00:01
In this problem, we're asked to read an evolutionary tree diagram, also known as a cladogram.
00:06
A cladogram shows the rough evolutionary relationships of a bunch of different species or animal types or plant types.
00:15
And it helps us organize that information in terms of time.
00:19
So on the left side of the cladogram, you will see the ancient past.
00:24
And then over hundreds of thousands or millions of years, it will bring you all the way to the right in the present.
00:31
So these are present categorizations of different species like the lungfish, amphibians, mammals, snakes, crocodiles, ostriches, and hawks.
00:40
You can see that as you move through time, you have these divisions or breaks.
00:46
Those represent common ancestors of these different species and where the species branched off from each other, evolving separately after that point.
00:56
So there's breaks one through six common ancestors.
01:00
Let's look at a couple of specific evolutionary changes that happened and place them on this evolutionary tree.
01:09
So here in between common ancestors one and two we we see the evolution of the tetrapod limb plan.
01:18
So tetrapod just means having four limbs.
01:21
It's a body plan where you have two arm -like limbs and two leg -like limbs.
01:26
This happened relatively early in this evolutionary tree.
01:29
And once we place the evolutionary change, we can then trace from left to right.
01:36
Every branch downstream from that change will have that evolutionary change.
01:44
Now, we could have some kind of strange evolution backwards.
01:49
In the case of snakes, we'll see that.
01:51
Although they had a tetrapod body plan, the limbs were lost.
01:56
But we still have little tiny vestigial bones in snakes that show that they do indeed have a tetrapod body plan...