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Dive into the research topics where Tobias B. Grun is active.

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Featured researches published by Tobias B. Grun.


Historical Biology | 2014

Drilling predation on the clypeasteroid echinoid Echinocyamus pusillus from the Mediterranean Sea (Giglio, Italy)

Tobias B. Grun; Diedrich Sievers; James H. Nebelsick

Drilling predation of cassid gastropods (tonnacean) on echinoids is common in marine environments but is rarely documented. Tests of the minute clypeasteroid Echinocyamus pusillus OF Müller (1776) were collected from the Mediterranean Sea (Isola del Giglio, Italy). Besides general morphology, features pertaining to the morphology and distribution of predatory boreholes were examined. Furthermore, borehole frequencies among different samples sites were compared. Cassid gastropods are assumed to be the originators of the boreholes. A total of 1061 tests were analysed for drilling rates with 15.3% drilled with predominantly single boreholes. The borehole morphology is strongly affected by the microstructure of the skeleton; the borehole outline is irregular if drilled within areas where ambulacral pores are present. Vertical borehole morphology is influenced by stereom density. The size frequencies of non-drilled and drilled specimens show significant differences. Comparisons of borehole size with test size show only a low correlation between predator and prey size. The distribution of boreholes shows a high site selectivity of the predator for the aboral side of the test and the petalodium.


Journal of Paleontology | 2017

Comparative drilling predation on time-averaged phosphatized and nonphosphatized assemblages of the minute clypeasteroid echinoid Echinocyamus stellatus from Miocene offshore sediments (Globigerina Limestone Formation, Malta)

Tobias B. Grun; Andreas Kroh; James H. Nebelsick

Abstract. Fossilized tests of 1,053 Echinocyamus stellatus (Capeder, 1906) from the Miocene Globigerina Limestone Formation exposed on the northern coast of Gozo (Maltese Islands) were analyzed for predation traces. Specimens mixed by time-averaging processes can be clearly separated into two distinct samples according to their preservation as phosphatized or nonphosphatized individuals. Overall, 11.1% of the tests reveal holes that are referred to the ichnospecies Oichnus simplex (Bromley, 1981). Because of the hole morphology and diameter, the holes are interpreted as predatory drill holes, most likely produced by cassid gastropods. Redeposited phosphatized echinoids derived from an earlier period of reduced sedimentation rates show drilling frequencies of 20.5%. Younger, autochthonous, nonphosphatized echinoids show drilling frequencies of 8.1%. In both samples, predators predominantly targeted the aboral side of the echinoid test, particularly on the petalodium.


Archive | 2016

The Skeleton of the Sand Dollar as a Biological Role Model for Segmented Shells in Building Construction: A Research Review

Tobias B. Grun; Layla Koohi Fayegh Dehkordi; Tobias Schwinn; Daniel Sonntag; Malte von Scheven; Manfred Bischoff; Jan Knippers; Achim Menges; James H. Nebelsick

Concrete double-curved shell constructions have been used in architectural design and building constructions since the beginning of the twentieth century. Although monolithic shells show a high stiffness as their geometry transfers loads through membrane forces, they have been mostly replaced by the more cost-efficient lattice systems. As lattice systems are covered by planar glass or metal panes, they neither reach the structural efficiency of monolithic shells, nor is their architectural elegance reflected in a continuous curvature. The shells of sand dollars’ – highly adapted sea urchins – combine a modular and multi-plated shell with a flexible, curved as well as smooth design of a monolithic construction. The single elements of the sand dollars’ skeleton are connected by calcite protrusions and can be additionally supported by organic fibres. The structural efficiency of the sea urchin’s skeleton and the principles behind them can be used for innovations in engineering sciences and architectural design while, at the same time, they can be used to illustrate the biological adaptations of these ecologically important animals within their environments. The structure of the sand dollar’s shell is investigated using modern as well as established imaging techniques such as x-ray micro-computed tomography (μCT), scanning electron microscopy and various optical imaging techniques. 3D models generated by μCT scans are the basis for Finite Element Analysis of the sand dollar’s shell to identify possible structural principles and to analyse their structural behaviour. The gained insights of the sand dollar’s mechanical properties can then be used for improving the state-of-the-art techniques of engineering sciences and architectural design.


