Showing papers in "Journal of Morphology in 1986"
TL;DR: An unusual circulatory supply to the eyes and brain is associated with the presence of the heater tissue in these fishes.
Abstract: Marlins, sailfish, and spearfishes have a heat-producing tissue beneath the brain and adjacent to the eyes. This tissue warms the brain and eyes while the rest of the body remains at water temperature. The heater tissue is derived from the superior rectus eye muscle. Only a portion of this eye muscle contains normal skeletal muscle tissue; the rest consists of the modified muscle tissue that is associated with heat production. The heat-producing portion is supplied with blood through a countercurrent heat exchanger that originates from the carotid artery. The vascular rate prevents the heat being produced by the tissue from being dissipated at the gill. An unusual circulatory supply to the eyes and brain is associated with the presence of the heater tissue in these fishes.
138 citations
TL;DR: As obligatory air‐breathers able to survive temporary and sometimes extended desiccation of a habitat, lungfishes are often permanent residents in areas from which most actinopterygian fishes are excluded.
Abstract: Remarkably little is known about the biology of the four Protopterus species, apart from certain detailed studies on their nesting behavior and estivating habits. What information we do have indicates that the species are essentially omnivorous carnivores (especially as predators on molluscs) and that they occupy a wide variety of habitats both lentic and lotic. As obligatory air-breathers able to survive temporary and sometimes extended desiccation of a habitat, lungfishes are often permanent residents in areas from which most actinopterygian fishes are excluded.
All four species are able to survive prolonged dry periods. The methods they employ in so doing are varied, and include the secretion of subterranean cocoons, lying-up in water-filled subsurface burrows, or simply burrowing into moist regions of the substrate. Some populations of at least two species live in permanent water and so do not estivate, although they apparently retain the ability to do so.
Three of the four species spawn in some form of seemingly constructed or prepared nest. The architecture of these nests shows marked inter- and intraspecific variability and is likely to be determined largely by various environmental factors. All three species show some type of parental care. The breeding biology of the fourth species, P. amphibius, is still unknown.
Other aspects of the breeding biology and behavior of Protopterus require a great deal more investigation, as does the biology of the young.
131 citations
TL;DR: The dipnoans are not the closest sister group of tetrapods, independently if living forms only are considered, or fossil forms included.
Abstract: Dipnoans are osteichthyans, and are the sister group of crossopterygians (actinistians, onychodontiforms, porolepiforms, osteolepiforms, and including tetrapods). They share with crossopterygians the following derived features: anocleithrum, connection between the preopercular and infraorbital sensory lines, true enamel on teeth, cosmine, sclerotic ring with more than four plates, submandibular series, archipterygium, and process of endochondral bone formation. These features characterize the sarcopterygians (crossopterygians and dipnoans), whereas the intracranial joint, double-headed hyomandibula, and three extrascapulae are synapomorphies of crossoptery gians. Rhipidistians (onychodontiforms, porolepiforms, osteolepiforms, and including tetrapods) are characterized by two synapomorphies, the presence of an extratemporal and narrow submandibular bone(s). Plicidentine, four infradentaries, three coronoids, and a fenestra ventro-lateralis are synapomorphies of porolepiforms, osteolepiforms, and tetrapods. The tetrapods are most closely related to panderichthyid osteolepiforms (with which they share labyrinthodont plicidentine, three pairs of median skull roof bones, flat skull with high dorsally situated orbits, and marginal position of external naris). The common ancestor of dipnoans and tetrapods is also the common ancestor of crossopterygians (including tetrapods) and dipnoans; in other words, the hypothetical common ancestor of all sarcopterygians. The dipnoans are not the closest sister group of tetrapods, independently if living forms only are considered, or fossil forms included.
129 citations
TL;DR: The feeding mechanism of the South American lungfish, Lepidosiren paradoxa retains many primitive teleostome characteristics, and the hyoid apparatus plays a major role in mediating expansion of the oral cavity.
Abstract: The feeding mechanism of the South American lungfish, Lepidosiren paradoxa retains many primitive teleostome characteristics. In particular, the process of initial prey capture shares four salient functional features with other primitive vertebrates: 1) prey capture by suction feeding, 2) cranial elevation at the cranio-vertebral joint during the mouth opening phase of the strike, 3) the hyoid apparatus plays a major role in mediating expansion of the oral cavity and is one biomechanical pathway involved in depressing the mandible, and 4) peak hyoid excursion occurs after maximum gape is achieved. Lepidosiren also possesses four key morphological and functional specializations of the feeding mechanism: 1) tooth plates, 2) an enlarged cranial rib serving as a site for the origin of muscles depressing the hyoid apparatus, 3) a depressor mandibulae muscle, apparently not homologous to that of amphibians, and 4) a complex sequence of manipulation and chewing of prey in the oral cavity prior to swallowing. The depressor mandibulae is always active during mouth opening, in contrast to some previous suggestions. Chewing cycles include alternating adduction and transport phases. Between each adduction, food may be transported in or out of the buccal cavity to position it between the tooth plates. The depressor mandibulae muscle is active in a double-burst pattern during chewing, with the larger second burst serving to open the mouth during prey transport. Swallowing is characterized by prolonged activity in the hyoid constrictor musculature and the geniothoracicus. Lepidosiren uses hydraulic transport achieved by movements of the hyoid apparatus to position prey within the oral cavity. This function is analogous to that of the tongue in many tetrapods.
