First report of Eocene gadiform fishes from the Trans-Urals (Sverdlovsk and Tyumen regions, Russia)

Abstract

The recent 2014–2017 controlled excavations carried out in quarries of Sverdlovsk and Tyumen regions, Ural and Western Siberia, are contributing to the knowledge of the middle to late Eocene marine fauna from the Turgay Strait, mainly composed of invertebrates and cartilaginous and bony fishes. Here we present a preliminary report of the bony fishes collected during the campaigns carried out in two Eocene Trans-Urals localities. The sediments of these localities were deposited in a large epicontinental marine basin during the middle to late Eocene, when the Turgay Strait connected the Arctic waters to the North and the Peritethys to the South. Most of the bony fish material examined can be assigned to codfishes (Gadiformes) according to morphological comparison with living and fossil taxa. In particular, nearly complete three-dimensionally preserved lower jaws are confidently assigned to the Merlucciidae, whereas isolated vertebrae and bones are referred to as Gadiformes incertae sedis. This report documents the easternmost occurrence of this group of fishes in the northern hemisphere during the early phases of their radiation, revealing their presence into the Turgay Strait before its closure.

Confronting Sources of Systematic Error to Resolve Historically Contentious Relationships: A Case Study Using Gadiform Fishes (Teleostei, Paracanthopterygii, Gadiformes)

“…The explosive diversification within Macrouridae, which gave rise to more than half of the extant gadiform species, occurred in the Late Cretaceous to mid Paleocene ( \documentclass[12pt]{minimal} \usepackage{amsmath} \usepackage{wasysym} \usepackage{amsfonts} \usepackage{amssymb} \usepackage{amsbsy} \usepackage{upgreek} \usepackage{mathrsfs} \setlength{\oddsidemargin}{-69pt} \begin{document} }{}$\sim $\end{document} 61.6 Ma; 72.5–60.0 Ma). The presence of the oldest fossil gadiforms from the Danian and Selandian of Europe and South Australia suggest a bipolar distribution by the early Paleogene, with gadoids reported in the Paleocene of North Atlantic area and North Sea Basin ( Schwarzhans 2003 , 2004 ; Kriwet and Hecht 2008 ; Schwarzhans and Bratishko 2011 ; Schwarzhans 2012 ; Marramá et al 2019 ) and macrouroids reported in both the North Sea Basin and the Southern Ocean ( Schwarzhans 1985 ; Kriwet and Hecht 2008 ; G. Carnevale, personal communication). Macrouridae traditionally have been recognized as comprising four subfamilies: Macrourinae, Bathygadinae, Trachyrincinae, and Macrouroidinae ( Marshall 1965 ; Cohen 1984 ; Iwamoto 1989 ; Nolf and Steurbaut 1989 ; Cohen et al 1990 ; Endo 2002 ).…”

“…Phylogeny inferred for 58 taxa based on Maximum likelihood analyses of 8,244 loci (1,784,738 bp) and using a partitioned data set by codon position and best evolutionary models (P1: GTR \documentclass[12pt]{minimal} \usepackage{amsmath} \usepackage{wasysym} \usepackage{amsfonts} \usepackage{amssymb} \usepackage{amsbsy} \usepackage{upgreek} \usepackage{mathrsfs} \setlength{\oddsidemargin}{-69pt} \begin{document} }{}$+$\end{document} F \documentclass[12pt]{minimal} \usepackage{amsmath} \usepackage{wasysym} \usepackage{amsfonts} \usepackage{amssymb} \usepackage{amsbsy} \usepackage{upgreek} \usepackage{mathrsfs} \setlength{\oddsidemargin}{-69pt} \begin{document} }{}$+$\end{document} R4; P2: GTR \documentclass[12pt]{minimal} \usepackage{amsmath} \usepackage{wasysym} \usepackage{amsfonts} \usepackage{amssymb} \usepackage{amsbsy} \usepackage{upgreek} \usepackage{mathrsfs} \setlength{\oddsidemargin}{-69pt} \begin{document} }{}$+$\end{document} F \documentclass[12pt]{minimal} \usepackage{amsmath} \usepackage{wasysym} \usepackage{amsfonts} \usepackage{amssymb} \usepackage{amsbsy} \usepackage{upgreek} \usepackage{mathrsfs} \setlength{\oddsidemargin}{-69pt} \begin{document} }{}$+$\end{document} R5; P3: GTR \documentclass[12pt]{minimal} \usepackage{amsmath} \usepackage{wasysym} \usepackage{amsfonts} \usepackage{amssymb} \usepackage{amsbsy} \usepackage{upgreek} \usepackage{mathrsfs} \setlength{\oddsidemargin}{-69pt} \begin{document} }{}$+$\end{document} F \documentclass[12pt]{minimal} \usepackage{amsmath} \usepackage{wasysym} \usepackage{amsfonts} \usepackage{amssymb} \usepackage{amsbsy} \usepackage{upgreek} \usepackage{mathrsfs} \setlength{\oddsidemargin}{-69pt} \begin{document} }{}$+$\end{document} R7). Paleobiogeographic distribution of gadiform occurrences in the Paleocene and Eocene with potential migration routes of gadoids (yellow), macrouroids (white), and unknown (red) gadiform fishes according to Schwarzhans (1985 , 2012 ), Nolf and Dockery (1993) , Kriwet and Hecht (2008) , Schwarzhans and Bratishko (2011) , Marramá et al 2019 , and G. Carnevale (personal communication).…”

Lower Paleocene foraminiferal assemblages from the Tibeisale Formation in the Arctic region of Western Siberia

“…This attribution is supported by the works of Akhmet'ev et al ( , b, 2010, Iakovleva ( , 2011, Iakovleva and Heilmann-Clausen (2010), , and . Additional stratigraphic and paleoenvironmental data were obtained from the discovery of shark teeth , remains of teleost bones (Marrama et al, 2019), otoliths , mollusks (Trubin, 2018;, and trace fossils . Research on the diversity and biostratigraphy of foraminiferal assemblages had been formerly supplied by and .…”

“…In terms of stratigraphy, the Tavda Formation has been attributed to the Middle and Upper Eocene based on pollen, dinoflagellate cysts and magnetostratigraphy (Akhmet'ev et al , b, 2010Iakovleva, , 2011Iakovleva, and Heilmann-Clausen, 2010;. Additional stratigraphic and paleoenvironmental information was provided by findings of shark tees , teleost bone remains (Marrama et al 2019), otoliths , molluscs (Trubin, 2018;, and trace fossils ). Studies on the diversity and biostratigraphy of foraminiferal assemblages were previously provided by and .…”