The early ontogeny of Jurassic thecideoid brachiopods and its contribution to the understanding of thecideoid ancestry

Abstract: A collection of very early brephic juveniles from the Upper Aalenian of the Cotswolds, England, has provided the first opportunity to study the ontogeny of thecideoids prior to the recognizable development of a median septum. Traced towards their origin, the enduring characters of thecideides appear to be cementation, a delthyrium closed by a pseudodeltidium, an almost circular dorsal valve with a prominent erect bilobed cardinal process, well‐defined inner socket ridges, widely spaced lateral adductor muscle fields, tubercles, fibrous secondary shell lining both valves and probably endopunctae. The subperipheral rim and median septum so characteristic of adult thecideoids are undeveloped in the earliest juveniles. Initiation of the development of the free ventral wall in the ventral valve is identified as an important event in thecideoid ontogeny. Further important discoveries arising from the study are that the crura‐like outgrowths which form the brachial bridge in thecideides are not structurally homologous with the crura of spiriferides or terebratulides and that during their earliest ontogenetic development thecidellinids and thecideids are indistinguishable. Also, the identification of morphological characters correlative with both palaeontological and neontological approaches to thecideoid phylogeny has important implications for thecideide taxonomy. Interpretation of the morphology exhibited by the Cotswold specimens introduces the probability that during their earliest ontogeny moorellinin, thecidein and lacazellin dorsal valves follow the same development pattern and the described ontogenetic sequence has been corroborated by evidence from Jurassic rocks of Argentina, North America and France, from Cretaceous rocks of England, Central Europe and Czechoslovakia, also from extant species from the Atlantic, Indian and Pacific oceans, and to an extent which suggests the pattern of ontogenetic development revealed has been typical of thecideoids throughout their history.     

Spiriferide brachiopods from the Famennian (Late Devonian) Hongguleleng Formation of western Junggar,Xinjiang, northwestern China

Junggar is one of the most important areas in the study of the Upper Devonian and Lower Carboniferous in the Junggar-Hinggan Stratigraphic Region. Nevertheless, abundant benthic fossils await modern taxonomic studies. In this paper, six genera and eight species of Famennian spiriferide brachiopods are described from the Duguer Member and its equivalents of the Hongguleleng Formation in western Junggar, adding new data to the Rugaltarostrum Subassemblage of the “Palaeospirifer”–Megalopterorhynchus Brachiopod Assemblage of this area. Five previously recognized species within this subassemblage are revised, including: Cyrtospirifer junggarensis F.M. Zhang [now Ulbospirifer? junggarensis (F.M. Zhang)]; Tenticospirifer tenticulum transversus F.M. Zhang [now Cyrtospirifer transversus (F.M. Zhang)]; Tenticospirifer koketekensis F.M. Zhang [now Cyrtospirifer koketekensis (F.M. Zhang)]; Mucrospirifer quadratus F.M. Zhang (now “Mucrospirifer” quadratus F.M. Zhang); and Mucrospirifer bouchadi (Muir-Wood) (now Tylothyris cf. novamexicana Stainbrook). Three additional species, Cyrtiorina houi n. sp., Goungjunspirifer sinicus F.M. Zhang, and Cyrtospirifer procumbens Simorin in Litvinovich et al., are described. Ulbospirifer? junggarensis and Goungjunspirifer sinicus are characterized by a prismatic layer. Cyrtiorina houi shows a moderately high and triangular ventral interarea, with delthyrium covered by pseudodeltidium with a rounded foramen. Cyrtospirifer procumbens can be distinguished from other species of this genus by its shallow, clearly limited sulcus with prominent primary plications, and high ventral interarea. Cyrtospirifer transversus has an alate to subpentagonal outline. Cyrtospirifer koketekensis has rounded and distinct flank plications. The ventral delthyrium of “Mucrospirifer” quadratus is covered by a pseudodeltidium. Tylothyris cf. novamexicana develops an angular sulcus in cross-section. Comparisons with the coeval brachiopod faunas from various regions indicate that, biogeographically, western Junggar has a close relationship with the Tarbagatai Mountain Range, northeastern Kazakhstan, central Kazakhstan, and Karaganda Basin, and a certain affinity with North America.     

