Evolution of Whales Objective To provide evidence for

Evolution of Whales Objective: To provide evidence for evolution through tracing the history of whales Bell work: The initial amount of Uranium 227 in a sample of rock is 16 g and the half life of U 227 is 3, 400 years. How much time has passed if there are 2 g of U 227 remaining? 16 g/2 = 8 g/2 = 4 g/2 = 2 g A total of 3 half lives have passed 3, 400 years x 3 half lives = 10, 200 years passed since death © Getting Nerdy, LLC N 2 N C 14 2 C 14 14 N 2 C CC 14 N 2 14 N 2

Whales are mammals, just like you, and their ancestors once lived on land. How do we know this? There are several ways that we can determine if organisms are related to one another. = ? © Getting Nerdy, LLC

HOMOLOGOUS STRUCTURES Sometimes, scientists can look at the homologous structures shared by the two organisms. Remember that a homologous structure is a structure that shows how certain species have inherited a trait from an ancestor. © Getting Nerdy, LLC

MISSING LINK: transitional fossil that exhibits traits common to both an ancestral group and its descendants © Getting Nerdy, LLC

MISSING LINK: the discovery of the Archaeopteryx bridged the gap between the dinosaur and present day birds, like chickens. © Getting Nerdy, LLC

SIMILARITIES IN DNA: We can also compare the DNA to note how many base pairs match up. Our DNA and a chimpanzee’s are 98% the same, demonstrating that we are related to one another. However, we only share 7% of our DNA with bacteria. Chimp Human Bacteria 7% 98% © Getting Nerdy, LLC

Who Am I? Human Who Am I? Rabbit Who Am I? Cow Who Am I? Pig EMBRYOLOGICAL : We can observe the Because. EVIDENCE they are all embryonic development of various species of organisms to see if they are related. For example, the chart above shows the development of a pig, rabbit, cow, and human. Why do they all share a related development? vertebrates – they have a backbone! © Getting Nerdy, LLC

Anyhow, back to the whales… so how did they come to live in the ocean? On your sheet, you will see steps to reconstruct the evolution of the whale from land to sea. Read the descriptions and use the traits drawn to help you draw the journey of the ancestral whale to present day. © Getting Nerdy, LLC

MESONYCHID (55 MYA): Extinct land mammals with whale like teeth. Covered in fur and stripes similar to a tiger. Had four legs with feet that resembled hooves of a horse, and a long snout and tail. © Getting Nerdy, LLC Based on the fossil record, and because whales are air-breathing mammals, scientists believe that they must have descended from a land dwelling mammal, such as the Mesonychid that lived near the ocean 55 million years ago.

PAKICETUS (50 MYA): Mesonychid evolved into a wolf-sized meat-eater that ate mostly fish. Fur covered with a head that is becoming whale shaped with sharp teeth. Had four legs, small ears, and a long tail. © Getting Nerdy, LLC

AMBULOCETUS (48 MYA): Lived in both water and land. Heard sound through its lower jaw, leading to the sound receiving system of modern whales. Has webbed feet and uses hind legs for powerful underwater kicks. Head becomes longer and thinner resembling a lizard in shape. Pakicetus evolved into a land dwelling animal with shorter legs and webbed feet. This animal was able to swim well and was therefore able to survive off of the abundant supply of food in the ocean. © Getting Nerdy, LLC

RHODOCETUS (46 MYA): Hind limbs are reduced (smaller) and tail has become modified into a fin at the end, an adaptation that allows for more efficient swimming. Forelimbs are now completely fused together as front fins Head is similar to an alligator in shape. © Getting Nerdy, LLC

BASISLOSAURUS ISIS (37 MYA): Body is more elongated and the modified tail has become wider at the end, creating a larger tail fin. Hindlimbs are further reduced and barely visible. Forelimbs are now noticeably fins. Head is similar to a dolphin in shape. © Getting Nerdy, LLC

DORUDON (34 MYA): . Primitive whales. These organisms lived strictly in the sea. Nostrils have moved toward the top of the head to become the blowhole. Forelimbs are paddle-like flippers and hindlimbs are absent. © Getting Nerdy, LLC

DORUDON (34 MYA): Virtually complete skeleton of Dorudon atrox excavated in Wadi Hitan, Egypt. Excavated by a team led by Philip Gingerich. For more, check out www-personal. umich. edu/~gingeric/PDGwhales/Whales. htm © Getting Nerdy, LLC Photo used with permission granted from thedesignspace. net.

Wanna see it in action? Watch as the whale ancestors you just created evolve into a modern day whale in this “In for a Swim” video! Also check out the Smithsonian’s whale evolution video. © Getting Nerdy, LLC