Central Costa Rica Research Articles

Sistema reproductivo, comportamiento de apareamiento y ecología básica de un caracol tropical extremadamente raro: Drymaeus tripictus (Stylommatophora: Bulimulidae)

Very little is known about the ecology and biology of Drymaeus tripictus, an extremely rare and endemic land snail species from Costa Rican highlands. I studied the ecology and reproductive biology of D. tripictus from April 2009 through June 2010 in an old forest, a young forest and a Cupressus lusitanica plantation in central Costa Rica. Every three months I visited each habitat and collected specimens in 20 random sampling plots (3x3 m2 each). I observed the snail’s activity and microhabitat preference in the field, and in the laboratory I recorded high definition videos of its mating behavior and analyzed reproductive morphology with light microscopy. The snail is more abundant in the old forest (0.017 ind./m(2)) and prefers leaves with little epiphyllous cover (0-25 % cover, chi-square test, p <0.0001). During the dry season the snails become active between 20:00 pm and 8:00 am (chi-square = 22.65, df=3, p < 0.0001); they are inactive mainly during the afternoon (11:00 am to 16:59 pm). I found active individuals mostly on the upper side of leaves, where they feed (Chi-square =6.76, df=1, p = 0.0093). Mating is unilateral, by shell mounting, with cryptic phallus intromission and without role switching or multiple mating. Its reproductive system is morphologically similar to that of Drymaeus costaricensis. Mating behavior is as expected for snails with high-spired shells, except for the lack of role switching. The density of D. tripictus is low even when compared with other endangered bulimulids.

Bahia Aventuras: ecotourism in Central America

Subject area The case includes issues in sustainable enterprises, marketing management, organizational development, organizational behavior, entrepreneurship, organizational leadership and small business management. Study level/applicability The Bahia Aventuras case may be used at both the undergraduate and graduate levels of study within most business school curricula (BSBA, MBA and MS). Potential courses may include building sustainable enterprises, marketing management, organizational development, organizational behavior, entrepreneurship, organizational leadership and small business management. Case overview Bahia Aventuras is an ecotourism company in Costa Rica. A local entrepreneur, Walter Brenes, started the company in 2007 to specialize in marine tours, including whale watching, bird viewing and snorkeling. However, the founder had no business training and confronts both internal and external challenges to achieve sustainable success, both financially and environmentally. Internally, there were few financial control systems in place and as a result Walter's ability to accurately account for revenues and expenses was limited. Bahia Aventuras and Walter also faced external challenges. Construction of a new highway was likely, and that could bring more competition, including hotel chains such as the Marriott and Sheraton. Government regulation cut both ways for the company. He was the classic small businessperson, who needed help in moving to the next stage of development for his small business. Thus, a small ecotourism business was caught in the middle of rapid economic development, a growing national infrastructure and increasing pressures to preserve and protect the coastal ecosystem and rainforest of south central Costa Rica. He was just trying to figure out how to “stay alive” as a business. The case has a tragic ending for the owners. Both Walter and his partner, along with one of their tour guides, died in a car accident. But family, friends and the community has kept Walter's vision alive, and Bahia Aventuras continues to day. Expected learning outcomes Upon completion of the Bahia Aventuras case, each participant will be able to: Describe the economic development and growth prospects of ecotourism within Costa Rica. Evaluate the socio-economic challenges which confront Costa Rica as a developing nation within the Central American region. Describe how Costa Rica's environmental regulations have affected the continued growth and development of ecotourism within the country. Describe the complex set of relationships that may exist between small business owners, their employees, regulatory agencies and the local community. Apply management skills and competencies to analyze and propose feasible solutions to organizational performance problems. Explain how the implementation of sustainable business practices may serve as a catalyst for the creation of shared value for organizational stakeholders as enabled through economic growth, attainment of social equity and preservation of the environment. Supplementary materials Teaching notes are available for educators only. Please contact your library to gain login details or email support@emeraldinsight.com to request teaching notes.

