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Smaers JB, Turner AH, Gómez-Robles A, Sherwood CC. A cerebellar substrate for cognition evolved multiple times independently in mammals. eLife 2018; 7:e35696. [PMID: 29809137 PMCID: PMC6003771 DOI: 10.7554/elife.35696] [Citation(s) in RCA: 35] [Impact Index Per Article: 5.8] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 02/06/2018] [Accepted: 05/21/2018] [Indexed: 12/21/2022] Open
Abstract
Given that complex behavior evolved multiple times independently in different lineages, a crucial question is whether these independent evolutionary events coincided with modifications to common neural systems. To test this question in mammals, we investigate the lateral cerebellum, a neurobiological system that is novel to mammals, and is associated with higher cognitive functions. We map the evolutionary diversification of the mammalian cerebellum and find that relative volumetric changes of the lateral cerebellar hemispheres (independent of cerebellar size) are correlated with measures of domain-general cognition in primates, and are characterized by a combination of parallel and convergent shifts towards similar levels of expansion in distantly related mammalian lineages. Results suggest that multiple independent evolutionary occurrences of increased behavioral complexity in mammals may at least partly be explained by selection on a common neural system, the cerebellum, which may have been subject to multiple independent neurodevelopmental remodeling events during mammalian evolution.
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Affiliation(s)
- Jeroen B Smaers
- Department of AnthropologyStony Brook UniversityNew YorkUnited States
- Center for the Advanced Study of Human PaleobiologyStony Brook UniversityNew YorkUnited States
| | - Alan H Turner
- Department of Anatomical SciencesStony Brook UniversityNew YorkUnited States
| | - Aida Gómez-Robles
- Department of Genetics, Evolution and EnvironmentUniversity College LondonLondonUnited Kingdom
- Department of AnthropologyThe George Washington UniversityWashingtonUnited States
| | - Chet C Sherwood
- Department of AnthropologyThe George Washington UniversityWashingtonUnited States
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Loza CM, Scarano AC, Galliari FC, Soibelzon LH, Negrete J, Carlini AA. The tympanic region of Otaria byronia (Otariidae, Carnivora) - morphology, ontogeny, age classes and dimorphism. J Anat 2018; 232:54-71. [PMID: 29082536 PMCID: PMC5735057 DOI: 10.1111/joa.12717] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Accepted: 09/04/2017] [Indexed: 11/30/2022] Open
Abstract
Here we describe and explore for the first time the ontogeny and sexual dimorphism of the auditory region of Otaria byronia. We studied the tympanic region of skulls of 237 specimens of different ages and sexes. Geometric morphometric methods were used to analyze the tympanic bulla. In addition, 3D reconstructions of the tympanic bulla were performed using computed tomography analysis scans and a serial wearing technique. We provide a description of the external and internal morphology of the tympanic bulla in both sexes and across different stages (bioclasses). The average shape of the bulla in O. byronia has a subtriangular contour, with variations between sexes and ages. Each stage (bioclasses I, II, and III) is characterized by the respective mean shape of the tympanic bulla and designated as a morphoclass (1, 2, and 3). In all cases, the ectotympanic shows greater surface area than the endotympanic, as in other otariids, in contrast to Phocidae. During ontogeny, the relative size of the ectotympanic increases, growing in all directions and covering the endotympanic. This pattern is seen to the greatest extent in adult males, in which the ectotympanic forms an extremely well-developed apophysis jugulare. No differences in internal morphology of the tympanic cavity were recorded between ages and sexes. The bulla does not increase in thickness in successive age classes; in fact, the walls are extremely thin in the adult stages, despite the extensive development of its processes. This pattern is opposite that observed in Phocidae. In morphoclass 3, adult males older than 7 years undergo hypermorphic change that results in a peramorphic condition when compared to adult females. These changes probably follow the same pattern shown by the rest of the skull and contribute to the marked sexual dimorphism of the species.
