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1.
Triploblastic animals more than 1 billion years ago: trace fossil evidence from india 总被引：3，自引：0，他引：3
Some intriguing bedding plane features that were observed in the Mesoproterozoic Chorhat Sandstone are biological and can be interpreted as the burrows of wormlike undermat miners (that is, infaunal animals that excavated tunnels underneath microbial mats). These burrows suggest that triploblastic animals existed more than a billion years ago. They also suggest that the diversification of animal designs proceeded very slowly before the appearance of organisms with hard skeletons, which was probably the key event in the Cambrian evolutionary explosion, and before the ecological changes that accompanied that event. 相似文献
2.
The Cambrian conundrum: early divergence and later ecological success in the early history of animals 总被引：1，自引：0，他引：1
Erwin DH Laflamme M Tweedt SM Sperling EA Pisani D Peterson KJ 《Science (New York, N.Y.)》2011,334(6059):1091-1097
Diverse bilaterian clades emerged apparently within a few million years during the early Cambrian, and various environmental, developmental, and ecological causes have been proposed to explain this abrupt appearance. A compilation of the patterns of fossil and molecular diversification, comparative developmental data, and information on ecological feeding strategies indicate that the major animal clades diverged many tens of millions of years before their first appearance in the fossil record, demonstrating a macroevolutionary lag between the establishment of their developmental toolkits during the Cryogenian [(850 to 635 million years ago (Ma)], and the later ecological success of metazoans during the Ediacaran (635 to 541 Ma) and Cambrian (541 to 488 Ma) periods. We argue that this diversification involved new forms of developmental regulation, as well as innovations in networks of ecological interaction within the context of permissive environmental circumstances. 相似文献
3.
Specimens of the small bivalved animal Fordilla troyensis Barrande from New York State show that this fossil is the oldest known pelecypod mollusk and not a conchostracan arthropod. This finding extends the range of the class Pelecypoda backward in time from the Early Ordovician (about 495 million years ago) to the Early Cambrian (about 540 to 570 million years ago). The morphology of Fordilla troyensis suggests that it lived infaunally and that it was ancestral to the pelecypod subclasses Heteroconchia and Isofilibranchia. 相似文献
4.
Phosphatized univalves, recovered from the Lower Cambrian ( approximately 530 million years old) Qiongzhusi Formation in southern China, are recognized as early instars belonging to bradoriid ostracodes whose later instars are bivalved. The univalved form is the primitive larval character for shell-secreting crustaceans, although most post-Cambrian ostracodes bypassed this developmental phase. The univalved-bivalved transition during early on-togeny represents an important evolutionary event in ostracodes, with implications for crustacean classification, and implies that the ostracode ancestor achieved this bivalved capacity before the appearance of mineralized skeletons during the "Cambrian explosion." 相似文献
5.
Conodonts are zoologically enigmatic, toothlike phosphatic microfossils occurring in marine sedimentary rocks ranging in age from Cambrian to Triassic. Dimpled spheres of less than 1 millimeter in diameter are sporadic associates of conodonts and have identical chemical composition and microstructure. Mineralogy, morphology, and occurrence of these spheres suggest that they are pearls secreted by the conodont-bearing animal. 相似文献
6.
In a problematical fauna discovered in Australia, 152 meters below diagnostic Lower Cambrian species, are fossilized remains belonging in the phylum Coelenterata. These jellyfish-like fossils were defined as a new class(Dipleurozoa) by Harrington and Moore because of their strong bilateral symmetry and differentiated extremities. The class was not reported elsewhere before many specimens were discovered recently in the Shawangunk (Tuscarora) formation at Delaware Water Gap, Pennsylvania. Three new species belonging to a new genus can be recognized, the indication being that the class ranges stratigraphically from the infra-Cambrian to at least the Lower Silurian, and geographically from Australia to eastern North America. 相似文献
7.
The set of viable design elements available for animals to use in building skeletons has been fully exploited. Analysis of animal skeletons in relation to the multivariate, theoretical "Skeleton Space" has shown that a large proportion of these options are used in each phylum. Here, we show that structural elements deployed in the skeletons of Burgess Shale animals (Middle Cambrian) incorporate 146 of 182 character pairs defined in this morphospace. Within 15 million years of the appearance of crown groups of phyla with substantial hard parts, at least 80 percent of skeletal design elements recognized among living and extinct marine metazoans were exploited. 相似文献
8.
