Animal mimicry, whether done for defensive or predatory reasons, has produced over the course of evolution some of the most bizarre adaptations in nature: birds that pretend to be caterpillars, fish that look like rocks, spiders that disguise themselves as ants…
Even in this complex panorama, the viper’s strategy Pseudocerastes urarachnoides stands out for its strangeness: on the top of its tail it has… a spider, which it uses to attract the birds it feeds on. Now a study published on The Anatomical Record reveals the secrets of this structure, which is even more curious than it might seem.
Bird bait
Pseudocerastes urarachnoides it is a relatively new species: discovered for the first time in Iran in 1968, it was described and named only in 2006; before then, it was thought that the fake spider on the tail was a tumor, or in any case some specific neoformation of that only specimen we had available.
The discovery of new individuals has revealed that what is found on the tail of this viper is a bait: the animal uses it to attract small birds, and attacks them when they come within reach of its jaws.
The problem with having so few specimens available is that it is difficult to analyze them without damaging them: the team from the Field Museum in Chicago that conducted the study had to resort to the X-ray computed tomography (XCT) technique, which allows a structure to be reconstructed in 3D without the need to destroy it. Applied to the Iranian viper, XCT revealed something curious: the snake’s skeleton is perfectly normal, even at the tip of the tail.
The paleontologist’s frustration
The false spider is therefore a fleshy “growth”, not a deformation of the caudal vertebrae of the viper – unlike what happens in other snakes that use similar strategies, for example the rubber boa. It’s not just any detail: the Field Museum study was conducted with the help of a paleontologist from the Krakow Academy of Sciences, who said studying the skeleton of snakes can be “frustrating.”
Structures like that of the Iranian viper, in fact, are not preserved in the fossil record: looking only at the skeleton it is impossible to imagine what the animal has on the tip of its tail.
A discussion that can be applied to fossil snakes: we know what shape their skeleton had, but a structure like the fake spider Pseudocerastes urarachnoides it is impossible to locate by looking at the remains alone.
In short, extinct animals (not just snakes) may have had decidedly stranger shapes than those that emerge from their fossils.