SULCIPENTAMERUS (PENTAMERIDA, BRACHIOPODA) FROM THE LOWER SILURIAN WASHINGTON LAND GROUP, NORTH GREENLAND

Abstract:  The brachiopod Sulcipentamerus , previously considered a common endemic pentameride genus in the Lower Silurian (Aeronian) of South China, is reported from largely coeval strata in the Hauge Bjerge, Ymers Gletcher and Odins Fjord formations (Washington Land Group) of North Greenland. Two species are present. In eastern North Greenland, S . cf. dorsoplanus occurs in carbonate strata of Aeronian – early Telychian age, whereas in the western region, a new species, S . lunatus sp. nov., is described. The identification of both forms as Sulcipentamerus is indicated by their relatively long ventral median septum and dorsal inner hinge plates. The new species, Sulcipentamerus lunatus sp. nov., is characterized by a nonlobate shell, a narrow but sharply defined interarea bordering the delthyrium and a deeply concave pseudodeltidium. Despite the two known occurrences of the genus in South China and Greenland, the Sulcipentamerus -bearing Harpidium Fauna of North Greenland (northeastern part of Laurentia) was quite distinct from both the Aeronian–Telychian brachiopod faunas of South China and the southern half of Laurentia. In general, the Aeronian pentameride brachiopod faunas of these three regions are strongly endemic, in contrast to their more tightly clustered counterparts from Avalonia, Baltica, Siberia, Kazakhstan, Tadzhikistan, Kolyma and Novaya Zemlya.     

The tube-like structures on the juvenile shells of earliest strophomenides and billingsellides as evidence of their life cycles

Possible life cycle of some ancient plectambonitoids (order Strophomenida) from the Middle Ordovician of Russia is reconstructed based on the well-preserved specimens composing the ontogenetic series. Four regions may be distinguished on their shell surface: protegulum, brephic shell, neanic shell and adult shell. The posterior margin of ventral protegulum bears pedicle sheath, which is a tubular outgrowth with a 40-μm-wide aperture at the distal end. The protegulum and brephic shell have common type of microstructure that possibly is spherular; the neanic and adult shells are fibrous. The strophomenide ontogeny possibly was similar to that of recent discinides. The strophomenide life cycle possibly included the planktotrophic juvenile stage; the protegulum and brephic shell were formed in the water column. The aperture of the pedicle sheath was possibly used as an anal opening of the floating juvenile and as an attachment organ during the settlement; at early adult stages, the sheath erased, the anus closed, and the animal started to lie on the ventral valve. The origin of the order Strophomenida and its relative groups is possibly connected with the loss of the pedicle lobe; judging by some strophomenide morphological features, true pedicle was present in the strophomenide ancestors. The tubes on the ventral umbones of strophomenides and billingsellides are not homologous as pedicle sheaths of strophomenides are formed at the planktotrophic swimming stage, and the tubes surrounding the pedicles of billingsellides were formed by deltidial plates of almost adult shell after settling.     

The development of GABA-like immunoreactivity in the thoracic ganglia of the locust Schistocerca gregaria