120 citations
TL;DR: This paper reviews the cardiorespiratory morphology and physiology of the living lungfishes, in the special context of their highly effective use of both air and water for gas exchange.
Abstract: This paper reviews the cardiorespiratory morphology and physiology of the living lungfishes, in the special context of their highly effective use of both air and water for gas exchange. Particular emphasis is placed on describing those features of the circulatory and respiratory systems that distinguish Neoceratodus from the Lepidosirenidae (Protopterus, Lepidosiren), and which, in turn, distinguish lungfishes from other aquatic vertebrates. Morphological and physiological characters that represent the plesiomorphic condition for the living Dipnoi are indicated (e.g., separate atrial chambers, vertical septum in ventricle, pulmonary veins, conal valves, twisting of bulbus cordis), as are those characters that may be shared derived features of the Lepidosirenidae (e.g., paired lungs, reduced anterior gill arches, well-developed spiral valve in conus). Morphological and physiological comparisons and contrasts with tetrapods are made to elucidate systematic relationships of the Dipnoi with other vertebrates.
118 citations
TL;DR: It is concluded that, despite locally abundant populations of lungfish in rivers of southeast Queensland, the species is still at risk of extinction from a number of natural or artificial causes.
Abstract: The literature on the biology of the Australian lungfish, Neoceratodus forsteri (Krefft, 1870), over the past 115 years is reviewed Relevant unpublished information on the habits, environment, and distribution of the lungfish is included Topics covered are the discovery and taxonomic position of the species, the appearance and habits of adults and juveniles, their environment and distribution (historical and modern), their oviposition and development, and their diet and catching methods It is concluded that, despite locally abundant populations of lungfish in rivers of southeast Queensland, the species is still at risk of extinction from a number of natural or artificial causes
112 citations
TL;DR: This study uses bivariate and discriminant function analyses to compare the limb morphology of adult dogs and wild canid species, and then compares ontogenetic allometry of four dog breeds with staticAllometry of domestic andWild canids.
Abstract: Biomechanical hypotheses are often invoked to explain the characteristic scaling of limb proportions. Patterns of static allometry and morphologic diversity, however, may also reflect the developmental mechanisms underlying morphologic change. In this study I document the importance of such developmental influences on the evolution of limb morphology in the extremely polymorphic domestic dog and in wild canid species. I use bivariate and discriminant function analyses to compare the limb morphology of adult dogs and wild canid species. I then compare ontogenetic allometry of four dog breeds with static allometry of domestic and wild canids. Results reveal, first, that there is considerable similarity between dogs and wild canid species; many wolf-like canids cannot be distinguished from domestic dogs of equivalent size. However, all dogs are consistently separated from fox-sized, wild canids by subtle but evolutionarily significant differences in olecranon, metapodial, and scapula morphology. Second, in domestic dogs the pattern of static allometry is nearly identical to that of ontogenetic allometry. This finding can be attributed to simple heterochronic alterations of postnatal growth rates. Apparently the diversity of limb proportions among adult domestic dogs and the observed difference between dogs and wild canids are somewhat predetermined, as they directly reflect the diversity of limb proportions evident during development of the domestic dog.
108 citations
TL;DR: Neural synapomorphies corroborate the phylogenetic hypotheses that actinistians, amphibians, and dipnoans are each monophyletic taxa and that lepidosirenid apomorphies may have arisen by paedomorphosis.
Abstract: The phylogenetic affinity of lungfishes has been disputed since their discovery, and they have variously been considered the sister group of actinistians, the sister group of amphibians, or equally related to actinopterygians and crossopterygians. Previous discussions of these hypotheses have considered neural characters, but there has been no general survey of the nervous systems of sarcopterygians that examines the bearing of neural characters on these hypotheses in the context of a cladistic analysis. Such a survey of representatives of all living sarcopterygian groups reveals at least twenty-three characters that are possible apomorphies at some hierarchical level among sarcopterygians. Neural synapomorphies corroborate the phylogenetic hypotheses that actinistians, amphibians, and dipnoans are each monophyletic taxa. The hypothesis that Latimeria is the sister group of amphibians is the least corroborated, as only a single possible synapomorphy, presence of cervical and lumbar enlargements of the spinal cord, supports this hypothesis. The hypothesis that lungfishes are the sister group of amphibians is supported by two possible synapomorphies: loss of a saccus vasculosus and the presence of neurocranial endolymphatic sacs. The hypothesis that actinistians are the sister group of lungfishes is the most corroborated, based on five possible synapomorphies: presence of a superficial isthmal nucleus, a laminated dorsal thalamus with marked protrusion into the third ventricle, olfactory peduncles, evaginated cerebral hemispheres with pronounced septum ependymale, and electroreceptive rostral organs. However, all five characters may be plesiomorphic for bony fishes. The nervous systems of Latimeria and Neoceratodus are very similar to each other, as are the nervous systems of lepidosirenid lungfishes, caecilians, and salamanders. If Neoceratodus is the most plesiomorphic species of living lungfishes, then lepidosirenid apomorphies may have arisen by paedomorphosis. Our inability to examine the neural characters of a relevant outgroup (rhipidistians) may result in many sarcopterygian plesiomorphic characters being interpreted as apomorphic characters, due to the wide distribution of paedomorphic characters among living sarcopterygians and their possible resemblance to plesiomorphic characters present in living outgroups that can be examined.
