Jaime Andres Villafaña Navea

Conclusions
Most of the studies of the fossil record of chondrichthyans from the eastern Pacific of South America are focused on fossiliferous localities ranging from the middle Miocene to Pliocene (Carrillo-Briceño et al., 2018; Villafaña and Rivadeneira, 2018, and references therein). Therefore, the faunal composition and distribution of this group from older time intervals (i.e., late Oligocene-early Miocene) of the eastern Pacific of South America is poorly known and understood. In order to cover this lack of information, Jaime collaborated in a publication about the Oligocene-early Miocene fossil record of chondrichthyans from Ecuador. Of the total described taxa (2 orders, 1 family, 8 genera, and 16 species), 19 represent new records for Ecuador, 10 new records for the Central Eastern Pacific and four new records for South America. Two paleobathymetric analyses were performed using the described taxa to estimate the most probable depositional environment, which was determined as outer neritic.
In another publication, Jaime reviewed and described the fossil record of early Miocene chondrichthyans from Chile. In this study I was able to describe 8 new records (1 superfamily, 1 family, 2 genera, and 4 species) from the early Miocene of Chile, including a new extinct species of sawshark Pristiophorus homboldti. All the previous and new findings described in this publication indicate that: 1) the faunal composition of early Miocene chondrichthyans from Chile was different in comparison to the rest of the Neogene and also to that reported from other localities along the eastern Pacific, and 2) the fauna from the early Miocene of Chile experienced significant biogeographic changes from the past to the recent.
As was stated above, the fossil record of chondrichthyans from the middle Miocene to Pliocene of the eastern Pacific of South America was widely described in previous publications, however, some groups were less studied than others. For sharks, the genus Heterodontus forms part of this group, being only reported from some localities along the Chilean and Peruvian coasts (Muizon and DeVries, 1985; Carrillo-Briceño et al., 2013). Jaime collaborated as a second author in a publication that described in detail for the first time the tooth morphology of this heterodontid genus from the eastern Pacific of South America. The morphological characteristics of both lateral anterior teeth described in this study agree with those of the Francisci-type (Reif, 1976).
Conversely to Heterodontus, the great white shark (GWS) is the second most abundant species in the temperate Pacific of South America (Villafaña and Rivadeneira, 2018). He analysed the fossil record of the GWS from three Pliocene localities (Caldera, Coquimbo and Pisco) based on the main criteria to define paleo-nursery areas (high frequency of juveniles, food availability, and shallow-water depths). According to the size and life stages established for extant specimens (Fergusson, 1996; Boldrocchi et al., 2017), the specimens from Caldera (Chile) and Pisco (Peru) mostly represent subadults (≥300 to 360 cm for males and ≥300 to 450 for females), whereas juveniles (175 cm to 300 cm) dominate in Coquimbo (Chile). Therefore, the results of this publication suggest that Coquimbo is the first nursery area of the GWS in the fossil record.
In addition to the new species Pristiophorus humboldti, another sawshark genus was recently described from the middle Miocene-early Pliocene of Chile by Jaime. In this study, he collaborated in the first description of the genus Pliotrema, which only was mentioned in previous studies but not studied in detail (Case, 1973; Welton, 1974). The specimen described in this publication represents a well-preserved rostral spine, which shares the morphological characters for its assignment to the genus Pliotrema. However, the diagnostic features used to identify it on generic level (i.e., serrations along the posterior cutting edge) is distinctly different to that observed in any known extinct and extant specimens.
In the case of batoids from the eastern Pacific of South America, Jaime described in detail the fossil remains of the genus Aetomylaeus from one locality in Peru and six localities in Chile. The material described can be unambiguously assigned to genus Aetomylaeus based on the morphological characters observed in extinct and extant specimens within the genus. Also, this study confirms the high variability of tooth row numbers and the morphological variation within tooth rows in the genus Aetomylaeus (Hovestadt and Hovestadt-Euler, 2013).
Although the eastern Pacific of South America hosts the richest fossiliferous localities in South America with marine vertebrate remains (including sharks), records of bony fishes are poorly known (e.g., Long, 1993; Walsh, 2001). For this, he collaborated in a study, which will increase the knowledge of the bony fish fossil record along the eastern Pacific of South America. In this study, the team described 27 fossil remains, including dentaries, neurocrania, pharyngeal tooth plates, opercular bones and rostra. The fauna includes the first records from Chile (Sardinops cf. sagax), the eastern Pacific of South America (e.g., Labrodon sp.), South America (Sarda sp.), the Southern Hemisphere (e.g., Semicossyphus sp.) and the Neogene period (Gymnosarda sp.). All this assemblage contributes to understand the past diversity of fishes in Chile and its relation with other localities along the temperate Pacific of South America. In addition to allowing us to infer the depositional paleoenvironments of this geological formation based on a paleobathymetric analysis.
In this project, Jaime also considered Europe as a study region of the chondrichthyan fossil record. He described an elasmobranch assemblage from the lower Miocene Upper Marine Molasse of the Simsee area in Southern Germany. The 37 elasmobranch taxa reported include 26 sharks and 11 batoids. The biogeographic analysis of the Simsee fauna from the past to the recent show different biogeographic dynamics. These changes could have been influenced by the intense tectonic, climatic and oceanographic events that occurred during the early Miocene of Europe (Rögl, 1999). The results of this study confirm the similarity of closely adjacent localities in Europe due to the connection through seaway passages.
In a final study, he analysed the biogeographic dynamics of the studied associations, which are complex with 27% of the genera from the Neogene of Europe being now globally extinct whereas the proportion of regionally extinct genera varied (40-56%) depending on the analysed region. The result of the diversity trajectories also shows marked differences between regions. In general, the peaks in diversity (i.e., high number of occurrences, genera and origination rates) are mainly associated to warm climatic events and the opening of sea passages between the regions during the early and middle Miocene (Nebelsick, 1992; Rögl, 1999). In the case of the extinction rates, the peaks also coincide with regional and global climatic (i.e., cooling episodes) and oceanographic events (Gürs, 2001; Westerhold et al., 2020). (For references see Jaime’s publications and PhD thesis.)