192 research outputs found
Measures of performance : the Swedish case
Series statement handwritten on cover"To be presented at The Meeting with the Rate of Return Group, MIT, June 9-12, 1981."Includes bibliographical reference
Retinofugal projections in the lepidosirenid lungfishes
Autoradiographic and silver methods indicate that the African and South American lungfishes, Protopterus and Lepidosiren , lack ipsilateral retinal projections. Contralaterally, the retina projects to the preoptic nucleus of the hypothalamus, to four discrete areas located in the lateral neuropil of the thalamus, to a superficial pretectal neuropil, to the upper half of the tectal neuropil, and to a laterally situated basal optic neuropil located in the rostral tegmentum. The overall pattern of the primary retinofugal projections is markedly similar to that of amphibians which suggests that lungfishes may be more closely related to amphibians than to actinopterygian fishes. Neotenic trends in both lepidosirenid lungfishes and urodeles may be expressions of parallelism, hence Latimeria and Neoceratodus must be examined to resolve this phylogenetic problem. A 300-fold range in the size of the eye, indicated by the number of ganglion cells present, occurs among lungfishes, salamanders and frogs. This variation may have implications for recognizing the morphological expression of selection operating on the visual systems of lepidosirenids and amphibians.Peer Reviewedhttp://deepblue.lib.umich.edu/bitstream/2027.42/50000/1/901740402_ftp.pd
Development of the chondrocranium in the suckermouth armored catfish Ancistrus cf. triradiatus (Loricariidae, Siluriformes)
Lungfish neural characters and their bearing on sarcopterygian phylogeny
The phylogenetic affinity of lungfishes has been disputed since their discovery, and they have variously been considered the sister group of actinistians, the sister group of amphibians, or equally related to actinopterygians and crossopterygians. Previous discussions of these hypotheses have considered neural characters, but there has been no general survey of the nervous systems of sarcopterygians that examines the bearing of neural characters on these hypotheses in the context of a cladistic analysis. Such a survey of representatives of all living sarcopterygian groups reveals at least twenty-three characters that are possible apomorphies at some hierarchical level among sarcopterygians. Neural synapomorphies corroborate the phylogenetic hypotheses that actinistians, amphibians, and dipnoans are each monophyletic taxa. The hypothesis that Latimeria is the sister group of amphibians is the least corroborated, as only a single possible synapomorphy, presence of cervical and lumbar enlargements of the spinal cord, supports this hypothesis. The hypothesis that lungfishes are the sister group of amphibians is supported by two possible synapomorphies: loss of a saccus vasculosus and the presence of neurocranial endolymphatic sacs. The hypothesis that actinistians are the sister group of lungfishes is the most corroborated, based on five possible synapomorphies: presence of a superficial isthmal nucleus, a laminated dorsal thalamus with marked protrusion into the third ventricle, olfactory peduncles, evaginated cerebral hemispheres with pronounced septum ependymale, and electroreceptive rostral organs. However, all five characters may be plesiomorphic for bony fishes. The nervous systems of Latimeria and Neoceratodus are very similar to each other, as are the nervous systems of lepidosirenid lungfishes, caecilians, and salamanders. If Neoceratodus is the most plesiomorphic species of living lungfishes, then lepidosirenid apomorphies may have arisen by paedomorphosis. Our inability to examine the neural characters of a relevant outgroup (rhipidistians) may result in many sarcopterygian plesiomorphic characters being interpreted as apomorphic characters, due to the wide distribution of paedomorphic characters among living sarcopterygians and their possible resemblance to plesiomorphic characters present in living outgroups that can be examined.Peer Reviewedhttp://deepblue.lib.umich.edu/bitstream/2027.42/50281/1/1051900418_ftp.pd
AMNIOTE PHYLOGENY AND THE IMPORTANCE OF FOSSILS
Several prominent cladists have questioned the importance of fossils in phylogenctic inference, and it is becoming increasingly popular to simply fit extinct forms, if they are considered at all, to a cladogram of Recent taxa. Gardiner's (1982) and LØvtrup's (1985) study of amniote phylogeny exemplifies this differential treatment, and we focused on that group of organisms to test the proposition that fossils cannot overturn a theory of relationships based only on the Recent biota. Our parsimony analysis of amniote phylogeny, special knowledge contributed by fossils being scrupulously avoided, led to the following best fitting classification, which is similar to the novel hypothesis Gardiner published: (lepidosaurs (turtles (mammals (birds, crocodiles)))). However, adding fossils resulted in a markedly different most parsimonious cladogram of the extant taxa: (mammals (turtles (lepidosaurs (birds, crocodiles)))). That classification is like the traditional hypothesis, and it provides a better fit to the stratigraphic record. To isolate the extinct taxa responsible for the latter classification, the data were successively partitioned with each phylogenetic analysis, and we concluded that: (1) the ingroup, not the outgroup, fossils were important; (2) synapsid, not reptile, fossils were pivotal; (3) certain synapsid fossils, not the earliest or latest, were