The Experts below are selected from a list of 258 Experts worldwide ranked by ideXlab platform
David A. Ebert - One of the best experts on this subject based on the ideXlab platform.
-
first records of the seven gilled notorynchus cepedianus and six gilled Hexanchus griseus sharks chondrichthyes hexanchiformes hexanchidae found in the galapagos marine reserve
Journal of Fish Biology, 2020Co-Authors: Salome Buglass, David A. Ebert, Shannon Nagy, Paulina Sepa, Alan Turchik, K L Bell, Fernando Rivera, Jonatha GiddensAbstract:This study reports the first records of cowsharks (Hexanchidae) in the Galapagos Islands, in particular Notorynchus cepedianus and Hexanchus griseus, observed between depths of 210 and 418 m on footage from free-falling autonomous deep ocean cameras. These sightings provide new information on the habitat preferences and range distribution for N. cepedianus, and the first records of H. griseus in Ecuadorian waters. Our findings support the formulation of regional conservation strategies for these large apex predator species, and highlight our limited biological knowledge of Galapagos' deep-water ecosystems. This article is protected by copyright. All rights reserved.
-
first records of the seven gilled notorynchus cepedianus and six gilled Hexanchus griseus sharks chondrichthyes hexanchiformes hexanchidae found in the galapagos marine reserve
Journal of Fish Biology, 2020Co-Authors: Salome Buglass, David A. Ebert, Shannon Nagy, Paulina Sepa, Alan Turchik, K L Bell, Fernando Rivera, Jonatha GiddensAbstract:This study reports the first records of cowsharks (Hexanchidae) in the Galapagos Islands, in particular Notorynchus cepedianus and Hexanchus griseus, observed between depths of 210 and 418 m on footage from free-falling autonomous deep-ocean cameras. These sightings provide new information on the habitat preferences and range distribution for N. cepedianus and the first records of H. griseus in Ecuadorian waters. The findings support the formulation of regional conservation strategies for these large apex predator species and highlight the limited biological knowledge of Galapagos' deep-water ecosystems.
-
RESEARCH ARTICLE Preliminary Observations of Population Genetics and Relatedness of the Broadnose Sevengill Shark, Notorynchus cepedianus, in Two Northeast Pacific Estuaries
2016Co-Authors: Shawn Larson, Debbie Farrer, Dayv Lowry, David A. EbertAbstract:The broadnose sevengill shark, Notorynchus cepedianus, a common coastal species in the eastern North Pacific, was sampled during routine capture and tagging operations con-ducted from 2005–2012. One hundred and thirty three biopsy samples were taken during these research operations in Willapa Bay, Washington and in San Francisco Bay, Califor-nia. Genotypic data from seven polymorphic microsatellites (derived from the related sixgill shark, Hexanchus griseus) were used to describe N. cepedianus genetic diversity, popula-tion structure and relatedness. Diversity within N. cepedianus was found to be low to moder-ate with an average observed heterozygosity of 0.41, expected heterozygosity of 0.53, and an average of 5.1 alleles per microsatellite locus. There was no evidence of a recent popula-tion bottleneck based on genetic data. Analyses of genetic differences between the two sampled estuaries suggest two distinct populations with some genetic mixing of sharks sampled during 2005–2006. Relatedness within sampled populations was high, with per-cent relatedness among sharks caught in the same area indicating 42.30 % first-order rela-tive relationships (full or half siblings). Estuary-specific familial relationships suggest that management of N. cepedianus on the U.S. West Coast should incorporate stock-specific management goals to conserve this ecologically important predator
-
Preliminary Observations of Population Genetics and Relatedness of the Broadnose Sevengill Shark, Notorynchus cepedianus, in Two Northeast Pacific Estuaries.
