Cetacea

For Cetacea, the clade that includes whales, dolphins, and porpoises, such "timetrees" specify the closest evolutionary relatives of the bowhead whale (Figs. 1.1 and 1.2) and more distantly related clades of species (Gatesy et al., 2013).

From: The Bowhead Whale , 2021

Cetacea (Whales, Dolphins, Porpoises)

Christopher Dold , in Fowler's Zoo and Wild Animal Medicine, Volume 8, 2015

Biology

Cetacea is the order of mammals that includes whales, dolphins, and porpoises. Cetaceans are found throughout the world's oceans but most species types have specific or common ranges ( Table 43-1). Fossil evidence indicates that cetaceans are marine mammal descendants, a group of land mammals that were characterized by being even toed and having an oblong skull and slim limbs with significant similarities to that of early whales. 60 The two suborders within the extant order Cetacea are Mysticete and Odontocete. Within the suborder Mysticete, baleen whales, 13 species exist in four families. Baleen whales such as blue and humpback whales are so named for the large plates of keratinized baleen they have instead of teeth. They feed on krill and fish by swallowing large volumes of prey and water and then forcing the water out past the baleen, capturing and then swallowing the prey. At least 70 species exist within the suborder Odontocete, toothed whales, in 40 genera and 10 families. This suborder varies greatly in size—from the largest sperm whale (Physeter macrocephalus) to the smallest Hector's dolphin (Cephalorhynchus hectori). Toothed whales are known to be social animals that exist in both small and large groups; large groupings of over 100 dolphins are known as superpods. Family groups have been documented in several species, and socialized feeding strategies are known to be part of the natural history of these animals. Both aquatic and marine cetacean species exist, and both have evolved anatomically and behaviorally for life in an aquatic environment. Nearly all cetacean species are fish eating, or picivorous, and every species has evolved to specialize in its niche.

The cetaceans found in zoologic parks, oceanaria, and stranding rehabilitation centers are almost exclusively odontocetes (of the families Delphinidae and Monodontidae). Most reported clinical experience has been developed through work with the bottlenose dolphin (Tursiops truncatus, T. t. gilli, and T.t. aduncus), given its relative ubiquity in zoologic parks and oceanaria, as well as in research and rehabilitation facilities. Other odontocete species, including the killer whale (Orcinus orca), the beluga whale (Delphinapterus leucas), the Pacific white-sided dolphin (Lagenorhynchus obliquidens), the harbor porpoise (Phocoena phocoena), the short finned pilot whale (Globicephala macrorhyncus), the Commerson's dolphin (Cephalorhynchus commersonii), and the spotted dolphin (Stenella frontalis), and some freshwater species such as the Amazon river dolphin (Inia geoffrensis) are successfully housed in zoos and oceanaria. Husbandry and veterinary care developed for Tursiops may generally be extrapolated directly to the other species, with some exceptions, including drug dosing and safety, as well as logistical application of diagnostic and therapeutic techniques.

Since the preponderance of species found in zoologic parks, oceanaria, and rehabilitation settings are odontocetes, this chapter will focus only on their regular as well as medical care, particularly that of members of the families Delphinidae and Monodontidae.

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Neoceti

R. Ewan Fordyce , in Encyclopedia of Marine Mammals (Second Edition), 2009

II Changing Concepts of Names

The name Cetacea was first used in a modern sense by Brisson in 1762 for genera and species of living whales, dolphins, and porpoises. Until the mid-1800s, high-level classification was based on superficial features, with no implication that patterns amongst living cetaceans had arisen by evolution. In the 1860s, W. H. Flower ( Fig. 1), who was perhaps the first cetologist to use evolutionary principles, was instrumental in establishing formal names for the living cetaceans: Mysticeti and Odontoceti (Table I). Flower implied that these were real groups (in modern terms, clades). The discovery of fossils broadened the concept of Cetacea in the earlier 1800s. Initially, most fossils were recognized as related to living species, and modern generic names (e.g., Delphinus and Balaena) were often used for such material. The discovery of the archaic Eocene whale Basilosaurus in the 1830s eventually led Flower in 1883 to name another formal group of cetaceans, the extinct Archaeoceti. Thus, the concept of Cetacea was expanded to include three suborders, one extinct (Archaeoceti), and two living (Odontoceti and Mysticeti) (Fig. 2).

Figure 1. W. H. Flower, an influential cetacean systematist from the later 1800s (from Cornish 1904).