Manipulating tropical fire ants to reduce the coffee berry borer

1. The coffee berry borer Hypothenemus hampei (Coleoptera, Curculionidae) (Ferrari) is the most important pest of coffee production worldwide.2. The hypothesis that the tropical fire ant, Solenopsis geminata Westwood, indirectly protects the coffee berry borer by suppressing other ant species that are the coffee berry borer's primary predators was tested.3. It was found that removing S. geminata from coffee plots significantly increased the disappearance of adult coffee berry borer beetles from coffee berries compared with control plots. An average of 6% of beetles disappeared from plots with S. geminata whereas 23% of beetles disappeared from plots from which S. geminata was removed. This pattern was observed on two shade coffee farms with marked differences in ant species composition, one in the rainforest in central Costa Rica and one in the cloudforest in northwest Costa Rica.4. If the results of this small‐scale study can be replicated on the farm level, then S. geminata suppression may represent a new management technique for the coffee berry borer throughout Central and South America.

Interplate seismicity at the CRISP drilling site: The 2002 Mw 6.4 Osa Earthquake at the southeastern end of the Middle America Trench

AbstractWe investigate potential relations between variations in seafloor relief and age of the incoming plate and interplate seismicity. Westward from Osa Peninsula in Costa Rica, a major change in the character of the incoming Cocos Plate is displayed by abrupt lateral variations in seafloor depth and thermal structure. Here a Mw 6.4 thrust earthquake was followed by three aftershock clusters in June 2002. Initial relocations indicate that the main shock occurred fairly trenchward of most large earthquakes along the Middle America Trench off central Costa Rica. The earthquake sequence occurred while a temporary network of OBH and land stations ∼80 km to the northwest were deployed. By adding readings from permanent local stations, we obtain uncommon P wave coverage of a large subduction zone earthquake. We relocate this catalog using a nonlinear probabilistic approach within both, a 1‐D and a 3‐D P wave velocity models. The main shock occurred ∼25 km from the trench and probably along the plate interface at 5–10 km depth. We analyze teleseismic data to further constrain the rupture process of the main shock. The best depth estimates indicate that most of the seismic energy was radiated at shallow depth below the continental slope, supporting the nucleation of the Osa earthquake at ∼6 km depth. The location and depth coincide with the plate boundary imaged in prestack depth‐migrated reflection lines shot near the nucleation area. Aftershocks propagated downdip to the area of a 1999 Mw 6.9 sequence and partially overlapped it. The results indicate that underthrusting of the young and buoyant Cocos Ridge has created conditions for interplate seismogenesis shallower and closer to the trench axis than elsewhere along the central Costa Rica margin.

Las fallas Purires y Picagres, y su relación con la secuencia sísmica del Puriscal de 1990

New morphotectonic, structural, and seismological interpretations have allowed us to define the neotectonics of the region located between the northwestern border of the Talamanca cordillera and the southern flanks of Aguacate Mounts, along the central-western sector of the Central Costa Rican Deformed Belt. The principal tectonic structures identified in this study are the Purires, Zapote, Jaris, Bajos de Jorco and Picagres faults. They constitute a set of northwest dextral-slip faults, traversing for more than 45 km the previous mountains ranges. Transtensive and transpressive structures were identified along these faults. Another recognized structure is the Junquillo fault, a predominantly east-west sinistral fault that lies between the Purires and Picagres faults.The three stages of the 1990 Puriscal shallow seismic sequence are reviewed in this study and are related with some of the previous faults. The seismic activity began with a seismic swarm that showed a peak of activity between May and June. The swarm showed a migration of activity between the Picagres and Purires faults. A right-lateral surface fault rupture with a length of 400 m, associated with two seismic events occurred on June 8 (00:31 GMT; Md 4.8) and June 9 (00:34 GMT; Md 4.8), breaks a sector of the eastern branch of Charcon transtensive structure of the Picagres fault. The seismic sequence continued with the Barbacoas earthquake of June 30 (Ms 5.1). This earthquake and its aftershocks located until July 11, rupture a 9 km length segment of the Purires fault. Finally, the Piedras Negras earthquake of December 22, 1990 (Ms 5.7) and its aftershocks occurred until December 30, caused a rupture of 11 km length of the Picagres fault.

