Showing papers in "Journal of Morphology in 2002"
TL;DR: It is concluded that bone deposition rates measured in extant birds cannot simply be extrapolated to their fossil relatives, and developmental plasticity in modern birds may be reduced in association with the shortened developmental time during the later evolution of the ornithurine birds.
Abstract: Patterns of bone microstructure have frequently been used to deduce dynamics and processes of growth in extant and fossil tetrapods. Often, the various types of primary bone tissue have been associated with different bone deposition rates and more recently such deductions have extended to patterns observed in dinosaur bone microstructure. These previous studies are challenged by the findings of the current research, which integrates an experimental neontological approach and a paleontological comparison. We use tetracycline labeling and morphometry to study the variability of bone deposition rates in Japanese quail (Coturnix japonica) growing under different experimental conditions. We compare resulting patterns in bone microstructure with those found in fossil birds and other dinosaurs. We found that a single type of primary bone varies significantly in rates of growth in response to environmental conditions. Ranging between 10–50 μm per day, rates of growth overlap with the full range of bone deposition rates that were previously associated with different patterns of bone histology. Bone formation rate was significantly affected by environmental/experimental conditions, skeletal element, and age. In the quail, the experimental conditions did not result in formation of lines of arrested growth (LAGs). Because of the observed variation of bone deposition rates in response to variation in environmental conditions, we conclude that bone deposition rates measured in extant birds cannot simply be extrapolated to their fossil relatives. Additionally, we observe the variable incidence of LAGs and annuli among several dinosaur species, including fossil birds, extant sauropsids, as well as nonmammalian synapsids, and some extant mammals. This suggests that the ancestral condition of the response of bone to environmental conditions was variable. We propose that such developmental plasticity in modern birds may be reduced in association with the shortened developmental time during the later evolution of the ornithurine birds. J. Morphol. 254:232–246, 2002. © 2002 Wiley-Liss, Inc.
219 citations
TL;DR: A new reconstruction of the pelvic and hindlimb muscles of the large theropod dinosaur Tyrannosaurus rex is developed, using data from both extant and fossil turtles, lepidosaurs, and archosaurs to constrain inferences concerning the soft‐tissue structures in T. rex.
Abstract: In this article, we develop a new reconstruction of the pelvic and hindlimb muscles of the large theropod dinosaur Tyrannosaurus rex. Our new reconstruction relies primarily on direct examination of both extant and fossil turtles, lepidosaurs, and archosaurs. These observations are placed into a phylogenetic context and data from extant taxa are used to constrain inferences concerning the soft-tissue structures in T. rex. Using this extant phylogenetic bracket, we are able to offer well-supported inferences concerning most of the hindlimb musculature in this taxon. We also refrain from making any inferences for certain muscles where the resulting optimizations are ambiguous. This reconstruction differs from several previous attempts and we evaluate these discrepancies. In addition to providing a new and more detailed understanding of the hindlimb morphology of T. rex--the largest known terrestrial biped--this reconstruction also helps to clarify the sequence of character-state change along the line to extant birds.
215 citations
TL;DR: Compared to the forelimb character states of tupaiines, those of Ptilocercus are more similar to those of other archontans and it is proposed that the attributes of theForelimb of PtILocERCus are primitive for the Tupaiidae.
Abstract: In this study, the forelimb of 12 species of tupaiids was analyzed functionally and compared to that of other archontan mammals. Several differences that relate to differential substrate use were found in the forelimb morphology of tupaiids. These differences included shape of the scapula, length and orientation of the coracoid process, size of the lesser tuberosity, shape of the capitulum, length of the olecranon process, and shape of the radial head and central fossa. The forelimb of the arboreal Ptilocercus lowii, the only ptilocercine, is better adapted for arboreal locomotion, while that of tupaiines is better adapted for terrestrial (or scansorial) locomotion. While the forelimb of the arboreal Ptilocercus appears to be habitually flexed and exhibits more mobility in its joints, a necessity for movement on uneven, discontinuous arboreal supports, all tupaiines are characterized by more extended forelimbs and less mobility in their joints. These restricted joints limit movements more to the parasagittal plane, which increases the efficiency of locomotion on a more even and continuous surface like the ground. Even the most arboreal tupaiines remain similar to their terrestrial relatives in their forelimb morphology, which probably reflects the terrestrial ancestry of Tupaiinae (but not Tupaiidae). The forelimb of Urogale everetti is unique among tupaiines in that it exhibits adaptations for scratch-digging. Several features of the tupaiid forelimb reflect the arboreal ancestry of Tupaiidae and it is proposed that the ancestral tupaiid was arboreal like Ptilocercus. Also, compared to the forelimb character states of tupaiines, those of Ptilocercus are more similar to those of other archontans and it is proposed that the attributes of the forelimb of Ptilocercus are primitive for the Tupaiidae. Hence, Ptilocercus should be considered in any phylogenetic analysis that includes Scandentia.
188 citations
TL;DR: The Tiupampa fossils were therefore more agile than most living didelphids and resembled the condition observed in living dasyurids more, complementing a previous study performed on the forelimb of these fossils.
Abstract: This article analyzes the adaptations of the hindlimb of two Early Paleocene marsupials, Mayulestes ferox and Pucadelphys andinus. This analysis is based on detailed comparisons with various extant marsupials, both South American and Australian. In the case of the South American opossums, original myological data were collected and osteological–myological associations were related to their locomotor behavior. The use of Australian genera helped to improve the appraisal of the locomotory habits of the fossil taxa. Several features are indicative of the ability of Mayulestes to climb or walk on uneven surfaces (e.g., very mobile hip joint, astragalocalcaneal joint pattern), and some other features emphasize a relative agility (e.g., strongly everted iliac blades, morphology of the distal epiphysis of the femur, medially stabilized cruroastragalar joint). Pucadelphys exhibits a hindlimb relatively similar morphologically to that of Mayulestes, but with features indicating slightly increased agility and a terrestrial component that is more emphasized than in Mayulestes. The Tiupampa fossils were therefore more agile than most living didelphids and resembled the condition observed in living dasyurids more. These conclusions complement a previous study performed on the forelimb of these fossils. J. Morphol. 253:76–108, 2002. © 2002 Wiley-Liss, Inc.