Table I. History of First Records for Names of Higher Divisions of the Cetacea

Author (date) Formal name Status
Linnaeus (1758) Cete A forgotten or little-used name for Cetacea
Brisson (1762) Cetacea First formal use of name
Gray (1864) Mysticete Formal precursor to Mysticeti
Gray (1864) Denticete A forgotten or little-used name for Odontoceti
Flower (1865) Odontocete Formal precursor to Odontoceti
Haeckel (1866) Autoceta A forgotten or little-used name for Neoceti
Flower (1867) Odontoceti First formal use of name
Flower (1867) Mystacoceti A forgotten or little-used name for Mysticeti
Cope (1869) Mysticeti First formal use of name
Gill (1871) Zeuglodontia A forgotten or little-used name for Archaeoceti
Flower (1883) Archaeoceti First formal use of name
Fordyce and Muizon (2001) Neoceti Formalization of a name used by J.G. Mead in an oral paper delivered at North American Paleontological Convention, 1996, Washington, DC

Based partly on Rice (1998).

Figure 2. Changing concepts of the Cetacea. (A) Pre-evolutionary classification as used by Jardine and others, early to mid-1800s. Species are clustered on the basis of sometimes-superficial features. Genealogical relationships are not particularly implied. (B) Interpretation of cetacean diphyly, as used by Slijper (cladogram based on a phylogeny from Slijper 1979). (C) Composite simple cladogram showing current understanding of Cetacea. Crown-group Cetacea (Neoceti) has two sister taxa, Odontoceti and Mysticeti; included genera represent most of the recognized crown families; only a few fossil genera are included.

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Hybridism

Martine Bérubé , Per J. Palsbøll , in Encyclopedia of Marine Mammals (Third Edition), 2018

II Evidence of Matings Between Marine Mammal Species

In Cetacea , most putative hybrids have been reported in the absence of observed mating behaviors between the parental species. However, within the delphinidae, several incidences of interspecific matings have been observed in captivity between species that are thought to hybridize in the wild as well, such as Atlantic spotted (S. frontalis) and bottlenose dolphins (Tursiops truncatus) (Herzing et al., 2003; Herzing and Elliser, 2013). Interspecific mating attempts have also been observed between pinniped species where no hybrids have yet been identified. Such mating behavior appears to be aggressive and usually the heterospecific male is much larger than the female, which often do not survive such interactions. This kind of aggressive interspecific mating was first observed between a male gray seal (Halichoerus grypus) and a female harbor seal (Phoca vitulina) (Wilson, 1975). Later reports of aggressive interspecific matings include: An attempted mating between a male New Zealand sea lion (Phocarctos hookeri) and a dead female New Zealand fur seal (Arctocephalus forsteri); a South American sea lion male (Otaria flavescens) and a South American fur seal female (A. australis); a female California sea lion (Zalophus californianus) and a male Steller sea lion (Eumetopias jubatus); as well as between male southern elephant seals (Mirounga leonina) and female Australian fur seals (A. pusillus) (Wilson, 1979; Miller et al., 1996). The aggressive mating attempts by male sea lions with heterospecific females has been interpreted as "excess of violent sexual selection" (Miller et al., 1996). Aggressive mating behaviors are widespread in the family Otariidae, and hence the number of hybrids may be higher than reported.

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Marine Mammals, Extinctions of

Glenn R. VanBlaricom , ... Robert L. BrownellJr., in Encyclopedia of Biodiversity, 2001

I.A.3. Pinnipedia

Although pinnipeds and cetacea often use similar aqueous habitats, the pinnipeds have many obvious differences from the cetacea in form and function. Features shared by most pinnipeds, including the phocids, otariids, and odobenids, are summarized in Table II. The largest pinnipeds are adult males of the highly dimorphic southern elephant seal, exceeding 5   m in length and reaching 3700   kg in mass. Adult male northern elephant seals are only slightly smaller. Walruses are also quite large, reaching 3.5   m and 1500   kg.

Despite many anatomical, physiological, and ecological features obviously associated with life at sea, pinnipeds are best regarded as amphibious. All species utilize solid substrata for breeding or for postbreeding maternal care. Solid substrata are also used as short-term resting sites and for protracted periods in some species during molting of the skin and pelage. Although the proportion of time spent on land ("hauled out") over the long term varies significantly among species and age and sex categories, generally the pinnipeds spend a major portion of their lives on land near shore or on pack or shorefast ice at sea.

