| 1. |
- 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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| 2. |
- Benson, Roger B. J., et al.
(författare)
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Cope's rule and the adaptive landscape of dinosaur body size evolution
- 2018
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Ingår i: Palaeontology. - : John Wiley & Sons. - 0031-0239 .- 1475-4983. ; 61:1, s. 13-48
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Forskningsöversikt (refereegranskat)abstract
- The largest known dinosaurs weighed at least 20million times as much as the smallest, indicating exceptional phenotypic divergence. Previous studies have focused on extreme giant sizes, tests of Cope's rule, and miniaturization on the line leading to birds. We use non-uniform macroevolutionary models based on Ornstein-Uhlenbeck and trend processes to unify these observations, asking: what patterns of evolutionary rates, directionality and constraint explain the diversification of dinosaur body mass? We find that dinosaur evolution is constrained by attraction to discrete body size optima that undergo rare, but abrupt, evolutionary shifts. This model explains both the rarity of multi-lineage directional trends, and the occurrence of abrupt directional excursions during the origins of groups such as tiny pygostylian birds and giant sauropods. Most expansion of trait space results from rare, constraint-breaking innovations in just a small number of lineages. These lineages shifted rapidly into novel regions of trait space, occasionally to small sizes, but most often to large or giant sizes. As with Cenozoic mammals, intermediate body sizes were typically attained only transiently by lineages on a trajectory from small to large size. This demonstrates that bimodality in the macroevolutionary adaptive landscape for land vertebrates has existed for more than 200million years.
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| 3. |
- Borinder, Niclas H., et al.
(författare)
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Postcranial osteology of the basally branching hadrosauroid dinosaur Tanius sinensis from the Upper Cretaceous Wangshi Group of Shandong, China
- 2021
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Ingår i: Journal of Vertebrate Paleontology. - : Taylor & Francis. - 0272-4634 .- 1937-2809. ; 41:1
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Tidskriftsartikel (refereegranskat)abstract
- Tanius sinensis was one of the first dinosaur species to be named from China. It was established on a partial skeleton recovered by a joint Sino-Swedish expedition in 1923. The fossils were excavated from Upper Cretaceous strata of the Jiangjunding Formation (Wangshi Group) in Shandong Province, and although their discovery dates back almost 100 years, they have not been reassessed in detail since their initial description in 1929. This omission is critical because T. sinensis is now recognized as one of the stratigraphically youngest non-hadrosaurid hadrosauroid taxa. Here, we re-evaluate the postcranial osteology of T. sinensis as a prelude to an anatomical and phylogenetic revision of the species. We examined the holotype and all currently referred specimens of T. sinensis first-hand, and identified a unique postcranial character state combination incorporating tall dorsal neural spines, a reduced postacetabular ridge on the ilium, a fully enclosed flexor tunnel formed by the distal condyles of the femur, and a lunate proximal end on metatarsal III. Comparisons with other species of Tanius confirm that: (1) T. chingkankouensis is a nomen dubium erected on non-diagnostic composite material; (2) T. laiyangensis was established on indeterminate hadrosaurid remains that are not attributable to Tanius; and (3) the anecdotal assignments of Bactrosaurus prynadai and Tsintaosaurus spinorhinus to Tanius cannot be substantiated. Close inspection of the holotype caudal vertebra further reveals a possible healed bite trace consistent with a prey-predator interaction. Lastly, our calculated average body mass estimate for T. sinensis of between 2091-3533 kg suggests that it was one of the largest non-hadrosaurid hadrosauroids.
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| 4. |
- Brink, Kirstin S., et al.
(författare)
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Amniote faunal revision of the Pictou Group (Permo-Carboniferous), Prince Edward Island, Canada
- 2013
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Ingår i: Comptes rendus. Palevol. - : Elsevier. - 1631-0683 .- 1777-571X. ; 12:7–8, s. 473-485
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Tidskriftsartikel (refereegranskat)abstract
- The amniote faunal assemblages from the Pictou Group (Prince Edward Island, Canada) are re-evaluated for the first time in 50 years. Fossils recovered from formations within this group (Orby Head, Hillsborough River, and Kildare Capes) indicate the presence of a parareptile, representing the first occurrence of a non-synapsid amniote from the PEI redbeds. The amniote taxa from PEI are re-described within the context of current research, providing the basis for an updated faunal list for the vertebrate-bearing formations within the Pictou Group. The presence of a parareptile, diadectid, and possibly two synapsids (caseid and/or varanopid), together with the absence of edaphosaurids and definitive ophiacodontids, suggests similarities with the upland Bromacker and Richards Spur localities of Germany and Oklahoma, respectively. However, more research and new fossil discoveries are needed to confidently resolve the systematics and palaeoecology of amniotes from the Lower Permian of Atlantic Canada.
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| 5. |
- Campione, Nicolas E., 1982-, et al.
