Charles Darwin was the scientist who published this idea in 1858 On the Origin of Species… He proposed that a small and useful change, developed in relation to the environmental conditions would lead to a change in form or behaviour that, if advantageous, would persist in the species. Such small changes would lead to evolutionary change over time. These small changes can be seen to happen is some modern day species over time.
In examining different species, Darwin observed in many cases, that the change of form was significant. He proposed the idea of modular evolution where changes happened very quickly and locally at one time, giving a change that, if advantageous, was seen as a leap forward in evolution. Over time, where the environmental conditions were stable, the form and behaviour of species would be stable and show little change. Only when a significant factor changes the conditions within a habitat would other random changes become more advantageous. This concept is difficult to observe in reality, but it does rationalize the changes seen in fossils.
A recent find from China, Darwinopterus modularis, demonstrates this concept quite well. This is an advanced pterosaur in many features, but it has retained the long tail of the early pterosaurs. This species helps to link the changes between the Rhamphorhynchoidea and the Pterodactyloidea.This pterosaur has been placed in a group called the Monofenestrata, which includes Darwinopterus and also encompasses all of the Pterodactyloidea.
Darwin C R, 1859, On the Origin of Species by Means of Natural Selection, or the Preservation of Favoured Races in the Struggle for Life. London, John Murray.
Lu J, Unwin D M, Jin X, Liu Y and Ji Q., 2009, Evidence for modular evolution in a long-tailed pterosaur with a pterodactyloid skull, Proceedings of the Royal Society B., Published online before print October 14, 2009, doi: 10.1098/rspb.2009.1603
Proceedings of the Royal Society B - October 2009
Monofenestrata? Single-windowed? Probably not. I drew a rhamphorhynchus once with tortoiseshell fur. Possibly I should study up to get a little more accuracy. This is an interesting blog. Thanks!
ReplyDeleteThe two forward openings on the skull of Rhamphorhynchoid pterosaurs, becomes a large single forward opening on the skull of Pterodactyloid pterosaurs. It is one way of grouping the pterosaurs which seems to work well. Of course, you would need to look at lots of other key features such as the length of the wing metacarpal and the tail length.
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