Sirenians and Other Marine Mammals

Berta, Annalisa; Sumich, James L.; Kovacs, Kit M.

doi:10.1016/b978-0-12-397002-2.00005-3

Cited by 17 publications

(24 citation statements)

References 79 publications

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“…It is important to note that pinnipeds do not chew or masticate their prey (Berta et al, 2015;Franco-Moreno et al, 2021). Instead, extant pinnipeds trap and swallow their prey whole, with little to no prey processing by the cheek teeth (Franco-Moreno et al, 2021;Gentry & Johnson, 1981;Peredo et al, 2022).…”

Section: Discussionmentioning

confidence: 99%

Mechanical properties of the California sea lion (Zalophus californianus) and northern elephant seal (Mirounga angustirostris) lower jaws explain trophic plasticity

Nieto-Miranda

Aguilar-Medrano

Hernández‐Camacho

et al. 2023

The Anatomical Record

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The fossil record of pinnipeds documents a suite of morphological changes that facilitate their ecological transition from a terrestrial to an aquatic lifestyle. Among these is the loss of the tribosphenic molar and the behavior typically associated with it in mammals: mastication. Instead, modern pinnipeds exhibit a broad range of feeding strategies that facilitate their distinct aquatic ecologies. Here, we examine the feeding morphology of two species of pinnipeds with disparate feeding ecologies: Zalophus californianus, a specialized raptorial biter, and Mirounga angustirostris, a suction specialist. Specifically, we test whether the morphology of the lower jaws facilitates trophic plasticity in feeding for either of these species. We used finite element analysis (FEA) to simulate the stresses during the opening and closing of the lower jaws in these species to explore the mechanical limits of their feeding ecology. Our simulations demonstrate that both jaws are highly resistant to the tensile stresses experienced during feeding. The lower jaws of Z. californianus experienced the maximum stress at the articular condyle and the base of the coronoid process. The lower jaws of M. angustirostris experienced the maximum stress at the angular process and were more evenly distributed throughout the body of the mandible. Surprisingly, the lower jaws of M. angustirostris were even more resistant to the stresses experienced during feeding than those of Z. californianus. Thus, we conclude that the superlative trophic plasticity of Z. californianus is driven by other factors unrelated to the mandible's tensile resistance to stress during feeding.

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Section: Discussionmentioning

confidence: 99%

Mechanical properties of the California sea lion (Zalophus californianus) and northern elephant seal (Mirounga angustirostris) lower jaws explain trophic plasticity

Nieto-Miranda

Aguilar-Medrano

Hernández‐Camacho

et al. 2023

The Anatomical Record

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“…All modern crown cetaceans (Neoceti) form a monophyletic group that in turn comprises two monophyletic sister clades, the Parvorder Odontoceti, with 80 currently recognized species of toothed whales, dolphins, and porpoises in 30 genera of 10 families, and the Parvorder Mysticeti, with 16 recognized species in six genera of four families (Berta et al, 2015). Odontocetes and mysticetes presumably diverged ~34 Ma (Fordyce, 2018).…”

Section: Neoceti (Crown Cetacea) Tonguesmentioning

confidence: 99%

“…brains and complex social behavior. It includes the largest species known to have ever lived (Berta et al, 2015). From flukes and flippers to blowholes and baleen, cetaceans are truly atypical mammals (Pyenson, 2019).…”

mentioning

confidence: 99%

Cetacean tongue mobility and function: A comparative review

Werth

Crompton

2023

Journal of Anatomy

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Cetaceans are atypical mammals whose tongues often depart from the typical (basal) mammalian condition in structure, mobility, and function. Their tongues are dynamic, innovative multipurpose tools that include the world's largest muscular structures. These changes reflect the evolutionary history of cetaceans' secondary adaptation to a fully aquatic environment. Cetacean tongues play no role in mastication and apparently a greatly reduced role in nursing (mainly channeling milk ingestion), two hallmarks of Mammalia. Cetacean tongues are not involved in drinking, breathing, vocalizing, and other non‐feeding activities; they evidently play no or little role in taste reception. Although cetaceans do not masticate or otherwise process food, their tongues retain key roles in food ingestion, transport, securing/positioning, and swallowing, though by different means than most mammals. This is due to cetaceans' aquatic habitat, which in turn altered their anatomy (e.g., the intranarial larynx and consequent soft palate alteration). Odontocetes ingest prey via raptorial biting or tongue‐generated suction. Odontocete tongues expel water and possibly uncover benthic prey via hydraulic jetting. Mysticete tongues play crucial roles driving ram, suction, or lunge ingestion for filter feeding. The uniquely flaccid rorqual tongue, not a constant volume hydrostat (as in all other mammalian tongues), invaginates into a balloon‐like pouch to temporarily hold engulfed water. Mysticete tongues also create hydrodynamic flow regimes and hydraulic forces for baleen filtration, and possibly for cleaning baleen. Cetacean tongues lost or modified much of the mobility and function of generic mammal tongues, but took on noteworthy morphological changes by evolving to accomplish new tasks.

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“…The sirenian epidermis, the outermost skin layer, is restructured compared to its terrestrial sister taxa. While skin appendages (hair follicles, sebaceous glands, and sweat glands) are associated with the epidermis, they project deep into the dermal layer and are absent (sweat glands) or sparsely distributed (e.g., vibrissae, specialized tactile hairs scattered over the body) in sirenians 43 . Consistent with previous reports [43][44][45][46] , we observed a thin epidermis and a thick dermis in the dugong (Figure 4a) and the West Indian manatee (Figure S4).…”

Section: The Integumentary Systemmentioning

confidence: 99%

Sirenian genomes illuminate the evolution of fully aquatic species within the mammalian superorder Afrotheria

Tian,

Zhang,

Kang

et al. 2023

Preprint

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Sirenians of the diverse superorder Afrotheria were the first mammals to retransition from land to water and are the sole herbivorous marine mammals, but little is known about the underlying genomic changes. Here, we generated a chromosome-level dugong (Dugong dugon) genome. A comparison of our assembly and a recent West Indian manatee genome with other afrotherian genomes revealed possible molecular solutions to aquatic life by sirenians, including a shift in daily activity patterns (circadian clock) and tolerance to a high-iodine plant diet mediated through changes in the iodide transporter NIS (SLC5A5) and its co-transporters. Functional in vitro assays confirmed that sirenian amino acid substitutions alter the properties of the circadian clock protein PER2 and NIS. Sirenians show evidence of convergent regression of integumentary system (skin and its appendages) genes with cetaceans, the only other fully aquatic mammal group. Our analysis also uncovered gene losses that may be maladaptive in a modern environment, including a candidate gene (KCNK18) for sirenian cold stress syndrome likely lost during their evolutionary shift in daily activity patterns. Finally, genomes from nine Australian locations and the functionally extinct Okinawan population confirm and date a genetic break on the Australian east coast and highlight the need for whole-genome resequencing data from small or isolated dugong populations worldwide for conservation and genetic management.

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Sirenians and Other Marine Mammals

Cited by 17 publications

References 79 publications

Mechanical properties of the California sea lion (Zalophus californianus) and northern elephant seal (Mirounga angustirostris) lower jaws explain trophic plasticity

Mechanical properties of the California sea lion (Zalophus californianus) and northern elephant seal (Mirounga angustirostris) lower jaws explain trophic plasticity

Cetacean tongue mobility and function: A comparative review

Sirenian genomes illuminate the evolution of fully aquatic species within the mammalian superorder Afrotheria

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