Abstract
The occurrence and diversity of elasmobranchs from the Oligocene–Miocene boundary from Tropical America is poorly known in comparison with the paleodiversity from younger Neogene intervals of the region. Here we describe a new elasmobranch assemblage from the rich fossil site of Montañita-Olón (Dos Bocas Formation, Santa Elena, Ecuador), where other vertebrates have already been described: for example, sea turtles and cetaceans. We report a total of 27 elasmobranch taxa, 19 of which are new fossil records for Ecuador, 10 new records for the Central Eastern Pacific and four new records for South America. Additionally, in order to reconstruct the environment where these marine remains were deposited, we performed abundance, paleobathymetric and habitat preference analyses, concluding that they were likely deposited in an outer neritic (open shelf) environment. The study of Oligocene and early Miocene marine elasmobranchs faunas in Tropical America is key to addressing the issues in the evolutionary history of this group.
Highlights
The Oligocene–Miocene transition (OMT) was an important period for the evolutionary history of the marine biota in the northern margins of South America, especially due to the significant changes that affected marine biota in the Pacific and proto-Caribbean region (Johnson, Sánchez-Villagra & Aguilera, 2009)
We present a revision of a new elasmobranch assemblage from the Oligocene–Miocene boundary (Dos Bocas Formation) of the Santa Elena Province, Ecuador, on the margin of the Eastern Central Pacific (ECP) (Fig. 1)
P. barnesi are reported for the first time in the fossil record of the ECP
Summary
The Oligocene–Miocene transition (OMT) was an important period for the evolutionary history of the marine biota in the northern margins of South America, especially due to the significant changes that affected marine biota in the Pacific and proto-Caribbean region (Johnson, Sánchez-Villagra & Aguilera, 2009). The study of Oligocene and early Miocene marine elasmobranch faunas is a proxy that allows us to address issues in evolutionary history in Tropical America, offering new light on factors that drove changes in biogeographic patterns of elasmobranchs before the closure of the CAS (Carrillo-Briceño et al, 2018) This oceanographic event resulted in a barrier that isolated the marine biota in both oceanic regions (ECP and WCA) (Lessios, 2008; Coates & Stallard, 2013; Leigh, O’Dea & Vermeij, 2014). The new elasmobranch assemblage, among other marine vertebrates found in the Dos Bocas Formation, including sea turtles (Cadena, Abella & Gregori, 2018), a new genus dolphin (Tanaka et al, 2017), and actinopterygian remains, increases the fossil record of the region and represents a critical window into marine tropical vertebrate faunas in the ECP during the OMT
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