PloS one, 2015Co-Authors: Shawn D. Larson, Debbie Farrer, Dayv Lowry, David A. EbertAbstract:The broadnose sevengill shark, Notorynchus cepedianus, a common coastal species in the eastern North Pacific, was sampled during routine capture and tagging operations conducted from 2005–2012. One hundred and thirty three biopsy samples were taken during these research operations in Willapa Bay, Washington and in San Francisco Bay, California. Genotypic data from seven polymorphic microsatellites (derived from the related sixgill shark, Hexanchus griseus) were used to describe N. cepedianus genetic diversity, population structure and relatedness. Diversity within N. cepedianus was found to be low to moderate with an average observed heterozygosity of 0.41, expected heterozygosity of 0.53, and an average of 5.1 alleles per microsatellite locus. There was no evidence of a recent population bottleneck based on genetic data. Analyses of genetic differences between the two sampled estuaries suggest two distinct populations with some genetic mixing of sharks sampled during 2005–2006. Relatedness within sampled populations was high, with percent relatedness among sharks caught in the same area indicating 42.30% first-order relative relationships (full or half siblings). Estuary-specific familial relationships suggest that management of N. cepedianus on the U.S. West Coast should incorporate stock-specific management goals to conserve this ecologically important predator.
-
Redescription of Hexanchus nakamurai Teng 1962, (Chondrichthyes: Hexanchiformes: Hexanchidae), with designation of a neotype
Zootaxa, 2013Co-Authors: David A. Ebert, William T. WhiteAbstract:Hexanchus nakamurai Teng, 1962 is one of two valid nominal species in the genus Hexanchus ; the other being H. griseus . The taxonomic history of H. nakamurai is somewhat convoluted due to questions about the validity of whether it constituted a publication or an unpublished dissertation. The issue appeared to have been resolved once it was determined that the Teng’s original description met the criteria under the International Commission on Zoological Nomenclature code (Article 8a) of a publication. However, recent molecular studies have indicated that the western North Atlantic H . nakamurai (=? H. vitulus ) may be distinct from western Indian Ocean H. nakamurai . Compounding the issue is the loss of the holotype of H. nakamurai from Taiwan. A neotype is herein designated and the species redescribed based on the neotype and eight additional Taiwanese specimens.
Shawn Larson - One of the best experts on this subject based on the ideXlab platform.
-
RESEARCH ARTICLE Preliminary Observations of Population Genetics and Relatedness of the Broadnose Sevengill Shark, Notorynchus cepedianus, in Two Northeast Pacific Estuaries
2016Co-Authors: Shawn Larson, Debbie Farrer, Dayv Lowry, David A. EbertAbstract:The broadnose sevengill shark, Notorynchus cepedianus, a common coastal species in the eastern North Pacific, was sampled during routine capture and tagging operations con-ducted from 2005–2012. One hundred and thirty three biopsy samples were taken during these research operations in Willapa Bay, Washington and in San Francisco Bay, Califor-nia. Genotypic data from seven polymorphic microsatellites (derived from the related sixgill shark, Hexanchus griseus) were used to describe N. cepedianus genetic diversity, popula-tion structure and relatedness. Diversity within N. cepedianus was found to be low to moder-ate with an average observed heterozygosity of 0.41, expected heterozygosity of 0.53, and an average of 5.1 alleles per microsatellite locus. There was no evidence of a recent popula-tion bottleneck based on genetic data. Analyses of genetic differences between the two sampled estuaries suggest two distinct populations with some genetic mixing of sharks sampled during 2005–2006. Relatedness within sampled populations was high, with per-cent relatedness among sharks caught in the same area indicating 42.30 % first-order rela-tive relationships (full or half siblings). Estuary-specific familial relationships suggest that management of N. cepedianus on the U.S. West Coast should incorporate stock-specific management goals to conserve this ecologically important predator
-
Relatedness and polyandry of sixgill sharks, Hexanchus griseus, in an urban estuary
Conservation Genetics, 2011Co-Authors: Shawn Larson, Dayv Lowry, Jeff Christiansen, Denise Griffing, Jimiane Ashe, Kelly AndrewsAbstract:The bluntnose sixgill shark ( Hexanchus griseus ) is a widely distributed species found in tropical and temperate waters of every ocean, yet we know relatively little about their basic biology including their life history and population structure. From 2003–2007, we collected over 300 biopsy samples from sixgills during research operations in Puget Sound, WA, USA. Genotypic data using ten polymorphic microsatellites were used to describe sixgill genetic diversity, relatedness and mating pattern. Diversity within sixgills was found to be moderate with an average observed heterozygosity of 0.45, an average expected heterozygosity of 0.61, an average of 12 alleles per locus, and an average allelic richness of eight within microsatellite loci. Our data suggests all of the sampled individuals come from one intermixing population, and we found no historical evidence of significant population bottlenecks. Many of the sharks were sampled using longline techniques with several sharks captured at the same time and place. Similarly, multiple sharks were sampled on several occasions during research events at the Seattle Aquarium. The proportion of individuals that were full- or half-siblings was high among sharks sampled at the same time and place (range 0.65–0.87). Analysis of the genetic relationship between one large female washed ashore and 71 of her near-term pups suggested a polyandrous mating system with as many as nine males contributing to her offspring. This study is the first to investigate genetic diversity, relatedness and paternity within sixgill sharks and sheds light on important conservation implications for this little known shark population.