149 citations
TL;DR: In Descemet's membrane, fibrous long spacing (FLS) fiber‐like structures, which are arranged in parallel to the endothelium, were observed by both TEM and SEM, which is the first report of SEM observations of FLS fiber-like structures on the endothelial surface of DesceMET's membrane.
Abstract: Corneas of tadpole, mouse, rat, guinea pig, rabbit, cat, cattle, and human were examined by TEM and SEM in a comparative study. The differences between species were noted mainly by using TEM. Bowman's layer showed a tendency to be well developed in higher mammals. Tadpoles lack a Bowman's layer, lower mammals have a thin Bowman's layer, and higher mammals have a thick Bowman's layer. The boundary between the substantia propria and Descemet's membrane was distinct in higher mammals. On the other hand, there are no differences in thickness of the collagen fibrils that constitute Bowman's layer and those of the substantia propria. NaOH digestion was utilized for SEM preparation. SEM imaging revealed a textured appearance of the epithelial side of Bowman's layer. In Descemet's membrane, fibrous long spacing (FLS) fiber-like structures, which are arranged in parallel to the endothelium, were observed by both TEM and SEM. To our knowledge, this is the first report of SEM observations of FLS fiber-like structures on the endothelial surface of Descemet's membrane. SEM at a plane normal to the plane of the cornea showed that Descemet's membrane has a piled laminar structure. Descemet's membrane is closely associated with the collagen layer of the substantia propria. Collagen fibrils invading from the substantia propria into Descemet's membrane were observed with both TEM and SEM.
147 citations
TL;DR: The basis for flight is discussed, how different animals have solved the problem of producing lift, how animal wings meet the requirements of strength and rigidity, how wing forms are adapted to various flight modes, and how flight kinematics are related to flight behavior and speed are discussed.
Abstract: By combining appearance and behavior in animals with physical laws, we can get an understanding of the adaptation and evolution of various structures and forms. Comparisons can be made between animal bodies and various technical constructions. Technical science and theory during the latest decades have resulted in considerable insight into biological adaptations, but studies on structures, forms, organs, systems, and processes in the living world, used in the right way, have also aided the engineer in finding wider and better solutions to various problems, among them in the design of micro-air vehicles (MAVs). In this review, I discuss the basis for flight and give some examples of where flight engineering and nature have evolved similar solutions. In most cases technology has produced more advanced structures, but sometimes animals are superior. I include how different animals have solved the problem of producing lift, how animal wings meet the requirements of strength and rigidity, how wing forms are adapted to various flight modes, and how flight kinematics are related to flight behavior and speed. The dynamics of vorticity is summarized. There are a variety of methods for the determination of flight power; it has been estimated adequately by lifting-line theory, by physiological measurements, and from mass loss and food intake. In recent years alternative methods have been used, in which the mechanical power for flight is estimated from flight muscle force used during the downstroke. Refinements of these methods may create new ways of estimating flight power more accurately. MAVs operate at the same Reynolds numbers as large insects and small birds and bats. Therefore, studies on animal flight are valuable for MAV design, which is discussed here.
123 citations
TL;DR: This study constitutes the first demonstration of supraspecific tooth‐to‐tooth dental homologies in nonmammalian vertebrates.
Abstract: The dentitions of lamniform sharks are said to exhibit a unique heterodonty called the "lamnoid tooth pattern." The presence of an inflated hollow "dental bulla" on each jaw cartilage allows the recognition of homologous teeth across most modern macrophagous lamniforms based on topographic correspondence through the "similarity test." In most macrophagous lamniforms, three tooth rows are supported by the upper dental bulla: two rows of large anterior teeth followed by a row of small intermediate teeth. The lower tooth row occluding between the two rows of upper anterior teeth is the first lower anterior tooth row. Like the first and second lower anterior tooth rows, the third lower tooth row is supported by the dental bulla and may be called the first lower intermediate tooth row. The lower intermediate tooth row occludes between the first and second upper lateral tooth rows situated distal to the upper dental bulla, and the rest of the upper and lower tooth rows, all called lateral tooth rows, occlude alternately. Tooth symmetry cannot be used to identify their dental homology. The presence of dental bullae can be regarded as a synapomorphy of Lamniformes and this character is more definable than the "lamnoid tooth pattern." The formation of the tooth pattern appears to be related to the evolution of dental bullae. This study constitutes the first demonstration of supraspecific tooth-to-tooth dental homologies in nonmammalian vertebrates.
120 citations
TL;DR: Results from an immunohistochemical analysis visualized with confocal laser‐scanning microscopy shows the development of serially repeated units in the nervous system of Bonellia viridis support the systematic inclusion of the Echiura within the Annelida.
Abstract: Despite several unquestionably homologous characters with Annelida, the Echiura have generally been considered to form a distinct taxon due to apparent lack of segmentation: neither in the body cavity nor in any other structures of the adult animals have clear signs of a metameric organization been observed. However, it must be considered that this lack of segmentation could represent a secondary condition and that Echiura are derived from segmented ancestors. An immunohistochemical analysis visualized with confocal laser-scanning microscopy (cLSM) shows the development of serially repeated units in the nervous system of Bonellia viridis. This organization corresponds to the metameric ganglia typical of Annelida. Antibodies against the neurotransmitters serotonin (5-hydroxytryptamine) and FMRFamide label distinct subsets of neurons. Their perikarya are arranged in discrete repetitive units in the ventral nerve cord of different larval stages. Labeling of neurotubuli using antibodies against different tubulin isoforms provides additional support for the metameric character of the nervous system. Contrary to previous descriptions, the peripheral nerves extending from the ventral nerve cord into the body wall musculature are paired and are evenly distributed; their arrangement corresponds to that of the serotoninergic perikarya. Morphological and neurochemical differentiation of the nervous system clearly proceeds from anterior to posterior, indicating the occurrence of a posterior growth zone. The serial ganglionic organization of the nervous system of Articulata is generally regarded as having evolved in conjunction with repetitive muscular units, in particular with the formation of typical annelid segments. Therefore, these results are interpreted as an indication that Echiura are derived from segmented ancestors and thus support the systematic inclusion of the Echiura within the Annelida.
