Evolution of Whales and Dolphins
Dolphins and porpoises and whales belong to either of two cetacean families, the Platanistidae (fresh-water dolphins) or Delphinidae (including all other dolphins, the porpoises, the porpoises and cetaceans commonly called whales). The difference between porpoises and dolphins has led to considerable confusion, as it can be called by both names. There is, however, a technical difference: true porpoises are limited to a few species in the family Delphinidae with spade-shaped teeth; all the rest are dolphins (Green. 1990)
But, how did Whales and Dolphins evolve? In Nicholas Humphrey’s essay “The social function of intellect,” (Humphrey, 1976) said: “The open sea is an environment where technical knowledge can bring little benefit and thus complex societies – and high intelligence – are contraindicated (dolphins and whales provide, maybe, a remarkable and unexplained exception)” in 1976 and this began the Machiavellian intelligence” hypothesis,” which says that more intelligent animals evolved into social or grouping and cooperating animals. This is now widely accepted, though it has received little attention in the controversies that may concern the evolution of whales except from a few cetologists.
Science is day by day adding to our knowledge about animal social systems and behavior. Of the mammals known as dolphins and whales (which are actually the same), only eighty-five or so species remain, and only four of these have received almost all of the attention in investigation of their evolution: the killer whale (Orcinus orca), Bottlenose Dolphin (Tursiops spp.), humpback whale (Megaptera novaeangliae), and sperm whale (Psyseter macrocephalus). These have been studied in greatest detail, but because the sperm whale has the largest brain on earth, has great commercial significance, and has a highly social lifestyle, it has received the most attention.
Studies of animal culture have not normally includedwhales. However, several field studies have now been undertaken. Observing patterns of behavioral variation in wild populations that cannot be explained by either genetic or environmental factors shows there is good evidence for culture in several cetacean species. The bottlenose dolphin (Tursiops) shows the best promise of possessing sophisticated social learning abilities, including vocal and motor imitation, though other species have not been studied. Others have observed imitation and teaching in killer whales. We can not depend on experimental data for evidence of culture in whales. The complex and stable vocal and behavioral culture of groups of killer whales (Orcinus orca) seem to have no parallel except among humans. They are an independent group that has evolved cultural faculties. Important in the study are the world-wide movements of cetaceans, the great variety in marine environment and large temporal scales, relative to that on land, as well as stable matrilineal social groups. “There have been suggestions of gene-culture coevolution in cetaceans, and culture may be implicated in some unusual behavioural [sic] and life-history traits of whales and dolphins.” (Rendell. 2001)
Sperm whales’ interaction with one another are easily seen and studied. Thus, their daily routine, their routines of birth, predation, and death have been studied extensively by many. Some of their behaviors are unusual and unexpected when compared to land-bound animals’ sociological and ecological routines. As mentioned above, some of the elements of sperm whale biology are due to their ecology and behavior.
The sperm whale is of the order Cetacea (dolphins and whales.) The cetaceans evolved from ungulate-like creatures that made their way back into the oceans perhaps 60 million years ago, during the Oligocene epoch (more about that later). About 25-35 million years ago, the misticetes, or baleen whales separated from the odontocetes, or toothed whales.
In contrast to fish, there are bones in whales’ fins that look like huge, jointed hands. Their spines move vertically, characteristic more of a running mammal than of the horizontal movement of fish. Recent fossil discoveries in Pakistan have solved this mystery and it is possible to see the stages in the transition of these cetaceans from land to sea.
Traditionally, it was assumed whales were related to mesonychids that were carnivorous and hoofed, looking rather like wolves and a sister group of artiodactyls. These animals had unusual triangular teeth that are similar to those of whales. Therefore scientists believed whales evolved from a form of esonychid.
However, since 1990, DNA data has indicated that whales should be included among artiodactyls, a sister group of hoppopotamids. In their evolution, dolphins and whales began with an animal with a long nose and sleek body, with short legs, like weasels
About 60 million years ago, as whales first entered the water, they looked kind of like a crocodile, with their long noses and short legs. About 25-35 million years ago, the misticetes, or baleen whales separated from the odontocetes, or toothed whales. Gradually their legs grew smaller, as they spent more time in the water, and began to look like sea otters, with abilities to dive for long periods of time, developed longer front legs than hind legs, which shrank, for they still went onto land at times. Their long tales began to act as a rudder and eventually evolved into a wide tail at the bottom, with “flukes” that helped guide them and helped them swim faster. The nostrils moved farther and farther back on their heads in certain species and gradually ended up on top of their head and are known as “blowholes.” Some of the species lost their variegated teeth and retained only stumps of teeth that were like even, spade shapes.
The oldest fossil whales are in a group known as the archaeocetes. Archaeocetes show several features that modern whales lack. Their teeth, like most land mammals, show several types (molars and bicuspids, etc.) in the mouth. Modern whales either lack teeth, or have teeth that are all virtually identical in shape and size. Archaeocetes also had nostrils on the end of the nose, like land mammals, rather than a blowhole on the top of the head. Some had substantial hind limbs that could be seen outside the animal’s body. The earliest archaeocetes had limbs and pelvis attached to the vertebrae by a sacral joint, but later on the limbs and pelvis became detached from the rest of the skeleton, though the bones still remain.