The fossil Pteridinium, a distinctive component of a worldwide early metazoan (Ediacaran)assemblage, is provisionally recorded from probable early Cambrian strata in eastern California. In context with other evidence, this finding implies a Cambrian age for the Ediacaran fauna and approximate coincidence of limits between Phanerozoic-Cryptozoic, Paleozoic-Precambrian, and Cambrian-Precambrian. 相似文献
9.
Careful analysis of x-ray scattering intensities of demineralized metaanthracites and high-rank anthracites formed during the Pennsylvanian geological period has revealed the presence of three-dimensional (hkl) reflections of graphite, demonstrating unequivocally that coals graphitize with metamorphism. Graphitization has been observed also with a coal formed before the Cambrian period, much earlier than most coals. A significant degree of graphitization occurs by coalification when the graphite-like layers attain a size of 25 to 30 angstroms as compared to 100 A or more by the heat treatment of amorphous carbons. 相似文献
10.
Examples that indicate collective behavior in the fossil record are rare. A group association of specimens that belong to a previously unknown arthropod from the Chengjiang Lagerst?tte, China, provides evidence that such behavior was present in the early Cambrian (about 525 million years ago), coincident with the earliest extensive diversification of the Metazoa, the so-called Cambrian explosion event. The chainlike form of these specimens is unique for any arthropod, fossil or living, and most likely represents behavior associated with migration. 相似文献
11.
Development of the animal body plan is controlled by large gene regulatory networks (GRNs), and hence evolution of body plans must depend upon change in the architecture of developmental GRNs. However, these networks are composed of diverse components that evolve at different rates and in different ways. Because of the hierarchical organization of developmental GRNs, some kinds of change affect terminal properties of the body plan such as occur in speciation, whereas others affect major aspects of body plan morphology. A notable feature of the paleontological record of animal evolution is the establishment by the Early "Cambrian of virtually all phylum-level body plans. We identify a class of GRN component, the kernels" of the network, which, because of their developmental role and their particular internal structure, are most impervious to change. Conservation of phyletic body plans may have been due to the retention since pre-Cambrian time of GRN kernels, which underlie development of major body parts. 相似文献
12.
The Chinese Early Cambrian Chengjiang fauna includes three different anomalocaridids, a globally spread, extinct marine group including the largest known Cambrian animals. Anomalocaridids were active predators, and their presence implies that a complex ecosystem appeared abruptly in the earliest Phanerozoic. Complete specimens display several sets of characters shared only with some other exclusively Cambrian forms. This evidence indicates that anomalocaridids, Opabinia, and Kerygmachela form a monophyletic clade. Certain features indicate arthropod affinities of the lade, and for this group an unnamed (sub)phylum-level taxon within an arthropod (super)phylum is proposed. 相似文献
13.
The Ediacarian, here defined as the initial period and system of the Phanerozoic Eon, is characterized by the oldest known multicellular animal life. The distinctive biotal assemblage comprises naked Metazoa, represented in the type region by 26 species in 18 genera and 4 or more phyla, plus simple metazoan surface tracks. Elements of this unique biota appeared worldwide at low paleolatitudes, following terminal Proterozoic glaciation. Ediacarian history lasted from about 670 million to 550 million years ago. This interval, plus Early Cambrian, was the time during which metazoan life diversified into nearly all of the major phyla and most of the invertebrate classes and orders subsequently known. 相似文献
14.
An analysis of the range of morphology among arthropods demonstrates that disparity among living arthropods is similar to that in Cambrian arthropods. The range of morphological design resulting from the Cambrian "explosion" has been overestimated, reflecting a tendency to separate as "problematic" taxa that cannot be accommodated in the classification on the basis of the living biota. Problematic taxa are largely an artifact of an inadequate taxonomy. Special evolutionary processes may not be necessary to explain the early radiation of the metazoans. 相似文献
15.
Fossiliferous Cambrian, Ordovician, Mississippian, and Pennsylvanian rocks, never before found in southern Mexico, have been discovered in the Nochixtlán region. Superjacent unfossiliferous sedimentary rocks may be Permian in age. Early Paleozoic and late Paleozoic intervals of marine sedimentation were bounded by intervals of positive tectonism and erosion. 相似文献
16.
