| 1. |
- Bazzi, Mohamad
(författare)
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100 million years of shark macroevolution : A morphometric dive into tooth shape diversity
- 2021
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Doktorsavhandling (övrigt vetenskapligt/konstnärligt)abstract
- Few vertebrate clades exhibit the evolutionary longevity and versatility of sharks, which constitute nearly half of all current chondrichthyan biodiversity and represent an ecological diversity of mid-to-apex trophic-level predators in both marine and freshwater environments. The rich fossil record of shark teeth from Mesozoic and Cenozoic rocks also makes the group amenable to large-scale quantitative analyses. This thesis reconstructs the morphological tooth disparity of dominant lamniform (Mackerel sharks) and carcharhiniform (Ground sharks) clades over the last 100 million years. The relative diversity of these major lineages is strongly skewed, with lamniforms, including the famous White shark, making up less than 3% of the total species richness, whereas carcharhiniforms, such as Tiger sharks, comprise over 290 described species. Paradoxically, this long-recognized disproportionate representation was reversed in the distant geological past. Indeed, the fossil record shows that lamniforms accounted for nearly all of the documented shark diversity during the final stages of the Late Cretaceous — the terminal time interval of the ‘Age of Dinosaurs’, which ended 66 million years ago. The causes of this radical diversity turnover are debated, with recent research suggesting that competition and/or climate change drove major shifts in shark evolution. Perhaps more surprisingly, most analyses of diversity dynamics of sharks centre largely on taxonomic data, thus omitting more direct proxies of ecology, such as morphological diversity, or disparity. To mitigate this shortfall, I adopt a Procrustes framework combined with phylogenetic comparative and multivariate statistics to shed light on the deep-time morphological evolution of sharks. My work indicates that the end-Cretaceous mass extinction initiated a sustained evolutionary turnover in ecological dominance between lamniforms and carcharhiniforms. More specifically, the morphospace of these clades, indicate a selective extinction at the K/Pg Boundary affecting ‘large-bodied’ anacoracid lamniform sharks, whereas triakid carcharhiniforms proliferated in the extinction aftermath, perhaps as a response to new prey sources. Overall, my thesis suggests that the modern shark assemblages are the synergistic result of feeding ecology (including dietary niche breadth) and environmental shifts in global sea levels and temperature acting over the last 100 million years.
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| 2. |
- 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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| 3. |
- Bazzi, Mohamad, et al.
(författare)
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Late Cretaceous (Campanian) actinopterygian fishes from the Kristianstad Basin of southern Sweden
- 2016
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Ingår i: Geological Society Special Publication. - : Geological Society. - 0305-8719. ; 434, s. 277-292, s. 277-292
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Tidskriftsartikel (refereegranskat)abstract
- Although a diverse range of aquatic vertebrates are documented from the Upper Cretaceous (mid-Campanian) marine strata of the Kristianstad Basin in southern Sweden, only chondrichthyans and marine amniotes have been described in detail to date. In contrast, coeval actinopterygians are virtually unreported, yet their remains are extremely abundant at most sampled localities. A comprehensive assessment of these fossils has identified the first Late Cretaceous actinopterygian fauna from the Fennoscandian Shield, incorporating indeterminate lepisosteids, the durophagous pycnodontid Anomoeodus subclavatus, the predatory pachycormid Protosphyraena sp., a large ichthyodectid, pachyrhizodontids resembling Pachyrhizodus, the enchodontid Enchodus cf. gladiolus and indeterminate small teleosts. These taxa are diagnosed mainly from isolated teeth and scales, implying substantial taphonomic loss prior to burial. Moreover, the prolific recovery of actinopterygian skeletal remnants in recent excavations suggests that historical collecting biases, rather than ecological paucity, have contributed to their under-representation in the Swedish Cretaceous record. Palaeobiogeographically, the Kristianstad Basin actinopterygians show compositional resemblance to assemblages from the Northern European Platform and the Western Interior Seaway of North America, advocating distributional communication across the Boreal proto-Atlantic Ocean.
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| 4. |
- Bazzi, Mohamad, et al.