Otariids use terrestrial habitats near shore for breeding, postpartum maternal care, molting, and resting. Preferred hauling sites are those near areas of high oceanic productivity and those free of large terrestrial predators. Thus, hauling grounds for otariids typically are islands or mainland locations protected by cliffs or rough terrain from land predators. Often, the hauling grounds are localized at high latitude or the upwelling zones of mid-latitude eastern boundary currents, such as the Humboldt, California, and Benguela currents, where production of preferred food species is high and temporally predictable. Optimal hauling grounds for breeding otariids are few in number and often limited in size. Breeding activities of otariids are highly synchronous, occurring during a narrow time window when food availability for lactating females and newly produced juveniles is seasonally optimal. As a consequence of the various spatial and temporal constraints, pinniped breeding typically involves conditions of extreme crowding on haul-out sites.

Phocids and walruses haul out for the same purposes as otariids. Unlike otariids, phocids and walruses use two very different kinds of substrata. About half of the phocid species use coastal land for hauling grounds, selecting sites for largely the same reasons described for otariids. Thus, timing and location of breeding for land-breeding phocids and otariids are generally similar. As a consequence, reproductive activities for many land-breeding phocids also occur under conditions of extreme crowding. Known exceptions include some populations of harbor seals with spatially dispersed, largely aqueous breeding systems and the three recent species of monk seal (one now extinct) with temporally asynchronous breeding systems at low latitude. The walrus and the remaining phocids breed or care for young, rest, and molt on ice at high latitudes rather than on land. Ice as a substratum varies widely over time and among locations in stability, vulnerability to predators, and provision of access to the surrounding sea. Thus, among ice-breeding pinnipeds there are significant resultant variations in social and breeding strategies and in the degree of crowding at hauling sites. A major predator of ice-hauling phocids, the polar bear, is present in ice-covered marine habitats of the Arctic region but not the Antarctic. This pattern has many interesting consequences for interhemispheric differences in the ecology of ice-hauling pinnipeds.

Some phocid species or subspecies occur only in aquatic habitats. Two subspecies of ringed seal occur only in Lake Saimaa, Finland, and Lake Ladoga, Russia, respectively. The Caspian seal is found only in the Caspian Sea and the Baikal seal only in Lake Baikal, both in Russia. A population of harbor seals occurs year-round in Lake Iliamna, Alaska, but the degree of exchange, via river connection to populations of harbor seals in nearby Bristol Bay, is unknown.

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Cetacean Fossil Record

R. Ewan Fordyce , in Encyclopedia of Marine Mammals (Second Edition), 2009

I Introduction

The fossil record of Cetacea—whales, dolphins extends back more than 50 million years ( Fig. 1). Hundreds of species are known, based on fossils from near-shore to deep-ocean marine strata and, occasionally, freshwater sediments. Remains vary from less common near-complete skeletons through skulls and teeth to abundant single and usually undiagnostic bones (Fordyce and Muizon, 2001). The taxonomy at family level is adequate to review the diversity and spatiotemporal distribution of fossil Cetacea, although cladistic relationships of families and other taxa to one another, and clade names, are volatile, and cetologists should use cladistic results with caution. Standard zoological techniques are used in taxonomy, classification, and analysis of function. Routine geological techniques are used to date fossils, to interpret sedimentary environments, and to extract geochemical signals such as isotopes from fossils. The fossil record shows patterns of evolution and extinction that link strongly with biological and physical environmental change in the oceans. Fossils provide the only direct means of dating clade origins and thus calibrating molecular clocks.

Figure 1. Stratigraphic record and inferred relationships of family-level clades of Cetacea. Timescale shows absolute time, Epochs (e.g., Eocene) and their subdivisions (e.g., early, middle), and Stages (e.g., Priabonian). Bars show age ranges for family-level cetacean taxa: crown clades and wholly extinct clades (infilled bars), stem clades (heavy dash), and grades (open bars). Accuracy of ranges varies between different groups and different time intervals. Inferred relationships follow literature cited in text. Some, but not all, major regions of uncertainty are indicated.

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Cetartiodactyla

Barry Berkovitz , Peter Shellis , in The Teeth of Mammalian Vertebrates, 2018

Introduction

Members of the suborder Cetacea, like the sirenians, are fully aquatic large mammals. The suborder is divided into two parvorders: Mysticeti (baleen whales) and Odontoceti (toothed whales). Whales inhabit the temperate and polar oceanic zones. In the aquatic environment, sound is of great importance for communication between individuals. In addition, toothed whales use echolocation in hunting, to detect prey and to judge the distance from the prey. There is some evidence that mysticete whales emit sound pulses that could be related to foraging ( Stimpert et al., 2007), but echolocation abilities have not been conclusively demonstrated.

