Reptiles appear globally – from slow worms in Germany, to dragon lizards in Australia, and Komodo monitors in Indonesia. Despite their variety of body forms and lifestyles, most reptiles have tails, which can be involved in balance and movement or used as a weapon. The latter strategy was employed also by dinosaurs, like Stegosaurus and Ankylosaurus, who used their tails as giant spiked weapons. Some species of extant reptiles have also evolved specialized spiked tail scales during their long evolutionary history over millions of years. However little is known about why exactly the tail spikes evolved, and if they are employed as weapons just as in dinosaurs.
Now researchers from the Museum für Naturkunde in Berlin showed: Lizards living in rocky habitats are significantly more likely to have evolved tail armor than their relatives who live in other habitat types, for example, species that burrow underground or those that live in trees. These findings, published in Biology Letters by MfN researchers Till Ramm and Johannes Müller with Emily Roycroft, their colleague at the University of Melbourne, gives new insights into what drives the independent evolution of similar physical characteristics, and clarifies the evolution of tail spines in reptiles.
“A fundamental goal in evolutionary biology is understanding how selective pressures shape the extensive phenotypic diversity of life.” says lead author Till Ramm.
To understand what factors lead to the evolution of tail armor, he collated a data set including 2877 reptile species and recorded details on their tails, as well as their habitat. While it has been previously suggested that tail armor evolves in response to pressure from predators, Ramm and colleagues showed that microhabitat use predicts the evolution of tail armor. Most likely, the animals use their armored tails to prevent attacks by predators by blocking access to their rocky habitats. This strategy seems so successful, that it evolved over 30 times independently in different groups of reptiles. “These findings highlight the complex interaction between environment and predator-prey interactions as drivers in the evolution of defensive morphologies in reptiles.” concludes Prof. Müller.
Published: Ramm T, Roycroft EJ, Müller J. 2020 Convergent evolution of tail spines in squamate reptiles driven by microhabitat use. Biol. Lett. 20190848.