Integration of Arrival-Time Datasets for Consistent Quality Control: A Case Study of Amphibious Experiments along the Middle America Trench

We have integrated waveform and arrival‐onset data collected in Costa Rica as part of the National Science Foundation (NSF)‐sponsored Costa Rica Seismogenic Zone Experiment (CRSEIZE) and along central Costa Rica and Nicaragua as part of the German SFB 574 program. The five arrays, composed of different sensor types (one‐ and three‐component land and ocean bottom seismometers and hydrophones), were archived using different software packages (Antelope and SEISAN) and were automatically and manually picked using various quality criteria resulting in a disparate set of pick weights. We evaluate pick quality using automated arrival detection and picking algorithm based on the wavelet transform and Akaike information criterion picker. The consistency of the arrival information over various scales provides a basis for assigning a quality to the analyst pick. Approximately 31% of P arrival times and 26% of S times have been classified as high‐quality picks (quality 0–1). An additional 21% of P times and 27% of S arrivals are good quality (quality 2–3). The revised quality picks are mapped directly into new pick weights for inversion studies. We explore the effect of new weighting and removal of poor data by relocating hypocenters through a minimum 1D velocity model and conducting double‐difference local earthquake tomography (LET). Analysis of the hypocenter relocation and seismic velocity tomography results suggest that using the improved quality determinations have a greater effect on improving sharpness in the velocity images than on the magnitude of hypocentral movement. Online Material: Figures of waveforms, event statistics, and tomography; and tables of station and event parameters, station qualities, velocity model, and hypocentral parameters.

The seismogenic zone in the Central Costa Rican Pacific margin: high-quality hypocentres from an amphibious network

Transition from subduction of normal to thickened oceanic crust occurs in the central portion of the Costa Rican margin, where large interplate earthquakes (M * 7) and abundant interseismic seismicity have been associated with subduction of bathymetric highs. We relocated *1,300 earthquakes recorded for 6 months by a combined on- and offshore seismological network using probabilistic earthquake relocation in a 3D P-wave velocity model. Most of the seismicity originated at the seismogenic zone of the plate boundary, appearing as an 18° dipping, planar cluster from 15 to 25–30 km depth, beneath the continental shelf. Several reverse focal mechanisms were resolved within the cluster. The upper limit of this interseismic interplate seismicity seems to be controlled primarily by the overlying-plate thickness and coherency, which in turn is governed by the erosional processes and fluid release and escape at temperatures lower than *100 to 120° C along the plate boundary. The downdip limit of the stick–slip behaviour collocates with relative low temperatures of *150 to 200° C, suggesting that it is controlled by serpentinization of the mantle wedge. The distribution of the interseismic interplate seismicity is locally modified by the presence of subducted seamounts at different depths. Unlike in northern Costa Rica, rupture of large earthquakes in the last two decades seems to coincide with the area defined by the interseismic interplate seismicity.

Role of the Faculty Mentor in an Undergraduate Research Experience

ABSTRACTResearch experience for undergraduate (REU) programs are designed to recruit students to science and engineering research careers by allowing the students to conduct research with faculty mentors. International research experiences can enhance the research experience by allowing the student to conduct research in a unique environment and also provide the student with a more global perspective. This paper describes the outcomes of an international REU program in which students quantify hydrological and biogeochemical fluxes in a tropical montane forest in central Costa Rica. Having the students at a central research station location and focusing their research on a common research problem is an important aspect of an international REU program, to avoid a feeling of isolation and to ensure that the students remain safe in their research and during their free time. However, this shared experience can highlight differences among the faculty mentors and make the students evaluate their individual experience more critically. To better understand the relationship between the REU student and their faculty mentor(s), we conducted pre- and post-trip focus groups to understand the students' experience in the REU and the manner in which the faculty mentor can affect that experience and the desire to continue in research. Results of the pre-trip focus group suggest that the undergraduate students are most concerned about their projects and give little to no thought about the faculty mentor with whom they will be completing their research. Post-trip results from 2011 and 2012 suggest that mentors had a much greater impact on the experience than expected. Many students said that their future research/graduate school plans were affected by their REU mentor relationship, and that while they might not have considered the importance of faculty mentors before the research experience, they now recognize the mentor as a crucial aspect of a research project. Using a classification system commonly used in management research, the mentoring styles were classified with management classification styles as autocratic, democratic, or laissez-faire. The overall results suggest that the student-to-mentor relationship created through these authentic experiences is one of the most important aspects of REU programs, and that the mentoring style not only determines the research productivity of the student, but also appears to influence the decision of that student to conduct research in the future and/or attend graduate school. The mentoring style also affects research productivity and allows students to identify the characteristics they perceive as important to success in a graduate program. While this paper focuses on a single REU program, the results provide baseline data to examine the role of the faculty mentor across other REU programs and in decisions about graduate research by both the student and the faculty. Mentoring styles and student expectations of their mentors should be taken into consideration when developing a research experience and pairing mentors with prospective students.

