Holger Preuschoft

Biology of the sauropod dinosaurs: the evolution of gigantism

The herbivorous sauropod dinosaurs of the Jurassic and Cretaceous periods were the largest terrestrial animals ever, surpassing the largest herbivorous mammals by an order of magnitude in body mass. Several evolutionary lineages among Sauropoda produced giants with body masses in excess of 50 metric tonnes by conservative estimates. With body mass increase driven by the selective advantages of large body size, animal lineages will increase in body size until they reach the limit determined by the interplay of bauplan, biology, and resource availability. There is no evidence, however, that resource availability and global physicochemical parameters were different enough in the Mesozoic to have led to sauropod gigantism.

Mechanisms for the acquisition of habitual bipedality: are there biomechanical reasons for the acquisition of upright bipedal posture?

Morphology and biomechanics are linked by causal morphogenesis (‘Wolffs law’) and the interplay of mutations and selection (Darwins ‘survival of the fittest’). Thus shape‐based selective pressures can be determined. In both cases we need to know which biomechanical factors lead to skeletal adaptation, and which ones exert selective pressures on body shape. Each bone must be able to sustain the greatest regularly occurring loads. Smaller loads are unlikely to lead to adaptation of morphology. The highest loads occur primarily in posture and locomotion, simply because of the effect of body weight (or its multiple). In the skull, however, it is biting and chewing that result in the greatest loads. Body shape adapted for an arboreal lifestyle also smooths the way towards bipedality. Hindlimb dominance, length of the limbs in relation to the axial skeleton, grasping hands and feet, mass distribution (especially of the limb segments), thoracic shape, rib curvatures, and the position of the centre of gravity are the adaptations to arboreality that also pre‐adapt for bipedality. Five divergent locomotor/morphological types have evolved from this base: arm‐swinging in gibbons, forelimb‐dominated slow climbing in orang‐utans, quadrupedalism/climbing in the African apes, an unknown mix of climbing and bipedal walking in australopithecines, and the remarkably endurant bipedal walking of humans. All other apes are also facultative bipeds, but it is the biomechanical characteristics of bipedalism in orang‐utans, the most arboreal great ape, which is closest to that in humans. If not evolutionary accident, what selective factor can explain why two forms adopted bipedality? Most authors tend to connect bipedal locomotion with some aspect of progressively increasing distance between trees because of climatic changes. More precise factors, in accordance with biomechanical requirements, include stone‐throwing, thermoregulation or wading in shallow water. Once bipedality has been acquired, development of typical human morphology can readily be explained as adaptations for energy saving over long distances. A paper in this volume shows that load‐carrying ability was enhanced from australopithecines to Homo ergaster (early African H. erectus), supporting an earlier proposition that load‐carrying was an essential factor in human evolution.

Stress-Strength Relationships in the Mandibles of Hominoids

No matter how a primate acquires its food and what sorts of things it eats, mastication is an important step in food processing. According to Crompton and Hiiemae (1969), Hiiemae (1978, this volume), Hiiemae and Kay (1973), Kay and Hiiemae (1974), Beyron (1964) and Ahlgren (1966), chewing is done in all primates (so far investigated) in largely the same fashion. In a cyclic movement, the mandible is lowered (opening stroke), adducted (closing stroke), and finally moved in the power stroke upwards and inwards with the lower teeth exerting compressive and shearing forces on the food particles pressed against the upper teeth. This is done on one side only, called the biting side.

