Lizards

Evolutionary history: “Lizard” is a familiar and useful name, but lizards do not form a single formal evolutionary group. The term traditionally covers numerous branches of the squamate reptiles (Squamata) while excluding snakes. That distinction does not reflect their actual evolutionary tree: snakes arose from within the broader radiation of lizard-like squamates, meaning that “lizards” without snakes form what biologists call a paraphyletic group. The roots of squamate evolution extend more than 240 million years into the Triassic, while the common ancestor of the major living lineages probably existed by the early Jurassic.

Appearance and lifestyle: The familiar four-legged lizard body plan represents only part of their extraordinary anatomical diversity. Limbs have been reduced or lost independently in multiple evolutionary lineages, producing many completely legless lizards that can easily be mistaken for snakes. Their size ranges from minute species only a few centimetres long to Komodo dragons exceeding three metres, and their lifestyles include climbing, burrowing, swimming, rock dwelling and even gliding between trees. Tail autotomy – deliberately shedding part of the tail to escape a predator – has evolved in many groups. Reproduction can be equally remarkable: some lizard species and populations are capable of parthenogenesis, producing offspring without fertilisation by a male.

Ecological role: Lizards occupy an enormous variety of ecological niches. Many are predators of insects and other invertebrates, larger species may hunt vertebrates, and lizards themselves provide an important food source for birds, mammals, snakes and other predators. Herbivorous and omnivorous species can have equally important roles, with fruit- and nectar-feeding lizards contributing to seed dispersal and even pollination, particularly in island ecosystems. Around eight thousand living species are currently recognised under the traditional concept of lizards, encompassing geckos, chameleons, skinks, agamids, iguanas, monitor lizards and many other lineages. Habitat loss and fragmentation, invasive species, climate change and unsustainable collection threaten numerous species, making habitat conservation and responsible reptile keeping increasingly important.