Torsion and Bending in the Neck and Tail of Sauropod Dinosaurs and the Function of Cervical Ribs: Insights from Functional Morphology and Biomechanics

The long necks of sauropods have been subject to many studies regarding their posture and flexibility. Length of the neck varies among groups. Here, we investigate neck posture and morphology in several clades from a mechanical viewpoint. Emphasis is put on comparing sauropod necks and tails with structures in living archosaurs and mammals. Differences in the use made of necks and tails lead to clear-cut differences in the mechanical loads occurring in the same models. Ways of sustaining loads are identified by theoretical considerations. If the observed skeletal structures are suited to resist the estimated loading in a particular posture, this concordance is taken as an argument that this posture or movement was of importance during the life of the individual. Apart from the often-discussed bending in side view, we analyze the often overlooked torsion. Because torsional stresses in a homogenous element concentrate near the periphery, a cylindrical cross section gives greatest strength, and the direction of forces is oblique. In a vertebrate neck, during e.g. shaking the head and twisting the neck, oblique muscles, like the mm. scaleni, if activated unilaterally initiate movement, counterbalance the torsional moments and keep the joints between neck vertebrae in equilibrium. If activated bilaterally, these muscles keep the neck balanced in an energy-saving upright posture. The tendons of the mm. scaleni may have ossified as cervical ribs The long cervical ribs in brachiosaurids and mamenchisaurids seem to have limited flexibility, whereas the shorter cervical ribs in Diplodocidae allowed free movement. The tails of sauropods do not show pronounced adaptation to torsion, and seem to have been carried more or less in a horizontal, extended posture. In this respect, sauropod tails resemble the necks of herbivorous cursorial mammals. These analyses provide an improved understanding of neck use that will be extended to other sauropods in subsequent studies.     

The enthesis of the elbow-joint capsule of the dog humerus

The enthesis of the elbow-joint capsule in the dog is described histologically in relation to the specific mechanical forces that operate in different regions along its line of attachment. Special attention is given to the collagen fibre-bone interface in those parts of the capsule that are highly affected by mechanical stress. The histological features of the enthesis are heterogeneous along the entire circumference of the attachment site. Three types of collagen fibre-bone interconnections can be distinguished: (1) periosteal insertion: attachment to the periosteum of the humerus; (2) bony insertion: attachment directly to peripheral osteons; (3) fibrocartilaginous insertion: attachment to the bone via fibrocartilage. The periosteal insertion covers the greatest part of the joint capsule attachment line, along the peripheral borders of the radial and olecranon fossae. In contrast, bony insertions and fibrocartilaginous insertions are focally arranged: bony insertions in the caudoproximal aspect of the olecranon fossa, related to nutrient foramina; fibrocartilaginous insertions in combination with the attachment of distinct ligaments. This distribution reflects a strict relation between the type of enthesis and the biomechanical stress at the attachment site. The periosteal insertion type is predominant in entheses adjacent to pouches of a loose joint capsule -- i.e., regions less dependent on the high tensile strength of collagen fibres. Fibrocartilaginous insertions characterise areas of the joint capsule which are subjected to high biomechanical traction during joint movement. Both structurally and functionally, the entheses of the fibrous layer of the joint capsule are similar to those of tendons and ligaments.     

Do ribs actually have a bare area? A new analysis

Recognition of macroscopic rib pathology requires an in-depth understanding of anatomy, especially of the attachment of muscle tendons and aponeuroses. Distinguishing periosteal reaction from residual aponeurotic tissues and the rugosity associated with muscle attachments, requires knowledge of these structures. The ribs of twenty cadavers were examined to establish the distribution of muscle attachments and aponeuroses, and their variations. A unique observation was that the entire rib surface is covered by tendon attachments and aponeuroses, without evidence of bare areas that are so prominent in other parts of the skeleton. Discrepancies between rugose regions and the extent of tendon attachments were occasionally noted, with the tendons or aponeuroses extending beyond the areas of attachments of the muscle fibers. Variable dessication of aponeurotic tissues can compromise appearance of normal bone, and may be responsible for past overdiagnosis of periosteal reaction.     

