| 1. |
- Clarkson, ENK, et al.
(författare)
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Ontogeny and structure of a new, miniaturised and spiny olenid trilobite from Southern Sweden
- 2002
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Ingår i: Palaeontology. - : Wiley. - 1475-4983 .- 0031-0239. ; 45, s. 1-22
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Tidskriftsartikel (refereegranskat)abstract
- Several hundred specimens of a tiny olenid trilobite, Ctenopyge ceciliae sp. nov., have been found in stinkstone nodules in the upper Cambrian Peltura scarabaeoides Zone in southern Sweden. This exceptionally spinose form is known only from disarticulated specimens, but is quite well preserved, and all growth stages are represented. The early ontogenetic stages are exceptionally small, the protaspis being only half the size of that of the associated Peltura species. There may have been no more than three thoracic segments. Thus the whole ontogeny was compressed, and this together with the very small size of the adult indicates a true miniaturisation. Whereas the likely control of the origin of the tiny C. ceciliae was basically progenesis, the extreme spinosity had a different origin; allometric growth or possibly peramorphosis. C. ceciliae is small enough for the spines to have appreciably retarded sinking through frictional effects, and this small trilobite is interpreted as a free-swimming or floating form.
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| 2. |
- Ebbestad, JOR, et al.
(författare)
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Redescription of Holmia inusitata (Trilobita) from the Lower Cambrian of Scandinavia
- 2003
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Ingår i: Palaeontology. - : Wiley. - 1475-4983 .- 0031-0239. ; 46:5, s. 1039-1054
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Tidskriftsartikel (refereegranskat)abstract
- Well-preserved topotype material of Holmia inusitata Ahlberg and Bergstrom, in Ahlberg et at., from the Lower Cambrian of Lauselva, southern Norway, allows a redescription of the species. Intraspecific variation of characters, such as the expansion and relative length (sagittal) of the anterior glabellar lobe and the curvature and length of the ocular lobes, is shown. The species is, however, considered a typical member of Holmia. A discussion of character variation and distribution within species of Holmia further demonstrates a great degree of intrageneric variation. Thus, the newly erected Baltobergstroemia Lieberman is regarded as a subjective synonym of Holmia, since the differences between the two genera can only effectively be applied to the type species. The age of the succession with H. inusitata is not well constrained by regional lithological correlations or by an acritarch assemblage, and lacks the well-differentiated faunas of the uppermost zones in the Lower Cambrian of Scandinavia. It is obvious that it must be older than the Holmia kjerulfi-group Zone, and strata with H. inusitata are, therefore, maintained as a discrete zone underlying that zone.
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| 3. |
- Eriksson, Mats
(författare)
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The palaeobiogeography of Silurian ramphoprionid Polychaete annelids
- 2002
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Ingår i: Palaeontology. - : Wiley. - 1475-4983 .- 0031-0239. ; 45, s. 985-996
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Tidskriftsartikel (refereegranskat)abstract
- Silurian palaeobiogeography of the Ramphoprionidae (Annelida; Polychaeta) is outlined. Members of the family are reported from northern Europe (Estonia, Sweden and England), the Russian Arctic (Severnaya Zemlya), and the Canadian Arctic (Baillie-Hamilton Island), These areas were located fairly close to the palacoequator during the Silurian and a faunal exchange is indicated by the broad, intercontinental distribution of the family. A few taxa may, however, have been endemic, Ramphoprionids had long stratigraphical ranges and were generally fairly rare during the Silurian, infrequently exceeding ten per cent of the jawed polychaete faunas.
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| 4. |
- Cohen, B. L., et al.