responsible. The critical nature of the synapsid fossils seemed to lie in the particular combination of primitive and derived character slates they exhibited. Classifying those fossils, along with mammals, as the sister group to the lineage consisting of birds and crocodiles resulted in a relatively poor fit to data; one involving a 2—4 fold increase in evolutionary reversals! Thus, the importance of the critical fossils, collectively or individually, seems to reside in their relative primitive-ness, and the simplest explanation for their more conservative nature is that they have had less time to evolve. While fossils may be important in phylogenetic inference only under certain conditions, there is no compelling reason to prejudge their contribution. We urge systematists to evaluate fairly all of the available evidence.Peer Reviewedhttp://deepblue.lib.umich.edu/bitstream/2027.42/73857/1/j.1096-0031.1988.tb00514.x.pd
The Osteology of the Basal Archosauromorph Tasmaniosaurus triassicus from the Lower Triassic of Tasmania, Australia
Proterosuchidae are the most taxonomically diverse archosauromorph reptiles sampled in the immediate aftermath of the Permo-Triassic mass extinction and represent the earliest radiation of Archosauriformes (archosaurs and closely related species). Proterosuchids are potentially represented by approximately 15 nominal species collected from South Africa, China, Russia, Australia and India, but the taxonomic content of the group is currently in a state of flux because of the poor anatomic and systematic information available for several of its putative members. Here, the putative proterosuchid Tasmaniosaurus triassicus from the Lower Triassic of Hobart, Tasmania (Australia),is redescribed. The holotype and currently only known specimen includes cranial and postcranial remains and the revision of this material sheds new light on the anatomy of the animal, including new data on the cranial endocast. Several bones are re-identified or reinterpreted, contrasting with the descriptions of previous authors. The new information provided here shows that Tasmaniosaurus closely resembles the South African proterosuchid Proterosuchus, but it differed in the presence of, for example, a slightly downturned premaxilla, a shorter anterior process of maxilla, and a diamond-shaped anterior end of interclavicle. Previous claims for the presence of gut contents in the holotype of Tasmaniosaurus are considered ambiguous. The description of the cranial endocast of Tasmaniosaurus provides for the first time information about the anatomy of this region in proterosuchids. The cranial endocast preserves possibly part of the vomero-nasal (= Jacobson's) system laterally to the olfactory bulbs. Previous claims of the absence of the vomero-nasal organs in archosaurs, which is suggested by the extant phylogenetic bracket, are questioned because its absence in both clades of extant archosaurs seems to be directly related with the independent acquisition of a non-ground living mode of life
Development of the chondrocranium in the suckermouth armored catfishAncistrus cf.triradiatus (Loricariidae, Siluriformes)
Applikationsutveckling för visualisering av positioner på personal vid katastrofinsatser
This master's thesis presents the development and evaluation of an application visualising the operators' current positions in disaster area operations. The application was developed to address limitations in their current working methods, which currently rely on verbal communication and manual position mapping. The requirements and needs of the end-users were identified at the beginning of the study. Then, the application was developed over three iterations and improved iteratively based on the requirements and results of the evaluations. The proposed solution visualises the operators' positions on a map that can be supported in an off-the-grid environment. End-users evaluated the application to measure the level of usability and the impact the new system would have. The findings indicated that an application can impact today's operations by providing operators with better situational awareness. Further, the application could lead to more safe and efficient operations. Overall, this master's thesis adds to the continuous improvement of operational capabilities in disaster areas using technology
Applikationsutveckling för visualisering av positioner på personal vid katastrofinsatser
This master's thesis presents the development and evaluation of an application visualising the operators' current positions in disaster area operations. The application was developed to address limitations in their current working methods, which currently rely on verbal communication and manual position mapping. The requirements and needs of the end-users were identified at the beginning of the study. Then, the application was developed over three iterations and improved iteratively based on the requirements and results of the evaluations. The proposed solution visualises the operators' positions on a map that can be supported in an off-the-grid environment. End-users evaluated the application to measure the level of usability and the impact the new system would have. The findings indicated that an application can impact today's operations by providing operators with better situational awareness. Further, the application could lead to more safe and efficient operations. Overall, this master's thesis adds to the continuous improvement of operational capabilities in disaster areas using technology
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