98 citations
TL;DR: The morphology and function of the tongue and hyoid apparatus in Varanus were examined by anatomical and experimental techniques, finding that the long, narrow tongue is most likely related to the mechanics of tongue protrusion; the increased amount, strength, and complexity of hyobranchial movement isrelated to the fact that thehyobranchium inVaranus replaces the tongue in many functions.
Abstract: The morphology and function of the tongue and hyoid apparatus in Varanus were examined by anatomical and experimental techniques. Morphological features unique to Varanus include a highly protrusible tongue that has lost a roughened dorsal surface, an exceptionally strong and mobile hyobranchial apparatus, a well-defined joint between the ceratohyal and anterior process, and a series of distinct muscles inserting at the anterior hyobranchial region. Varanus is also unusual among lizards in a number of feeding behaviors; it ingests prey entirely by inertial feeding, as the tongue does not participate in food transport. Further specializations include an increased reliance on hyobranchial movements in drinking and pharyngeal packing and compression. The long, narrow tongue is most likely related to the mechanics of tongue protrusion; the increased amount, strength, and complexity of hyobranchial movement is related to the fact that the hyobranchium in Varanus replaces the tongue in many functions. Previous hypotheses for the origin of these adaptations are discussed, and the difficulties of attributing these specializations to any specific scenario of adaptation or constraint are emphasized.
96 citations
TL;DR: Six fiber types have been described in the ambiens muscle of red‐eared turtles and there is a decreasing gradient of oxidative staining and an increasing gradient of glycolytic staining along an axis from the superficial to deep regions of the muscle.
Abstract: Six fiber types have been described in the ambiens muscle of red-eared turtles. These include one slow oxidative type, two fast oxidative types, two fast oxidative and glycolytic types, and one fast glycolytic type. Fiber types are non-randomly distributed throughout cross sections of the muscle. There is a decreasing gradient of oxidative staining and an increasing gradient of glycolytic staining along an axis from the superficial to deep regions of the muscle. The slow oxidative fibers are predominantly located within one or two fascicles of the superficial surface of the muscle. The fast glycolytic fibers are predominant in deep fascicles.
In contrast to previous reports of histochemically monotypic intrafusal fibers in turtle muscle, ambiens muscle spindles have been observed containing one to eleven intrafusal fibers, including two fiber types. Fiber diameter and area are consistently smaller than observed in most extrafusal fibers. Spindles are predominantly located in superficial and cranial fascicles of the ambiens muscle and are located in regions characterized by extrafusal fibers with high oxidative activity.
96 citations
TL;DR: Estivation in Protopterus is an episodic event characterized by elaboration of a cocoon as ambient water is withdrawn, a state of torpor, and distinctive cardiorespiratory and metabolic changes.
Abstract: Estivation in Protopterus is an episodic event characterized by elaboration of a cocoon as ambient water is withdrawn, a state of torpor, and distinctive cardiorespiratory and metabolic changes. Among the more striking of these features is a decrease in oxygen consumption, a complete reliance on air breathing to satisfy metabolic need, a slowing of the heart rate, and a drop in blood pressure. The initiating mechanism for these dramatic changes is not known. As yet, specific “estivating factors” have not been identified. However, the pattern of decrease in oxygen uptake during estivation and starvation are quite similar, suggesting that a common factor may be involved in both. Attempts to implicate suppression of thyroid function in the onset of estivation have been unconvincing. Although initiating mechanisms for estivation in Protopterus remain uncertain, once estivation sets in a variety of adaptive changes occur that enable the estivating lungfish to survive for months to years without ingesting food or water. Among these are oliguria and a shift in metabolic pathways. Although estivation in Protopterus has been characterized with respect to cardiorespiratory and metabolic parameters, no attempt is made to extrapolate from the biologic processes in Protopterus to other lepidosirenid lungfish or to other genera.
TL;DR: Three major morphological features–‐an autostylic jaw suspension, tooth plates, and a reduced but highly mobile branchial apparatus–‐largely determine the special cranial morphology of living dipnoans and are directly related to these feeding functions.
Abstract: Living lungfishes capture prey by means of suction and then use a simple “hydraulic” transport system to position it for processing between the tooth plates. Three major morphological features–-an autostylic jaw suspension, tooth plates, and a reduced but highly mobile branchial apparatus–-largely determine the special cranial morphology of living dipnoans and are directly related to these feeding functions. Within Dipnoi, however, there are many striking and functionally significant differences between Neoceratodus and the lepidosirenid genera. These include the structure of the tooth plates, lower jaw, jaw articulation, skull roof, tongue, lips, and jaw closing and opening muscles. For example, the rami of the lower jaw of Neoceratodus flex slightly at the symphysis, and the jaw joint is “unrestrictive.” As a result, the upper and lower tooth plates can be ground against each other in a fashion distinct from the precise and restricted occlusion of lepidosirenids. Understanding the anatomy and function of these features will ultimately aid in interpreting the evolution of dipnoan feeding systems.
