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1.
Graham E. Budd Sören Jensen 《Biological reviews of the Cambridge Philosophical Society》2017,92(1):446-473
The earliest evolution of the animals remains a taxing biological problem, as all extant clades are highly derived and the fossil record is not usually considered to be helpful. The rise of the bilaterian animals recorded in the fossil record, commonly known as the ‘Cambrian explosion’, is one of the most significant moments in evolutionary history, and was an event that transformed first marine and then terrestrial environments. We review the phylogeny of early animals and other opisthokonts, and the affinities of the earliest large complex fossils, the so‐called ‘Ediacaran’ taxa. We conclude, based on a variety of lines of evidence, that their affinities most likely lie in various stem groups to large metazoan groupings; a new grouping, the Apoikozoa, is erected to encompass Metazoa and Choanoflagellata. The earliest reasonable fossil evidence for total‐group bilaterians comes from undisputed complex trace fossils that are younger than about 560 Ma, and these diversify greatly as the Ediacaran–Cambrian boundary is crossed a few million years later. It is generally considered that as the bilaterians diversified after this time, their burrowing behaviour destroyed the cyanobacterial mat‐dominated substrates that the enigmatic Ediacaran taxa were associated with, the so‐called ‘Cambrian substrate revolution’, leading to the loss of almost all Ediacara‐aspect diversity in the Cambrian. Why, though, did the energetically expensive and functionally complex burrowing mode of life so typical of later bilaterians arise? Here we propose a much more positive relationship between late‐Ediacaran ecologies and the rise of the bilaterians, with the largely static Ediacaran taxa acting as points of concentration of organic matter both above and below the sediment surface. The breaking of the uniformity of organic carbon availability would have signalled a decisive shift away from the essentially static and monotonous earlier Ediacaran world into the dynamic and burrowing world of the Cambrian. The Ediacaran biota thus played an enabling role in bilaterian evolution similar to that proposed for the Savannah environment for human evolution and bipedality. Rather than being obliterated by the rise of the bilaterians, the subtle remnants of Ediacara‐style taxa within the Cambrian suggest that they remained significant components of Phanerozoic communities, even though at some point their enabling role for bilaterian evolution was presumably taken over by bilaterians or other metazoans. Bilaterian evolution was thus an essentially benthic event that only later impacted the planktonic environment and the style of organic export to the sea floor. 相似文献
2.
Alicia S. Arroyo David López-Escardó Colomban de Vargas I?aki Ruiz-Trillo 《Biology letters》2016,12(9)
Animals with bilateral symmetry comprise the majority of the described species within Metazoa. However, the nature of the first bilaterian animal remains unknown. As most recent molecular phylogenies point to Xenacoelomorpha as the sister group to the rest of Bilateria, understanding their biology, ecology and diversity is key to reconstructing the nature of the last common bilaterian ancestor (Urbilateria). To date, sampling efforts have focused mainly on coastal areas, leaving potential gaps in our understanding of the full diversity of xenacoelomorphs. We therefore analysed 18S rDNA metabarcoding data from three marine projects covering benthic and pelagic habitats worldwide. Our results show that acoels have a greater richness in planktonic environments than previously described. Interestingly, we also identified a putative novel clade of acoels in the deep benthos that branches as sister group to the rest of Acoela, thus representing the earliest-branching acoel clade. Our data highlight deep-sea environments as an ideal habitat to sample acoels with key phylogenetic positions, which might be useful for reconstructing the early evolution of Bilateria. 相似文献
3.
