Shy ghosts: iguanian lizards at ‘La Buitrera’ (Candeleros Formation, Cenomanian - Turonian).

SEBASTIÁN APESTEGUÍA; FEDERICO L. AGNOLÍN; GABRIEL LÍO

La Plata

Jornada; XX Jornadas Argentinas de Paleontologia de Vertebrados; 2004

Museo de La Plata

The official interpretation says that the extant South American lizards arrived from North America in two successive waves: at the Late Campanian and during the Pleistocene. However, a different scenario is being depicted by the discovery of Early Cretaceous basal squamatans in Brazil, an isolated lower jaw in Early Campanian outcrops of North Patagonia with purported teioid affinities, and the Malagasy Late Campanian cordylid with iguanian dental replacement. They all constitute a confusing record but prove that different lineages of Gondwanan native lizards lived in South America, at least between Jurassic and Late Cretaceous times, sharing restricted adaptive zones with the sphenodontians. Although very elusive and scarce, an incomplete lizard frontal was found at ‘La Buitrera’ facies of the Candeleros Fm., at Río Negro Province. The fused nature of the frontals and its hourglass shape are iguanian synapomorphic traits (although also present in some anguids and xenosaurids), which combined with the profusely tuberculate ornamentation pattern, diagnoses Iguanidae, the purported earliest iguanians. Although the finding of derived acrodontan iguanians at the Early Jurassic of India (Gondwana) and the Aptian of Mongolia (Laurasia) shows a rather cosmopolitan distribution for the group, the Iguanidae are restricted to much younger (Maastrichtian) strata, such as the dubious Brazilian iguanid Pristiguana, and several Mongolian taxa. The ‘Mid Cretaceous’ specimen here described, although poorly preserved, suggests that, as Estes and Price proposed, iguanians had an important Gondwanan chapter, and the iguanids could have been arose in South America, where they are more abundant today.