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The anatomy of the Walrus head (Odobenus rosmarus). Part 3: The eyes and their function in Walrus ecology
... This includes well-developed facial muscles (Domning, 1977;Fay, 1982, Kastelein et al., 1991, 1993Marshall et al., 1998a;Marshall et al., 2008), elaborate vibrissae (Dosch, 1915;Bryden et al., 1978;Kamiya & Yamasaki, 1981;Fay, 1982;Reep et al., 1998;Marshall et al., 2006), and complex innervation for fine motor control of vibrissae as well as sensitive vibrotactile sensation from mystacial vibrissae (Kastelein & Van Gaalen, 1988;Marshall et al., 1998b;Bachteler & Dehnhardt, 1999;Reep et al., 2001;Marshall et al., 2007;Bauer et al., 2012). Other convergent morphological features within this specialized niche include increased width of the rostrum, a broad cranium, relatively large body size compared to the size of the head, and relatively small eyes (Kastelein et al., 1993;Murie, 1872;Fay, 1982). ...
Several mammalian lineages, most notably cetaceans, sirenians, and pinnipeds, have independently reverted to the marine environment of their long-ago, pre-mammalian ancestors. Other mammals have also adapted to coastal, estuarine, or freshwater habitats. These include various members of the Carnivora and Rodentia, along with some other living and extinct mammals. Because water is dense, heavy, viscous, and incompressible, feeding in water poses challenges, especially for animals whose ancestors evolved in terrestrial settings. Many secondarily aquatic mammals separately adopted similar functional and structural solutions to acquire, ingest, and process food, particularly suction feeding, filter feeding, raptorial (“seizing”) grasping of prey, or adaptations to remove prey from benthic sediments. This led to striking examples of convergence with other mammals or with other aquatic animals, including sharks, bony fishes, marine reptiles, and birds. Most instances of convergence involve close similarities in jaws, dentition, and musculature, overall shape of the head and mouth, methods for separating food from water, and neural and behavioral adaptations to locate and capture prey. Following discussion of basic principles underlying aquatic mammalian feeding, we outline numerous examples of convergence in extant and extinct taxa.
Pinnipeds are a clade of semi-aquatic carnivorous fin-footed marine mammals that descended from the superfamily Arctoidea within the suborder Canifornia. This is the same suborder that gave rise to bears (Ursidae) and weasels (mustilidae) (Arnason et al. 2006; Delisle and Strobeck 2005). The Mustilidae are thought to be the most closely related species to pinnipeds.(Arnason and Widegren 1986) Approximately 33 million years ago, the Otariidae (eared seals) and Obinidae (walruses) split from the Phocidae (true seals). A later split occurred, separating Otariidae and Obinidae.(Arnason et al. 2006) The transition of pinnipeds from land to water evolved simultaneously with their ability to see in air and underwater equally well.(Hanke et al. 2009a; Schusterman 1981; Schusterman and Balliet 2006) Many anatomical and physiological adaptations occurred to allow pinnipeds these amazing visual abilities.
The earliest phocid seals evolved 30–24 million years ago (Ma) in the western North Atlantic. There remains uncertainty in evolutionary relationships, with molecular data positioning phocids as the sister group to all other pinnipeds (fur seals, sea lions, and walruses), while morphology places them as sister to the extinct Desmatophocidae. The two major subfamilies of extant seals, Monachinae (southern seals) and Phocinae (northern seals) diverged 18 Ma and diversified in the North Atlantic and Paratethyan region. Both clades colonized the southern hemisphere, although southern hemisphere phocines quickly went extinct, while monachine seals declined in diversity in the North Atlantic. Monachines and phocines exhibited opposing body size trends with monachines increasing and phocines decreasing in size. Phocids are the only pinnipeds to display four feeding strategies: pierce, grip and tear, suction, and filter-feeding. Phocids were ancestrally shallow water divers with increased diving capabilities evolving among some large-bodied taxa. In terms of mating systems, ice breeding appears to have independently evolved in both clades. Although faunal dynamics are inadequately studied there is evidence during the Plio-Pleistocene for the replacement of desmatophocids and walruses by otariids and phocids and for the replacement of otariids by phocids in South America.KeywordsMonachinaePhocinaeDesmatophocidaePierceGrip and tear and filter-feedingPelvic oscillationLateral undulation
In this study, we present first data concerning the morphological observations of the orbital region, eye tunics, upper and lower eyelids, superficial gland of the third eyelid with the third eyelid, and lacrimal gland in captive adult male Asiatic black bear. The following research methods were used in the work: the eyeball morphometry, the orbital region description, macroscopic description, morphometric and histological analysis of the eye tunics and selected the accessory organs of the eye (Fontana–Masson, hematoxylin & eosin (H&E), Methyl-green-pyronin Y (MGP Y), Movat pentachrome, and picro-Mallory trichrome) as well as histochemical examination (PAS, AB pH 1.0, AB pH 2.5, AB pH 2.5/PAS and HDI). The eyeball of the Asiatic black bear was a spherical shape, while the periorbita was funnel/conical-shaped and the eye socket was of the open type. The cornea was absent of the Bowman’s membrane similar to all domestic dogs and some wild dogs. There were palisades of Vogt in the corneal limbus epithelium similar to the Canidae. Degenerative choroidal tapetum lucidum similar to ranch mink (Mustelidae) has been found. The pupil was big and round in shape. The ciliary muscle, dilatator and sphincter muscle were well developed, similar to the pinnipeds. The lens was biconvex round, similar to the Canidae. The retina was composed similarly to the diurnal terrestrial carnivores. In both eyelids were observed very well-developed tarsal glands, ciliary glands and sebaceous glands. The orbital zone in the eyelids was characterized by lymphoid follicles, diffuse lymphocytes and specialized high endothelial venules. In the anterior palpebral margin of the upper eyelid, soft and short eyelashes were observed, while in the lower eyelids they were absent. The third eyelid was T-shaped and composed of the hyaline tissue, and it contained CALT, similar to that in Canidae. The superficial gland of the third eyelid was a multilobar alveolar branched complex with seromucous nature, while the lacrimal gland was also a multilobar acinar branched complex gland, but producing a mucous–serous secretion. The results of our research indicate that the features of the anatomy of the eye and orbital region in Asiatic black bear are also typical of the Ursidae family. Moreover, a detailed analysis of the morphological eye region may be useful in comparative studies and veterinary diagnostics in this bear species.
