This is Pterodactylus. Well, it was. It’s now called Scaphognathus and for those who know, it’s really not even very close to Pterodactylus as pterosaurs go (for a start, it’s a non-pterodactyloid) with a positive hatful of characters that clearly separate the two.
Of course taxonomic revisions are a constant theme of palaeontology, but this would seem to be a rather extreme case. Part of this of course is down to the age of the original specimen (the photo above is of a cast), consistent taxonomy is hardly at a peak now, so back in the early 1830s, dramatic lumping of this kind can hardly be considered a huge sin in hindsight. However, this is also a good demonstration of a far more common issue in biology as a whole: the more data you have, the harder it can be to sort out your taxonomy as previously distinctive characters can turn out to be less useful that originally thought.
Consider the pterosaurs. When the original Pterodactylus specimen turned up, it was obviously completely different to anything else then known. You could instantly distinguish it from any other vertebrate by the wing finger alone, let alone anything else in the skeleton. It was then perhaps not a surprise that the next few pterosaurs to appear, like Scaphognathus, despite some obvious differences, were put into Pterodactylus based on their even more obvious similarities – these were, after all, obviously pterosaurs. However, once it became clear that there were some important differences, as well and the similarities, then thinks like Dimorphodon and Scaphognathus were separated out into their own genera. This is an extreme example, but the principle is the same and constantly resurfaces.
Even the best taxonomic work and definitions can eventually crumble under the weight of new data, and if the original was also based on rather poor material or what turned out to have little going for it apart from characters that are no longer unique, then still more problems will inevitably arise. Thus what this ultimately boils down to is the fact that taxonomy is always going to be an ongoing process. Not only does every new taxon need to be described and diagnosed, but a large part of the time, this has a knock-on effect meaning that other things now also need to be revised or redefined as a result of the new information. As I have lamented before, taxonomy as a field, both in biology and palaeontology seems to be every dwindling as money is funnelled into for ‘sexy’ subjects, despite basic taxonomy being the absolute foundation of all biological research and this underappreciated field can only cause problems if this trend continues.