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Affiliation(s)
- C. M. Loza
- División Paleontología de VertebradosMuseo de La PlataFacultad de Ciencias Naturales y MuseoUniversidad Nacional de La PlataLa PlataArgentina
| | - A. C. Scarano
- División Paleontología de VertebradosMuseo de La PlataFacultad de Ciencias Naturales y MuseoUniversidad Nacional de La PlataLa PlataArgentina
- Departamento de Ciencias AmbientalesUniversidad Nacional de AvellanedaBuenos AiresArgentina
- Consejo Nacional de Investigaciones Científicas y TécnicasBuenos AiresArgentina
| | - F. C. Galliari
- División Paleontología de VertebradosMuseo de La PlataFacultad de Ciencias Naturales y MuseoUniversidad Nacional de La PlataLa PlataArgentina
- Consejo Nacional de Investigaciones Científicas y TécnicasBuenos AiresArgentina
| | - L. H. Soibelzon
- División Paleontología de VertebradosMuseo de La PlataFacultad de Ciencias Naturales y MuseoUniversidad Nacional de La PlataLa PlataArgentina
- Consejo Nacional de Investigaciones Científicas y TécnicasBuenos AiresArgentina
| | - J. Negrete
- Departamento de Biología de Predadores TopeInstituto Antártico ArgentinoBuenos AiresArgentina
| | - A. A. Carlini
- División Paleontología de VertebradosMuseo de La PlataFacultad de Ciencias Naturales y MuseoUniversidad Nacional de La PlataLa PlataArgentina
- Consejo Nacional de Investigaciones Científicas y TécnicasBuenos AiresArgentina
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Affiliation(s)
- Eva K Sawyer
- Neuroscience Graduate Program, Vanderbilt University, Nashville, TN, and Department of Bioengineering, University of California, Berkeley, Berkeley, CA, USA
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Sawyer EK, Turner EC, Kaas JH. Somatosensory brainstem, thalamus, and cortex of the California sea lion (Zalophus californianus). J Comp Neurol 2016; 524:1957-75. [PMID: 26878587 PMCID: PMC4833517 DOI: 10.1002/cne.23984] [Citation(s) in RCA: 21] [Impact Index Per Article: 2.6] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 01/13/2016] [Revised: 02/08/2016] [Accepted: 02/09/2016] [Indexed: 12/18/2022]
Abstract
Pinnipeds (sea lions, seals, and walruses) are notable for many reasons, including their ape-sized brains, their adaptation to a coastal niche that combines mastery of the sea with strong ties to land, and the remarkable abilities of their trigeminal whisker system. However, little is known about the central nervous system of pinnipeds. Here we report on the somatosensory areas of the nervous system of the California sea lion (Zalophus californianus). Using stains for Nissl, cytochrome oxidase, and vesicular glutamate transporters, we investigated the primary somatosensory areas in the brainstem, thalamus, and cortex in one sea lion pup and the external anatomy of the brain in a second pup. We find that the sea lion's impressive array of whiskers is matched by a large trigeminal representation in the brainstem with well-defined parcellation that resembles the barrelettes found in rodents but scaled upward in size. The dorsal column nuclei are large and distinct. The ventral posterior nucleus of the thalamus has divisions, with a large area for the presumptive head representation. Primary somatosensory cortex is located in the neocortex just anterior to the main vertical fissure, and precisely locating it as we do here is useful for comparing the highly gyrified pinniped cortex with that of other carnivores. To our knowledge this work is the first comprehensive report on the central nervous system areas for any sensory system in a pinniped. The results may be useful both in the veterinary setting and for comparative studies related to brain evolution.