James W. Hagadorn Stephen A. Schellenberg David J. Bottjer 《Lethaia: An International Journal of Palaeontology and Stratigraphy》2000,33(3):142-156
The Lower Cambrian Poleta Formation in the White-Inyo Mountains of eastern California contains well-preserved and laterally extensive exposures of the large looping and meandering trace fossil Taphrhelminthopsis nelsoni n.isp. Such traces are typical features on upper bed surfaces of Lower Cambrian shallow marine sandstones and occur with Ediacaran fossils at other localities. Morphologic, sedimentologic and goniogram analyses suggest that the inferred tracemaker was a large soft-bodied echinozoan- or mollusc-grade animal with a volume greater than 14 cm3 that actively grazed or ingested sediment at the sediment-water interface. Although portions of these traces appear to reflect relatively 'complex' behavior, looping patterns are not periodic as expected for a systematic foraging strategy. T. nelsoni traces are patchy in distribution and commonly associated with suspect-microbial features, suggesting that tracemakers may have been targeting microbial-based or related concentrations of food resources. Such behavioral patterns are typical of shallow late Neoproterozoic-early Cambrian settings, and like suspect-microbial structures are later restricted to deep marine or stressed settings. 相似文献
4.
Andreas Wanninger Tim Wollesen 《Biological reviews of the Cambridge Philosophical Society》2019,94(1):102-115
Molluscs are extremely diverse invertebrate animals with a rich fossil record, highly divergent life cycles, and considerable economical and ecological importance. Key representatives include worm‐like aplacophorans, armoured groups (e.g. polyplacophorans, gastropods, bivalves) and the highly complex cephalopods. Molluscan origins and evolution of their different phenotypes have largely remained unresolved, but significant progress has been made over recent years. Phylogenomic studies revealed a dichotomy of the phylum, resulting in Aculifera (shell‐less aplacophorans and multi‐shelled polyplacophorans) and Conchifera (all other, primarily uni‐shelled groups). This challenged traditional hypotheses that proposed that molluscs gradually evolved complex phenotypes from simple, worm‐like animals, a view that is corroborated by developmental studies that showed that aplacophorans are secondarily simplified. Gene expression data indicate that key regulators involved in anterior–posterior patterning (the homeobox‐containing Hox genes) lost this function and were co‐opted into the evolution of taxon‐specific novelties in conchiferans. While the bone morphogenetic protein (BMP)/decapentaplegic (Dpp) signalling pathway, that mediates dorso‐ventral axis formation, and molecular components that establish chirality appear to be more conserved between molluscs and other metazoans, variations from the common scheme occur within molluscan sublineages. The deviation of various molluscs from developmental pathways that otherwise appear widely conserved among metazoans provides novel hypotheses on molluscan evolution that can be tested with genome editing tools such as the CRISPR/Cas9 (clustered regularly interspaced short palindromic repeats/clustered regularly interspaced short palindromic repeats‐associated protein9) system. 相似文献
5.
STEPHEN P. HESSELBO 《Lethaia: An International Journal of Palaeontology and Stratigraphy》1988,21(2):139-146
A new trace fossil, Raaschichnus gundersoni , from the Upper Cambrian St. Lawrence Formation of Wisconsin, was produced by an aglaspidid arthropod. The rusophyciform trace, which occurs singly and in series, is distinctive in showing marks left by the tail-spine. Other trace fossils previously considered to have been made by aglaspidids were probably excavated by animals lacking a tail-spine and with appendage morphologies very different from the aglaspidids of Wisconsin. 相似文献
6.
RICHARD A. FORTEY ADOLF SEILACHER 《Lethaia: An International Journal of Palaeontology and Stratigraphy》1997,30(2):105-112
A set of criteria is suggested for associating a trace fossil with a plausible fossil: (1) close association in the field; (2) concurrent stratigraphic range; (3) a minimal choice of candidates available that could have made the trace; (4) consistent size range between trace fossil population and that of the maker; and (5) consistent biogeographic ranges for both. In the Upper Cambrian Andam Formation of Oman, there is a rare, direct association between trilobite body fossils and the trace fossil Cruziana in the same rock succession. An association of the trilobite Maladioidella cf. colcheni with the trace fossil Cruziana semiplicata is supported by the criteria listed. Maladioidella is associated with C. semiplicata over a wide geographical area in western Gondwana. It is therefore likely that some Cruziana species were made by trilobites. 相似文献
7.
