Adaptive Evolution of Sea Lions and Walruses

Repenning, Charles A.

doi:10.2307/2412512

Cited by 97 publications

(74 citation statements)

References 8 publications

Supporting

Mentioning

Contrasting

Unclassified

Order By: Relevance

“…Perhaps it is not possible to have both greatly expanded olfactory and respiratory turbinates due to the multiple functional demands placed on the cranium, such as feeding and vision as well as conditioning incoming air and olfaction. Consistent with this, Repenning (1976) observed that a reduction in olfactory turbinates was associated with greatly enlarged orbits in extant and extinct pinnipeds, including the oldest known genus, Enaliarctos (ca. 22 million years old, Berta et al 1989).…”

Section: Discussionsupporting

confidence: 59%

Aquatic adaptations in the nose of carnivorans: evidence from the turbinates

Valkenburgh¹,

Curtis²,

Samuels³

et al. 2011

Journal of Anatomy

111

View full text Add to dashboard Cite

Inside the mammalian nose lies a labyrinth of bony plates covered in epithelium collectively known as turbinates. Respiratory turbinates lie anteriorly and aid in heat and water conservation, while more posterior olfactory turbinates function in olfaction. Previous observations on a few carnivorans revealed that aquatic species have relatively large, complex respiratory turbinates and greatly reduced olfactory turbinates compared with terrestrial species. Body heat is lost more quickly in water than air and increased respiratory surface area likely evolved to minimize heat loss. At the same time, olfactory surface area probably diminished due to a decreased reliance on olfaction when foraging under water. To explore how widespread these adaptations are, we documented scaling of respiratory and olfactory turbinate surface area with body size in a variety of terrestrial, freshwater, and marine carnivorans, including pinnipeds, mustelids, ursids, and procyonids. Surface areas were estimated from high-resolution CT scans of dry skulls, a novel approach that enabled a greater sampling of taxa than is practical with fresh heads. Total turbinate, respiratory, and olfactory surface areas correlate well with body size (r 2 ‡ 0.7), and are relatively smaller in larger species. Relative to body mass or skull length, aquatic species have significantly less olfactory surface area than terrestrial species. Furthermore, the ratio of olfactory to respiratory surface area is associated with habitat. Using phylogenetic comparative methods, we found strong support for convergence on 1 : 3 proportions in aquatic taxa and near the inverse in terrestrial taxa, indicating that aquatic mustelids and pinnipeds independently acquired similar proportions of olfactory to respiratory turbinates. Constraints on turbinate surface area in the nasal chamber may result in a trade-off between respiratory and olfactory function in aquatic mammals.

show abstract

Section: Discussionsupporting

confidence: 59%

Aquatic adaptations in the nose of carnivorans: evidence from the turbinates

Valkenburgh¹,

Curtis²,

Samuels³

et al. 2011

Journal of Anatomy

111

View full text Add to dashboard Cite

show abstract

“…On that basis, the walrus might have been predicted to have sweat orifices more proximally situated than those of any other pinniped, since it is the most sparsely haired of all (Scheffer 1964). My finding that the sweat orifice is consistently distal to those of the sebaceous ducts in fetal walruses implies phyletic relationship to the Otariidae (recently confirmed by Tedford 1976, andRepenning andTedford 1977). The shift in relative positions of the ductal orifices before birth implies pre-adaptation to the sparsely haired condition in later life.…”

Section: Pilosebaceous Unitsmentioning

confidence: 76%

“…The ancestor of this form apparently made its way from the Pacific to the Atlantic via the Central American Seaway between 5 and 8 million years ago; some time later, the Pacific stock(s) became extinct. The modern walruses of the North Pacific region were derived from the Atlantic stock, having made their way back to the Pacific via the Arctic Ocean sometime within the last million years (Repenning 1976). The single species of living walrus, Odobenus rosmarus, is holarctic in distribution, though by no means uniformly distributed or morphologically alike in all areas.…”

Section: Systematics and Taxonomymentioning

confidence: 99%

Ecology and Biology of the Pacific Walrus,Odobenus rosmarus divergensIlliger

Fay¹

1982

North American Fauna

387

567

View full text Add to dashboard Cite

“…Evidence for this is provided by the oldest fossil pinniped, Enaliarctos mealsi, which retained cutting carnassial teeth and trochleated interphalangeal articulations that would have enabled it to grasp food using its forelimbs during prey processing [68]. Enaliarctos may even have routinely brought prey on to land to perform processing [69]. This feeding mode is clearly distinct to raptorial biting underwater using the jaws alone, and illustrates how viewing fossils within the context of our framework can help to guide palaeoecological interpretations.…”

Section: Evolutionary and Ecological Implicationsmentioning

confidence: 87%

A behavioural framework for the evolution of feeding in predatory aquatic mammals

et al. 2017

View full text Add to dashboard Cite

Extant aquatic mammals are a key component of aquatic ecosystems. Their morphology, ecological role and behaviour are, to a large extent, shaped by their feeding ecology. Nevertheless, the nature of this crucial aspect of their biology is often oversimplified and, consequently, misinterpreted. Here, we introduce a new framework that categorizes the feeding cycle of predatory aquatic mammals into four distinct functional stages ( prey capture, manipulation and processing, water removal and swallowing), and details the feeding behaviours that can be employed at each stage. Based on this comprehensive scheme, we propose that the feeding strategies of living aquatic mammals form an evolutionary sequence that recalls the land-to-water transition of their ancestors. Our new conception helps to explain and predict the origin of particular feeding styles, such as baleen-assisted filter feeding in whales and raptorial 'pierce' feeding in pinnipeds, and informs the structure of present and past ecosystems.

show abstract

Adaptive Evolution of Sea Lions and Walruses

Cited by 97 publications

References 8 publications

Aquatic adaptations in the nose of carnivorans: evidence from the turbinates

Aquatic adaptations in the nose of carnivorans: evidence from the turbinates

Ecology and Biology of the Pacific Walrus,Odobenus rosmarus divergensIlliger

A behavioural framework for the evolution of feeding in predatory aquatic mammals

Contact Info

Product

Resources

About