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The sensitivity of the vibrissae of a Pacific walrus (Odobenus rosmarus divergens). Part 1
... The mystacial vibrissal field is divided into macro-and microvibrissae in rodents (e.g., Brecht et al., 1997). Similar morphological and function divisions have also been described in pinnipeds (Dehnhardt, 1994;Dehnhardt, Sinder, & Sachser, 1997;Grant, Wieskotten, Wengst, Prescott, & Dehnhardt, 2013;Kastelein & Van Gaalen, 1988;Mattson & Marshall, 2016;Sprowls, 2017). For pinnipeds performing object recognition tasks (active touch), the behavioral trend is for large, lateral macrovibrissae to be used to determine size, orientation, and general shape of an object, whereas shorter, more numerous medial microvibrissae are used for fine-scale tactile resolution. ...
... Few data are available for the tactile discrimination capability of walruses. Psychophysical testing of a single walrus, however, demonstrated that they use mystacial vibrissae to detect size differences down to a surface area of 0.4 cm 2 in test objects (Kastelein & Van Gaalen, 1988). As in other pinnipeds, the subject used "longer vibrissae," presumably macrovibrissae, to locate the test object and smaller, most ventromedial vibrissae above the upper lip to discriminate between the smallest objects. ...
The successful return of mammals to aquatic environments presented numerous sensory challenges to overcome. Aquatic habitats reduced the utility of vision and the type of chemoreception important in terrestrial perception. In several orders, the sense of touch assumed greater importance, especially when enhanced by the development of vibrissal (sensory hair) systems. Species of two extant orders, Sirenia and Cetacea, lost all of their hairs except for vibrissae. In the former, these hairs cover the entire bodies of the two families, Trichechidae and Dugongidae. Hairs in adult cetaceans are more constrained (e.g., some river dolphins and baleen whales) and are restricted primarily to rostral regions. Pinnipeds and sea otters retained their pelage, but in addition have elaborated their mystacial and other facial vibrissae. High numbers of vibrissal receptors, associated dense innervation, prominence of neural tracts, and hypertrophy of brain areas associated with touch suggest an importance of tactile senses for aquatic mammals. Experimental testing has demonstrated the exquisite tactile sensitivity of many marine mammal species. Sensory hairs contribute to that tactile sensitivity in both haptic and mechanosensory contexts. Several, if not most, pinniped species, seals and sea lions, can track prey based on mechanoreception alone. In this review we will discuss the neurobiological and behavioral evidence for the tactile senses of marine mammals.
... Walruses, bearded seals and sirenians converge on a suite of morphological features and benthic behaviors (Fay, 1982;Kastelein & Mosterd, 1989;Kastelein et al., 1994;Marshall et al., 1998aMarshall et al., , 2000Marshall et al., , 2003Marshall et al., , 2006. 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). ...
... Walruses, bearded seals and sirenians converge on a suite of morphological features and benthic behaviors (Fay, 1982;Kastelein & Mosterd, 1989;Kastelein et al., 1994;Marshall et al., 1998aMarshall et al., , 2000Marshall et al., , 2003Marshall et al., , 2006. 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.
... The mammalian vibrissal follicle-sinus complex is composed of specialized sensory structures that respond to vibrotactile cues in the environment that are transmitted to the brain (Halata, 1975;Marshall et al., 2006), presumably by afferent fibers of the trigeminal nerve's maxillary division. The vibrissal follicle-sinus complex in both bearded seals and walruses is hypothesized to be associated with their use of benthic suction feeding (Kastelein & van Gaalen, 1988;Marshall et al., 2006). Specifically, the well-developed vibrissal follicle-sinus complex may allow individuals to detect and discriminate between prey located on or near the seafloor. ...
Secondarily aquatic tetrapods have many unique morphologic adaptations for life underwater compared with their terrestrial counterparts. A key innovation during the land-to-water transition was feeding. Pinnipeds, a clade of air-breathing marine carnivorans that include seals, sea lions, and walruses, have evolved multiple strategies for aquatic feeding (e.g., biting, suction feeding). Numerous studies have examined the pinniped skull and dental specializations for underwater feeding. However, data on the pinniped craniofacial musculoskeletal system and its role in aquatic feeding are rare. Therefore, the objectives of this study were to conduct a comparative analysis of pinniped craniofacial musculature and examine the function of the craniofacial musculature in facilitating different aquatic feeding strategies. We performed anatomic dissections of 35 specimens across six pinniped species. We describe 32 pinniped craniofacial muscles—including facial expression, mastication, tongue, hyoid, and soft palate muscles. Pinnipeds broadly conform to mammalian patterns of craniofacial muscle morphology. Pinnipeds also exhibit unique musculoskeletal morphologies—in muscle position, attachments, and size—that likely represent adaptations for different aquatic feeding strategies. Suction feeding specialists (bearded and northern elephant seals) have a significantly larger masseter than biters. Further, northern elephant seals have large and unique tongue and hyoid muscle morphologies compared with other pinniped species. These morphologic changes likely help generate and withstand suction pressures necessary for drawing water and prey into the mouth. In contrast, biting taxa (California sea lions, harbor, ringed, and Weddell seals) do not exhibit consistent craniofacial musculoskeletal adaptations that differentiate them from suction feeders. Generally, we discover that all pinnipeds have well-developed and robust craniofacial musculature. Pinniped head musculature plays an important role in facilitating different aquatic feeding strategies. Together with behavioral and kinematic studies, our data suggest that pinnipeds’ robust facial morphology allows animals to switch feeding strategies depending on the environmental context—a critical skill in a heterogeneous and rapidly changing underwater habitat.
