X-ray imaging reveals the spider-tailed horned viper's uncanny tail lure is built from modified scales, not bone
Researchers used X-ray computed tomography to scan the preserved holotype of the spider-tailed horned viper (Pseudocerastes urarachnoides), a rare snake native to Iran's Zagros Mountains, and found that its spider-like tail appendage is composed entirely of elongated, modified scales with no bony skeleton inside. The findings were published in the scientific journal The Anatomical Record. The species was formally described as new to science in 2006, though a specimen had been collected as early as 1968.
The spider-tailed horned viper uses the tip of its tail — which closely resembles a moving spider — to lure birds into striking distance in the rocky cliffs of western Iran. The snake's body blends into the surrounding stone, and when a bird swoops toward what appears to be an arachnid prey item, the viper strikes. The behavior was first captured on video in 2008, though the species' tail structure had puzzled scientists since the original 1968 specimen was collected.
The new study, led by Dr. Georgios Georgalis of the Polish Academy of Sciences in Kraków and co-authored by Sara Ruane, associate curator of herpetology at the Field Museum in Chicago, scanned the 1968 holotype specimen using a new X-ray computed tomography lab at the Field Museum that became operational in late 2024. The holotype was among the first specimens scanned. Georgalis told CNN he and colleagues initially expected the tail vertebrae to show unusual or "alien" shapes, as seen in some other snake species such as sand boas and rubber boas.
Instead, the scans revealed that the tail vertebrae were normal and typical of most vipers. The spider-like lure is built entirely from elongated and modified scales, with no bony element present. Georgalis noted this finding carries a broader implication for paleontology: "If we had these remains only as fossils today, we would not be able to reconstruct or imagine its spider-like tail morphology," he wrote, calling it a reminder that fossil remains do not offer the complete picture of how extinct animals looked or behaved.