共查询到20条相似文献,搜索用时 0 毫秒
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J. Alistair Crame Alan G. Beu Jon R. Ineson Jane E. Francis Rowan J. Whittle Vanessa C. Bowman 《PloS one》2014,9(12)
The extensive Late Cretaceous – Early Paleogene sedimentary succession of Seymour Island, N.E. Antarctic Peninsula offers an unparalleled opportunity to examine the evolutionary origins of a modern polar marine fauna. Some 38 modern Southern Ocean molluscan genera (26 gastropods and 12 bivalves), representing approximately 18% of the total modern benthic molluscan fauna, can now be traced back through at least part of this sequence. As noted elsewhere in the world, the balance of the molluscan fauna changes sharply across the Cretaceous – Paleogene (K/Pg) boundary, with gastropods subsequently becoming more diverse than bivalves. A major reason for this is a significant radiation of the Neogastropoda, which today forms one of the most diverse clades in the sea. Buccinoidea is the dominant neogastropod superfamily in both the Paleocene Sobral Formation (SF) (56% of neogastropod genera) and Early - Middle Eocene La Meseta Formation (LMF) (47%), with the Conoidea (25%) being prominent for the first time in the latter. This radiation of Neogastropoda is linked to a significant pulse of global warming that reached at least 65°S, and terminates abruptly in the upper LMF in an extinction event that most likely heralds the onset of global cooling. It is also possible that the marked Early Paleogene expansion of neogastropods in Antarctica is in part due to a global increase in rates of origination following the K/Pg mass extinction event. The radiation of this and other clades at ∼65°S indicates that Antarctica was not necessarily an evolutionary refugium, or sink, in the Early – Middle Eocene. Evolutionary source – sink dynamics may have been significantly different between the Paleogene greenhouse and Neogene icehouse worlds. 相似文献
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We inferred the incidence of nucleotide conversions in the COI and 16S rRNA mitochondrial genes of members of the Symphyta
and basal Apocrita (Hymenoptera). Character-state reconstructions in both genes suggested that conversions between A and T
(AT transversions) occurred much more frequently than any other type of change, although we cannot wholly discount an underlying
transition bias. Parsimony analysis of COI nucleotide characters did not recover phylogeny; e.g., neither the Tenthredinoidea
nor Apocrita were recovered as monophyletic. However, analysis of COI amino acid characters did recover these relationships,
as well as others based on fossil and morphological evidence. Analysis of 16S rRNA characters also recovered these relationships
providing conversions between A and T were down-weighted. Analysis of the combined data sets gave relatively strong support
for various relationships, suggesting that both data sets supported similar topographies. These data sets, both separately
and combined, suggested that the phytophagous Siricidae were more closely related to the predominantly parasitic Apocrita
than were the ectoparasitic Orussoidea. This suggests that the wasp parasitic lifestyle did not have a single origin, unless
the Siricidae have more recently reverted to phytophagy. Alternatively, parasitism evolved twice independently, once in the
Orussoidea and again in the Apocrita. The latter scenario is supported by the observation that the evolution of parasitism
was accompanied by a tendency for the larvae to develop inside plant tissues. Adaptations that accompanied the movement of
wasps into a confined, wood-boring habitat may have preadapted them to becoming ectoparasitic.
Received: 27 March 1996 / Accepted: 2 August 1996 相似文献
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Jason Hilton 《植物学报(英文版)》1998,40(11)
The earliest identified seed-plants are found in Latest Devonian aged sediments from Northwest Europe and North America and are believed to have evolved from within the progymnosperms, a group of anatomically advanced pteridophytic plants. However, current evidence makes it problematic to determine from which particular progynmospermous lineage the seed-plants evolved, with the major contender being the Aneurophytalean progymnosperms. The evidence for the ancestral stock to the seed-plants is summarised and the morphologies of the earliest known seed-plants are considered. From their first geological occurrence, the seed-plants are morphologically diverse to such an extent that the identification of a single potential ancestral morphology is impossible. In the light of the evidence so far presented, the precise origin of the seed-plants is unresolved and in need of new evidence relating to the progynmosperm/seed-plant transition. Future lines of research are also suggested. 相似文献
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David W. Morgens 《Journal of molecular evolution》2013,77(4):185-196
Translation, coded peptide synthesis, arguably exists at the heart of modern cellular life. By orchestrating an incredibly complex interaction between tRNAs, mRNAs, aaRSs, the ribosome, and numerous other small molecules, the translational system allows the interpretation of data in the form of DNA to create massively complex proteins which control and enact almost every cellular function. A natural question then, is how did this system evolve? Here we present a broad review of the existing theories of the last two decades on the origin of the translational system. We attempt to synthesize the wide variety of ideas as well as organize them into modular components, addressing the evolution of the peptide-RNA interaction, tRNA, mRNA, the ribosome, and the first proteins separately. We hope to provide both a comprehensive overview of the literature as well as a framework for future discussions and novel theories. 相似文献
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A Mesoamerican origin of cherimoya (Annona cherimola Mill.): Implications for the conservation of plant genetic resources 下载免费PDF全文
N. Larranaga F. J. Albertazzi G. Fontecha M. Palmieri H. Rainer M. van Zonneveld J. I. Hormaza 《Molecular ecology》2017,26(16):4116-4130
