Cetartiodactyl is comprised of
two orders of mammals: Cetacea and Artiodactyla. Dolphins, whales, and other
aquatic mammals are more closely related to each other than to any other
mammal, thus uniting them in the group Cetacea. “Recent molecular evidence suggests that Cetacea evolved from
artiodactyl ancestors, making Artiodactyla non-monophyletic unless Cetacea is
included” (Poor, 2014). Artiodactyls (also known as
“even toed ungulates”) consist of animals such as deer, camels, hippopotamuses,
pigs and other fossil relatives. These animals have an even number of digits on
their hands and feet. Early fossil of whales also indicated an even-numbered of
digits on their feet, which suggests a relationship towards Artiodactyla. Artiodactyl
and Cetaceans don’t resemble to their ancestors. Cetaceans are specialized for
an aquatic environment. In order to be equipped for an aquatic lifestyle, they
had to inherit traits and give features that would make them adaptable towards
a wet environment. Convergent evolution allows organisms that are not closely
related to independently evolve similar traits to adapt to similar
environments. Due to convergent evolution, these aquatic mammals lost their
hind limbs except for their pelvic vestiges, their forelimbs transformed into
flippers, they became hairless, a flattened tail for swimming, nostrils
relocated to the top of their head (spouts), gained a lot of excess fat (blubber).

Other classes such as reptiles and aves evolved different traits. Reptiles
evolved watertight ears along the top of the head, third eyelid in some,
sensory organs are located on top of the head allows them to have control of
their senses when submerged. Aves evolved webbed feet, water diving, feet and bills
for water feeding. Seals are remarkably adapted to a sea environment, they have
sleek and powerful necks and bodies that is encased in blubber and a flattened
tail. Blubber helps insulate them in freezing conditions. They have loosely
interlocked vertebrae makes them flexible to surf the currents and navigate
through ice and rocky shores. When under water, their nostrils close and shut
even tighter as the water pressure increases. Seals can even eat underwater
without inhaling water and their corneas are flattened so their pupils can
dilate. 

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