The Devonian Period
Now, I want to talk to you very quickly about some final computer simulations that give us an important take home message. I want to talk to you about the Devonian. The Devonian is a period in geological history where the most extraordinary events occurred in plant evolution. It was probably the most superb episode of morphological and anatomical diversification. It's an interesting time.
It's also an accessible time because most of the plants that existed in the Devonian were morphologically at least in the beginning, very simple. Basically, these plants were mechanical tuning forks.
Here, is just a little diagram of how you can mathematically describe the morphologies of early vascular plants. You really need only three parameters. You need to know the probability of branching. You need to know the angle created between two companion axes and, you need to know how they're twisted with respect to the horizontal.
If you can quantify these three things, you can create a universe of all mathematically conceivable geometries and morphologies fir early vascular land plants. I'll just show you three slices though that universe, giving you some of the shapes that are possible. By the way, what are the numbers shown on these slices through the universe? They are the quantification of the ability of these simulated plants to intercept sunlight and to mechanically sustain their own weight. You can quantify what they're doing in biological function.
Now, one of the fun things is that you can go into this universe and identify where the earliest vascular land plants are. Then ask the computer to search in its vicinity for something that's better at intercepting sunlight and sustaining mechanical force. Keep that search going until you reach an endpoint. Here is what the computer gives me.
Here is the earliest vascular land plant:
and here is what you see in terms of searching.
It ends there.
By the way, the earliest vascular land plants look something like this:
and as you go up in the fossil record, you see things that look like this:
then, you see things that look like this:
Not a bad rendition of the early history of land plants. But we have to be careful. The apparent agreement between these simulations and the early history of land plants could be entirely fortuitous.