(författare)
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The brachiopod fold : a neglected body plan hypothesis
- 2003
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Ingår i: Palaeontology. - : Wiley. - 0031-0239 .- 1475-4983. ; 46:1, s. 59-65
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Tidskriftsartikel (refereegranskat)abstract
- Attention is drawn to Nielsen's radical body plan concept, here named the 'brachiopod fold hypothesis', under which brachiopods and phoronids are recognized to be transversely folded across the ontogenetic anterior–posterior axis so that, to make useful comparisons with other phyla, these organisms must be conceptually unfolded. Under the hypothesis brachiopod brachial and pedicle shell valves are respectively 'anterior' and 'posterior' rather than 'dorsal' and 'ventral' as traditionally described. The hypothesis makes sense of the symmetry axes of the brachiopod shell, is consistent with various indications from fossil and Recent brachiopods, and gives rise to predicted patterns of axis–determining gene expression that differ from those obtaining under the traditional view of the body plan, whilst the variety of folding movements in different lineages implies that superficially dissimilar morphogenetic folds may be fundamentally homologous. Convergent folding patterns are noted in some other organisms. A previous conjecture that inarticulate linguloid brachiopods were derived from halkieriid–like ancestors is elaborated with proposals that recognize possible functional continuities of coelomic and marginal sclerite functions, and it is noted that an ancestrally facultative fold could have become incorporated by genetic assimilation into the brachiopod developmental program. An experimental approach is outlined to test the possibility that some members of the 'small shelly fauna' may have been members of the halkieriid–like brachiopod stem lineage and it is also suggested that buoyancy modification may have been an important function of mineralization amongst Lower Cambrian floaters and swimmers, since negative buoyancy would facilitate access to the benthic niche.
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| 5. |
- Holmer, Lars E., et al.
(författare)
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A stem group brachiopod from the Lower Cambrian - support for a Micrina (Halkieriid) ancestry.
- 2002
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Ingår i: Palaeontology. - : Wiley. - 0031-0239 .- 1475-4983. ; 45:5, s. 875-882
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Tidskriftsartikel (refereegranskat)abstract
- The shell structure of the Lower Cambrian Mickwitzia, a bilaterally symmetrical bivalve hitherto doubtfully assigned to the Brachiopoda, confirms that the genus shares characters with linguliform brachiopods. The columnar lamination of its organophosphatic shell is homologous with that characterizing acrotretides. The shell, however, is also pervaded by striated apatitic tubes indistinguishable from those permeating the sclerites of the problematic organophosphatic, laminar–shelled Micrina which is close to Halkieria. No crown group brachiopods have such tubes that are presumed to have contained setae. The presence of both these features in the Mickwitzia shell suggests that the stock is a stem group brachiopod with a halkieriid ancestry.
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| 6. |
- Johanson, Zerina, et al.
(författare)
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The braincase and palate of the tetrapodomorph sarcopterygian Mandageria fairfaxi: morphological variability near the fish-tetrapod transition
- 2003
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Ingår i: Palaeontology. - : Wiley. - 0031-0239 .- 1475-4983. ; 46:2, s. 271-293
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Tidskriftsartikel (refereegranskat)abstract
- The braincase of the Late Devonian tristichopterid sarcopterygian Mandageria fairfaxi, from Canowindra, NSW, Australia, differs radically from the conservative pattern present in other 'osteolepiforms' (stem–group tetrapodomorph fishes) and non–dipnoan sarcopterygian fishes in general. The basioccipital region is short, displaced anteriorly, and either unossified or loosely articulated to the exoccipital, leaving most or all of the notochordal tunnel open ventrally. The exoccipital complex, which is developed into a large saddle that would have rested on top of the notochord, carries large, triangular articular facets on its posterior face and appears to have formed part of a functional neck joint, a synovial articulation between the skull and vertebral column that allows the former to rotate against the latter. Such a joint is characteristic of post–Devonian tetrapods, but unknown in other sarcopterygians. We infer that the ventrally open notochordal tunnel allowed gentle flexion of the cranial notochord during (predominantly vertical) rotational movement at the occiput; this is a mechanically unique solution to the problem of creating a mobile neck. Other unusual features of Mandageria include a posteriorly located lateral commissure, and structures on the entopterygoid and lateral commissure that may have been associated with an elaborate spiracular tract.
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| 7. |
- Williams, Alwyn, et al.
(författare)
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Shell structure and inferred growth, functions and affinities of the sclerites of the problematic Micrina
- 2002
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Ingår i: Palaentology. - : Wiley. - 1475-4983. ; 45:5, s. 845-873
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Tidskriftsartikel (refereegranskat)abstract
- e stratiform laminae of Micrina sclerites originally consisted of rheomorphic successions of monolayers of micrometric–sized, apatitic tablets, presumably interleaved with chitin and glycosaminoglycans (GAGs). Paired laminae enclose slot–like chambers swelling into lobes distally that originally contained GAGs and deposits of spherulitic and prismatic apatite. The laminae are pervaded by apatitic tubes, apparently secreted by microvillous setoblasts and containing, at the surface, chitinous setae. Internal markings suggest that the triangular (sellate) sclerite supported a pair of muscles and the planospiral (mitral) sclerite, a medial muscle and gonadal sacs flanked by a pair of crescentic muscle bases. Both sclerites were secreted by a mantle with a circumferential fold. The sellate and mitral sclerites are homologized with the anterior and posterior shells of Halkieria and could have become the dorsal and ventral valves of the ancestral brachiopod by a sequence of transformations. These include: the folding of the halkieriid body axis; accelerated mixoperipheral growth of the anterior (dorsal) shell to enclose, with the posterior (ventral) shell, a mantle cavity lined with modified ciliated epithelium of the foot; reduction of sclerite–secreting epithelium to the locus of the brachiopod pedicle epithelium; and the anterior (dorsal) spread of gonadal lamellae.