(författare)
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Open Access publishing at the KTH Royal Institute of Technology : Statistics for 2011-2021
- 2022
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Rapport (populärvet., debatt m.m.)abstract
- In 2011, KTH Royal Institute of Technology adopted a policy on scientific publishing geared towards creating full accessibility of research output. The main objective of this report is to assess the long-term effects of this policy. To that end, we collected and analysed publishing data at KTH, along with related expenditures. More specifically, we track changes in counts and shares in open access publishing over the past decade, as well as describe trends at multiple levels of analysis, ranging from conference proceedings to journal article publishing at KTH and its affiliated schools. Additionally, we provide insight into both the past and present state of open access publishing, and briefly discuss the future of open access publishing at KTH. This report is aimed towards all interested in publishing practices at KTH. Throughout this report, we use concepts and definitions derived from prior year documentation and analysis of open access publishing at KTH.
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| 5. |
- Bazzi, Mohamad, et al.
(författare)
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Southern higher-latitude lamniform sharks track mid-Cretaceous environmental change
- 2022
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Ingår i: Gondwana Research. - : Elsevier. - 1342-937X.
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Tidskriftsartikel (refereegranskat)abstract
- The mid-Cretaceous (Albian and Cenomanian, 113–93.9 Myr) marked a transformative interval of shark evolution during which lamniforms (mackerel sharks) diversified as dominant marine predators. Yet, their radiation dynamics relative to major biotic turnovers delimiting the Albian–Cenomanian and Cenomanian–Turonian boundaries are incompletely understood. Here, we use the high-resolution dental fossil record of lamniforms to track changing morphological disparity and tooth size through a succession of mid-Cretaceous shark assemblages from higher-palaeolatitude (up to ∼ 58°S) settings in Australia. Our geometric morphometric analyses and evolutionary model fitting reveal stable disparity throughout the late Albian–late Cenomanian. By contrast, lamniform disparity increased in the early Turonian, which might reflect local habitat differences and/or intraspecific variability through heterodonty. Nevertheless, clade-specific partial disparity increases are evident among small-bodied carchariids, and couple with a trend towards larger teeth as a proxy for body-size in coeval anacoracids. We correlate these signals with recovery after the Oceanic Anoxic Event 2, which severely disrupted latest Cenomanian marine ecosystems and apparently instigated disjunct responses in shark communities occupying epeiric versus outer neritic environments.
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| 6. |
- Bazzi, Mohamad, et al.
(författare)
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Static Dental Disparity and Morphological Turnover in Sharks across the End-Cretaceous Mass Extinction
- 2018
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Ingår i: Current Biology. - : CELL PRESS. - 0960-9822 .- 1879-0445. ; 28:16, s. 2607-2615
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Tidskriftsartikel (refereegranskat)abstract
- The Cretaceous-Palaeogene (K-Pg) mass extinction profoundly altered vertebrate ecosystems and prompted the radiation of many extant clades [1, 2]. Sharks (Selachimorpha) were one of the few larger-bodied marine predators that survived the K-Pg event and are represented by an almost-continuous dental fossil record. However, the precise dynamics of their transition through this interval remain uncertain [3]. Here, we apply 2D geometric morphometrics to reconstruct global and regional dental morphospace variation among Lamniformes (Mackerel sharks) and Carch-arhiniformes (Ground sharks). These clades are prevalent predators in today's oceans, and were geographically widespread during the late Cretaceous-early Palaeogene. Our results reveal a decoupling of morphological disparity and taxonomic richness. Indeed, shark disparity was nearly static across the K-Pg extinction, in contrast to abrupt declines among other higher-trophic-level marine predators [4, 5]. Nevertheless, specific patterns indicate that an asymmetric extinction occurred among lamniforms possessing lowcrowned/triangular teeth and that a subsequent proliferation of carcharhiniforms with similar tooth morphologies took place during the early Paleocene. This compositional shift in post-Mesozoic shark lineages hints at a profound and persistent K-Pg signature evident in the heterogeneity of modern shark communities. Moreover, such wholesale lineage turnover coincided with the loss of many cephalopod [6] and pelagic amniote [5] groups, as well as the explosive radiation of middle trophic-level teleost fishes [1]. We hypothesize that a combination of prey availability and post-extinction trophic cascades favored extant shark antecedents and laid the foundation for their extensive diversification later in the Cenozoic [7-10].
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| 7. |
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| 8. |
- Bazzi, Mohamad, et al.
