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Bowman CIW, Young MT, Schwab JA, Walsh S, Witmer LM, Herrera Y, Choiniere J, Dollman KN, Brusatte SL. Rostral neurovasculature indicates sensory trade-offs in Mesozoic pelagic crocodylomorphs. Anat Rec (Hoboken) 2021; 305:2654-2669. [PMID: 34428341 DOI: 10.1002/ar.24733] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 02/23/2021] [Revised: 06/09/2021] [Accepted: 06/23/2021] [Indexed: 01/04/2023]
Abstract
Metriorhynchoid thalattosuchians were a marine clade of Mesozoic crocodylomorphs that evolved from semi-aquatic, "gharial"-like species into the obligately pelagic subclade Metriorhynchidae. To explore whether the sensory and physiological demands of underwater life necessitates a shift in rostral anatomy, both in neurology and vasculature, we investigate the trigeminal innervation and potential somatosensory abilities of metriorhynchoids by digitally segmenting the rostral neurovascular canals in CT scans of 10 extant and extinct crocodyliforms. The dataset includes the terrestrial, basal crocodyliform Protosuchus haughtoni, two semi-aquatic basal metriorhynchoids, four pelagic metriorhynchids and three extant, semi-aquatic crocodylians. In the crocodylian and basal metriorhynchoid taxa, we find three main neurovascular channels running parallel to one another posteroanteriorly down the length of the snout, whereas in metriorhynchids there are two, and in P. haughtoni only one. Crocodylians appear to be unique in their extensive trigeminal innervation, which is used to supply the integumentary sensory organs (ISOs) involved with their facial somatosensory abilities. Crocodylians have a far higher number of foramina on the maxillary bones than either metriorhynchoids or P. haughtoni, suggesting that the fossil taxa lacked the somatosensory abilities seen in extant species. We posit that the lack of ISO osteological correlates in metriorhynchoids is due to their basal position in Crocodyliformes, rather than a pelagic adaptation. This is reinforced by the hypothesis that extant crocodyliforms, and possibly some neosuchian clades, underwent a long "nocturnal bottleneck"-hinting that their complex network of ISOs evolved in Neosuchia, as a sensory trade-off to compensate for poorer eyesight.
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Affiliation(s)
| | - Mark T Young
- School of GeoSciences, Grant Institute, University of Edinburgh, Edinburgh, UK
| | - Julia A Schwab
- School of GeoSciences, Grant Institute, University of Edinburgh, Edinburgh, UK
| | - Stig Walsh
- Department of Natural Sciences, National Museum of Scotland, Edinburgh, UK
| | - Lawrence M Witmer
- Department of Biomedical Sciences, Heritage College of Osteopathic Medicine, Ohio Center for Ecology and Evolutionary Studies, Ohio University, Athens, Ohio, USA
| | - Yanina Herrera
- Consejo Nacional de Investigaciones Científicas y Técnicas, División Paleontología Vertebrados, Museo de La Plata, Facultad de Ciencias Naturales y Museo, La Plata, Buenos Aires, Argentina
| | - Jonah Choiniere
- Evolutionary Studies Institute, University of the Witwatersrand, Johannesburg, South Africa
| | - Kathleen N Dollman
- Evolutionary Studies Institute, University of the Witwatersrand, Johannesburg, South Africa
| | - Stephen L Brusatte
- School of GeoSciences, Grant Institute, University of Edinburgh, Edinburgh, UK
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2
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Bronzati M, Benson RBJ, Evers SW, Ezcurra MD, Cabreira SF, Choiniere J, Dollman KN, Paulina-Carabajal A, Radermacher VJ, Roberto-da-Silva L, Sobral G, Stocker MR, Witmer LM, Langer MC, Nesbitt SJ. Deep evolutionary diversification of semicircular canals in archosaurs. Curr Biol 2021. [PMID: 33930303 DOI: 10.1016/j.cub.2021.2503.2086] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Key Words] [MESH Headings] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 04/18/2023]
Abstract
