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Sökning: WFRF:(Ahlberg Per E.) > Ahlberg Per E.

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  • 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
    • 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.
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  • Bazzi, Mohamad, et al. (författare)
  • Feeding ecology has shaped the evolution of modern sharks
  • 2021
  • Ingår i: Current Biology. - : Cell Press. - 0960-9822 .- 1879-0445. ; 31:23, s. 5138-5148.e4
  • Tidskriftsartikel (refereegranskat)abstract
    • Sharks are iconic predators in today’s oceans, yet their modern diversity has ancient origins. In particular, present hypotheses suggest that a combination of mass extinction, global climate change, and competition has regulated the community structure of dominant mackerel (Lamniformes) and ground (Carcharhiniformes) sharks over the last 66 million years. However, while these scenarios advocate an interplay of major abiotic and biotic events, the precise drivers remain obscure. Here, we focus on the role of feeding ecology using a geometric morphometric analysis of 3,837 fossil and extant shark teeth. Our results reveal that morphological segregation rather than competition has characterized lamniform and carcharhiniform evolution. Moreover, although lamniforms suffered a long-term disparity decline potentially linked to dietary “specialization,” their recent disparity rivals that of “generalist” carcharhiniforms. We further confirm that low eustatic sea levels impacted lamniform disparity across the end-Cretaceous mass extinction. Adaptations to changing prey availability and the proliferation of coral reef habitats during the Paleogene also likely facilitated carcharhiniform dispersals and cladogenesis, underpinning their current taxonomic dominance. Ultimately, we posit that trophic partitioning and resource utilization shaped past shark ecology and represent critical determinants for their future species survivorship.
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