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PubMed1986

Microanatomy of the renicule of Balaena mysticetus.

Renicules from twelve bowhead whales (Balaena mysticetus) were examined utilizing light, scanning electron, and transmission electron microscopes. The basic organization of the renicule into capsule, cortex, sporta perimedullaris, medulla, and calyx is described. Despite less than perfect preservation resulting from environmental and logistical conditions at the collecting sites, it has been possible to document the basic microstructure of most components of the renicule of this endangered species. Several unusual features were observed. The absence of smooth muscle fibers (other than in vessel walls) from the capsule, sporta perimedullaris, and calyx wall is a departure from what is reported in other cetaceans as is the consistent presence of arcuate arteries in the substance of the sporta perimedullaris. Large subcapsular veins are present but do not appear to represent connecting elements in an alternative venous return through capsular and interrenicular veins. Elastic fibers are seen only in the sporta perimedullaris and the calyx wall, whereas reticular fibers are most abundant in the medullary stroma. Finally, enlarged cells with clear cytoplasm are seen in the tunica media of the glomerular afferent arterioles extending a variable, but always considerable, distance toward the interlobular arteriole. These cells are presumed to represent an extended array of the epithelioid cells common in the afferent arterioles of the juxtaglomerular apparatus of other mammalian kidneys.

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PubMed1987

Position of the larynx in odontoceti (toothed whales).

This study examines the positional relationships of the odontocete (toothed whale) larynx to further an understanding of their breathing, swallowing, and vocalizing abilities. Seventeen specimens representing nine cetacean genera (Delphinus, Stenella, Tursiops, Grampus, Delphinapterus, Globicephala, Kogia, Mesoplodon, and Phocoena) were studied post mortem. Nine specimens were sectioned in the midsagittal plane and the position of the larynx relative to vertebral levels, skull base, and palatal structures was recorded. In eight specimens that could not be bisected for reasons of large size or condition of preservation, the larynx was removed by a ventral approach for further dissection. The results show that the upper respiratory tract of the odontocetes has evolved away from a basic mammalian pattern. Laryngeal position among terrestrial mammals usually corresponds to the level of cervical vertebrae 1-3. The odontocete larynx, however, lies rostral to the level of the atlas and extends to the presphenoidal synchondrosis. Its extension above the level of the foramen magnum is due to three factors: 1) The larynx is elongated into a tubular extension that projects beyond the soft palate into the nasopharynx; 2) the neck region is shortened owing to the highly compressed cervical vertebrae; and 3) the skull base is oriented in the same direction as the cervical vertebrae because of the horizontal and fusiform alignment of the head and thorax. Whereas the larynx of most terrestrial mammals is separable from the nasopharynx, that of the odontocetes studied may be permanently intranarial, held in place by the palatopharyngeal sphincter. Laryngeal position may affect their vocal abilities, allowing odontocetes to simultaneously swallow and echolocate.

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PubMed1988

Existence of vocal folds in the larynx of odontoceti (toothed whales).

Odontocetes (toothed whales) vocalize for communication and echolocation. The mechanisms of sound production, however, remain unclear. Their larynx has long been thought to lack vocal folds and, thus, was considered incapable of generating sounds. This study investigates internal anatomy of the odontocete larynx to: 1) describe the morphology of any folds found, 2) determine any structural homologies between these folds and the vocal folds of terrestrial mammals, and 3) assess their possible function in sound production. Larynges of 24 odontocetes representing ten genera (Delphinus, Stenella, Lagenorhynchus, Tursiops, Grampus, Delphinapterus, Globicephala, Kogia, Mesoplodon, and Phocoena) were studied post mortem. Nine specimens were cut midsagittally, and the remainder were dorsally opened to reveal internal anatomy. Results show that, contrary to established belief, vocal folds are consistently present. They are not isolated bands or "cords," but appear continuous with the internal laryngeal membrane. The attachments of these folds are the same as in terrestrial mammals, thus indicating homology with true mammalian vocal folds. These folds extend from the midline of the thyroid cartilage to the base of the arytenoid cartilages, sometimes to a discrete process. The vocal folds are elongated and oriented in a vertical plane, parallel to airflow direction. Vocal fold morphology varies, appearing as true bifurcated structures, a trifurcated fold, or a single midline fold. Laryngeal ventricles and vestibular folds are also consistently found lateral to the vocal folds. The vocal folds may divide the airstream within the larynx into three separate air currents. Fold vibrations may produce initial laryngeal sound used in echolocation or communication.

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PubMed1990

Microanatomy of the lung of the bowhead whale Balaena mysticetus.

The lungs from six bowhead whales harvested by Alaskan Eskimos have been examined with light and electron microscopes. Airways ranging from 1 to 40 mm in luminal diameter are lined by a pseudostratified ciliated epithelium containing numerous mucus-secreting cells. The underlying lamina propria-tela submucosa of these airways contains tubuloalveolar glands, plasma cells, and lymphatic accumulations in addition to both elastic and collagenous fibrillar elements. Cartilage extends to the level of the respiratory airways, but smooth muscle is absent from airways larger than 3 mm, and tubuloalveolar glands are absent from airways smaller than 3 mm. Respiratory airways are lined by pseudostratified, simple cuboidal, and simple squamous epithelia. Alveolar ducts are lined by simple squamous epithelium exclusively. A connective tissue core composed mostly of elastic fibers supports the walls of the alveolar ducts. Neither smooth muscle nor cartilage has been observed in these structures. Alveoli contain the typeical cetacean double capillary bed separated by a thick septum composed mainly of collagenous connective tissue. Alveoli are lined by a simple squamous epithelium similar to that encountered in alveolar ducts and respiratory airways. This epithelium is composed of type I and II pneumocytes closely appressed to an underlying capillary network. The type II pneumocytes contain typical lamellar bodies and tubular myelin can be seen in the air spaces. The lung is surrounded by a thick (X = 2.5 mm) visceral pleura rich in blood vessels and elastic fibers.