The Afrotheria clade includes a large group of extant mammals, and the aardvark (Orycteropus afer) is the only representative of the order Tubulidentata in it. Here, we studied the morphological nature of the orbital region, eye tunics, upper and lower eyelids, superficial gland of the third eyelid, the third eyelid, deep gland of the third eyelid, and lacrimal gland in post‐mortem specimens obtained from three captive aardvarks, two young and one adult. The obtained samples were analyzed using macroscopic, histological, and histochemical methods. We observed choroidal tapetum lucidum fibrosum in all specimens, which was typical for aardvarks. The superficial gland of the third eyelid was a compound multilobar tubular branched gland of a mucous nature. The deep gland of the third eyelid produced a serous secretion. The seromucous secretion was typical for the lacrimal gland. We compared the morphological data of the O. afer skull with that from other endemic African mammals in the Afrotheria clade. We found that other authors provided different anatomical names for some bones and foramina located within the orbit. The types and function of eyelid glands, as well as eyeball glands of aardvarks, can primarily be connected with their habitat. Our study may constitute an introduction to the ontogenesis of individual eyeball glands in aardvarks. This article is protected by copyright. All rights reserved.
Chapter 3 is a comprehensive overview of the ecology and behaviour of Atlantic walrus (Odobenus rosmarus rosmarus). We describe the classification, distribution, habitat requirements, morphology, reproduction, vital parameters, general behaviour, foraging and energy requirements, natural predators, diseases and parasites.
This chapter is a comprehensive overview of anthropogenic impacts on Atlantic walrus (Odobenus rosmarus rosmarus). We describe how Atlantic walruses are affected by hunting, fishery, anthropogenic noise (ships, aircraft), industrial activities (marine oil and gas exploration and exploitation, and mining), pollution and tourism.
Sea otters (Enhydra lutris) are amphibious mammals that maintain equal in-air and underwater visual acuity. However, their lens-based underwater accommodative mechanism presumably requires a small pupil that may limit sensitivity across light levels. In this study, we consider adaptations for amphibious living by assessing the tapetum lucidum, retina, and pupil dynamics in sea otters. The sea otter tapetum lucidum resembles that of terrestrial carnivores in thickness and fundic coverage. A heavily rod-dominated retina appears qualitatively similar to the ferret and domestic cat, and a thick outer nuclear layer relative to a thinner inner nuclear layer is consistent with nocturnal vertebrates and other amphibious carnivores. Pupil size range in two living sea otters is smaller relative to other amphibious marine carnivores (pinnipeds) when accounting for test conditions. The pupillary light response seems slower than other aquatic and terrestrial species tested in comparable brightness, although direct comparisons require further assessment. Our results suggest that sea otters have retained features for low-light vision but rapid adjustments and acute underwater vision may be constrained across varying light levels by a combination of pupil shape, absolute eye size, and the presumed coupling between anterior lens curvature and pupil size during accommodation.
Sensory receptors are specialized cells for transducing information from an animal’s environment into nerve impulses that are transmitted to the central nervous system for processing and integration to detect external variables and initiate responses that enhance survival. Each type of receptor has its own sensory modality such as photoreception (vision), mechanoreception (hearing, pressure, vibration, orientation, and acceleration), chemoreception (taste and smell), thermoreception (temperature), electroreception (electric field), and magnetoreception (magnetic field), although not all receptor types are present in every species, and some are more highly developed (i.e., provide greater acuity) than others. Although marine mammals evolved from terrestrial ancestors, the propagation and reception of light and sound in air and water are so different that these sensory systems have been modified for either a fully aquatic (Cetacea and Sirenia) or amphibious (pinnipeds and sea otters) lifestyle. Specialized tactile hairs (vibrissae) in some marine mammals, tactile sensitivity in the forepaws of sea otters, and electroreception in at least one species of Cetacea provide additional sensory information under disphotic (twilight) or aphotic (no solar light) conditions, which characterize most of the marine environment and some freshwater habitats. In contrast, chemosensory (olfaction and gustation) ability shows a convergent, evolutionary reduction associated with the transition from a terrestrial to aquatic life. Finally, emerging evidence indicates a magnetic sensory ability in Cetacea and pinnipeds for orientation and navigation during individual dives and long-distance migrations.
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