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A physical trait that all organisms in the pinniped order have is flippers. The animals in this order are seals, sea lions, and walruses and their flippers help to propel them through the water.  Pinniped species also have well developed whiskers and large eyes which helps them hunt, as they are carnivores. Pinnipeds use their large molars to eat prey whole. Another physical characteristic they share is body shape. All pinnipeds have a similar body that is shaped like a spindle, which is helpful when swimming.

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Many aquatic animals have blubber, and pinnipeds are no exception. Their blubber helps them to keep warm, like insulation. Thermoregulation is very important for pinniped species. They have many ways to cool down and their bodies are naturally able to keep warm because of blubber and fur.

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Pinniped species live in the water and on land. They find resources in the water and they only eat other animals, which makes them carnivores. To obtain this food they take deep dives into the ocean and use their large eyes and whiskers to help them find food. Their whiskers have an amazing capability to smell distant scents. When mating pinnipeds have to make sure they choose the right land environment, whether that be sand, ice, or rock. This also happens when giving birth, all species have specific preferences. Another behavioral characteristic is the way they try to keep cool. Many species in the pinniped order will cover themselves with cool sand or dig holes to lay in.

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Most pinniped species live in coastal areas, but they can live in a variety of climates, from icy to tropic. An important part of their habitat is the ability to come onto land. Pinnipeds can live on ice, sand, or rock. They come onto land to mate and give birth. The habitat that pinnipeds live in has to be filled with many resources, such as smaller fish and crustaceans, to fulfill their need for food.

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The Hawaiian Monk Seal lives in the waters surrounding the Northwestern Hawaiian Islands. They use the coral reefs to find plentiful resources and this provides them with an abundance. They will come ashore and lay on the beaches and sometimes use nearby vegetation as shelter during storms. This is unique to this specific species of pinniped because most aquatic carnivores do not live near Hawaii. Another characteristic of this seal is that it does not have external ears, meaning you cannot see them on the outside of the body. This trait is evident in all Phocidae (seals) as well as only two fore flippers. Most of a Hawaiian Monk Seal's body is a dark color, which is different from other types of pinnipeds.

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The Sub-Antarctic Fur Seal lives on islands surrounding the South Atlantic and Indian oceans. They come onto the rocky shores when spending time out of the water. This species of fur seal has external ears, which normal seals (Phocids) do not have. They have four very broad and short flippers as well as a short snout. They use their four flippers to move smoother on land. The Sub-Antarctic Fur Seal is either a dark grey or brown color on top and a warm brown and white on the underside of it's body. Another trait specific to this species is that they like to travel to find different temperatures of water. They typically breed during November or December.

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The Pacific Walrus lives in the Bering Sea in the Pacific. They travel to different islands to mate on land. One very unique thing specific to the Walrus is tusks. The Pacific Walrus also has very large teeth. This pinniped species has a bulky body with boxy flippers. A behavioral characteristic of the Pacific Walrus is that they spend time on land in large numbers.

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Hawaiian Monk Seal:
Kingdom - Animalia
Phylum - Chordata
Class - Mammalia
Order - Pinnipedia
Family - Phocidae
Genus - Monachus
Species - Monachus Schauinslandi

Sub-Antarctic Fur Seal:
Kingdom - Animalia
Phylum - Chordata
Class - Mammalia
Order - Pinnipedia
Family - Otariidae
Genus - Arctocephalus
Species - Arctocephalus Tropicalis

Pacific Walrus:
Kingdom - Animalia
Phylum - Chordata
Class - Mammalia
Order - Pinnipedia
Family - Odobenidae
Genus - Odobenus
Species - Odobenus Rosmarus Divergens

Taxonomy can show relatedness because of similarities and differences in classification. In these exemplary organisms, one could tell that they are closely related because the taxonomy is identical up until family. The more two species have in common while being classified, the closer they are to each other. Species is the most specific way to classify an organism and then genus. These things are good indicators to compare similar organisms.

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Pinniped species are believed to of diverged from mammals like bears and dogs. The first living pinniped was the enaliarctos. These animals were thought to of used both their front and hind flippers for swimming, which is different than modern pinnipeds as they only use one. The comparison from the enaliarctos to pinnipeds now shows many similarities, such as the bone structure of the tail and spine. The enaliarctos fossil also shows how pinnipeds must have shared a common ancestor as the bones are relatively close to those of land mammals.

Enaliarctos mealsi fossil-Late Oligocene/Early Miocene Period (around 22 mya)

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Pinniped species are thought to have evolved from an animal similar to this one. Puijila is essentially a walking seal, with many otter like features. This fossil demonstrates the earlier phases of pinniped evolution and the transitions the animals made. This fossil shows that pinnipeds came from organisms that use to have legs meant for walking. It also shows the relatedness because of the tail and similarity in the flipper/leg structure.

Puijila Fossil-Oligocene Period (around 24 mya)

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This fossil is relatively newer and it was found in South Africa. The Homiphoca fossil shows the relatedness of pinnipeds because the skeletal structure is very similar to those of Antarctic seals. This once again proves that all seals, sea lions, and walruses had to of diverged from a common ancestor.