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Affiliation(s)
- Eva K Sawyer
- Neuroscience Graduate Program, Vanderbilt University, Nashville, Tennessee, 37240
| | - Emily C Turner
- Department of Psychology, Vanderbilt University, Nashville, Tennessee, 37240
| | - Jon H Kaas
- Department of Psychology, Vanderbilt University, Nashville, Tennessee, 37240
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Meise K, Mueller B, Zein B, Trillmich F. Applicability of single-camera photogrammetry to determine body dimensions of pinnipeds: Galapagos sea lions as an example. PLoS One 2014; 9:e101197. [PMID: 24987983 PMCID: PMC4079256 DOI: 10.1371/journal.pone.0101197] [Citation(s) in RCA: 17] [Impact Index Per Article: 1.7] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [MESH Headings] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 09/05/2013] [Accepted: 06/03/2014] [Indexed: 11/23/2022] Open
Abstract
Morphological features correlate with many life history traits and are therefore of high interest to behavioral and evolutionary biologists. Photogrammetry provides a useful tool to collect morphological data from species for which measurements are otherwise difficult to obtain. This method reduces disturbance and avoids capture stress. Using the Galapagos sea lion (Zalophus wollebaeki) as a model system, we tested the applicability of single-camera photogrammetry in combination with laser distance measurement to estimate morphological traits which may vary with an animal's body position. We assessed whether linear morphological traits estimated by photogrammetry can be used to estimate body length and mass. We show that accurate estimates of body length (males: ±2.0%, females: ±2.6%) and reliable estimates of body mass are possible (males: ±6.8%, females: 14.5%). Furthermore, we developed correction factors that allow the use of animal photos that diverge somewhat from a flat-out position. The product of estimated body length and girth produced sufficiently reliable estimates of mass to categorize individuals into 10 kg-classes of body mass. Data of individuals repeatedly photographed within one season suggested relatively low measurement errors (body length: 2.9%, body mass: 8.1%). In order to develop accurate sex- and age-specific correction factors, a sufficient number of individuals from both sexes and from all desired age classes have to be captured for baseline measurements. Given proper validation, this method provides an excellent opportunity to collect morphological data for large numbers of individuals with minimal disturbance.
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Affiliation(s)
- Kristine Meise
- Department of Animal Behaviour, University of Bielefeld, Bielefeld, Germany
| | - Birte Mueller
- Department of Animal Behaviour, University of Bielefeld, Bielefeld, Germany
| | - Beate Zein
- Department of Animal Behaviour, University of Bielefeld, Bielefeld, Germany
| | - Fritz Trillmich
- Department of Animal Behaviour, University of Bielefeld, Bielefeld, Germany
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Khamas WA, Smodlaka H, Leach-Robinson J, Palmer L. Skin histology and its role in heat dissipation in three pinniped species. Acta Vet Scand 2012; 54:46. [PMID: 22889205 PMCID: PMC3502088 DOI: 10.1186/1751-0147-54-46] [Citation(s) in RCA: 28] [Impact Index Per Article: 2.3] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 04/30/2012] [Accepted: 07/24/2012] [Indexed: 11/10/2022] Open
Abstract
BACKGROUND Pinnipeds have a thick blubber layer and may have difficulty maintaining their body temperature during hot weather when on land. The skin is the main thermoregulatory conduit which emits excessive body heat. METHODS Thorough evaluation of the skin histology in three pinniped species; the California sea lion-Zalophus californianus, the Pacific harbor seal-Phoca vitulina richardsi, and the Northern elephant seal-Mirounga angustirostris, was conducted to identify the presence, location and distribution of skin structures which contribute to thermoregulation. These structures included hair, adipose tissue, sweat glands, vasculature, and arteriovenous anastomoses (AVA). Thermal imaging was performed on live animals of the same species to correlate histological findings with thermal emission of the skin. RESULTS The presence and distribution of skin structures directly relates to emissivity of the skin in all three species. Emissivity of skin in phocids (Pacific harbor and Northern elephant seals) follows a different pattern than skin in otariids (California sea lions). The flipper skin in phocids tends to be the most emissive region during hot weather and least emissive during cold weather. On the contrary in otariids, skin of the entire body has a tendency to be emissive during both hot and cold weather. CONCLUSION Heat dissipation of the skin directly relates to the presence and distribution of skin structures in all three species. Different skin thermal dissipation patterns were observed in phocid versus otariid seals. Observed thermal patterns can be used for proper understanding of optimum thermal needs of seals housed in research facilities, rescue centers and zoo exhibits.