LYSTROSAURUS MURRAYI (THERAPSIDA, DICYNODONTIA): BONE HISTOLOGY, GROWTH AND LIFESTYLE ADAPTATIONS

Abstract:  Examination of the bone microstructure of Lystrosaurus murrayi from India and South Africa reveals a predominance of fibrolamellar bone tissue, which suggests rapid periosteal osteogenesis and an overall fast growth. Four distinct ontogenetic stages have been identified based on tissue type, organization of the primary osteons, incidence of growth rings, secondary reconstruction and endosteal bone deposition. An indeterminate growth strategy is proposed for Lystrosaurus . Inter-elemental histovariability suggests differential growth rate of the skeletal elements within the same individual, and among different individuals. The high cortical thickness of the dorsal ribs, an extensive secondary reconstruction in the cortical region of different skeletal elements that resulted in erosionally enlarged channels from the perimedullary to the midcortical region, and trabecular infilling of the medullary region even in the diaphyseal sections of the limb bones suggest at least a semi-aquatic lifestyle for L. murrayi .     

Unusual histology and morphology of the ribs of mosasaurs (Squamata)

We report the presence of two previously unrecognized features in the dorsal ribs of mosasaurs: first, the presence of extremely dense, pervasive extrinsic fibres (anchoring soft tissue to bone, sometimes called Sharpey's fibres); and second, high intraspecific variation in costal bone compactness. Extensive extrinsic fibres are developed in the dorsal ribs of the mosasaurs Tylosaurus proriger and Eonatator sternbergi. The dorsal ribs of these mosasaurs are also characterized by a longitudinally ridged texture that almost completely covers the bone. Pervasive extrinsic fibres and ridged textures are absent in the mosasaur Selmasaurus russelli as well as the dorsal ribs of extant semi‐aquatic reptiles (e.g. crocodyliforms) and mosasaurs' close extant relatives and analogues (e.g. snakes and varanids). Similar ridged textures characterize the dorsal ribs of several other mosasaur taxa but are developed to a lesser extent (e.g. Mosasaurus, Clidastes, Platecarpus and Ectenosaurus), but in no other taxa have pervasive extrinsic fibres been reported. We interpret these osteohistological features in T. proriger and E. sternbergi as evidence of tendinous attachment of extensive and highly differentiated axial musculature capable of producing great stresses, most likely related to stabilization of the trunk relative to contralateral movements of the tail during carangiform locomotion. We also report the compactness indices (percentage of space occupied by bone rather than cavities) for these large mosasaur ribs, which are much higher than previously reported. This suggests high intraspecific variation in bone compactness that complicates its use in reconstructing mosasaur palaeoecology.     

Evolution and functional significance of tendon ossification in woodcreepers (Aves: Passeriformes: Dendrocolaptinae)

The woodcreepers, a clade of scansorial, neotropical birds, are distinctive among passerines in having extensive tendon ossification. Dissection of 42 of the 50 species indicates that such ossification in the hindlimb is limited almost entirely to tendons of insertion of the crural muscles. Most crural muscles have ossifications, and in all but one the ossified tendons are long and thin. Preliminary dissection revealed a similar pattern among ossified wing tendons. Phylogenetic analysis suggests that extensive tendon ossification is a synapomorphy of the woodcreepers. The species of Dendrocincla, which form a clade, show secondary reduction of ossification in some tendons, which may be correlated with increased intraspecific variation and with an expansion of foraging habits and postures to include nonscansorial behaviors. In contrast, the larger woodcreepers, other than Drymornis bridgesii and Nasica longirostris, form a clade with virtually no loss in ossification or evidence of intraspecific variation, even in large series of two species. Phylogenetic losses do not occur for the primary flexor of the ankle (M. tibialis cranialis), whereas two extensors (Mm. fibularis longus and gastrocnemius pars lateralis) show a complex pattern of derivation and loss. Previous biomechanical studies demonstrate that ossification increases the stiffness of tendons, making them stretch less under a given force. These structural and phylogenetic patterns are consistent with the view that hindlimb tendon ossification in woodcreepers is an adaptation to resist increased forces that act to extend the limb during vertical climbing. © 1993 Wiley-Liss, Inc.     

Three-dimensional ultrastructure of human tendons.

The three-dimensional ultrastructure of human tendons has been studied. Epitenon and peritenon consist of a dense network of longitudinal, oblique and transversal collagen fibrils crossing the tendon fibres. The internal structure of tendon fibres is also complex. The collagen fibrils are oriented not only longitudinally but also transversely and horizontally. The longitudinal fibrils do not run only parallel but also cross each other forming spirals (plaits). These fibril bundles are bound together by a three-dimensional collagen fibril network of endotenon. In the myotendinous junction the surface of the muscle cells form processes. A network of tendineal collagen fibrils fills the recesses between the muscle cell processes penetrating the basement membrane of these processes. This complex ultrastructure of human tendons most likely offers a good buffer system against longitudinal, transversal, horizontal as well as rotational forces during movement and activity.     

