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Precambrian and early Cambrian palaeobiology of India: Quo Vadis. PROCEEDINGS OF THE INDIAN NATIONAL SCIENCE ACADEMY 2021. [DOI: 10.1007/s43538-021-00029-2] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/25/2022]
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2
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Mucin CYS domains are ancient and highly conserved modules that evolved in concert. Mol Phylogenet Evol 2009; 52:284-92. [DOI: 10.1016/j.ympev.2009.03.035] [Citation(s) in RCA: 31] [Impact Index Per Article: 2.1] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 09/17/2008] [Revised: 03/17/2009] [Accepted: 03/27/2009] [Indexed: 11/22/2022]
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BUDD GRAHAME, JENSEN SÖREN. A critical reappraisal of the fossil record of the bilaterian phyla. Biol Rev Camb Philos Soc 2007. [DOI: 10.1111/j.1469-185x.1999.tb00046.x] [Citation(s) in RCA: 18] [Impact Index Per Article: 1.1] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/27/2022]
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5
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Fedonkin MA, Simonetta A, Ivantsov AY. New data on Kimberella, the Vendian mollusc-like organism (White Sea region, Russia): palaeoecological and evolutionary implications. ACTA ACUST UNITED AC 2007. [DOI: 10.1144/sp286.12] [Citation(s) in RCA: 55] [Impact Index Per Article: 3.2] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/04/2022]
Abstract
AbstractThe taphonomic varieties of over 800 specimens of Kimberella (collected from the Vendian rocks of the White Sea region) provide new evidence of the animal's anatomy such as: shell morphology, proboscis, mantle, possibly respiratory folds and possibly musculature, stomach and glands. Feeding tracks, crawling trails and, presumably, escape structures preserved along with the body imprint provide insights on the mode of locomotion and feeding of this animal. The shield-like dorsal shell reached up to 15 cm in length, 5–7 cm in width, and 3–4 cm in height. The shell was stiff but flexible. Evidence of dorso-ventral musculature and fine transverse ventral musculature suggests arrangement in a metameric pattern. Locomotion may have been by means of peristaltic waves, both within the sediment and over the surface of the sea floor, by means of a foot resembling that of monoplacophorans. Respiration may have been through a circumpedal folded strip (possibly an extension of the mantle). Feeding was accomplished by a retractable proboscis bearing terminal hook-like organs and provided with a pair of structures interpreted here as glands. Whilst feeding, Kimberella moved backwards. The structural complexity of Kimberella poses questions about the time of origin of the triploblastic metazoans.
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Affiliation(s)
- M. A. Fedonkin
- Paleontological Institute, Russian Academy of Sciences, Profsoyuznaya ul., 123, Moscow, 117997 Russia (e-mail: )
- Honorary Research Fellow, School of Geosciences, Monash University, Melbourne, Victoria 3800, Australia
| | - A. Simonetta
- Dipartimento di Biologia Animale e Genetica ‘Leo Pardi’, Universita degli studi di Firenze, via Romana 17, 50125 Florence, Italy
| | - A. Y. Ivantsov
- Paleontological Institute, Russian Academy of Sciences, Profsoyuznaya ul., 123, Moscow, 117997 Russia (e-mail: )
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Raff EC, Villinski JT, Turner FR, Donoghue PCJ, Raff RA. Experimental taphonomy shows the feasibility of fossil embryos. Proc Natl Acad Sci U S A 2006; 103:5846-51. [PMID: 16571655 PMCID: PMC1416897 DOI: 10.1073/pnas.0601536103] [Citation(s) in RCA: 103] [Impact Index Per Article: 5.7] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/18/2022] Open
Abstract
The recent discovery of apparent fossils of embryos contemporaneous with the earliest animal remains may provide vital insights into the metazoan radiation. However, although the putative fossil remains are similar to modern marine animal embryos or larvae, their simple geometric forms also resemble other organic and inorganic structures. The potential for fossilization of animals at such developmental stages and the taphonomic processes that might affect preservation before mineralization have not been examined. Here, we report experimental taphonomy of marine embryos and larvae similar in size and inferred cleavage mode to presumptive fossil embryos. Under conditions that prevent autolysis, embryos within the fertilization envelope can be preserved with good morphology for sufficiently long periods for mineralization to occur. The reported fossil record exhibits size bias, but we show that embryo size is unlikely to be a major factor in preservation. Under some conditions of death, fossilized remains will not accurately reflect the cell structure of the living organism. Although embryos within the fertilization envelope have high preservation potential, primary larvae have negligible preservation potential. Thus the paleo-embryological record may have strong biases on developmental stages preserved. Our data provide a predictive basis for interpreting the fossil record to unravel the evolution of ontogeny in the origin of metazoans.
