Brian D. Metscher

• Ph.D.
• Senior Researcher at University of Vienna

The chondrocranium provides the key initial support for the fetal brain, jaws and cranial sensory organs in all vertebrates. The patterns of shaping and growth of the chondrocranium set up species-specific development of the entire craniofacial complex. The 3D development of chondrocranium have been studied primarily in animal model organisms, such...

The use of red ochre in funerary rituals holds continued interest for archaeologists and anthropologists given its ubiquity and debates surrounding its function. Despite this, and efforts into distinguishing corpse treatments on a histological level, there has been no experimental attempt to identify the potential effects of ochre treatments on sof...

Bone is an evolutionary novelty of vertebrates, likely to have first emerged as part of ancestral dermal armor that consisted of osteogenic and odontogenic components. Whether these early vertebrate structures arose from mesoderm or neural crest cells has been a matter of considerable debate. To examine the developmental origin of the bony part of...

Palaeoradiology is increasingly being used in archaeological and forensic sciences as a minimally invasive alternative to traditional histological methods for investigating bone microanatomy and its destruction by diagenetic processes. To better understand ancient mortuary practices, taphonomic studies using microCT scanning methods are gaining an...

Recent technological advances have broadened the application of palaeoradiology for non-destructive investigation of ancient remains. X-ray microtomography (microCT) in particular is increasingly used as an alternative to histological bone sections for interpreting pathological alterations, trauma, microstructure, and, more recently, bioerosion wit...

Background Sturgeons belong to an early‐branching lineage often used as a proxy of ancestor‐like traits of ray‐finned fishes. However, many features of this lineage, such as the transitory presence and the eventual loss of dentition, exemplify specializations that, in fact, provide important information on lineage‐specific evolutionary dynamics. R...

Recent advances have broadened the application of palaeoradiology for non-destructive investigation of ancient remains. X-ray microtomography (microCT) in particular is increasingly used as an alternative to histological bone sections for interpreting pathological alterations, trauma, microstructure, and more recently bioerosion with direct or anci...

Background: In both larval and adult anurans, blood separation and respiratory physiology have remained an enigma. While various blood separation mechanisms have been proposed, the same structure is seen as playing a key role: the conus arteriosus. However, previous findings on its internal structure are contradictory, depending on the specifics of...

The egg tooth development is similar to the development of all the other vertebrate teeth except earliest developmental stages because the egg tooth develops directly from the oral epithelium instead of the dental lamina similarly to null generation teeth. The developing egg tooth of Natrix natrix changes its curvature differently than the egg toot...

The vomeronasal organ (VNO), nasal cavity, lacrimal duct, choanal groove, and associated parts of the superficial (soft tissue) palate are called the naso‐palatal complex. Despite the morphological diversity of the squamate noses, little is known about the embryological basis of this variation. Moreover, developmental data might be especially inter...

X-ray microtomography (microCT) enables histological-scale 3D imaging of many types of biological samples, but it has yet to rival traditional histology for differentiation of tissue types and cell components. This report presents prima facie results indicating that a simple lead(II) acetate staining solution can impart preferential X-ray contrast...

Minor workers of some ant species belonging to the Colobopsis cylindrica (Fabricius, 1798) (COCY) species group can suicidally eject their sticky and potentially toxic mandibular gland reservoir content (MGRC) to ward off putative arthropod opponents. Since the MGRC can also be ejected non-suicidally as droplets at the mandible base, it was hypothe...

Background: Despite the diverse morphology of the adult squamate naso-palatal complex - consisting of the nasal cavity, vomeronasal organ (VNO), choanal groove, lacrimal duct and superficial palate - little is known about the embryology of these structures. Moreover, there are no comprehensive studies concerning development of the nasal cavity and...

Preprint at https://biorxiv.org/cgi/content/short/2020.09.18.303024v1 Submitted to Journal of Anatomy X-ray microtomography (microCT) enables histological-scale 3D imaging of many types of biological samples, but it has yet to rival traditional histology for differentiation of tissue types and cell components. This report presents prima facie resu...

The egg tooth of squamates evolved to facilitate hatching from mineralized eggshells. Squamate reptiles can assist their hatching with a single unpaired egg tooth (unidentates) or double egg teeth (geckos and dibamids). Egg tooth ontogeny in two gekkotan species, the leopard gecko Eublepharis macularius and the mourning gecko Lepidodactylus lugubri...

During their evolutionary history, modern sharks developed different tooth mineralization patterns that resulted in very distinct histological patterns of the tooth crown (histotypes). To date, three different tooth histotypes have been distinguished: (i) orthodont teeth, which have a central hollow pulp cavity in the crown, encapsulated by a promi...