115 citations
TL;DR: It is argued that this focus on changes in size and shape has restricted the kinds of questions that have been asked about the patterns of developmental change in phylogeny, which has narrowed the ability to address some of the most fundamental questions about development and evolution.
Abstract: One of the most persistent questions in comparative developmental biology concerns whether there are general rules by which ontogeny and phylogeny are related. Answering this question requires conceptual and analytic approaches that allow biologists to examine a wide range of developmental events in well-structured phylogenetic contexts. For evolutionary biologists, one of the most dominant approaches to comparative develop- mental biology has centered around the concept of hetero- chrony. However, in recent years the focus of studies of heterochrony largely has been limited to one aspect, changes in size and shape. I argue that this focus has restricted the kinds of questions that have been asked about the patterns of developmental change in phylogeny, which has narrowed our ability to address some of the most fundamental questions about development and evo- lution. Here I contrast the approaches of growth hetero- chrony with a broader view of heterochrony that concen- trates on changes in developmental sequence. I discuss a general approach to sequence heterochrony and summa- rize newly emerging methods to analyze a variety of kinds of developmental change in explicit phylogenetic contexts. Finally, I summarize a series of studies on the evolution of development in mammals that use these new approaches. J. Morphol. 252:82-97, 2002. © 2002 Wiley-Liss, Inc.
110 citations
TL;DR: The comparison of both techniques shows that X‐ray tomography is a promising new technique for the investigation of insect anatomy, and a cladistic analysis of characters of the head and additional data resulted in the following branching pattern.
Abstract: Internal and external features of the head of Priacma serrata were studied with X-ray microtomography and with histological methods. The comparison of both techniques shows that X-ray tomography is a promising new technique for the investigation of insect anatomy. The still somewhat coarse resolution of the X-ray data is compensated for by advantages like the nondestructive and artifact-free data acquisition. The head of P. serrata and other adults of Archostemata is characterized by many derived features. Muscular features of Priacma, especially muscles of the labium and pharynx, differ strongly from what is found in other groups of Coleoptera. Several character states are considered as autapomorphies of Archostemata: scale-like surface structures, constricted neck, strongly reduced tentorium, and the plate-like, enlarged prementum. The scales provide a protecting surface pattern and may have evolved with a more exposed lifestyle. The enlarged prementum forms a lid, which closes the mouth and covers the ligula when it is pulled back by contraction of the unusually strong submento-premental muscle. The presence of four cone-shaped protuberances on the dorsal side of the head is considered an autapomorphy of Cupedidae. The galea with a narrow stalk and a round and pubescent distal galeomere is another autapomorphy of this family. It has probably evolved as an adaptation to pollen-feeding. The shape of the mandible of Cupedidae is plesiomorphic compared to what is found in adults of Ommatidae. The vertical arrangement of apical teeth is an autapomorphy of the latter family. The lateral insertion of the antenna in Priacma is a groundplan feature of Cupedidae. The dorsal shift is a synapomorphy of all other cupedid genera. A cladistic analysis of characters of the head and additional data resulted in the following branching pattern: ((Crowsoniella + (Omma + Tetraphalerus)) + (Micromalthus + (Priacma + (Paracupes + (Cupes + Tenomerga + Prolixocupes + Rhipsideigma + Distocupes + (Adinolepis + Ascioplaga)))))). J. Morphol. 252:298–314, 2002. © 2002 Wiley-Liss, Inc.
108 citations
TL;DR: Comparative studies of skeletal developmental morphology demonstrate that limbs with fewer than five digits do not result from a simple truncation of a putative ancestral developmental program, and the developmental and adult morphologies in two‐, three‐, and four‐digit Hemiergis are neither predicted nor explained by a simple model of heterochrony involving either chondrogenesis or osteogenesis.
Abstract: Digit loss is a common theme in tetrapod evolution that may involve changes in several developmental processes. The skink genus Hemiergis provides an ideal model to study these processes in closely related taxa: within three Western Australian Hemiergis species, digit quantity ranges between two and five. For three consecutive reproductive seasons, gravid females of Hemiergis were collected in the field and their embryos prepared for histological analysis of limb skeletal development (chondrogenesis and osteogenesis). Comparative studies of skeletal developmental morphology demonstrate that limbs with fewer than five digits do not result from a simple truncation of a putative ancestral (five-digit) developmental program. The developmental and adult morphologies in two-, three-, and four-digit Hemiergis are neither predicted nor explained by a simple model of heterochrony involving either chondrogenesis or osteogenesis. In postnatal Hemiergis, digit number and relative limb length do not correlate in a simple linear fashion. Instead, limb size and digit reduction may correlate with substrate conditions and burrowing behavior. J. Morphol. 254:211–231, 2002. © 2002 Wiley-Liss, Inc.
TL;DR: Investigation of muscle development in two chiton species from embryo hatching until 10 days after metamorphosis shows that the “segmented” character of the polyplacophoran shell musculature is a secondary condition, thus contradicting earlier theories that regarded the Poly Placophora as primarily eumetameric (annelid‐like).
Abstract: We investigated muscle development in two chiton species, Mopalia muscosa and Chiton olivaceus, from embryo hatching until 10 days after metamorphosis. The anlagen of the dorsal longitudinal rectus muscle and a larval prototroch muscle ring are the first detectable muscle structures in the early trochophore-like larva. Slightly later, a ventrolaterally situated pair of longitudinal muscles appears, which persists through metamorphosis. In addition, the anlagen of the putative dorsoventral shell musculature and the first fibers of a muscular grid, which is restricted to the pretrochal region and consists of outer ring and inner diagonal muscle fibers, are generated. Subsequently, transversal muscle fibers form underneath each future shell plate and the ventrolateral enrolling muscle is established. At metamorphic competence, the dorsoventral shell musculature consists of numerous serially repeated, intercrossing muscle fibers. Their concentration into seven (and later eight) functional shell plate muscle bundles starts after the completion of metamorphosis. The larval prototroch ring and the pretrochal muscle grid are lost at metamorphosis. The structure of the apical grid and its atrophy during metamorphosis suggests ontogenetic repetition of (parts of) the original body-wall musculature of a proposed worm-shaped molluscan ancestor. Moreover, our data show that the "segmented" character of the polyplacophoran shell musculature is a secondary condition, thus contradicting earlier theories that regarded the Polyplacophora (and thus the entire phylum Mollusca) as primarily eumetameric (annelid-like). Instead, we propose an unsegmented trochozoan ancestor at the base of molluscan evolution.