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Affiliation(s)
- Elizabeth C Raff
- Department of Biology and Indiana Molecular Biology Institute, Indiana University, Myers Hall 150, 915 East Third Street, Bloomington, IN 47405, USA.
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Farrell AH, Hohenstein KA, Shain DH. Molecular Adaptation in the Ice Worm, Mesenchytraeus solifugus: Divergence of Energetic-Associated Genes. J Mol Evol 2004; 59:666-73. [PMID: 15693622 DOI: 10.1007/s00239-004-2658-z] [Citation(s) in RCA: 11] [Impact Index Per Article: 0.6] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/14/2022]
Abstract
The ice worm, Mesenchytraeus solifugus, is the largest glacially obligate metazoan and among only a few metazoan species that complete their life cycle at 0 degrees C. We conducted a large-scale sequencing analysis of cDNAs isolated from ice worm anterior segments. Sequence comparisons among an available group of ice worm, arthropod, chordate, and nematode homologues suggest that ice worms encode proteins that are less bulky, are less polar, and contain fewer charged residues. Also, subunits of the catalytic F1 ATP synthase complex appear to have diverged more rapidly than other ice worm genes examined, suggesting a role in cold-temperature adaptation. Modeling of F1 ATP synthase beta and gamma subunits identified nonconservative, ice worm-specific amino acid substitutions at subunit contact sites and at sites proximal to the catalytic site.
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Affiliation(s)
- Angela H Farrell
- Biology Department, 315 Penn Street, Rutgers The State University of New Jersey, Camden, NJ 08102, USA
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Simonetta AM. Are the traditional classes of arthropods natural ones? Recent advances in palaeontology and some considerations on morphology. ACTA ACUST UNITED AC 2004. [DOI: 10.1080/11250000409356579] [Citation(s) in RCA: 5] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 10/21/2022]
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9
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Delgado S, Casane D, Bonnaud L, Laurin M, Sire JY, Girondot M. Molecular evidence for precambrian origin of amelogenin, the major protein of vertebrate enamel. Mol Biol Evol 2001; 18:2146-53. [PMID: 11719563 DOI: 10.1093/oxfordjournals.molbev.a003760] [Citation(s) in RCA: 57] [Impact Index Per Article: 2.5] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/13/2022] Open
Abstract
Although molecular dating of cladogenetic events is possible, no molecular method has been described to date the acquisition of various tissues. Taking into account the specificity of the major protein in enamel in formation (amelogenin), we were able to develop such a method for enamel. Indeed, because the amelogenin protein is exclusively involved in enamel formation and mineralization and because it lacks pleiotropic effects, this protein is a good candidate to estimate the date of acquisition of this highly mineralized tissue. We searched DNA banks for similarities between the amelogenin sequence and other sequences. Similarities were found only to exon 2 of SPARC (osteonectin) in two protostomians and in eight deuterostomians, and to exon 2 of three SPARC-related deuterostomian genes (SC1, hevin, and QR1). The other amelogenin exons did not reveal significant similarities to other sequences. In these proteins, exon 2 mainly encodes the peptide signal that plays the essential role in enabling the protein to be ultimately localized in the extracellular matrix. We tested the significance of the exon 2 similarities. The observed values were always significantly higher than the expected randomly generated similarities. This demonstrates a common evolutionary origin of this exon. The phylogenetic analyses of exon 2 sequences indicated that exon 2 was duplicated to amelogenin from an ancestral SPARC sequence in the deuterostomian lineage before the duplication of deuterostomian SPARC and SC1/hevin/QR1. We were able to date the origin of the latter duplication at approximately 630 MYA. Therefore, amelogenin exon 2 was acquired before this date, in the Proterozoic, long before the so-called "Cambrian explosion," the sudden appearance of several bilateralian phyla in the fossil record at the Proterozoic-Phanerozoic transition. This sudden appearance has been often suggested to reflect intensive cladogenesis during this period. However, molecular dating of protostomian-deuterostomian divergence and of the cladogenesis among several major clades of Bilateralia lead to a different conclusion: many bilateralian clades were already present during the late Proterozoic. It has previously been proposed that these bilateralians were not mineralized and that they had low fossilization potential. Our results strongly suggest that late Proterozoic fossils possessing a mineralized tissue homologous to enamel might be found in the future.