Their hind legs had almost completely disappeared by38 million years ago. The long body was thin and the skeletons of these early whales have been mistaken for giant lizard bones. At this time, the whale lived entirely in the ocean and was quite large, as whales are today. But they still had not completely evolved, as they lacked the “melon organ” that allows whales to sing and use ultrasound as effectively as modern whales. Their brains were small and they probably were not as social as modern whales. They also still had tiny, but well formed hind legs that they only used to grasp the other gender when mating.
The sperm whales had radiated into a number of different species by about 15 million years ago, but only three survive today: the sperm whale itself (Physeter macrocephalus), the pygmy sperm whale (Kogia beviceps) and dwarf sperm whale (Kogia simus), which at 2-4 m long are much smaller than the sperm whale. Some dolphins and porpoises still have the long “nose” that has evolved into a long beak-like snout. Dolphins split off from the whale family, though they still retain many of the whales’ characteristics.
The modern-day whale still has the remnants of hind legs in their bones, in the form of an extra, floating bone, the remnant of the thigh bone, in the area of the lower stomach. Their hind legs almost completely disappeared by38 million years ago, though today whales are captured that still have “legs” protruding from their bodies.
Struthers’ commentary on the dissection of a right whale and gives us some interesting facts concerning the pelvic anatomy of the majority of modern day whales:
Nothing can be imagined more useless to the animal than rudiments of hind legs entirely buried beneath the skin of a whale, so that one is inclined to suspect that these structures must admit of some other interpretation. Yet, approaching the inquiry with the most skeptical determination, one cannot help being convinced, as the dissection goes on, that these rudiments [in the Right Whale] really are femur and tibia. The synovial capsule representing the knee-joint was too evident to be overlooked. An acetabular cartilage, synovial cavity, and head of femur, together represent the hip-joint. Attached to this femur is an apparatus of constant and strong ligaments, permitting and restraining movements in certain directions; and muscles are present, some passing to the femur from distant parts, some proceeding immediately from the pelvic bone to the femur, by which movements of the thigh-bone are performed; and these ligaments and muscles present abundant instances of exact and interesting adaptation. But the movements of the femur are extremely limited, and in two of these whales the hip-joint as firmly anchylosed, in one of them on one side, in the other on both sides, without trace of disease, showing that these movements may be dispensed with. The function point-of-view fails to account for the presence of a femur in addition to processes from the pelvic bone. Altogether, these hind legs in this whale present for contemplation a most interesting instance of those significant parts in an animal — rudimentary structures.” [Struthers, p. 142-143]
The dolphins breathe through their nose, but whales’ nostrils drifted back farther and farther onto the top of the head in the fossils found. Today it is just a double or single blowhole, and the ears are closed and internal, detecting only vibrations from the lower jaw. They “speak” through a “melon organ” or pad of fat.
Milinkovitch used results from molecular studies to determine that sperm whales were more closely related to the baleen whales (mysticeti) than to toothed whales (Odontoceti) (Milinkovitch. 1997). But his conclusion was not well accepted, as sperm whales have substantial teeth and a single, rather than double nostrilled blowhole. More recently, scientists came back to the traditional arrangement, that the sperm whale is an odontocete. The evidence and recent molecular analyses strongly indicate the mystecetes and all other extant cetaceans is the oldest division in the ancestral tree.
The pygmy sperm whale (Kogia beviceps) and dwarf sperm whale (Kogia simus), are much smaller. The kogiids seem to have separated from the lineage that led to the sperm whale at least 9 millions years ago, making the sperm whale the myse phylogenetically distinct of all the seventy-five-odd species of living odontocetes. (Chadwick. 2001)
Hind limb bud images, dolphin embryo and fetus development show that dolphins and whales are descended from mammals, as they have the characteristics of hind legs, which are visible in the remaining atavistic bones, an embryo that has hind legs which disappear. There are photographs of hind limb buds on a five-week-old Pantropical Spotted Dolphin embryo, and 1.5 to 4-month fetus development taken by Professor J.G.M. Thewissen which are available on the Web (Thewissen. 2006).
Sirenians and elephants are evolved from a common ancestor. Like whales, sirenians returned to the water. Though hind limbs on whales may be hard to find, many sirenians (Manatees) still retain vestigial toenails like their elephant cousins, and share other traits in common with modern elephants.
There seems to be a controversy over the origins of modern whales which retain vestigial hind limb rudiments. Creationists call this vestige bone disease and say these remnants were designed for copulation only (which they are used for), but science says this is how evolution works –finding new purpose for old structures. In an out of date publication by Creationists they claim that there is no bone in the whale descended from the thigh leg bones, but new fossil finds of early whales contain complete leg bones from basilosaurus, and a reconstruction of the creature’s likely appearance shows it has rudimentary legs.
On questions on the dating of varied early whales one might suggest further reading on whale evolution, the evolution of eco-location, the nursing of the young (suggesting common ancestry with land mammals), and the brain of humans vs. cetacea (Hasegawa. 1997).
