The Cape Verde giant skink (Chioninia coctei), also called Bibron's skink, Cocteau's skink, and lagarto in Cape Verdean Portuguese, is a recently extinct species of large lizard (skink) that was endemic to some of the Barlavento Islands of Cape Verde before disappearing in the 20th century.
Taxonomy
The Cape Verde giant skink was first given the specific name Euprepes coctei by French zoologists André Marie Constant Duméril and Gabriel Bibron in 1839. The holotype was a specimen at the National Museum of Natural History in Paris, one of five collected in 1784 by João da Silva Feijó in Ilhéu Branco, taken to Ajuda near Lisbon, and looted by the Napoleonic Army in 1808. The name coctei honors French physician and zoologist Jean-Théodore Cocteau (1798–1838). Since Duméril and Bibron ignored the history of the specimen, they listed its origin as "the coast of Africa" and the species remained in obscurity until it was rediscovered in 1873 by Cape Verdean doctor Frederico Hopffer. Portuguese zoologist José Vicente Barbosa du Bocage assigned the species to its own monotypic genus, Macroscincus (lit. "large skink").
In 2001, a Mitochondrial DNA study nested Macroscincus within a group of several Cape Verdean skink species assigned to the wastebasket genus Mabuya, suggesting a common origin in West Africa during the Late Miocene or Early Pliocene, dispersal to Cape Verde and subsequent adaptive radiation. The phylogeny of Mabuya was resolved in 2016, placing Cape Verdean skinks in the genus Chioninia, establishing Trachylepis of Africa and Madagascar as its sister genus, and limiting Mabuya to the Neotropics.
Description
The Cape Verde giant skink was very large and robust compared to other skink species. Adults could attain a snout-to-vent length (SVL) of . The tail was less than half the length of the body. It was described as prehensile and powerful, well adapted to climb trees, which surprised 19th century scientists who only knew Cape Verde giant skinks from denuded, arid islets. However, other authors noted that the species was capable of autotomy, which would be contradictory for a prehensile tail. The long digits, equivalent to a SENI (Scincidae Ecological Niche Index) value of 0.13, are consistent with a low canopy arboreal niche.
The teeth were located labiolingually, compressed, multicuspate, pleurodontid and pterygoid.
There were three color morphs: grey, yellow, and intermediate. There was no banding but the body had dark stippled blotches and freckles with a yellow green-grey standard background. The underside was largely devoid of freckles, with a solid color lighter than the back. Dorsal scales were small and keeled in more than one hundred rows at the midsection but the osteodermal covering was less developed than in other skinks. The lower eyelid had a unique transparent "window" below.
Males reached their maximum size quicker than females, had a larger head, more robust jaws, and longer hindlegs. Older males had thick, hanging dewlaps that are unusual for skinks.
Distribution
Subfossil remains of Cape Verde giant skink were found in the northwestern islands of São Vicente and Santa Luzia, and the islets Branco and Raso, which along with the smaller islet Pássaros were united into the paleoisland "Mindelo" during the colder stages of the Pleistocene. Testimonies of local fishermen also place giant skinks in São Nicolau island, but this remains unproven. São Nicolau was not connected by land to other islands during the Pleistocene.
Behaviour and ecology
The behavior of the Cape Verde giant skink is largely unknown due to the lack of ethology studies before its extinction, though convergent evolution has been noted with two extant species: the African striped skink (Trachylepis striata) from southern and eastern Africa, adapted to a low canopy arboreal niche, and Vaillant's mabuya (Chioninia vaillanti), another large, herbivorous skink that is endemic to the southern Sotavento Islands of Cape Verde.
The transparent lower eyelid may have been an adaptation to spot predators below while giant skinks slept on the lower canopy with their eyes closed. In that case the predator's extinction would have long preceded the Cape Verde giant skink's own. The need of light for this strategy would indicate that the giant skink was crepuscular and slept during the day. The barn owl is known to have eaten skinks before and after human arrival. The unusual dewlap of old males could have played some role in territoriality.