《Palaeoworld》2022,31(1):30-40
Oldhamia trace fossils represent a complex horizontal burrow system usually associated with microbial mats, occurring in the upper part of the Cambrian Stage 2 of the Terreneuvian Series, with a peak in abundance during Stage 3 and 4 of Series 2, and then rapidly disappearing in the Wuliuan Stage of the Miaolingian Series. We here report Oldhamia radiata from the Cambrian Series 2 Xinji Formation in western Henan of North China, associated with microbial mats, as evidenced by the presence of wrinkle structures. The distinctive patterns indicate the exploitation of microbial mats by the tracemakers of O. radiata, featuring a specific feeding strategy under the mats where possibly anoxic and sulfidic conditions prevailed during the early Cambrian. 相似文献
8.
Jun Sun Xiaoping Chen Mantang Wang Jinlong Li Quanlin Zhong Dongliang Cheng 《Ecology and evolution》2020,10(23):13395
Understanding the scaling between leaf size and leafing intensity (leaf number per stem size) is crucial for comprehending theories about the leaf costs and benefits in the leaf size–twig size spectrum. However, the scaling scope of leaf size versus leafing intensity changes along the twig leaf size variation in different leaf habit species remains elusive. Here, we hypothesize that the numerical value of scaling exponent for leaf mass versus leafing intensity in twig is governed by the minimum leaf mass versus maximum leaf mass (M min versus M max) and constrained to be ≤−1.0. We tested this hypothesis by analyzing the twigs of 123 species datasets compiled in the subtropical mountain forest. The standardized major axis regression (SMA) analyses showed the M min scaled as the 1.19 power of M max and the ‐α (−1.19) were not statistically different from the exponents of M min versus leafing intensity in whole data. Across leaf habit groups, the M max scaled negatively and isometrically with respect to leafing intensity. The pooled data''s scaling exponents ranged from −1.14 to −0.96 for M min and M max versus the leafing intensity based on stem volume (LIV). In the case of M min and M max versus the leafing intensity based on stem mass (LIM), the scaling exponents ranged from −1.24 to −1.04. Our hypothesis successfully predicts that the scaling relationship between leaf mass and leafing intensity is constrained to be ≤−1.0. More importantly, the lower limit to scaling of leaf mass and leafing intensity may be closely correlated with M min versus M max. Besides, constrained by the maximum leaf mass expansion, the broad scope range between leaf size and number may be insensitive to leaf habit groups in subtropical mountain forest. 相似文献
9.
Jan Bergström 《Ichnos》2013,20(1):3-13
In this attempt to synthesize present knowledge into a coherent story, the Cambrian explosion is interpreted to represent a true adaptive radiation, an event similar to Phanerozoic radiation events in principle but unique in its possibilities. A model of bilaterian evolution helps explain how this particular event involved the sudden initiation of major coelomate phyla. In many of these groups, preservable skeletons are part of the basic body plan. Biochemical‐sequence analyses indicate that acoelomates and pseudocoelomates branched off long before the coelomate radiation. The great differences between Vendian and Cambrian ichnofaunas, therefore, may be the result of a major shift in composition from Vendian acoelomate‐pseudocoelomate‐procoelomate faunas to Phanerozoic faunas dominated by new coelomate groups. 相似文献
10.
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
11.
Abstract: The Cambrian index fossil Treptichnus pedum is reported from the Puerto Blanco Formation near Pitiquito, Sonora, Mexico, and new occurrences of the Neoproterozoic index fossil Cloudina are reported from the underlying La Ciénega Formation. Considered together, these fossils constrain the location of the Ediacaran/Cambrian boundary in Mexico. The suite of fossils in this sequence is important because it provides an independent biostratigraphic datum for constraining the position of Laurentia during the onset of metazoan diversification, for testing proposed lithostratigraphic correlations among western North American Neoproterozoic–Cambrian successions, and for testing regional tectonic paradigms such as the Mojave-Sonora Megashear hypothesis. 相似文献
12.