Combining a typology and a conceptual model of cropping system to explore the diversity of relationships between ecosystem services: The case of erosion control in coffee-based agroforestry systems in Costa Rica

With increasing pressure on farmers to improve the performance of their cropping systems, there is a growing need to design cropping systems that respond concurrently to environmental, agronomic and socioeconomic constraints. However, the trade-offs between ecosystem services, including provisioning services, can vary considerably from plot to plot. Using a typology of agricultural practices to adapt a conceptual model of the cropping system can provide an instrument to support the design of cropping systems that take into account the diversity of environmental and socioeconomic conditions and trade-offs within a study site. This method was tested to design coffee-based agroforestry systems mitigating soil erosion in central Costa Rica, a case study with a high-value crop in a complex relationship to its biophysical environment. A generic plot-scale conceptual model representing the effect of agricultural practices and environmental factors was designed, with erosion reduction, coffee production and gross margin as the outputs. Quantitative data on agricultural practices and costs were then collected over two years on a sample of plots in an 18km2 watershed upstream of a hydroelectric dam. A typology of these plots was built based on agricultural management practices; the resulting groups were further characterized by socioeconomic and environmental variables. The critical variables from each group of plots were used to adapt the conceptual model to the groups from the typology. The four groups found were (1) low-intensity management; (2) intensive management; (3) shaded agroecosystem, and (4) intensive agrochemical management. The conceptual model helped analyze the key processes and trade-offs for each group and helped make recommendations of adapted erosion control practices. The model showed that for some groups, less time-consuming erosion control actions not impacting coffee production might be more suitable, such as drainage canals, terraces, and vegetative barriers. In contrast, other groups had better socioeconomic or environmental conditions that opened the possibility of using shade trees or manual weed control (as opposed to herbicide use) to control erosion.This method finds its application in the plot-scale design and prototyping of agricultural systems that better respond to specific constraints, and can provide more relevant basis for discussion with farmers in participative methods. It also presents the advantage of requiring little data acquisition, although it can be further developed through integrating numerical relationships for quantitative modeling.

Crustal structure across the Costa Rican Volcanic Arc

AbstractIsland arcs are proposed to be essential building blocks for the crustal growth of continents; however, island arcs and continents are fundamentally different in bulk composition: mafic and felsic, respectively. The substrate upon which arcs are built (oceanic crust versus large igneous province) may have a strong influence on crustal genesis. We present results from an across‐arc wide‐angle seismic survey of the Costa Rican volcanic front which test the hypothesis that juvenile continental crust is actively forming at this location. Travel‐time tomography constrains velocities in the upper arc to a depth of ~15 km where average velocities are &lt;6.5 km/s. The upper 5 km of crust is constrained by velocities between 4.0 and 5.5 km/s, which likely represent sediments, volcaniclastics, flows, and small intrusions. Between 5 and 15 km depth, velocities increase slowly from 5.5 to 6.5 km/s. Crustal thickness and lower crustal velocities are roughly constrained by reflections from an inferred crust‐mantle transition zone. Crustal thickness beneath the volcanic front in Costa Rica is ~40 km with best‐fit average lower‐crustal velocities between 6.8 and 7.1 km/s. Overall, velocities across the arc in central Costa Rica are at the high‐velocity extreme of bulk continental crust velocities and are lower than modern island arc velocities, suggesting that continental compositions are created at this location. These data suggest that preexisting thick crust of the Caribbean Large Igneous Province has a measurable effect on bulk composition. This thickened arc crust may be a density filter for mafic material and thereby support differentiation toward continental compositions.

