Juergen Freund, www.juergenfreund.com
Natalie Roberts
Watford, Hertfordshire, UK
Several years ago, I watched a documentary about the fossil of an early amphibian, once encased in a stone nodule. When it was discovered, in Victorian times, five toes were uncovered on each foot, then the excavation stopped. However, some stone was still left around the feet.
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A couple of years before the documentary was recorded, curiosity led to further excavation. This was rewarded by the discovery of extra toes. There were in fact eight on each foot.
As well as a salutary lesson on not letting expectations prevent the completion of your research, this early amphibian proved that not all early land dwellers conformed to the five-digit rule. There was initial evolutionary experimentation; but only the five-toed amphibians were successful enough to pass on their genes.
Richard Swifte
Darmstadt, Germany
Limbs evolved from fish fins, and the first primitive digits appeared in fish-like, four-limbed animals in the Devonian period, 420 to 360 million years ago. These creatures were the ancestors of amphibians and ultimately reptiles, birds and mammals, and they exhibited variety in the number of digits, often having more than five.
The fossil record suggests that as these digits evolved accompanying bones and joints allowing more sophisticated use, their number reduced to no more than five. Subsequent evolution never increased this number.
In fact, many later animals have reduced the number still further when five weren’t needed. For example, the dinosaur branch known as theropods ended up with three fingers on each arm, or even two in the case of tyrannosaurs, while their probable descendants the birds mostly have four toes, and some just three or even two in the case of the ostrich.
Horses’ hooves are the result of just one toe developing to support the animals’ weight while galloping, with the other toes withering away. In humans and our ape relatives, one finger evolved into the opposing thumb, which allowed us to better grasp things.
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