The transitional inner ear of whales evolved from land to sea mammals. Professor Hans Thewissen explained the differences of earbone fossils, the incus and tympanic, in his web publication, The Thewissen Lab (Thewissen, 2001). But scientists have many e xamples of hind limb rudiments, such as one found in 1958, caught in the Bering Sea, where an x-ray revealing bone structures and a photograph taken of the protrusions on the whale’s body, showed the whale had small legs. Even better, in 1919, a historical record and photos of a female humpback with protruded hind limbs including femur, tibia and tarsus was made. In 1914, there was a study of protruded limbs on whale and dolphin embryos.
A female sperm whale was caught in 1956. Upon examining the interior of the limb, partially cartilaginous bones were found, corresponding to the pelvis, femur, and possibly to the tibia. As there are numerous examples of this feature, a list of catches between 1956 and 1963 of whales caught and discovery of hind limb protrusions, including the approximate percentage of whales with this feature may be found on the web. (Ogawa. 1957)
The Oligocene epoch was crucially important in the evolution of dolphins and whales. The Oligocene epoch, part of the Tertiary Period in the Cenozoic Era, only lasted from about 33.7 to 23.8 million years ago, though many major changes occurred during this short time. These include the appearance of the first elephants with trunks, early horses, and the appearance of many grass plants that would eventually produce vast tracts of grasslands in Mongolia and North America for these animals to eat in the following epoch, the Miocene. Two modern lineages of cetaceans had evolved during this epoch from archaeocete ancestors. Interestingly, in the late Oligocene, the whale Aetiocetus, from Oregon, developed skull and jaw features typical of baleen whales, so it is considered to be the earliest mysticete. Yet it also had a full set of teeth.
By the Miocene period, whales of both lineages were relatively common and are found as fossils in many marine deposits. As a result of the cooling trend prevalent throughout the Oligocene period, the lives and habitats of many organisms were directly affected. In the oceans, marine biotic provinces became more fragmented as sea dwellers capable of withstanding cooler temperatures congregated to places further from the warmer equator, where other species could better survive. The cooling trend was also responsible for the reduced diversity in marine plankton, the foundation of the food chain.
On land, mammals such as horses, deer, camel, elephants, cats, dogs, and primates began to dominate, except in Australia. The continuation of land mammal faunal migration between Asia and North America was responsible for the dispersion of several lineages onto new continents. The “bulk feeding” in the open grasslands and savannas that occurred in this period resulted in the increase of general herbivores’ size. As an example, ungulates continued to get larger throughout the Oligocene period. (Thewissen. 2006)
Families of both toothed and baleen whales are known to have evolved by the late Miocene and are still found today. These include the baleen whale families Balaenopteridae (including the blue whale) and Balaenidae (right whales), and the toothed whale families Delphinidae (dolphins and killer whales), Physeteridae (sperm whales), Monodontidae (belugas and narwhals), Phocaenidae (porpoises), and Ziphiidae (beaked whales).
During this last century, whales became very important evolutionary study specimens and whaling came under strict scrutiny and criticism, considering the discovery of great intelligence and sociability of the whale. The Minke whale, a rare whale, is known for its uncanny ability to recover from blows to the head and other means of anesthetizing it to prepare it for the kill. Recently, a Norwegian whaling boat in northern waters was reeling in a harpooned minke whale, when the animal revived. It rammed the ship, causing the mast to break and sent two crew members in the crow’s nest toppling into the sea, breaking the ribs of one. Then the whale escaped. The news spread around the world with the headline: “Don’t Get Mad, Get Even.” (Chadwick. 2006)
Chadwick, Douglas, Whales, Dolphins and Porpoises, 2nd ed. Checkmark Books, 1999 National Geographic.
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Humphrey, Nicholas. www.humphrey.org.uk/papers/1976SocialFunction.pdf” “The Social Function of Intellect,” in Bateson, P.P.G. And Hinde, R.A., Eds. Growing Points in Ethology, (1976) chapter 9, pages 303-317. Cambridge University Press.
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Ogawa, R., and Kamiya, T.A. (1957) “Case of the Cachalot [Sperm Whale] With Protruded Rudimentary Hind Limbs.” Scientific Reports of the Whales Research Insititute, No. 12, p. 197-208.
Ogawa, R., and Kamiya, T.A. “Case of the Cachalot [Sperm Whale] With Protruded Rudimentary Hind Limbs.” Scientific Reports of the Whales Research Insititute, No. 12, p. 197-208. (1957).
Rendell, Luke and Whitehead, Hal.
Behavioral and Brain Sciences (2001), 24: 309-324 Cambridge University Press
Struthers, John, M.D., Professor of Anatomy in the University of Aberdeen. (1881) “On the Bones, Articulations, and Muscles of The Rudimentary Hind-Limb of the Greenland Right-Whale (Balaena mysticetus).” Journal of Anatomy and Physiology (London), Vol. 15, p. 141-321.
Thewissen, Hans. “Digital Library of Dolphin Development.” The Thewissen Lab. November 4, 2006. < tp:/ / www.neoucom.edu/DEPTS/ANAT/Thewissen/
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