-
Microsatellite loci within sixgill sharks, Hexanchus griseus
Molecular Ecology Resources, 2009Co-Authors: Shawn Larson, Deborah Tinnemore, Chris T. AmemiyaAbstract:Novel sixgill shark (Hexanchus griseus) microsatellite loci were developed and tested on five shark species. A suite of microsatellite loci previously developed for lemon sharks (Negaprion brevirostris) was also tested. Data on 15 microsatellites are presented including primer sequences, number of alleles (a), observed (HO) and expected heterozygosities (HE), and FIS values for sixgill sharks (a = 10–69, HO = 0.24–1.00, HE = 0.76–0.96 and FIS = –0.21–0.60), sevengill sharks (Notorynchus cepedianus) (a = 6–40, HO = 0.20–0.73, HE = 0.59–0.94 and FIS = –0.47–0.58), Pacific spiny dogfish (Squalus acanthias) (a = 3–13, HO = 0.00–0.96, HE = 0.24–0.93 and FIS =–0.52–1.00), angle sharks (Squatina californica) (a = 1–4, HO = 0.00–1.00, HE = 0.60–1.00 and FIS =–1.00–0.25), and leopard sharks (Triakis semifasciata) (a = 3–16, HO = 0.20–1.00, HE = 0.53–0.92 and FIS = –0.57–1.00). A final suite of 14 microsatellites (13 developed from sixgill sharks and one from lemon sharks) were found to be polymorphic and conform to Hardy–Weinberg equilibrium within sixgill sharks.
-
sixgill shark Hexanchus griseus conservation ecology project update
2005Co-Authors: Shawn Larson, Jeff ChristiansenAbstract:The existence of sixgill sharks was an "open secret" among Puget Sound divers, recreational and commercial fishermen, scientists and naturalists, but few people in the general public knew that Puget Sound and Seattle's Elliott Bay contained a well-established, but rarely seen shark population. Anecdotal evidence (acquired from personal reports of divers and fishermen) suggests that Puget Sound's sixgills are long-lived and slow-growing, and appear to have established movement corridors and territories that remain relatively fixed over time. Sixgills prey upon Puget Sound's dogfish, skates and other non- or low-value commercial fishes, and like other apex predators are highly vulnerable to changes in their environment (Ebert 1986). Worldwide concern over the effects of fishing on shark populations was brought to the forefront of public attention in Seattle by publicity surrounding the catching of several bluntnose sixgill sharks from Elliott Bay during the summer of 2000. These sharks were fished from an area where local divers had reported frequent encounters with known individual sharks in shallow waters (Duwamish Head, Elliott Bay). After the fishing pressure, no sharks were sighted in this area for several months. Eventually sharks were re-sighted in the area but not the individuals previously identified. This apparent direct affect of fishing pressure on the local sixgill population caused concern within the local diving and scientific communities. State regulators responded to these concerns by placing a temporary closure on the taking of these sharks in Puget Sound. The Seattle Aquarium was instrumental in acting as an informational liaison between the public and the Washington Department of Fish and Wildlife (WDFW) to obtain the closure. Lack of information on the abundance of sixgills in Puget Sound/Georgia Basin, their movement patterns, and basic biological parameters, dictated a cautious approach to allowing harvest of sixgill sharks.
Dayv Lowry - One of the best experts on this subject based on the ideXlab platform.
