Friday, 29 May 2009

Pterosaur Classification

The concept of classifying pterosaurs into a family hierarchy is a complex business. The current test for species does not apply to extinct animals unless DNA comparisons can be made. This is not possible for pterosaurs.

A species can be defined as occurring “when interbreeding can produce viable offspring”. To get around this problem, fossil species are arranged in Clades. These are groups of animals with similar characteristics. For this reason, scientists cannot be certain that their comparisons produce a valid result, so there is a level of disagreement amongst the scientific community as to the true lineage and relationships of many pterosaurs.

To complicate this further, pterosaurs exhibit a trend called convergent evolution. Because the success of different groups depends upon the physical limitations of flight, there is a limit to the variation in wing and body mass change that will be tolerated in natural systems. This can make unrelated pterosaurs look very similar.

The big classification difference is seen between the long tailed pterosaurs (Rhamphorhynchoidea) and the short tailed pterosaurs (Pterodactyloidea). The two main groups can be divided into family clades which exhibit a common range of major characteristics with relative ease in most cases – then the job gets extremely difficult.

The people who, in my world of logic, have made the most perceptive attempts to classify the pterosaurs, based on current knowledge, are Harry Seeley, Peter Wellnhofer and David Unwin. There have been many other brave attempts which have produced quite credible lineages, but have been less accepted within the scientific community. The main argument now that the fossil record is better known is where the family divisions should be placed and what the families should be called. I am happy to follow the current lead of David Unwin at present, until a better model is devised.

ORDER PTEROSAURIA (After Unwin 2006)
Suborder Rhamphorhynchoidea
Family Dimorphodontidae
Family Anurognathidae
Family Campylognathoididae
Family Rhamphorhynchidae
Suborder Pterodactyloidea
Superfamily Ornithocheiroidea
Family Istiodactylidae
Family Ornithocheiridae
Family Pteranodontidae
Family Nyctosauridae
Superfamily Ctenochasmatoidea
Family Gallodactylidae
Family Pterodactylidae
Family Ctenochasmatidae
Superfamily Dsungaripteroidea
Family Germanodactylidae
Family Dsungaripteridae
Superfamily Azhdarchoidea
Family Lonchodectidae
Family Tapejaridae
Family Azhdarchidae

The current consensus (which is probably changing as you read) will develop constantly as new ideas are incorporated and new research is completed. There are many possibilities for naming the groups, but the general relationship of family groups will be similar in any scheme as can be seen in the diagram below;

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