TL;DR: This study is based on the examination of histological sections of specimens of different ages and of adult ossicles from macerated skulls representing a wide range of taxa and aims at addressing several issues concerning the evolution of the ear ossicle in marsupials.
Abstract: This study is based on the examination of histological sections of specimens of different ages and of adult ossicles from macerated skulls representing a wide range of taxa and aims at addressing several issues concerning the evolution of the ear ossicles in marsupials. Three-dimensional reconstructions of the ear ossicles based on histological series were done for one or more stages of Monodelphis domestica, Caluromys philander, Sminthopsis virginiae, Trichosurus vulpecula, and Macropus rufogriseus. Several common trends were found. Portions of the ossicles that are phylogenetically older develop earlier than portions representing more recent evolutionary inventions (manubrium of the malleus, crus longum of the incus). The onset of endochondral ossification in the taxa in which this was examined followed the sequence; first malleus, then incus, and finally stapes. In M. domestica and C. philander at birth the yet precartilaginous ossicles form a supportive strut between the lower jaw and the braincase. The cartilage of Paauw develops relatively late in comparison with the ear ossicles and in close association to the tendon of the stapedial muscle. A feeble artery traverses the stapedial foramen of the stapes in the youngest stages of M. domestica, C. philander, and Sminthopsis virginiae examined. Presence of a large stapedial foramen is reconstructed in the groundplan of the Didelphidae and of Marsupialia. The stapedial foramen is absent in all adult caenolestids, dasyurids, Myrmecobius, Notoryctes, peramelids, vombatids, and phascolarctids. Pouch young of Perameles sp. and Dasyurus viverrinus show a bicrurate stapes with a sizeable stapedial foramen. Some didelphids examined to date show a double insertion of the Tensor tympani muscle. Some differences exist between M. domestica and C. philander in adult ossicle form, including the relative length of the incudal crus breve and of the stapes. Several differences exist between the malleus of didelphids and that of some phalangeriforms, the latter showing a short neck, absence of the lamina, and a ventrally directed manubrium. Hearing starts in M. domestica at an age in which the external auditory meatus has not yet fully developed, the ossicles are not fully ossified, and the middle ear space is partially filled with loose mesenchyme. The ontogenetic changes in hearing abilities in M. domestica between postnatal days 30 and 40 may be at least partially related to changes in middle ear structures.
TL;DR: Outgroup comparison with all other molluscan classes and related phyla suggests that the cord‐like, nonganglionized cerebral system in the Polyplacophora is a reduced condition rather than a primitive mollUScan condition.
Abstract: Neurogenesis in the chiton Mopalia mus- cosa (Gould, 1846) was investigated by applying differen- tial interference contrast microscopy, semithin serial sec- tioning combined with reconstruction techniques, as well as confocal laser scanning microscopy for the detection of fluorescence-conjugated antibodies against serotonin and FMRFamide. The ontogeny of serotonergic nervous struc- tures starts with cells of the apical organ followed by those of the cerebral commissure, whereas the serotonergic pro- totroch innervation, pedal system, and the lateral cords develop later. In addition, there are eight symmetrically arranged serotonergic sensory cells in the dorsal pretro- chal area of the larva. FMRFamide-positive neural ele- ments include the cerebral commissure, specific "ampul- lary" sensory cells in the pretrochal region, as well as the larval lateral and pedal system. In the early juvenile the cerebral system no longer stains with either of the two antibodies and the pedal system lacks anti-FMRFamide immunoreactivity. Outgroup comparison with all other molluscan classes and related phyla suggests that the cord-like, nonganglionized cerebral system in the Polypla- cophora is a reduced condition rather than a primitive molluscan condition. The immunosensitivity of the pedal commissures develops from posterior to anterior, suggest- ing independent serial repetition rather than annelid-like conditions and there is no trace of true segmentation during nervous system development. Polyplacophoran neurogenesis and all other available data on the subject contradict the idea of a segmented molluscan stem spe- cies. J. Morphol. 253:109 -117, 2002. © 2002 Wiley-Liss, Inc.
TL;DR: An analysis of long bone mass to body mass in 64 different species of mammals, spanning three orders of magnitude in body mass, is presented, suggesting that the largest sauropod dinosaurs approached this limit.
Abstract: Most analyses on allometry of long bones in terrestrial mammals have focused on dimensional allometry, relating external bone measurements either to each other or to body mass. In this article, an analysis of long bone mass to body mass in 64 different species of mammals, spanning three orders of magnitude in body mass, is presented. As previously reported from analyses on total skeletal mass to body mass in terrestrial vertebrates, the masses of most appendicular bones scale with significant positive allometry. These include the pectoral and pelvic girdles, humerus, radius+ulna, and forelimb. Total hindlimb mass and the masses of individual hindlimb bones (femur, tibia, and metatarsus) scale isometrically. Metapodial mass correlates more poorly with body mass than the girdles or any of the long bones. Metapodial mass probably reflects locomotor behavior to a greater extent than do the long bones. Long bone mass in small mammals ( 50 kg) mammals, probably because of the proportionally shorter long bones of large mammals as a means of preserving resistance to bending forces at large body sizes. The positive allometric scaling of the skeleton in terrestrial animals has implications for the maximal size attainable, and it is possible that the largest sauropod dinosaurs approached this limit.
TL;DR: The Namibian Kuibis Quartzite fossils of Rangea are preserved three‐dimensionally owing to incomplete collapse of the soft tissues under the load of instantaneously deposited sand, and it is proposed that the irregularly distributed dark spots on the fusiform units of the petaloid of Thaumaptilon represent a kind of macrocilia and that the units are homologous with the ctenophoran comb organs.
