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1.
  • Lindgren, Johan, et al. (författare)
  • Soft-tissue evidence for homeothermy and crypsis in a Jurassic ichthyosaur
  • 2018
  • Ingår i: Nature. - Nature Publishing Group. - 0028-0836 .- 1476-4687. ; 564:7736, s. 359-365
  • Tidskriftsartikel (refereegranskat)abstract
    • <p>Ichthyosaurs are extinct marine reptiles that display a notable external similarity to modern toothed whales. Here we show that this resemblance is more than skin deep. We apply a multidisciplinary experimental approach to characterize the cellular and molecular composition of integumental tissues in an exceptionally preserved specimen of the Early Jurassic ichthyosaur Stenopterygius. Our analyses recovered still-flexible remnants of the original scaleless skin, which comprises morphologically distinct epidermal and dermal layers. These are underlain by insulating blubber that would have augmented streamlining, buoyancy and homeothermy. Additionally, we identify endogenous proteinaceous and lipid constituents, together with keratinocytes and branched melanophores that contain eumelanin pigment. Distributional variation of melanophores across the body suggests countershading, possibly enhanced by physiological adjustments of colour to enable photoprotection, concealment and/or thermoregulation. Convergence of ichthyosaurs with extant marine amniotes thus extends to the ultrastructural and molecular levels, reflecting the omnipresent constraints of their shared adaptation to pelagic life.</p>
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2.
  • Lindgren, Johan, et al. (författare)
  • Soft-tissue evidence for homeothermy and crypsis in a Jurassic ichthyosaur
  • 2018
  • Ingår i: Nature. - Nature Publishing Group. - 0028-0836. ; 564:7736, s. 359-365
  • Tidskriftsartikel (refereegranskat)abstract
    • Ichthyosaurs are extinct marine reptiles that display a notable external similarity to modern toothed whales. Here we show that this resemblance is more than skin deep. We apply a multidisciplinary experimental approach to characterize the cellular and molecular composition of integumental tissues in an exceptionally preserved specimen of the Early Jurassic ichthyosaur Stenopterygius. Our analyses recovered still-flexible remnants of the original scaleless skin, which comprises morphologically distinct epidermal and dermal layers. These are underlain by insulating blubber that would have augmented streamlining, buoyancy and homeothermy. Additionally, we identify endogenous proteinaceous and lipid constituents, together with keratinocytes and branched melanophores that contain eumelanin pigment. Distributional variation of melanophores across the body suggests countershading, possibly enhanced by physiological adjustments of colour to enable photoprotection, concealment and/or thermoregulation. Convergence of ichthyosaurs with extant marine amniotes thus extends to the ultrastructural and molecular levels, reflecting the omnipresent constraints of their shared adaptation to pelagic life.
3.
  • Ahlberg, Per E., et al. (författare)
  • A near-tetrapod from the Baltic Middle Devonian
  • 2000
  • Ingår i: Palaeontology. - 0031-0239 .- 1475-4983. ; 43, s. 533-548
  • Tidskriftsartikel (refereegranskat)abstract
    • <p>The tetrapodomorph sarcopterygian Livoniana multidentata gen. et sp. nov, is described on the basis of lower jaw fragments from the Middle Devonian (late Givetian) of Latvia and Estonia. It possesses a suite of derived characters previously only known fromtetrapods, which first appear in the late Devonian (late Frasnian), and a phylogenetic analysis places it on the internode between Panderichthys and the base of the Tetrapoda.The analysis also reveals that the 'Elpistostegalia' are paraphyletic to Tetrapoda, with Elpistostege closer to tetrapods than is Panderichthys. Owing to incompleteness of thematerial, there is almost no overlap between the data sets for Elpistostege and Livoniana;the analysis places the two genera in an unresolved trichotomy. In addition to the tetrapodfeatures, Livoniana has a strikingly autapomorphic dentary dentition comprising multiple tooth rows. It thus provides evidence both for the unexpectedly early evolution of tetrapodcharacteristics and for morphological radiation around the fish-tetrapod transition.</p>
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10.
  • Álvaro, J. Javier, et al. (författare)
  • Global Cambrian trilobite palaeobiogeography assessed using parsimony analysis of endemicity
  • 2013
  • Ingår i: Early Palaeozoic Biogeography and Palaeogeography. - Geological Society of London. - 0435-4052. - 978-1-86239-373-8 ; Memoir 38:38, s. 273-296
  • Bokkapitel (refereegranskat)abstract
    • Palaeobiogeographical data on Cambrian trilobites obtained during the twentieth century are combined in this paper to evaluate palaeoceanographic links through c. 30 myr, once these arthropods biomineralized. Worldwide major tectonostratigraphic units are characterized at series intervals of Cambrian time and datasets of trilobite genera (629 for Cambrian Series 2, 965 for Cambrian Series 3, and 866 for the Furongian Series) are analysed using parsimony analysis of endemicity. Special attention is given to the biogeographical observations made in microcontinents and exotic terranes. The same is done for platform-basinal transects of well-known continental margins. The parsimony analysis of endemicity analysis resulted in distinct palaeogeographical area groupings among the tectonostratigraphic units. With these groupings, several palaeobiogeographical units are distinguished, which do not necessarily fit the previously proposed biogeographical realms and provinces. Their development and spatial distributions are broadly controlled by Cambrian palaeoclimates, palaeogeographical conditions (e.g. carbonate productivity and anoxic conditions) and ocean current circulation.
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