Living archosaurs (birds and crocodylians) have disparate locomotor strategies that evolved since their divergence ∼250 mya. Little is known about the early evolution of the sensory structures that are coupled with these changes, mostly due to limited sampling of early fossils on key stem lineages. In particular, the morphology of the semicircular canals (SCCs) of the endosseous labyrinth has a long-hypothesized relationship with locomotion. Here, we analyze SCC shapes and sizes of living and extinct archosaurs encompassing diverse locomotor habits, including bipedal, semi-aquatic, and flying taxa. We test form-function hypotheses of the SCCs and chronicle their evolution during deep archosaurian divergences. We find that SCC shape is statistically associated with both flight and bipedalism. However, this shape variation is small and is more likely explained by changes in braincase geometry than by locomotor changes. We demonstrate high disparity of both shape and size among stem-archosaurs and a deep divergence of SCC morphologies at the bird-crocodylian split. Stem-crocodylians exhibit diverse morphologies, including aspects also present in birds and distinct from other reptiles. Therefore, extant crocodylian SCC morphologies do not reflect retention of a "primitive" reptilian condition. Key aspects of bird SCC morphology that hitherto were interpreted as flight related, including large SCC size and enhanced sensitivity, appeared early on the bird stem-lineage in non-flying dinosaur precursors. Taken together, our results indicate a deep divergence of SCC traits at the bird-crocodylian split and that living archosaurs evolved from an early radiation with high sensory diversity. VIDEO ABSTRACT.
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Affiliation(s)
- Mario Bronzati
- Departamento de Biologia, Universidade de São Paulo, Av. Bandeirantes 1900, Ribeirão Preto-SP 14040-091, Brazil.
| | - Roger B J Benson
- Department of Earth Sciences, University of Oxford, South Parks Road, OX13AN Oxford, UK; Evolutionary Studies Institute, University of the Witwatersrand, Braamfontein, Private Bag 3, Johannesburg WITS2050, South Africa.
| | - Serjoscha W Evers
- Department of Earth Sciences, University of Oxford, South Parks Road, OX13AN Oxford, UK; Department of Geosciences, University of Fribourg, Chemin du Musée 4, 1700 Fribourg, Switzerland
| | - Martín D Ezcurra
- Sección Paleontología de Vertebrados, CONICET-Museo Argentino de Ciencias Naturales "Bernardino Rivadavia", Ángel Gallardo 470, C1405DJR Buenos Aires, Argentina; School of Geography, Earth and Environmental Sciences, University of Birmingham, Edgbaston, B15 2TT Birmingham, UK
| | - Sergio F Cabreira
- Avenida Antônio Bozzetto 305, Faxinal do Soturno-RS 97220-000, Brazil
| | - Jonah Choiniere
- Evolutionary Studies Institute, University of the Witwatersrand, Braamfontein, Private Bag 3, Johannesburg WITS2050, South Africa
| | - Kathleen N Dollman
- Evolutionary Studies Institute, University of the Witwatersrand, Braamfontein, Private Bag 3, Johannesburg WITS2050, South Africa
| | - Ariana Paulina-Carabajal
- Instituto de Investigaciones en Biodiversidad y Medioambiente (INIBIOMA), CONICET-Universidad Nacional del Comahue, Quintral 1250 (8400), San Carlos de Bariloche, Argentina
| | - Viktor J Radermacher
- Evolutionary Studies Institute, University of the Witwatersrand, Braamfontein, Private Bag 3, Johannesburg WITS2050, South Africa
| | | | - Gabriela Sobral
- Staatliches Museum für Naturkunde Stuttgart, Rosenstein 1, Suttgart 70191, Germany
| | - Michelle R Stocker
- Department of Geosciences, Virginia Tech, 926 West Campus Drive, Blacksburg, VA 24061, USA
| | - Lawrence M Witmer
- Department of Biomedical Science, Heritage College of Osteopathic Medicine, Ohio University, Athens, OH 45701, USA
| | - Max C Langer
- Departamento de Biologia, Universidade de São Paulo, Av. Bandeirantes 1900, Ribeirão Preto-SP 14040-091, Brazil
| | - Sterling J Nesbitt
- Department of Geosciences, Virginia Tech, 926 West Campus Drive, Blacksburg, VA 24061, USA.