(författare)
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Tooth morphology elucidates shark evolution across the end-Cretaceous mass extinction
- 2021
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Ingår i: PLoS biology. - : Public Library of Science (PLoS). - 1544-9173 .- 1545-7885. ; 19:8
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Tidskriftsartikel (refereegranskat)abstract
- Sharks (Selachimorpha) are iconic marine predators that have survived multiple mass extinctions over geologic time. Their prolific fossil record is represented mainly by isolated shed teeth, which provide the basis for reconstructing deep time diversity changes affecting different selachimorph clades. By contrast, corresponding shifts in shark ecology, as measured through morphological disparity, have received comparatively limited analytical attention. Here, we use a geometric morphometric approach to comprehensively examine tooth morphologies in multiple shark lineages traversing the catastrophic end-Cretaceous mass extinction-this event terminated the Mesozoic Era 66 million years ago. Our results show that selachimorphs maintained virtually static levels of dental disparity in most of their constituent clades across the Cretaceous-Paleogene interval. Nevertheless, selective extinctions did impact apex predator species characterized by triangular blade-like teeth. This is particularly evident among lamniforms, which included the dominant Cretaceous anacoracids. Conversely, other groups, such as carcharhiniforms and orectolobiforms, experienced disparity modifications, while heterodontiforms, hexanchiforms, squaliforms, squatiniforms, and dagger synechodontiforms were not overtly affected. Finally, while some lamniform lineages disappeared, others underwent postextinction disparity increases, especially odontaspidids, which are typified by narrow-cusped teeth adapted for feeding on fishes. Notably, this increase coincides with the early Paleogene radiation of teleosts as a possible prey source, and the geographic relocation of disparity sampling "hotspots," perhaps indicating a regionally disjunct extinction recovery. Ultimately, our study reveals a complex morphological response to the end-Cretaceous mass extinction and highlights an event that influenced the evolution of modern sharks.
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| 9. |
- Conte, Gabriele Larocca, et al.
(författare)
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Reassessment of a large lamniform shark from the Upper Cretaceous (Santonian) of Italy
- 2019
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Ingår i: Cretaceous research (Print). - : Elsevier BV. - 0195-6671 .- 1095-998X. ; 99, s. 156-168
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Tidskriftsartikel (refereegranskat)abstract
- To date, only a few partially articulated chondrichthyan specimens are known from the Upper Cretaceous marine fossil record of northern Italy. Here, we re-evaluate the taxonomic status and geological age of selachian remains originally discovered during the 19th century from the Castellavazzo locality. The described specimen is largely embedded in matrix with minute exposure of joined and moderately deformed sequentially stacked vertebral centra. Computed tomography (CT) image-data obtained of the specimen enabled the identification of potential cranial-cartilage elements located in close proximity to teeth and are here interpreted as remnants of the jaws. Based on tooth and vertebral morphology the specimen is in all likelihood an adult lamniform shark with a measured 3.5 m length. Using ordinary least-squares regression analysis (OLS) and proportion-based calculations, we estimated a total-length (TL) of 596.27 and 632.5-672.64 cm respectively. We prefer the size estimation derived through OLS bivariate regression; however, in the present analysis, reliance on a small sample size (n = 11) and evidence for differential scaling between taxa impose limitations on the precision of our size prediction. Planktonic foraminifera examined from the surrounding matrix of the slab preserving shark vertebral centra and teeth indicate a Santonian age (Dicarinella asymetrica zone). Although, the specimen could not confidently be assigned beyond the ordinal-level, the sheer centrum size, gross dental morphology, and depositional environment, are indicative of a pelagic apex-predator comparable to coeval lamniforms, with a specific resemblance towards cretoxyrhinids, reported from elsewhere along the peri-Tethyan shelf of Europe and Western Interior Seaway of North America. Finally, the re-emergence of this historical specimen, here re-described using cutting-edge techniques, is of great importance as it contributes to the otherwise poor record of extinct lamniform shark skeletons.
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| 10. |
- Hashimoto, T., et al.
(författare)
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Beamline test of a transition-edge-sensor spectrometer in preparation for kaonic-atom measurements
- 2017
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Ingår i: IEEE Transactions on Applied Superconductivity. - 1051-8223. ; 27:4
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Tidskriftsartikel (refereegranskat)abstract
- We are developing a new technique to apply transition-edge sensors (TESs) to X-ray spectroscopy of exotic atoms, especially of kaonic atoms. To demonstrate the feasibility of this pioneering project, performance of a TES-based X-ray detector was evaluated in pion- and kaon-beam environments at particle accelerators.We successfully observed X-rays from pionic-carbon atoms with a resolution as good as 7 eV FWHM at 6 keV. Also at a kaon beamline, we confirmed that the TES spectrometer will be able to achieve our resolution goal, 6 eV, in our first scientific campaign to measure X-rays from kaonic-helium atoms.
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