TL;DR: This view of homology suggests that the evolution of avian bipedality was accompanied by few myological transformations, despite profound modification of the skeleton.
Abstract: Data from adult birds, crocodilians, Sphenodon, squamates, turtles, and from the chick embryo are compared to test conflicting hypotheses of homology of the deep dorsal thigh muscles of birds and other reptiles. This comparison suggests that: 1) avian Mm. iliofemoralis externus and iliotrochan- tericus caudalis (herein renamed "iliofemoralis cranialis") are homologous with M. iliofemoralis of other reptiles; 2) avian Mm. iliotrochanterici cranialis and medius are homologous with one of two divisions of M. pubo-ischio-femo- ralis internus found in other reptiles (pars dorsalis of Crocodylia); 3) avian M. iliofemoralis internus (herein renamed "cuppedicus") is homologous with the other division of M. pubo-ischio-femoralis internus (pars medialis of Crocody- lia). This hypothesis implies a minimum of seven transformations in the number of muscles and their positions of origin and insertion in the evolution of Aves, five of which are recapitulated during ontogeny of the chick. The traditional recognition of three muscles in the "iliotrochantericus group" is topographically accurate, but it is a misnomer and has been a source of misdirection when these muscles are studied in a phylagenetic context. Varia- tions within Aves in the presence of the iliotrochantericus muscles (cranialis or medius) and the iliofemoralis muscles (externus or cranialis) are results of heterochronic perturbations of a conserved developmental program. Unlike most previous interpretations, this view of homology suggests that the evolu- tion of avian bipedality was accompanied by few myological transformations, despite profound modification of the skeleton.
TL;DR: Among the acanthopterygian fishes, the Labridae possess the most highly integrated and specialized pharyngeal jaw apparatus and have contributed significantly in the development of a double muscle sling operating the lower jaw.
Abstract: Among the acanthopterygian fishes, the Labridae possess the most highly integrated and specialized pharyngeal jaw apparatus. The integrated feature involves many osteological components and aspects of muscle form, architecture, composition, and function. The upper jaw articulates by means of a true diarthrosis with the pharyngeal process of the parasphenoid, whereas the lower jaw has established physical contact with the cleithrum. Complex muscle fusions have contributed significantly in the development of a double muscle sling operating the lower jaw. The original levator externus 4 fuses with the central head of the obliquus posterior, whereas the original levator posterior combines with the lateral head of the obliquus posterior as well as with the adductor branchialis 5. During the masticatory cycle, both upper and lower jaws undergo complex movement orbits resulting in shearing and crushing functions. Shearing occurs as the forward moving upper jaw collides with the dorsally held lower jaw. Crushing is effected by an extreme posterodorsal movement of the lower jaw against the retracted upper jaw, thereby establishing full occlusion of the teeth. The specialized morphological and functional design of the labrid pharyngeal jaw apparatus is similar to that found in cichlids. In sharp contrast to primitive acanthopterygian fishes, the Labridae and Cichlidae exhibit a spectacular morphological diversity that parallels their ecological diversification. Our combined functional and historical analysis has established a correlation between the complex integration of the pharyngeal jaw apparatus and morphological and ecological diversity in the Labridae and Cichlidae.
TL;DR: It is shown that many features taken to be diagnostic of the Dipnoi by some workers were not present in its early members; failure to recognize this fact has led to erroneous hypotheses about dipnoan‐amphibian relations.
Abstract: Stratigraphical and paleoecological evidence indicates that lungfishes evolved in shallow marine conditions. Devonian genera had large gill chambers, and the details of bony supports of the gill arches of the Late Devonian Griphognathus whitei demonstrate that the arches were all functional. These data, together with an analysis of the body forms of the Devonian genera, indicate that they were dependent on gill (and possibly skin) respiration. The oldest known dipnoans, Uranolophus and Speonesydrion, are held to be representative to two lineages that can be recognized by their buccal and branchial features. One had a “rasping” dentition formed of denticles and marginal ridges that were continually shed and remodelled; the other had a “crushing” dentition characterized by the presence of variously modelled dentine masses that continued growth throughout the life of the animal. A list of buccal and branchial characters associated with these modes of feeding is presented. Because the relations of the Dipnoi have to be examined in terms of the features possessed by the group when it first appeared as a separate entity, the final part of the paper makes an attempt to define the primitive dipnoan morphotype. It is shown that many features taken to be diagnostic of the Dipnoi by some workers were not present in its early members; failure to recognize this fact has led to erroneous hypotheses about dipnoan-amphibian relations.
TL;DR: A comparison of the ampullae of Lorenzini among 40 species of skates (Rajoidei) demonstrates a close relationship between inferred electroreceptive capabilities and feeding mechanisms.