Thermal stabilization of collagen in skin and decalcified bone

The state of collagen molecules in the fibres of tail tendon, skin and demineralized bone has been investigated in situ using differential scanning calorimetry (DSC). Hydroxyproline analysis and tissue digestion with bacterial collagenase and trypsin were used to confirm that the common cause of all the DSC endotherms was collagen denaturation. This occurred within a narrow temperature range in tendons, but over a wide temperature range in demineralized bone and old skin and demonstrated that in tendon and demineralized bone at least the same type I collagen molecule exists in different thermal states. Hypothesizing that this might be caused by different degrees of confinement within the fibre lattice, experiments were performed to measure the effect of changing the lattice dimensions by extracting the collagen into dilute solution with pepsin, swelling the lattice in acetic acid, and contracting the lattice by dehydration. A theoretical analysis was undertaken to predict the effect of dehydration. Results were consistent with the hypothesis, demonstrating that collagen molecules within the natural fibres of bone and old skin are located at different intermolecular spacings, revealing differences between molecules in the magnitude of either the attractive or repulsive forces controlling their separation. One potential cause of such variation is known differences in covalent cross-linking.     

Prenatal ossification as an indicator of exposure to toxic agents

Following exposure to bromodeoxyuridine (BUDR), acetazolamide (ACZM), trypan blue (TRBL), cortisone (CORT), or diphenylhydantoin (DPH), alizarin-stained, cleared fetuses were examined at 18 days postcoitus for unossified cervical vertebral centra; number of ossified caudal vertebrae; number of ribs; and ossification of sternebrae, metatarsals, metacarpals, and phalangeal rows. At all teratogenic doses, in no vehicle-treated groups, and rarely in lower-dose groups, there were significant increases in frequency of unossified cervical centra, the first vertebra (C1) being most often affected, and C7 least often affected. In the high-dose CORT group, there was a significant correlation between unossified C1 and cleft palate. No association between abnormality and reduced ossification of cervical vertebrae was seen in other series examined, nor was there any correlation between litter size and abnormality. With minor complications, the number of ossified caudal vertebrae was significantly reduced after exposure at teratogenic dose levels to all compounds except DPH. Although caudal and cervical ossification were correlated with each other in those series examined, neither was correlated with abnormality. Frequency of 14 ribs was increased in BUDR, ACZM, and TRBL but not CORT or DPH. Other parameters were essentially unaffected. Significantly increased frequency of abnormality, when contrasted with untreated or vehicle-treated groups, was seen at high-dose levels in all but DPH treatments, and mortality was increased in ACZM D9-11, TRBL, and CORT. These studies show that reduced ossification of cervical centra is an excellent indicator of prenatal exposure to noxious substances, and caudal vertebrae appear to be useful as well. Increased frequency of 14 ribs occurred for all strong teratogens utilized if they were administered on day 7 or day 8 postcoitus.     

Actin stress fibres and cell-cell adhesion molecules in tendons: organisation in vivo and response to mechanical loading of tendon cells in vitro.

Tendons consist of parallel longitudinal rows of cells separated by collagen fibres. The cells are in intimate contact longitudinally within rows, and laterally via sheet-like lateral cell processes between rows. At points of contact, they are linked by gap junctions. Since tendons stretch under load, such cell contacts require protection. Here we describe the organisation of the actin cytoskeleton and actin-based cell-cell interactions in vivo and examine the effect of cyclic tensile loading on tendon cells in vitro. Cells within longitudinal rows contained short longitudinally running actin stress fibres. Each fibre was aligned with similar fibres in the cells longitudinally on either side, and fibres appeared to be linked via adherens junctions. Overall, these formed long oriented rows of stress fibres running along the rows of tendon cells. In culture, junctional components n-cadherin and vinculin and the stress fibre component tropomyosin increased in strained cultures, whereas actin levels remained constant. These results suggest that: (1) cells are linked via actin-associated adherens junctions along the line of principal strain; and (2) under load, cells appear to attach themselves more strongly together, and assemble more of their cytoplasmic actin into stress fibres with tropomyosin. Taken together, this suggests that cell-cell contacts are protected during stretch, and also that the stress fibres, which are contractile, may provide an active mechanism for recovery from stretch. In addition, stress fibres are ideally oriented to monitor tensile load and thus may be important in mechanotransduction and the generation of signals passed via the gap junction network.     