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Affiliation(s)
- S Delgado
- UMR 8570, Evolution et Adaptations des Systèmes Ostéomusculaires, Paris, France
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Siveter DJ, Williams M, Waloszek D. A phosphatocopid crustacean with appendages from the Lower Cambrian. Science 2001; 293:479-81. [PMID: 11463912 DOI: 10.1126/science.1061697] [Citation(s) in RCA: 78] [Impact Index Per Article: 3.4] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/02/2022]
Abstract
Here we describe a phosphatocopid arthropod with preserved soft anatomy from Lower Cambrian rocks of Shropshire, England, which provides evidence for the occurrence of Crustacea, including Eucrustacea, in the Early Cambrian. The find identifies an important, stratigraphically early source of well-preserved fossils (Konservat-Lagerstätte).
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Affiliation(s)
- D J Siveter
- Department of Geology, University of Leicester, Leicester LE1 7RH, UK.
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Berbee ML, Carmean DA, Winka K. Ribosomal DNA and resolution of branching order among the ascomycota: how many nucleotides are enough? Mol Phylogenet Evol 2000; 17:337-44. [PMID: 11133188 DOI: 10.1006/mpev.2000.0835] [Citation(s) in RCA: 58] [Impact Index Per Article: 2.4] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/22/2022]
Abstract
Molecular phylogenies for the fungi in the Ascomycota rely heavily on 18S rRNA gene sequences but this gene alone does not answer all questions about relationships. Particularly problematical are the relationships among the first ascomycetes to diverge, the Archiascomycetes, and the branching order among the basal filamentous ascomycetes, the Euascomycetes. Would more data resolve branching order? We used the jackknife and bootstrapping resampling approach that constitutes the "pattern of resolved nodes" method to address the relationship between number of variable sites in a DNA sequence alignment and support for taxonomic clusters. We graphed the effect of increasing sizes of subsamples of the 18S rRNA gene sequences on bootstrap support for nodes in the Ascomycota tree. Nodes responded differently to increasing data. Some nodes, those uniting the filamentous ascomycetes for example, would still have been well supported with only two thirds of the 18S rRNA gene. Other nodes, like the one uniting the Archiascomycetes as a monophyletic group, would require about double the number of variable sites available in the 18S gene for 95% neighbor-joining bootstrap support. Of the several groups emerging at the base of the filamentous ascomycetes, the Pezizales receive the most support as the first to diverge. Our analysis suggests that we would also need almost three times as much sequence data as that provided by the 18S gene to confirm the basal position for the Pezizales and more than seven times as much data to resolve the next group to diverge. If more data from other genes show the same pattern, the lack of resolution for the filamentous ascomycetes may indicate rapid radiation within this clade.