Funktionsanpassungen in Form und Struktur an Haifischzähnen

An der Oberflache von Selachierzahnen befindet sich eine dem Schmelz der Saugetiere analoge Schicht, die von Reif erstmals eingehend elektronen-rastermikroskopisch untersucht worden ist. Die mechanische Widerstandsfahigkeit dieser 0,2–0,9 mm dicken Schicht ist groser als diejenige des Dentins.SummaryThe surface of selachian teeth is covered by a 0.2–0.9 mm layer which is analogous to the enamel in mammals. The first detailed study on this material with the aid of a scanning electron microscope was made by Reif (1973b).The mechanical resistance of this tissue is greater than that of dentine. Various forms of “enamel-like tissue” do occur. They obviously are correlated with the shape of a tooth and the stresses to which it may be subject: The “single-crystallite enamel” covers the crushing teeth, it is apparently resistant against compressive stresses. The “parallel-fibred enamel” of fangs and cutting teeth is resistant to tensile stresses. Underneath it, there is a “fibrous enamel”, the fibres of which are randomly orientated in space. This tissue seems to be resistant against compression. Fangs as well as cutting teeth are covered by a “shiny layer” which excludes the occurrence of fissures in the “parallel fibred enamel”.The “single-crystallite enamel”-caps on crushing teeth can be considered as “shell-constructions” in a mechanical sence. Their resistance often is increased by a surface relief. The distribution of stresses within the “shell” and the structure of the “enamel” are discussed in detail. The shapes of the elements seem to be optimally adapted to the stresses that may occur.Fangs and cutting teeth are in a mechanical sence triangular consoles. The calculation of the stresses which occur under a number of external forces shows that the real shapes are normally bodies of uniform strength against accurately defined loads.The points or areas of application as well as the directions of the latter correspond to special shapes. In view of the few informations available about biting behaviour in sharks, the considered loads seem to be quite reasonable representations of the forces to which a sharks teeth are exposed.The positions and orientation of the enamel-fibres on fangs and cutting teeth are in perfect accordance with the pattern of trajectories in a homogeneous tooth model under stresses equal to those evoked by the above-mentioned loads.The fibre pattern is the clearer developed, the greater the stresses at a special point are.Some particular trajectorial patterns, which would appear under certain conditions, are not realised as far as we know today. We assume, that these theoretically possible variations of loading do not occur in the investigated forms, because the animals do not bite this way.According to our observations, in teeth as well as in primitive vertebrates, the same close relationship between shape and function seems to exist, as has been found repeatedly in the postcranial skeleton of mammals. In view of the way of exchange of shark teeth it can only be a case of “preadaptation”.ZusammenfassungAn der Oberfläche von Selachierzähnen befindet sich eine dem Schmelz der Säugetiere analoge Schicht, die von Reif erstmals eingehend elektronen-rastermikroskopisch untersucht worden ist. Die mechanische Widerstandsfähigkeit dieser 0,2–0,9 mm dicken Schicht ist größer als diejenige des Dentins.Je nach der Gestalt und der dadurch bestimmten Beanspruchung der Zähne sind verschiedene Formen von “Schmelz” ausgebildet: der allem Anschein nach sehr druckfeste “Einzelkristallitschmelz” der Quetschzähne und der zugfeste “parallelfaserige Schmelz” der Fang- und Schneidezähne. Vielfach kommt daneben noch ein “wirrfaseriger Schmelz” vor, der unter Umständen Zugspannungen aufzunehmen scheint. Fang- und Schneidezähne sind von einer sehr dünnen “Glanzschicht” bedeckt, welche Rißbildung verhindert.Die aus “Einzelkristalliten” aufgebauten Schmelzkappen der Quetschzähne können als flächig unterstützte Schalentragwerke im mechanischen Sinne interpretiert werden. Ihre Festigkeit wird oft durch ein Oberflächenrelief erhöht. Die Lastabtragung innerhalb der Schale und die Feinstruktur des “Schmelzes” werden im Detail diskutiert. Die Gestalt der Elemente scheint jeweils an die mechanische Beanspruchung optimal angepaßt zu sein.Die Fang- und Schneidezähne stellen im mechanischen Sinne dreieckige Konsolen dar. Eine Berechnung der Spannungen in derartigen Konsolen zeigt, daß die tatsächlich vorgefundenen Formen in der Regel “Körper gleicher Festigkeit” gegenüber genau definierbaren Beanspruchungen darstellen. Diese Beanspruchungen sind oft einfache Kombinationen aus Flächen- bzw. Punktlasten. Diese Last-Kombinationen erscheinen vom biologischen Standpunkt aus, bei Berücksichtigung des Wenigen, was wir über das Verhalten von Haien wissen, sinnvoll und wahrscheinlich.Die Anordnung der “Schmelzfasern” an der Oberfläche von Fang- oder Schneidezähnen entspricht dem Verlauf von Spannungs-Trajektorien in einem homogenen Zahnmodell unter Beanspruchungen, wie sie von den obengenannten Lasten hervorgerufen werden. Die Fasermuster sind um so deutlicher ausgeprägt, je höher die Spannungen im jeweiligen Teil des Zahnes sind.Manche der bei bestimmten Belastungen zu erwartenden Trajektorienmuster sind in Haifischzähnen nach unseren bisherigen Kenntnissen nicht in Form von Fasermustern realisiert. Es wird unterstellt, daß diese theoretisch möglichen Belastungen bei den untersuchten Tieren während des Lebens nicht auftreten.Aus den Befunden wird gefolgert, daß hier, d.h. auch bei Zähnen und auch bei primitiven Vertebraten der gleiche enge Zusammenhang zwischen Form und Funktion besteht, wie er am postcranialen Skelet von Säugetieren mehrfach nachgewiesen worden its. Es kann sich angesichts der Funktionsweise von Haifischzähnen nur um eine “Präadaptation” handeln.

