Martha Richter

A palaeobiologist’s guide to ‘virtual’ micro-CT preparation

This paper provides a brief but comprehensive guide to creating, preparing and dissecting a ‘virtual’ fossil, using a worked example to demonstrate some standard data processing techniques. Computed tomography (CT) is a 3D imaging modality for producing ‘virtual’ models of an object on a computer. In the last decade, CT technology has greatly improved, allowing bigger and denser objects to be scanned increasingly rapidly. The technique has now reached a stage where systems can facilitate large-scale, non-destructive comparative studies of extinct fossils and their living relatives. Consequently the main limiting factor in CT-based analyses is no longer scanning, but the hurdles of data processing (see disclaimer). The latter comprises the techniques required to convert a 3D CT volume (stack of digital slices) into a virtual image of the fossil that can be prepared (separated) from the matrix and ‘dissected’ into its anatomical parts. This technique can be applied to specimens or part of specimens embedded in the rock matrix that until now have been otherwise impossible to visualise. This paper presents a suggested workflow explaining the steps required, using as example a fossil tooth of Sphenacanthus hybodoides (Egerton), a shark from the Late Carboniferous of England. The original NHMUK copyrighted CT slice stack can be downloaded for practice of the described techniques, which include segmentation, rendering, movie animation, stereo-anaglyphy, data storage and dissemination. Fragile, rare specimens and type materials in university and museum collections can therefore be virtually processed for a variety of purposes, including virtual loans, website illustrations, publications and digital collections. Micro-CT and other 3D imaging techniques are increasingly utilized to facilitate data sharing among scientists and on education and outreach projects. Hence there is the potential to usher in a new era of global scientific collaboration and public communication using specimens in museum collections. Richard Leslie Abel, MSK Laboratory, Department of Surgery and Cancer, Charring Cross Hospital, Imperial College, W6 8RF London, United Kingdom. richard.abel@imperil.ac.uk and Image and Analysis Centre, Mineralogy Department, Natural History Museum, Cromwell Road, SW7 5BD London, United Kingdom. Carolina Rettondini Laurini, Laboratorio de Paleontologia Departamento de Biologia FFCLRP USP, Av. Bandeirantes, 3900 CEP 14040-901, Bairro Monte Alegre, Ribeirao Preto, SP, Brazil. xirra.carolina@gmail.com PE Article Number: 15.2.6T Copyright: Palaeontological Association May 2012 Submission: 12 May 2011. Acceptance: 25 April 2012 Abel, Richard Leslie, Laurini, Carolina Rettondini, and Richter, Martha 2012. A palaeobiologist’s guide to ‘virtual’ micro-CT preparation. Palaeontologia Electronica Vol. 15, Issue 2;6T,17p; palaeo-electronica.org/content/issue-2-2012-technical-articles/233-micro-ct-workflow ABEL ET AL.: MICRO-CT WORKFLOW Martha Richter, Department of Palaeontology, Natural History Museum, Cromwell Road, SW7 5BD London, United Kingdom. m.richter@nhm.ac.uk

Fishes and the Break-up of Pangaea

This volume, in honour of Peter L. Forey, is about fishes as palaeobiogeographic indicators in the Mesozoic and Cenozoic. The last 250 million years in the history of Earth have witnessed the break-up of Pangaea, affecting the biogeography of organisms. Fishes occupy almost all freshwater and marine environments, making them a good tool to assess palaeogeographic models. The volume begins with studies of Triassic chondrichthyans and lungfishes, with reflections on Triassic palaeogeography. Phylogeny and distribution of Late Jurassic neoselachians and basal teleosts are broached, and are followed by five papers about the Cretaceous, dealing with SE Asian sharks, South American ray-finned fishes and coelacanths, European characiforms, and global fish palaeogeography. Then six papers cover Tertiary subjects, such as bony tongues, eels, cypriniforms and coelacanths. There is generally a good fit between fish phylogenies and the evolution of the palaeogeographical pattern, although a few discrepancies question details of current palaeogeographic models and/or some aspects of fish phylogeny.

On the squamation of Australerpeton cosgriffi Barberena, a temnospondyl amphibian from the Upper Permian of Brazil

Abdominal scales of a juvenile specimen of Australerpeton cosgriffi Barberena 1998 are made of primary compact bone rich in osteocyte lacunae; vascular canals and primary osteons are rare with no sign of remodelling of the tissue by resorption and redeposition. In contrast, the abdominal scales of an adult of the same species shows extensive reworking of the bone tissue. The scale grows by apposition of lamellar bone peripherally around the whole scale; the presence of Sharpey fibers in the periphery of the scales both basally and externally suggests that they remained deeply embedded in the dermis; the embryonic scale is completely remodelled in the adult by resorption and redeposition which produces a cancellous bone with large erosion bays and secondary osteons. Remodelling by resorption and redeposition is confined to the core of the scales and does not affect its periphery, contrary to what happens in sarcopterygians with cosmoid scales. The possible biological functions of the squamation in this species, such as mechanical protection, dry protection, cutaneous respiration, hydrostatic control and calcium reservoir, are discussed.

New Permian fauna from tropical Gondwana

Terrestrial vertebrates are first known to colonize high-latitude regions during the middle Permian (Guadalupian) about 270 million years ago, following the Pennsylvanian Gondwanan continental glaciation. However, despite over 150 years of study in these areas, the biogeographic origins of these rich communities of land-dwelling vertebrates remain obscure. Here we report on a new early Permian continental tetrapod fauna from South America in tropical Western Gondwana that sheds new light on patterns of tetrapod distribution. Northeastern Brazil hosted an extensive lacustrine system inhabited by a unique community of temnospondyl amphibians and reptiles that considerably expand the known temporal and geographic ranges of key subgroups. Our findings demonstrate that tetrapod groups common in later Permian and Triassic temperate communities were already present in tropical Gondwana by the early Permian (Cisuralian). This new fauna constitutes a new biogeographic province with North American affinities and clearly demonstrates that tetrapod dispersal into Gondwana was already underway at the beginning of the Permian.