Summary The development of GABA-like immunoreactivity was investigated in embryonic and juvenile locusts using an antibody raised against GABA-protein conjugates. GABA-like immunoreactivity was first detectable in the neuropile of embryonic ganglia at 55% development, and in neuronal somata at 62% development. The total number of immunoreactive somata increased between 62% and 85% embryonic development, and followed an anterio-posterior pattern of expression. At 85% development, the number of immunoreactive somata reached adult levels and no change in number was then seen. In embryonic stages and first and second juvenile instars two dorsal and four ventral groups of somata were labeled in all three thoracic ganglia, whilst in later juvenile instars one of the dorsal groups was visible as a separate entity only in the metathoracic ganglion. These early patterns were modified by alterations in the positions of some of the groups during late embryogenesis and during juvenile development to produce the adult pattern. The results show that the development of GABA expression is similar to that of other neurotransmitters. The characteristics of the development of immunoreactivity indicate that some of these immunoreactive clusters may be derived from clonally related neurones. Finally, we demonstrate the presence of immunoreactive somata and processes in embryos, which correspond to those of identified local and intersegmental interneurones studied in the adult.Abbreviations Ab1–3 first-third abdominal ganglion - CON connective - CI _1–3 common inhibitors 1–3 - CTC tract - DC I–VII dorsal commissures I–VII - DIT dorsal intermediate tract - DMT dorsal median tract - LDT lateral dorsal tract - LF lateral fibres - o, iLVT outer and inner lateral ventral tract - MVT median ventral tract - N1–5 nerves 1–5 - aPT anterior perpendicular tract - PT perpendicular tract - aRT anterior ring tract - R1–5 nerve roots 1–5 - PVC posterior ventral commissure - SMC supra-median commissure - T3 metathoracic neuromere - TT T tract - aVAC anterior ventral association centre - VC I ventral commissure I - d,vVCII dorsal and ventral parts of ventral commissure II - VF ventral fibres - VIT ventral intermediate tract - VLT ventral lateral tract - VMT ventral median tract - (d,v)LAG (dorsal and ventral) lateral anterior group - LDG lateral dorsal group - LVG lateral ventral group - MDG medial dorsal group - MPG medial posterior group - MVG medial ventral group     

GEOGRAPHIC VARIATION AND HETEROCHRONY IN TWO SPECIES OF COWRIES (GENUS CYPRAEA)

Geographic variation in the marine, Indo-Pacific cowry, Cypraea caputserpentis, involves clinal variations that parallel the ontogenetic development of adult shell characteristics. Cypraea caputdraconis, a closely related species endemic to Easter Island and Sala y Gómez, is morphologically similar to juvenile C. caputserpentis. Using multivariate measures of size and shape, I examine these patterns as a possible outcome of heterochrony, or changes in the timing of developmental events in ontogeny. Whorl-expansion rates of juvenile shells are significantly higher in C. caputdraconis when compared to C. caputserpentis and are negatively correlated with surface seawater temperatures among populations of C caputserpentis. High expansion rates, often associated with slow growth, result in a delay in the onset of lateral callus development and subsequent paedomorphosis. Ontogenetic trajectories calculated from growth series of adult and preadult shells indicate that paedomorphosis results from the combined effects of neoteny and post-displacement. Paedomorphosis among cowries may result from the advantages of larger body size relative to shell size under reduced predation intensities and associated increases in fecundity.     

Scanning electron microscopy of glochidia and juveniles of the freshwater mussel,Hyriopsis myersiana

Summary

The ultrastructure of early stages of the mussel, Hyriopsis (Limnoscapha) myersiana (Lea, 1856), was observed by scanning electron microscopy from the glochidial period until the onset of the juvenile stage 10 days later. Further observations were performed for an additional 13 days to assess juvenile development. Glochidia extracted from the brood chambers have a hookless, semi-oval and equivalve calcareous shell with numerous pores in the internal surface, pits in the external surface and cuticular spines in the ventral region. Keratin fibers with a random arrangement in the cuticle of the glochidial shell were also detected. The appearance of the foot within 10 days of in vitro glochidial culture was considered the main feature of metamorphosis to the juvenile stage. Another change during the following 13 days was the formation of a new periostracum exhibiting growth lines under the old glochidial shell. This development occurs mainly in the anterior region and is followed by hardening of the periostracum matrix by calcium deposition. Periostracum growth gradually became apparent in the lateral and posterior regions at the end of this period. The retraction of spines and the alteration of the external surface of the old shell are also described. It is speculated that transcuticular filaments identified in the juvenile stage may have sensory or metabolic exchange functions. The prominent foot, gradually covered by long dense cilia, shows rhythmical movements which suggest a role in feeding. Similarly, cilia present in the mantle may also be involved in the capture of food, while microvilli may facilitate absorption of dissolved materials. Longer cilia, sparsely distributed in the mantle, may function as chemo- or tactile sensors.     