Abstract: A comparison of the ampullae of Lorenzini among 40 species of skates (Rajoidei) demonstrates a close relationship between inferred electroreceptive capabilities and feeding mechanisms. Three general lines of morphological modifications are noted. (1) Whereas the majority of ampullary pores are located on the ventral surface of the dorsoventrally flattened body, the relative proportion of ventral pores is significantly lower on species inhabiting aphotic waters. (2) The ventral pores on more piscivorous species are distributed over a larger portion of body surface than they are on those species that feed primarily on invertebrates. Ventral pores in this latter group are more noticeably concentrated around the mouth and their densities on the adult are inversely related to the overall mobility of preferred prey species. (3) The size of each ampulla and the number of alveoli associated with it are directly related to the habitat depth occupied by each species. Shallow-water species have smaller ampullae with fewer alveoli than deeper-dwelling (> 1,000 m) species. The general distribution of ampullary pores on deep dwelling rajoids appears to compensate for reduced visual input, whereas their relative densities are a measure of the system's resolution and reflect major differences in feeding strategies. The increased ampullary size and complexity observed in deep-sea rajoids provides mechanisms to increase both the sensitivity and signal-to-noise ratios.
TL;DR: The presence of the prominent circular muscle in both the esophagus and the stomach is postulated to be advantageous to an herbivorous fish, however, other ultrastructural features of the gastrointestinal tract of the luderick are similar to those described in carnivorous fish and appear to show no specialization for herbivory.
Abstract: The gastrointestinal tract of Girella tricuspidata, an herbivorous teleost, is differentiated into esophagus, stomach, pyloric caeca, intestine, and rectum. The mucosa of the esophagus consists almost entirely of elongated secretory cells, with an underlying submucosa and prominent circular and longitudinal muscle layers. The anterior part of the stomach contains a mucous surface epithelium and a network of tubular glands having only one type of glandular cell, to which secretion of both pepsinogen and HCl is attributed. The tubular glands are not present in the pyloric region. The gastric wall contains well developed circular muscle and submucosal layers. The pyloric caeca contain a mucosa containing two types of exocrine cells. The nature and function of secretions from these cells is discussed. The intestinal mucosa is differentiated into an anterior (ca. 30%) and a posterior section. The enterocytes of the anterior portion show evidence of lipid absorption, while those of the posterior intestine and rectum show considerable pinocytotic activity. The pyloric caeca, intestine, and rectum have a layer of submucosa and a thin layer of circular muscle. The presence of the prominent circular muscle in both the esophagus and the stomach is postulated to be advantageous to an herbivorous fish. However, other ultrastructural features of the gastrointestinal tract of the luderick are similar to those described in carnivorous fish and appear to show no specialization for herbivory.
TL;DR: The mammalian secondary palate may be interpreted as one of a number of methods, seen in the mammal‐like reptiles, for strengthening the rostrum.
Abstract: The secondary palate of mammals is a bony shelf that closes the ventral aspect of the rostrum. The rostrum, therefore, approximates to a tapered semicylindrical tube that is theoretically a mechanically efficient structure for resisting the forces of biting, including the more prolonged bouts of mastication typical of mammals. Certain mammal-like reptiles illustrate stages in the development of the palate in which the shelves projecting medially from each premaxilla and maxilla do not meet in the midline. We evaluate several geometric properties of sections through the rostrum of the American opossum (Didelphis virginiana). For loading at the incisors and canines, these properties indicate the structural strength and stiffness in both bending and torsion of the rostrum and of single maxillae. We then repeat the analysis but progressively omit segments of the palatal shelf, a procedure which simulates, in reverse, the evolutionary development of the structure. The results demonstrate that the secondary palate contributes significantly to the torsional strength and stiffness of the rostrum of Didelphis and to the strength of each maxilla in lateromedial bending. The major evolutionary implications of the results are that the rapid increase in rostral strength with small increments of the palatal shelves may have been a significant factor in the development of the complete structure. The results indicate that there was a marked jump in torsional strength and stiffness when the shelves met in the midline, which is likely to have been important in the subsequent development of the diverse masticatory mechanisms of cynodonts and mammals. On the basis of this analysis the mammalian secondary palate may be interpreted as one of a number of methods, seen in the mammal-like reptiles, for strengthening the rostrum.
TL;DR: Three regions of the byssus of the marine mussel Mytilus edulis L. are distinct in structural organization at the macroscopic and microscopic level and in amino acid composition.
Abstract: Three regions of the byssus of the marine mussel Mytilus edulis L. are distinct in structural organization at the macroscopic and microscopic level and in amino acid composition. The threads that emanate from the stem at the base of the foot are divided into two regions. The proximal, elastic region has a crimped, densely staining cortex enclosing an interior matrix of spiral fibers, and its amino acid composition reflects protein heterogeneity. The more distal, rigid region has a straight, tubular cortex surrounding an inner matrix of linearly arranged bundles of fibrils and has a composition approximating pure collagen. The plaque, or disc-shaped portion, which mediates attachment to various substrates, is distinguished by a surface matrix of collagen-like fibers similar to those of the thread region and anchored on an inner spongy matrix. Compositional evidence exists for a collagenous component, a catechol-rich protein, and at least one other accessory protein in the plaque.