... We observed, specifically, that during the size discrimination task Lo moved her nose and whiskers to the edges of a shape to judge its width (Figure 1b; Figure 3c, Supplementary Movie 1). Large head and whisker movements around object edges and over object surfaces has previously been documented in size discrimination tasks in walrus (Kastelein, 1988), California sea lion 8 (Dehnhardt and Dücker, 1996) and Harbor seals (Grant et al., 2013b), although movements were not specifically measured in these studies. Similarly, humans also feel around the edges of large objects with their fingertips, termed contour-following, to judge size and shape (Gibson, 1962;Klatzky et al., 1987). ...
Active sensing is the process of moving sensors to extract task-specific information. Whisker touch is often referred to as an active sensory system since whiskers are moved with purposeful control. Even though whisker movements are found in many species, it is unknown if any animal can make task-specific movements with their whiskers. California sea lions (Zalophus californianus) make large, purposeful whisker movements and are capable of performing many whisker-related discrimination tasks. Therefore, California sea lions are an ideal species to explore the active nature of whisker touch sensing. Here, we show that California sea lions can make task-specific whisker movements. California sea lions move their whiskers with large amplitudes around object edges to judge size, make smaller, lateral stroking movements to judge texture and make very small whisker movements during a visual task. These findings, combined with the ease of training mammals and measuring whisker movements, makes whiskers an ideal system for studying mammalian perception, cognition and motor control.
... associated with groups of small hairs in the spaces between the mystacial vibrissae", and suggested that these might be important in chemical signaling. The mystacial vibrissae of walrus are numerous, mobile, and highly sensitive(Yablokov and Klevezal' 1964;Ling 1977;Kastelein et al. , 1991aKastelein & van Gaalen 1988;Milne et al. 2020).22 Ethology and Behavioral Ecology of the Walrus (Odobenus rosmarus), with. . . ...
Communication; sexual dimorphism; sexual selection; social behavior; social organization; walrus; weapon
... associated with groups of small hairs in the spaces between the mystacial vibrissae", and suggested that these might be important in chemical signaling. The mystacial vibrissae of walrus are numerous, mobile, and highly sensitive(Yablokov and Klevezal' 1964;Ling 1977;Kastelein et al. , 1991aKastelein & van Gaalen 1988;Milne et al. 2020).22 Ethology and Behavioral Ecology of the Walrus (Odobenus rosmarus), with. . . ...
Large tusks characterize the extant walrus (Odobenus rosmarus) and its extinct relatives. Those socially selected organs vary between the walrus and fossil relatives, intraspecifically, and between the sexes. Tusks are used in innumerable interactions on land and in water, including fights during rut. “Play fighting” appears even in young calves that lack tusks. Complex sounds resembling those of rutting males underwater and at the water surface occur throughout the year; some are produced by young males. Short-range graded communication (acoustic; tactile; chemical) is important but has scarcely been investigated. Underwater communication within traveling or feeding groups is likely to occur, but also has not been investigated. Specialized integumentary “bosses” on the chests and necks of adult males probably function in optical signaling. Knowledge of movements, diving, feeding, rhythms, time-activity budgets, and effects of weather on behavior has increased greatly; little information is available on associated finer-scale behavioral structure. Field observations on benthic feeding and seabird predation have revealed previously unknown and ecologically interesting behaviors. Walruses are the most gregarious species of pinniped and are almost always in groups in the water and on land or ice, and in extensive body contact with one another. Gregariousness enables huddling for warmth and cultural transmission of information. Many anecdotes from over more than a century suggest more complex social structure than usually assumed, and the species expresses extensive social play that continues into adulthood. In light of those traits, plus the species’ high intelligence and longevity, low reproductive rate, and site fidelity, it seems timely to investigate cultural aspects of the walrus social system.
... In extant sirenians and Od. rosmarus, mystacial vibrissae aid in food detection during benthic feeding (Fay, 1982;Reep et al., 1998Reep et al., , 2001Kastelein and van Gaalen, 1988;Kastelein et al., 1990). The hypothesis of benthic feeding for Os. ...
Twelve new specimens of fossil walruses are described from four Miocene units in California. The new material represents five taxa: (1) a specimen from the Santa Margarita Formation referred to Imagotaria downsi; (2) a specimen from the Valmonte Diatomite Member of the Monterey Formation referred to cf. Pontolis magnus; (3) six specimens from the Monterey Formation referred to a new species of Pontolis (Pontolis barroni, sp. nov.); (4) one specimen from the Oso Member of the Capistrano Formation referred to a new species of Pontolis (Pontolis kohnoi, sp. nov.); (5) three specimens from the Oso Member referred to a new genus and species (Osodobenus eodon, gen. et sp. nov.). A phylogenetic analysis suggests that both the Dusignathinae and an expanded concept of the genus Pontolis represent monophyletic groups. We provide phylogenetic definitions for clade names of odobenids. Two of the new species are represented by specimens of males, females, and juveniles. Analysis of these specimens shows that the dental anatomy of later diverging basal odobenids is more variable than previously considered. The specific pattern of variation is lineage specific and likely corresponds to the intermediate dental morphology of late Miocene odobenids. Osodobenus eodon, gen. et sp. nov., is the first basal odobenid with tusk-like canines, a longitudinally arched palate, and an enlarged infraorbital foramen. These features are plausibly correlated with benthic suction feeding in the odobenins (Pliocene to Recent) and so Os. eodon may represent a case of convergent evolution of benthic feeding in the late Miocene.
http://zoobank.org/urn:lsid:zoobank.org:pub:530A114B-46E9-4E6F-A847-8B17FAFD4327
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.
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