Structure,crystallography, and morphogenesis of the cryptic shell of the terrestrial slug Limax maximus (Mollusca,gastropoda)

The structure and crystallography of the internal shell of the pulmonate gastropod slug Limax maximus were studied at the levels of light and scanning electron microscopy, revealing patterns of shell ontogeny and morphogenesis. The calcified portion of the slightly convex ovoid shell is composed of a single palisade layer of calcitic crystals. Numerous projections, 100 μm in width at the dorsal tip, are found on the dorsal surface of the shell and coincide with local nucleation sites of primordial calcium salt deposition onto the periostracum. With continued calcification these projections coalesce ventrally, forming the single crystalline shell layer. The organic portion of the shell includes the periostracum and an extensive PAS-staining conchiolin. In EDTA-etched preparations, conchiolin appears as a spongy network of fibers throughout the shell. Both horizontal and vertical components of the conchiolin are present, the former of variable thickness and occurring in an intercrystalline manner, the latter always occurring normal to the horizontal set. Macromorphogenic growth is characterized by three distinct temporal stages. Primary growth occurs radially from the umbonal region. Secondary growth is synonymous with shell thickening. Tertiary growth is characterized by both a lateral component, in which the shell extends beyond the primary growth boundaries, and a ventral component, in which the shell continues to grow in thickness. SEM of the ventral shell surface reveals a pattern of growth at the crystalmatrix interface. Proteinaceous fibers of the conchiolin occur unidirectionally in horizontal rows. Zones of incipient calcitic crystallization onto these hypostracal fiber bundles are contrasted by zones of increasing crystallization until the fibrous template (reduced hypostracum) is completely covered by crystals.     

Earliest ontogeny of Early Palaeozoic Craniiformea: implications for brachiopod phylogeny

Popov, L.E., Bassett, M.G., Holmer, L.E., Skovsted, C.B. & Zuykov, M.A. 2010: Earliest ontogeny of Early Palaeozoic Craniiformea: implications for brachiopod phylogeny. Lethaia, Vol. 43, pp. 323–333. Well preserved specimens of the Early Palaeozoic craniiform brachiopods Orthisocrania and Craniops retain clear evidence of a lecithotrophic larval stage, indicating the loss of planktotrophy early in their phylogeny. The size of the earliest mineralized dorsal shell was <100 μm across, and the well preserved shell structure in these fossil craniiforms allows their earliest ontogeny to be compared directly with that of living Novocrania, in which the first mineralized dorsal shell (metamorphic shell) is secreted only after settlement of the lecithotrophic larvae. Immediately outside this earliest shell (early post‐metamorphic or brephic shell) and in the rest of the dorsal valve the primary layer in both fossil and living craniiforms has characteristic radially arranged laths, which are invariably lacking in the earliest dorsal shell. The ventral valve of the fossil specimens commonly preserves traces of an early attachment scar (cicatrix), which is equal in size to the dorsal metamorphic shell, and the brephic post‐metamorphic ventral valve also has a primary shell with radially arranged laths. However, a primary shell with radial laths is completely lacking in the ventral valve of living Novocrania, indicating that heterochrony may have been involved in the origin of the encrusting mode of life in living craniids; the entire ventral valve of Recent craniids (with the possible exception of Neoancistrocrania) may correspond to the earliest attachment scar of some fossil taxa such as Orthisocrania. It is also probable that the unique absence of an inner mantle lobe as well as the absence of lobate cells in Novocrania could be the result of heterochronic changes. The dorsal valve of both fossil and living craniiforms has a marked outer growth ring, around 500 μm across, marking the transition to the adult, and a significant change in regime of shell secretion. The earliest craniiform attachment is considered to be homologous to the unique attachment structures described recently in polytoechioids (e.g. Antigonambonites) and other members of the strophomenate clade. However, unlike the craniiforms, polytoechioids and strophomenates all have planktotrophic larvae, and planktotrophy is most probably a plesiomorphic character for all Brachiopoda. □Brachiopoda, Craniiformea, Early Palaeozoic, ontogeny, phylogeny.     