-
RESEARCH ARTICLE Preliminary Observations of Population Genetics and Relatedness of the Broadnose Sevengill Shark, Notorynchus cepedianus, in Two Northeast Pacific Estuaries
2016Co-Authors: Shawn Larson, Debbie Farrer, Dayv Lowry, David A. EbertAbstract:The broadnose sevengill shark, Notorynchus cepedianus, a common coastal species in the eastern North Pacific, was sampled during routine capture and tagging operations con-ducted from 2005–2012. One hundred and thirty three biopsy samples were taken during these research operations in Willapa Bay, Washington and in San Francisco Bay, Califor-nia. Genotypic data from seven polymorphic microsatellites (derived from the related sixgill shark, Hexanchus griseus) were used to describe N. cepedianus genetic diversity, popula-tion structure and relatedness. Diversity within N. cepedianus was found to be low to moder-ate with an average observed heterozygosity of 0.41, expected heterozygosity of 0.53, and an average of 5.1 alleles per microsatellite locus. There was no evidence of a recent popula-tion bottleneck based on genetic data. Analyses of genetic differences between the two sampled estuaries suggest two distinct populations with some genetic mixing of sharks sampled during 2005–2006. Relatedness within sampled populations was high, with per-cent relatedness among sharks caught in the same area indicating 42.30 % first-order rela-tive relationships (full or half siblings). Estuary-specific familial relationships suggest that management of N. cepedianus on the U.S. West Coast should incorporate stock-specific management goals to conserve this ecologically important predator
-
feeding behavior of subadult sixgill sharks Hexanchus griseus at a bait station
PLOS ONE, 2016Co-Authors: Bryan Mcneil, Shawn D. Larson, Dayv Lowry, Denise GriffingAbstract:This is the first in-situ study of feeding behaviors exhibited by bluntnose sixgill sharks. Bait was placed beneath the Seattle Aquarium pier situated on the waterfront in Elliott Bay, Puget Sound, Washington at 20m of water depth. Cameras and lights were placed around the bait box to record sixgill shark presence and behavior while feeding. Analysis of feeding behavior revealed that sixgills utilize a bite comparable to many other elasmobranchs and aquatic vertebrates, have the ability to protrude their upper jaw, change their feeding behavior based on the situation, and employ sawing and lateral tearing during manipulation. The versatility of their feeding mechanism and the ability of sixgills to change their capture and food manipulation behaviors may have contributed to the species’ worldwide distribution and evolutionary success.
-
Preliminary Observations of Population Genetics and Relatedness of the Broadnose Sevengill Shark, Notorynchus cepedianus, in Two Northeast Pacific Estuaries.
PloS one, 2015Co-Authors: Shawn D. Larson, Debbie Farrer, Dayv Lowry, David A. EbertAbstract:The broadnose sevengill shark, Notorynchus cepedianus, a common coastal species in the eastern North Pacific, was sampled during routine capture and tagging operations conducted from 2005–2012. One hundred and thirty three biopsy samples were taken during these research operations in Willapa Bay, Washington and in San Francisco Bay, California. Genotypic data from seven polymorphic microsatellites (derived from the related sixgill shark, Hexanchus griseus) were used to describe N. cepedianus genetic diversity, population structure and relatedness. Diversity within N. cepedianus was found to be low to moderate with an average observed heterozygosity of 0.41, expected heterozygosity of 0.53, and an average of 5.1 alleles per microsatellite locus. There was no evidence of a recent population bottleneck based on genetic data. Analyses of genetic differences between the two sampled estuaries suggest two distinct populations with some genetic mixing of sharks sampled during 2005–2006. Relatedness within sampled populations was high, with percent relatedness among sharks caught in the same area indicating 42.30% first-order relative relationships (full or half siblings). Estuary-specific familial relationships suggest that management of N. cepedianus on the U.S. West Coast should incorporate stock-specific management goals to conserve this ecologically important predator.
