Having briefly covered the presence of a tail vane (or otherwise) in various pterosaurs and glossed over their structure, it’s time to deal with a trickier subject – their shape.
Most palaeoart illustrations of tail vanes show a diamond or kite-like outline for a tail vane, but this shape is not actually seen in any adult rhamphorhynchoids. A long, narrow and paddle-shaped vane is seen in Sordes and Pterorhynchus and thus is likely the norm for the scaphognathines (the group to which both probably belong) at least. The biggest adult specimens of Rhamphorhynchus have a vane that is roughly in the shape of an equilateral triangle with one side at the tip of the tail and the correspondingly opposite apex lying anteriorly (like an arrow pointing forwards). So where does the diamond tail concept come from?
The key above is the word ‘adult’ – while previously specimens of Rhamphorhynchus were split into quite a number of species, more recently these were brought together as a single species by Chris Bennett, but one represented by numerous juvenile animals. Specimens of Rhamphorhynchus do have a diamond or kite tail vane, but none of them are adults (though they may be close to adult size), and indeed the presence of different vane shapes does correlate with the apparent age of the animals, thus these shapes do seem to be part of an ontogenetic sequence leading up to the adult shape of a triangle. The youngest specimens have a rather thing leaf shape or spear-head shaped tail, mid-sized specimens have the diamond or kite and one especially large and adult animal has the triangle.
The diamond has persisted in palaeoart for a number of reasons. First of all it’s already the most commonly illustrated tail van both in the literature and in reconstructions and thus will inevitable serve as a model for those following. It’s also present in probably the most specimens, and is present in the specimens that were referred to the type species of Rhamphorhycnhus. However, the application of this tail vane to pretty much every rhamphorhynchoid is clearly incorrect. Not only do we know that there is variation in the tail vane shape in rhamphorhynchoids (meaning that it’s not really more right or wrong to use a paddle vane or a triangular vane for anything outside of the scaphognathines or rhamphorhynchines) but adult Rhamphorhynchus probably don’t have a diamond tail.
It’s really time to ditch the diamond and I’d love to see some more illustrations of rhamphs without them. Sure, some Rhamphorhynchus had them, but probably not the adults that are most often illustrated and outside of that it’s hard to justify the use of the diamond all the time. Variety is, so we are oft told, the spice of life, so let’s see a bit of spice in those rhamphorhynchoid illustrations.