A historical vertebrate collection from the Middle Miocene of the Peruvian Amazon

Abstract

The Miocene aquatic and terrestrial fossil record from western Amazonia constitute a clear evidence of the palaeoenvironmental diversity that prevailed in the area, prior to the establishment of the Amazon River drainage. During the Miocene, the region was characterized by a freshwater megawetland basin, influenced by episodic shallow-marine incursions. A fossil vertebrate collection from the middle Miocene strata of the Pebas Formation is here studied and described. This historical collection was recovered in 1912 along the banks of the Itaya River (Iquitos, Peru), during a scientific expedition led by two scientists of the University of Zurich, Hans Bluntschli and Bernhard Peyer. Our findings include a total of 34 taxa, including stingrays, bony fishes, turtles, snakes, crocodylians, and lizards. Fishes are the most abundant group in the assemblage (~ 23 taxa), including the first fossil record of the freshwater serrasalmids Serrasalmus, and Mylossoma, and the hemiodontid Hemiodus for the Pebas system, with the latter representing the first fossil be discovered for the entire Hemiodontidae. The presence of a representative of Colubroidea in the middle Miocene of Iquitos supports the hypothesis of arrival and dispersal of these snakes into South America earlier than previously expected. This fossil assemblage sheds light on the palaeoenvironments, and the geographical/temporal range of several aquatic/terrestrial lineages inhabiting the Amazonian region.

Fish otoliths from the middle Miocene Pebas Formation of the Peruvian Amazon

“…from the Bluntschli and Peyer collection O otolith, B skeletal remains, S scales, T teeth. Fossil records of "B, " "S, " and "T" were reported previously in Carrillo-Briceño et al (2021)…”

“…Localities: The fossil invertebrates and vertebrates from Iquitos collected during the Bluntschli and Peyer expedition come from seven different layers (see de Greve, 1938, table 1;Carrillo-Briceño et al, 2021, table 1). The studied specimens come from layers VI and I [see Table 1 and Carrillo-Briceño et al (2021)]. Both layers VI and I are associated with the same outcrop section at the Telefunkenstation (telegraph station) site (de Greve, 1938).…”

“…The lack of historical information on the stratigraphic context of the fossiliferous layers and outcrops prevented Carrillo-Briceño et al (2021) from obtaining more detailed information on the stratigraphic position of each of the layers. The fossiliferous localities visited during the 1912 expedition were likely situated within the urban area or the vicinity of the city of Iquitos and, due to water erosion and more than a century's worth of urban growth, establishing their exact locations may not be possible.…”

“…Environments recorded in the Pebas Fm. include fluvio-lacustrine, shallow lacustrine, lacustrine, and mangrove-like areas; there is also some evidence of marine incursions (Carrillo-Briceño et al, 2021). The biostratigraphy of these depositional sequences has primarily been based on the abundant mollusk assemblages, as well as on pollen and ostracods (Alvim et al, 2021;Boonstra et al, 2015;Jaramillo et al, 2017;Linhares et al, 2017;Roddaz et al, 2005;Salas-Gismondi et al, 2015;Wesselingh et al, 2002Wesselingh et al, , 2006Wesselingh et al, , 2010.…”

“…This study aims at providing descriptions of the fossil otoliths collected near the city of Iquitos (Department of Loreto, Fig. 1) during the Bluntschli and Peyer expedition of 1912 (see Carrillo-Briceño et al, 2021). This collection represents only the second record of otoliths from the Pebas Wetland System after Monsch (1998), the latter being reviewed as far as possible from his documentation.…”