Abstract: The Namibian Kuibis Quartzite fossils of Rangea are preserved three-dimensionally owing to incomplete collapse of the soft tissues under the load of instantaneously deposited sand. The process of fossilization did not reproduce the original external morphology of the organism but rather the inner surface of collapsed organs, presumably a system of sacs connected by a medial canal. The body of Rangea had tetraradial symmetry, a body plan shared also by the White Sea Russian fossil Bomakellia and possibly some other Precambrian frond-like fossils. They all had a complex internal anatomy, smooth surface of the body, and radial membranes, making their alleged colonial nature unlikely. Despite a different style of preservation, the Middle Cambrian Burgess Shale frond-like Thaumaptilon shows several anatomical similarities to Rangea. The body plan of the Burgess Shale ctenophore Fasciculus, with its numerous, pinnately arranged comb organs, is in many respects transitional between Thaumaptilon and the Early Cambrian ctenophore Maotianoascus from the Chengjiang fauna of South China. It is proposed that the irregularly distributed dark spots on the fusiform units of the petaloid of Thaumaptilon represent a kind of macrocilia and that the units are homologous with the ctenophoran comb organs. These superficial structures were underlain by the complex serial organs, well represented in the fossils of Rangea. The Precambrian "sea-pens" were thus probably sedentary ancestors of the ctenophores.
TL;DR: The arrangement and cytology of these tissues include: the outer peritoneal layer and subjacent collagen fibers, myoid cells and diverse other cells and tissues, e.g., fibrocytes, presumptive mesenchyme, macrophages, granulocytes, nerves, and blood vessels are described.
Abstract: Although the testis in teleosts has been investigated for many years, little attention has been paid to the structure of the outer layers that enclose the testis and to their possible contributions to its organization. The present study in a protogynous male labrid, Thalassoma bifasciatum (bluehead wrasse), describes the arrangement and cytology of these tissues (for convenience, referred to collectively as the outer wall, OW) which include: the outer peritoneal layer and subjacent collagen fibers, myoid cells and diverse other cells and tissues, e.g., fibrocytes, presumptive mesenchyme, macrophages, granulocytes, nerves, and blood vessels. Beneath the OW are two compartments; one is the gamete-laden spermatocysts, the other the interstitium, which is composed of cells and tissues that lie between the spermatocysts. Both OW and interstitium contain similar kinds of tissues and cells. Moreover, the layers of the OW immediately subjacent to the peritoneum are continuous with that in the interstitium. It is suggested that the continuity between these two areas provides opportunities for the exchange of cells that could aid in the maintenance and reorganization of the testis and with the myoid and neural tissue to establish an extensive, coordinated motile system that aids movement of sperm from spermatocysts to the ducts. A recent report on the reexamination of the germinal epithelium concept and its identification in the common snook, Centropomus undecimalis, stimulated us to examine the feasibility of applying this concept to gonad organization and gamete development in T. bifasciatum. In addition, the ultrastructure of the Sertoli cell and formation of spermatocysts are described. Spermatocysts increase in size during the development of gametes. Observations and discussion are presented suggesting how Sertoli cells may accommodate this growth and how new populations of these cells may arise in the mature adult. Finally, ultrastructural characteristics for each stage of spermatogenesis are presented and, using (3H)thymidine and autoradiography, data on the chronology of spermatogonia-sperm cycle are included.
TL;DR: The chorioallantoic placenta of M. heathi and its relatives warrants recognition as a new morphotype for reptiles, defined here as the “Type IV” placente, the first new type of chorio allantois to be defined formally for reptiles in over half a century.
Abstract: New World skinks of the genus Mabuya exhibit a unique form of viviparity that involves ovulation of tiny (1 mm) eggs and provision of virtually all of the nutrients for embryonic development by placental means. Studies of the Brazilian species M. heathi reveal that the chorioallantoic placenta is unlike those reported in any other squamate genus and exhibits striking specializations for maternal–fetal nutrient transfer. The uterine lining is intimately apposed to the chorioallantois, with no trace of an intervening shell membrane or of epithelial erosion; thus, the placenta is epitheliochorial. The uterus exhibits multicellular glands that secrete organic material into the uterine lumen. Opposite the openings of these glands, the chorion develops areolae, invaginated pits that are lined by absorptive, columnar epithelium. A single, mesometrial placentome develops, formed by radially oriented uterine folds that project into a deep invagination of the chorion. Uterine epithelium of the placentome appears to be syncytial and secretory and overlies a rich vascular supply. The apposed chorionic epithelium is absorptive in morphology and contains giant binucleated cells that bear microvilli. Several specializations of the placental membranes of M. heathi are found among eutherian mammals, signifying evolutionary convergence that extends to histological and cytological levels. The chorioallantoic placenta of M. heathi and its relatives warrants recognition as a new morphotype for reptiles, defined here as the “Type IV” placenta. This is the first new type of chorioallantoic placenta to be defined formally for reptiles in over half a century. J. Morphol. 254:121–131, 2002. © 2002 Wiley-Liss, Inc.
TL;DR: Biomechanical modeling of the cranial apparatus in four clariid representatives showing a gradual increase in the hypertrophy of the jaw adductors is used to investigate whether bite force actually increased, and static bite modeling shows that the apparenthypertrophy results in an increase in bite force.
Abstract: Within clariid fishes several cranial morphologies can be discerned. Especially within anguilliform representatives an increase in the degree of hypertrophy of the jaw adductors occurs. The hypertrophy of the jaw adductors and skeletal modifications in the cranial elements have been linked to increased bite force. The functional significance of this supposed increase in bite force remains obscure. In this study, biomechanical modeling of the cranial apparatus in four clariid representatives showing a gradual increase in the hypertrophy of the jaw adductors (Clarias gariepinus, Clariallabes melas, Channallabes apus, and Gymnallabes typus) is used to investigate whether bite force actually increased. Static bite modeling shows that the apparent hypertrophy results in an increase in bite force. For a given head size, the largest bite forces are predicted for C. apus, the lowest ones for C. gariepinus, and intermediate values are calculated for the other species. In addition, also in absolute measures differences in bite force remain, with C. apus biting distinctly harder than C. gariepinus despite its smaller head size. This indicates that the hypertrophy of the jaw adductors is more than just a correlated response to the decrease in absolute head size. Further studies investigating the ecological relevance of this performance difference are needed.