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3
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Bronzati M, Benson RBJ, Evers SW, Ezcurra MD, Cabreira SF, Choiniere J, Dollman KN, Paulina-Carabajal A, Radermacher VJ, Roberto-da-Silva L, Sobral G, Stocker MR, Witmer LM, Langer MC, Nesbitt SJ. Deep evolutionary diversification of semicircular canals in archosaurs. Curr Biol 2021; 31:2520-2529.e6. [PMID: 33930303 DOI: 10.1016/j.cub.2021.03.086] [Citation(s) in RCA: 24] [Impact Index Per Article: 8.0] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 10/21/2020] [Revised: 02/04/2021] [Accepted: 03/25/2021] [Indexed: 01/02/2023]
Abstract
Living archosaurs (birds and crocodylians) have disparate locomotor strategies that evolved since their divergence ∼250 mya. Little is known about the early evolution of the sensory structures that are coupled with these changes, mostly due to limited sampling of early fossils on key stem lineages. In particular, the morphology of the semicircular canals (SCCs) of the endosseous labyrinth has a long-hypothesized relationship with locomotion. Here, we analyze SCC shapes and sizes of living and extinct archosaurs encompassing diverse locomotor habits, including bipedal, semi-aquatic, and flying taxa. We test form-function hypotheses of the SCCs and chronicle their evolution during deep archosaurian divergences. We find that SCC shape is statistically associated with both flight and bipedalism. However, this shape variation is small and is more likely explained by changes in braincase geometry than by locomotor changes. We demonstrate high disparity of both shape and size among stem-archosaurs and a deep divergence of SCC morphologies at the bird-crocodylian split. Stem-crocodylians exhibit diverse morphologies, including aspects also present in birds and distinct from other reptiles. Therefore, extant crocodylian SCC morphologies do not reflect retention of a "primitive" reptilian condition. Key aspects of bird SCC morphology that hitherto were interpreted as flight related, including large SCC size and enhanced sensitivity, appeared early on the bird stem-lineage in non-flying dinosaur precursors. Taken together, our results indicate a deep divergence of SCC traits at the bird-crocodylian split and that living archosaurs evolved from an early radiation with high sensory diversity. VIDEO ABSTRACT.
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Affiliation(s)
- Mario Bronzati
- Departamento de Biologia, Universidade de São Paulo, Av. Bandeirantes 1900, Ribeirão Preto-SP 14040-091, Brazil.
| | - Roger B J Benson
- Department of Earth Sciences, University of Oxford, South Parks Road, OX13AN Oxford, UK; Evolutionary Studies Institute, University of the Witwatersrand, Braamfontein, Private Bag 3, Johannesburg WITS2050, South Africa.
| | - Serjoscha W Evers
- Department of Earth Sciences, University of Oxford, South Parks Road, OX13AN Oxford, UK; Department of Geosciences, University of Fribourg, Chemin du Musée 4, 1700 Fribourg, Switzerland
| | - Martín D Ezcurra
- Sección Paleontología de Vertebrados, CONICET-Museo Argentino de Ciencias Naturales "Bernardino Rivadavia", Ángel Gallardo 470, C1405DJR Buenos Aires, Argentina; School of Geography, Earth and Environmental Sciences, University of Birmingham, Edgbaston, B15 2TT Birmingham, UK
| | - Sergio F Cabreira
- Avenida Antônio Bozzetto 305, Faxinal do Soturno-RS 97220-000, Brazil
| | - Jonah Choiniere
- Evolutionary Studies Institute, University of the Witwatersrand, Braamfontein, Private Bag 3, Johannesburg WITS2050, South Africa
| | - Kathleen N Dollman
- Evolutionary Studies Institute, University of the Witwatersrand, Braamfontein, Private Bag 3, Johannesburg WITS2050, South Africa
| | - Ariana Paulina-Carabajal
- Instituto de Investigaciones en Biodiversidad y Medioambiente (INIBIOMA), CONICET-Universidad Nacional del Comahue, Quintral 1250 (8400), San Carlos de Bariloche, Argentina
| | - Viktor J Radermacher
- Evolutionary Studies Institute, University of the Witwatersrand, Braamfontein, Private Bag 3, Johannesburg WITS2050, South Africa
| | | | - Gabriela Sobral
- Staatliches Museum für Naturkunde Stuttgart, Rosenstein 1, Suttgart 70191, Germany
| | - Michelle R Stocker
- Department of Geosciences, Virginia Tech, 926 West Campus Drive, Blacksburg, VA 24061, USA
| | - Lawrence M Witmer
- Department of Biomedical Science, Heritage College of Osteopathic Medicine, Ohio University, Athens, OH 45701, USA
| | - Max C Langer
- Departamento de Biologia, Universidade de São Paulo, Av. Bandeirantes 1900, Ribeirão Preto-SP 14040-091, Brazil
| | - Sterling J Nesbitt
- Department of Geosciences, Virginia Tech, 926 West Campus Drive, Blacksburg, VA 24061, USA.
