide some data to the study of the living and buried environments ofmacrobiota. They lived in the lower energy and clear environment, and fixed on a soupground with rich water (about 79% water). Currents, possibly ocean currents, could pull out the macroalgal holdfasts from the soupground and break off the macroalgal foliations. After such events, the corpses of macro-organisms would be covered in a reduced environment by the deposits. Afterwards, a new community, including regenerating and undying macro-organisms, lived continuously on a new deposit. 相似文献
15.
Giovanni Mussini;Frances S. Dunn; 《Biological reviews of the Cambridge Philosophical Society》2024,99(1):110-130
The end-Neoproterozoic transition marked a gradual but permanent shift between distinct configurations of Earth's biosphere. This interval witnessed the demise of the enigmatic Ediacaran Biota, ushering in the structured trophic webs and disparate animal body plans of Phanerozoic ecosystems. However, little consensus exists on the reality, drivers, and macroevolutionary implications of end-Neoproterozoic extinctions. Here we evaluate potential drivers of late-Neoproterozoic turnover by addressing recent findings on Ediacaran geochronology, the persistence of classical Ediacaran macrobionts into the Cambrian, and the existence of Ediacaran crown-group eumetazoans. Despite renewed interest in the possibility of Phanerozoic-style ‘mass extinctions’ in the latest Neoproterozoic, our synthesis of the available evidence does not support extinction models based on episodic geochemical triggers, nor does it validate simple ecological interpretations centred on direct competitive displacement. Instead, we argue that the protracted and indirect effects of early bilaterian innovations, including escalations in sediment engineering, predation, and the largely understudied impacts of reef-building, may best account for the temporal structure and possible selectivity of late-Neoproterozoic extinctions. We integrate these processes into a generalised model of early eumetazoan-dominated ecologies, charting the disruption of spatial and temporal isotropy on the Ediacaran benthos as a consequence of diversifying macrofaunal interactions. Given the nature of resource distribution in Ediacaran ecologies, the continuities among Ediacaran and Cambrian faunas, and the convergent origins of ecologically disruptive innovations among bilaterians we suggest that the rise of Phanerozoic-type biotas may have been unstoppable. 相似文献
16.
Numerous macro-organisms of the Doushantuo macrobiota, which were found in the black carbonaceous mudstone of the upper Neoproterozoic Ediacraan Doushantuo Formation in Jiangkou County, Guizhou Province, China, are considered to live on sea floor by their holdfasts. The appearance and preserved forms of the macroalgal holdfasts may provide some data to the study of the living and buried environments of macrobiota. They lived in the lower energy and clear environment, and fixed on a soupground with rich water (about 79 water). Currents, possibly ocean currents, could pull out the macroalgal holdfasts from the soupground and break off the macroalgal foliations. After such events, the corpses of macro-organisms would be covered in a reduced environment by the deposits. Afterwards, a new community, including regenerating and undying macro-organisms, lived continuously on a new deposit. __________ Translated from Acta Micropalaeontologica Sinica, 2005, 23(2): 154-C164 [译自: 微体古生物学报] 相似文献
17.
Evidence is provided showing that in two species of Phaeocystis (P. globosa and P. pouchetii) the colonial cells possess a much higher growth rate than the single cells when grown under identical conditions. Based on the DNA-cell-cycle method gross growth rate of colony cells exceeded those of co-occurring single cells by a factor 1.5 up to 3.8. The dominance of colonies in blooms of Phaeocystis can therefore be primarily due to their significantly high growth rate allowing a rapid bloom formation.Both Phaeocystis species showed ultradian growth but differed in timing of the initiation of the second DNA replication phase. In both species the first DNA-replication period started at the end of the (local) light period and was completed in the early dark period. In P. globosa this was immediately followed by the second DNA-replication period (first half of the dark period). In P. pouchetii this process was delayed by ca. 12 h until the middle of the light period (local noon).Flow cytometric analysis of the cell size and chlorophyll fluorescence showed little variation in colony and single cells of P. pouchetii. In contrast, colonies of P. globosa showed often the presence of two cell morphs, co-occurring in the same colony. The size of both morphs was identical but they differed in chlorophyll fluorescence up to a factor 4. In general the high chlorophyll cell morph dominated (>70% of the total colony cells). Both colony cell morphs were observed in cultures, mesocosms differing in N/P ratio but also in the field. 相似文献
18.
