Computed tomography scanning as a tool for linking the skeletal and otolith‐based fossil records of teleost fishes

Abstract

Micro-computed tomography (lCT) scanning now represents a standard tool for non-destructive study of internal or concealed structure in fossils. Here we report on otoliths found in situ during routine lCT scanning of threedimensionally preserved skulls of Palaeogene and Cretaceous fishes. Comparisons are made with isolated otolith-based taxa to attempt correlations between the body fossil and otolith fossil records. In situ otoliths previously extracted mechanically from specimens of Apogon macrolepis and Dentex laekeniensis match our lCT models. In some cases, we find a high degree of congruence between previously independent taxonomic placements for otolith and skeletal remains (Rhinocephalus, Osmeroides, Hoplopteryx). Unexpectedly, in situ otoliths of the aulopiform Apateodus match isolated otoliths of Late Cretaceous age previously interpreted as belonging to gempylids, a group of percomorph fishes that do not appear in the body fossil record until the Palaeogene. This striking example of convergence suggests constraints on otolith geometry in pelagic predators. The otoliths of Apateodus show a primitive geometry for aulopiforms and lack the derived features of Alepisauroidea, the lizardfish clade to which the genus is often attributed. In situ otoliths of Early Cretaceous fishes (Apsopelix and an unidentified taxon) are not well preserved, and we are unable to identify clear correlations with isolated otolith morphologies. We conclude that the preservation of otoliths suitable for lCT scanning appears to be intimately connected with the taphonomic history, lithological characteristics of surrounding matrix, and syn-and postdepositional diagenetic effects.

Otoliths in situ in the stem teleostCavenderichthys talbragarensis(Woodward, 1895), otoliths in coprolites, and isolated otoliths from the Upper Jurassic of Talbragar, New South Wales, Australia

“…Cavenderichthys talbragarensis is only the second Jurassic teleost species known with otoliths in situ, the other being Leptolepis normandica (see Delsate, 1997;Nolf, 2013), and the third stem teleost with otoliths in situ (including the Early Cretaceous Apsopelix anglicus in Schwarzhans et al, 2018). It confirms the low degree of morphological diversification of stem teleost otoliths as suggested by Schwarzhans (2018).…”

“…It has been argued that these two records partly complement each other due to mineralogical differences and fossilization potentials (Nolf, 1985(Nolf, , 2013Schwarzhans and Carnevale, 2017). It is, however, also true that the systematic interpretation of isolated otoliths largely depends on correlation with extant otoliths, a situation that becomes particularly complex in Mesozoic rocks with the predominance of extinct teleost groups from which otoliths are unknown (Schwarzhans, 2018;Schwarzhans et al, 2018). Articulated identifiable fossil fish skeletons with otoliths in situ thus represent the only means of linking these two rich and mostly separate records of extinct fishes and provide vital calibration points for the interpretation of isolated otoliths.…”

“…The discovery of otoliths in situ depends largely on the lucky splitting of the fossiliferous rock to expose the otolith, or at least part of it, on the surface of the slab without damaging its fragile composition. Invasive preparation techniques are avoided as much as possible, but applications of noninvasive methods (casting from voids: Schwarzhans, 2007;micro-computed tomography [CT] scanning: Schwarzhans et al, 2018; X-ray fluorescence [XRF] spectrometry: this study) have yielded promising results.…”

The Phylogeny of Carangiform Fishes: Morphological and Genomic Investigations of a New Fish Clade

“…OR centuries, studies on the evolution of fishes were based on surveys and analyses of anatomical characters. Comparisons among wet and dry skeletons (e.g., Olney et al, 1993;Holcroft and Wiley, 2015), and surveys of characters through different visualization techniques, such as scanning electron microscopy and histology (e.g., Webb, 1989a;Ghedotti et al, 2018), x-ray computed tomography (e.g., Schaefer, 2003;Webb et al, 2006;Schwarzhans et al, 2018), and magnetic resonance imaging (e.g., Chakrabarty et al, 2011;Graham et al, 2014), have helped identify a wealth of anatomical features that have facilitated our interpretation of fish evolution (e.g., Potthoff et al, 1986;Springer and Johnson, 2004;Hilton et al, 2015). These techniques have helped us discover, differentiate, and assess the homology and phylogenetic significance of particular anatomical features (e.g., Johnson, 1975;Gemballa and Britz, 1998), were critical for identifying characters that suggested novel placements of taxa within the broader phylogeny of fishes (e.g., Rosen and Parenti, 1981;Johnson and Patterson, 1993;Stiassny, 1993), allowed researchers to assess the intrarelationships of lineages of fishes hypothesized to be closely related (e.g., Parenti, 1981;Baldwin and Johnson, 1996;Harold and Weitzman, 1996), or aided the search for the sister group of well-established clades (e.g., Gill and Mooi, 1993;Johnson and Brothers, 1993).…”

Morphology and phylogenetic relationships of fossil snake mackerels and cutlassfishes (Trichiuroidea) from the Eocene (Ypresian) London Clay Formation

“…; Schwarzhans et al . ). Isolated teeth from the early Paleocene (Danian) of Angola (Dartevelle & Casier ) are attributed to the trichiurid † Eutrichiurides , but their affinities are also subject to question (see below).…”