Question

The cladogram below was created to show the evolutionary relationships between different vertebrates.

Answer 1

Which of the following inferences can be made, based on this information?

Answer 2

Having a bony skeleton did not provide an evolutionary advantage to sharks or ray-finned fish.
Birds and sharks do not share a common evolutionary ancestor.
Rabbits and primates diverged more recently than crocodiles and birds.
Amphibians and birds share a more recent common evolutionary ancestor than sharks and birds.

Answer 3

@e.mccormick @TheSmartOne @nincompoop

Answer 4

@CountryGurl15

Understanding cladograms or phylogenies. There are two topology types, rooted and unrooted.

Rooted trees make an inherent statement of relative times. Note RELATIVE. You may not be able to use the fact that rooted trees make a statement about the time and ordering of speciation events, the splits, to figure out which split is older.

If you put a finger on any two of the terminal taxa, such as shark and bird and move down the tree where your fingers meet is the most recent common ancestor. IMPORTANT: you must never move down to a split and then back up towards the terminal taxa. So in your above question, you would move down sharks and have to stop at the first split, while for birds you would move through 5 splits (technical name is node) . The branches between the splits (nodes) are called internodes.

You cannot use the information from a tree alone to figure out if a trait was beneficial or not. That kind of information requires much more knowledge than when and where the trait(s) appeared.

You can compare nodes at some points for age, but not others. For instance, we can tell that the split (node) between amphibians and the branches leading to birds, mammals, and reptiles is older than the split between birds/crocodiles and primates/rabbits. We cannot determine which split (node) is older, birds/crocodiles or primates/rabbits.

You can figure this out be counting how many splits (nodes) you have to go through from the first node to the two nodes of interest. Notice if you do this for the bird/crocodile group and the primate/rabbit group, they both go through the same number of nodes.

You cannot do this comparison on unrooted trees.

You should now be able to test each answer and see which one is correct.

Answer 5

Wow, thanks so much! This really helped me figure this question out =)

Answer 6

@CountryGurl15 No problem. I should mention that although the terminal groups here are groups of species, the terminal groups can be a wide variety of sources. They can be genes, species, sub-species, members of the same family (like human family, not the taxonomic rank), or populations of a species.

FYI, I have published several papers that used phylogenetic methods, so if you have other questions tag me.