Homiphoca capensis-Pliocene (around 5 mya)

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The fossil shown below is an ancestor of pinnipeds. This is in the more recent stages of evolution as the sturdy leg structures are no longer evident as they were in puijila. This fossil is very similar to both enaliarctos and modern pinnipeds because of the tail, hip, and hind flipper structures. This shows that they are all related.

Acrophoca longirostris-Late Miocene/Early Pliocene (around 5 or 6 mya)

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The pteronarctos is a relative of the enaliarctos. Their are also major similarities between this fossil and the homiphoca fossil. The structure around the eyes is alike as well as the narrow jaw. This relatedness shows the evolution of the pinnipeds was all very connected and the transitions were smooth.

Pteronarctos goedertae-Miocene (around 12 mya)

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Seals, sea lions, and walruses all share the basic structure and functions. The fossils show the similar anatomical structure and how they have progressed. All pinnipeds have flippers, long, wide bodies, and tails. Certain species have slightly different shapes of flippers to allow their specific body propel through the water. For example, walruses have boxy flippers and fur seals have short flippers. The fossils and anatomical structure show that pinnipeds have evolved because they use to have four strong limbs, similar to otters, now they have flat flippers and spend the majority of their time in the water. A homologous structure in the animal kingdom is the structure of the "flipper" or the forelimb. All animals use them differently whether it be swimming, flying, or running. Each species uses their fore arm to benefit them in their environment and that is what seals, sea lions, and walruses do when swimming and diving.

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Embryology can often be a good indicator of relatedness of organisms. It proves that pinnipeds and mammals are closely connected in the image below. The embryo on the left is a polar bear, the middle is a walrus, and the right is a seal. They all look very similar which proves that pinnipeds came from a common land mammal such as a bear. The embryos of all three share the same skeletal structure and the forelimbs are alike as well. The walrus and the seal look almost identical because of their flippers, spindle-shaped bodies, and developing tails, this means that they are closely taxonomically related.

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The karyotype below is a comparison of a harbor seal, which is a pinniped, and a human. The chromosomes show some differences, but they are also similar in certain areas. Karyotypes are great ways of comparing the relatedness of organisms because they allow scientists to study evolution right in front of their eyes. The more two organisms have in common in their DNA, the more likely they are to be ancestors or in a similar classification. In this particular karyotype the seal and the human show that some chromosomes are homologous which proves that they diverged away from each other, but did share an earlier ancestor that was a mammal. Scientists have found out from chromosomal and DNA comparisons that the harbor seal shares almost eighty percent of the same DNA humans have.

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The type of speciation that the pinniped species went through was gradualism. This is because the species slowly passed down adaptations to become the semi-aquatic carnivores they are today. The fossils showed this as well, in the order of puijila, enaliarctos, pteronarctos, acrophoca, and homiphoca. Their was a slow shift in the forearms and they eventually turned into flippers, this did not happen suddenly (like in punctuated equilibrium). Pinnipeds descended from bears and otter like mammals and over millions of years developed a body that allows them to live in a variety of environments.

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Pinnipeds most likely went through co-evolution because all of the species have grown separately without much influence on each other's evolution. They have stayed relatively similar in their characteristics, functions, and structures. The evolution of pinnipeds also shows signs of divergence. This is because they all evolved from a common ancestor, a bear or otter, into separate species. However, they share many identical features.

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Seals, sea lions, and walruses do not mate randomly. They come onto shores or islands and search for a partner. Males will try to attract females with noises such as growls and barks. They get each other's attention as a way of flirting which is not random. This disrupts genetic equilibrium, therefore, pinnipeds have evolved. Pinnipeds will also choose a partner that is in the same geographic location which prevents random mating as well.

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Pinnipeds can be found all over the world and in a variety of climates. The different species have found where they belong and they are very widespread. For example, The Hawaiian Monk Seal lives in waters surrounding Hawaii and the Sub-Antarctic Fur Seal lives near the Indian Ocean. These two locations represents the diversification of the pinniped order. All of the pinniped species evolved from a common ancestor (bear) and now have become diverse and different.

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Pinniped species have experienced descent with modification because they had to transition from walking mammals to aquatic mammals. This took millions of years, hence a gradual evolution. Each generation had to of adapted slightly for this to be possible. These species also most likely go through stabilizing natural selection. This is because the extremes for seals, sea lions, and walruses can be dangerous if they are related to size. An extremely large or small pinniped is going to suffer in their environment because they will have a harder time swimming, as well as mating. Both of Darwin's theories relate to the evolution of pinnipeds as the bear ancestor had to transition into the aquatic mammals we know of today.

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This phylogenetic tree shows that each species in the separate genus' is closer than species in separate families. This is similar to taxonomy and how classification can show relatedness.

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Sub-Antarctic Fur Seals are good examples of organisms that experience gene flow. These animals like to travel and migrate (immigration/emigration) to different temperatures of water. This can introduce new genetic material into a different population that they might be traveling to. The migration of these fur seals can lead to genetic variation and disrupt genetic equilibrium.