Teiidae

Teiidae: Whiptails, Racerunners, and Tegus

The Teiidae family represents a diverse group of lizards native to the Americas, commonly referred to by names such as whiptails, racerunners, and tegus. This family is taxonomically positioned as sister to the Gymnopthalmidae, with both forming the superfamily Teiioidea. The Teiidae family is notable for its approximately 150 species, which are organized into eighteen genera and two subfamilies: Teiinae and Tupinambinae.

Morphology and Behavior

Members of the Teiidae family exhibit several distinguishing physical traits. They are characterized by large, rectangular scales on their ventral side that form distinct transverse rows, while their dorsal scales are typically small and granular. Their head scales are separate from the skull bones, and their teeth are solid at the base, firmly attached to the jaw bones. A consistent feature across all teiids is a forked, snake-like tongue, and they all possess well-developed limbs. Behaviorally, teiids are predominantly terrestrial, though some are semi-aquatic. They are diurnal, meaning they are active during the day, and their diet is primarily carnivorous or insectivorous, with some species supplementing their intake with plant matter. They are active foragers, moving rapidly between cover objects within their preferred temperature range. Teiids are oviparous, laying eggs, and some species are known to produce very large clutches.

Parthenogenesis

A remarkable aspect of the Teiidae family is the presence of several obligately parthenogenetic species. These species consist entirely of females, reproducing clonally without the need for male fertilization. Such lineages are typically hybrid in origin, arising from the hybridization of two or more species. The precise meiotic mechanisms that allow these lizards to bypass fertilization are a subject of ongoing scientific research. In laboratory studies, particularly with Aspidoscelis neomexicanus, a behavior known as pseudocopulation has been observed. In this scenario, one female adopts a male-like role to mount another female, which can stimulate reproductive fertility. Individuals can switch these roles throughout their lives. While not observed in all parthenogenetic varieties, the existence of pseudocopulation in some all-female lineages suggests they reproduce unisexually.

Fossil Record and Taxonomy

The evolutionary history of Teiidae extends back to the Late Cretaceous period, with fossil relatives like the Barbatteiidae. The earliest known member of the crown-group Teiidae is Lumbrerasaurus, dating to the Early Eocene of Argentina. Fragmentary fossils suggest Tupinambine teiids may have briefly colonized Europe during the Late Eocene, a phenomenon potentially explained by trans-Atlantic oceanic dispersal. The genus Wautaugategu is known from the Middle Miocene of Georgia, USA, indicating that tupinambines must have naturally migrated to North America from South America before the Great American Interchange. Today, the Teiidae family is divided into two subfamilies, Teiinae and Tupinambinae, encompassing eighteen genera and approximately 150 species. Recent taxonomic revisions have included the resurrection of genera, the description of new genera, and the division of the large genus Cnemidophorus. In technical literature, Teiidae are sometimes referred to as macroteiids, in contrast to the microteiids of the sister family Gymnopthalmidae.