In number 11 of this series we looked at Neil Shubin's discovery of the fossil Tiktaalik. It is an amazing intermediate form between fish and land animals complete with both lungs and gills as well as ribs, a jaw, a flat head and teeth. Crucially it displayed the beginnings of leg bones that are common to all modern tetrapods. It had a humerus, radius, ulna and wrist bones but also retained the fin-ray bones of it's fish ancestors.
Tiktaalik is just one of many fossils that display the journey of our ancestors from the sea to life on dry land.
This picture shows just a few samples of many fossils that have been discovered from this important period of life's history between 385 and 360 million years ago.
More than 2000 specimens of Eusthenopteron have been collected from the same location at the Miguasha cliffs. These were surface-hunting fish and probably never came onto the land but the front fin was supported by bones identifiable as a humerus, ulna and radius, and the rear fins by a femur, fibula and tibia although bones distal to a wrist or ankle are not present.
Acanthostega had a number of primitive features. One of those was the proportion of the bones in the forearm. In most tetrapods, the ulna is longer than the radius but in the fish it’s the other way round - and that was the condition in Acanthostega. It was basically still an inhabitant of the water. Its limbs were too floppy and its backbone too weak to support itself on land. Not only that, but despite the presence of lungs, Acanthostega had very fish-like gills. Possibly the most amazing feature of this species was the fact that it had eight fingers.
Nearer the amphibian side of the gap 20 million years later comes Ichthyostega discovered in Greenland in 1932 and buried there in the days when Greenland was at the equator. This creature had seven toes.
Icthyostega is a really enigmatic animal. It’s got some features in which some limbs elements, like the humerus, are more primitive than that of Acanthostega, and yet other aspects of the anatomy of Icthyosthega suggest it was more terrestrial. Acanthostega seems to be almost certainly entirely aquatic, but Icthyostega has a really robust front limb that looks as though it could at least raise the front body off the ground, whereas the hind limb is a paddle and points backwards towards the animal’s tail.
This is just a very brief introduction to a few of the stars of this amazing collection of fossils. Those who continue to claim that there are no transitional species really have not looked at the evidence. Our ancestors developed lungs, legs, necks craniums and inner ears that made life on land possible. These fossils are not isolated examples. Many of these species are represented by hundreds or even thousands of specimens.
Life experimented with various formations of limb bones - TuIerpeton had six fingers - and today the same pattern of big bone >> two thinner bones >> lots of bones >> digits is the basic shape of the limbs of thousands of modern species from bats to birds to horses and humans.
| Part 1 - Protein Functional Redundancy - - - - - - - - | Part 2 - DNA Functional Redundancy |
| Part 3 - ERVs | Part 4 - Smelly Genes |
| Part 5 - Vitamin C | Part 6 - Human Chromosome 2 |
| Part 7 - Human Egg Yolk Gene | Part 8 - Jumping Genes |
| Part 9 - Less Chewing More Thinking | Part 10 - Non-Coding DNA |
| Part 11 - Tiktaalik | Part 12 - Lenski's E.coli Experiment |
| Part 13 - Morris Minor Bonnets | Part 14 - Joey Goes to Oz |
| Part 15 - Robinson Crusoe | Part 16 - Aquatic Mammals |
| Part 17 - Belyaev's Silver Foxes |