TL;DR: The evolution of limited neoteny in newts as a correlated response to the inhibition of land‐drive behavior is discussed and the ontogenetic sequence of cranial osteogenesis through adulthood is described.
Abstract: 62901 ABSTRACT The ontogenetic sequence of cranial osteogenesis through adulthood is described in samples of newts from completely metamorphosing and partially neotenic populations. Cranial ossification proceeds in the same sequence in both samples. Seven stages of cranial development are described on the basis of conspicuous events that occur during ontogeny. These include four larval stages, metamorphs, efts, and adults. Neotenic adults have skulls that are metamorphosed completely and indistinguishable from the skulls of non-neotenic adults. Neoteny in these newts does not involve the skull and is limited to the postmetamorphic retention of some gill structures and, thus, is termed "limited neoteny." The evolution of limited neoteny in newts as a correlated response to the inhibition of land-drive behavior is discussed. Adult cranial osteology has played an im- portant role in the classification of salaman- ders (notably, Cope, 1889; Dunn, '26; Noble, '31; Regal, '66; Tihen, '58; Wake, '66; Wake and Ozeti, '69). Many previous studies have detailed aspects of cranial structure and on- togeny, and related them to ecological spe- cializations and metamorphosis (Fox, '54; Monath, '65; Papendieck, '54; Parker and Dunn, '64; Regal, '66; Srinivasachar, '62; Worthington and Wake, '71; and references therein). Because neoteny (Pierce and Smith, '79) occurs in all families of urodeles (Porter, '721, meaningful comparisons of adult cranial structures are sometimes difficult to achieve. Likewise, because of differences in larval on- togeny, comparisons of larval cranial struc- tures are also difficult to use (Larsen, '63). Comparisons of complete ontogenetic se- quences can provide a better basis from which to group salamander taxa and to inter- pret the ontogenetic details of neoteny and metamorphosis that are needed to support theoretic models relating ontogeny to ph;-Lg- eny (Alberch et al., '79; Alberch, '85; Fink, '82). Nevertheless, whole sequences of skull development have been described for only seven species of salamanders (Salamandra salamandra, Stadtmuller, '24; Eurycea bisli- neata, Wilder, '25; Triturus vulgaris, Erd- mann, '33; Ambystoma mexicanum, Keller, '46; Ambystoma texanum, Bonebrake and Brandon, '71; Rhyacotriton olympicus, Wor- thington and Wake, '71; and Aneides lugub ris, Wake et al., '83).
TL;DR: The morphology and histology of the tongue in Sphenodon punctatus are described and used to infer function and to determine character state polarities in lepidosaurs.
Abstract: The morphology and histology of the tongue in Sphenodon punctatus are described and used to infer function and to determine character state polarities in lepidosaurs. The tongue lacks an anterior notch and is covered with filamentous papillae, including specialized gustatory papillae containing taste buds. Lingual glands are restricted to mucocytes covering the papillae. Three intrinsic tongue muscles are identified and shown to be discrete fiber systems and not merely elaborations of the M. hyoglossus. These muscles interact with a connective tissue skeleton, particularly three septal planes, to cause changes in tongue shape. Tongue protrusion is probably caused by hyoid protraction and contraction of posterior genioglossus fibers; retraction by hyoid retraction, hyoglossus contraction, and contraction of anterior genioglossus fibers. It is argued that taste is important in prey discrimination and possibly in courtship. Vomeronasal function is probably mediated by inhalation and not tongue movement. Insertion of genioglossus fibers into the buccal floor is a derived feature of lepidosaur tongues. Derived features of squamate tongues include an anterior bifurcation, a divided genioglossus comprising medial and lateral portions, ventral transverse and circular muscle fiber systems around the hyoglossus, and the presence of a median septum. The tongue of the squamate family Iguanidae shares many plesiomorphic features with Sphenodon.
TL;DR: It is concluded that, among Recent taxa, lungfishes and tetrapods are sistergroups, with coelacanths as the plesiomorphic sister‐group to that combined group, and Rhipidistians are a paraphyletic group distributed amongst the recent taxa.
Abstract: Problems surrounding the relationships of lungfishes are intricately connected with the search for the origin of tetrapods. Early in the history of lungfish research, the emphasis was on attempts to determine whether lungfishes were more closely related to fishes or to tetrapods. Later there was a shift towards a search for particular ancestors and ancestral groups, an approach that not only introduced problems relative to the concept of ancestry but also stultified attempts to classify the sarcopterygians. Cladistic analysis, on the other hand, has placed the inquiry into lungfish relationships on a surer footing, in which alternative theories are more open to criticism. It is concluded that, among Recent taxa, lungfishes and tetrapods are sistergroups, with coelacanths as the plesiomorphic sister-group to that combined group. Rhipidistians are a paraphyletic group distributed amongst the Recent taxa.
TL;DR: Using immuno‐electrophoretic methods, the polyphenolic protein and the cystine‐rich protein were shown to form high molecular weight aggregates with aging of the byssus.