Zoomorphology | 2018

Morphology and porosity of the spines of the sea urchin Heterocentrotus mamillatus and their implications on the mechanical performance

Christoph Lauer; Tobias B. Grun; Isabel Zutterkirch; Raouf Jemmali; James H. Nebelsick; Klaus G. Nickel

Spines of the slate pencil sea urchin Heterocentrotus mamillatus Linnaeus, 1758, are in focus of biomimetic research as they feature a “graceful” failure behaviour under uniaxial compression dissipating energy and resisting high loads even after high strain. This study elucidates and quantifies the organization of calcitic trabeculae and pores in large primary spines of the slate pencil urchin H. mamillatus by image analysis from scanning electron microscopy, X-ray micro-computed tomography (µCT) and gravimetry. This study delivers a detailed distribution of porosities within the whole spine and shows that parts of the spines have a much higher porosity then hitherto thought. The central part (medulla) of the high-magnesium calcitic stereom of H. mamillatus spines has a porosity range of 75% to nearly 90%. From this innermost structure, more than 200 radially aligned, but often sinuous trabeculae extend to the spine rim. The structure of this complicated meshwork (radiating layer) is best seen in basal cross sections and was confirmed by µCT scans. The radiating layer has a porosity range from 40–70% and is irregularly separated by the dense growth layers (15–35% porosity). Growth layers were classified in proximal and distal growth layers with numbers ranging within a single animal between 3–14 and 2–7, respectively. These growth layers are characteristic for H. mamillatus spines and play a major role in their remarkable mechanical properties. The porosity of the spine increases from base to tip. Biological and mechanical implications of the variations are discussed.


PALAIOS | 2017

RECOGNIZING TRACES OF SNAIL PREDATION ON THE CARIBBEAN SAND DOLLAR LEODIA SEXIESPERFORATA

Tobias B. Grun

Abstract: Cassid gastropods are well-known drilling predators of a whole suite of echinoids which are common in both Recent and fossil environments. In many cases, the identification of cassids as possible predators is based on drill hole morphology only. A detailed study of drill hole characteristics is thus imperative for predator recognition and provided here by a thorough descriptive and statistical analysis. Fifty drill holes in the sand dollar Leodia sexiesperforata produced by the predatory gastropod Cassis tuberosa are analyzed for recognizable characters and compared to 174 drill holes in 289 denuded and empty tests from San Salvador, the Bahamas. The drill holes in dead tests are identical to the freshly drilled holes. Drill holes show subcircular to elliptical outlines with irregular margins and can feature notches produced by the predator. The cross-sectional drill hole profile range from concave parabolic to sigmoidal. The collected tests reveal a drilling intensity of 59.5% with only three individuals (1.74%) featuring multiple drill holes. The high drilling intensity and the presence of almost exclusively single drill holes indicate a high drilling success rate for the cassid predator in Caribbean ecosystems. Although the results suggest size selectivity, taphonomic processes and handling effects of the predator might result in a weaker selectivity than that inferred directly from the investigated material. Cassis tuberosa drills predominantly into the oral side of the test (86.3%) particularly in the area below the internal organs (90.9%). Most drill holes occur in the anterior part of the sand dollars test (66.7%).


Acta Palaeontologica Polonica | 2015

Taphonomy of a Clypeasteroid Echinoid Using a New Quasimetric Approach

Tobias B. Grun; James H. Nebelsick

A new quasimetric approach is used to statistically analyze taphonomic data from a commonly occurring shallow water clypeasteroid echinoid in order to obtain metric equivalent measurements of taphonomic alteration on an interval-like scale. This technique takes the character condition as well as its proportion into account and translates the taphonomic alteration into data, which behave as interval scaled and thus allows for the use of parametric as well as non-parametric statistics. Tests of Echinocyamus pusillus from Giglio Island (Mediterranean Sea, Italy) were analyzed with respect to a suite of taphonomic features including abrasion of the test surface, tubercles, ambulacral and genital pore margins as well as, if present, the outline and cross section of predatory drillholes. The degree of fragmentation and encrustation was also determined. Taphonomic features were analyzed using a semi-quantitative approach with three degrees of test alteration including non-altered, moderately altered, and highly altered which were statistically analyzed using non-parametric statistics due to highly non-normal distributed data. Abrasion intensities vary among different surface characters, with exposed areas of the test showing higher abrasion intensities than sheltered areas. Fragmentation occurs in low frequencies (7%) and fractures in the tests are almost absent (1.7%). Encrustation rates by bryozoans and serpulids can cover up to 80% of the test surface, but vary strongly among individuals and sample sites. Encrustation is independent of test size and prolongs overall test survival by crossing plate boundaries. The presence of drillholes in decreasing test preservation potentials is discussed with respect to analytical parameters.