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Affiliation(s)
- M L Berbee
- Department of Botany, University of British Columbia, Vancouver, British Columbia, V6T 1Z4, Canada.
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Robson P, Wright GM, Youson JH, Keeley FW. The structure and organization of lamprin genes: multiple-copy genes with alternative splicing and convergent evolution with insect structural proteins. Mol Biol Evol 2000; 17:1739-52. [PMID: 11070061 DOI: 10.1093/oxfordjournals.molbev.a026272] [Citation(s) in RCA: 22] [Impact Index Per Article: 0.9] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/12/2022] Open
Abstract
Lamprin is a unique structural protein which forms the extracellular matrix of several cartilaginous structures found in the lamprey. Lamprin is noncollagenous in nature but shows sequence similarities to elastins and to insect structural proteins. Here, we characterize the structure and organization of lamprin genes, demonstrating the presence of multiple similar but not identical copies of the lamprin gene in the genome of the lamprey. In at least one species of lamprey, Lampetra richardsoni, the multiple gene copies are arranged in tandem in the genome in a head-to-tail orientation. Lamprin genes from Petromyzon marinus contain either seven or eight exons, with exon 4 being alternatively spliced in all genes, resulting in a total of six different lamprin transcripts. All exon junctions are of class 1,1. An unusual feature of the lamprin gene structure is the distribution of the 3' untranslated region sequence among multiple exons. A TATA box and cap sequence have been identified in upstream sequences in close proximity to the transcription start site, but no CAAT box could be identified. Sequence and gene structure comparisons between lamprins, elastins, and insect structural proteins suggest that the regions of sequence similarity are the result of a process of convergent evolution.
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Affiliation(s)
- P Robson
- Division of Cardiovascular Research, Hospital for Sick Children and Department of Biochemistry, University of Toronto, Toronto, Canada
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Jenner RA. Evolution of animal body plans: the role of metazoan phylogeny at the interface between pattern and process. Evol Dev 2000; 2:208-21. [PMID: 11252564 DOI: 10.1046/j.1525-142x.2000.00060.x] [Citation(s) in RCA: 62] [Impact Index Per Article: 2.6] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/20/2022]
Abstract
Comprehensive integrative studies are the hallmark of evolutionary developmental biology. A properly defined phylogenetic framework takes a central place in such analyses as the meeting ground for observation and inference. Molecular phylogenies take this place in many current studies on animal body plan evolution. In particular, 18S rRNA/DNA sequence analyses have yielded a new view of animal evolution that is often contrasted with a presumed traditional or classical view. First, I expose this traditional view to be a simplified historical abstraction that became textbook dogma. Second, I discuss how two recent important studies of animal body plan evolution, examining the evolution of the platyhelminth body plan and the evolutionary significance of indirect development and set-aside cells, have actively incorporated two problematic aspects of the newly emerging molecular view of animal evolution: incomplete and unresolved phylogenies.
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Affiliation(s)
- R A Jenner
- Institute for Biodiversity and Ecosystem Dynamics, University of Amsterdam, The Netherlands.
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Bromham LD, Hendy MD. Can fast early rates reconcile molecular dates with the Cambrian explosion? Proc Biol Sci 2000; 267:1041-7. [PMID: 10874755 PMCID: PMC1690629 DOI: 10.1098/rspb.2000.1108] [Citation(s) in RCA: 38] [Impact Index Per Article: 1.6] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/12/2022] Open
Abstract
Molecular dates consistently place the divergence of major metazoan lineages in the Precambrian, leading to the suggestion that the 'Cambrian explosion' is an artefact of preservation which left earlier forms unrecorded in the fossil record. While criticisms of molecular analyses for failing to deal with variation in the rate of molecular evolution adequately have been countered by analyses which allow both site-to-site and lineage-specific rate variation, no analysis to date has allowed the rates to vary temporally. If the rates of molecular evolution were much higher early in the metazoan radiation, molecular dates could consistently overestimate the divergence times of lineages. Here, we use a new method which uses multiple calibration dates and an empirically determined range of possible substitution rates to place bounds on the basal date of divergence of lineages in order to ask whether faster rates of molecular evolution early in the metazoan radiation could possibly account for the discrepancy between molecular and palaeontological date estimates. We find that allowing basal (interphylum) lineages the fastest observed substitution rate brings the minimum possible divergence date (586 million years ago) to the Vendian period, just before the first multicellular animal fossils, but excludes divergence of the major metazoan lineages in a Cambrian explosion.
