A Pliocene\u2013Pleistocene continental biota from Venezuela

Jorge D Carrillo-Briceño,Carlos Jaramillo,Edwin-Alberto Cadena,Torsten M Scheyer,José L O Birindelli,Martin Chavez-Hoffmeister,Juan D Carrillo,Mónica R Carvalho,Alfredo A Carlini,Felipe Vallejo,Damián Ruiz-Ramoni,Rodolfo Sánchez,Aldo F Rincón,Massimo Delfino,Marcelo R Sánchez-Villagra,Leonardo Kerber,Douglas S Jones,Raúl Trejos-Tamayo,Georgios L Georgalis

doi:10.1186/s13358-020-00216-6

Abstract

The Pliocene–Pleistocene transition in the Neotropics is poorly understood despite the major climatic changes that occurred at the onset of the Quaternary. The San Gregorio Formation, the younger unit of the Urumaco Sequence, preserves a fauna that documents this critical transition. We report stingrays, freshwater bony fishes, amphibians, crocodiles, lizards, snakes, aquatic and terrestrial turtles, and mammals. A total of 49 taxa are reported from the Vergel Member (late Pliocene) and nine taxa from the Cocuiza Member (Early Pleistocene), with 28 and 18 taxa reported for the first time in the Urumaco sequence and Venezuela, respectively. Our findings include the first fossil record of the freshwater fishes Megaleporinus, Schizodon, Amblydoras, Scorpiodoras, and the pipesnake Anilius scytale, all from Pliocene strata. The late Pliocene and Early Pleistocene ages proposed here for the Vergel and Cocuiza members, respectively, are supported by their stratigraphic position, palynology, nannoplankton, and 86Sr/88Sr dating. Mammals from the Vergel Member are associated with the first major pulse of the Great American Biotic Interchange. In contrast to the dry conditions prevailing today, the San Gregorio Formation documents mixed open grassland/forest areas surrounding permanent freshwater systems, following the isolation of the northern South American basin from western Amazonia. These findings support the hypothesis that range contraction of many taxa to their current distribution in northern South America occurred rapidly during at least the last 1.5 million years.

Highlights

During the Miocene, the coastal marine areas of northern South America arid regions of northern Colombia and northwestern Venezuela today were influenced by a complex hydrographic system that flowed mostly from western Amazonia into the Proto-Caribbean Sea (Díaz de Gamero 1996; Hoorn et al 2010; Aguilera et al 2013)
By the late Miocene to early Pliocene, extreme environmental changes took place in the region (Jaramillo et al 2010; SánchezVillagra et al 2010; Scheyer et al 2013). These changes were linked to major hydrographic processes that occurred as a consequence of the northern Andes uplift (Mora et al 2010; Albert et al 2018), which may have led to the separation between the northern peripheral drainages of western Amazonia, creating habitat partitioning that drove vicariance in many groups including fishes, crocodylians, turtles, and aquatic snake communities (Lundberg et al 1998, 2010; Schargel et al 2007; Sánchez-Villagra et al 2010; Scheyer et al 2013; Cadena et al 2020)
Two samples that seemed pristine and did not show evidences of probable alteration yielded Early Pleistocene ages when compared to the global seawater 87Sr/86Sr curve for the Neogene (McArthur et al 2001)

Summary

Introduction

During the Miocene, the coastal marine areas of northern South America arid regions of northern Colombia and northwestern Venezuela today were influenced by a complex hydrographic system that flowed mostly from western Amazonia into the Proto-Caribbean Sea (Díaz de Gamero 1996; Hoorn et al 2010; Aguilera et al 2013).Editorial handling: Daniel MartySome of the best-known terrestrial and aquatic vertebrate faunas that document the changing biodiversity during that time are preserved in the middle–late Miocene Socorro and Urumaco formations, in northwestern Venezuela (e.g., Sánchez-Villagra et al 2010). By the late Miocene to early Pliocene, extreme environmental changes took place in the region (Jaramillo et al 2010; SánchezVillagra et al 2010; Scheyer et al 2013) These changes were linked to major hydrographic processes that occurred as a consequence of the northern Andes uplift (Mora et al 2010; Albert et al 2018), which may have led to the separation between the northern peripheral drainages of western Amazonia, creating habitat partitioning that drove vicariance in many groups including fishes, crocodylians, turtles, and aquatic snake communities (Lundberg et al 1998, 2010; Schargel et al 2007; Sánchez-Villagra et al 2010; Scheyer et al 2013; Cadena et al 2020). The continental facies of the Codore Formation (El Jebe and Algodones members) were deposited in floodplain environments (exposed during long periods to subaerial conditions) (Quiroz and Jaramillo 2010)

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Discussion

Conclusion