Orca: Evolutionary Origin, Characteristics, Habitat, Reproduction

The killer whale ( Orcinus orca ), also known as killer whale, is an aquatic mammal belonging to the Delphinidae family, of which it is the largest species. The largest male found weighed 10 tons and was approximately 9.8 meters long.

This toothed whale is also known for its coloration, in black and white tones. In this animal the sexual dimorphism is evident. Thus, males are longer and heavier than females. In addition, the tail fin of the male reaches 1.8 meters, while in the female it measures 0.9 meters.

Despite its large body dimensions, the killer whale is considered one of the fastest moving marine mammals . When swimming, they could reach speeds of over 56 km / h.

This ability to swim is used by the Orcinus orca to capture some of its prey. To hunt cetaceans, like a young sperm whale, it chases it until it gets tired. Once the prey is exhausted, it prevents it from rising to the surface, causing death by drowning.

Orcas have complex societies, thus forming stable social groups. This type of organization is known as matrilineal, where descendants live with their mothers for most of their lives.

Evolutionary origin

One of the theories that try to explain the origin of the killer whale states that this mammal probably descended from terrestrial carnivorous animals, which inhabited 60 million years ago, during the period known as the Paleocene.

The relationship between these ancestors, known as mesonychia, with current killer whales is based on some similar elements of the skull, teeth and other morphological structures.

Mesonychians were the size of a wolf, but with hoofed legs. Due to food needs, these animals began to enter the water. This originated an evolutionary process that lasted millions of years.

In this, the limbs underwent modifications for swimming, lost their fur and the dental structure adapted to the new marine diet. The teeth were triangular, very similar to those of the killer whale. Because of this, it was long claimed that cetaceans evolved from a form of mesonychians.

However, in the early 1990s, analysis of the DNA of the fossils provided new information, suggesting the inclusion of cetaceans within the group of artiodactyls.

Thus, the discovery of Pakicetus skeletons supports that this proto whale derives from artiodactyls, and not from mesonychians as previously thought. At the taxonomic level, cetarthiodactyls are a clade of mammals that relates artiodactyls to cetaceans.

Scientists estimate that the killer whale divided into several subgroups around 200,000 years ago. This evolution would be associated with changes in the climate after the last ice age.

The North Pacific transient ecotype probably separated from the rest of the killer whales 700,000 years ago. The two Antarctic ecotypes were differentiated 700,000 years ago.

characteristics

Vocalizations

Like all cetaceans, the killer whale depends on the sound they make underwater to orient themselves, communicate and feed. It has the ability to produce three types of vocalizations: whistles, clicks, and pulsed calls. Clicks are used to guide your movement while browsing and for social interactions.

The resident killer whales of the northeast Pacific are more vocal than those that transit the same waters. Transient groups could be quiet to avoid attracting the attention of prey.

Each grouping has similar flames, making up what is known as a dialect. This is made up of various types of repetitive calls, which form complex distinctive patterns of the group.

This way of communicating probably fulfills the function of maintaining cohesion and identity among members of the population.

Size

The killer whale is the largest member of the Delphinidae family. The streamlined body of the male can measure between 6 and 8 meters in length and the weight could be around 6 tons. The female is smaller, its length is between 5 and 7 meters and weighs 3 to 4 tons.

The largest species ever recorded was a male, who weighed 10 tons and measured 9.8 meters. The largest female measured 8.5 meters and weighed 7.5 tons. The calf weighs approximately 180 kilograms at birth and is 2.4 meters long.

Fins

One aspect that differentiates males from females is the dorsal fin. In males, it is shaped like an elongated isosceles triangle, and can reach up to 1.8 meters high. In females, it is shorter and curved, measuring only 0.9 meters.

This structure can be slightly curved to the left or right side. The killer whale’s pectoral fins are rounded and large.

Skin

The integument of the Orcinus orca is characterized by having a highly developed dermal layer. Thus, it has a dense network of collagen fibers and insulating adipose tissue, which could measure from 7.6 to 10 centimeters.

Coloration

One characteristic that distinguishes the killer whale is the color of its skin. The dorsal region is very intense black. The throat and chin are white, from which a strip of the same color arises that extends through the belly and reaches the tail, where it branches out in the shape of a trident.

Over the eye it has an oval white patch. Behind the dorsal fin it has a whitish gray spot, with the peculiarity of having a similarity to a horse saddle.

The pectoral fins and the tail fin are black, but the tail fin has a white back. In the lower part of the flanks there is a white area, as a consequence of the expansion of the strip in the caudal region.

In the young, all the white areas that the adults have have a yellow-orange hue. In the same way, until the year of life the black color may not be so intense, but rather a dark gray tone.

In few occasions the killer whale could be white. These species have been spotted in the Bering Sea, off the coast of Russia and off Saint Island. Laurent, in French Guyana.

Head

The orca’s skull is much larger than that of the rest of the species that make up its family. Adult males have lower jaws and occipital ridges of greater length than females.

It has a wide temporal fossa, with a fairly deep inner surface. The characteristic of this area, formed by the frontal and parietal bones, allows the animal to exert greater pressure when biting. In this way, the orca can hunt and consume large animals.

The teeth are large and compressed at the root, in the anteroposterior region. When the mouth is closed, the teeth located in the upper jaw fit into the spaces that exist in the lower teeth.

The central and rear teeth help to keep the prey in place. The front is slightly angled outwards, protecting them from any sudden movement.

Taxonomy

Animal Kingdom.

Sub kingdom Bilateria.

Chordate Phylum.

Vertebrate sub phylum.

Tetrapoda superclass.

Mammalia class.

Sub class Theria.

Infraclass Eutheria.

Order Cetacea.

Family Delphinidae (Gray, 1821.)

