Anatomy of Dolphins

Insights into Body Structure and Function

Bruno Cozzi, Stefan Huggenberger, Helmut A Oelschläger

• Publisher: Academic Press
• Year: 2016
• ISBN:
  9780124076556
• Topic: Scienze biologiche
• Subtopic: Zoologia

The Anatomy of Dolphins: Insights into Body Structure and Function is a precise, detailed, fully illustrated, descriptive, and functionally oriented text on the anatomy and morphology of dolphins. It focuses on a number of delphinid species, with keynotes on important dolphin-like genera, such as the harbor porpoise. It also serves as a useful complement for expanding trends and emphases in molecular biology and genetics.

The authors share their life-long expertise on marine mammals in various disciplines. Written as a team rather than being prepared as a collection of separate contributions, the result is a uniform and comprehensive style, giving each of the different topics appropriate space. Many color figures, which use the authors' access to wide collections of unique dolphin and whale material, round out this exceptional offering to the field.

• Includes high-quality illustrations, drawings, halftone artwork, photographic documentations, microphotos, and tables detailing dolphin anatomy, function, and morphology
• Facilitates education and training of students of all basic research and applied sciences dedicated to marine biology and the medical care of marine mammals
• Brings together the current knowledge and information on this topic, including those in obscure past or non-English publications, or scattered in short chapters in volumes
• Covers a number of delphinid species and serves as a useful complement for expanding trends in molecular biology and genetics

Chapter 1

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

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.

Keywords

Odontoceti

bottlenose dolphin

killer whale

Risso’s dolphin

long-finned pilot whale

common dolphin

history

Evolutionary Biology of Whales and Dolphins

Dolphins and whales (Cetacea), in addition to manatees (Sirenia), are the only mammals that are fully adapted to life in water. The numerous adaptations to the aquatic environment represent an amazing evolution level (Laitman, 2007; Reidenberg, 2007). The monophyly of the Cetacea is well established by morphological and molecular biological characteristics. The traditional systematic classification in toothed whales (Odontoceti) and baleen whales (Mysticeti) is well secured. The ancestors of cetaceans were land mammals from the group of even-toed hoofed animals that lived about 60 million years ago. Their close relationship with the Artiodactyla is clear from molecular studies that indicate that the cetaceans are closely related to the hippos (Hippopotamidae) (Price et al., 2005). Therefore, the cetaceans are now nested within the Artiodactyla and the whole group is called accordingly Cetartiodactyla in modern textbooks.

On the morphological level, fossil finds of nearly complete skeletons revealed that the ankle joint (hock) of middle-Eozän Archaeoceti were clearly like that of even-toed ungulates since they had a talus (astragalus) of the typical double-pulley form, an autapomorphy^a of Artiodactyla. Further apomorphies of Cetartiodactyla are the par-axis extremities and the fibroelastic type of penis with a proximal sigmoid flexure. In comparison with the hippos, cetaceans share a multiloculare (multichamber) stomach system, the nearly hairless skin, and the structure of the larynx entrance (Frey et al., 2015).

The Cetacea derived from the Mesonychidae, a group from the main line of ungulates († condylarths) in the Paleocene. From them the archaeocetes emerged in the lower Eocene, about 50 million years ago, as the first group fully adapted to the aquatic lifestyle. Due to their endothermy, it was possible for the archeocetes to populate all sea habitats regardless of the ambient temperature and also large river systems. Moreover, the fact that oxygen uptake via lungs is more effective compared with respiration by gills because of the higher oxygen content in air, this was probably one of the advantages for the evolution of these agile giant forms in the water. The sizes of cetaceans ranging from approximately 1.25 m of length and 25 kg weight for the La Plata dolphin (Pontoporia blainvillei) up to a length of 33.5 m and 190 t for the blue whale (Balaenoptera musculus), the largest animal that ever lived on earth. Other characteristics of mammals that may have a positive effect in the conquest of the aquatic environment were the completely separate two-chambered heart with an efficient circulation system, nucleus-free red blood cells, the placenta and the protected embryonic development, intensive parental care and thus greater success reproduction rate, highly social behavior repertoire and well-developed auditory organs as a basis for the development of an echolocation system. The ability for advanced hearing under water, that is, the reduced mastoid process to detach ear bones from the skull, was found in all baleen and toothed whales since the Oligocene (around 30 million years ago). Additionally, the first anatomical characteristics of echolocation were found in the earliest toothed whales of the Oligocene (Uhen, 2007). Among these characteristics are the facial fossa that houses the nasal complex and large basicranial fossae that housed the pterygoid sinuses (see Chapter 5) (Fordyce and Muizon, 2001).

Odontoceti (toothed whales)

Next to the baleen whales (Balaenopteroidea, Mysticeti), four monophyletic groups of toothed whales can be distinguished: Physeteroidea, Ziphioidea, Platanistoidea (river dolphins), and Delphinoidea (Huggenberger and Klima, 2015). In contrast to baleen whales, the toothed whales are characterized by the single blowhole and teeth.

1. Physeteroidea

The Physeteroidea divide into two groups, the Physeteridae (sperm whales, one species) and...