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Evolutionary Timeline of the Whale

Basilosaurus

Ambulocetus

Sinonyx

Modern Day Whale

Most recent whale alive

From the early to middle Eocene, about 50 million years ago. The ambulocetus was the first organism in the whales evolution that evolved predominately to thrive in water.

From the late Paleocene, about 60 million years ago

  • Sinonyx, a mesonychid, had atypical features for a meonychid, which show that it was already developing adaptations that would become the basis of the whale's life.

Adaptations and Enviorment

Lived during late Eocene and latest part of the middle Eocene, 35-45 million years ago

  • Blowholes help the whale which helps the whale breathe air.
  • It was given to whales since they are aquatic, so then need a way to release that air from their body
  • Whales really don't have an hair on their bodies. Its little to none.
  • From about 40 million years ago, whales became aquatic animals which means they lost that hair since it wouldn't keep them warm in order for them to survive. So instead it gave them blubber.
  • Whales also have blubber to help keep them warm.
  • Since the ocean can be really cold to live in, overtime nature gave whales blubber, which is a thick, fat layer of tissue, so they could survive by keeping them warm so they could survive the cold waters

The legs in the ambulocetus show the transition between fins on whales and legs that can walk on land.

  • Elongated Muzzle: superior for catching fish (all fish-hunting whales and dolphins have elongated muzzles)
  • In an environment where fish are a plentiful food source of the lakes/water bodies of Pakistan and India, having an elongated muzzle to help one catch those fish would be the superior feature.

Adaptations and Enviorment

  • Very narrow shearing teeth
  • Given the food sources available, and the fact that the Sinonyx was a carnivore, more simple and sharp teeth would be most favorable for catching in prey. With a mostly fish-based diet in an environment close to the water, teeth commonly found in carnivores definitely are a helpful adaptation.

Marked the time period when whales were no longer land animals and became one with the sea

  • It had the ability to walk on land but their strong and short legs worked better in water.
  • The feet also evolved to improve swimming ability.
  • This feature changed so the Ambulocetus can hunt for pray better in water. The strong legs and webbed feet helps to move the large organism in order to feed on prey that are quick.
  • The legs show the transition between land dominated Pakicetus and the water dominated Rodhocetus.
  • When discovered in Egypt, they were found with feet and toes and the only thing they saw was a fully usable tail.
  • The tail was formed the help the Basilosaurus move around in the water since it was no longer a land mammel, yet there was still feet and toes
  • The Basilosaurus was more snake like and was twice as long as a modern day killer whale.
  • Since they had marrow in their bones, it made them more buoyant. Which helps them float and move since they only had a tale to move.
  • Since they were like a snake they could move side to side and up and down with their tale. So they needed something more to help them move and they got a longer snake like body.

The face of the Ambulocetus also shows the evolution between land creatures and water creatures; specifically the ears and mouth.

  • Enlarged jugular foramen/large opening in the skull base
  • The purpose of the jugular foramen is to transmit Cranial nerves IX, X, and XI ethrough the internal jugular vein pass in the jugular foramen. A large jugular foramen, which is characterstic of present-day whales, would allow the large animal to grow, and not be restricted in the amount it could grow to because of nerve transmission.
  • The ear structure appeared to only work in water. The structure is more internal than external, which is very different from than its ancestor(Pakicetus) which had an ear that worked on land.
  • This transformation was due how to the need to find prey in water and protect itself from predators.
  • The mouth of the Ambulocetus evolved so it can swallow its prey underwater.
  • It is similar to how Crocodiles kills and eats.
  • This shows us the how the Ambulocetus evolved into being able to hunt in water which is essential to surviving .

52MYA

40MYA

46MYA

60MYA

2017

Dorudon

Rodhocetus

Pakicetus

The size of the Rodhocetus' limbs, especially the hind legs

  • It primarily swam at the surface, which was powered by alternate strokes of the hind legs.
  • This change has mostly due to the fact the legs and the tails could work together to swim faster than in Ambulocetus. Swimming better was an advantage to survive and competing in water
  • This organism is from the early Eocene of Pakistan, about 52 million years ago. Pakicetus is an intermediate between the Sinonyx and later whales.