ONTOGENETIC NICHE SHIFT IN THE BRACHIOPOD TEREBRATALIA TRANSVERSA: RELATIONSHIP BETWEEN THE LOSS OF ROTATION ABILITY AND ALLOMETRIC GROWTH

Abstract: Many articulated brachiopods experience marked life habit variations during ontogeny because they experience their fluid environment at successively higher Reynolds numbers, and they can change the configuration of their inhalant and exhalant flows as body size increases. We show that the extant brachiopod Terebratalia transversa undergoes a substantial ontogenetic change in reorientation governed by rotation around the pedicle. T. transversa′s reorientation angle (maximum ability to rotate on the pedicle) decreases during ontogeny, from 180 degrees in juveniles to 10–20 degrees in individuals exceeding 5 mm, to complete cessation of rotation in individuals larger than 10 mm. Rotation ability is substantially reduced after T. transversa achieves the adult lophophore configuration and preferred orientation with respect to ambient water currents at a length of 2.5–5 mm. We hypothesize that the rotation angle of T. transversa is determined mainly by the position of ventral and dorsal points of attachment of dorsal pedicle muscles relative to the pedicle. T. transversa shows a close correlation between the ontogenetic change in reorientation angle and ontogeny of morphological traits that are related to points of attachment of dorsal pedicle muscles, although other morphological features can also limit rotation in the adult stage. The major morphological change in cardinalia shape and the observed reduction of rotation affect individuals 2.5–10 mm in length. The position of ventral insertions of dorsal pedicle muscles remains constant, but contraction of dorsal pedicle muscles is functionally handicapped because dorsal insertions shift away from the valve midline, rise above the dorsal valve floor, and become limited by a wide cardinal process early in ontogeny (<5 mm). The rate of increase of cardinal process width and of distance between dorsal pedicle muscle scars substantially decreases in the subadult stage (5–10 mm), and most of the cardinalia shell traits grow nearly isometrically in the adult stage (>10 mm). T. transversa attains smaller shell length in crevices than on exposed substrates. The proportion of small‐sized individuals and population density is lower on exposed substrates than in crevices, indicating higher juvenile mortality on substrates prone to grazing and physical disturbance. The loss of reorientation ability can be a consequence of morphological changes that strengthen substrate attachment and maximize protection against biotic or physical disturbance (1) by minimizing torques around the pedicle axis and/or (2) by shifting energy investments into attachment strength at the expense of the cost involved in reorientation.     

Higher risk of fatality by predatory attacks in earlier ontogenetic stages of modern Nautilus pompilius in the Philippines: evidence from the ontogenetic analyses of shell repairs

The shell repair scars of modern Nautilus pompilius in the Philippines presumably due to sub‐lethal predatory attacks were examined throughout ontogeny ranging from hatching to maturity, revealing the higher risk of fatality in earlier ontogenetic stages. The examinations throughout ontogeny demonstrate that: (1) sub‐lethal predatory attacks by other organisms have no preferred position through ontogeny; (2) the sizes of shell repair scars are similar throughout ontogeny and, therefore, the width and length of shell repair scars relative to shell diameter decrease from hatching towards maturity; and (3) the proportion of sub‐lethal predatory attacks within 10 mm increments of shell diameter are similar irrespective of shell diameter or decrease approaching maturity. The numbers of the irregular, radiating, black shell repair scars, indicating injury to the soft parts at shell breakage, decrease at a diameter >80 mm and none were found at <56 mm in shell diameter. Furthermore, the rarity of juvenile trapping data might be related to the higher fatality from predatory attacks in earlier ontogenetic stages, providing crucial information for the conservation of N. pompilius.     