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Affiliation(s)
- Wael A Khamas
- College of Veterinary Medicine, Western University of Health Sciences, 309 E. Second Street, Pomona, CA 91766-1854, USA
| | - Hrvoje Smodlaka
- College of Veterinary Medicine, Western University of Health Sciences, 309 E. Second Street, Pomona, CA 91766-1854, USA
| | - Jessica Leach-Robinson
- College of Veterinary Medicine, Western University of Health Sciences, 309 E. Second Street, Pomona, CA 91766-1854, USA
| | - Lauren Palmer
- The Marine Mammal Care Center Fort MacArthur, 3601S. Gaffey St., San Pedro, CA 90731, USA
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Labrada-Martagón V, Aurioles-Gamboa D, Castro-González MI. Relation of dental wear to the concentrations of essential minerals in teeth of the California sea lion Zalophus californianus californianus. Biol Trace Elem Res 2007; 115:107-26. [PMID: 17435255 DOI: 10.1007/bf02686023] [Citation(s) in RCA: 12] [Impact Index Per Article: 0.7] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Received: 05/22/2006] [Revised: 06/05/2006] [Accepted: 06/10/2006] [Indexed: 10/22/2022]
Abstract
Tooth wear in marine mammals has been attributed to age, feeding habits, behavior, and contaminants. Advanced tooth wear in some California sea lions, including some of very young age (<5 yr), in the Gulf of California, suggests that there are variations in chemical composition of tooth parts, wherein the concentrations of certain trace minerals might be anomalous, making them more susceptible to erosion. The concentrations of the essential minerals Ca, P, K, Na, Fe, Mg, and Zn in the dentition of Zalophus c. californianus are documented for the first time and are compared for sea lion teeth with different degrees of wear. Canine teeth and molars from 45 skulls collected at 15 localities since 1978 were digested in perchloric acid and analyzed using atomic adsorption spectrometry, the results being expressed in milligrams per 100 g. An index of tooth wear (Id) was established, involving the average wear on the teeth and the age of the organism. No significant difference was detected in the variables, but there was one between ages (p = 0.02). A higher degree of wear was observed up to 7 yr of age than from this age onward. Mineral concentrations did not explain the excessive wear observed (correlation, p > 0.09; ANOVA, p > 0.15); however, the Ca concentration of the teeth was inversely proportional to the age of the animal (sexes combined, p = 0.026) and particularly significant for the females (r2 = 0.112, r = -0.335, p = 0.039). Females could be more prone to decalcification because of their annual bone investment in their offspring. Animals of both sexes were susceptible to tooth wear as their age increased, but the higher frequency of animals between 4 and 7 yr suggests an impact on survival at early stages probably linked to deficient feeding and chronic malnutrition.
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Affiliation(s)
- Vanessa Labrada-Martagón
- Centro Interdisciplinario de Ciencias Marinas, Instituto Politécnico Nacional, Av IPN s/n, Colonia Playa de Santa Rita, La Paz, Baja California Sur, México
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Mass AM. A high-resolution area in the retinal ganglion cell layer of the Steller's sea lion (Eumetopias jubatus): a topographic study. Dokl Biol Sci 2004; 396:187-90. [PMID: 15354821 DOI: 10.1023/b:dobs.0000033272.90536.a6] [Citation(s) in RCA: 4] [Impact Index Per Article: 0.2] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 04/30/2023]
Affiliation(s)
- A M Mass
- Severtsov Institute of Ecology and Evolution, Russian Academy of Sciences, Leninskii pr. 33, Moscow, 117071 Russia
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Abstract
Maneuverability is critical to the performance of fast-swimming marine mammals that use rapid turns to catch prey. Overhead video recordings were analyzed for two sea lions (Zalophus californianus) turning in the horizontal plane. Unpowered turns were executed by body flexion in conjunction with use of the pectoral and pelvic flippers, which were used as control surfaces. A 90 degree bank angle was used in the turns to vertically orient the control surfaces. Turning radius was dependent on body mass and swimming velocity. Relative minimum radii were 9-17% of body length and were equivalent for pinnipeds and cetaceans. However, Zalophus had smaller turning radii at higher speeds than cetaceans. Rate of turn was inversely related to turn radius. The highest turn rate observed in Zalophus was 690 degrees s(-1). Centripetal acceleration measured up to 5.1 g for Zalophus. Comparison with other marine mammals indicates that Zalophus has a morphology that enhances instability, thus providing enhanced turning performance. Enhanced turning performance is necessary for sea lions to forage after highly elusive prey in structurally complex environments.
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Affiliation(s)
- Frank E Fish
- Department of Biology, West Chester University, West Chester, PA 19383, USA.