Abstract: The acellular attachment organ (byssus) of the marine mussel Mytilus edulis L. is composed of threads that emanate from the body of the mussel to adhesive discs that anchor the threads to rocks, sand and other mussels. Three proteins have been purified by immunohistological methods and located to specific regions of the byssus. A collagenous protein with subunit molecular weights of 53,000, 55,000 and 65,000 is found in the matrix of the elastic thread region. Its 73,000-MW precursor was extracted from foot glands in the area proximal to the animal body and was identified by immune cross-reactivity. A cystine-rich, acidic protein was found in all regions of the byssus associated with a third protein, the polyphenolic protein. The L-dopa-containing polyphenolic protein appears in the cortex of the entire thread and adhesive plaque and at the substrate-plaque interface. Antiserum to this protein stains spherical vesicles in the phenol gland of the foot. Using immuno-electrophoretic methods, the polyphenolic protein and the cystine-rich protein were shown to form high molecular weight aggregates with aging of the byssus.
TL;DR: The anatomy and histology of the white sturgeon digestive system is described for the adult stage and the first 36 days of posthatch development and the anatomical characteristics coincide with physiological data collected throughout the life history of this species.
Abstract: The anatomy and histology of the white sturgeon digestive system is described for the adult stage and the first 36 days of posthatch development. Although the adult gut is only 87% of standard length, absorptive surface area is effectively increased by the thick mucosa of the postgastric gut and by lengthening of the gut due to the presence of the spiral valve and the pyloric caecum. Modifications of the gut of this species, relative to that of other chondrosteans, are consistent with its durophagous feeding habits. The arrangement of the intestinal epithelium differs from that of most fish and is organized so that absorptive activities occur in deeper regions, whereas goblet cells dominate the lumenally exposed epithelium. The gut develops from an intraembryonic yolk endoderm. At conclusion of the endogenous nutrition phase the alimentary canal is similar to the adult form and a functional gastric region is present. The anatomical characteristics coincide with physiological data collected throughout the life history of this species.
TL;DR: Lepisosteus and Amia possess a polyural caudal skeleton with a one‐to‐one relationship between ural centra and hypurals; the number of hypural may be reduced in adult Lepisostspecies.
Abstract: The centra of Lepisosteus are perichondral ossifications of arcualia (i.e., arcocentra), whereas those of Amia are direct perichordal ossifications (i.e., autocentra) that enclose the arcualia. The preural centra of Lepisosteus are monospondylous, whereas the ural centra are formations of inter- and basidorsal arcualia. In contrast, the preural centra of Amia are diplospondylous, whereas preural centrum 1 (and sometimes preural centrum 2) and ural centra are monospondylous. The ural centra of Lepisosteus are expansions of dorsal arcualia, but those of Amia are expansions of the basiventral autocentrum. This explains the fusion of the neural arches with the ural centra and the presence of autogenous hypurals in Lepisosteus, in contrast to the situation in Amia in which the compound ural neural arch (the fused ural neural arches) is free, and the hypurals are fused to the ural centra. Lepisosteus possesses true epurals, which are modified neural spines, whereas in Amia the "epurals" are positioned between the neural spines like radials. Lepisosteus and Amia possess a polyural caudal skeleton with a one-to-one relationship between ural centra and hypurals; the number of hypurals may be reduced in adult Lepisosteus.
TL;DR: The morphology of the skull and of the posterior vertebrae indicate that heterochrony, or change in timing of development, has resulted in the miniaturization of Idiocranium russeli.
Abstract: Idiocranium russeli is among the smallest species of caecili- ans. The morphology of the skull (e.g., small, widely spaced dermal elements, retention of cartilaginous remnants) and of the posterior vertebrae (incomplete development, retention of a postvertebral notochord) indicate that hetero- chrony, or change in timing of development, has resulted in the miniaturiza- tion of the species. The pattern is apparently a progenetic one, characterized by early offset of development (see Alberch et al., '79). Other unique features of osteology (e.g., extensive sphenethmoid development) correlate with the burrowing habit of the species and may have arisen to compensate for proge- netic effects. Several features of the myology, neurology, and visceral morphol- ogy are correlated with miniaturization as well. Reproductive maturity occurs at approximately 75 mm total length; gonads are proportionately small, but other aspects of reproductive morphology are typical of direct-developing caecilians.
TL;DR: Recognition of an accepted mode of coelomogenesis in P. americanus, correlated with morphological details of adult nemertine vessels, affirms the view that nemERTine vessels are coelomic homologues.
Abstract: Formation of lateral vessels in the esophageal region of Prosorhochmus americanus embryos and coelomogenesis in the pygidial region of larval Magelona sp. are examined and compared. Earliest vessel rudiments of P. americanus are composed of a compact band of mesodermal cells (mesodermal band), lying on a layer of extracellular matrix (ECM) and lacking intercellular junctions. Rudiments are surrounded by presumptive muscle cells. Rudiments at later stages of differentiation possess lumina of differing sizes formed by a separation of apposing cell apices (schizocoely). Aohagrens junctions are apparent between lining cels of vessels following cavitation, and overlying muscle cells exhibit many myofilaments. Mesodermal bands of the recognized coelomate, Magelona sp. consist of glycogen-rich, mesodermal cells resting on ECM and joined by adhaerens junctions. Some of the cells possess a rudimentary cilium. Coelom formation occurs as a splitting of the cell band as is the case for P. americanus. Recognition of an accepted mode of coelomogenesis in P. americanus, correlated with morphological details of adult nemertine vessels, affirms the view that nemertine vessels are coelomic homologues.