-
Relatedness and polyandry of sixgill sharks, Hexanchus griseus, in an urban estuary
Conservation Genetics, 2011Co-Authors: Shawn Larson, Dayv Lowry, Jeff Christiansen, Denise Griffing, Jimiane Ashe, Kelly AndrewsAbstract:The bluntnose sixgill shark ( Hexanchus griseus ) is a widely distributed species found in tropical and temperate waters of every ocean, yet we know relatively little about their basic biology including their life history and population structure. From 2003–2007, we collected over 300 biopsy samples from sixgills during research operations in Puget Sound, WA, USA. Genotypic data using ten polymorphic microsatellites were used to describe sixgill genetic diversity, relatedness and mating pattern. Diversity within sixgills was found to be moderate with an average observed heterozygosity of 0.45, an average expected heterozygosity of 0.61, an average of 12 alleles per locus, and an average allelic richness of eight within microsatellite loci. Our data suggests all of the sampled individuals come from one intermixing population, and we found no historical evidence of significant population bottlenecks. Many of the sharks were sampled using longline techniques with several sharks captured at the same time and place. Similarly, multiple sharks were sampled on several occasions during research events at the Seattle Aquarium. The proportion of individuals that were full- or half-siblings was high among sharks sampled at the same time and place (range 0.65–0.87). Analysis of the genetic relationship between one large female washed ashore and 71 of her near-term pups suggested a polyandrous mating system with as many as nine males contributing to her offspring. This study is the first to investigate genetic diversity, relatedness and paternity within sixgill sharks and sheds light on important conservation implications for this little known shark population.
Shawn D. Larson - One of the best experts on this subject based on the ideXlab platform.
-
decrease in sightings of sixgill sharks Hexanchus griseus in elliott bay seattle wa united states a comparison between 2003 2005 and 2008 2015
Frontiers in Marine Science, 2019Co-Authors: Denise Griffing, Jeff Christiansen, Joel Hollander, Tim E Carpenter, Shawn D. LarsonAbstract:The Bluntnose Sixgill Shark, Hexanchus griseus, is a large predatory shark, has a worldwide distribution and is listed as near-threatened by the International Union of Conservation of Nature (IUCN). The Seattle Aquarium collected observations of free-swimming Sixgill Sharks in Elliott Bay, Washington, under the aquarium’s pier in 20 m of water from 2003 to 2005 and again from 2008 to 2015 using the same methodology. Compared to total Sixgill sightings between 2003-2005 (273) fewer total Sixgills were sighted at the aquarium’s research station between 2008-2015 (33). The reason for the observed decline in sightings in unknown but based on data from other studies on Sixgills in Puget Sound during the same timeperiod the authors hypothesize the decrease may be due to natural variability of juvenile Sixgill recruitment to Elliott Bay.
-
feeding behavior of subadult sixgill sharks Hexanchus griseus at a bait station
PLOS ONE, 2016Co-Authors: Bryan Mcneil, Shawn D. Larson, Dayv Lowry, Denise GriffingAbstract:This is the first in-situ study of feeding behaviors exhibited by bluntnose sixgill sharks. Bait was placed beneath the Seattle Aquarium pier situated on the waterfront in Elliott Bay, Puget Sound, Washington at 20m of water depth. Cameras and lights were placed around the bait box to record sixgill shark presence and behavior while feeding. Analysis of feeding behavior revealed that sixgills utilize a bite comparable to many other elasmobranchs and aquatic vertebrates, have the ability to protrude their upper jaw, change their feeding behavior based on the situation, and employ sawing and lateral tearing during manipulation. The versatility of their feeding mechanism and the ability of sixgills to change their capture and food manipulation behaviors may have contributed to the species’ worldwide distribution and evolutionary success.
-
Preliminary Observations of Population Genetics and Relatedness of the Broadnose Sevengill Shark, Notorynchus cepedianus, in Two Northeast Pacific Estuaries.