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| 8. |
- Cederstrom, Peter, et al.
(författare)
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Moulting, ontogeny and sexual dimorphism in the Cambrian ptychopariid trilobite Strenuaeva inflata from the northern Swedish Caledonides
- 2011
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Ingår i: Palaeontology. - : Wiley. - 1475-4983 .- 0031-0239. ; 54, s. 685-703
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Tidskriftsartikel (refereegranskat)abstract
- Three thousand seven hundred disarticulated remains together with several articulated specimens of the Cambrian Series 2 ptychopariid trilobite Strenuaeva inflata Ahlberg and Bergstrom, 1978 have been collected from the Tornetrask area, northern Sweden. The material provides significant new data on the morphology, ontogeny, moulting and enrolment of the species. Two distinct morphotypes, possibly an expression of sexual dimorphism, are recognized. The morph with a pair of bulbs in the frontal area, interpreted as brood pouches, is considered to represent females. Statistical treatment of the length/width ratio in cranidia reveals isometric growth during ontogeny for both morphotypes. The transition from the meraspid to holaspid ontogenetic period has been established through recognition of the successive development of the number of thoracic segments in articulated late meraspides. Throughout its life cycle, S. inflata went through 11 meraspid degrees and at least 17 holaspid growth stages. Inferred moult ensembles and exuviae reveal the successive opening of cephalic sutures and the function of the rostral plate during exuviation. As in other ellipsocephalid trilobites in which enrolment is known, the pygidium and two or three thoracic segments of S. inflata are concealed beneath the cephalon (spiral enrolment) during complete enrolment.
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| 9. |
- Rees, Jan, et al.
(författare)
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Aquatic birds from the Upper Cretaceous (Lower Campanian) of Sweden and the biology and distribution of hesperornithiforms
- 2005
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Ingår i: Palaeontology. - : Wiley. - 1475-4983 .- 0031-0239. ; 48:6, s. 1321-1329
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Tidskriftsartikel (refereegranskat)abstract
- Isolated skeletal elements of three hesperornithiform taxa are recorded from marine strata of latest early Campanian (sensu germanico) age in the Kristianstad Basin, southern Sweden. The material comprises Hesperornis rossicus Nessov and Yarkov, one of the largest Mesozoic aquatic birds known to date, Hesperornis sp. and Baptornis sp. The holotype (a dorsal vertebra) of Parascaniornis stensioei Lambrecht is re-examined, and the nominal species is here considered as a nomen dubium because no diagnostic features can be found that separate the type from dorsals of Baptornis advenus. The distribution and palaeobiology of hesperornithiforms are reviewed.
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| 10. |
- Siverson, Mikael, et al.
(författare)
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Anacoracid sharks from the Albian (lower cretaceous) Pawpaw shale of Texas
- 2007
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Ingår i: Palaeontology. - : Wiley. - 1475-4983 .- 0031-0239. ; 50:4, s. 939-950
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Tidskriftsartikel (refereegranskat)abstract
- Recent collecting from the Pawpaw Shale in northeast Texas has yielded several hundred teeth of anacoracid sharks. The material allows for a much-needed revision of the Late Albian anacoracids from North America. The previously recognized Squalicorax sp., also referred to as S. volgensis in more recent publications, is a mix of two different species: S. priscoserratus sp. nov. and S. pawpawensis sp. nov. In addition to these two new species, a single tooth is assigned to S. aff. S. baharijensis. Our data indicate that anacoracids were considerably more diverse group in the North American Cretaceous than previously thought. We attribute much of the underestimation of diversity to vague species concepts, poor preparation techniques and the associated lack of attention to certain dental features, in particular neck morphology, root surface porosity and the root's vascularization.
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