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Affiliation(s)
- L D Bromham
- Department of Zoology, University of Queensland, Brisbane, Australia.
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15
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Müller WEG, Skorokhod A, Müller IM. Receptor Tyrosine Kinase, an Autapomorphic Character of Metazoa: Identification in Marine Sponges. ACTA BIOLOGICA HUNGARICA 1999. [DOI: 10.1007/bf03543061] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/30/2022]
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16
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Affiliation(s)
- A B Smith
- Department of Palaeontology, Natural History Museum, Crornwell Road, London SW7 5BD, UK.
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Conway Morris S. The question of metazoan monophyly and the fossil record. PROGRESS IN MOLECULAR AND SUBCELLULAR BIOLOGY 1999; 21:1-19. [PMID: 9928534 DOI: 10.1007/978-3-642-72236-3_1] [Citation(s) in RCA: 6] [Impact Index Per Article: 0.2] [Reference Citation Analysis] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 02/10/2023]
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Bromham L, Rambaut A, Fortey R, Cooper A, Penny D. Testing the Cambrian explosion hypothesis by using a molecular dating technique. Proc Natl Acad Sci U S A 1998; 95:12386-9. [PMID: 9770496 PMCID: PMC22841 DOI: 10.1073/pnas.95.21.12386] [Citation(s) in RCA: 104] [Impact Index Per Article: 4.0] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/03/1998] [Indexed: 11/18/2022] Open
Abstract
Molecular studies have the potential to shed light on the origin of the animal phyla by providing independent estimates of the divergence times, but have been criticized for failing to account adequately for variation in rate of evolution. A method of dating divergence times from molecular data addresses the criticisms of earlier studies and provides more realistic, but wider, confidence intervals. The data are not compatible with the Cambrian explosion hypothesis as an explanation for the origin of metazoan phyla, and provide additional support for an extended period of Precambrian metazoan diversification.
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Affiliation(s)
- L Bromham
- Department of Zoology, University of Oxford, Oxford OX1 3PS, United Kingdom.
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19
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Abstract
The early evolution of metazoans is a major focus of biological attention, but is the historical record revealed in the Cambrian "explosion" an accurate reflection of original events? The key questions concern the nature of the earliest animals and when they originated. One widely-mooted suggestion is that planktotrophic larvae, typified by the annelidan trochophore and echinoid pluteus, existed long before the metazoan radiations evident in the Cambrian fossil record. This idea could be consistent for recent evidence of divergence times, based on molecular "clocks," of phyla appearing well before the Cambrian. Now a surprising new discovery of eggs with blastomeres and embryos with well-defined anatomy from the Cambrian (c.530 Myr ago) of China and Siberia promises to extend the arena of debate. In one case a convincing ontogeny can be traced from eggs to adult tube-dwelling cnidarians. In the other example a possible protostome, unhatched and wrapped around the egg, shows segmentation and possibly nascent sclerites. In both, these cases development is direct, i.e., there is no evidence for any planktotrophic larval stage. The implications for our perceptions of both the Cambrian 'explosion' and metazoan phylogeny could be considerable.
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Affiliation(s)
- S C Morris
- Department of Earth Sciences, University of Cambridge, United Kingdom.
