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Excerpts from Jim Conrad's
Naturalist Newsletter
entry dated September 11, 2022, notes from San Pedro Huimilpan, elevation about 2400m (7900ft), N20.315° W100.281°, Querétaro state, MÉXICO
SOUTHERN BUNCHGRASS LIZARD
In a grassy fruit orchard on a mountain slope at the eastern side of San Pedro Huimilpan, the above lizard was fairly well camouflaged as it remained motionless in the sunny, sheep-grazed grass. North Americans who pay attention to lizards may recognize this as a spiny, or fence lizard. For example, with its general form, rough scaliness, lines running along its body, and blocky head, it's somewhat like the Texas Spiny Lizard seen in Texas.
Spiny and fence lizards are members of the big lizard-genus Sceloporus, which embraces 113 or so species occurring only in the Americas from Canada south to Panama. The genera's center of species diversity is here in Mexico. Its species' numbers resonate with the fact that the Mexican highlands are a global biodiversity hotspot with an exceptionally high number of species of different organism types endemic just to this area.
No field guides for lizards is available for this part of the world so for me identification to species level comes down to doing an image search on the Internet, using the keywords "Sceloporus Querétaro." Our lizard matches pictures labeled as the Southern Bunchgrass Lizard, SCELOPORUS AENEUS, for example at the international Reptile-Database.Org website.
Southern Bunchgrass Lizards are endemic just to the highlands of central Mexico, in the states of Puebla, Jalisco, Mexico, Guanajuato, Guerrero, central-western Michoacán, and here in Querétaro, at elevations between 2000-3000m (6500-9900ft).
One reason the species has an English name is because several researchers have looked at its life history. An interesting feature of the species is that it's described as "almost viviparous." The term "viviparous" refers to producing living young instead of eggs from within the body. Eggs may form inside the mother's body, but that's also where the eggs hatch. The great majority of reptiles lay eggs externally. In general, viviparity is considered an adaptation to cold climates because the cooler the climate, the greater the problems for outside-laid eggs.
Rodolfo García-Collazo and others in 2012 published a study entitled "Egg retention and intrauterine embryonic development in Sceloporus aeneus (Reptilia: Phrynosomatidae): implications for the evolution of viviparity." In that study they found that our lizard's viviparous inclination depended on environmental factors. They write of our lizard that "... populations from high elevations retain intrauterine embryos to more advanced stages than those from low elevations." Usually a species is one way or another, so our lizard being "almost viviparous" is something special.
A 2020 study by Raciel Cruz-Elizalde and others entitled "Sexual Dimorphism and Feeding Ecology of the Black-bellied Bunchgrass Lizard Sceloporus aeneus (Squamata: Phrynosomatidae) in Central Mexico" found that male Southern Bunchgrass Lizards are larger than females. In many species the opposite is true. Females in the study ate a greater variety of foods than males. For both sexes, insects accounted for about 70% of the diet, especially ants, beetles and the "true bugs," the Hemiptera. About 20% of the food comprised spiders and other arachnids, and 10% plant material. Southern Bunchgrass Lizards use the "sit and wait" strategy for obtaining food, which the individual in our photos seemed to be doing.