Knowledge on the structure and distribution of genetic diversity is a key aspect to plan and execute an efficient conservation and utilization of the genetic resources of any crop as well as for determining historical demographic inferences. In this work, a large data set of 1,765 accessions of cherimoya (Annona cherimola Mill, Annonaceae), an underutilized fruit tree crop native to the Neotropics and used as a food source by pre‐Columbian cultures, was collected from six different countries across the American continent and amplified with nine highly informative microsatellite markers. The structure analyses, fine representation of the genetic diversity and an ABC approach suggest a Mesoamerican origin of the crop, contrary to previous reports, with clear implications for the dispersion of plant germplasm between Central and South America in pre‐Columbian times. These results together with the potential distribution of the species in a climatic change context using two different climate models provide new insights for the history and conservation of extant genetic resources of cherimoya that can be applied to other currently underutilized woody perennial crops. 相似文献
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装饰品(personal ornament)是旧石器时代中晚期遗址中一类较特殊的遗存,作为早期人类现代行为的重要标志,它的出现及其学术意义一直受到国际学术界的关注和重视。西方考古学界对装饰品的研究开始较早,理论方法成熟,成果丰硕。我国此遗存发现较少,在研究手段和程度方面与西方存在一定的差距。本文从装饰品的定义与分类、发现与研究现状、功能与作用、出现原因及研究意义的探讨等方面入手,对西方学术界对装饰品的研究现状和进展进行梳理,对我国发现的相关材料与研究进展做简要介绍与评述,希望能对我国旧石器时代装饰品的研究提供有价值的参考资料与思路。 相似文献
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Frederic L. Pryor 《American anthropologist》1986,88(4):879-894
Using the standard cross-cultural sample, I show that the presence of agriculture in precapitalist societies is only weakly related to the richness of the environment and climate, but is more highly related to the population density. However, the density argument, which is based on the presence of diminishing returns in gathering and hunting, allows many exceptions. A series of other explanations for engaging in agriculture, particularly related to the reduction of risk occurring in the overreliance on other food production modes, are explored. Such an approach forces us to address a somewhat different question: Why haven't all societies adopted agriculture, at least to supply a small portion of their nourishment? Several societies are examined which, by any conventional theory including those proposed in this article, should be engaged in at least some agriculture; but they are not. If this puzzle of the absence of agriculture is solved, we will be considerably further in understanding the nature of the transition to agriculture. 相似文献
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Katsuhiko Ono Yukie Hirahara Hitoshi Gotoh Tadashi Nomura Hirohide Takebayashi Hisao Yamada Kazuhiro Ikenaka 《Neurochemical research》2018,43(1):186-194
One of the unsolved problems in the research field of oligodendrocyte (OL) development has been the site(s) of origin of optic nerve OLs and its precursor cells (OPCs). It is generally accepted that OLs in the optic nerve are derived from the brain, and thus optic nerve OLs are immigrant cells. We previously demonstrated the brain origin of optic nerve OPCs in chick embryos. However, the site of optic nerve OPC origin has not been examined experimentally in developing rodents for the past two decades. We have recently reported that optic nerve OPCs in mice arise in the preoptic area by E12.5 and gradually migrate caudally and enter the optic nerve. These OPCs give rise to myelinating OLs in the optic nerve in the postnatal or adult stages. Surprisingly, there are species differences with respect to the origin of optic nerve OPCs between chicks and mice. Here, we summarize the site of OPC origin in the optic nerve based on our own previous and recent results, and discuss possible mechanisms underlying these species differences. 相似文献
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The Origin of Adrenal Cortical Mitochondria and Liposomes: a Preliminary Report 总被引:6,自引:6,他引:0 下载免费PDF全文
W. Duane Belt 《The Journal of cell biology》1958,4(3):337-340
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The phylogenetic and geographic origins of bats (Chiroptera) remain unknown. The earliest confirmed records of bats date from
the early Eocene (approximately 51 Ma) in North America with other early Eocene bat taxa also being represented from Europe,
Africa, and Australia. Where known, skeletons of these early taxa indicate that many of the anatomical specializations characteristic
of bats had already been achieved by the early Eocene, including forelimb and manus elongation in conjunction with structural
changes in the pectoral skeleton, hind limb reorientation, and the presence of rudimentary echolocating abilities. By the
middle Eocene, the diversification of bats was well underway with many modern families being represented among fossil forms.
A new phylogenetic analysis indicates that several early fossil bats are consecutive sister taxa to the extant crown group
(including megabats), and suggests a single origin for the order, at least by the late Paleocene. Although morphological studies
have long placed bats in the Grandorder Archonta, (along with primates dermopterans, and tree shrews), recent molecular studies
have refuted this hypothesis, instead strongly supporting placement of bats in Laurasiatheria. Primitively, proto-bats were
likely insectivorous, under-branch hangers and elementary gliders that exploited terminal branch habitats. Recent work has
indicated that a number of other mammalian groups began to exploit similar arboreal, terminal branch habitats in the Paleocene,
including multituberculates, eulipotyphlans, dermopterans, and plesiadapiforms. This may offer an ecological explanation for
morphological convergences that led to the erroneous inclusion of bats within Archonta: ancestral archontan groups as well
as proto-bats apparently were exploiting similar arboreal habitats, which may have led to concurrent development of homoplasic
morphological attributes. 相似文献
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Scholars frequently posit maize as the staple food of Chavín civilization and some even argue that this crop provided the critical stimulus for its development. Stable carbon isotope analysis permits an evaluation of these hypotheses because maize, the only C4 cultigen consumed in pre-Hispanic Peru, leaves an unambiguous imprint on the bone chemistry of its consumers that allows the calculation of its relative importance in the diet. Analysis of osteological samples from Chavín de Huántar and Huaricoto indicates that although maize was eaten, C3 foods like potatoes and quinoa constituted the bulk of the dietary intake during the development and climax of highland Chavín civilization (ca. 850-200 B.C.). The authors briefly explore possible reasons for the secondary importance of maize in the Initial Period/Early Horizon subsistence systems of this region, a pattern already established by the late Preceramic period (ca. 2000 B.C.). 相似文献
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