Raíz secundaria embrional asociada a la germinación de Garcinia intermedia (Clusiaceae) y su posible papel en la supervivencia de las plántulas

Germination tests on Garcinia intermedia (Clusiaceae) seeds showed the growth of two types of roots: additionally to the primary root, a secondary root crosses the seed lengthwise. To determine its possible role on the survival and growth of this species, 90 seedlings at least six months old (collected in Central Costa Rica) were planted in plastic bags with organic soil, and placed in a greenhouse. The seedlings were treated as follows: treatments in which the primary or secondary root was cut off, and a control group with both roots intact (30 replicates each). After three months 10 seedlings/month/treatment were extracted to measure their height, basal diameter, root length (main and secondary root), and biomass of the stem, roots and seed (without its coat). Control seedlings had the highest growth, followed by those without secondary roots. Nonetheless, more than 90% of the seedlings whose primary roots were cut off, survived after five months of the excision treatment, in part due to the capacity of this species to regenerate its radical system through the seed reserves, sprouting of a primary-like root, and/or the growth stimulus of the secondary root (60% of the total: 20% with sprouts from the primary root stump, 13.3% with a growth stimulus of the secondary root, and 26.7% with both conditions). The length of the sprouted roots was significantly different only on those plants that were extracted during the first two monthly measurements, when compared with the control (F6 = 18.6, F7 = 16.0, p < 0.01).

Oxynetra: Facies and DNA Barcodes Point to a New Species from Costa Rica (Hesperiidae: Pyrginae: Pyrrhopygini)

Oxynetra stangelandi Grishin & Burns, new species, from high elevations of Area de Conservacion Guanacaste (ACG) in northwestern Costa Rica, is most similar to Oxynetra hopfferi Staudinger, known from mountains of central and southern Costa Rica and western Panama. These hesperiid species differ mainly in body color pattern and in DNA barcodes. We compare their barcodes, nucleotide by nucleotide, together with barcodes of a congener and a species of the related genus Olafia, and use the barcode data to show phylogenetic relationships. We describe the new species, its discovery, its male and female genitalia, and its life history as a cloud forest herbivore of Prunus annularis (Rosaceae). In ACG, no other skippers feed on this plant species, and no other skippers of the tribe Pyrrhopygini feed on plants in the family Rosaceae. Various stages of O. stangelandi belong to mimicry complexes. Although our adults, which are reared from wild-caught caterpillars, are split between the sexes (4 males, 6 females), there are scarcely any females of Oxynetra in the world's museums.

Neotectonic faulting and forearc sliver motion along the Atirro-Rio Sucio fault system, Costa Rica, Central America

The Atirro–Rio Sucio fault system forms a major northwest-trending strike-slip fault zone in east-central Costa Rica. We examined the kinematics and temporal evolution of this fault system through geomorphic, structural, and seismologic analysis. This 150-km-long strike-slip fault zone traverses the northern flank of the paleovolcanic Cordillera de Talamanca and extends northwestward into the active Cordillera Volcanica Central. Historical seismicity includes frequent minor swarms and occasional moderate-magnitude (M 5.0–6.5) damaging earthquakes. Field geomorphic evidence, fault kinematic data, and earthquake focal mechanisms are consistent in showing dextral slip along the mapped traces of northwest-striking faults. Continuity with other transcurrent faults in northwest Costa Rica indicates that the Atirro–Rio Sucio fault system may form the southeastern end of a regional network of northwest-trending dextral faults that accommodate margin-parallel displacement of the Central American forearc sliver. The Atirro–Rio Sucio fault system originates within the Central Costa Rica Deformed Belt inboard of the indenting Cocos Ridge. We infer that ridge collision drives lateral escape of crustal fragments northwestward along an array of dextral Central Costa Rica Deformed Belt faults including the major structures of the Atirro–Rio Sucio fault system. This zone of arc-parallel extrusion thus represents the root of the Central American forearc sliver. Consistent with recent geodynamic models, we propose that northwestward sliver escape along the Atirro–Rio Sucio faults is driven by rigid indentation of the aseismic Cocos Ridge into southern Costa Rica.