(författare)
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Morphology and evolutionary significance of the atlas-axis complex in varanopid synapsids
- 2011
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Ingår i: Acta Palaeontologica Polonica. - : Polska Akademia Nauk Instytut Paleobiologii (Institute of Paleobiology, Polish Academy of Sciences). - 0567-7920 .- 1732-2421. ; 56:4, s. 739-748
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Tidskriftsartikel (refereegranskat)abstract
- The atlas−axis complex has been described in few Palaeozoic taxa, with little effort being placed on examining variation of this structure within a small clade. Most varanopids, members of a clade of gracile synapsid predators, have well preserved atlas−axes permitting detailed descriptions and examination of morphological variation. This study indicates that the size of the transverse processes on the axis and the shape of the axial neural spine vary among members of this clade. In particular, the small mycterosaurine varanopids possess small transverse processes that point posteroventrally, and the axial spine is dorsoventrally short, with a flattened dorsal margin in lateral view. The larger varanodontine varanopids have large transverse processes with a broad base, and a much taller axial spine with a rounded dorsal margin in lateral view. Based on outgroup comparisons, the morphology exhibited by the transverse processes is interpreted as derived in varanodontines, whereas the morphology of the axial spine is derived in mycterosaurines. The axial spine anatomy of Middle Permian South African varanopids is reviewed and our interpretation is consistent with the hypothesis that at least two varanopid taxa are present in South Africa, a region overwhelmingly dominated by therapsid synapsids and parareptiles.
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| 6. |
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| 7. |
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| 8. |
- Campione, Nicolas E., 1982-, et al.
(författare)
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Varanops brevirostris (Eupelycosauria: Varanopidae) from the Lower Permian of Texas, with discussion of varanopid morphology and interrelationships
- 2010
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Ingår i: Journal of Vertebrate Paleontology. - : Informa UK Limited. - 0272-4634 .- 1937-2809. ; 30:3, s. 724-746
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Tidskriftsartikel (refereegranskat)abstract
- A comprehensive revision of Varanops brevirostris on the basis of a large, well-preserved specimen from a new Lower Permian locality in Texas provides valuable new anatomical information and additional autapomorphies for this varanopid synapsid taxon. These include the loss of the postorbital boss, the presence of a smooth transition between the dorsal and lateral surfaces of the postorbital, hypertrophied basipterygoid processes, the presence of deep, elongate lateral neural spine excavations, posterior dorsal vertebrae with dorsally tapered neural spines, and a deep groove proximal to the femoral fourth trochanter. Furthermore, this specimen is the first fully developed adult specimen of Varanops, and it preserves the most complete lower jaw of the taxon. A revised phylogenetic analysis places V. brevirostris as the sister taxon to the Varanodon-Watongia clade. A stratocladistic analysis assessing varanopid relationships by incorporating a stratigraphic character into the analysis recovers the same topology among varanodontines, but an alternate topology between mycterosaurines and Elliotsmithia longiceps.
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| 9. |
- Cuthbertson, Robin S., et al.
(författare)
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A new species of mosasaur (Squamata: Mosasauridae) from the Pierre Shale (lower Campanian) of Manitoba
- 2007
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Ingår i: Canadian journal of earth sciences (Print). - : NRC Research Press. - 0008-4077 .- 1480-3313. ; 44:5, s. 593-606
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Tidskriftsartikel (refereegranskat)abstract
- Plioplatecarpus nichollsae, sp. nov., from the lower Campanian (Pembina Member, Pierre Shale Formation) is diagnosed by the following: a thickened ventral rim of the external naris, a short supratemporal fenestra, a frontal shield with well-developed posterolateral lappets that overlap the parietal dorsally, proximal rib shafts with an approximately circular (but not inflated) cross section, a scapula shaped as in other Plioplatecarpus species but approximately the same size (not larger) than the coracoid, and a moderately large parietal foramen that reaches the frontoparietal suture but does not invade the frontal. The last two characters require that the diagnosis of the genus Plioplatecarpus be emended. With other Plioplatecarpus species, P. nichollsae shares a robust humerus with a distal expansion at least as great as the total length of the bone, a rectangular preorbital frontal shield, a "peg and socket" postorbitofrontal-jugal articulation, a transversely directed ectopterygoid process of the pterygoid, a large, robust quadrate with a distinct eminence on the posterior surface of its shaft, an unossified gap in the ventral wall of the basioccipital, and at least 11 pygal vertebrae. P. nichollsae also shares primitive features with Platecarpus, as well as features apparently intermediate betweenPlatecarpus and Plioplatecarpus. Revision of the genus Platecarpus, currently hypothesized to be both paraphyletic and polyphyletic, as well as a better understanding of the early Campanian mosasaur fauna from the Morden area, are necessary before the phylogenetic significance of some of these characters, and therefore the relationships of Plioplatecarpus nichollsae, can be fully resolved.
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| 10. |
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