While many creatures on Earth have tail stings, only one is known to science for having a spider-like tail. The spider-tailed horned viper (Pseudocerastes urarachnoides), native to Iran, stands out for its unique tail that mimics an arachnid, complete with eerie ‘legs’.
According to a new study in The Anatomical Record, researchers have used high-resolution micro-CT scans to explore this viper’s anatomy for the first time, revealing insights into its peculiar tail.
The findings highlight a case of “extreme” evolution affecting the snake’s scaly skin rather than its skeleton. Initially, when scientists discovered a specimen decades ago, they suspected the tail’s odd growth might be a deformity.
However, further research showed this spider-like appendage is not a defect but a functional adaptation the viper uses to lethal effect. Footage of P. urarachnoides shows it using its tail to lure prey, resembling a spider moving across rocks.
frameborder=”0″ allow=”accelerometer; autoplay; clipboard-write; encrypted-media; gyroscope; picture-in-picture; web-share” referrerpolicy=”strict-origin-when-cross-origin” allowfullscreen>
The snake remains motionless, blending with its rocky environment. By occasionally flicking its tail, it creates the illusion of a spider, effectively attracting prey. This mimicry technique, known as caudal luring, is seen in many snake species.
Most snakes that use their tails for luring don’t have the advantage of a realistic spider-like appearance. Researchers revisited the initial 1968 specimen of the spider-tailed horned viper, housed at the Field Museum in Chicago, which later became the species’ holotype.
Sara Ruane from the Field Museum noted, “The spider appendage is so realistic that when it moves, it’s hard to believe it isn’t a real spider.” Even handling the specimen reveals how lifelike the tail appears.
It wasn’t until a 2006 study recognized P. urarachnoides as a distinct species, after identifying another individual with the same tail characteristic. This showed the tail wasn’t a one-off anomaly.
The original specimen was initially thought to have a genetic anomaly or possibly a tumor, as recounted in the 2006 research. This specimen remained largely ignored for decades until the recent flurry of studies.
Despite varied research, the snake’s skeletal anatomy had yet to be thoroughly examined. In this new analysis, led by Georgios Georgalis from the Polish Academy of Sciences, micro-computed tomography (μCT) was employed on the holotype at the Field Museum’s XCT Lab.
Georgalis, primarily a paleontologist, explored the snake’s vertebrae to understand its unusual tail. Surprisingly, the scans revealed no skeletal structure supporting the spider-like legs, only soft tissue made of keratin, similar to human fingernails.
This indicates the spider-like tail evolved through changes in the snake’s scales rather than its skeleton. The “spider-leg” pattern on the tail is entirely composed of modified scales, creating long, flexible filaments. One enlarged oval on top results from the fusion and enlargement of multiple scales, exemplifying extreme skin evolution.
Ruane suggests this discovery underscores how little we may know about the appearances of extinct creatures. “Without any bone in the tail and the rarity of soft tissue preservation, a fossil wouldn’t reveal this prey-catching adaptation,” she explained.
The findings are detailed in The Anatomical Record.
This article was fact-checked by Rachel Garner and edited by Clare Watson. While we pride ourselves on our process, we are only human. If you spot a mistake, please let us know.