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Xu X, Choiniere J, Tan Q, Benson RBJ, Clark J, Sullivan C, Zhao Q, Han F, Ma Q, He Y, Wang S, Xing H, Tan L. Two Early Cretaceous Fossils Document Transitional Stages in Alvarezsaurian Dinosaur Evolution. Curr Biol 2018; 28:2853-2860.e3. [PMID: 30146153 DOI: 10.1016/j.cub.2018.07.057] [Citation(s) in RCA: 19] [Impact Index Per Article: 3.2] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 04/23/2018] [Revised: 06/04/2018] [Accepted: 07/24/2018] [Indexed: 10/28/2022]
Abstract
Highly specialized animals are often difficult to place phylogenetically. The Late Cretaceous members of Alvarezsauria represent such an example, having been posited as members of various theropod lineages, including birds [1-11]. A 70-million-year ghost lineage exists between them and the Late Jurassic putative alvarezsaurian Haplocheirus [12], which preserves so few derived features that its membership in Alvarezsauria has recently been questioned [13]. If Haplocheirus is indeed an alvarezsaurian, then the 70-million-year gap between Haplocheirus and other alvarezsaurians represents the longest temporal hiatus within the fossil record of any theropod subgroup [14]. Here we report two new alvarezsaurians from the Early Cretaceous of Western China that document successive, transitional stages in alvarezsaurian evolution. They provide further support for Haplocheirus as an alvarezsaurian and for alvarezsaurians as basal maniraptorans. Furthermore, they suggest that the early biogeographic history of the Alvarezsauria involved dispersals from Asia to other continents. The new specimens are temporally, morphologically, and functionally intermediate between Haplocheirus and other known alvarezsaurians and provide a striking example of the evolutionary transition from a typical theropod forelimb configuration (i.e., the relatively long arm and three-digit grasping hand of typical tetanuran form in early-branching alvarezsaurians) to a highly specialized one (i.e., the highly modified and shortened arm and one-digit digging hand of Late Cretaceous parvicursorines such as Linhenykus [1, 15]). Comprehensive analyses incorporating data from these new finds show that the specialized alvarezsaurian forelimb morphology evolved slowly and in a mosaic fashion during the Cretaceous.
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Affiliation(s)
- Xing Xu
- Key Laboratory of Vertebrate Evolution and Human Origins, Institute of Vertebrate Paleontology and Paleoanthropology, Chinese Academy of Sciences, 142 Xiwai Street, Beijing 100044, China; CAS Center for Excellence in Life and Paleoenvironment, 142 Xiwai Street, Beijing 100044, China; Centre for Research and Education on Biological Evolution and Environment, 163 Xianlin Road, Nanjing University, Nanjing 210045, China.