Background Despite the diverse morphology of the adult squamate naso-palatal complex – consisting of the nasal cavity, vomeronasal organ (VNO), choanal groove, lacrimal duct and soft palate –little is known about the embryology of these structures. Moreover, there are no comprehensive studies concerning development of the nasal cavity and VNO in re...

Background Despite the diverse morphology of the adult squamate naso-palatal complex – consisting of the nasal cavity, vomeronasal organ (VNO), choanal groove, lacrimal duct and superficial palate – little is known about the embryology of these structures. Moreover, there are no comprehensive studies concerning development of the nasal cavity and V...

Background The morphological structures of organisms form tightly integrated but mutually independent character complexes (modules) linked through common development and function. Even though their abundance, diversity, and complex caste systems make camponotine ants ideal subjects to research developmental modularity and phenotypic integration, no...

A multidisciplinary project based in Austria and Brunei, titled “Voluntary self-sacrifice in exploding ants: a mechanism to defend coevolved microbiomes?” studies the evolution, phylogeny, and ecology of the extraordinary “exploding ants” of Southeast Asia. In addition to their enigmatic biology, they possess highly specialized minor and major work...

Micro-computed tomography (micro-CT or microtomography) is a non-destructive imaging technique using X-rays which allows the digitisation of an object in three dimensions. The ability of micro-CT imaging to visualise both internal and external features of an object, without destroying the specimen, makes the technique ideal for the digitisation of...

In most vertebrates, pharyngeal arches form in a stereotypic anterior-to-posterior progression. To gain insight into the mechanisms underlying evolutionary changes in pharyngeal arch development, here we investigate embryos and larvae of bichirs. Bichirs represent the earliest diverged living group of ray-finned fishes, and possess intriguing trait...

Laboratory-based X-ray NanoCT Explores Morphology of a Zebrafish Embryo - Volume 24 Supplement - Simone Ferstl, Brian Metscher, Mark Miiller, Sebastian Allner, Martin Dierolf, Madleen Busse, Klaus Achterhold, Bernhard Gleich, Franz Pfeiffer

We present high-resolution X-ray microtomography (microCT) to enhance the standard morphological description of a recently described centipede, Eupolybothrus liburnicus Akkari, Komerički, Weigand, Edgecombe and Stoev, 2017. The 3D images of the holotype and paratype specimens are considered here as cybertypes for the species–a universal and virtual...

Volume rendering of Eupolybothrus liburnicus, male holotype CHP 545. Rotation along body axis. (MPG)

Volume rendering of Eupolybothrus liburnicus, female paratype CHP 583. Rotation along body axis and lateral virtual sectioning with highlighted eggs (orange). (MP4)

Volume rendering of Eupolybothrus liburnicus, male holotype CHP 545, showing intermediate tergite and prefemora of legs 15 with highlighted right prefemoral knob (cyan). (MP4)

In the hyperdiverse ant genus Pheidole Westwood, 1839, the worker caste evolved into two morphologically distinct subcastes: minor workers and soldiers. The evolution of soldiers, which are larger in size than minor workers and have disproportionately larger heads, are thought to be key to Phediole’s success. Although many studies have focused on e...

Massive biotic change occurred during the Eocene as the climate shifted from warm and equable to seasonal and latitudinally stratified. Mild winter temperatures across Arctic intercontinental land bridges permitted dispersal of frost-intolerant groups until the Eocene-Oligocene boundary, while trans-Arctic dispersal in thermophilic groups may have...

Despite the wide variety of adaptive modifications in the oral and facial regions of vertebrates, their early oropharyngeal development is considered strictly uniform. It involves sequential formation of the mouth and pharyngeal pouches, with ectoderm outlining the outer surface and endoderm the inner surface, as a rule. At the extreme anterior dom...

Over the past two decades, the development of methods for visualizing and analysing specimens digitally, in three and even four dimensions, has transformed the study of living and fossil organisms. However, the initial promise that the widespread application of such methods would facilitate access to the underlying digital data has not been fully a...

Colobopsis sp. nrSA is an ant species of the Southeast Asian Colobopsis cylindrica group (formerly in the genus Cam-ponotus), which is currently being studied in the course of a long-term project focusing on the ecology and evolution of its members. We herein describe the morphological diversity of a colony fragment in an artificial nest establishe...

Dual-energy computed tomography (DECT) uses two different x-ray energy spectra in order to differentiate between tissues, materials or elements in a single sample or patient. DECT is becoming increasingly popular in clinical imaging and preclinical in vivo imaging of small animal models, but there have been only very few reports on ex vivo DECT of...

The Mastigitae is a small supertribe of ant-like stone beetles that currently includes nine extant and five extinct genera. Extinct taxa are known within tribes Clidicini and Mastigini; the latter with one genus discovered in Baltic amber. For the first time, a Mesozoic genus of the tribe Mastigini is described, Clidicostigus arachnipes Jałoszyński...

