Introduction
Many types of snakes and lizards carry horns on their heads. But how these reptiles hunt for food may determine whether the horns are an asset or a burden. Researchers say that the vast majority of horned lizard and snake species lie in wait and ambush their prey rather than chase it down. The horns and other protrusions provide camouflage for animals that remain largely still, but they may be costly for more active reptiles, revealing the presence of both the prey and the predators.
Animals
Previous studies suggest that lizards and snakes have repeatedly evolved horns on their heads, brows, and protruding from their noses. Earlier research proposed that these decorations may serve various functions, such as being used in aggression, defense, or breaking up body outlines to avoid detection. But Federico P. Banfai, a herpetologist at the University of Antwerp in Belgium, and his colleagues wondered whether the camouflage benefits of horns still aid animals that move a lot while hunting. If not, or if the horns hinder the animal’s movement, it might discourage the evolution of protrusions in the more active species.
Research
The team compiled previously published datasets that classified lizards and snakes either as ambush predators or active chasers, leading to 1,939 different species with 175 species bearing horns – defined as cavities of bone or keratin on the animal’s nose or brows or head. The team plotted the presence or absence of horns and the hunting style of the reptiles on a previously published evolutionary tree of lizards and snakes, discovering that horned features evolved independently about 69 times. Of course, horns were much more common in ambush predators than in the more active species. Of the horned lizards, 164 – 94 percent – were also relatively ambush predators, with just 11 – 6 percent – classified as active predators.
Experiments and Results
Horns may be a blessing for some species but a burden in others, Banfai says. “Animals that need to move a lot may suffer from having large appendages on their heads. These horns could make them more visible to both prey and predators since the structure that enlarges their heads and silhouette might make them more obvious while moving.”
Conclusion
Banfai believes there are many opportunities to delve deeper into why horns appear or do not appear in the animal kingdom. For example, the horned viper Cerastes cerastes lays eggs that sometimes hatch a mix of horned offspring and hornless ones, and it’s not clear why. Some amphibians and invertebrates have horn-like structures, so researchers could test whether food strategies might be a factor there, too.
The work that Booschow hopes to see is testing the virtual evolutionary experiments that animals conduct with their horns. “So far, the potential benefits and costs of horns in reptiles are just hypotheses,” Booschow says. It wouldn’t be easy to test all of these ideas, he notes, but it could help researchers find the evolutionary roots of this wild ornament.
Source: https://www.sciencenews.org/article/lizards-snakes-horns-camouflage
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