Tissue diversity and evolutionary trends of the dermal skeleton of Silurian thelodonts

Previously described scale morphotypes of Silurian thelodonts, constrained by their representation as isolated dermal denticles are reassessed to provide a more robust character basis for their inclusion in future phylogenetic studies. As relatively common microfossils, thelodonts are important biostratigraphical markers, but their interrelationships with geologically younger species known by complete skeletons are still unresolved. We examined scales of 21 known morphotypes from north-eastern Europe, Siberia and central Asia and described their distinct tissue arrangements considering (1) thickness and direction of dentine tubules, (2) presence or absence of a pulp canal, (3) number and position of pulp canals, (4) the presence or absence of a distinct outer crown layer and (5) the extent of Sharpeys fibres penetrating the scale base. We correlated the traditional thelodont scale type morphologies with these distinct scale histologies, as found in Silurian thelodonts. In addition, a new histological type for thelodont scales, the Talimaalepis type, is described to represent a new taxon, from the Early-Mid Silurian. Our study suggests that, through time, there is a general trend of increasing complexity in thelodont dermal tissue structures. Three types of dentine and internal scale organisations were distinguished in Silurian species studied, namely (1) irregular, thin tubular dentine; (2) irregular, thick tubular dentine, with two subtypes as a function of pulp canal development and (3) regular, tubular dentine (orthodentine).

Shark teeth from Pirabas Formation (Lower Miocene), northeastern Amazonia, Brazil

The shark fauna (Chondrichthyes: Elasmobranchii) of Pirabas Formation is one of the most representative and diversified of the Neogene of South America. This fauna is associated with the early Miocene transgression resulting from the global sea level rise. In this paper, the composition of the Pirabas shark fauna is re-evaluated based on new fossil findings. The occurrence of the following taxa is confirmed: Carcharhinus sp.1, Carcharhinus sp.2, Carcharhinus cf. macloti, Carcharhinus priscus, Galeocerdo sp., Sphyrna cf. media, Hemipristis serra, Carcharodon subauriculatus, Isurus sp., Ginglymostoma sp., Nebrius obliquus.

Dental Histology of a Characoid Fish from the Plio-Pleistocene of Acre, Brazil

The histology of premaxillary teeth of Colossoma sp. from the Solimöes Formation of Northern Brazil is described, in comparison with Recent material. Analysis by light and scanning electron microscopy shows that they share with those of the serrasalminids, histological (though not anatomical) features of carnivorous fishes. The enameloid in both groups displays surface‐parallel images of calcified fibres along the periphery of the teeth while internally, these images present a random distribution. Such similarities suggest that both the serrasalminids and myleinids may have evolved from carnivorous ancestors. The serrasalminids remain carnivorous, while the herbivorous habit of the myleinids may have been acquired secondarily. This change of diet is probably related to changes in the shape of the teeth which are used for crushing fruits, seeds and leaves. The teeth in adult Colossoma are unicuspid, though not conical. The molar or incisive form of these teeth may have evolved independently from the conical‐shaped primitive dentition of the characoids, without passing through any stage of fusion of dental papillae, which is observed in the ontogenetic development of other characoids.

The contribution of Sir Arthur Smith Woodward to the palaeoichthyology of Brazil – Smith Woodward's types from Brazil

Abstract Sir Arthur Smith Woodward published many scientific works on fossil fishes from Brazil, among them the description of 14 new species and the redefinition of two lectotypes. This paper provides an illustrated, taxonomic update on the following taxa, together with comments on their repository and other relevant remarks: Lissodus nitidus (Woodward, 1888), Rhinoptera prisca Woodward, 1907, ‘Lepidotes’ mawsoni Woodward, 1888, ‘Lepidotes’ souzai Woodward, 1908a, Calamopleurus mawsoni (Woodward, 1902), ‘Belonostomus’ carinatus Mawson & Woodward, 1907, Paleopiquitinga brasiliensis (Woodward, 1939), Lignobrycon ligniticus (Woodward, 1898), Brycon avus (Woodward, 1898), Steindachneridion iheringi (Woodward, 1898), Scombroclupeoides scutata (Woodward, 1908a), Macracara prisca Woodward, 1939, Mawsonia gigas Woodward, 1907, Mawsonia minor Woodward, 1908a; Vinctifer comptoni (Agassiz, 1841) and Notelops brama (Agassiz, 1841).

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

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.

Arthur Smith Woodward: His Life and Influence on Modern Vertebrate Palaeontology

Arthur Smith Woodward was the Natural History Museum’s longest-serving Keeper of Geology and the world’s leading expert on fossil fish. He was also an unwitting victim of the Piltdown fraud, which overshadowed his important scientific contributions. The aim of this book is to honour Smith Woodward’s contributions to vertebrate palaeontology, discuss their relevance today and provide insights into the factors that made him such an eminent scientist. The last few years have seen a resurgence in fossil vertebrate (particularly fish) palaeontology, including new techniques for the ‘virtual’ study of fossils (synchrotron and micro CT-scanning) and new research foci, such as ‘Evo-Devo’ – combining fossils with the development of living animals. This new research is built on a strong foundation, like that provided by Smith Woodward’s work. This collection of papers, authored by some of the leading experts in their fields, covers the many facets of Smith Woodward’s life, legacy and career. It will be a benchmark for studies on one of the leading vertebrate palaeontologists of his generation.