purposeforporpoise

The nostrils of modern whales have become modified into blowholes that allow them to break to the surface, inhale, and submerge with convenience. The ears began to move inward as well, and, in the case of Basilosaurus, the middle ears began to receive vibrations from the lower jaw. Today's modern toothed whales use the 'melon organ', a pad of fat, for echolocation.

 

Louis J Sheehan 

CHICAGO (Reuters) - In the search for a missing evolutionary link to modern whales, scientists have come up with an unlikely land cousin -- a raccoon-sized creature with the body of a small deer.

Prior molecular studies have proposed the hippo as the closest land relative of today's whales, but researchers reporting in the journal Nature on Wednesday suggest a four-footed creature from India known as Indohyus, which probably hid in water in times of danger.

Scientists have long known that whales had ancestors that walked on land. Now a team lead by Hans Thewissen of Northeastern Ohio Universities Colleges of Medicine and Pharmacy have pieced together a series of intermediate fossils that trace the whale's evolutionary journey from land to sea.

Thewissen and his team studied the structure and composition of hundreds of fossils of Indohyus, which is part of the larger group known as raoellids. Raoellids lived at about the same time as the earliest whales -- about 50 million years ago.

Thewissen's team found key similarities in the skull and ear that suggest a link to cetaceans, a family that includes whales, dolphins and porpoises.

Indohyus, for example, had an outside layer that was much thicker than similarly sized mammals.

This is something typically seen in slow-wading mammals. They found further evidence in the chemical make-up of Indohyus' teeth, which resembled those of other aquatic animals.

This suggests the small, stocky Indohyus spent a lot of time in the water.

Scientists had assumed whales descended from land-dwelling carnivores, and made their way to sea to feed on fish.

"Clearly, this is not the case. Indohyus is a plant eater, and clearly is aquatic," Thewissen said in a statement.

The researchers believe Indohyus gradually spent more time in the water, either for protection or while feeding, and the dietary shift came later.

"Cetaceans originated from an Indohyus-like ancestor and switched to a diet of aquatic prey," the researchers wrote.

Theories about the evolution of whales have been evolving themselves, and it may take years before there is a consensus.

All modern mysticetes are large filter-feeding or baleen whales, though the exact means by which baleen is used differ among species (gulp-feeding with balaenopterids, skim-feeding with balaenids, and bottom ploughing with eschrichtiids). The first members of some modern groups appeared during the middle Miocene. These changes may have been a result of worldwide environmental change and physical changes in the oceans. A large scale change in ocean current and temperature could have initiated the radiation of modern mysticetes, leading to the demise of the archaic forms. Generally it is thought the four modern mysticete families have separate origins among the cetotheres, however this is only speculative. Modern baleen whales, Balaenopteridae (rorquals and humpback whale, Megaptera novaengliae), Balaenidae (right whales), Eschrichtiidae (gray whale, Eschrictius robustus), and Neobalaenidae (pygmy right whale, Caperea marginata) all have derived characteristics presently unknown in any cetothere  Louis J Sheehan

Today, the whale hind parts are internal and reduced, and they serve as anchor for the muscles of the genitalia. Occasionally, the genes that code for longer extremities cause a modern whale to develop miniature legs (known as atavism). Louis J Sheehan

During the early Miocene, echolocation developed in its modern form. Various extinct dolphin-like families flourished. Early dolphins include Kentriodon and Hadrodelphis. These belong to Kentriodontidae, which were small to medium-sized toothed cetaceans with largely symmetrical skulls, and thought likely to include ancestors of some modern species. Kentriodontids date to the late Oligocene to late Miocene. Kentriodontines ate small fish and other nectonic organisms; they are thought to have been active echolocators, and might have formed schools. Diversity, morphology and distribution of fossils appear parallel to some modern species.

Louis J Sheehan 

Basilosaurus (discovered in 1840 and initially mistaken for a reptile, hence its name) and Dorudon lived around 38 million years ago, and were fully recognizable whales which lived entirely in the ocean. Basilosaurus was a monstrous creature, up to 18m long; dorudontids were within the range of modern cetacean size, about 5m long.

