Fins to feet – tetrapod evolution


Imagine the first forests were growing around water margins – things like rivers and lakes. These trees were dropping lots of limbs and logs and this was actually providing an environment for things like crustaceans to hide in the nooks and crannies.

There were animals called lobe-finned fish like Eusthenopteron here that were becoming very skilled at looking for these food items in these sorts of environments and that developed these stronger fins at the front and at the rear here.

Well the first backboned animals on land were called tetrapods – that means four legged animals. They had evolved from the lobe-finned fish and we think they were slowly tempted on land little by little, by the food that was running around on the forest floor. These were things like insects and spiders and millipedes. Slowly, little by little, they were able to spend more and more time up eating these items on land.

We can see the fins on Eusthenopteron here were becoming more and more like what we consider legs today. The legs here had digits on them as well and there were also characteristics that were helping them spend a lot longer above the waterline.

One of the main ones being these little holes here at the top of the skull called spiracles that was allowing them to take gulps of air whilst it was close to the waterline and also helping it see things above the waterline – you’ll notice that the eyes are now on the top of the head.

Well a slab of rock from the Genoa River in eastern Victoria has the preserved footprints or trackways of two of these animals from 370 million years ago. They were actually footprints made underwater but they were made by an animal very similar to Acanthostega here and we can actually see in the trackway the clear impressions of these digits – fingers and toes here, and on a second trackway on the same slab you can actually see where its belly or its tail had made scrape marks between the footprints as well.

Well the next chapter in the story is animals that were able to spend all of their time above the water level. Backboned animals such as Pederpes here has a number of characteristics that tell us it was living almost all the time above the waterline. It had features like the nostrils here which were showing us that its head was above water a lot of the time and it was able to breathe in a way a bit like we are breathing at the moment.

It also had ribs, which show that it gave support to the internal organs and was keeping its body above the ground and also these very strong limbs were showing us it was able to support itself fully. 

About this Video

Wayne Gerdtz, Museum Victoria, explains the evolution of backboned animals from water to land.
Length: 02:49