Does eco-certification have environmental benefits? Organic coffee in Costa Rica

Eco-certification of coffee, timber and other high-value agricultural commodities is increasingly widespread. In principle, it can improve commodity producers' environmental performance, even in countries where state regulation is weak. But eco-certification will have limited environmental benefits if, as one would expect, it disproportionately selects for producers already meeting certification standards. Rigorous evaluations of the environmental effects of eco-certification in developing countries that control for selection bias are virtually nonexistent. To help fill this gap, we use detailed farm-level data to analyze the environmental impacts of organic coffee certification in central Costa Rica. We use propensity score matching to control for selection bias. We find that organic certification improves coffee growers' environmental performance. It significantly reduces chemical input use and increases adoption of some environmentally friendly management practices.

Andersonian and Coulomb stresses in Central Costa Rica and its fault slip tendency potential: new insights into their associated seismic hazard

Abstract Plate boundary forces acting within the Cocos Plate that is being subducted at a rate of 8.5–9.0 cm a −1 towards N32°E below the Caribbean Plate and the Panama microplate are found responsible for contemporaneous superimposed compressive, wrench and extensive fault patterns in Central Costa Rica. The stress inversion of fault-slip planes and focal mechanisms reveals a prevailing convergence-imposed N20°–45°E almost horizontal compression. Ellipsoid R values [ R =(σ 1 –σ 2 )/(σ 2 –σ 3 )] in the range of 0.3–0.05 and 0.8–0.93 are responsible for the permutation of σ 2 to σ 3 and σ 2 to σ 1 , respectively, and show typical Andersonian configurations with one stress axis vertical or close to it. Coulomb failure stress (CFS) analysis reveals that up to 5 bars (0.5 MPa) of tectonic loading are being imposed on east–west thrusts and on critically oriented conjugate NW- and NE-trending strike-slip faults. Non-optimally oriented structures are potential targets for reactivation even with 2 bars (0.2 MPa) of load. Triggering and interaction with volcanic activity is highly suspected in one documented recent case. When the regional fault population was tested for its slip tendency (τ / σ n ), a good correlation with CFS results was found.

Biogeographically dynamic genetic structure bridging two continents in the monotypic Central American rodentOtotylomys phyllotis

Central America is an ideal region in which to study patterns of historical divergence and population genetic differentiation, because of its extraordinarily dynamic biogeographical, tectonic, and climatic history. The rodent Ototylomys phyllotis is the only extant species of the genus Ototylomys and is distributed within this region from the Isthmus of Tehuantepec, Mexico, to central Costa Rica, offering an excellent opportunity to study spatial and temporal patterns of population structure of the species and to explain the ecological and evolutionary processes responsible for those patterns. We estimated the genetic diversity and structure within and between populations of O. phyllotis, times of divergence, and migration patterns using mitochondrial DNA and a comprehensive combination of phylogenetic and phylogeographical computational analyses. Our results support monophyly of the genus Ototylomys. We identified three major phylogeographical lineages within O. phyllotis that are linked to its diversification and coincide with the main geological features that shaped Middle America. The origin of the genus was before 3.35 Mya, prior to the Great American Biotic Interchange (GABI), and its initial occurrence was near the centre of its current distribution (Honduras/El Salvador), from which it later spread (3.20–2.84 Mya) following a series of GABI pulses. The species showed an initial northward dispersal to the Chiapas and Guatemala highlands (2.27 Mya) followed by diversification. A later dispersal (1.82 Mya) occurred toward both the south (Nicaragua, Costa Rica) and the north (Belize). The Yucatan peninsula was colonized (0.8 Mya) by individuals from Belize. Extremely high radiation and range expansion occurred throughout the entire range, the highest of which was in the Yucatan peninsula (0.125 Mya). © 2012 The Linnean Society of London, Biological Journal of the Linnean Society, 2012, 107, 593–610.

What can phylogeographic breaks in the livebearer Poeciliopsis turrubarensis tell about fish community boundaries in western Costa Rica?