TL;DR: The morphology and possible function of the specialized mucous glands in the three species of Rana are compared with the breeding glands of other frogs and with the hedonic glands of some urodeles (Salamandridae and Plethodontidae), which are known to produce pheromonal substances during courtship.
Abstract: A structural and ultrastructural study was carried out on the cutaneous glands in some species of Rana (R. dalmatina, R. iberica, R. italica, R. “esculenta,” and R. perezi), giving particular attention to the mucous secretory units. Two different types of mucous glands occur in R. dalmatina, R. iberica, and R. italica. Besides the ordinary mucous units, which are randomly distributed over the body surface in both males and females, a further population of mucous glands was observed on the male dorsal skin. The latter is recognizable by the peculiar morphology of the epithelial cells and some characteristics of the secretory product. Specialized mucous glands are absent in both sexes of R. “esculenta” and R. perezi. The possible adaptive role of the specialized mucous glands is discussed in light of the absence of vocal sacs in males of R. dalmatina, R. iberica, and R. italica. Chemosignals released by sexually dimorphic mucous units may replace vocal communication during the breeding season and so play an important role in female attraction and/or territorial announcement. The morphology and possible function of the specialized mucous glands in the three species of Rana are compared with the breeding glands of other frogs and with the hedonic glands of some urodeles (Salamandridae and Plethodontidae), which are known to produce pheromonal substances during courtship. J. Morphol. 254:328–341, 2002. © 2002 Wiley-Liss, Inc.
TL;DR: Three‐dimensional images by whole‐mount immunostaining clarified the innervation pattern in the peripheral nervous system in detail and seemed to reflect the inactive nekto‐benthic life of the idiosepiid cuttlefish in the eelgrass bed.
Abstract: The idiosepiid cuttlefish is a suitable organism for behavioral, genetic, and developmental studies. As morphological bases for these studies, organization of the nervous system was examined in Idiosepius paradoxus Ortmann, 1881, using Cajal's silver technique and immunohistochemical staining with anti-acetylated alpha-tubulin antibody. The nervous architecture is generally identical to that described in Sepia and Loligo, but some features characterize the idiosepiid nervous system. The olfactory system is highly developed in the optic tract region. The dorsolateral lobes show large neuropils, connected with each other by a novel well-fasciculated commissure. Each olfactory lobe is subdivided into two lobules. The neuropils of the anterior and the posterior chromatophore lobes are very poorly developed. Neuronal gigantism is not extensive in the brain; enlarged neuronal cells are visible only in the perikaryal layer of the posterior subesophageal mass. The giant nerve fiber system is of the Sepia type; the axons are not markedly thick and the first-order giant fibers do not fuse with each other at the chiasma. Three-dimensional images by whole-mount immunostaining clarified the innervation pattern in the peripheral nervous system in detail. Two commissural fibers link the left and right posterior funnel nerves ventrally and dorsally. The stellate commissure, which is absent in Sepia and Sepiola, connects the stellate ganglia with each other. A branch of the visceral nerve innervating the median pallial adductor muscle is characteristically thick. Tubulinergic reactivity of the cilia and axons reveals the presence of many ciliated cells giving off an axon toward brain nerves in the surface of the funnel, head integument, arm tips, and epidermal lines. Some of these features seem to reflect the inactive nekto-benthic life of the idiosepiid cuttlefish in the eelgrass bed.
TL;DR: The sequence of epidermal layers in some apteria and in interfollicular epidermis in the zebrafinch embryo was studied and the production of β‐keratin in natal down feathers and beak was ultrastructurally analyzed in embryos before hatching.
Abstract: Little is known of the lipid content of beta-keratin-producing cells such as those of feathers, scutate scales, and beak. The sequence of epidermal layers in some apteria and in interfollicular epidermis in the zebrafinch embryo (Taeniopygia guttata castanotis) was studied. Also, the production of beta-keratin in natal down feathers and beak was ultrastructurally analyzed in embryos from 3-4 to 17-18 days postdeposition, before hatching. Two layers of periderm initially cover the embryo, but there are eventually 6-8 over the epidermis of the beak. In the beak and sheath cells of feathers, peridermal granules are numerous at 12-14 days postdeposition but they are less frequent in apteria. These granules swell and disappear during sheath or peridermal degeneration at 15-17 days postdeposition. A thin beta-keratin layer forms under the periderm among feather germs of pterylous areas but is discontinuous or disappears in apteria. In differentiating cells of barbs, barbules, and calamus cells of natal down, electron-dense beta-keratin filaments form bundles oriented along the main axis of these cells. Cells of the pulp epidermis and collar, at the base of the follicle, contain lipids and bundles of alpha-keratin filaments. Degenerating pulp cells show vacuolization and nuclear pycnosis. During beta-keratin packing, keratin bundles turn electron-pale, perhaps due to the addition of lipids to produce the final, homogenous beta-keratin matrix. In contrast to the situation in feathers, in the cells of beak beta-keratin packets are irregularly oriented. In both feather and beak epidermal cells the Golgi apparatus and smooth endoplasmic reticulum produce vesicles containing lipid-like material which is also found among forming beta-keratin. The contribution of lipids or lipoprotein to the initial aggregation of beta-keratin molecules is discussed.
TL;DR: There is no evidence that body curvatures are limited by the ganoid squamation in Polypterus or Lepisosteus to any larger extent than by a type of integument devoid of ganoids scales in teleostomes of similar body shape.