Development of the musculature in the limpet Patella (Mollusca, Patellogastropoda)

 Whole-mount technique using fluorescent-labelled phalloidin for actin staining and confocal laser scanning microscopy as well as semi-thin serial sectioning, scanning and transmission electron microscopy were applied to investigate the ontogeny of the various muscular systems during larval development in the limpets Patella vulgata L. and P. caerulea L. In contrast to earlier studies, which described a single or two larval shell muscles, the pretorsional trochophore-like larva shows no less than four different muscle systems, namely the asymmetrical main head/foot larval retractor muscle, an accessory larval retractor with distinct insertion area, a circular prototroch/velar system, and a plexus-like pedal muscle system. In both Patella species only posttorsional larvae are able to retract into the shell and to close the aperture by means of the operculum. Shortly after torsion the two adult shell muscles originate independently in lateral positions, starting with two fine muscle fibres which insert at the operculum and laterally at the shell. During late larval development the main larval retractor and the accessory larval retractor become reduced and the velar muscle system is shed. In contrast, the paired adult shell muscles and the pedal muscle plexus increase in volume, and a new mantle musculature, the tentacular muscle system, and the buccal musculature arise. Because the adult shell muscles are entirely independent from the various larval muscular systems, several current hypotheses on the ontogeny and phylogeny of the early gastropod muscle system have to be reconsidered. Received: 23 June 1998 / Accepted: 25 November 1998     

Development of the pedicle in the articulate brachiopod Terebratalia transversa (Brachiopoda,Terebratulida)

Summary The development of the pedicle in the articulate brachiopod Terebratalia transversa has been examined by electron microscopy. The posterior half of the free-swimming larva comprises a non-ciliated pedicle lobe that contains the primordium of the juvenile pedicle at its distal end. During settlement at five to six days post-fertilization, the pedicle lobe secretes a sticky sheet that attaches the larva to the substratum. As metamorphosis proceeds, the epithelium in the posterior half of the pedicle lobe produces a thin overlying cuticle, and the pedicle primordium develops into a stalk-like anchoring organ. The juvenile pedicle protrudes through the gape that occurs between the posterior margins of the shell valves. A cup-like canopy, called the pedicle capsule, lines the posterior end of the shell and surrounds the newly formed pedicle. The core of the juvenile pedicle is filled with a solid mass of connective tissue. Numerous tonofibrils occur in the pedicle epithelium, and the overlying cuticle consists of amorphous material covered by a thin granular fringe. By one year post-metamorphosis, a body cavity develops anterior to the pedicle. Two pairs of adjustor muscles extend from the posterior end of the shell and traverse the cavity to insert in the pedicle. The connective tissue core of the pedicle in sub-adult specimens lacks muscle cells but contains numerous fibroblasts and collagen fibers. Three regions are recognizable in the connective tissue compartment of the adult pedicle: a subepithelial layer of non-fibrous connective tissue, a central fibrous zone, and a proximal mass of tissue that resembles cartilage.List of abbreviations as adhesive sheet - bc body cavity - bv brachial valve of shell - cf collagen fibrils - ct connective tissue - cu cuticle - di diductor muscle - ec epithelial cell - f fibroblast - fz fibrous zone - g gut - gc granular cell - gd gastric diverticulum - ht hinge tooth - ia interarea of pedicle valve - icl inner cuticular layer - lo lophophore - lu lumen of gut - m mesenchyme - ma mantle - ml mantle lobe - ocl outer cuticular layer - p periostracum - pc pedicle capsule - pce pedicle capsule epithelium - pcl pedicle collar of shell - pcn pedicle connectives - pd pedicle - pe pedicle epithelium - pl pedicle lobe - pv pedicle valve of shell - pzc proximal zone of cartilage-like tissue - s substratum - sel subepithelial layer - t tendon - tf tonofibril - vam ventral adjustor muscle     

