The viper's spider-like lure formed in scales, with no matching skeletal element
A micro-CT study of the spider-tailed horned viper's sole holotype found that modified external scales make its spider-like lure. The tail vertebrae have some anatomical distinctions, yet the researchers found no bony element corresponding to the exterior appendages. One museum specimen cannot resolve how the structure varies within the species.
Science··Midday
Modified scales create the spider-like form
Pseudocerastes urarachnoides is an Iranian viper that moves the spider-like structure at its tail tip to attract birds. Researchers micro-CT scanned holotype FMNH 170929, held at the Field Museum, and built three-dimensional models along the vertebral column. Flexible, filament-like scales form the radiating appendages, while many enlarged scales merge into the central oval portion. The lure's spider-like shape therefore resides in the modified outer covering rather than in bone.[1]
The bones retain subtler distinctions
The scan counted 183 vertebrae in the holotype, followed by a terminal fusion. The caudal region has unusual haemapophyses, a sharper mid-tail decrease in centrum length and fusion at the tip. Researchers nevertheless detected no skeletal element matching the lure appendages above it. The tail bones retain distinctive traits. None of the recorded features amounts to a bony replica of the conspicuous external structure.[1], [2]
A single specimen leaves variation unresolved
The detailed anatomical account of this species rests on its only known holotype. The sample used to compare centrum lengths is also small, and the paper says the data cannot sustain robust statistical conclusions. Skeletal anatomy in the genus's two other species has yet to be examined. The study establishes that scales form the external lure in this individual and that no matching skeletal element was detected; variation among individuals and development of the structure remain questions for additional specimens and higher-resolution imaging.[1]
