\n \u201cIn some other snakes, like sand boas and rubber boas, the vertebrae at the tip of the tail have extreme shapes that look really alien,\u201d said lead study author Dr. Georgios Georgalis, an associate professor in the Institute of Systematics and Evolution of Animals at the Polish Academy of Sciences in Krak\u00f3w. \u201cWe wanted to investigate if the spider-tailed horn viper\u2019s tail was similarly strange inside.\u201d\n <\/p>\n
\n Instead, the researchers uncovered something unexpected \u2014 and it\u2019s a lesson in why skeletons don\u2019t always tell the complete story of animals, both living and long extinct.\n <\/p>\n
\n While a doctoral student, Ruane first saw a \u201cmind-blowing\u201d video in 2008 of a spider-tailed horned viper moving its unusual tail to lure birds.\n <\/p>\n
\n Other vipers are known to flick their tails, especially baby vipers with bright green or neon yellow tail tips that might appear like a wiggly worm to unsuspecting frogs.\n <\/p>\n
\n \u201cBut the apparatus on the tip of the spider tail viper is on a whole other level,\u201d Ruane said.\n <\/p>\n
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\n The viper is elusive, using its musculature to live along dramatic cliff faces. The creature\u2019s extreme habitat makes it challenging to study or collect in the wild.\n <\/p>\n
\n \u201cSome of the video I\u2019ve seen of these snakes in action shows them in tiny crevices that you would never think any animal is able to cling onto very well, let alone a snake that doesn\u2019t have any limbs,\u201d Ruane said. \u201cWhen it actually grabs a bird, sometimes the whole snake goes flying off the rock face along with the bird. The snake\u2019s whole style of life is also pretty wild.\u201d\n <\/p>\n
\n When Ruane and Georgalis met at a conference in 2023, he expressed an interest in studying the viper\u2019s holotype. As a paleontologist, Georgalis studies modern snakes to understand the fragmented fossil remains of ancient extinct ones.\n <\/p>\n
\n Ruane recalled thinking the timing was excellent because the Field Museum was getting a new X-ray computed tomography, or XCT, lab. The technology enables the scanning of objects to create thousands of X-rays, resulting in 3D renderings that can peer inside structures without damaging specimens \u2014 such as the inside of a snake\u2019s tail.\n <\/p>\n
\n Snake skeletons have hundreds of vertebrae, which means that snake vertebral columns have been poorly studied in the past, said Dr. Kurt Schwenk, professor emeritus in the department of ecology and evolutionary biology at the University of Connecticut in Storrs. Schwenk was not involved in the study.\n <\/p>\n
\n The holotype was one of the first specimens to be scanned once the lab was up and running in late 2024. The scans revealed that the vertebrae within the tail were normal and typical of most vipers, Georgalis said.\n <\/p>\n
\n Instead, the fleshy appendage is composed of elongated and modified scales, he said, with no bony element present.\n <\/p>\n
\n \u201cIf we had these remains only as fossils today, we would not be able to reconstruct or imagine its spider-like tail morphology,\u201d Georgalis wrote in an email. \u201cThis is a \u2018painful\u2019 reminder that fossil remains in paleontology do not afford the \u2018absolute truth\u2019 on how magnificent were once extinct reptiles and other now lost animals.\u201d\n <\/p>\n
\n As a reptile morphologist, Schwenk didn\u2019t expect that the lure would include anything other than soft tissue.\n <\/p>\n
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\n \u201cModifications of the scales into various structures, such as spines, horns, knobs, etc., are fairly common in lizards and snakes and outside of the head, rarely, if ever, involve the underlying skeleton,\u201d Schwenk wrote in an email.\n <\/p>\n
\n While snake vertebrae are typically shorter in the tail, Schwenk noticed that the tail vertebrae seemed unusually slight in the spider-tailed horned viper.\n <\/p>\n
\n \u201cHaving shorter vertebrae in the tail makes it especially flexible,\u201d Schwenk said. \u201cThis would enhance the tail\u2019s ability to make the tight, sinuous bends used to create the realistic, spider-like movements of the lure.\u201d\n <\/p>\n
\n Questions remain about the spider-tailed horned viper, such as how it evolved this interesting feature, known as a caudal lure, on the end of its tail.\n <\/p>\n
\n \u201cIf you look at the two species that are most closely related to the spider-tailed viper, they\u2019ve got funny-looking tails,\u201d Ruane said of the Persian horned viper and the Field\u2019s horned viper.\n <\/p>\n
\n \u201cIt seems smaller than it should be, and very keratinized,\u201d Ruane said of the hard, dry outer coating of the tail, \u201cand at least on the specimens I\u2019ve seen, it\u2019s a different color. The snake is sort of a sandy brown or gray, and then the tail is black.\u201d\n <\/p>\n
\n Many snakes twitch their tails, whether to scare off predators or lure prey, but the spider-tailed horned viper may be an extreme example, such as rattlesnakes, of how features evolve over time out of certain behaviors, she said.\n <\/p>\n
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\n Future research could focus on what genetic mechanisms may have been turned on or off to make the spider-like appendage appear, Ruane added.\n <\/p>\n
\n Schwenk said he believes the behavior was likely present in the viper\u2019s ancestors.\n <\/p>\n
\n \u201cThe spider-tailed viper has taken this ancestral behavior and modified it into something really spectacular,\u201d Schwenk said. \u201cThe spider-like structure in combination with sinuous motions of the tail create an impression of a moving spider that is so realistic that the first time I saw a video of the behavior I was completely fooled. It\u2019s a wonderful example of the power of natural selection to shape animal form and function.\u201d\n <\/p>\n