Mexican Spiny-tailed Iguana, Ctenosaura pectinata
Mexican Spiny-tailed Iguana, Juvenile, Ctenosaura pectinata. Photograph taken within a residential community in the greater Alamos area, Alamos, Sonora, March 2019. Photograph and identification courtesy of David F Smith, Alamos, Sonora.
Mexican Spiny-tailed Iguana, Ctenosaura pectinata. Photograph taken in the greater Xochicalco area, Moreles, March 2018. Photograph and identification courtesy of David F Smith, Alamos, Sonora.
Mexican Spiny-tailed Iguana, Juvenile, Ctenosaura pectinata. Photographs taken within a residential community in the greater Alamos area, Alamos, Sonora, February 2018 to April 2019. Photographs and identifications courtesy of David F Smith, Alamos, Sonora.
Mexican Spiny-tailed Iguana, Ctenosaura pectinata. Photographs taken in Zihuantanejo, Guerrero, March 2019. Photographs courtesy of Ron Woheau, Zihuantanejo. Identifications courtesy of Gary Nafis, Californiaherps.com. The identification of the iguana(s) in the second and third photographs should be considered as tentative.
The Mexican Spiny-tailed Iguana, Ctenosaura pectinata, is a member of the Iguanidae family of Lizards. The Iguanidae family has seven hundred members placed in forty genera. There are fifteen global species in the Ctenosaura genus. They are also known as the Western Spiny-tailed Iguana, Guerreran Spiny-tailed Iguana, or simply Spiny-tailed Iguana and in Mexico as Lguana-espinosa Mexicana.
Mexican Spiny-tailed Iguanas are characterized by their large tail that is covered in distinctive keeled scales. They are one of the largest members of their genus, reaching up to 1.3 m (4 feet 3 inches) in total length, with the males being slightly larger than the females that only reach 1.0 m (3 feet 3 inches) in length. Sexual dimorphism is also displayed with adult males possessing a dorsal spiny crest that is typically bigger than those on adult females. They have an elongated and depressed head with a pronounced transverse gular fold. A series of larger scutes extend from their eye to their snout, forming a border that abruptly separates the lateral surface of their head from the superior side. Their nostrils lie anterior to the end of this crest. The scales on their back are small and flat, while the scales on their abdomen are rhombic and much larger, each with a longitudinal keel. Mexican Spiny-tailed Iguanas vary in color dorsally from brown or gray to brownish-black, with a yellowish ventral surface. They often, but not always, possess an irregular piebald pattern on their head or dorsal areas. While their tails may be banded with light and dark crossbands, they lack a clear or well developed crossband pattern on their body. Some males exhibit yellowish colors on the lateral sides of their body, while some females exhibit an orange coloration. The young are bright green in color and unmarked, except for black tail bands, and become darker with age.
Mexican Spiny-tailed Iguanas are social and adapted to living in groups, unlike other species in the Ctenosaura genus. While they are primarily terrestrial, they are skilled climbers. They prefer rocky areas with plenty of crevices to hide, adequate places to bask in the sun, and nearby trees to climb. Mexican Spiny-tailed Iguanas are diurnal and mate in the spring. Males display their dominance and interest in a female by head bobbing, eventually chasing the female until he can catch and subdue her. After copulation, the female digs a nest in loose soil, where she lays up to 50 eggs after a gestation period of 8 to 10 weeks. After 90 days, the eggs hatch and the bright green young dig their way out of the sand. Hatchlings first appear around July, and are abundant in August. Mexican Spiny-tailed Iguanas demonstrate an ontogenetic diet shift, with the juveniles consuming a different diet than the adults. While insects are rare in adult diets, they constitute the majority of the food eaten by juveniles. Adults are primarily herbivorous and consume a variety of flowers, leaves, stems, and fruit. All age classes consume some plant parts, with flowers and leaves of legumes being most abundant, but non-adult lizards demonstrate the widest food niche. One explanation for this behavior is that while juveniles can consume plants, they choose to primarily consume insects because they provide a more nutritious diet. This explanation is based on the observation that the juvenile hindgut, where plant matter is broken down, is similar to that of herbivorous adults. Consuming insects can compensate for size-related nutritional needs and digestive limitations in juveniles. Mexican Spiny-tailed Iguanas move quickly and use their speed to escape predators. When cornered, they will bite and lash with their tails. They are preyed upon by Boa Constrictors, Eagles, Hawks, Ocelts, Pumas, Jaguars and Humans. Invasive species, such as free-ranging and feral cats and dogs, also prey on all age classes. The Mexican Spiny-tailed Iguanas have lifespans of up to fifteen years in the wild.
Mexican Spiny-tailed Iguanas is endemic to Mexico being found along the Pacific coast of Mexico in the states of Sinaloa, Nayarit, Jalisco, Colima, Michoacán, Morelos, Guerrero, Puebla, and Oaxaca. They are occasionally found as far north as Benjamin Hill, Sonora, likely translocated by roads and railways, however, this area is too arid for hatchlings to survive. They have become invasive outside of their natural range in Florida and southern Texas in the United States.
The Mexican Spiny-tailed Iguana may be confused with the Sonoran Spiny-tailed Iguana, Ctenosaura macrolopha (whitish-gray or tan in color with a series of 4 to 12 well-defined dark dorsal bands that nearly extend to their ventral scales).
From a conservation perspective, the Mexican Spiny-tailed Iguana is considered to be of Least Concern due to their wide distribution. Their population seems to be structured in isolated subpopulations, with very large concentrations in some areas and none in others. There is no data available on their population trends or fine-scale density and size information. It is suspected that there has been a decline in their population due to conversion of their natural habitat for agricultural, ranching, and urban uses. The Mexican Spiny-tailed Iguana is widely and heavily hunted for food consumption, medicinal and traditional purposes, and to produce fashion items. Males and females are hunted throughout the year, however during the breeding season hunting is strongly biased to collect pregnant females. This bias may cause localized population declines and negatively impact their stable age structure. While there are legal sources for the trade markets, a substantial amount are sourced from the wild in unknown quantities. Another major threat to this species is habitat fragmentation and destruction caused by human activities. Throughout their range, logging and large-scale agriculture displaces and fragments their population. This may reduce their genetic variability to some degree, and may become a larger threat with the expansion of human development.