Early Devonian (Late Emsian) shark fin remains (Chondrichthyes) from the Paraná Basin, southern Brazil.

Martha Richter,Elvio P Bosetti,Rodrigo S Horodyski

doi:10.1590/0001-3765201720160458

Abstract

We report on the pioneering discovery of Devonian fish remains in the Paraná Basin, which represents the southernmost record of fishes from that period in mainland South America. The material comes from an outcrop at the lower portion of the São Domingos Formation, within Sequence C of the Paraná-Apucarana sub-basin in Tibagi, State of Paraná. Marine invertebrates are abundant in the same strata. The dark colored fish remains were collected in situ and represent natural moulds of partially articulated shark fin rays (radials). No elements such as teeth or prismatic cartilage have been preserved with the fins rays. This can be attributed to the dissolution of calcium-phosphatic minerals at the early stages of fossilization due to diagenetic processes possibly linked to strong negative taphonomic bias. This may have contributed to the fact that fishes remained elusive in the Devonian strata of this basin, despite substantial geological work done in the Paraná State in recent decades. In addition, the scarcity of fish fossils may be explained by the fact that the Devonian rock deposits in this basin originated in a vertebrate impoverished, cold marine environment of the Malvinokaffric Realm, as previously suspected.

Highlights

The Devonian was a pivotal time for the evolution of fishes and one in which all the large classes of fishes co-existed
When marine fossils, including brachiopods, molluscs, trilobites, echinoderms, annelids and cnidarians were found in the extensive exposures of rocks of Devonian age in the State of Paraná in southern Brazil (e.g. Clarke 1913, Petri 1948, Lange 1967, Melo 1988, Zabini et al 2012, Bosetti et al 2012, Horodyski 2014), many palaeontologists started reporting the strange and apparently inexplicable absence of fossil fishes in these rocks
Disarticulated chondrichthyan remains were reported from the Parnaíba and the Amazon basin in Brazil as well as from other Devonian rocks elsewhere in South America

Summary

Introduction

The Devonian was a pivotal time for the evolution of fishes and one in which all the large classes of fishes co-existed. Many of the groups that dominated the seas and continental waters at the time did not survive the end of the Devonian. When marine fossils, including brachiopods, molluscs, trilobites, echinoderms, annelids and cnidarians were found in the extensive exposures of rocks of Devonian age in the State of Paraná in southern Brazil Clarke 1913, Petri 1948, Lange 1967, Melo 1988, Zabini et al 2012, Bosetti et al 2012, Horodyski 2014) , many palaeontologists started reporting the strange and apparently inexplicable absence of fossil fishes in these rocks.

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