Eocene Data Record of Yaberinella jamaicensis Vaughan (Foraminifera, Soritidae) from the Nicoya Peninsula, Costa Rica
The dataset contains five data files over three individual records of Yaberinella jamaicensis Vaughan 1928 (Foraminifera, Soritidae) from the Nicoya Peninsula of Costa Rica. They include (1) species record with systematic descriptions of three finds made on the southern peninsula, (2) sampling site map of Yaberinella-bearing limestone samples, (3) table with the larger benthic foraminiferal assemblages, (4) photomicrograph set illustrating the species finds, and (5) proloculus size diagram of two different populations. Yaberinella jamaicensis is a Caribbean miscellaneous species of soritid foraminifera known from Jamaica, Nicaraguan Rise, Nicaragua, Panamá and Costa Rica (Vaughan 1928; Cole 1952; Butterlin 1981; Adams et al. 1986; Robinson 1993; 2004; BouDhager-Fadel 2018). Butterlin (in Adams et al. 1986) reported the first find from Costa Rica. Two further records in two different limestone deposits from the southern coastal area confirm his record, giving new reliable insights into the distribution and biostratigraphical range of this quite particular soritid species. The examined Yaberinella-bearing samples FB 3/7 (IGSN:CCV0012) and FB 6/2 (IGSN:CCV0013) consist of bioclastic larger foraminiferal-calcareous algal packstone and rudstone. In both microfacies the Yaberinella jamaicensis specimens appear as accessory or main foraminiferal species, respectively, within lepidocyclinid and nummulitid dominant assemblages. In biostratigraphical terms, the examined sample material reveals two different successive foraminiferal assemblages: (1) Yaberinella jamaicensis-Lepidocyclina macdonaldi from the Bartonian (sample FB 6/2) and (2) Yaberinella jamaicensis-Lepidocyclina chaperi-Asterocyclina minima from the Priabonian (sample FB 3/7). Butterlin in Adams et al. (1986) has previously reported the Yaberinella jamaicensis-Lepidocyclina macdonaldi assemblage from Costa Rica to belong to the middle Eocene. Later, Robinson (2004) considers the Lepidocyclina-Yaberinella assemblage on Jamaica to be constrained to the Bartonian (NP7-16?). The assemblages in Costa Rica record indeed a wider stratigraphical range of the Lepidocyclina-Yaberinella assemblage comprising both Eocene stages, the Bartonian and Priabonian. The new data from the Nicoya Peninsula show the lepidocyclinid index species allow to accurately date Yaberinella-bearing rocks. They confirm in fact the middle-upper Eocene range of the genus Yaberinella in the American bioprovince. In addition, the biometric data of proloculus size record large variation within the different populations, revealing the proloculus size as a non-reliable criterion for distinguishing between the different species of the genus Yaberinella. This size range is rather likely caused by the species dimorphism, meaning the common occurrence of micro- and megalospheric specimens. These Caribbean species finds from the Nicoya Peninsula prove the species habitat extended to the Pacific side of the Costa Rican island arc.
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The examined material comprises different limestone rock samples from which thin sections were prepared in order to determine their microfacies and larger foraminiferal assemblages. They all were collected during sedimentological field research on Tertiary shallow-marine carbonate deposits from the forearc sedimentary succession unconformably overlying the Mesozoic basaltic basement on the Nicoya Peninsula. Two samples labelled FB 3/7 and FB 6/2 bear abundant specimens, including test and test fragments of the foraminiferal species Yaberinella jamaicensis. Sample FB 3/7 (microfacies MF10 after Calvo 1987) comes from Eocene shallow-marine carbonates of the Punta Cuevas section. In contrast, sample FB 6/2 (microfacies MF 18 after Calvo 1987) comes from Eocene rounded shallow-marine limestone clasts reworked in the lower Miocene Santa Teresa conglomerate (Mora 1985; Calvo 1987). The sample ages were determined on the basis of the accompanying larger foraminiferal assemblages. Their ranges yield a precise stage age for each sample. This procedure was crucial in order to constrain the biostratigraphical range of Yaberinella jamaicensis in two different populations. In order to precise the species determination, biometric data, including proloculus size measures were gathered and plotted in a diagram to compare size variations within the population and with the species topotype and the smaller species variation Yaberinella jamaicensis var. trelawniensis Vaughan as well. In each specimen examined, the proloculus size includes two measurements, comprising the smaller and larger diameter values of the mostly asymmetrical proloculus. The proloculus size data plotted in the diagram could have been influenced by two significant factors: (1) the occurrence of dimorphism within the populations and (2) measurement values from chambers of eventually bilocular specimens. The diagnostic features of the specimens examined are characteristic for the original species of the genus, Yaberinella jamaicensis Vaughan. Several photomicrographs to detail the structure of the endoskeleton with additional descriptions documenting the species were systematically made to help understand our taxonomic approach.