Neogene sharks and rays from the Brazilian ‘Blue Amazon’

Abstract

The lower Miocene Pirabas Formation in the North of Brazil was deposited under influence of the proto-Amazon River and is characterized by large changes in the ecological niches from the early Miocene onwards. To evaluate these ecological changes, the elasmobranch fauna of the fully marine, carbonate-rich beds was investigated. A diverse fauna with 24 taxa of sharks and rays was identified with the dominant groups being carcharhiniforms and myliobatiforms. This faunal composition is similar to other early Miocene assemblages from the proto-Carribbean bioprovince. However, the Pirabas Formation has unique features compared to the other localities; being the only Neogene fossil fish assemblage described from the Atlantic coast of Tropical Americas. Phosphate oxygen isotope composition of elasmobranch teeth served as proxies for paleotemperatures and paleoecology. The data are compatible with a predominantly tropical marine setting with recognized inshore and offshore habitats with some probable depth preferences (e.g., Aetomylaeus groups). Paleohabitat of taxa particularly found in the Neogene of the Americas ( †Carcharhinus ackermannii, †Aetomylaeus cubensis) are estimated to have been principally coastal and shallow waters. Larger variation among the few analyzed modern selachians reflects a larger range for the isotopic composition of recent seawater compared to the early Miocene. This probably links to an increased influence of the Amazon River in the coastal regions during the Holocene.PLOS ONE | https://doi.org/10.1371/journal.pone

Reappraisal of the Eocene whiptail stingrays (Myliobatiformes, Dasyatidae) of the Bolca Lagerstätte, Italy

“…Teeth of Taeniura sp. are also reported from the lower Miocene of Brazil (Aguilera et al, ) and from the Pliocene of Libya (Pawellek et al, ), although it is not clear whether the authors recognized their affinities with Taeniurops ( T. grabata or T. cavernosa ) or Taeniura ( T. lymma or T. lessoni ). Therefore, the oldest remains referable to neotrygonines are from Eocene tropical shallow Tethyan localities (Bolca and Fayum area; Figure ).…”

Neogene Caribbean elasmobranchs: diversity, paleoecology and paleoenvironmental significance of the Cocinetas Basin assemblage (Guajira Peninsula, Colombia)

“…In a few cases when only small or fragmented teeth were available, bulk samples were taken (1-1.5 mg of enameloid and dentine). Based on previous studies, isotopic data provide valuable information about the paleoecology of sharks along stratigraphic sequences (Fischer et al, 2012(Fischer et al, , 2013aKocsis et al, 2014;Leuzinger et al, 2015;Aguilera et al, 2017a). All samples were cleaned in deionized water in an ultrasonic bath to reduce sedimentary contamination.…”

“…The specimens are morphologically similar to those of Nebrius sp. reported from the Cantaure Formation (Burdigalian) in the Falcon Basin, Venezuela and Pirabas Formation (Aquitanian-Burdigalian), Brazil (Aguilera et al, 2017a). For summarized information about taxonomy and the stratigraphic range of Nebrius in the Americas see Carrillo-Briceño et al (2016a, p. 6).…”

“…Our Rhynchobatus sp. specimens resemble those from the Neogene of Venezuela and other locations in tropical America (Carrillo-Briceño et al, 2016a;Aguilera et al, 2017a). We refrain from taxonomic identification at the species level of our specimens because the range of dental variation in extant species is unknown, and little is known about fossil species from the Americas (Carrillo-Briceño et al, 2016a).…”

“…Dietary preferences of the elasmobranch paleofauna from the Cocinetas Basin. Briceño et al, 2016a;Aguilera et al, 2017a). Due to the scarce fossil record of this extinct species, it is difficult to propose a determined biostratigraphic and geographical range.…”