Prey capture in lizards: differences in jaw–neck–forelimb coordination

Fish body muscles are arranged along the vertebral column in three‐dimensional W‐shaped blocks, called myomeres. Each myomere is separated from its neighbours by a collagenous sheet, the myoseptum, and embedded in these myosepta and in positions that are conserved throughout gnathostome evolution are distinct tendons. Within teleosts these tendons often ossify. Ossification is usually intramembranous but cartilaginous structures within the tendons have also been reported. Ossified myoseptal tendons are homologous to intermuscular bones and appear only in teleosts. The phylogenetic signal of myoseptal tendon ossfication has not been tested previously, although the presence and morphology of intermuscular bones have been used to infer phylogenetic relationships. We sample over a broad phylogenetic range of teleost fishes to test for (1) the effects of phylogenetic history on the presence of intermuscular bones and (2) morphological correlations with the presence of intermuscular bones. Body shape and fin position as well as vertebral number and aspect ratio are characters that are likely to affect the distribution of stresses along myoseptal tendons, and are therefore good functional predictors of myoseptal tendon ossification. We use the summary information by Patterson & Johnson for a list of species with intermuscular bones and reanalyse the homology of intermuscular bones to myoseptal tendons. We find that there is a phylogenetic signal in the distribution of four out of six ossified tendons, but that after correcting for phylogenetic relationships there are still morphological predictors for the presence of all ossified tendons. © 2012 The Linnean Society of London, Biological Journal of the Linnean Society, 2012, 106 , 607–622.     

Chondroid bone and secondary cartilage contribute to apical dentary growth in juvenile Atlantic salmon

The microstructure and tissue composition of the dentary bone in Atlantic salmon salmo salar parr were examined using a variety of histological and whole‐mount techniques. Proximally, the dentary is composed of typical cellular lamellar bone with Sharpey's fibres extending dorsally, proximally and ventrally. Meckel's cartilage is located medially through the entire length of the dentary, and degrades distally resulting in a short transitional zone between hyaline cartilage and connective tissue. At the distal tip of the dentary, isogenic clusters of chondrocytes of periosteal origin were observed secreting small amounts of pericellular cartilage matrix within the bone matrix. These characteristics are highly indicative of secondary chondrogenesis, and suggest that the apical part of the dentary bone in Atlantic salmon does not grow via 'pure' intramembranous ossification, but rather via a modified mode of periosteal ossification involving secondary cartilage and chondroid bone. Furthermore, the unusual mode of gender‐related dentary growth (kype formation) in adult male Atlantic salmon could be the continuation of a general mode of salmonid apical dentary growth.     

The first evidence of osteomyelitis in a sauropod dinosaur

Osteomyelitis is reported for the first time in a sauropod dinosaur. The material (MCS‐PV 183) comes from the Anacleto Formation (Campanian, Late Cretaceous), at the Cinco Saltos locality, Río Negro Province, Argentina. The specimen consists of 16 mid and mid‐distal caudal vertebrae of a titanosaur sauropod. Evidence of bacterial infection is preserved in all of these vertebrae. The main anomalies are as follows: irregular ‘microbubbly’ texture of bone surfaces produced by periosteal reactive bone, abscesses on the rims of the anterior articular surfaces of two centra, numerous pits on centra anterior articulation surfaces, erosions on the anterior articulation of the vertebral centra, a vertical groove in posterior articular face of all the centra and disruption of the prezygapophysis and postzygapophysis (mainly the articular face) from the vertebra 19 and beyond. The last anomaly is increasingly pronounced in more distal elements of the series. Thin sections reveal that the anomalous cortical tissue is composed of avascular and highly fibrous bone matrix. The fibres of the bone matrix are organized into thick bundles oriented in different directions. Both morphological and histological abnormalities in the MCS‐PV 183 specimen are pathognomonic for osteomyelitis.     