Royal Society Open Science | 2018

Structural design of the minute clypeasteroid echinoid Echinocyamus pusillus

Tobias B. Grun; James H. Nebelsick

The clypeasteroid echinoid skeleton is a multi-plated, light-weight shell construction produced by biomineralization processes. In shell constructions, joints between individual elements are considered as weak points, yet these echinoid skeletons show an extensive preservation potential in both Recent and fossil environments. The remarkable strength of the test is achieved by skeletal reinforcement structures and their constructional layouts. Micro-computed tomography and scanning electron microscopy are used for microstructural and volumetric analyses of the echinoids skeleton. It is shown that strengthening mechanisms act on different hierarchical levels from the overall shape of the skeleton to skeletal interlocking. The tight-fitting and interlocking plate joints lead to a shell considered to behave as a monolithic structure. The plates architecture features distinct regions interpreted as a significant load-transferring system. The internal support system follows the segmentation of the remaining skeleton, where sutural layout and stereom distribution are designed for effective load transfer. The structural analysis of the multi-plated, yet monolithic skeleton of Echinocyamus pusillus reveals new aspects of the micro-morphology and its structural relevance for the load-bearing behaviour. The analysed structural principles allow E. pusillus to be considered as a role model for the development of multi-element, light-weight shell constructions.


American Malacological Bulletin | 2017

Shell Fouling and Behavior of the Caribbean Predatory Gastropod Cassis tuberosa

Tobias B. Grun; James H. Nebelsick

Abstract: The gastropod Cassis tuberosa (Linnaeus, 1758) usually lives in and on soft sediments and sea grass meadows. This carnivorous snail is primarily a semi-epifaunal and nocturnal hunter that, during daytime, rests burrowed in sediments. Around the Bahamian island of San Salvador, C. tuberosa has extended its behavior from nocturnal to metaturnal; feeding both night and day. This modification also involves further changes in behavior as an individual was observed resting epifaunally between rocks during the day even though this substrate was surrounded by soft bottoms. Epifaunal Cassis specimens are entirely encrusted primarily by coralline algae, but also by various green algae accompanied by vagile snails and crabs. The high degree of encrustation suggests that these snails do not remain burrowed for long periods of time. Cassis has thus extended its resting behavior from a semi-endofaunal to an epifaunal mode of life. The fouled shells also function as mobile benthic substrates for various organisms.


PLOS ONE | 2018

Structural design of the echinoid’s trabecular system

Tobias B. Grun; James H. Nebelsick

The multi-plated skeleton of echinoids is made of the stereom, a light-weight construction which resembles a micro-beam framework. Although the two-dimensional design of the stereom has been studied, its spatial architecture is only little known. It is, however, imperative to understand the spatial architecture of the trabecular system in order to interpret its structural principles of this load-bearing construction. The echinoid’s trabecular system is thus analyzed in-depth with respect to eight topological descriptors. The echinoid’s plates are divided into two regions, the center of which consists of an unordered stereom, and the margin which consists of an ordered stereom. The eight trabecular descriptors indicate that the basal topology of the two plate regions are similar. The trabecular system predominantly consists of short and stocky trabeculae that show little tortuosity. The majority of trabeculae intersect in a 3N configuration, where three trabeculae intersect in one common node. Trabeculae in the 3N configuration intersect in an angle of around 120° resulting in a planar and triangular motif. These planar elements, when arranged in an angular off-set, can resist multi-dimensional loads. Results also show that the trabecular orientation perpendicular to the plate’s surface is at an angle of 60°. The trabecular orientation in the plate’s horizontal plane is directional. Both trabecular orientations reflect a construction which is capable of resisting applied loads and can distribute these loads over the entire skeleton. The spatial architecture of the echinoid’s trabecular system is thus considered to be a performative light-weight and load-bearing system.


Journal of the Royal Society Interface | 2018

Structural stress response of segmented natural shells: a numerical case study on the clypeasteroid echinoid Echinocyamus pusillus

Tobias B. Grun; Malte von Scheven; Manfred Bischoff; James H. Nebelsick

The skeleton of Echinocyamus pusillus is considered as an exceptional model organism for structural strength and skeletal integrity within the echinoids as demonstrated by the absence of supportive collagenous fibres between single plates and the high preservation potential of their skeletons. The structural principles behind this remarkably stable, multi-plated, light-weight construction remain hardly explored. In this study, high-resolution X-ray micro-computed tomography, finite-element analysis and physical crushing tests are used to examine the structural mechanisms of this echinoids skeleton. The virtual model of E. pusillus shows that the material is heterogeneously distributed with high material accumulations in the internal buttress system and at the plate boundaries. Finite-element analysis indicates that the heterogeneous material distribution has no effect on the skeletons strength. This numerical approach also demonstrates that the internal buttress system is of high significance for the overall skeletal stability of this flattened echinoid. Results of the finite-element analyses with respect to the buttress importance were evaluated by physical crushing tests. These uniaxial compression experiments support the results of the simulation analysis. Additionally, the crushing tests demonstrate that organic tissues do not significantly contribute to the skeletal stability. The strength of the echinoid shell, hence, predominantly relies on the structural design.

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Achim Menges

University of Stuttgart

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