Woodlice are fully terrestrial crustaceans and are known to be sensitive to water loss. Their half‐ellipsoidal shapes represent simple models in which to investigate theoretical assumptions about organism morphology and rates of exchange with the environment. We examine the influence of surface area and mass on the desiccation rates in three eco‐morphologically different species of woodlice: Oniscus asellus, Porcellio scaber, and Armadillidium vulgare. Our analysis indicates that the rate of water loss of an individual depends on both the initial weight and the body surface area. Interspecific and intraspecific analyses show that the mass‐specific water loss rate of a species decreases along with the ratio of surface area to volume. In particular, we show that body shape explains the difference in mass‐specific water loss rates between A. vulgare and P. scaber. This observation also explains several known ecological patterns, for example, the distribution and survivorship of individuals. However, in addition to body size and shape, water loss in terrestrial isopods depends also on the coefficient of permeability (i.e., a measure of water loss rate per surface unit), which is high in O. asellus and lower (and at similar levels) in P. scaber and A. vulgare. We discuss morphological, physiological, and behavioral aspects of water loss avoidance in terrestrial isopods. J. Morphol. 276:1283–1289, 2015. © 2015 Wiley Periodicals, Inc. 相似文献
13.
Damesella paronai is the earliest enrolled odontopleurid trilobite to be found in the fossil record. Whereas its interlocking devices were very poorly developed, its trunk shows advanced articulations, which only lack an articulating facet, though an anterior notch is present in the outer part of each pleura. Its body pattern and structures did not allow it an encapsulated enrolment style. On the other hand, it is coeval with the early asaphid Monkaspis daulis, found in the same beds and at the same level. This co-inhabiting trilobite had a more advanced structure that enabled it to achieve a fully enrolled, encapsulated style. These superior structures enhance the preservation of enrolled specimens of M. daulis, and it seems to be generally the case that more elegant structures actually improve preservation. The evolutionary trends of the lineages of these two trilobites show that while odontopleurids were very conservative, using the same enrolment style throughout their history, the asaphids developed different enrolment styles, which was one factor in giving them a capacity to occupy different ecological niches and a greater range of environments. 相似文献
14.
Lauren C. Sallan 《Biological reviews of the Cambridge Philosophical Society》2014,89(4):950-971
Ray‐finned fishes (Actinopterygii) dominate modern aquatic ecosystems and are represented by over 32000 extant species. The vast majority of living actinopterygians are teleosts; their success is often attributed to a genome duplication event or morphological novelties. The remainder are ‘living fossils’ belonging to a few depauperate lineages with long‐retained ecomorphologies: Polypteriformes (bichirs), Holostei (bowfin and gar) and Chondrostei (paddlefish and sturgeon). Despite over a century of systematic work, the circumstances surrounding the origins of these clades, as well as their basic interrelationships and diagnoses, have been largely mired in uncertainty. Here, I review the systematics and characteristics of these major ray‐finned fish clades, and the early fossil record of Actinopterygii, in order to gauge the sources of doubt. Recent relaxed molecular clock studies have pushed the origins of actinopterygian crown clades to the mid‐late Palaeozoic [Silurian–Carboniferous; 420 to 298 million years ago (Ma)], despite a diagnostic body fossil record extending only to the later Mesozoic (251 to 66 Ma). This disjunct, recently termed the ‘Teleost Gap’ (although it affects all crown lineages), is based partly on calibrations from potential Palaeozoic stem‐taxa and thus has been attributed to poor fossil sampling. Actinopterygian fossils of appropriate ages are usually abundant and well preserved, yet long‐term neglect of this record in both taxonomic and systematic studies has exacerbated the gaps and obscured potential synapomorphies. At the moment, it is possible that later Palaeozoic‐age teleost, holostean, chondrostean and/or polypteriform crown taxa sit unrecognized in museum drawers. However, it is equally likely that the ‘Teleost Gap’ is an artifact of incorrect attributions to extant lineages, overwriting both a post‐Palaeozoic crown actinopterygian radiation and the ecomorphological diversity of stem‐taxa. 相似文献
15.