Abstract: A bony ganoid squamation is the plesiomorphic type in actinopterygians. During evolution, it was replaced by weak and more flexible elasmoid scales. We provide a comparative description of the integument of "ganoid" fishes and "nonganoid" fishes that considers all dermal components of mechanical significance (stratum compactum, morphology of ganoid scales, and their regional differences) in order to develop a functional understanding of the ganoid integument as a whole. Data were obtained for the extant "ganoid" fishes (Polypteridae and Lepisosteidae) and for closely related "lower" actinopterygians (Acipenser ruthenus, Amia calva) and "lower" sarcopterygians (Latimeria chalumnae, Neoceratodus forsteri). Body curvatures during steady undulatory locomotion, sharp turns, prey-strikes, and fast starts in "ganoid" fishes were measured from videotapes. Extreme body curvatures as measured in anesthetized specimens are never reached during steady swimming, but are sometimes closely approached in certain situations (sharp turns, prey-strike). During extreme body curvatures we measured high values of lateral strain on the convex and on the concave side of the body. Scale overlap changes considerably (66-127% in Lepisosteus, 42-140% in Polypterus). The ganoid squamation forms a protective coat, but at the same time it permits extreme body curvatures. This is reflected in characteristic morphological features of the ganoid scales, such as an anterior process, concave anterior margin, and peg-and-socket articulation. These characters are most pronounced in the anterior body region, where maximum changes in scale overlap are required. The anterior processes and anterior concave margin, together with the attached stratum compactum, guide movements in a horizontal plane during bending. Displacements of scales relative to each other are possible for scales of different scale rows, but are impeded in scales of the same scale row due to the peg-and-socket articulation. Furthermore, ganoid scale rows, fibers of collagen layers of the stratum compactum, and the lateral myoseptal structures follow the same oblique orientation, which is needed to achieve extreme body curvatures. There is no evidence that body curvatures are limited by the ganoid squamation in Polypterus or Lepisosteus to any larger extent than by a type of integument devoid of ganoid scales in teleostomes of similar body shape. Our results essentially contradict former functional interpretations: 1) Ganoid scales do not especially limit body curvature during steady undulatory locomotion; 2) They do not act as torsion-resisting devices, but may be able to damp torsion together with the stratum compactum and internal body pressure.
TL;DR: The existence of a distinct pair of cephalic retractors, which is also found in basal gastropods and cEPhalopods, as well as new data on scaphopod shell morphogenesis and recent cladistic analyses, indicate that the Scaphopoda may be more closely related to the Gastropoda and Cephalopoda than to the Bivalvia.
Abstract: We applied fluorescence staining of F-actin, confocal laser scanning microscopy, as well as bright-field light microscopy, SEM, and TEM to examine myogenesis in larval and early juvenile stages of the tusk-shell, Antalis entalis. Myogenesis follows a strict bilaterally symmetrical pattern without special larval muscle systems. The paired cephalic and foot retractors appear synchronously in the early trochophore-like larva. In late larvae, both retractors form additional fibers that project into the anterior region, thus enabling retraction of the larval prototroch. These fibers, together with the prototroch, disappear during metamorphosis. The anlagen of the putative foot musculature, mantle retractors, and buccal musculature are formed in late larval stages. The cephalic captacula and their musculature are of postmetamorphic origin. Development of the foot musculature is dramatically pronounced after metamorphosis and results in a dense muscular grid consisting of outer ring, intermediate diagonal, and inner longitudinal fibers. This is in accordance with the proposed function of the foot as a burrowing organ based on muscle-antagonistic activity. The existence of a distinct pair of cephalic retractors, which is also found in basal gastropods and cephalopods, as well as new data on scaphopod shell morphogenesis and recent cladistic analyses, indicate that the Scaphopoda may be more closely related to the Gastropoda and Cephalopoda than to the Bivalvia. J. Morphol. 254:53–64, 2002. © 2002 Wiley-Liss, Inc.
TL;DR: The data and several other examples available from the literature support the idea that the lengthening of intrauterine retention of eggs and the shortening of the subsequent external incubation of eggs are associated with reduction in the thickness of the eggshell, at least in some lineages of oviparous squamates.
Abstract: The concept of the oviparity-viviparity continuum refers to the wide range in the length of intrauterine egg retention and, hence, in the stage of embryonic development at oviposition existing in squamates. The evolutionary process underlying this continuum may involve not only a lengthening of egg retention in utero, but also a marked reduction in the thickness of the eggshell. The idea that there may exist a negative correlation between the developmental stage reached by the embryo at oviposition and the eggshell thickness within squamates, although supported by the comparison of oviparous vs. viviparous species, has seldom been evaluated by comparing eggshell thickness of oviparous forms with different lengths of intrauterine egg retention. Eggs of two distinct oviparous clades of the lizard Lacerta vivipara were compared. The eggs laid by females from Slovenian and Italian populations have thicker eggshells, contain embryos on average less developed at the time of oviposition, and require a longer incubation period before hatching than the eggs laid by females from French oviparous populations. Our data and several other examples available from the literature support the idea that the lengthening of intrauterine retention of eggs and the shortening of the subsequent external incubation of eggs are associated with reduction in the thickness of the eggshell, at least in some lineages of oviparous squamates. The current hypotheses that may account for this correlation are presented and a few restrictions and refinements to those hypotheses are discussed. In particular, other changes, such as increased vascularization of the oviduct and of the extraembryonic membranes, may play the same role as the decrease of eggshell thickness in facilitating prolonged intrauterine egg retention in squamates. Future studies should also consider the hypothesis that the length of intrauterine retention might directly depend on the extent of maternal-fetal chemical communication through the eggshell barrier.
TL;DR: Studies of both the fossil record and intrapopulational variation of extant populations reveal regularities in the origin of variation that directly affect the patterns of diversity observed at higher taxonomic levels.
Abstract: Classic hypotheses of vertebrate morphology are being informed by new data and new methods. Long nascent issues, such as the origin of tetrapod limbs, are being explored by paleontologists, molecular biologists, and functional anatomists. Progress in this arena will ultimately come down to knowing how macroevolutionary differences between taxa emerge from the genetic and phenotypic variation that arises within populations. The assembly of limbs over developmental and evolutionary time offers examples of the major processes at work in the origin of novelties. Recent comparative developmental analyses demonstrate that many of the mechanisms used to pattern limbs are ancient. One of the major consequences of this phenomenon is parallelism in the evolution of anatomical structures. Studies of both the fossil record and intrapopulational variation of extant populations reveal regularities in the origin of variation. These examples reveal processes acting at the level of populations that directly affect the patterns of diversity observed at higher taxonomic levels. J. Morphol. 252:15–28, 2002. © 2002 Wiley-Liss, Inc.
TL;DR: This article provides the first study at the ultrastructural level of seasonal variation in the sexual segment of the kidney of a squamate, the natricine snake Seminatrix pygaea, and shows that synthesis of secretory product is initiated with the onset of spermatogenic activity in the spring and culminates with completion of spermiation in the fall.