TL;DR: Although many granulocytes were found in the connective tissue, granulopoiesis does not seem to be a major function and Gut‐associated haemopoietic tissue in goldfish resembles diffuse lymphoid tissue and may be involved in intestinal immune responses.
Abstract: The head kidney and spleen are major sites of haemopoiesis in fish; a secondary center is found in loose connective tissue of the intestine. In this study we determined the nature of gut-associated haemopoietic tissue in the goldfish, Carassius auratus, using light and electron microscopy. This tissue is a loose stroma of reticular cells and fibers vascularized by capillaries, venules, and arterioles. The cellular population includes lymphoblasts, small and medium-sized lymphocytes, plasmocytes, macrophages, and various granulocytes. The most abundant granulocyte is the mast cell, whose large granules stain with Alcian blue and toluidine blue. Heterophils are found in the intestinal connective tissue as well as two other granulocytes: one with ovoid granules having dense parallel lamellae and another with granules containing crystalline inclusions. Immature forms of both granulocytes were also noted. Macrophages containing phagocytosed debris were often located close to the epithelium; they were observed forming clusters with lymphocytes. The epithelium contained a number of migrating leucocytes including lymphocytes and lymphoblasts, macrophages, and heterophils. Although many granulocytes were found in the connective tissue, granulopoiesis does not seem to be a major function. Gut-associated haemopoietic tissue in goldfish resembles diffuse lymphoid tissue and may be involved in intestinal immune responses.
TL;DR: A new phylogeny of the Dipnoi is presented, with the basic structure being defined by the conclusions drawn from Campbell and Barwick's ('83) work, namely, that patterns of dentition characterized by expanding growth and fusion of denticles or of the development of organized tooth plates each arose only once in evolution.
Abstract: Miles ('77) has produced the only comprehensive cladistic analysis of the Dipnoi. His phylogeny involves both definitely and uncertainly placed genera. An analysis of the data for the definitely placed genera, using a Wagner routine, showed that his phylogeny is similar to two of eight equally parsimonious cladograms. Analysis of the data for all the genera of Miles's phylogeny produced sixteen equally parsimonious cladograms. They have a wide range of topologies, none of which corresponds to Miles's phylogeny. It is shown that Miles employed some character weighting to obtain his phylogeny. A cladogram is presented based on Campbell and Barwick's ('83, '84) study of early dipnoan dentitions. The phylogenetic conclusions drawn from Campbell and Barwick's work are dependent on stratigraphic and functional data. The resulting cladogram differs from all the trees produced by the re-analysis of Miles's complete phylogeny; it is less parsimonious and requires that the type of dentition consisting of a shagreen of small denticles that are shed during growth is an advanced dipnoan feature rather than a primitive one. Campbell and Barwick's ('83) phylogeny is favored since, for theoretical and practical reasons, parsimony is not a good criterion for choosing between the possible phylogenies for dipnoans. Campbell and Barwick's ('83) phylogenetic conclusions are based on a richer empirical base and are more consistent with observed functional trends. A new phylogeny of the Dipnoi is presented, with the basic structure being defined by the conclusions drawn from Campbell and Barwick's ('83) work, namely, that patterns of dentition characterized by expanding growth and fusion of denticles or of the development of organized tooth plates each arose only once in evolution. The addition of Miles's ('77) characters, using the principle of parsimony, gives the fine structure of the phylogeny.
TL;DR: Evidence is provided that periosteal attachments, characterizing the soft‐tissue bone interface, are a necessary structural prerequisite for compensatory movement and invariance of the relative positions of muscles, tendons, and ligaments during long bone growth.
Abstract: This study addressed the problem of how soft structures maintain approximately the same relative positional relationships during long bone growth. Attachments of the popliteus muscle, semitendinosus tendon, medial collateral knee ligament, and extensor retinaculum were examined histologically in rabbits, aged 2-60 days, to determine the manner in which soft structures attached to long bones during growth. Soft structures inserted principally into fibrous periosteum or perichondrium in the age range studied. However, an extensive collagen fiber framework within the cellular periosteum and perichondrium, present by at least 2 days of age, linked the fibrous periosteum or perichondrium to subjacent bone or cartilage. Maturation of soft tissue-bone interfaces was viewed from two related perspectives. The first stressed temporal patterning of cartilage and bone differentiation. The second emphasized incorporation of attachments of soft structures into bone and cartilage matrices during growth and remodeling. Differentiation and remodeling of bone and cartilage varied not only with age, but also between regions of attachment of single muscles and ligaments. Insertion regions were characterized by the presence of coarse-fibered periosteal bone and chondroid bone, both morphologically intermediate between fibrocartilage and lamellar bone. These results provide evidence that periosteal attachments, characterizing the soft-tissue bone interface, are a necessary structural prerequisite for compensatory movement and invariance of the relative positions of muscles, tendons, and ligaments during long bone growth.