Ontogeny and evolution within the Myophorellidae (Bivalvia): Paedomorphic trends

The role of heterochronic phenomena in molluscan evolution is insufficiently understood but potentially significant. The aim of this paper is to explore some paedomorphic trends in the evolution of the Myophorellidae (Bivalvia: Trigoniida). Early ontogeny of general shell shape and ornamentation of one species of Steinmanella was analyzed and compared to data obtained for three species of Myophorella: two belonging to the subgenus M. (Promyophorella) (one from the Jurassic and one from the Cretaceous) and one belonging to the Jurassic M. (Myophorella). For general shell shape, a geometric morphometric analysis was performed on lateral views of the shells. Regarding ornamentation, flank costal disposition on the marginal carina, tubercle separation and relative development of the sub-commarginal subset of flank costae were quantified. A qualitative analysis was also performed. A two-trend shell shape development is considered as primitive. The first trend is marked by a relative reduction of the posterior margin together with a relative elongation of the shell. A tangential opisthogyrate growth component characterizes the second trend. There is a transitional stage where both trends interact. Early flank ornamentation is characterized by two or three sub-commarginal costae, continuous through the area, after which oblique costae with fine tubercles start to form. The subgenus M. (Myophorella) evolved by paedomorphic retention of juvenile shell shape and ornamentation, resulting in a large shell with coarse tubercles. Shell morphology in Steinmanella evolved by paedomorphic suppression of the primitive second trend in the development of the shell, resulting in an orthogyrate shell shape, and the retention of juvenile ornamentation (coarse tubercles, more sub-commarginal costae, juvenile rates of costal disposition). The paedomorphic (most likely by deceleration) retention of juvenile shell morphology within the Myophorellidae seems to have been recurrent within the group, resulting in many cases of convergence, and obscuring the phylogenetic relationships among its species.     

Cranial and appendicular ontogeny of Bactrosaurus johnsoni,a hadrosauroid dinosaur from the Late Cretaceous of northern China

Abstract: The juvenile anatomy of various cranial and appendicular elements of the hadrosauroid dinosaur Bactrosaurus johnsoni is described in detail. Growth changes are documented from juvenile to adult stages for each skeletal element available. In the studied skull, ontogenetic trends consist of: development of features on the ventral surface of the frontal; reduction in the slope of the posteromedial process of the premaxilla; a posterior shift of the dorsal process of the maxilla; development of concavities on the medial surface of the prefrontal; increased robustness and development of the ventral flange of the jugal; decreased curvature of the long axis of the quadrate; increased ventral deflection of the dentary; and changes in the length/width proportions and depth of the anterior surface of the predentary. In the appendicular skeleton, the majority of ontogenetic variation from juvenile to adult occurs in the limb bones, including increased robustness of the deltopectoral crest of the humerus; relative shortening of the ulna; increased development of the fourth trochanter and mediolateral widening of the distal end of the femur; increased expansion of the cnemial crest of the tibia; and the increased prominence of articular protuberances and flanges of the metatarsals. A survey of the phylogenetically informative characters present in B. johnsoni indicates that several characters concerning the frontal, maxilla, jugal, quadrate, predentary, dentary, scapula, humerus and ilium are affected by ontogeny. Nevertheless, the majority of phylogenetic characters are not ontogenetically variable, suggesting that a substantial amount of the information provided by juvenile and subadult specimens for phylogenetic inference is reliable in basal hadrosauroids.     

Dynamic body acceleration increases by 20% during flight ontogeny of greylag geese Anser anser

Despite our knowledge of the biophysical and behavioural changes during flight ontogeny in juvenile birds, little is known about the changes in the mechanical aspects of energy expenditure during early flight development, particularly in migratory species. Here, we investigate in a unique experimental setup how energy expended during flights changes over time beginning with early ontogeny. We calculate overall dynamic body acceleration (ODBA) as a proxy for energy expenditure in a group of hand raised greylag geese Anser anser trained to fly behind a microlight aircraft. We propose two potential hypotheses; energy expenditure either increases with increasing physiological suitability (the ‘physical development hypothesis’), or decreases as a result of behavioural improvements mitigating flight costs (the ‘behavioural development hypothesis’). There was a significant temporal increase of flight duration and ODBA over time, supporting the ‘physical development hypothesis’. This suggests that early on in flight ontogeny behavioural development leading to flight efficiency plays a weaker role in shaping ODBA changes than the increased physical ability to expend energy in flight. We discuss these findings and the implications of flight development on the life history of migratory species.     