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Fossil Sites, Noted

R. Ewan Fordyce , in Encyclopedia of Marine Mammals (Second Edition), 2009

I Introduction

Fossil marine mammals—Cetacea, Sirenia, Desmostylia, Pinnipedia and other aquatic carnivores—are known from hundreds of sites worldwide ( Fig. 1). Localities span from modern tropics to poles, in both north and south and on all major continents, but with most in northern temperate regions. Usually, sites preserve marine sedimentary rocks, which have been exposed on land through sea level fall and/or uplift, followed by erosion. There are a few records (dredgings) from the deep ocean, and there are some important fresh water sites for secondarily nonmarine species. Fossils give only a general guide to former distributions in ancient oceans. Sites vary from rich localized concentrations at sites a few tens of meters across, to scattered occurrences across many kilometer which become significant at the regional level, and they range in age from Eocene to Pleistocene (Fig. 2). The case studies below, given in sequence from oldest to youngest, span all the major time intervals and oceans.

Figure 1. Selected localities for fossil marine mammals. Slightly revised from figure 1, in Fossil Sites, R. E. Fordyce, "Encyclopedia of Marine Mammals," W.F. Perrin et al. (eds), © Elsevier 2002.

Figure 2. Geological age ranges for key localities for fossil marine mammals discussed under case studies. Revised from figure 2, in Fossil Sites, R. E. Fordyce, "Encyclopedia of Marine Mammals," W.F. Perrin et al. (eds), © Elsevier 2002.

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Urinary System, Genital Systems, and Reproduction

Bruno Cozzi , ... Helmut Oelschläger , in Anatomy of Dolphins, 2017

The Accessory Male Glands

The only accessory male gland present in Cetacea is the prostate ( Fig. 9.48). According to Matthews (Matthews, 1950, cited by Yablokov et al., 1972), the prostate of dolphins consists of a diffuse part and a lobular part. The dispersed tissue is located around the seminal collicle, close to the seminal ducts and the beginning of the urethra. The (multi)lobular part of the gland is located close to the roots of the penis and related to a well-developed m. bulbocavernosus. y

Figure 9.48. Prostate gland of T. truncatus.

The absence of seminal vesicles in dolphins may be substituted by a dilated tubular structure abutting the distal two-thirds of the testis (Brook et al., 2000). Since the same authors report that tubule diameters at the distal end of the testis decreased by as much as 2 mm after ejaculation, it is possible that the large vas deferens allows storage of seminal fluid in the absence of seminal vesicles in dolphins (Matthews, 1950).

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Mammals

L. Marino , in Evolution of Nervous Systems, 2007

3.21.1 Cetacean Evolution, Phylogeny, and Ecology

The origin and evolutionary history of the Cetacea represents one of the most dramatic physiological and behavioral transformations in the biological record. The first suborder, Archaeoceti, contained approximately 25 (known) genera ( Thewissen, 1998) and derived from near-shore Indo-Pakistani locales (Thewissen et al., 1996). Archaeocetes shared a common ancestry with modern Artiodactyla (the even-toed ungulates) over 60   Mya (Thewissen et al., 2001) and survived until the late Eocene, around 37   Mya (Barnes et al., 1985) when the modern suborders, Mysticeti (comprising 13 species of baleen and rorqual whales) and Odontoceti (comprising 67 species of toothed whales, dolphins, and porpoises) appeared (Barnes et al., 1985).

Today, modern cetaceans have large brains and are streamlined predators that are widely diversified, inhabiting all oceans and many rivers. Their dietary strategies range from straining of krill to predation on other marine mammals. Their social groups span from two or three individuals to herds of thousands. They are long-lived with relatively long juvenile periods, are wide-ranging, and have complex social structures. Furthermore, in odontocetes a sophisticated echolocation system has evolved.

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Natural History and Evolution of Dolphins: Short History of Dolphin Anatomy

Bruno Cozzi , ... Helmut Oelschläger , in Anatomy of Dolphins, 2017

Abstract

The numerous adaptations of dolphins and whales (Cetacea) to the aquatic environment represent an amazing evolution level. Among these adaptations are specializations of the musculoskeletal, the respiratory, and the sensory systems. The anatomical research on dolphins started with the Greek philosopher Aristotele more than 2300 years ago. However, during the "dark centuries" of the Middle Ages the scientific work was completely eliminated until the German bishop Albertus Magnus recapitulated Aristotele's work. New anatomical research was restarted during the Renaissance and Edward Tyson set new standards for cetacean anatomy in the 17th century. Today, new anatomical studies on marine mammals are often integrative, combining methods and ways of thinking largely gleaned from terrestrial animals and human medicine. This comparison of holds great promise for the understanding of modern marine mammalogy.

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