Responses of morphology and biomass allocation of roots to frequency of nitrogen (N) pulse potentially influence the fitness of plants, but such responses may be determined by root size. We grew 12 plant species of three functional groups (grasses, forbs, and legumes) under two N pulse frequencies (high vs. low supply frequency) and two N amounts (high vs. low supply amount). Compared to low-amount N supply, high-amount N supply stimulated biomass accumulation and root growth by either increasing the thickness and length of roots or decreasing the root mass fraction. Compared to low-frequency N supply, high-frequency N supply improved biomass accumulation and root growth in forbs or grasses, but not in legumes. Furthermore, the magnitude of the response to N frequency was significantly negatively correlated with root size at the species scale, but this was only true when the N amount was high. We conclude that root responses to N frequency are related to plant functional types, and non-legume species is more sensitive to N frequency than legume species. Our results also suggest that root size is a determinant of root responses to N frequency when N supply amount is high. 相似文献
16.
M. Gabriela Mngano Luis A. Buatois Beatriz G. Waisfeld Diego F. Muoz N. Emilio Vaccari Ricardo A. Astini 《Proceedings. Biological sciences / The Royal Society》2021,288(1944)
Trilobites, key components of early Palaeozoic communities, are considered to have been invariably fully marine. Through the integration of ichnological, palaeobiological, and sedimentological datasets within a sequence-stratigraphical framework, we challenge this assumption. Here, we report uncontroversial trace and body fossil evidence of their presence in brackish-water settings. Our approach allows tracking of some trilobite groups foraying into tide-dominated estuaries. These trilobites were tolerant to salinity stress and able to make use of the ecological advantages offered by marginal-marine environments migrating up-estuary, following salt wedges either reflecting amphidromy or as euryhaline marine wanderers. Our data indicate two attempts of landward exploration via brackish water: phase 1 in which the outer portion of estuaries were colonized by olenids (Furongian–early late Tremadocian) and phase 2 involving exploration of the inner to middle estuarine zones by asaphids (Dapingian–Darriwilian). This study indicates that tolerance to salinity stress arose independently among different trilobite groups. 相似文献
17.
Maarten J M Christenhusz Mark W Chase Michael F Fay Oriane Hidalgo Ilia J Leitch Jaume Pellicer Juan Viruel 《Annals of botany》2021,127(5):681
Background and AimsExtant plant groups with a long fossil history are key elements in understanding vascular plant evolution. Horsetails (Equisetum, Equisetaceae) have a nearly continuous fossil record dating back to the Carboniferous, but their phylogenetic and biogeographic patterns are still poorly understood. We use here the most extensive phylogenetic analysis to date as a framework to evaluate their age, biogeography and genome size evolution.MethodsDNA sequences of four plastid loci were used to estimate divergence times and investigate the biogeographic history of all extant species of Equisetum. Flow cytometry was used to study genome size evolution against the framework of phylogenetic relationships in Equisetum.Key ResultsOn a well-supported phylogenetic tree including all extant Equisetum species, a molecular clock calibrated with multiple fossils places the node at which the outgroup and Equisetum diverged at 343 Mya (Early Carboniferous), with the first major split among extant species occurring 170 Mya (Middle Jurassic). These dates are older than those reported in some other recent molecular clock studies but are largely in agreement with a timeline established by fossil appearance in the geological record. Representatives of evergreen subgenus Hippochaete have much larger genome sizes than those of deciduous subgenus Equisetum, despite their shared conserved chromosome number. Subgenus Paramochaete has an intermediate genome size and maintains the same number of chromosomes.ConclusionsThe first divergences among extant members of the genus coincided with the break-up of Pangaea and the resulting more humid, warmer climate. Subsequent tectonic activity most likely involved vicariance events that led to species divergences combined with some more recent, long-distance dispersal events. We hypothesize that differences in genome size between subgenera may be related to the number of sperm flagellae. 相似文献
18.