| | - Jonah Choiniere
- Evolutionary Studies Institute, University of the Witwatersrand, Private Bag 3, Johannesburg WITS 2050, South Africa; Department of Vertebrate Paleontology and Richard Gilder Graduate School, American Museum of Natural History, Central Park West at 79(th) Street, New York, NY 10024, USA
| | - Qingwei Tan
- Long Hao Institute of Geology and Paleontology, Jia 29, Fengzhou Road, Hohhot, Nei Mongol 010010, China
| | - Roger B J Benson
- Evolutionary Studies Institute, University of the Witwatersrand, Private Bag 3, Johannesburg WITS 2050, South Africa; Department of Earth Sciences, University of Oxford, South Parks Road, Oxford OX1 3AN, UK
| | - James Clark
- Department of Biological Sciences, George Washington University, 2023 G Street NW, Washington, DC 20052, USA; Centre for Vertebrate Evolutionary Biology, Yunnan University, 2 Green Lake North Road, Kunming 650091, China
| | - Corwin Sullivan
- Department of Biological Sciences, University of Alberta, 11455 Saskatchewan Drive, Edmonton, AB T6G 2E9, Canada; Philip J. Currie Dinosaur Museum, 9301 112 Avenue, Wembley, AB T0H 3S0, Canada
| | - Qi Zhao
- Key Laboratory of Vertebrate Evolution and Human Origins, Institute of Vertebrate Paleontology and Paleoanthropology, Chinese Academy of Sciences, 142 Xiwai Street, Beijing 100044, China
| | - Fenglu Han
- School of Earth Sciences, China University of Geosciences, 388 Lumo Road, Wuhan 430074, China
| | - Qingyu Ma
- Key Laboratory of Vertebrate Evolution and Human Origins, Institute of Vertebrate Paleontology and Paleoanthropology, Chinese Academy of Sciences, 142 Xiwai Street, Beijing 100044, China
| | - Yiming He
- School of Earth Sciences and Engineering, Nanjing University, 163 Xianlin Road, Nanjing 210045, China
| | - Shuo Wang
- College of Life Science, Capital Normal Univerity, 105 West 3(rd) Ring Road North, Beijing 100048, China
| | - Hai Xing
- Beijing Museum of Natural History, Beijing Academy of Science and Technology, 126 South Tianqiao Street, Beijing 100050, China
| | - Lin Tan
- Long Hao Institute of Geology and Paleontology, Jia 29, Fengzhou Road, Hohhot, Nei Mongol 010010, China
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Watanabe A, Eugenia Leone Gold M, Brusatte SL, Benson RBJ, Choiniere J, Davidson A, Norell MA. Vertebral Pneumaticity in the Ornithomimosaur Archaeornithomimus (Dinosauria: Theropoda) Revealed by Computed Tomography Imaging and Reappraisal of Axial Pneumaticity in Ornithomimosauria. PLoS One 2015; 10:e0145168. [PMID: 26682888 PMCID: PMC4684312 DOI: 10.1371/journal.pone.0145168] [Citation(s) in RCA: 14] [Impact Index Per Article: 1.6] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [MESH Headings] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/24/2015] [Accepted: 11/30/2015] [Indexed: 11/19/2022] Open
Abstract
Among extant vertebrates, pneumatization of postcranial bones is unique to birds, with few known exceptions in other groups. Through reduction in bone mass, this feature is thought to benefit flight capacity in modern birds, but its prevalence in non-avian dinosaurs of variable sizes has generated competing hypotheses on the initial adaptive significance of postcranial pneumaticity. To better understand the evolutionary history of postcranial pneumaticity, studies have surveyed its distribution among non-avian dinosaurs. Nevertheless, the degree of pneumaticity in the basal coelurosaurian group Ornithomimosauria remains poorly known, despite their potential to greatly enhance our understanding of the early evolution of pneumatic bones along the lineage leading to birds. Historically, the identification of postcranial pneumaticity in non-avian dinosaurs has been based on examination of external morphology, and few studies thus far have focused on the internal architecture of pneumatic structures inside the bones. Here, we describe the vertebral pneumaticity of the ornithomimosaur Archaeornithomimus with the aid of X-ray computed tomography (CT) imaging. Complementary examination of external and internal osteology reveals (1) highly pneumatized cervical vertebrae with an elaborate configuration of interconnected chambers within the neural arch and the centrum; (2) anterior dorsal vertebrae with pneumatic chambers inside the neural arch; (3) apneumatic sacral vertebrae; and (4) a subset of proximal caudal vertebrae with limited pneumatic invasion into the neural arch. Comparisons with other theropod dinosaurs suggest that ornithomimosaurs primitively exhibited a plesiomorphic theropod condition for axial pneumaticity that was extended among later taxa, such as Archaeornithomimus and large bodied Deinocheirus. This finding corroborates the notion that evolutionary increases in vertebral pneumaticity occurred in parallel among independent lineages of bird-line archosaurs. Beyond providing a comprehensive view of vertebral pneumaticity in a non-avian coelurosaur, this study demonstrates the utility and need of CT imaging for further clarifying the early evolutionary history of postcranial pneumaticity.