Significance Oral teeth and skin denticles share a deep, 450-million-year-old, evolutionary relationship among vertebrates. We investigate how teeth evolved from simpler denticles using sharks as an evolutionary developmental model. The striking ability of shark teeth to regenerate rapidly and continuously is not shared by denticles, and we suggest...

A new genus, Wallaceochromis, is described for the chromidotilapiine cichlids of the Pelvicachromis humilis group. It differs from Pelvicachromis sensu stricto in the number and arrangement of tubular infraorbitals, a straighter and sloping dorsal head profile with a low supraoccipital crest, higher abdominal vertebral counts (14-15 vs. 13-14), and...

Increases in human populations along coasts have altered the estuarine nursery habitats that are important for many aquatic organisms. These perturbations include changes to the sensory environment due to increased turbidity resulting from runoff and nutrient loading; these changes are occurring faster than fish species can become adapted to the ne...

Developmental studies are fundamental to understanding specialized morphologies. The baculum (os penis) is a heterotopic bone in the glans penis, which is probably subject to sexual selection and may play a role in reproductive isolation between closely related species. In this ongoing study, the pre‐ and postnatal development of the reproductive o...

The evolution of oral teeth is considered a major contributor to the overall success of jawed vertebrates. This is especially apparent in cartilaginous fishes including sharks and rays, which develop elaborate arrays of highly specialized teeth, organized in rows and retain the capacity for life-long regeneration. Perpetual regeneration of oral tee...

The appearance of toothed vertebrates has proven a major determinant of the overall success of this lineage. This is most apparent in sharks and rays (elasmobranchs), which further retain the capacity for life-long tooth regeneration. Given their comparatively basal phylogenetic position, elasmobranchs therefore offer the opportunity for crucial in...

Developmental studies are fundamental to understanding specialized morphologies. The baculum (os penis) is a heterotopic bone in the glans penis, which is probably subject to sexual selection and may play a role in reproductive isolation between closely related species. In this ongoing study, the pre- and postnatal development of the reproductive o...

This is the first in a planned series of studies in which we examine the cranial muscle ontogeny of exemplar taxa of actinopterygian clades to obtain a better understanding of the evolution of the cranial musculoskeletal system within the Actinopterygii. The Longnose Gar, Lepisosteus osseus, is a member of the basal actinopterygian family Lepisoste...

A fundamental and enduring problem in evolutionary biology is to understand how populations differentiate in the wild, yet little is known about what role organismal development plays in this process. Organismal development integrates environmental inputs with the action of gene regulatory networks to generate the phenotype. Core developmental gene...

We review the state-of-the-art approaches currently applied in myriapod taxonomy, and we describe, for the first time, a new species of millipede (Ommatoiulus avatar n. sp., family Julidae) using high-resolution X-ray microtomography (microCT) as a substantive adjunct to traditional morphological examination. We present 3D models of the holotype an...

Shark and ray (elasmobranch) dentitions are well known for their multiple generations of teeth, with isolated teeth being common in the fossil record. However, how the diverse dentitions characteristic of elasmobranchs form is still poorly understood. Data on the development and maintenance of the dental patterning in this major vertebrate group wi...

Detailed knowledge of histomorphology is a prerequisite for the understanding of function, variation, and development. In bats, as in other mammals, penis and baculum morphology are important in species discrimination and phylogenetic studies. In this study, nondestructive 3D-microtomographic (microCT, µCT) images of bacula and iodine-stained penes...

The baculum (os penis) has been extensively studied as a taxon-specific character in bats and other mammals but its mechanical function is still unclear. There is a wide consensus in the literature that the baculum is probably a sexually selected character. Using a novel approach combining postmortem manipulation and three-dimensional (3D) imaging,...

Snake lungs show a remarkable diversity of organ asymmetries. The right lung is always fully developed, while the left lung is either absent, vestigial, or well-developed (but smaller than the right). A 'tracheal lung' is present in some taxa. These asymmetries are reflected in the pulmonary arteries. Lung asymmetry is known to appear at early stag...

The ways in which embryo development can vary across individuals of a population determine how genetic variation translates into adult phenotypic variation. The study of developmental variation has been hampered by the lack of quantitative methods for the joint analysis of embryo shape and the spatial distribution of cellular activity within the de...

Female Pangoniinae in the tabanid fly genus Philoliche can display remarkably elongated proboscis lengths, which are adapted for both blood- and nectar-feeding. Apart from their role as blood-sucking pests, they represent important pollinators of the South African flora. This study examines the morphology of the feeding apparatus of two species of...

The link between the structure of the feeding apparatus, sensory modality (a sense or combination of senses relied on by an organism) and diet in early life history stage fishes is important for understanding ontogenetic shifts in foraging habitats during ontogeny. Species of the family Sciaenidae are used to examine how ontogenetic changes in feed...