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20
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Oliva M, Messina A, Ragone G, Caggese C, De Pinto V. Sequence and expression pattern of the Drosophila melanogaster mitochondrial porin gene: evidence of a conserved protein domain between fly and mouse. FEBS Lett 1998; 430:327-32. [PMID: 9688565 DOI: 10.1016/s0014-5793(98)00693-0] [Citation(s) in RCA: 14] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 02/08/2023]
Abstract
We have recently cloned a cDNA encoding mitochondrial porin in Drosophila melanogaster and shown its chromosomal localization (Messina et al., FEBS Lett. (1996) 384, 9-13). Such cDNA was used as a probe for screening a genomic library. We thus cloned and sequenced a 4494-bp genomic region which contained the whole gene for the mitochondrial porin or VDAC. It was found that this D. melanogaster porin gene contains five exons, numbered IA (115 bp), IB (123 bp), II (320 bp), III (228 bp) and IV (752 bp). The exons II, III and IV contain the protein coding sequence and the 3' untranslated sequence (3'-UTR). The first base in exon II precisely corresponds to the first base of the starting ATG codon. Exon IA corresponds to the 5'-UTR sequence reported in the published cDNA sequence. Exon IB corresponds to an alternative 5'-UTR sequence, demonstrated to be transcribed by 5'-RACE experiments. The exon-intron splicing borders and the length of the exon III perfectly match a homologous internal exon detected in the mouse genes. Such exon encodes a protein domain predicted by sequence transmembrane arrangement models to contain major hydrophilic loops and it is thus suspected to have a conserved distinct function. In situ hybridization experiments confirmed the localization of the genomic clone on the chromosome 2L at region 32B3-4. Together with genomic Southern blotting at various stringencies, the same experiment did not confirm the presence of a second genetic locus on D. melanogaster chromosomes. Northern blots demonstrated that the porin gene is a housekeeping one: three messages of approx. 1.2-1.6 kbp are transcribed in every fly developmental stage that was studied. They were shown to derive by an alternative usage of different promoters and polyadenylation sites.
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Affiliation(s)
- M Oliva
- Istituto di Scienze Biochimiche e Farmacologiche, Facoltà di Scienze M.F.N., Università di Catania, Italy
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Morris SC. The evolution of diversity in ancient ecosystems: a review. Philos Trans R Soc Lond B Biol Sci 1998. [DOI: 10.1098/rstb.1998.0213] [Citation(s) in RCA: 35] [Impact Index Per Article: 1.3] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/12/2022] Open
Abstract
On a perfect planet, such as might be acceptable to a physicist, one might predict that from its origin the diversity of life would grow exponentially until the carrying capacity, however defined, was reached. The fossil record of the Earth, however, tells a very different story. One of the most striking aspects of this record is the apparent evolutionary longueur, marked by the Precambrian record of prokaryotes and primitive eukaryotes, although our estimates of microbial diversity may be seriously incomplete. Subsequently there were various dramatic increases in diversity, including the Cambrian ‘explosion’ and the radiation of Palaeozoic–style faunas in the Ordovician. The causes of these events are far from resolved. It has also long been appreciated that the history of diversity has been punctuated by important extinctions. The subtleties and nuances of extinction as well as the survival of particular clades have to date, however, received rather too little attention, and there is still a tendency towards blanket assertions rather than a dissection of these extraordinary events. In addition, some but perhaps not all mass extinctions are characterized by long lag–times of recovery, which may reflect the slowing waning of extrinsic forcing factors or alternatively the incoherence associated with biological reassembly of stable ecosystems. The intervening periods between the identified mass extinctions may be less stable and benign than popularly thought, and in particular the frequency of extraterrestrial impacts leads to predictions of recurrent disturbance on timescales significantly shorter than the intervals separating the largest extinction events. Even at times of quietude it is far from clear whether biological communities enjoy stability and interlocked stasis or are dynamically reconstituted at regular intervals. Finally, can we yet rely on the present depictions of the rise and falls in the levels of ancient diversity? Existing data is almost entirely based on Linnean taxa, and the application of phylogenetic systematics to this problem is still in its infancy. Not only that, but even more intriguingly the pronounced divergence in estimates of origination times of groups as diverse as angiosperms, diatoms and mammals in terms of the fossil record as against molecular data point to the possibilities of protracted intervals of geological time with a cryptic diversity. If this is correct, and there are alternative explanations, then some of the mystery of adaptive radiations may be dispelled, in as much as the assembly of key features in the stem groups could be placed in a gradualistic framework of local adaptive response punctuated by intervals of opportunity.