PloS one, 2015Co-Authors: Shawn D. Larson, Debbie Farrer, Dayv Lowry, David A. EbertAbstract:The broadnose sevengill shark, Notorynchus cepedianus, a common coastal species in the eastern North Pacific, was sampled during routine capture and tagging operations conducted from 2005–2012. One hundred and thirty three biopsy samples were taken during these research operations in Willapa Bay, Washington and in San Francisco Bay, California. Genotypic data from seven polymorphic microsatellites (derived from the related sixgill shark, Hexanchus griseus) were used to describe N. cepedianus genetic diversity, population structure and relatedness. Diversity within N. cepedianus was found to be low to moderate with an average observed heterozygosity of 0.41, expected heterozygosity of 0.53, and an average of 5.1 alleles per microsatellite locus. There was no evidence of a recent population bottleneck based on genetic data. Analyses of genetic differences between the two sampled estuaries suggest two distinct populations with some genetic mixing of sharks sampled during 2005–2006. Relatedness within sampled populations was high, with percent relatedness among sharks caught in the same area indicating 42.30% first-order relative relationships (full or half siblings). Estuary-specific familial relationships suggest that management of N. cepedianus on the U.S. West Coast should incorporate stock-specific management goals to conserve this ecologically important predator.
-
observations on abundance of bluntnose sixgill sharks Hexanchus griseus in an urban waterway in puget sound 2003 2005
PLOS ONE, 2014Co-Authors: Denise Griffing, Shawn D. Larson, Jeff Christiansen, Joel Hollander, Tim E Carpenter, Charles R DossAbstract:The bluntnose sixgill shark, Hexanchus griseus, is a widely distributed but poorly understood large, apex predator. Anecdotal reports of diver-shark encounters in the late 1990’s and early 2000’s in the Pacific Northwest stimulated interest in the normally deep-dwelling shark and its presence in the shallow waters of Puget Sound. Analysis of underwater video documenting sharks at the Seattle Aquarium’s sixgill research site in Elliott Bay and mark-resight techniques were used to answer research questions about abundance and seasonality. Seasonal changes in relative abundance in Puget Sound from 2003–2005 are reported here. At the Seattle Aquarium study site, 45 sixgills were tagged with modified Floy visual marker tags, along with an estimated 197 observations of untagged sharks plus 31 returning tagged sharks, for a total of 273 sixgill observations recorded. A mark-resight statistical model based on analysis of underwater video estimated a range of abundance from a high of 98 sharks seen in July of 2004 to a low of 32 sharks seen in March of 2004. Both analyses found sixgills significantly more abundant in the summer months at the Seattle Aquarium’s research station.
Otero, Rodrigo A. - One of the best experts on this subject based on the ideXlab platform.
-
Neoselachians and Chimaeriformes (Chondrichthyes) from the latest CretaceousePaleogene of Sierra Baguales, southernmost Chile. Chronostratigraphic, paleobiogeographic and paleoenvironmental implications
Elsevier, 2013Co-Authors: Le Roux Jacobus, Hervé Allamand Francisco, Oyarzún, José Luis, Soto Acuña Sergio, Yury Yáñez, Roberto E., Gutierrez, Nestor M., Torres Teresa, Otero, Rodrigo A.Abstract:Artículo de publicación ISIThis paper discusses a well-represented fossil record of cartilaginous fishes (Chondrichthyes) from southern South America. The recovered samples allow the recognition of three assemblages with chronostratigraphic and paleogeographic value: i) typical Maastrichtian sharks and rays with affinities to eastern Pacific fauna, including the taxa Ischyrhiza chilensis, Serratolamna serrata, Centrophoroides sp. associated to Carcharias sp., and Dasyatidae indet.; ii) a scarce reworked assemblage of PaleoceneeEarly Eocene age including the taxa Otodus obliquus and Megascyliorhinus cooperi; iii) a rich assemblage with reworked taxa of Early to Middle Eocene age, together with autochthonous deposited Middle to Late Eocene taxa with close