Ontogeny of the Knee Joint in Humans, Great Apes and Fossil Hominids: Pelvi-Femoral Relationships during Postnatal Growth in Humans

Results of a study of the femoral bicondylar angle in adult and juvenile humans and great apes are presented. These results raise the question of whether or not the measurement reference of this angle is valid. This is because humans and great apes have a very different growth process of the distal epiphyseal suture of the femur during the period between birth and adulthood. The approximately 3 million years old juvenile femoral diaphyses attributed to Australopithecus afarensis (AL 333-110 and AL 333-111) were also studied. These specimens show an insertion of the diaphysis into the epiphysis of the simplified type typical of modern humans. This region is more convoluted in nonhuman anthropoids. Pelvifemoral interrelations are investigated through both longitudinal and cross-sectional radiographic studies of 23 human children. Growth changes in bicondylar and collo-diaphyseal angles, total femoral and femoral neck lengths, and interacetabular distance are correlated with age and to each other. These results are used to demonstrate the distinctive features of the Australopithecus afarensis fossil, AL 288-1.

Postcranial Skeleton of a Macaque Trained for Bipedal Standing and Walking and Implications for Functional Adaptation

The postcranial skeleton of a Japanese macaque that had been trained for bipedalism over an 11-year period was studied. Considerable modifications in the hindlimb bones caused by bipedal postural and locomotor behaviour were observed. Changes occurred in joint morphology, articular dimensions and shape-dependent strength of long bones, reflecting the causal relationship between function and morphology. However, the conditions under which the modifications are developed are somewhat different from those in humans, as the monkeys bipedalism is distinct from that of humans. The modifications seem to result from a compromise between functional requirements and the genetically determined anatomy of the essentially quadrupedal monkey.

Biomechanical investigations on the skulls of reptiles and mammals

The skulls of reptiles and mammals can be loaded mechanically in three ways: the weight of the head acting downward, perhaps reinforced by a prey or bunch of food lifted from the ground or water surface; by forces acting in the plane of the tooth row, created by movements of the prey in relation to the head or by a movement of the head in relation to a fixed food object; and by the adduction of the mandible, which leads to reaction forces in the skull. While the former two evoke stress patterns comparable to that in a beam which is supported at its rear end (by the occipital condyle(s) and the neck muscles), the latter evoke stress patterns comparable to a beam supported at both ends. Its anterior bearing are the teeth which transmit a reaction force from the seized prey, the adductor muscles of the mandible move the intermediate part of the skull downward, and the posterior bearing is provided by the mandibular joint.Three-dimensional FEM-analysis of the flow of stresses within solid, homogeneous bodies under loads like those described above have been made. As a result, the stress flows have been found to correspond closely to the arrangements of bony material in the akinetic skulls of Crocodiles, Lacertilia, Sphenodon. Except crocodiles and chelonians, reptilian skulls often show large gaps between the load-bearing plates and rods. These gaps correspond to little stressed areas between the stress-bearing parts. One of the stress-bearing rods is the small braincase. In long, slender jaws like those in crocodiles the stresses are concentrated on the periphery, with more or less stress-free areas in the center of the cross sections.In many mammals (shrews, primates includingHomo), however, the very large bony nasal capsule and braincase lead to a distribution of the forces over large areas like in thin-walled shell structures, which are strong enough to sustain the existing forces, without reinforcing superstructures. Even the zygomatic arch can be dispensible.The decisive a priori factors which determine the development of either a rod- or a shell-like structure in a FEM model are1st the relative shape and length of the toothrow and its position in relation to the posterior part of the skull, especially the braincase, and 2nd the size of the nasal capsule and the braincase.We conclude that the exact form of the skull in both classes of animals is determined by 1st the shape and length of the jaws and 2nd by the space requirements of the olfactory and the optical sense organs, and the braincase. The second factor is an expression of the overall evolutionary level. The literature contains plausible biological arguments to explain the high selective influence of lifestyle characteristics on the first factor. These arguments usually cover also the position of the eye openings, the nasal opening and the relative height and length of the whole skull. If these factors are given, the exact morphology of the bony structure turns out to correspond completely to the pattern of stresses, and no other reasons behind skull shape must be searched.The arrangement of the muscles seems to follow in all cases the principle to distribute the force created at the origines on a large surface or on many individual bony elements.