This study asks if the geographic boundary delineating two fish communities in western Costa Rica is congruent with a phylogeographic break in a single widespread fish species Poeciliopsis turrubarensis (Poeciliidae) that spans this area. Such congruence would suggest that a common historical event (e.g. geological or climatic) could be responsible for both patterns. It was found that there was a shared break across a region in central Costa Rica suggesting a common cause may be responsible for both the abrupt shift in fish community composition and the genetic break in P. turrubarensis.

Calizas lutetianas del arco interno Paleógeno de Costa Rica

We present new sedimentologic and biostratigraphic data on the shallow-water limestone sequen-ce of the quebrada Concha, the type locality of the Eocene Parritilla Formation in central Costa Rica. This unitappears at the base of the about 4.500 m thick sedimentary sequence of the Cenozoic Valle Central basin, un-conformably overlying the Nicoya ophiolite complex. The Parritilla limestone contain a rich larger foraminife-ral fauna from the early Middle Eocene (Lutetian) represented by well-preserved and diverse specimens of theAmphistegina-Helicostegina-Lepidocyclina(Polylepidina) phylogenetic line. On the basis of the high biostrati-graphic resolution of the analyzed foraminiferal assemblage, we define the quebrada Concha sequence as a Lu-tetian type locality of Costa Rica and erect a new Eocene chronostratigraphic unit: the Parritillian. From a sedi-mentologic perspective, the Parritilla limestones represent a bioclastic carbonate sequence deposited on the south-ern border of the inner-arc basin in an open shallow-marine environment with locally restricted water circula-tion. In the study area, the uplifted ophiolite complex probably formed part of a neritic arc platform surroundingthe volcanic edifices. Although Lutetian carbonate sedimentation began in response to a rapid marine transgres-sion at ~49 Ma over the exposed basement, the carbonate development itself terminated abruptly with the depo-sition of the volcaniclastic sequence of the Caraigres Formation, resulting from the Eocene volcanic activity inadjoining areas. As suggested by these voluminous volcaniclastic deposits conformably overlying the Parritillalimestone sequence, the strong subsidence of the Lutetian arc platform was probably related to emergent ande-sitic edifices in the inner arc region of central Costa Rica.

Daños, efectos y amenaza de tsunamis en América Central

There have been 49 tsunamis in Central America since 1539 to 2000, 37 were in the Pacific and 12 in the Caribbean. Ten of them have a specific damage report, seven in the Pacific and the rest in the Caribbean. The total number of casualties due to local tsunamis is less than 500 but this number could be higher. Themain earthquake sources related to the reported tsunamis are the Cocos-Caribbean subduction Zone, the Polochic-Motagua-Swan Fault System and the North Panama Deformed Belt.An empirical estimation of tsunami hazard for Central America suggests that areas with higher tsunami poten-tial in the Pacific are the coasts from Nicaragua to Guatemala and Central Costa Rica; on the Caribbean side,Honduras Gulf Zone and the coasts of Panama and Costa Rica have a major hazard. Earthquakes of magnitudelarger than 7 with epicenters offshore or onshore (close to the coastline) could trigger tsunamis that would impact those zones.

Hallazgos de megamamíferos fósiles en Costa Rica

It has been confirmated the existence of at least 25 localities with the rests of fossil megamammals. In Bajo Barrantes (San Ramón) an assocíation of Villafranchian (?) fauna of south american origen was found. It is represented of Toxodon aff. platensis, megatherium and nylodons. It was also verified during quaternary different species of proboscideans like Mammuthu aff. imperator, Cuvernius hyodon and other mammals among them, Equus sp., stroll in this part of Central America. Mammuthus aff. -imperator shows che major geographical distribution known in northern part of the continent. If the finding of bisons in Nicaragua ís taken in consideration ic is concluded that the region between Southern Nicaragua and Central Costa Rica, has the maximum extensior of some species of big mammals; diverse geographycal barriers could have retarded their migratioa. Coexistence with man at the beggining of Holoceno could be an aditional factor helping to extintion. The rest of verrebrates found stratigraphycally between or under ignimbrites, do have few possibilities to be associated rests or numan tools while finalr. in volcanic or Holoceno sediments presenr híg probabilities of coexistence with man.