Tropical Tree Lizard, Urosaurus bicarinatus

Tropical Tree Lizard, Urosaurus bicarinatus. Photograph taken within a residential community in the greater Alamos area, Alamos, Sonora, February 2019. Photograph and identifications courtesy of David F Smith, Alamos, Sonora.

The Tropical Tree Lizard, Urosaurus bicarinatus, is a member of the Phrynosomatidae family, which includes Zebra-Tailed, Earless, Fringe-Toed, Spiny, Tree, Side-Blotched and Horned Lizards. The Phrynosomatidae family is a diverse family of lizards, sometimes classified as a subfamily, that is found from extreme southern Canada to Panama. There are one hundred twenty species in the Phrynosomatidae family placed in nine genera. There are eight species in the Urosaurus genus. The Tropical Tree Lizard is known in Mexico as Lagartija de árbol del Pacífico.

Tropical Tree Lizards are slender with weakly keeled granular dorsal scales and a fully developed gular fold. They have a single row of enlarged paravertebral scales on each side, a characteristic after which the species is named (bicarinatus). A discontinuous row of enlarged laterovertebral scales lie lateral to and separated from their paravertebral scales. Slightly enlarged, discontinuous rows of dorsolateral scales are scattered down their sides. They have enlarged plate-like head scales, and their dorsal surface is gray with five dark crossbands between their neck and rump. Their ventral surface is whitish with variable, scattered dark spots or pigmentation. Their throat is predominately reticulated light and dark, lacking coloration. Adults display a bluish color in the center of their chest. Sexual dimorphism is displayed with the males growing slightly larger than the females. Males and Females reach snout to vent lengths of 6.5 cm (2.6 inches) and 6.1 cm (2.4 inches), respectively.

Tropical Tree Lizards are diurnal, arboreal, and highly secretive. They primarily occupy deciduous trees, where they blend into the tree trunks and limbs. They depend mostly on their cryptic coloration to avoid detection, and are often only found by striking trunks and branches to startle them into movement. Reproduction coincides with the wet season from June through September, and females lay one to three (possibly four) clutches per season. Each clutch consists of three to eleven eggs. Hatching occurs during summer and fall after an incubation period of about sixty days. Hatchlings have a snout to vent length of 1.8 cm (0.7 inches) to 2.7 cm (1.1 inches) and resemble small adults. While their diet has not been extensively researched, it likely consists of small invertebrates such as insects. The Tropical Tree Lizard is poorly studied with very limited information available about their lifestyle and behavioral patterns including specific details on age, growth, longevity, movement patterns, and habitat use.

The Tropical Tree Lizard may be confused with the Long-tailed Brush Lizard, Urosaurus graciosus, due to their similar appearances. These species can be differentiated visually and geographically. The Long-tailed Brush Lizard has a proportionally longer tail and five to seven longitudinal rows of enlarged, keeled scales on the middle of their dorsum. Additionally, Long-tailed Brush Lizards occur in southwestern United States and extreme northwestern Mexico.

From a conservation perspective, the Tropical Tree Lizard is considered to be of Least Concern due to their wide distribution, tolerance of a broad range of habitats, and presumed large population size. No major threats have been identified for this species.