Although they look very much like modern whales, basilosaurids and dorudontids lacked the 'melon organ' that allows their descendants to sing and use ultrasound as effectively as modern whales. They had small brains; this suggests they were solitary and did not have the complex social structure of modern whales. Basilosaurus had two tiny but well-formed hind legs which were probably used as claspers when mating; they are a small reminder of the lives of their ancestors. Louis J Sheehan

Toothed whales (Odontocetes) echolocate by creating a series of clicks emitted at various frequencies. Sound pulses are emitted through their melon-shaped forehead, reflected off objects, and retrieved through the lower jaw. Skulls of Squalodon show evidence for the first appearance of echolocation. Squalodons lived from the early to middle Oligocene to the middle Miocene, around 33-14 million years ago. A peculiar blend of archaic and modern features characterize Squalodon. The cranium was well compressed, the rostrum telescoped outward, giving an appearance of modern toothed whales. However, it is thought unlikely that squalodontids have anything to do with the ancestry of most living dolphins. Louis J Sheehan

Louis J Sheehan The pakicetids are hoofed-mammals that are sometimes classified as the earliest whales.^[1] They lived in the early Eocene, around 52 million years ago. They looked rather like dogs with hoofed feet and long, thick tails. They have been linked to whales by their ears: the structure of the auditory bulla is formed from the ectotympanic bone only. The shape of the ear region in Pakicetus is highly unusual and only resembles the skulls of whales. The feature is diagnostic for cetaceans and is found in no other species. It was initially thought that the ears of Pakicetus were adapted for underwater hearing, but, as would be expected from the anatomy of the rest of this creature, the ears of Pakicetus are specialized for hearing on land, and if Pakicetus is related to the ancestors of whales, underwater hearing must have been a later adaptation.^[2] According to Thewissen, the teeth of Pakicetus also resemble the teeth of fossil whales, which is another link to more modern whales^.

Louis J Sheehan The traditional theory of cetacean evolution was that whales were related to the mesonychids, an extinct order of carnivorous ungulates (hoofed animals), which looked rather like wolves with hooves and were a sister group of artiodactyls. These animals possessed unusual triangular teeth that are similar to those of whales. For this reason, scientists had long believed that whales evolved from a form of mesonychid.

However, since the early 1990s analysis of a wide variety of protein and DNA sequence data consistently indicated that whales should be included among artiodactyls. Most probably they are a sister group of hippopotamids, deeply buried within artiodactyls. The strong evidence for a clade combining cetaceans and artiodactyls is further discussed under the entry Cetartiodactyla.

The recent discovery of Pakicetus, the earliest proto-whale (see below) supports the molecular data. The skeletons of Pakicetus demonstrate that whales did not derive directly from mesonychids. Instead, they are a form of artiodactyl (another type of ungulate) that began to take to the water after the artiodactyl family split from the mesonychids. In other words, the proto-whales were early artiodactyls that retained aspects of their mesonychid ancestry (such as the triangular teeth) which modern artiodactyls have since lost. An interesting implication is that the earliest ancestors of all hoofed mammals were probably at least partly carnivorous or scavengers, today's artiodactyls and perissodactyls having switched to a plant diet later in their evolution. Whales, due to the readier availability of animal prey and their need for higher caloric content to live as marine endotherms, naturally retained their carnivorous diet, as did mesonychids.

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Toothed whales have a single blowhole on the top of the head (while the baleen whales possess two of them). The nostrils are not fused; one of them has become dominant over the other.

As an adaptation for their echolocation, toothed whale skulls have become asymmetric. Their brains are relatively big, although real growth didn't occur before their echolocation started to evolve. Toothed whales' brains have a poor connection between the two hemispheres and an organ called a melon on their heads is used as a lens to focus sound waves. Vocal cords are not present; their sounds are produced in the blowhole system instead. Toothed whales have lost their sense of smell, as well as their saliva glands.