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Yoshimura K, Shindoh J, Kobayashi K. Scanning electron microscopy study of the tongue and lingual papillae of the California sea lion (Zalophus californianus californianus). Anat Rec 2002; 267:146-53. [PMID: 11997883 DOI: 10.1002/ar.10093] [Citation(s) in RCA: 40] [Impact Index Per Article: 1.8] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 11/09/2022]
Abstract
We observed the three-dimensional structures on the external surface and the connective tissue cores (CTCs) of the California sea lion (Zalophus californianus californianus), after exfoliation of the epithelium of the lingual papillae (filiform, fungiform, and vallate papillae), using scanning electron microscopy (SEM) and conventional light microscopy. Macroscopically, the tongue was V-shaped and its apex was rounded. At the posterior area of the tongue, five vallate papillae were arranged in a V shape. In the epithelium, numerous taste buds were distributed on the top of the vallate papillae. On the dorsal surface from the apex to the boundary between the anterior and posterior tongue, filiform papillae were densely distributed. The CTCs of the filiform papillae consisted of a main protrusion (primary core) and many small cores (secondary cores). From the apex to the anterior one-third of the tongue, dome-like fungiform papillae were densely distributed, whereas fewer were located at the posterior two-thirds of the tongue. Several taste buds were found in the epithelium on the fungiform papillae. The size of the filiform papillae gradually increased from the apex to the boundary between the anterior and posterior tongue. At the lingual radix, the conical papillae, which were bigger than any filiform papillae, were densely distributed. The morphological characteristics of the tongue of the California sea lion appear to have been transformed to adapt to an aquatic environment; however, they possess some structures similar to those of land mammals.
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Affiliation(s)
- Ken Yoshimura
- Department of Anatomy, Nippon Dental University at Niigata, 1-8 Hamaura-cho, Niigata City, Niigata 951-8580, Japan.
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Abstract
Drag forces acting on Steller sea lions (Eumetopias jubatus) were investigated from ‘deceleration during glide’ measurements. A total of 66 glides from six juvenile sea lions yielded a mean drag coefficient (referenced to total wetted surface area) of 0.0056 at a mean Reynolds number of 5.5×10(6). The drag values indicate that the boundary layer is largely turbulent for Steller sea lions swimming at these Reynolds numbers, which are past the point of expected transition from laminar to turbulent flow. The position of maximum thickness (at 34 % of the body length measured from the tip of the nose) was more anterior than for a ‘laminar’ profile, supporting the idea that there is little laminar flow. The Steller sea lions in our study were characterized by a mean fineness ratio of 5.55. Their streamlined shape helps to delay flow separation, reducing total drag. In addition, turbulent boundary layers are more stable than laminar ones. Thus, separation should occur further back on the animal. Steller sea lions are the largest of the otariids and swam faster than the smaller California sea lions (Zalophus californianus). The mean glide velocity of the individual Steller sea lions ranged from 2.9 to 3.4 m s(−)(1) or 1.2-1.5 body lengths s(−)(1). These length-specific speeds are close to the optimum swim velocity of 1.4 body lengths s(−)(1) based on the minimum cost of transport for California sea lions.
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Affiliation(s)
- L L Stelle
- Department of Zoology, University of British Columbia, Vancouver, Canada.
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Abstract
In the California sea lion (Zalophus californianus), the position of the tracheal bifurcation is fairly cranial compared with those of mammals in general. The right lung has the dorsal, ventral, medial and lateral bronchiole systems. The cranial lobe is formed by the first bronchiole of the dorsal bronchiole system. The middle lobe is formed by the first bronchiole of the lateral bronchiole system. The accessory lobe is formed by the first bronchiole of the ventral bronchiole system. The caudal lobe is formed by the remaining bronchioles of the dorsal and lateral bronchiole systems and all bronchioles of the medial bronchiole system. The left lung has the dorsal and lateral bronchiole systems. The middle lobe is formed by the first bronchiole of the lateral bronchiole system. The caudal lobe is formed by the remaining bronchioles of the lateral bronchiole system and all bronchioles of the dorsal bronchiole system.