Mechanical implications of pneumatic neck vertebrae in sauropod dinosaurs

The pre-sacral vertebrae of most sauropod dinosaurs were surrounded by interconnected, air-filled diverticula, penetrating into the bones and creating an intricate internal cavity system within the vertebrae. Computational finite-element models of two sauropod cervical vertebrae now demonstrate the mechanical reason for vertebral pneumaticity. The analyses show that the structure of the cervical vertebrae leads to an even distribution of all occurring stress fields along the vertebrae, concentrated mainly on their external surface and the vertebral laminae. The regions between vertebral laminae and the interior part of the vertebral body including thin bony struts and septa are mostly unloaded and pneumatic structures are positioned in these regions of minimal stress. The morphology of sauropod cervical vertebrae was influenced by strongly segmented axial neck muscles, which require only small attachment areas on each vertebra, and pneumatic epithelia that are able to resorb bone that is not mechanically loaded. The interaction of these soft tissues with the bony tissue of the vertebrae produced lightweight, air-filled vertebrae in which most stresses were borne by the external cortical bone. Cervical pneumaticity was therefore an important prerequisite for neck enlargement in sauropods. Thus, we expect that vertebral pneumaticity in other parts of the body to have a similar role in enabling gigantism.     

Tubular frameworks guiding orderly bone formation in the antler of the red deer (Cervus elaphus)

Deer antler is a bony tissue which re-grows every year after shedding. Growth speed and material properties of this tissue are truly remarkable, making it an interesting model for bone regeneration. Surprisingly, not much is known about the ultrastructure of the calcified tissues and the temporal sequence of their development during antler growth. We use a combination of imaging tools based on light and electron microscopy to characterize antler tissue at various stages of development. We observe that mineralized cartilage is first transformed into a bone framework with low degree of collagen fibril ordering at the micron level. This framework has a honeycomb-like appearance with the cylindrical pores oriented along the main antler axis. Later, this tissue is filled with primary osteons, whose collagen fibrils are mainly oriented along the pores, thus improving the antler's mechanical properties. This strongly suggests that to achieve very fast organ growth it is advantageous to have a longitudinal porous framework as an intermediate step in bone formation. The example of antler shows that geometric features of this framework are crucial, and a tubular geometry with a diameter in the order of hundred micrometers seems to be a good solution for fast framework-mediated bone formation.     

Antler development and coupled osteoporosis in the skeleton of red deer Cervus elaphus: expression dynamics for regulatory and effector genes

Antlers of deer display the fastest and most robust bone development in the animal kingdom. Deposition of the minerals in the cartilage preceding ossification is a specific feature of the developing antler. We have cloned 28 genes which are upregulated in the cartilaginous section (called mineralized cartilage) of the developing (“velvet”) antler of red deer stags, compared to their levels in the fetal cartilage. Fifteen of these genes were further characterized by their expression pattern along the tissue zones (i.e., antler mesenchyme, precartilage, cartilage, bone), and by in situ hybridization of the gene activities at the cellular level. Expression dynamics of genes col1A1, col1A2, col3A1, ibsp, mgp, sparc, runx2, and osteocalcin were monitored and compared in the ossified part of the velvet antler and in the skeleton (in ribs and vertebrae). Expression levels of these genes in the ossified part of the velvet antler exceeded the skeletal levels 10–30-fold or more. Gene expression and comparative sequence analyses of cDNAs and the cognate 5′ cis-regulatory regions in deer, cattle, and human suggested that the genes runx2 and osx have a master regulatory role. GC–MS metabolite analyses of glucose, phosphate, ethanolamine-phosphate, and hydroxyproline utilizations confirmed the high activity of mineralization genes in governing the flow of the minerals from the skeleton to the antler bone. Gene expression patterns and quantitative metabolite data for the robust bone development in the antler are discussed in an integrated manner. We also discuss the potential implication of our findings on the deer genes in human osteoporosis research.     

Size, structure and gender: lessons about fracture risk

The differences in age-related fracture risks among men and women must reflect gender differences in the relevant variables. We are concerned here with gender differences in structural variables that relate to the size and shape of bones. As children grow, their bones grow in diameter through periosteal modeling. Studies show that radial growth is driven by mechanical forces and is not just "genetically programmed". Moving bone mass farther from the center of the diaphysis makes it more effective in resisting bending and twisting forces, and disproportionately so in comparison to changes in bone mass. Gender differences in long bone structure appear to arise because the bone cells of males and females function in different hormonal environments which affect their responses to mechanical loading. In girls, bone formation on the metacarpal periosteal surface essentially stops at puberty, and is replaced by formation on the endosteal surface, reducing endosteal diameter until about age 20. Bone strength is 60% greater in male metacarpals than in those of females because bone is added periosteally in boys and endosteally in girls. At menopause endosteal resorption resumes, accompanied by slow periosteal apposition, weakening cortical structure. Similar phenomena occur in such critical regions as the femoral neck. Another fundamental gender difference in skeletal development is that whole body bone mineral content increases in linear proportion to lean body mass throughout skeletal maturation in boys, but in girls there is a distinct increase in the slope of this relationship at puberty, when estrogen rises. Frost's hypothesis is that this reflects an effect of estrogen on bone's mechanostat set point, and this is increasingly supported by data showing that estrogen and mechanical strain act through a common pathway in osteoblast-like cells. If Frost's hypothesis is correct, the mechanostat is set for maximal effect of mechanical loading on bone gain during the 2-3 years preceding menarche. During the childbearing years, the set point is at an intermediate level, and at menopause, it shifts again to place the skeleton into the metabolic equivalent of a disuse state. The most direct approach to resolving this problem would be to simulate the putative effect of estrogen on the set point itself.     