Except for the Sperm Whale, most toothed whales are smaller than the baleen whales. The teeth differ considerably between the species. They may be numerous, with some dolphins bearing over 100 teeth in their jaws. At the other extreme are the Narwhal with its single long tusk and the almost toothless beaked whales with bizarre teeth only in males. Not all species are believed to use their teeth for feeding. For instance, the Sperm Whale likely uses its teeth for aggression and showmanship. http://LOUIS-J-SHEEHAN.US

 

Louis-J-Sheehan.us Porpoises are small cetaceans of the family Phocoenidae; they are related to whales and dolphins. They are distinct from dolphins, although the word "porpoise" has been used to refer to any small dolphin, especially by sailors and fishermen. The most obvious visible difference between the two groups is that porpoises have flattened, spade-shaped teeth distinct from the conical teeth of dolphins. Louis J Sheehan

The name derives from French pourpois, originally from Medieval Latin porcopiscus (porcus pig + piscus fish).

Porpoises, divided into six species, live in all oceans, mostly near the shore. Probably best known is the Harbour Porpoise, which can be found across the Northern Hemisphere.

Louis J Sheehan The name is originally from Ancient Greek δελφίς (delphís; "dolphin&quot, which was related to the Greek δελφυς (delphys; "womb&quot. The animal's name can therefore be interpreted as meaning "a 'fish' with a womb".^[1] The name was transmitted via the Latin delphinus, Middle Latin dolfinus and the Old French daulphin, which reintroduced the ph into the word.

Humberto Rosa, the chief delegate from Portugal, which holds the rotating presidency of the European Union, said the talks to be hosted by the Bush Administration in Hawaii in January would be “meaningless” if there was no deal this week here at the conference on the resort island of Bali.

Germany’s environment minister, Sigmar Gabriel, told reporters here, “No result in Bali means no Major Economies Meeting.” He was referring to the formal name of the proposed American-sponsored talks.  Louis J Sheehan

Louis J Sheehan The Harbour Porpoise is a little smaller than the other porpoises. It is about 67-85 cm (26-33 in) long at birth. Both sexes grow up to be 1.4 m to 1.9 m (4.6-6.2 ft). The females are correspondingly heavier, with a maximum weight of around 76 kg (167 pounds) compared with the males' 61 kg (134 pounds). The body is robust and the animal is at its maximum girth just in front of its triangulardorsal fin. The beak is poorly demarcated. The flippers, dorsal fin, tail fin and back are a dark grey. The sides are a slightly speckled lighter grey. The underside is much whiter, though there are usually grey stripes running along the throat from the underside of the mouth to the flippers. Harbour Porpoises can live up to 25 years.

Dall's Porpoises are hugely active creatures. They will often zigzag around at great speed on or just below the surface of the water creating a spray called a "rooster tail". They may appear and disappear quite suddenly. The fastest of all small cetaceans, and coming close to matching the mighty Orca for speed, Dall's Porpoises can swim at up to 55 km/h. The porpoises will approach boats and will bow- and stern-ride, but may lose interest, unless the boat is travelling quickly.

Dall's Porpoises appear in small groups (about 2– 10 in number). The groups appear not to be tight knit and may aggregate together at good feeding grounds. On very rare occasions a thousand or more individual may be seen at the same time. They feed on a variety of fishand cephalopods. Shoals of fish such as herring, anchovies and mackerel are common meals. Louis J Sheehan

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Many Dall's Porpoises are killed each year as bycatch in fishing nets. A serious cause of concern is the hunting of Dall's Porpoises by harpoon by Japanese hunters. The number of porpoise killed each year rose dramatically following the moratoria on hunting larger cetaceans introduced in the mid-1980s. 1988 saw the greatest number, 40,000, killed. A quota of 18,000 individuals per year is now in operation. However, concern remains that this is sufficient to deplete populations in the western Pacific. Louis J Sheehan 