affinities to paleoichthyofaunas recovered from the North Atlantic, represented by Carcharias ‘hopei’, Odontaspis winkleri, Carcharoides catticus, Macrorhizodus praecursor, Carcharocles auriculatus, Striatolamia sp., Striatolamia macrota, Hexanchus agassizi, Notorhynchus sp., Myliobatis sp., Abdounia sp., Pristiophorus sp., Squatina sp., cf. Rhizoprionodon sp., Ischyodus sp., and one new species, Jaekelotodus bagualensis sp. nov. The studied samples include for the first time taxa with well established chronostratigraphic resolutions as well as taphonomic information that help clarifying the age of the fossil-bearing units. In addition, they provide relevant information about the evolution of the Magallanes (¼Austral) Basin from the Upper Cretaceous to the Paleogene, suggesting a probable connection with the Quiriquina Basin of south-central Chile during the latest Cretaceous. Finally, the studied assemblages indicate a latitudinal pattern of distribution that provides valuable data on the environmental evolution and temperature of southern South America during the Paleogene
-
Una edad eocena tardía propuesta para la Formación Loreto (península de Brunswick, extremo sur de Chile), basada en peces cartilaginosos fósiles, paleobotánica y evidencia radiógena
Servicio Nacional de Geología y Minería (SERNAGEOMIN), 2012Co-Authors: Otero, Rodrigo A., Yury Yáñez, Roberto E., Torres Teresa, Le Roux, Jacobus P., Hervé Francisco, Fanning C. Mark, Rubilar-rogers DavidAbstract:Indexación: Web of Science; ScieloABSTRACT. We present new data on the paleoichthyology, paleobotany and radiometric results of the Loreto Formation in the Brunswick Peninsula of southernmost Chile, that allow us to propose a Late Eocene age. The rich diversity of fossil cartilaginous fishes (Chondrichthyes, Elasmobranchii) recognized in upper levels of this unit includes the taxa Carcharías aff. 'hopef (Agassiz), Odontaspis sp., Carcharoides catticus (Philippi), Striatolamia macrota (Agassiz), Anomotodon sp., Macrorhizoduspraecursor (Leriche), Galeorhinus sp., Abdounia sp., Hexanchus sp., Squatina sp., Hexanchidae indet.,Myliobatis sp., Myliobatoidea indet., and Ischyodus dolloi Leriche. This assemblage has clear ecological affinities with Eocene Tethyan fauna previously described in the Northern Hemisphere, and also has common elements with Eocene cartilaginous fishes from Antarctica. Additionally, a paleobotanic study of this unit identified leaf imprints ofAsplenium sp., Pteris sp., Podocarpus sp., and abundant angiosperms including Nothofagus lanceolata Dusén, N. simplicidens Dusén, N. variabilis Dusén, N. cf. alessandri Espinosa, N. subferruginea (Dusén), Hydrangea sp. and Phyllites spp. Wood remains of Nothofagoxylon scalariforme Gothan and Araucariaceae cf. Araucarioxylon Kraus were also identified. Additionally, pollen grains indicate gymnosperms and angiosperms: Podocarpidites otagoensis Couper, Retitricolpites sp., Tricolpites sp., Liliacidites sp., Polyporina sp., Nothofagidites cincta Cookson, and Nothofagidites cranwellae Couper, having affinities with Eocene florae, and being consistent with the age of the fossil fishes. Finally, a SHRIMP U-Th-Pb analysis of two samples collected from the studied beds provided thirty-eight and sixty zircon grains, indicating a clear main peak at 36.48±0.47 Ma (MSWD=1.5) and 36,73±0.50 Ma (MSWD=0.65). The integrated results indicate that the upper part of the Loreto Formation has a minimum Priabonian age, supporting previous reassignations of this part of the formation into the Late Eocene, and differing from the Oligocene age proposed in its original definition.RESUMEN. El presente estudio integra nueva evidencia paleoictiológica, paleobotánica y resultados radiométricos que en conjunto permiten proponer una edad eocena tardía para la Formación Loreto, en la península de Brunswick del extremo sur de Chile. La rica diversidad de peces cartilaginosos fósiles (Chondrichthyes, Elasmobranchii) reconocida en niveles superiores de la mencionada unidad incluye los taxa Carcharias aff. hopei (Agassiz), Odontaspis sp., Carcharoides catticus (Philippi), Striatolamia macrota (Agassiz), Anomotodon sp., Macrorhizoduspraecursor (Leriche), Galeorhinus sp., Abdounia sp., Hexanchus sp., Squatina sp., Hexanchidae indet., Myliobatis sp., Myliobatoidea indet., e Ischyodus dolloi Leriche. Este conjunto muestra claras afinidades ecológicas con ictiofaunas del Eoceno tethyano previamente descritas en el Hemisferio Norte, a la vez que presenta elementos comunes con peces cartilaginosos del Eoceno de Antártica. Adicionalmente, el estudio paleobotánico en esta unidad identificó improntas referidas a Asplenium sp., Pteris sp. Podocarpus sp., y abundantes angiospermas, incluyendo Nothofagus lanceolata Dusén, N. simplicidens Dusén, N. variabilis Dusén, N. cf. alessandri Espinosa, N. subferruginea (Dusén), Hydrangea sp. y Phyllites spp. Además, se identificaron restos de troncos fósiles de Nothofagoxylon scalariforme Gothan y Araucariaceae cf. Araucarioxylon Kraus. Adicionalmente, se reconoció polen de las gimnospermas y angiospermas: Podocarpidites otagoensis Couper, Retitricolpites sp., Tricolpites sp., Liliacidites sp., Polyporina sp., Nothofagidites cincta Cookson y Nothofagidites cranwellae Couper, las que presentan afinidades con floras de edad eocena, siendo consistente con la edad de los peces fósiles. Finalmente, el análisis SHRIMP U-Th-Pb de dos muestras colectadas desde los estratos estudiados, han proporcionado 38 y 60 granos de circón respectivamente, indicando claros peaks principales en 36,48±0,47 Ma (MSWD=1,5) y 36,73±0,50 Ma (MSWD=0,65). Los resultados integrados indican que los estratos superiores de la Formación Loreto pueden ser acotados a una mínima edad priabo-niana, siendo consistente con reasignaciones previas al Eoceno Tardío para esta parte de la formación, y difiriendo de la edad oligocena originalmente propuesta en su definición.http://ref.scielo.org/x2rn6
-
A Late Eocene age proposal for the Loreto Formation (Brunswick Peninsula, southernmost Chile), based on fossil cartilaginous fishes, paleobotany and radiometric evidence
Andean geology, 2012Co-Authors: Otero, Rodrigo A., Le Roux, Jacobus P., Fanning C. Mark, Yury Yáñez, Roberto E.Abstract:We present new data on the paleoichthyology, paleobotany and radiometric results of the Loreto Formation in the Brunswick Peninsula of southernmost Chile, that allow us to propose a Late Eocene age. The rich diversity of fossil cartilaginous fishes (Chondrichthyes, Elasmobranchii) recognized in upper levels of this unit includes the taxa Carcharías aff. 'hopef (Agassiz), Odontaspis sp., Carcharoides catticus (Philippi), Striatolamia macrota (Agassiz), Anomotodon sp., Macrorhizoduspraecursor (Leriche), Galeorhinus sp., Abdounia sp., Hexanchus sp., Squatina sp., Hexanchidae indet.,Myliobatis sp., Myliobatoidea indet., and Ischyodus dolloi Leriche. This assemblage has clear ecological affinities with Eocene Tethyan fauna previously described in the Northern Hemisphere, and also has common elements with Eocene cartilaginous fishes from Antarctica. Additionally, a paleobotanic study of this unit identified leaf imprints ofAsplenium sp., Pteris sp., Podocarpus sp., and abundant angiosperms including Nothofagus lanceolata Dusén, N. simplicidens Dusén, N. variabilis Dusén, N. cf. alessandri Espinosa, N. subferruginea (Dusén), Hydrangea sp. and Phyllites spp. Wood remains of Nothofagoxylon scalariforme Gothan and Araucariaceae cf. Araucarioxylon Kraus were also identified. Additionally, pollen grains indicate gymnosperms and angiosperms: Podocarpidites otagoensis Couper, Retitricolpites sp., Tricolpites sp., Liliacidites sp., Polyporina sp., Nothofagidites cincta Cookson, and Nothofagidites cranwellae Couper, having affinities with Eocene florae, and being consistent with the age of the fossil fishes. Finally, a SHRIMP U-Th-Pb analysis of two samples collected from the studied beds provided thirty-eight and sixty zircon grains, indicating a clear main peak at 36.48±0.47 Ma (MSWD=1.5) and 36,73±0.50 Ma (MSWD=0.65). The integrated results indicate that the upper part of the Loreto Formation has a minimum Priabonian age, supporting previous reassignations of this part of the formation into the Late Eocene, and differing from the Oligocene age proposed in its original definition