Locomotion in Nocturnal Prosimians

Napier and Napier (1967), whose categorization has often been criticized and sometimes modified, but never replaced, divided the prosimians into the following locomotor categories: slow climbing (and bridging), branch running and walking, vertical clinging and leaping.

Size Dependence in Prosimian Locomotion and Its Implications for the Distribution of Body Mass

The mechanical requirements for arboreal life are reviewed and the constraints which these requirements impose on the body of a prosimian are defined. The mechanical necessities can be fulfilled only by animals which possess the appropriate morphological characters. It is incorrect to refer to these morphological traits directly as ‘adaptations’. Instead their a priori existence must be considered as the precondition for the acquisition of a certain life-style. Once such a life-style has been acquired, a strong selective pressure acts towards a further refinement of such ‘adaptations’ or ‘pre-adaptations’. Postcranial morphology must be seen in a context of following natural laws and is strictly related to the mechanics of posture and locomotion. The traits emphasised and explained here are body proportions – specifically the relative lengths of body segments and the distribution of (muscle) mass on these segments.

Biomimetic robotics should be based on functional morphology

Due to technological improvements made during the last decade, bipedal robots today present a surprisingly high level of humanoid skill. Autonomy, with respect to the processing of information, is realized to a relatively high degree. What is mainly lacking in robotics, moving from purely anthropomorphic robots to ‘anthropofunctional’ machines, is energetic autonomy. In a previously published analysis, we showed that closer attention to the functional morphology of human walking could give robotic engineers the experiences of an at least 6 Myr beta test period on minimization of power requirements for biped locomotion. From our point of view, there are two main features that facilitate sustained walking in modern humans. The first main feature is the existence of ‘energetically optimal velocities’ provided by the systematic use of various resonance mechanisms: (a) suspended pendula (involving arms as well as legs in the swing phase of the gait cycle) and matching of the pendular length of the upper and lower limbs; (b) inverted pendula (involving the legs in the stance phase), driven by torsional springs around the ankle joints; and (c) torsional springs in the trunk. The second main feature is compensation for undesirable torques induced by the inertial properties of the swinging extremities: (a) mass distribution in the trunk characterized by maximized mass moments of inertia; (b) lever arms of joint forces at the hip and shoulder, which are inversely proportional to their amplitude; and (c) twisting of the trunk, especially torsion. Our qualitative conclusions are three‐fold. (1) Human walking is an interplay between masses, gravity and elasticity, which is modulated by musculature. Rigid body mechanics is insufficient to describe human walking. Thus anthropomorphic robots completely following the rules of rigid body mechanics cannot be functionally humanoid. (2) Humans are vertebrates. Thus, anthropomorphic robots that do not use the trunk for purposes of motion are not truly humanoid. (3) The occurrence of a waist, especially characteristic of humans, implies the existence of rotations between the upper trunk (head, neck, pectoral girdle and thorax) and the lower trunk (pelvic girdle) via an elastic joint (spine, paravertebral and abdominal musculature). A torsional twist around longitudinal axes seems to be the most important.