review: radiometric dating if uranium-239 isotope has a half-life of 80 000 years, how many years...
TRANSCRIPT
Review: Radiometric Dating
If Uranium-239 isotope has a half-life of 80 000 years, how many years would it take for all but 1/8 of the uranium to decay?
100% Ur-239 ½ ¼
1/8
First Half-life Second Half-life Third Half-life
80 000 yrs 80 000 yrs 80 000 yrs
= 240 000 yearsIt takes 240 000 years for Uranium-239 to decay to 1/8 of its original amount (3 half-lives).
Biogeography: the scientific study of the geographic distribution of organisms based on both living species and fossils
Biogeography
Remember Pangaea–Fossils of the same species are found
on entirely different continents – Africa, India, and Antarctica
Fossil Distribution
• Mesosaurus – fossils found in both South America and Africa
• Lived during the Permian, when Africa and South America were joined
Fossil Distribution
• Similar species are found on different continents• Share a common ancestor that lived when the
continents were connected• When the continents separated, the populations
were isolated and they diverged into different species.
• Example: Different species of elephants are found in Africa and India
Current Distribution of Species
Current Distribution of Species
Indian Rhino African Rhino
Old World Monkeys (Africa/Asia)
New World Monkeys (America’s)
African Lion
American PumaIndian Tiger
Big Cats
Monkeys
Rhinos
• All of these species share common ancestors but are found far from each other today
• By looking at their current distribution and comparing it with the fossil record, we can establish both current and ancient biogeography
The Link with Biogeography
Example: Australian Marsupials• Australia has the largest and most diverse
population of marsupials in the world• Most other continents mostly have placental
mammals• Why is this??
Australian Marsupials• Marsupials evolved before placental mammals• When placental mammals began outcompeting
marsupials on other continents Australia had already separated and was isolated from them
• This allowed marsupials to diversify and evolve on Australia without competition from placental mammals
Homologous Features
“What can be more curious than the hand of a man, formed for grasping, that of a mole for digging, the leg of a horse, the paddle of a porpoise, and the wing of a bat, should all be constructed on the same pattern, and should include the same bones, in the same relative positions?”
-Darwin
Homologous Features• A flipper or a wing has
no use for fingers, so why should they have a five-fingered structure?
• Why should giraffes have the same number of neck bones as humans?
• If these features were built from scratch, there are more efficient ways to do it
• Homologous Feature: A structure with a common evolutionary origin that may serve different functions in modern species
Homologous Features
• In the forearms of different mammalian species, the same features can be seen
Homologous Features in Mammals
Homologous Features in Mammals
• We can use homologous features to “define” groups of organisms
• In fact those hallmark features of mammals are also homologous:– Live-birthed young–Milk-producing
mammary glands– Hair
• Some homologous features indicate common ancestry, but are no longer used
Some Features go out of Style
• Analogous Feature: a structure that performs the same function as another but is not similar in origin or anatomical structure
Analogous Features
• We observe similarities between unrelated species
• Consider dolphins and sharks
Similarities in Unrelated Species
• We can expect to see analogous features between species that fill similar ecological niches
Analogous Features
• Vestigial Feature: A non-functioning, or only marginally functioning, structure that is homologous to a full functioning structure in closely related species
Vestigial Features
• Vestigial features are homologous features– They just aren’t used by that species any more
Vestigial Features
• Hind Legs and Hips in Whales
Examples of Vestigiality
• When a feature is not used, it is more likely to become vestigial in time
• This can only happen if lack of use does not hurt a population’s chance of survival
• Birds can only become flightless if they have no need for wings
Why do Features become Vestigial?
• Birds can only become flightless if they have no need for wings– In the case of the
Kakapo, what might we guess about predators?
• No predators in New Zealand
Why do Features become Vestigial?