Revista geológica de América central

Erratum and addendum to the paper "Boid snake fossils from the Neogene of Southern Costa Rica", Revista Geológica de América Central, 2025, 72, 1-11

Spencer G. Lucas — 2025-06-03

The specimen recorded as CFM 2032 should be corrected to CFM 3032, in accordance with the internal database of the Geology Section of the Department of Natural History at the National Museum of Costa Rica. The fossil was collected in January 2007 by A. L. Valerio and C. Laurito and was preliminarily identified by A. Rincón as a vertebra belonging to the species Boa constrictor. Since then, it has remained stored under that designation in the collection of the National Museum of Costa Rica, until its review and formal publication in the present study.

Fluvial transformations in the lower Reventazón-Parismina basin, Costa Rica

Fabio Piedra Aguilar — 2025-01-27

An analysis using aerial photographs and satellite images was conducted on the courses of the Parismina and Reventazón rivers, near their confluence at Dos Bocas. Since 1973, the opening of a branch of the Parismina River, known as Quebrada Seca, has been observed, followed in later years by an increase in water infiltration through the Negritos and Sardinas channels. Currently, the waters of the Parismina River flow northward, creating a new course through its former branch at Quebrada Seca, which has separated its flow from the original confluence with Reventazón River. Its presents outlet into the Caribbean Sea occurs through the old Jalova Lagoon (southern boundary of Tortuguero National Park), approximately 7 km northwest of the town of Barra de Parismina. The Reventazón River, in turn, has shown alterations in its fluvial dynamics since 2016, occupying part of the abandoned course of the Parismina River. The modification of the river courses has occurred in three stages: (1) the Parismina River historically followed its course toward the Reventazón River, possibly until 2010, subsequently flowing into the Caribbean Sea at Barra de Parismina, (2) water infiltration and stagnation developed in the abandoned course of the Parismina River between 2010-2017, and (3) a reversal in flow direction occurred, leading to the Parismina River establishing its new course through Quebrada Seca starting in 2017. This work demonstrates the dynamic and changing nature of fluvial regimes.

Flood risk method for scarce-data catchments and municipalities

Adolfo Quesada-Román — 2025-04-30

Floods pose significant challenges in regions with limited resources and data, requiring simplified methodologies for effective risk assessment. This study presents a flexible framework for analyzing flood hazard, exposure, and vulnerability at the municipal level in data-scarce or developing countries. By integrating diverse data sources and employing statistical validation, the methodology ensures reliable results, even with minimal baseline information. It supports regional planning by facilitating flood risk calculations and extrapolations to watershed scales. While based on experiences in Central America, this approach is applicable globally, offering a systematic tool for flood risk assessments and environmental zoning in resource-constrained settings.

Hydrogeological characterization of the aquifer system located in the communities of Isla Chica and La Trocha, Los Chiles, Alajuela

Rigoberto Vargas — 2025-05-20

This research focuses on the hydrogeological characterization of the aquifer system in the Isla Chica and La Trocha communities. This system corresponds to a transboundary aquifer within the San Juan River basin (Costa Rica-Nicaragua). It is important to note that the groundwater is used by the local residents and migrants who live itinerantly in these areas. In addition, there are very few studies of this nature conducted in the region. This work identifies the presence of two aquifers: the first is a shallow, unconfined aquifer covered by a clay layer, with low transmissivity, consisting of intercalated layers of sand and clay that are captured through hand-dug wells. The second is a deeper, semi-confined aquifer, with an average thickness of 40 m, composed of volcaniclastic sands. This aquifer is exploited through drilled wells. The static level recorded for the drilled wells may reflect an equilibrium level between aquifers, typically ranging from 10 to 30 m deep. The deeper aquifer is overlain by a poorly permeable reddish clay layer with an average thickness of 30 m. The groundwater flow direction is from South to North, toward the San Juan River. Hydrogeochemically, the mixed water is classified as calcium bicarbonate. According to the GOD model, the vulnerability of the shallow aquifer to contamination is low to medium. The potential recharge, calculated using the method proposed by Schosinsky (2006), is estimated to be between 357.82 mm and 491.70 mm per year.

Focal mechanisms of felt earthquakes in Costa Rica during 2024

Lepolt Linkimer — 2025-04-30

This study presents 139 new focal mechanisms calculated in the context of the annual seismicity review of 2024. In total, the National Seismological Network (RSN) located 5378 events, whose combined energy is equivalent to an earthquake of moment magnitude (Mw) 6.6. Only ~3.8 % (204) of the earthquakes were perceived by the population. The focal mechanisms and locations of these events allowed the earthquake source to be grouped into five categories: faulting in the Caribbean and Panama upper plates, interplate seismogenic zone of the Cocos plate, internal deformation of the subducted Cocos plate, faulting in the boundary between the Cocos and Nazca plates, and faulting in the Cocos plate prior to subduction. The shallow (< 35 km) earthquakes in the upper-plates and in the Coco-Nazca boundary occurred mainly on strike-slip faults, while those related to subduction were reverse. The ten most significant earthquakes felt in 2024 reached magnitudes of Mw 5.5-6.2. The maximum intensity was V, observed in very small areas near the epicenters of six earthquakes (Mw 4.9 and 6.2).

Boid snake fossils from the Neogene of Southern Costa Rica

Spencer G. Lucas — 2025-05-06

Three dorsal vertebrae of boid snakes from the Upper Miocene deposits of southern Costa Rica are documented and tentatively assigned to Boa constrictor. These fossils represent the first described snake remains from Costa Rica and their earliest record from Central America north of Panama. Their presence supports the possibility of bidirectional snake dispersal between South and North America during the Late Miocene.

Late Miocene turtles from Southern Costa Rica

Robert E. Weems — 2025-05-19

Recent vertebrate fossil collections in southern Costa Rica have uncovered fragmentary remains of five fossil turtle taxa. These remains were recovered from deltaic sedimentary deposits of the Upper Miocene San Gerardo unit, which unconformably overlies the Early–Middle Miocene Térraba Formation. Most of these remains belong to the highly aquatic living turtle genera Dermatemys and Apalone. Other taxa, which are less frequently found, include Bairdemys and Pseudemys, as well as the extinct terrestrial tortoise Hesperotestudo. Except for the marine-tolerant Bairdemys, all genera exhibit North American affinities, suggesting that this assemblage likely predates the formation of the Central American land bridge and the subsequent biotic interchange with South America.

Taxonomic considerations about the paleo-ichthyofauna of the locality of Alto Guayacán, Uscari Formation, late Miocene-early Pliocene [N17 a N19]: record of the genus Nebrius and associated ichthyolites

César A. Laurito — 2025-05-20

Teeth remains and dermal scales of sharks of the Ginglymostomatidae family from the Uscari Formation are analyzed. The fossil remains were compared with similar elements of extant species included within the genera Nebrius and Ginglymostoma, raising the possibility that the genus Ginglymostoma is paraphyletic.