Vertebrate Zoology: A Study Guide - T. A. Dauda 2014

Multicellular Animals
Infraclass Eutheria, or Placental Mammals
Order Cetacea

The order Cetacea comprises about 90 species of aquatic mammals that inhabit seas and oceans worldwide, with the exception of a small number of South American, Chinese, and Indian river species. Due to their permanent aquatic lifestyle, these animals possess an elongated, torpedo-shaped, streamlined body with a disproportionately large HEAD. Hind limbs are absent, while forelimbs are modified into paddle-like flippers. Locomotion is driven by a highly developed horizontal tail fluke. Body Hair is practically nonexistent, except for sparse hairs on the head in certain species. The Skin is smooth, lacking sebaceous and Sweat Glands, and its outer layer is covered in mucus that reduces hydrodynamic drag during swimming. There is a single pair of Mammary Glands, with their teats opening into pocket-like folds located in the inguinal region. Pelvic bones are absent, which facilitates the birth of large offspring.

Cetaceans have a very high fat content in their bodies. For instance, the subcutaneous blubber layer in large species can reach up to 50 cm in thickness, with a total body mass exceeding 20 t. The Abundance of fat in the bones, Muscles, and Body Fluids protects the Organism from hypothermia in cold waters and reduces body density, which in large species is close to that of Water.

Cetaceans breathe atmospheric air. Their lung capacity depends on body size: relatively small dolphins hold 1–2 l of air, whereas the giant blue whale holds about 14,000 l. This Respiratory system achieves high efficiency through several structural adaptations, including a massive number of alveoli—for example, a 1.5-meter dolphin has three times as many alveoli as a human. This allows the animals to extend the pause between breaths, enabling certain species to remain underwater for 45 minutes or even longer. Breathing occurs through blowholes located on the top of the head, which open only briefly for exhalation and inhalation immediately after surfacing. During exhalation, pressurized vapor rushes out, often accompanied by atomized water spray that forms a blow or spout.

The olfactory Organs in cetaceans are vestigial, whereas Vision, Touch, and especially Hearing are well developed. Toothed whales are capable of echolocation; dolphins, for example, can emit and perceive ultrasound frequencies up to 150–200 kHz. Their reliance primarily on hearing is due to the fact that sound waves travel through water five times faster than through air.

Cetaceans reproduce in water. Their calves are born well-developed, large, and capable of swimming and following the mother immediately after birth. The body length of a newborn typically ranges from 1/4 to 1/2 of the parent's length. For instance, a Black Sea dolphin measuring 160–170 cm gives birth to a calf 80–85 cm long, while a sperm whale measuring 7–8 m produces offspring 3–3.5 m in length. The newborn emerges tail-first from the female's reproductive tract, unlike land mammals which are born head-first. The relatively short umbilical cord snaps naturally during birth. The mother gently pushes the newborn to the water's surface so it can take its first breath. Baleen whales give birth to a single calf every 2–3 years, belugas every year, and dolphins annually. Mothers are highly attentive to their offspring and never abandon a young in distress. During the Lactation period, young cetaceans grow very rapidly, fueled by the exceptionally rich milk. Calves of large whales gain up to 100 kg in mass per day, consuming 250–300 l of milk daily, which contains up to 50% fat (compared to only 3–4% in cow's milk). During nursing, the calf grasps the teat with its Tongue rolled into a tube, and the mother injects the milk directly into its Mouth. Whales reach sexual maturity at the age of 3–6 years, and sometimes later. The lifespan of toothed whales ranges from 20 to 30 years, with some individuals living up to 35 years.

The coastal waters of our country are home to 21 cetacean species, classified into 2 suborders.

Suborder Odontoceti (Toothed Whales). Toothed whales possess Teeth in the Oral Cavity. Depending on the species, their number ranges from 2 to 240, all sharing a uniform Structure featuring a simple single-cusped crown. Other characteristic features include a typically asymmetrical Skull, five-fingered flippers, and the absence of head hair. This suborder includes dolphins, sperm whales, and several other species.

Dolphins are small to medium-sized (1–10 m). They possess teeth in both jaws. The dorsal fin is located near the middle of the body, though it is absent in some species. Most dolphins are fast swimmers, reaching speeds of up to 40–50 km/h. Distributed primarily in warm and temperate latitudes, they lead a gregarious, social lifestyle. Some species adapt well to captivity and are trainable. Their diet consists mainly of fish. The Nervous system of dolphins is highly developed, with a Brain volume and structure comparable to that of humans. Nine species inhabit our national waters, primarily populating the Baltic and Black Seas, as well as northern and Far Eastern seas. The most common species are the short-beaked common dolphin, bottlenose dolphin, harbour porpoise, and white-beaked dolphin or beluga whale. Killer whales, much like other dolphins, are generally peaceful toward humans in the water, yet they actively hunt and kill whales and seals.

There are two known species of sperm whales: the sperm whale and the pygmy sperm whale. They differ significantly in size: the former measures 10 to 21 m in length, while the latter does not exceed 4 m. They lack teeth in the upper jaw, whereas the lower jaw bears 7–30 pairs of teeth on each side. The head is massive, housing a large spermaceti organ (lipid-filled cushion) in its anterior portion. Sperm whales are capable of deep diving (down to 300 m) and can remain submerged for over an hour. They feed primarily on cephalopods and occasionally fish. Distributed across warm seas, the sperm whale frequently ventures into the seas of the Far East.

Suborder Mysticeti (Baleen Whales). Baleen whales comprise 10 species of the largest mammals on Earth, distinguished by a specialized filtering apparatus in the mouth formed by keratinous plates known as whalebone or baleen. Each plate is anchored by its base to the upper jaw, while its frayed free edge hangs down into the toothless oral cavity. Their diet consists primarily of planktonic organisms—such as small crustaceans and Mollusks—which the animal filters out by straining large volumes of water. Occasionally, these whales may feed on small schooling fish. Found in all oceans, baleen whales undertake extensive Migrations. They typically spend the winter in tropical waters and migrate during the summer to cold and moderately warm seas, where plankton blooms abundantly at that time.

Most baleen whales are true giants. The smallest among them is the minke whale, measuring slightly under 10 m in length with a mass of about 10 t. The largest is the blue whale; individual specimens of this species can reach lengths of 30 m and masses of 160 t. The Stomach of a blue whale can hold up to 1.5 t of plankton. Following an 11-month gestation period, the female typically gives birth to a single calf measuring 7–8 m in length and weighing 2–3 t. Over 7 months of nursing, the calf grows up to 16 m in length and reaches a mass of up to 22 t. It achieves adulthood at the age of 2 years, by which time its average length reaches 24 m and its mass is approximately 30 t. Due to international agreements, most species of baleen whales are currently under conservation and human protection.

Cetaceans provide humans with a multitude of valuable products. Fat and meat are widely used in the food Processing industry. Whale meat contains 20–26% protein, making it a source of protein concentrates and dried Proteins essential for The production of ice cream, sauces, mayonnaise, and other foods. The meat of certain species is entirely suitable for human consumption. Whale oil is used as an additive to vegetable oils and in the manufacturing of margarine. In the light industry, it is utilized for tanning suede, finishing premium leather grades, and producing oil paints, oilcloth, linoleum, and other goods. The Connective Tissue left over from rendering fat is processed into gelatin and glue. Vitamins A₁, B₁, B₂, and B₁₂ are extracted from whale livers. The Pancreas supplies Insulin, a crucial medication for treating Diabetes Mellitus. In addition to these, cetaceans yield various other substances and Materials applied across a diverse range of human activities.