Genus Orcinus (Fitzinger, 1860)

Species Orcinus orca (Linnaeus, 1758)

Habitat and distribution

Orcinus orca is present in almost all the seas and oceans of the planet. It can live from the north to the Arctic Ocean; it could also be near the ice sheet or south of the Antarctic Ocean.

Despite being present in several tropical areas, this aquatic mammal shows a preference for cold waters, reaching a higher density in both polar regions.

Deep sea waters are usually found, between 20 and 60 meters. However, they can visit shallow coastal waters or dive in search of food.

It is an animal that rarely migrates due to climatic variations, however, it can move to other waters if food is scarce. In some habitats, the killer whale can be located seasonally, generally associated with the migratory movement carried out by its prey.

An example of this occurs on the Iberian coasts, where the presence of the killer whale, especially in the waters near the Strait of Gibraltar, becomes more frequent during the migrations of Thunnus spp .

Distribution

The killer whale appears to have the ability to positively select highly productive coastal habitats. Likewise, it discards the areas that are subject to strong fishing pressure, due to human disturbances and food shortages.

This is why it is rarely appreciated in the Mediterranean, as it is not very productive waters for the species.

In the North Pacific there are three ecotypes of killer whales: resident, transient and oceanic. These differ in terms of eating habits, distribution and behavior and social organization. In addition, they have some morphological and genetic variations.

Areas of concentration

The highest densities of the killer whale are found in the North Pacific, along the Aleutian Islands. In addition, they are in the Southern Ocean and in the Eastern Atlantic, specifically on the Norwegian coast.

Also a large number of these species inhabit the western North Pacific, in the Sea of ​​Okhotsk, in the Kuril Islands, the Commander Islands and Kamchatka. In the southern hemisphere they are located in Brazil and southern Africa.

They are usually distributed in the Eastern Pacific, on the coasts of British Columbia, Oregon and Washington. In the same way they can be seen in the Atlantic Ocean, in Iceland and in the Faroe Islands.

Researchers have observed the stationary presence of Orcinus orca  in the Canadian Arctic, on Macquarie Island and Tasmania. Eventually, there are populations in Patagonia, California, the Caribbean, northeast Europe, the Gulf of Mexico, New Zealand, and in southern Australia.

Reproduction

Females are sexually mature between 6 and 10 years, reaching their maximum level of fertility at 20. Males begin to mature between 10 and 13 years. However, they usually begin to mate when they are 14 or 15 years old, and the females stop reproducing at around 40 years of age.

The orca is a polygamous species; the male can have several pairs in the same reproductive season. It usually copulates with females that belong to groups other than the one it is in, thus avoiding inbreeding. In this way it contributes to the genetic diversity of the species.

The female has polyestric cycles, separated by periods of 3 to 16 months; invests a lot of energy in pregnancy and in raising her offspring. After 15 to 18 months the calf is born, which suckles for 12 months, being able to extend up to 2 years. He is also in charge of protecting her and teaching her to hunt.

Reproduction can occur every 5 years. The killer whale does not have a specific time of year to copulate, however, it usually happens in summer, with the calf being born in the fall or winter.

Feeding

Orcinus orca’s diet may vary between neighboring areas and even within the same area that it inhabits. This implies specializing their diet, adapting to the ecotype or the population where they are.

Some killer whales catch mostly fish, such as salmon or bluefin tuna, penguins, sea turtles, and seals. This differentiated selection of prey may be due to competition for trophic resources.

The species that live as residents in an area are usually piscivores, those that are transients in the area generally consume marine mammals. Oceanic killer whales generally base their diet on fish.

Hunting methods

Killer whales can band together, cooperating with each other to attack large cetaceans or schools of fish. The main hunting strategy is based on echolocation, which allows the animal to locate the prey and inform the rest of the group if an ambush is necessary to catch it.

This technique is important if you want to catch whales or other large cetaceans. Once they are located, they stop emitting sound waves, organizing themselves to isolate, exhaust and drown the prey.

Dams

Fishes

Some populations of killer whales that live in the Greenland Sea and Norway specialize in hunting herring, following the migration of that fish to the Norwegian coast. Salmon makes up 96% of the diet of those residing in the Northeast Pacific.

The method most used by the Orcinus orca to catch herring is known as a carousel. In this, the killer whale expels a burst of bubbles, causing the fish to be trapped in it. The mammal then strikes the “ball” that formed the herring with its tail, stunning or killing it. Later he consumes it one by one.

In New Zealand, rays and sharks are the preferred prey with these cetaceans. To catch sharks, the killer whale brings them to the surface, hitting them with its tail fin.

Mammals and birds

The Orcinus orca is a very effective predator among marine mammals, cetaceans attacking large as the gray whale and the sperm whale. Capturing these species usually takes several hours.

In general, they attack weak or young animals, chasing them until they are exhausted. Then it surrounds them, preventing them from surfacing to breathe.

Other species that make up the diet are sea lions, seals, walruses, sea lions, and sea otters. To capture them they can hit them with the tail or they can also rise in the air, falling directly on the animal.

Also, they could attack terrestrial mammals, such as deer that swim on the shore of coastal waters. In many areas, the killer whale could hunt seagulls and cormorants.

References

  1. Wikipedia (2019). Killer whale. Recovered from en.wikipedia.org.
  2. Burnett, E. (2009). Orcinus orca. Animal Diversity Web. Recovered from animaldiversity.org.
  3. ITIS (2019). Orcinus orca. Recovered from itis.gov.
  4. Suárez-Esteban, A., Miján, I. (2011). Orca, Orcinus orca. Virtual encyclopedia of Spanish vertebrates. Recovered from digital.csic. it is.
  5. Killer-whale.org (2019). Killer whale reproduction. Recovered from killer-whale.org.

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