From the middle Eocene, 46-7 million years ago. The Rodhocetus was still a both a land and water organism but it was the last in the whales ancestry. Most of the time the Rodhocetus spent it times in water.

A contemporary of the Basilosaurus, from about 40 million years ago

The size and shape of Rodhocetus evolved from the Ambulocetus in how the Rodhocetus was longer and slimmer. This can be traced to again how the organisms moves through water and the advantages of having a bigger body.

Adaptation and Enviroment

Dorudon specimens were younger Basilosaurus. In Egypt, the young Dorudon fossils where found with adult Basilosaurus fossils

Adaptations and Environment

  • Teeth similar to Sinonyx's, but more triangular and simplified (single cusp with front and back serrated): Teeth like these, which are similar to what sharks have, are helpful for a hunter of fish.
  • Sharp, triangular teeth would be helpful for a slower predator to catch easy prey, like fish, which were abundant in the area it dwelled in.

  • Dorudon was a predator with big sharp teeth and their fossilised stomachs showed they ate fish
  • Since they were now water mammals, the sharp teeth was given to them to help them get food, so they could survive in the sea.
  • Was about 5 meters in length
  • As there size in length went down, it made it more helpful for them to move around in the sea
  • The forelimbs were not mobile and the hand was found webbed
  • Since they were land animals they feet and toes, yet over time, their hind legs became immobile and they got webbed feet.

  • Eyes positioned close together on top of the skull allow Pakicetus, a semi-aquatic animal, to see above water even when submerged.
  • Since Pakicetus lived in present-day India and Pakistan, where heavy rains and droughts frequented, it most likely hung out in/near the lakes that were left after rain to catch prey and drink water. Being able to see while in the water would, of course, be advantageous for the Pakicetus.

  • When discovered, their tail was found on top of the skull since they curled up
  • Since they were found curled up, it suggests that their muscles powered the up and down swimming motion like modern day dolphins, which helped them move in the water
  • Their nostrol position
  • Since their nostrol had changed, the breathing helped them live in the water. Since it got changed it helped them to adapt from breathing O2 to H2O.

The spine and hip bones of the creature were not fused to entirely which allowed for greater flexibility while swimming. The legs of the Rodhocetus were also not fused together completely. This helped the animals to swim.

  • Joint between malleus and incus of the Pakicetus is at an abnormal angle between side and front
  • This ear adapation is part of the transition to the Ambulocetus, as the whale spends more and more time underwater. This positioning of the joint would improve underwater hearing.

Analysis Questions

Works Cited

"Evolutionary Experiments." Whale Evolution. N.p., n.d. Web. 25 Jan. 2017. The website had helped me find the differences from Basilosaurus and Dorudon. It also explained how they adapted differently and the same.

Prehistoric-wildlife, Darren Pepper. "Welcome to Prehistoric-wildlife.com, a Comprehensive Online Guide to Prehistoric Creatures." Prehistoric Wildlife. N.p., n.d. Web. 25 Jan. 2017.

1. The blubber of the modern day whale is critical to their survival today. In frigid temperatures, their 11 inch thick layers of fat help regulate their body temperature. This blubber also results in a streamlined body, making whales more energy-efficient for swimming. Another important adaptation of whales was their transformation from legs to fins, which made it possible for them to become fully aquatic animals. The sea provided a home with plentiful resources and food, so any animal that could adapt to survive in water had the advantage over solely land animals.

2. The evolution of whales and the adaptation of certain features are not limited to whales. The Rodhocetus and Ambulocetus are similar to Crocodiles and Alligators by being able walk on land and hunt in water, the long snout which helps them to catch prey, and they both are ambush predators. This shows how the difference of how some animals evolve into new species(whales) and other keep traits throughout time(Crocodiles)

3. Since whales live in water, their environment for the most part have remained fairly constant. The biggest change in whale's evolution is from land animal to a water animal. So I think the only changes that will come will be micro-evolution. Due to global warming and the melting of the ice caps, the increase of water might force the animals to do able to store food better and swim for longer distances. Overfishing the oceans may effect the food pyramid and eventually the whales, so they might have to evolve to find a better way to get food.

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