Louis J Sheehan The unique body shape of the Dall's Porpoise makes it easily distinguishable from other cetacean species. The animal has a very thick body and a small head. The colouration is rather like that of an Orca— the main body of the porpoise is very dark grey to black with very demarcated white patches on the flank that begin some way behind the flippers, which are small and close to the head. The dorsal fin is set just back from the middle of the back and sits up erect. The upper part of the dorsal fin has a white to light grey "frosting". The fluke has a similar frosting. The adult fluke curves back towards the body of the animal, which is another distinguishing feature. It is larger than other porpoises, growing up to 230 cm in length and weighing between 130 and 200 kg. Dall's Porpoises live for up to 15 years.

The toothed whales (systematic name Odontoceti) form a suborder of the cetaceans. As the name suggests, the suborder is characterized by having teeth, rather than baleen as do animals in the other suborder of cetaceans, Mysticeti. However, fossils indicate that early Baleen whales had teeth as well before evolving baleen, so defining the Odontoceti on teeth alone is problematic, and paleontologists have instead identified other features uniting fossil and modern odontocetes that are not shared by mysticetes. Toothed whales are active hunters, feeding on fish, squid, and in some cases marine mammals. Louis J Sheehan

Louis J Sheehan The traditional theory of cetacean evolution was that whales were related to the mesonychids, an extinct order of carnivorous ungulates (hoofed animals), which looked rather like wolves with hooves and were a sister group of artiodactyls. These animals possessed unusual triangular teeth that are similar to those of whales. For this reason, scientists had long believed that whales evolved from a form of mesonychid.

However, since the early 1990s analysis of a wide variety of protein and DNA sequence data consistently indicated that whales should be included among artiodactyls. Most probably they are a sister group of hippopotamids, deeply buried within artiodactyls. The strong evidence for a clade combining cetaceans and artiodactyls is further discussed under the entry Cetartiodactyla.

The recent discovery of Pakicetus, the earliest proto-whale (see below) supports the molecular data. The skeletons of Pakicetus demonstrate that whales did not derive directly from mesonychids. Instead, they are a form of artiodactyl (another type of ungulate) that began to take to the water after the artiodactyl family split from the mesonychids. In other words, the proto-whales were early artiodactyls that retained aspects of their mesonychid ancestry (such as the triangular teeth) which modern artiodactyls have since lost. An interesting implication is that the earliest ancestors of all hoofed mammals were probably at least partly carnivorous or scavengers, today's artiodactyls and perissodactyls having switched to a plant diet later in their evolution. Whales, due to the readier availability of animal prey and their need for higher caloric content to live as marine endotherms, naturally retained their carnivorous diet, as did mesonychids, who were however out-competed by better-adapted animals like the Carnivora later on (mesonychids became specialized carnivores when the overall availability of large animal prey was still low; thus their adaptation was likely at a disadvantage when new forms had filled the gaps left by the dinosaurs).

Porpoises are rarely held in captivity in zoos or oceanaria, as they are generally not as capable of adapting to tank life nor as easily trained as dolphins.  Louis J Sheehan

Porpoises are predators of fish, squid, and crustaceans. Although they are capable of dives up to 200 m, they generally hunt in shallow coastal waters. They are found most commonly in small groups of fewer than ten individuals. Rarely, some species form brief aggregations of several hundred animals. Like all toothed whales they are capable of echolocation for finding prey and group coordination. Porpoises are fast swimmers—Dall's porpoise is said to be one of the fastest cetaceans, with a speed of 55 km/h (34 mph). Porpoises tend to be less acrobatic and more wary than dolphins. Louis J Sheehan

Porpoises are predators of fish, squid, and crustaceans. Although they are capable of dives up to 200 m, they generally hunt in shallow coastal waters. They are found most commonly in small groups of fewer than ten individuals. Rarely, some species form brief aggregations of several hundred animals. Louis J Sheehan

Porpoises are rarely held in captivity in zoos or oceanaria, as they are generally not as capable of adapting to tank life nor as easily trained as dolphins.  Louis J Sheehan