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Affiliation(s)
- S. Conway Morris
- Department of Earth Sciences, University of Cambridge, Downing Street, Cambridge CB2 3EQ, UK
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22
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Affiliation(s)
- L E Maley
- Department of Earth and Space Sciences, University of California, Los Angeles, CA 90095-1567, USA
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Grenier JK, Garber TL, Warren R, Whitington PM, Carroll S. Evolution of the entire arthropod Hox gene set predated the origin and radiation of the onychophoran/arthropod clade. Curr Biol 1997; 7:547-53. [PMID: 9259556 DOI: 10.1016/s0960-9822(06)00253-3] [Citation(s) in RCA: 136] [Impact Index Per Article: 5.0] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 02/05/2023]
Abstract
BACKGROUND Dramatic changes in body size and pattern occurred during the radiation of many taxa in the Cambrian, and these changes are best documented for the arthropods. The sudden appearance of such diverse body plans raises the fundamental question of when the genes and the developmental control systems that regulate these designs evolved. As Hox genes regulate arthropod body patterns, the evolution of these genes may have played a role in the origin and diversification of the arthropod body plan from a homonomous ancestor. To trace the origin of arthropod Hox genes, we examined their distribution in a myriapod and in the Onychophora, a sister group to the arthropods. RESULTS Despite the limited segmental diversity within myriapods and Onychophora, all insect Hox genes are present in both taxa, including the trunk Hox genes Ultrabithorax and abdominal-A as well as an ortholog of the fushi tarazu gene. Comparative analysis of Hox gene deployment revealed that the anterior boundary of expression of trunk Hox genes has shifted dramatically along the anteroposterior axis between Onychophora and different arthropod classes. Furthermore, we found that repression of expression of the Hox target gene Distal-less is unique to the insect lineage. CONCLUSIONS A complete arthropod Hox gene family existed in the ancestor of the onychophoran/arthropod clade. No new Hox genes were therefore required to catalyze the arthropod radiation; instead, arthropod body-plan diversity arose through changes in the regulation of Hox genes and their downstream targets.
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Affiliation(s)
- J K Grenier
- Howard Hughes Medical Institute, University of Wisconsin, Madison 53708, USA
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Kirschvink JL, Ripperdan RL, Evans DA. Evidence for a Large-Scale Reorganization of Early Cambrian Continental Masses by Inertial Interchange True Polar Wander. Science 1997. [DOI: 10.1126/science.277.5325.541] [Citation(s) in RCA: 230] [Impact Index Per Article: 8.5] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/02/2022]
Affiliation(s)
- Joseph L. Kirschvink
- J. L. Kirschvink and D. A. Evans, Division of Geological and Planetary Sciences, California Institute of Technology, Pasadena, CA 91125, USA
- R. L. Ripperdan, Department of Geology, University of Puerto Rico, Mayaguez, Mayaguez 00681, Puerto Rico
| | - Robert L. Ripperdan
- J. L. Kirschvink and D. A. Evans, Division of Geological and Planetary Sciences, California Institute of Technology, Pasadena, CA 91125, USA
- R. L. Ripperdan, Department of Geology, University of Puerto Rico, Mayaguez, Mayaguez 00681, Puerto Rico
| | - David A. Evans
- J. L. Kirschvink and D. A. Evans, Division of Geological and Planetary Sciences, California Institute of Technology, Pasadena, CA 91125, USA
- R. L. Ripperdan, Department of Geology, University of Puerto Rico, Mayaguez, Mayaguez 00681, Puerto Rico
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