Abstract: In mature male snakes and lizards, a distal portion of the nephron is hypertrophied in relation to its appearance in females and immature males. This sexual segment of the male kidney apparently provides seminal fluid that is mixed with sperm and released into the female cloaca during copulation. In this article, we provide the first study at the ultrastructural level of seasonal variation in the sexual segment of the kidney of a squamate, the natricine snake Seminatrix pygaea. Previous workers have indicated that the sexual segment is secretory only when the testes are spermatogenically active. The sexual segment of the kidney in S. pygaea does not go through an extended period of inactivity but does show a cycle of synthesis and secretion that can be related to the spermatogenic cycle and mating activity. We show that synthesis of secretory product is initiated with the onset of spermatogenic activity in the spring and culminates with completion of spermiation in the fall. Secretion of the product, however, occurs in a premating period in March when the testes are inactive. Secretion during this premating period is probably necessary to provide time for the passage of the products down the ureter in order to mix with sperm during mating later in spring.
TL;DR: Although spermatophore transfer is simple in C. vittatus, the presence of modified anterior pleopods or elongate genital papillae (sexual tubes) in other paguroidean species suggests the possibility of a more complex insemination process in these other hermit crabs.
Abstract: Although mating has been described in several hermit crab species, the mechanics of spermatophore transfer have not previously been demonstrated. Evidence from pleopod and gonopore morphology, video observations, and inseminated females indicates that in Clibanarius vittatus the male applies a spermatophoric mass directly onto the female via the gonopores rather than with modified pleopods 1–2 (gonopods) and/or genital papillae as in many other decapods. The single second pleopod of males of C. vittatus has a simple endopod with no apparent modifications for sperm transfer. There are no genital papillae extending from the male gonopores. The globular spermatophores are aligned in rows surrounded by a seminal secretion in the male ducts (vasa deferentia that terminate in ejaculatory ducts opening to the exterior via the gonopores). During copulation, described from time-lapse video recordings, the ventral surface of the last thoracic segment of the male, bearing the gonopores, was apposed to the ventral cephalothorax of the female. A massive amount of seminal secretion containing spermatophore ribbons, termed here the spermatophoric mass and described for the first time in a hermit crab species, was observed covering the sternites and coxae of pereopods 1–5 of a recently copulated female. It is suggested that during copulation the male emits the contents of the ejaculatory ducts directly onto the female without the aid of gonopods or genital papillae. Although spermatophore transfer is simple in C. vittatus, the presence of modified anterior pleopods or elongate genital papillae (sexual tubes) in other paguroidean species suggests the possibility of a more complex insemination process in these other hermit crabs. J. Morphol. 253:166–175, 2002. © 2002 Wiley-Liss, Inc.
TL;DR: New techniques and conceptual frameworks offer new challenges and exciting opportunities for research on the biomechanics and physiology of vertebrate musculoskeletal design and locomotor performance, and new techniques and approaches for measuring muscle forces and length changes, together with activation patterns and movement, under dynamic conditions of more varied motor behavior are now also available.
Abstract: New techniques and conceptual frameworks offer new challenges and exciting opportunities for research on the biomechanics and physiology of vertebrate musculoskeletal design and locomotor performance. Past research based on electromyography and two-dimensional kinematics has greatly advanced the field of vertebrate functional morphology. Studies using these approaches have revealed much about vertebrate structure and function and have emphasized the importance of incorporating historical and developmental constraint and ecological context. Continued use of these experimental tools, but with greater emphasis on three-dimensional analysis of body movement, in combination with 3D kinetics and flow visualization of fluid movement past moving organisms, can now take advantage of the considerable advances in computing power and digital video technology. Indeed, surprisingly few detailed 3D analyses of movement for many locomotor modes and differing organisms are presently available. A challenge of 3D analyses will be to reduce the complexity of the data obtained in order to identify general principles of movement and biomechanics. New techniques and approaches for measuring muscle forces and length changes, together with activation patterns and movement, under dynamic conditions of more varied motor behavior are now also available. These provide the opportunity to study the mechanics and physiology of muscle function at greater depth and under more realistic conditions than has been previously possible. The importance of studying intact, behaving organisms under a broader range of locomotor conditions (other than steady state) and in the context of their natural environment remains a critical need for vertebrate biologists. This provides the much-needed opportunity for placing advances at more cellular and molecular levels into the context of whole organism function. Hence, studies at the organismal level remain paramount. J. Morphol. 252:38–51, 2002. © 2002 Wiley-Liss, Inc.
TL;DR: Phylogenetic information indicates that the primitive pattern involved narrow strap‐shaped cells, with low posteriorly overlapping edges and relatively smooth surfaces, and microornamentation differences involving other parts of the body and other squamate groups tend to corroborate this functional interpretation.
Abstract: Differences in surface structure (ober-hautchen) of body scales of lacertid lizards involve cell size, shape and surface profile, presence or absence of fine pitting, form of cell margins, and the occurrence of longitudinal ridges and pustular projections. Phylogenetic information indicates that the primitive pattern involved narrow strap-shaped cells, with low posteriorly overlapping edges and relatively smooth surfaces. Deviations from this condition produce a more sculptured surface and have developed many times, although subsequent overt reversals are uncommon. Like variations in scale shape, different patterns of dorsal body microornamentation appear to confer different and conflicting performance advantages. The primitive pattern may reduce friction during locomotion and also enhances dirt shedding, especially in ground-dwelling forms from moist habitats. However, this smooth microornamentation generates shine that may compromise cryptic coloration, especially when scales are large. Many derived features show correlation with such large scales and appear to suppress shine. They occur most frequently in forms from dry habitats or forms that climb in vegetation away from the ground, situations where dirt adhesion is less of a problem. Microornamentation differences involving other parts of the body and other squamate groups tend to corroborate this functional interpretation. Microornamentation features can develop on lineages in different orders and appear to act additively in reducing shine. In some cases different combinations may be optimal solutions in particular environments, but lineage effects, such as limited reversibility and different developmental proclivities, may also be important in their genesis. The fine pits often found on cell surfaces are unconnected with shine reduction, as they are smaller than the wavelengths of most visible light.