Morphological development of glochidia in artificial media through early juvenile of freshwater pearl mussel,Hyriopsis (Hyriopsis) bialatus Simpson, 1900

The morphological development and the sequence of organogenesis from glochidium to the early juvenile stage of the freshwater pearl mussel, Hyriopsis bialatus, were observed. Larvae of H. bialatus were cultured in standard tissue culture medium (M199) supplemented with common carp (Cyprinus carpio) plasma and they showed transformation within 10 days. Larval samples were collected every 2 days during glochidia development and subjected to histological processing. Three types of cell masses were developed during this period: the ventral plate (the foot rudiment), lateral pits (the gill rudiment), and the oral plate or endodermic sac (the origin of the digestive tract). The ventral plate gave rise to two foot lobes which fused into a single lobe. The gills were developed from the lateral pits next to the ventral plate, forming a pair of gill buds that became elongated and turned into gill bars. The digestive tract began with the formation of mouth by invagination of the oral plate (or endodermic sac) and formation of a tube underneath the growing foot. Several controversial aspects of organogenesis have been inferred, e.g., de novo formation of the anterior and posterior juvenile adductors, the fate of the mushroom body structure, and foot lobe formation from two separate precursor lobes. A mushroom body protruded into the mantle cavity and remained there throughout the transformation period. Moreover, the evidence of a supporting band (mucoid structure) in the mature glochidium of H. bialatus has never been reported in other freshwater mussel species, and its function and composition need to be further investigated.     

Earliest ontogeny of the Silurian orthotetide brachiopod Coolinia and its significance for interpreting strophomenate phylogeny

Well‐preserved juvenile specimens of the orthotetide brachiopod Coolinia pecten (Linnaeus, 1758 ) from the Silurian of Gotland, Sweden, demonstrate evidence of a planktotrophic larval habit. Larval shell morphology indicates the absence of a pedicle sheath: this character is otherwise typical of derived billingsellides, strophomenides and productides, which form the conventional strophomenide clade. The presence of a rudimentary colleplax structure in the larval shell of Colinia suggests instead a phylogenetic link to chiliate brachiopods and the enigmatic genus Salanygolina. This relationship suggests an early divergence of rhynchonellate and strophomenate brachiopods.     

Mosaic Evolution of the Basicranium in <Emphasis Type="Italic">Homo</Emphasis> and its Relation to Modular Development

Mosaic evolution describes different rates of evolutionary change in different body units. Morphologically these units are described by more relationships within a unit than between different units which relates mosaic evolution with morphological integration and modularity. Recent evidence suggests mosaic evolution at the human basicranium due to different evolutionary rates of midline and lateral cranial base morphology but this hypothesis has not yet been addressed explicitly. We this hypothesis and explore how mosaic evolution relates to modular development. Evolutionary data sets on midline (N = 186) and lateral (N = 86) basicranial morphology are compared with 3D data on pre- and postnatal basicranial ontogeny (N = 71). Our results support the hypothesis of mosaic evolution and suggest a modular nature of basicranial development. Different embryological basicranial units likely became differently modified during evolution, with relatively stable midline elements and more variable lateral elements. In addition, developmental data suggests that modularity patterns change throughout ontogeny. During prenatal ontogeny lateral basicranial elements (greater sphenoid wings and petrosal pyramids) change together compared with the midline base. Close to birth the greater sphenoid wings keep a spatially stable position, while the petrosal pyramids become dissociated and shifted posteriorly. After birth the greater sphenoid wings and petrosal pyramids change again jointly and with respect to midline cranial base elements. This sequential pattern of integration and modularization and re-integration describes human basicranial ontogeny in a way that is potentially important for the understanding of evolutionary change. Phylogenetic modifications of this pattern during morphogenesis, growth, and development may underlie the mosaic evolution of the hominin basicranium.