Shu DG Morris SC Han J Li Y Zhang XL Hua H Zhang ZF Liu JN Guo JF Yao Y Yasui K 《Science (New York, N.Y.)》2006,312(5774):731-734
Ediacaran assemblages immediately predate the Cambrian explosion of metazoans and should have played a crucial role in this radiation. Their wider relationships, however, have remained refractory and difficult to integrate with early metazoan phylogeny. Here, we describe a frondlike fossil, Stromatoveris (S. psygmoglena sp. nov.), from the Lower Cambrian Chengjiang Lagerst?tte (Yunnan, China) that is strikingly similar to Ediacaran vendobionts. The exquisite preservation reveals closely spaced branches, probably ciliated, that appear to represent precursors of the diagnostic comb rows of ctenophores. Therefore, this finding has important implications for the early evolution of this phylum and related diploblasts, some of which independently evolved a frondose habit. 相似文献
17.
Fluvial sediments in paleovaileys cut in the Ashburton surface of the Davenport province of central Australia form terrace remnants that appear to retain their original depositional tops and have probably existed as subaerial landforms since their inception. Marine fossils in sediments conformable with the fluvial sediments near the southeast margin of the province give a Cambrian age for the terraces; the Ashburton surface forming the ridgetops between the paleovalleys is Cambrian or older. 相似文献
18.
Repetski JE 《Science (New York, N.Y.)》1978,200(4341):529-531
Phosphatic dermal fragments of Anatolepis, interpreted as a heterostracan fish (class Agnatha), have been discovered in the Deadwood Formation of Late Cambrian age in northeastern Wyoming. This discovery extends back the age of the earliest known vertebrate fossils by approximately 40 million years. Other occurrences of Anatolepis in North America, Greenland, and Spitzbergen show that these fish had a widespread geographic distribution in Late Cambrian and Early Ordovician marine environments. 相似文献
19.
Molluscan phylogeny: the paleontological viewpoint 总被引：1，自引：0，他引：1
Stasek (1) theorized that the extant mollusks are the progeny of three separate lineages that separated before the phylum was well established. He wrote that no known intermediate forms, fossil or living, bridge the "enormous gaps between any two of the three lineages," and therefore treated each as a separate subphylum. These subphyla are (i) the subphylum Aculifera Hatscheck 1891, containing only the class Aplacophora, derived from the most primitive ancestors of the Mollusca; (ii) the subphylum Placophora von Jhering 1876, containing only the class Polyplacophora, and emphasizing the pseudometamerism of its more advanced premollusk ancestor; and (iii) the subphylum Conchifera Gegenbaur 1878, containing the Monoplacophora and the other classes derived from it. We point out that the Polyplacophora may be derived from the Monoplacophora instead of a more primitive ancestral stock. We also suggest that the Conchifera can be separated into two major lineages, each worthy of the rank of subphylum. The fossil record indicates that the Monoplacophora gave rise to the Gastropoda, Cephalopoda, Rostroconchia, and possibly Polyplacophora, and that the Pelecypoda and Scaphopoda are derived from the Rostroconchia. These last three classes thus form a lineage that diverged from the Monoplacophora in the Early Cambrian. They emphasized a shell form that in all groups is primitively open at both ends, allowing the gut to remain relatively straight, with an anterior mouth and posterior anus. They became burrowing (infaunal) deposit or filter feeders. We coin the term Diasoma (through-body) for the subphylum containing these three classes (Rostroconchia, Pelecypoda, and Scaphopoda). The remaining three classes (Monoplacophora, Gastropoda, and Cephalopoda) emphasize a conical univalved shell, usually twisted into a spiral. The relatively small single aperture forces the anus to lie close to the mouth, and the gut is bent into a "U." Most are surface-dwelling (epifaunal) grazers or carnivores. We coin the name Cyrtosoma (hunchback-body) for the subphylum containing these three classes. Strictly speaking, the cyrtosomes are the ancestors of the diasomes but, in fact, both subphyla appeared and began to diversify within a few million years in the Early Cambrian. Note added in proof: After proofs were corrected we were informed that the new genus Opikella (40) is preoccupied by (Opikella = Oepikella) Thorslund 1940, an Ordovican ostracod. We rename the mollusk genus Oepikila. 相似文献
20.
We have discovered numerous borings of Trypanites penetrating skeletons and synsedimentary cemented limestones in archaeocyathid reefs of the Forteau formation in southern Labrador. These are, to date, the oldest known macroborings. The discovery of these structures extends the record of large endolithic organisms 100 million years from the Lower Ordovician to the Lower Cambrian. This immediately postdates the appearance of metazoans with hard parts and confirms that endoliths have played a role in reef formation since the early Cambrian. 相似文献