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Affiliation(s)
- Akinobu Watanabe
- Division of Paleontology, American Museum of Natural History, New York, New York, United States of America
- Richard Gilder Graduate School, American Museum of Natural History, New York, New York, United States of America
| | - Maria Eugenia Leone Gold
- Division of Paleontology, American Museum of Natural History, New York, New York, United States of America
- Richard Gilder Graduate School, American Museum of Natural History, New York, New York, United States of America
| | | | - Roger B. J. Benson
- Department of Earth Sciences, University of Oxford, Oxford, United Kingdom
- Evolutionary Studies Institute and DST/NRF Centre of Excellence in Palaeosciences, University of the Witwatersrand, Johannesburg, South Africa
| | - Jonah Choiniere
- Evolutionary Studies Institute and DST/NRF Centre of Excellence in Palaeosciences, University of the Witwatersrand, Johannesburg, South Africa
| | - Amy Davidson
- Division of Paleontology, American Museum of Natural History, New York, New York, United States of America
| | - Mark A. Norell
- Division of Paleontology, American Museum of Natural History, New York, New York, United States of America
- Richard Gilder Graduate School, American Museum of Natural History, New York, New York, United States of America
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Otero A, Krupandan E, Pol D, Chinsamy A, Choiniere J. A new basal sauropodiform from South Africa and the phylogenetic relationships of basal sauropodomorphs. Zool J Linn Soc 2015. [DOI: 10.1111/zoj.12247] [Citation(s) in RCA: 41] [Impact Index Per Article: 4.6] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/27/2022]
Affiliation(s)
- Alejandro Otero
- Consejo Nacional de Investigaciones Científicas y Técnicas (CONICET); División Paleontología de Vertebrados; Museo de La Plata; Paseo del Bosque s/n; 1900 La Plata Argentina
- Evolutionary Studies Institute; Centre of Excellence in Palaeosciences; University of the Witwatersrand; Private Bag 3 Johannesburg Gauteng 2050 South Africa
| | - Emil Krupandan
- Biological Sciences Department; University of Cape Town; Private Bag Rondebosch Cape Town South Africa
| | - Diego Pol
- CONICET; Museo Paleontológico Egidio Feruglio; Av. Fontana 140 9100 Trelew Argentina
| | - Anusuya Chinsamy
- Biological Sciences Department; University of Cape Town; Private Bag Rondebosch Cape Town South Africa
| | - Jonah Choiniere
- Evolutionary Studies Institute; Centre of Excellence in Palaeosciences; University of the Witwatersrand; Private Bag 3 Johannesburg Gauteng 2050 South Africa
- NRF/Centre of Excellence in Palaeosciences; University of the Witwatersrand; Private Bag 3 Johannesburg Gauteng 2050 South Africa
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Abstract
This paper examines the impact of managed care on the informal learning process for nurses in a major US-based health organisation. Through the analysis of focus group data we report the nurses' view of the effect recent changes have had on the nurse/patient/care relationship. Managed care, our research indicates, has transformed the learning milieus for nurses with two effects. First, nurses have seen their need for informal learning increase while the time and context for that learning has diminished. Second, the process of teaching patients and families has also been adversely affected even as managed care creates the need for more patient education. We report the analysis of the data collected at group interviews involving nurses working in both hospital and community settings of a leading US-based HMO. All interviews took place during September of 1997 at various sites in California. This study is part of a larger Social Science Research Council of Canada funded investigation into managed care in the US and Canada.
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Affiliation(s)
- J P White
- Department of Sociology, University of Western Ontario, London, Canada.
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