KENNETH J. McNAMARA DAVID M. RUDKIN 《Lethaia: An International Journal of Palaeontology and Stratigraphy》1984,17(2):153-173
Examples of the trilobites Toxochasmops extensus (Boeck, 1838), Asaphiscus wheeleri Meek, 1874, Encrinurus mitchelli Foerste, 1888, Ogygopsis klotzi (Rominger, 1887), Paradoxides davidis Salter, 1863 and Oryctocephalus spp. which are interpreted as exuvial configurations, are described. Four specimens of Toxochasmops extensus arc known in which the pygidium rests either directly behind the eephalon, or with only three intervening thoracic segments. It is considered that during exuviation the old pygidium became wedged behind the cephalon. This facilitated its removal. An ecdysial configuration of Asaphiscus wheeleri is described which possesses inverted and partially rotated free cheeks. In addition, part of the thorax of the specimen is wedged obliquely behind the cephalon. This is considered to have aided withdrawal of the trilobite from its old exoskeleton. Two specimens of Encrinurus mitchelli are described which possess free cheeks inverted beneath the cranidium by lateral rotation, in a manner similar to that of A. wheeleri. Three examples of Ogygopsis klotzi are described, one a failed exuvia and two in which the free cheeks were inverted and rotated through 180° with respect to their original position and came to rest beneath the thorax. An identical exuvia of Paradoxides davidis trapezopyge is also described. Two specimens of Oryctocephalus exhibiting two different arrangements of inverted free cheeks are recorded. Possible mechanisms for each of these free cheek inversions are proposed. 相似文献
19.
John A. Finarelli Anjali Goswami 《Evolution; international journal of organic evolution》2013,67(12):3678-3685
Reconstructing evolutionary patterns and their underlying processes is a central goal in biology. Yet many analyses of deep evolutionary histories assume that data from the fossil record is too incomplete to include, and rely solely on databases of extant taxa. Excluding fossil taxa assumes that character state distributions across living taxa are faithful representations of a clade's entire evolutionary history. Many factors can make this assumption problematic. Fossil taxa do not simply lead‐up to extant taxa; they represent now‐extinct lineages that can substantially impact interpretations of character evolution for extant groups. Here, we analyze body mass data for extant and fossil canids (dogs, foxes, and relatives) for changes in mean and variance through time. AIC‐based model selection recovered distinct models for each of eight canid subgroups. We compared model fit of parameter estimates for (1) extant data alone and (2) extant and fossil data, demonstrating that the latter performs significantly better. Moreover, extant‐only analyses result in unrealistically low estimates of ancestral mass. Although fossil data are not always available, reconstructions of deep‐time organismal evolution in the absence of deep‐time data can be highly inaccurate, and we argue that every effort should be made to include fossil data in macroevolutionary studies. 相似文献
20.
The ～37 million-year-old Birket Qarun Locality 2 (BQ-2), in the Birket Qarun Formation of Egypt's Fayum Depression, yields evidence for a diverse primate fauna, including the earliest known lorisiforms, parapithecoid anthropoids, and Afradapis longicristatus, a large folivorous adapiform. Phylogenetic analysis has placed Afradapis as a stem strepsirrhine within a clade of caenopithecine adapiforms, contradicting the recently popularized alternative hypothesis aligning adapiforms with haplorhines or anthropoids. We describe an astragalus from BQ-2 (DPC 21445C), attributable to Afradapis on the basis of size and relative abundance. The astragalus is remarkably similar to those of extant lorises, having a low body, no posterior shelf, a broad head and neck. It is like extant strepsirrhines more generally, in having a fibular facet that slopes gently away from the lateral tibial facet, and in having a groove for the tendon of flexor fibularis that is lateral to the tibial facet. Comparisons to a sample of euarchontan astragali show the new fossil to be most similar to those of adapines and lorisids. The astragali of other adapiforms are most similar to those of lemurs, but distinctly different from those of all anthropoids. Our measurements show that in extant strepsirrhines and adapiforms the fibular facet slopes away from the lateral tibial facet at a gradual angle (112-126°), in contrast to the anthropoid fibular facet, which forms a sharper angle (87-101°). Phylogenetic analyses incorporating new information from the astragalus continue to support strepsirrhine affinities for adapiforms under varying models of character evolution. 相似文献