Context: Only a few methods have been published dealing with the visualization of heat-induced cracks inside bones and teeth. Aims: As a novel approach this study used nondestructive X-ray microtomography (micro-CT) for volume analysis of heat-induced cracks to observe the reaction of human molars to various levels of thermal stress. Materials...

With the recent and continuing discovery of further cryptic bat species, it is essential to find morphological species discriminating characters. Pipistrellus pipistrellus (common pipistrelle) and Pipistrellus pygmaeus (soprano pipistrelle) have been recognized as separate species since 1997, but no reliable morphological species discriminating tra...

Background: Cichlid fishes show considerable diversity in swim bladder morphology. In members of the subfamily Etroplinae, the connection between anterior swim bladder extensions and the inner ears enhances sound transmission and translates into an improved hearing ability. We tested the hypothesis that those swim bladder modifications coincide wi...

By examining development at the level of tissues and processes, rather than focusing on gene expression, we have formulated a general hypothesis to explain the dorso-ventral and anterior-posterior placement of paired appendage initiation sites in vertebrates. According to our model, the number and position of paired appendages are due to a commonal...

Avian forelimb digit homology remains one of the standard themes in comparative biology and EvoDevo research. In order to resolve the apparent contradictions between embryological and paleontological evidence a variety of hypotheses have been presented in recent years. The proposals range from excluding birds from the dinosaur clade, to assignments...

A well-developed suction pump in the head represents an important adaptation for nectar-feeding insects, such as Hymenoptera, Lepidoptera and Diptera. This pumping organ creates a pressure gradient along the proboscis, which is responsible for nectar uptake. The extremely elongated proboscis of the genus Prosoeca (Nemestrinidae) evolved as an adapt...

The dP4 of Desmanella engesseriZiegler, 1985 from a maxillary which includes the P2 and P3 in crypt, the P4 in eruption and fully erupted dP4 and M1, is described from Petersbuch 28 (Germany; Lower Miocene, MN3/4). The maxillary was studied using X-ray microtomography to make detailed images of the internal and external features of the sample. This...

While a number of studies have illustrated and analyzed 3D models of inner ears in higher vertebrates, inner ears in fishes have rarely been investigated in 3D, especially with regard to the sensory epithelia of the end organs, the maculae. It has been suggested that the 3D curvature of these maculae may also play an important role in hearing abili...

An assessment of the anatomical costs of extremely long proboscid mouthparts can contribute to the understanding of the evolution of form and function in the context of insect feeding behaviour. An integrative analysis of expenses relating to an exceptionally long proboscis in butterflies includes all organs involved in fluid feeding, such as the p...

Background In most modern bony fishes (teleosts) hearing improvement is often correlated with a close morphological relationship between the swim bladder or other gas-filled cavities and the saccule or more rarely with the utricle. A connection of an accessory hearing structure to the third end organ, the lagena, has not yet been reported. A recent...

Most investigations on the internal organization of soft-bodied animals such as cephalopods are based on classical serial sectioning (i.e. histological). Here, we demonstrate a state-of-the-art-technique of X-ray microtomography (micro-CT) for 3D imaging of soft-bodied organisms without mineralized structures. As a model, we chose the Hawaiian bobt...

With the discovery of further cryptic bat species, it is vital to find morphological species discriminating characters. Pipistrellus pipistrellus and P. pygmaeus have been recognized as separate species since 1997, but no reliable morphological species discriminating trait has been found. The baculum (os penis) has long been used successfully in sp...

X-ray microtomographic imaging is coming into more widespread use in life sciences research. Micro-CT produces whole-volume images of intact samples with resolutions extending into the range of light microscopy and is most powerful in combination with other imaging techniques. The versatility of lab-based micro-CT systems makes them well-suited to...

Several teleost species have evolved anterior extensions of the swim bladder which come close to or directly contact the inner ears. A few comparative studies have shown that these morphological specializations may enhance hearing abilities. This study investigates the diversity of swim bladder morphology in four Asian and African cichlid species a...

MicroCT volume image of acetylated alpha-tubulin immunostaining in a stage 23 chick embryo, immunostaining shown in yellow within the intact embryo. From Metscher and Müller, Developmental Dynamics 240:2301-2308, 2011.

X-ray microtomography (microCT) is a highly versatile imaging method, and with appropriate contrast stains and sample mounting, it can produce high-quality images of embryos at a wide range of developmental stages. The techniques presented here provide simple and robust methods for gel embedding and microCT scanning of vertebrate embryos. The speci...

Despite several recent analyses on the phylogeny of Neuroptera some questions still remain to be answered. In the present analysis we address these questions by exploring a hitherto unexplored character complex: the tentorium, the internal cuticular support structure of the insect head. We described in detail the tentoria of representatives of all...