another one of jonathan wells’ ‘icons’ of evolution

This one leads us into the concept of transitional fossils (the so-called ‘missing links’ whose apparent absence is dear to many creationists). Wells asks

Q: ARCHAEOPTERYX. Why do textbooks portray this fossil as the missing link between dinosaurs and modern birds — even though modern birds are probably not descended from it, and its supposed ancestors do not appear until millions of years after it? 

This whole idea of a ‘missing link’ is actually something of a misconception. Rather than ‘missing links’, we tend to talk about ‘intermediate features’. Thus Archaeopteryx shows a combination of physical features, some of which are characteristic of reptiles and others that are specialisations associated with birds. Its reptilian features include the presence of teeth in its jaw; clawed hands; and a long bony tail (among others). Yet it also has feathers – & the presence of asymmetrical flight feathers on its forelimbs suggest that it was capable of powered flight. As Alan Gishlick says, we can’t be sure that

the animal that we call Archaeopteryx was actually genetically transitional to living birds, or that it was a direct genetic ancestor to living birds. However, in a less strict sense… Archaeopteryx has a great many transitional features between living birds and Mesozoic dinosaurs: if it was not a direct ancestor, it was surely a close collateral ancestor.

What does he mean by ‘collateral’? Bascially, Archaeopteryx shows unique features that must come from the last common ancestor that it shared with birds i.e. it has features that show us what that last common ancestor may have looked like. And in fact, we can never be certain that a given fossil is a direct (lineal) ancestor of another – because we don’t have genetic or observation evidence to support that contention. Gishlick again: It is not the ancestry that is important to palaeontologists, but rather the ability to reconstruct the features of those ancestory.

This is why Wells’s claim that "supposed ancestors" are younger than Archaeopteryx is false. These younger, bird-like dinosaurs aren’t viewed by palaeontologists as ancestral to Archaeopteryx. But they do retain features of their last common ancestor (eg those feathers again) that give us some idea of what that ancestor looked like. 

Leave a Reply

Your email address will not be published. Required fields are marked *