The one that got away from Smith Woodward: cranial anatomy of Micrornatus (Acanthomorpha: Scombridae) revealed using computed microtomography

Abstract

The monotypic scombrid fish Micrornatus is represented by a single skull from the early Eocene (Ypresian) London Clay Formation of southeastern England. Although Arthur Smith Woodward substantially increased the diversity of scombrids and scombrid-like taxa known from this deposit, he seems not to have studied the fossil that would later be recognized as Micrornatus. Here we re-examine this specimen using computed microtomography, with two principal aims: first, a revised anatomical account with an emphasis on concealed features; and, second, 'proof-of-concept' for the tomographic study of fish crania from the London Clay. Scans reveal new details of the braincase, suspensorium and ventral hyoid arch. We compare the cranial anatomy of Micrornatus with other members of Eocoelopomini, a group also containing the genera Eocoelopoma, Palaeothunnus and possibly Landanichthys. Clarification of the taxonomy and phylogeny of early fossil scombrids is needed, and we suggest that computed tomography will be a useful tool for revealing the anatomical evidence needed to accomplish this goal.

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

“…Fossil specimens † Eutrichiurides winkleri and † Progempylus edwardsi were studied using μCT scanning. These had previously been mechanically prepared to expose external bones, and μCT presents an effective method of obtaining additional information on the internal anatomy of London Clay material (Beckett & Friedman ). Extant taxa were scanned to obtain details of internal osteological anatomy not available from radiography or the literature.…”

X-ray micro-computed tomography (micro-CT) of pyrite-permineralized fruits and seeds from the London Clay Formation (Ypresian) conserved in silicone oil: a critical evaluation

“…They recovered taxonomically useful information at a resolution of 100 m and concluded that the method would be suitable for application to all London Clay iron pyrite permineralized fossils. Beckett and Friedman (2015), Friedman et al (2015), and Johanson et al (2015) used micro-CT to study the anatomy of fish skulls from the London Clay Formation of the Isle of Sheppey. Walsh and Milner (2011 and references therein) studied bird skulls from the London Clay Formation using micro-CT with a focus on obtaining digital endocranial casts.…”

“…Marine invertebrates (e.g., Tracey et al 2002) include nautilids (Dzik and Gaź dzicki 2001) and teredinid bivalves, which bored into wood (Huggett and Gale 1995). Marine vertebrates include sharks (Casier 1966;Hooker et al 1980), teleost fish (e.g., Beckett and Friedman 2015), and turtles (Hooker et al 1980). Despite the large number of plant fossils, land mammals are extremely rare: the Isle of Sheppey site has yielded only seven specimens.…”

The English Chalk and London Clay: two remarkable British bony fish Lagerstätten

“…Computed tomography offers a virtual means of obtaining these internal details from three-dimensional material (e.g. Beckett & Friedman 2015). This approach is non-destructive, can also be applied to specimens from the London Clay encased in concretions that are not soluble in acid and, perhaps most significantly, preserves positional information about bones not firmly sutured to other parts of the skeleton.…”

“…Non-destructive computed tomography (CT; Sutton et al 2014) offers an approach to studying the remarkable fish fossils of the Chalk and London Clay without any of the drawbacks associated with traditional preparation techniques (Fig. 2;Beckett & Friedman 2015). We are currently re-studying the ray-finned fishes of the Chalk and London Clay using CT scanning, with the principal goals of better documenting their anatomy, relationships and, through the use of biomechanical models developed for living fishes (e.g.…”