Advantages in the Use of Aldehyde Fuchsin with Van Gieson's Picro-Fuchsin Counterstaining for Differentiating Bone and Cartilage

Specimens of bone were fixed in 10% neutral phosphate-buffered formalin or in Bouin's fluid and decalcified in 10% formic acid buffered with 10% sodium citrate. Materials were embedded in paraffin and 4-5 μ sections attached to slides were oxidized with 0.5% KMnO₄, decolorized in 1% oxalic acid, stained with aldehyde fuchsin, and counter-stained with Van Gieson's picro-fuchsin. Sections were dehydrated, cleared and mounted in a synthetic resin. Microscopically, the differentiation between bone and cartilage was seen as red and purple respectively, with connective tissue red; muscle and erythrocytes, yellow; and elastic fibres purple. The areas occupied by bone, cartilage and erythrocytes could be compared, and also the depth to which cartilage extended into the ossified sites. The advantages of this staining combination are: good contrasts in colour, ease of applying the stain, and virtual self-differentiation of the staining solutions.     

Post natal development of the neck system in the chicken (Gallus domesticus)

The lengths of several neck muscles and tendons and the length, width, and height of the cervical vertebrae and some additional distances were measured in the chicken in six post-hatching ontogenetic stages and adults. Each vertebra is characterized by a unique combination of growth rates. All increase most in length. Cranial and caudal width as well as height decreases relative to length during ontogeny. When the long dorsal neck muscles are assumed to provide the support for the weight of the head and half of the weight of the neck, the neck system evidently develops according to McMahon's elastic similarity theory. The assumption is justified also because the weights of head and neck together appeared to scale as predicted by elastic similarity. Short neck muscles show negative and tendons positive allometric growth, and long neck muscles grow isometrically relative to neck length. This growth pattern of the muscles and tendons is a direct consequence of the geometric relations of the different growth rates of the vertebrae.     

Skeletal microstructure of Stenopterygius quadriscissus (Reptilia,Ichthyosauria) from the Posidonienschiefer (Posidonia Shale,Lower Jurassic) of Germany

Ichthyosaurians (Ichthyosauria) are a major clade of secondarily aquatic marine tetrapods that occupied several major predatory niches during the Mesozoic Era. Multiple lines of evidence including isotopic, body shape and swimming modality analyses suggest they exhibited elevated growth and metabolic rates, and body temperatures. However, applications of osteohistological methods to test hypotheses regarding their physiology are few. Previous studies focused on the humeri, vertebrae and ribs from a small number of taxa. Here, we use osteohistological methods to describe the bone microstructure of over 30 cranial and post‐cranial elements from a nearly complete, articulated individual of Stenopterygius quadriscissus from the Posidonienschiefer Formation (Posidonia Shale, Lower Jurassic) of Germany. The specimen shows highly vascularized primary bone and spongious secondary bone in its limbs, suggesting an overall shift to a lighter spongious‐structured skeleton was achieved through multiple developmental mechanisms. The modified perichondral ossification in elements of the limbs distal to the stylopodium informs our understanding of functional morphology, including hydrodynamic forces on the paddles. The ribs show variation in cortical thickness and trabecular organization along their length. Cyclical growth is inferred from changes in vascularization and osteocyte density as well as the presence of annuli in primary fibrolamellar bone. Cranial elements, due to their relative density and better preservation of growth marks, may prove to be of particular importance in future skeletochronological studies of post‐Triassic ichthyosaurians. We infer and corroborate hypotheses of elevated growth rates and metabolic rates in ichthyosaurians, and the potential for thermoregulation similar to extant homeothermic ectotherms.