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Affiliation(s)
- S Nakakuki
- Department of Veterinary Anatomy, Faculty of Agriculture, Tokyo University of Agriculture and Technology, Japan
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McGrath CJ, Feeney D, Crimi AJ, Ruff J. Upper airway of the California sea lion: an anesthetist's perspective. Vet Med Small Anim Clin 1981; 76:548-9. [PMID: 6908776] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [What about the content of this article? (0)] [MESH Headings] [Subscribe] [Scholar Register] [Indexed: 01/22/2023]
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Bryden MM, Molyneux GS. Arteriovenous anastomoses in the skin of seals. II. The California sea lion Zalophus californianus and the northern fur seal Callorhinus ursinus (Pinnipedia: Otariidae). Anat Rec (Hoboken) 1978; 191:253-60. [PMID: 666020 DOI: 10.1002/ar.1091910210] [Citation(s) in RCA: 26] [Impact Index Per Article: 0.6] [Reference Citation Analysis] [What about the content of this article? (0)] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/23/2022]
Abstract
The structure, distribution and density of arteriovenous anastomoses (AVAs) were studied in body and flipper skin of a California sea lion and a nothern fur seal. In both animals AVAs consisted of arterial, intermediate and venous segments, and were generally larger and more tortuous in the sea lion than in the fur seal. In the sea lion the majority of AVAs (72%) occurred in the deeper region of the dermis, and the density was significantly greater in the flippers than in the body. In the northern fur seal most AVAs (76%) occurred in the superficial region of the dermis; the density of AVAs in flipper skin was significantly higher than in body skin, and the density in the hind flipper was significantly greater than in the foreflipper. Arteriovenous anastomoses are important in the regulation of body temperature in seals; when these animals are on land, AVAs function to dissipate body heat, and vascular thermoregulation occurs in the flippers but notover the general body surface. Due to differences in distribution and density, AVAs play a more significant role in thermoregulation in the northern fur seal than in the California sea lion.
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Abstract
Dissections, manipulation of ligamentary preparations, analysis of limb proportions, and quantitative aspects of forelimb myology are used to correlate forelimb morphology in fur seals and sea lions (sub-family Otariinae) with previously published data as to their locomotor function (English, '76a). Comparisons to structure and function in generalized fissiped carnivores are then used to elucidate locomotor adaptations in fur seals and sea lions. Unique features of forelimb function during swimming in these pinnipeds include the amounts of abduction-adduction and rotary movements used. Modifications of the size, attachments and fasicle architecture of the muscles and the structure and range of possible movement of the joints suggest that in fur seals and sea lions these movements (1) take place about the glenohumeral (shoulder) joints, (2) that the movements are probably finely controlled, and (3) that they contribute to the generation of massive forward thrust via the cooperative activity of muscles capable of generating large amounts of force throughout the range of movement. Recovery movements occur through a similarly large range, and modifications of forelimb anatomy either to minimize or overcome water resistance are noted. The adaptive significance of these modifications is interpreted as allowing fur seals and sea lions to swim at speeds necessary to feed on the fast swimming prey presumably abundant in their adaptive zone.
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Abstract
Dissections and manipulations of the hands of 14 specimens of four genera of fur seals and sea lions and of generalized fissiped carnivores were used to identify the structural modifications involved in formation of the expanded forelimb paddles characteristic of these pinnipeds. The morphological peculiarities were then correlated with differences in locomotor function, both on land and in the water, on the basis of previously published data, for the purpose of identifying modifications of structure and function which have adaptive vale. Structural differences found in the manus of fur seals and sea lions include: (1) reduction in size of the ulnar side of the carpus and a radial shift in the length-order of the digits, (2) development of musculature in the antebrachial fascia which attaches to the caudal margin of the flipper, (3) orientation of the radial side of the manus dorsal and radial to the rest of the hand, (4) increased range of possible midcarpal movement and in deviational mobility at the first and fifth digits, (5) attachment of forearm musculature onto radial digits and (6) well-developed hypothenar muscles and absence of thenar muscles. Modifications in hand structure are viewed as providing a morphological basis for employment of the hand to advantage during aquatic locomotion while maintaining thrust-producing and potentially energy-conserving capacities during movement on land. As such these differences in structure and function are viewed as adaptations to locomotion in the water and on land which are extensions of locomotor adaptations attributed to modifications of forelimb structure and function associated with the generation of massive aquatic locomotor thrust. The adaptive value of such modifications is interpreted as allowing fur seals and sea lions to swim with speed and thereby capture elusive fast-swimming prey while maintaining a level of terrestrial locomotor ability compatible with their amphibious mode of life.
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