| 11. |
- Bazzi, Mohamad, et al.
(författare)
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Feeding ecology has shaped the evolution of modern sharks
- 2021
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Ingår i: Current Biology. - : Cell Press. - 0960-9822 .- 1879-0445. ; 31:23, s. 5138-5148.e4
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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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| 12. |
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| 13. |
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| 14. |
- Pierce, Stephanie E., et al.
(författare)
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Vertebral architecture in the earliest stem tetrapods
- 2013
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Ingår i: Nature. - : Springer Science and Business Media LLC. - 0028-0836 .- 1476-4687. ; 494:7436, s. 226-229
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Tidskriftsartikel (refereegranskat)abstract
- The construction of the vertebral column has been used as a key anatomical character in defining and diagnosing early tetrapod groups(1). Rhachitomous vertebrae(2)-in which there is a dorsally placed neural arch and spine, an anteroventially placed intercentrum and paired, posterodorsally placed pleurocentra have long been considered the ancestral morphology for tetrapods(1,3-6). Nonetheless, very little is known about vertebral anatomy in the earliest stem tetrapods, because most specimens remain trapped in surrounding matrix, obscuring Important anatomical features(7-9). Here we describe the three-dimensional vertebral architecture of the Late Devonian stem tetrapod Ichthyostega using propagation phase-contrast X-ray synchrotron. microtomography. Our scans reveal a diverse array of new morphological, and associated developmental and functional, characteristics, including a possible posterior-to-anterior vertebral ossification sequence and the first evolutionary appearance of ossified sternal elements. One of the most intriguing features relates to the positional relationships between the vertebral elements, with the pleurocentra being unexpectedly sutured or fused to the intercentra that directly succeed them, indicating a 'reverse' rhachitomous design(10). Comparison of Ichthyostega with two other stem tetrapods, Acanthostegi and Pederpess, shows that reverse rhachitomous vertebrae may be the ancestral condition for limbed vertebrates. This study fundamentally revises our current understanding' of vertebral column evolution in the earliest tetrapods and raises questions about the presumed vertebral architecture of tetrapodomorph fish(12,13) and later, more crownward, tetrapods.
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| 15. |
- Abbassi, Nasrollah, et al.
(författare)
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Avian ichnia and other vertebrate trace fossils from the Neogene Red Beds of Tarom valley in north-western Iran
- 2016
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Ingår i: Historical Biology. - : Informa UK Limited. - 0891-2963 .- 1029-2381. ; 28:8, s. 1075-1089
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Tidskriftsartikel (refereegranskat)abstract
- The Neogene Red Beds of the Tarom valley (north-western Iran) include conglomerate, sandstone, marl and gypsum. Avian and mammal footprints were discovered in one of the sandstone layers at the base of a third Miocene stratigraphical unit in the Gilankesheh area located in the east Tarom valley. The avian ichnia include Aviadactyla vialovi, Avipeda filiportatis, Charadriipeda disjuncta, Charadriipeda isp. A and B and cf. Ornithotarnocia lambrechti. Bird feeding traces are preserved as bilobate, loop-shaped, sinusoidal and ring-like traces. We have also identified a reticulate texture of sole scale imprints in some of the avian ichnia. Two mammal footprints of camelid-like artiodactyls are also present with the avian ichno-assemblage.
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| 16. |
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| 17. |
- Ahlberg, Per, et al.
(författare)
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Cambrian stratigraphy of the Tomten-1 drill core, Västergötland, Sweden
- 2016
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Ingår i: GFF. - : Informa UK Limited. - 1103-5897 .- 2000-0863. ; 138:4, s. 490-501
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Tidskriftsartikel (refereegranskat)abstract
- The Tomten-1 drilling at Torbjörntorp in Västergötland, southern Sweden, penetrated 29.85 m of Cambrian Series 2, Cambrian Series 3, Furongian, and Lower–Middle Ordovician strata. Lithostratigraphically, the succession includes the File Haidar, Borgholm and Alum Shale formations, and the Latorp and Lanna limestones. The drill core succession is described herein for the first time, with special focus on the biostratigraphy of the Cambrian Alum Shale Formation. In the Cambrian Series 3, through Furongian Alum Shale Formation, agnostoids and trilobites have been identified to species level and the succession is subdivided into nine biozones (in ascending order): the Ptychagnostus gibbus, Ptychagnostus atavus, Lejopyge laevigata, Agnostus pisiformis, Olenus gibbosus, Parabolina spinulosa, Ctenopyge tumida, Ctenopyge bisulcata and Ctenopyge linnarssoni zones. The succession is interrupted by numerous stratigraphic gaps of variable magnitudes, as is evident from the biostratigraphy and conspicuous unconformities.
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