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PubMed2004

Neuroanatomy of the killer whale (Orcinus orca) from magnetic resonance images.

This article presents the first series of MRI-based anatomically labeled sectioned images of the brain of the killer whale (Orcinus orca). Magnetic resonance images of the brain of an adult killer whale were acquired in the coronal and axial planes. The gross morphology of the killer whale brain is comparable in some respects to that of other odontocete brains, including the unusual spatial arrangement of midbrain structures. There are also intriguing differences. Cerebral hemispheres appear extremely convoluted and, in contrast to smaller cetacean species, the killer whale brain possesses an exceptional degree of cortical elaboration in the insular cortex, temporal operculum, and the cortical limbic lobe. The functional and evolutionary implications of these features are discussed.

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PubMed2005

Morphomolecular neuronal phenotypes in the neocortex reflect phylogenetic relationships among certain mammalian orders.

The cytoarchitecture of the cerebral cortex in mammals has been traditionally investigated using Nissl, Golgi, or myelin stains and there are few comparative studies on the relationships between neuronal morphology and neurochemical specialization. Most available studies on neuronal subtypes identified by their molecular and morphologic characteristics have been performed in species commonly used in laboratory research such as the rat, mouse, cat, and macaque monkey, as well as in autopsic human brain specimens. A number of cellular markers, such as neurotransmitters, structural proteins, and calcium-buffering proteins, display a highly specific distribution in distinct classes of neocortical neurons in a large number of mammalian species. In this article, we present an overview of the morphologic characteristics and distribution of three calcium-binding proteins, parvalbumin, calbindin, and calretinin, and of a component of the neuronal cytoskeleton, nonphosphorylated neurofilament protein in the neocortex of various species, representative of the major subdivisions of mammals. The distribution of these neurochemical markers defined several species- and order-specific patterns that permit assessment of the degree to which neuronal morphomolecular specialization, as well as the regional and laminar distribution of distinct cell types in the neocortex, represents derived or ancestral features. In spite of the remarkable diversity in morphologic and cellular organization that occurred during mammalian neocortical evolution, such patterns identified several associations among taxa that closely match their phylogenetic relationships.

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PubMed2005

Cortical complexity in cetacean brains.

Cetaceans (dolphins, whales, and porpoises) have a long, dramatically divergent evolutionary history compared with terrestrial mammals. Throughout their 55-60 million years of evolution, cetaceans acquired a compelling set of characteristics that include echolocation ability (in odontocetes), complex auditory and communicative capacities, and complex social organization. Moreover, although cetaceans have not shared a common ancestor with primates for over 90 million years, they possess a set of cognitive attributes that are strikingly convergent with those of many primates, including great apes and humans. In contrast, cetaceans have evolved a highly unusual combination of neurobiological features different from that of primates. As such, cetacean brains offer a critical opportunity to address questions about how complex behavior can be based on very different neuroanatomical and neurobiological evolutionary products. Cetacean brains and primate brains are arguably most meaningfully conceived as alternative evolutionary routes to neurobiological and cognitive complexity. In this article, we summarize data on brain size and hemisphere surface configuration in several cetacean species and present an overview of the cytoarchitectural complexity of the cerebral cortex of the bottlenose dolphin.

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PubMed2003

Reconstructing cetacean brain evolution using computed tomography.

Until recently, there have been relatively few studies of brain mass and morphology in fossil cetaceans (dolphins, whales, and porpoises) because of difficulty accessing the matrix that fills the endocranial cavity of fossil cetacean skulls. As a result, our knowledge about cetacean brain evolution has been quite limited. By applying the noninvasive technique of computed tomography (CT) to visualize, measure, and reconstruct the endocranial morphology of fossil cetacean skulls, we can gain vastly more information at an unprecedented rate about cetacean brain evolution. Here, we discuss our method and demonstrate it with several examples from our fossil cetacean database. This approach will provide new insights into the little-known evolutionary history of cetacean brain evolution.

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PubMed1989

Magnetite biomineralization and geomagnetic sensitivity in higher animals: an update and recommendations for future study.

Magnetite, the only known biogenic material with ferromagnetic properties, has been identified as a biochemical precipitate in three of the five kingdoms of living organisms, with a fossil record that now extends back nearly 2 billion years. In the magnetotactic bacteria, protoctists, and fish, single-domain crystals of magnetite are arranged in membrane-bound linear structures called magnetosomes, which function as biological bar magnets. Magnetosomes in all three of these groups bear an overall structural similarity to each other, which includes alignment of the individual crystallographic [111] directions parallel to the long axis. Although the magnetosomes represent only a small volume fraction in higher organisms, enough of these highly energetic structures are present to provide sensitivity to extremely small fluctuations and gradients in the background geomagnetic field. Previous experiments with elasmobranch fish are reexamined to test the hypothesis that gradients played a role in their successful geomagnetic conditioning, and a variety of four-turn coil designs are considered that could be used to test the various hypotheses proposed for them.

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