Dolphins at a Glance
Dolphins are an amazing bunch of water-dwelling animals which are as most people will know by now, actually mammals that are specifically adapted for their aquatic lifestyles. They are highly regarded by people across the globe as being playful, social, intelligent and fascinating for their diversity and sometimes acrobatic propensity!
They greatly range in shape, size and habitat being fairly widely dispersed across the waters of the globe, including freshwaters. Some dolphins aren’t exactly the cute and friendly critters most people come to recognize and you will see in this guide: the river varieties are not as charming by way of looks as their marine relatives are.
Dolphin Evolution and Taxonomy
Dolphins belong to a suborder of animals called Cetacea that also includes other water-dwelling mammals such as whales and porpoises. There are five families of dolphin which hosts species that are divergent in the habitats which they reside and the adaptations they have to survive in them. The families are Delphinidae (ocean dolphins), Pontoporiidae (the brackish dolphins), Plantanistidae (Indian River dolphins) and Iniidae (new world river dolphins).
It’s understood that very early sea dwelling animals evolved a means of exiting the water and becoming terrestrial to later become mammalian. What’s interesting is later on in the evolutionary journey; some mammalian species that belonged to the order artiodactyl (an order that consists of animals such as bison, deer, and giraffes) followed a process of natural selection which led them back into the ocean about 48 million years ago.
Even though they dwell in the water, they still need to breathe oxygen from the air like their land-loving ancestors, however, dolphins can stay submerged under the water for extremely long periods of time allowing them to play, hunt, breed, and travel as they need to.
The common anatomical themes that occur in all dolphins are as follows:
Their bodies are generally streamlined and shaped in a similar way to a torpedo. This aids their ability to travel through water by pushing the water around their body as they propel themselves with their muscular tails to pick up speed.
Their back limbs and forelimbs are modified into flippers in much the same way as other aqueous animals like seals for instance. This allows them to gain as much drag as possible to get an initial push when accelerating.
Not all have long snouts; some are longer than others and can be described as being beaked or not beaked. They typically have conical teeth that are used to grip fish and prevent their prey from escaping from their mouth. The blowhole on the top of their head is used to inhale fresh air and expel stale air when they surface.
Dolphins also all have a dorsal fin which is found on most rounded animals that live in water and its function is to keep the animal stable as it moves. Without it, they would roll around as they speed through the water which wouldn’t be ideal at all.
Thick blubber is also present in all dolphins but the thickness can vary between species depending on the temperature of the waters they inhabit. It not only helps with temperature regulation but also with buoyancy, energy storage, and protection.
What do Dolphins Eat?
The dolphin diet can vary between species as it will wholly depend on their size, their hunting capabilities and their geographic location and the season. One thing is for sure, all species are predatory carnivores and most of them eat fish.
Articles of prey that are a top choice for oceanic species: squid, mackerel, shrimp, jellyfish, salmon, herring, mullet, catfish, octopus, and octopus.
Freshwater dolphins will eat a little bit differently and are adapted to do so: All kinds of fish, shrimp, krill, and amphibians.
Orcas are surprisingly the largest species of dolphin and it’s surprising because they are thought to be whales mostly due to their common name “the killer whale”. They take on much larger prey such as seals, sea lions, fish, and sadly, penguins.
You may also be wondering “what does a dolphin drink?” as the marine dolphins are constantly swimming in salt water, and as mammals, they must drink? Well, they obtain the water they need from the food they eat, so they do not actually drink the sea water which they swim in.
Marine Dolphin Species
Common bottlenose dolphin (Tursiops truncates)
This is the most familiar of the dolphin species and is the archetypal dolphins that are represented on TV, in cartoons, and in marine parks. They are very well dispersed and can be found in oceans worldwide, some living far out in the wider ocean whilst other populations can be seen closer to shore and these populations can differ in appearance and prefer different water temperatures.
Their brains are bigger than that of humans. Tests have concluded that these are highly intelligent animals that in engage in inquisitive, social and problem-solving activities. It’s even been recorded that they have a relationship with some fishermen by driving the fish into the nets and receiving their share of the catch!
Atlantic Spotted dolphin (Stenella frontalis)
The Atlantic Spotted Dolphin is another fairly recognizable species that inhabits the Gulf Stream and the temperate and tropical waters of the North Atlantic Ocean. This dolphin is highly recognizable due to the spots that cover its entire body found in more mature individuals, in fact, their age can be determined by their coloration as it changed as the dolphin grows.
They’re a very sociable species and can be found swimming in groups of between 5 and 15 members and can mix with the common bottlenose dolphins too! These groups of dolphins hunt at night, using cooperation to steer schools fish into each other’s path.
Hourglass dolphin (Lagenorhynchus cruciger)
A very small variety of dolphin that finds its home in the colder, Antarctic and Sub-Antarctic waters; the hourglass dolphin is a particularly pretty looking species. It gets its name from the stylish hourglass-shaped marking on its flanks.
Their groups from between5 and 10 individuals and like other species of dolphin they hunt together. They also share feeding grounds and group with other dolphin species when it comes to hunting, proving greater chances of success.
Freshwater Dolphin Species
South Asian river dolphin (Platanista gangetica)
One of the stranger members of the dolphin family and one that is also surrounded by mystery and folklore; The South Asian River Dolphin is certainly not the most beautiful to look at but it is fascinating in its own right.
There are two subspecies of this dolphin, Platanista gangetica gangetica is found in the Ganges and Brahmaputra Rivers in India, Bangladesh and Nepal whilst Platanista gangetica minor makes its home in the Indus River of Pakistan. They feed mostly on carp and catfish and they don’t congregate in as large groups as their ocean-dwelling cousins.
Amazon River dolphin (Inia geoffrensis)
The Amazon River Dolphin, also quite strange in appearance and also surrounded by mystery and folklore. It is said that during the evening, the dolphin transforms into a handsome man or woman who seduces people. They can be a mottled grey or full pink coloration and they usually hang out in pairs.
Don’t judge them on their looks, as they’re not aggressive and just as playful as their marine counterparts. They’re even less shy too but not as inquisitive or sociable with humans or each other.