Chen BY Liu JY Chang HH Chang CP Lo WY Kuo WH Yang CR Lin DP 《Biochemical and biophysical research communications》2007,357(4):1084-1089
The role of Hedgehog signaling in human basal cell hyperplasia formation and its progressing towards tumorigenesis was investigated. Hedgehog signaling members including PTCH1, GLI1, GLI2, and GLI3 were found co-localized with p63 expression in most hyperplastic basal cells, but rarely in normal basal cells, suggesting Hedgehog involvement in basal cell hyperplasia formation. Both CK-14 and CK-8 markers were found co-localized in the majority of hyperplastic basal cells, but relatively few in the normal basal cells, indicating a Hedgehog-promoted transitory differentiation. Furthermore, CK-14 and PTCH1 were found co-localized with CD44 in the hyerplastic basal cells, in a way similar to the CD44 co-localization with PTCH1 and GLI1 in the cancer cells. Together, the present study indicated Hedgehog involvement in forming basal cell hyperplasia and its progressing towards cancer, presumably by transforming the normal basal stem cells into the cancer stem cells where persistent Hedgehog activation might be mandatory for tumorigenesis. 相似文献
19.
Janne Suomela 《Plant Ecology》1996,127(1):77-83
Within-tree variability in leaf characteristics of the mountain birch (Betula pubescens ssp. tortuosa) was bioassayed for the autumnal moth (Epirrita autumnata) by rearing larvae on birch leaves in a laboratory and measuring their growth, consumption rate, approximate digestibility, efficiency of conversion of ingested food and efficiency of conversion of digested food. Only short shoot leaves, i.e. leaves of the same age, were used. The highest hierarchical level, which included trees and ramets within trees, accounted for most of the total variance in almost all the measured traits. Short shoots (within branches) accounted for more of the variance than branches (within trees/ramets) in most of the traits. The results suggest that differences in leaf quality were reflected in larval growth mainly by differences in food utilization efficiencies (postingestive effects) and less by differences in consumption rate (preingestive effects). The observed within-tree variation is probably a consequence of the modular structure, sectoriality and partial functional independence of tree parts. 相似文献
20.
JENNIFER N. LOHR CHRISTIAN LAFORSCH HENRIKE KOERNER JUSTYNA WOLINSKA 《The Journal of eukaryotic microbiology》2010,57(4):328-336
ABSTRACT. Caullerya mesnili is a protozoan endoparasite in the gut epithelium of Daphnia, which causes regular epidemics in lakes throughout Europe. Its classification has remained unchanged for over a century, leaving it placed with the Haplosporidia, despite speculation that this position is incorrect. The difficulty in classifying C. mesnili stems from its few known morphological and ecological characteristics, as well as a lack of genetic markers. Here we sequenced the nuclear small subunit (SSU) and internal transcribed spacer rDNA regions of C. mesnili samples from 10 locations. Based on sequence similarities, we suggest the re‐classification of C. mesnili to the Ichthyosporea, a class of protists near the animal–fungi divergence. We report average intragenomic variation of 0.75% and 2.27% in the SSU and internal transcribed spacer regions, respectively. From electron micrographs and light microscopy of histological sections we determined that C. mesnili spores grow within the intestinal epithelium where they establish themselves intercellularly. In addition, we confirmed previous accounts regarding the high virulence of this parasite. Caullerya mesnili reduces host lifespan, the number of clutches, and the total number of offspring. This high selection pressure placed on hosts supports the importance of C. mesnili as a model parasite for the study of host–parasite biology in permanent lakes. 相似文献