The Desert Horned Lizard, Phrynosoma platyrhinos, a member of the Phrynosomatidae family, is a medium-sized flat, and wide lizard. They are measured from snout to vent and reach upwards of 95 mm. Males are generally smaller than females and have post-anal scales, larger femoral pores, and a wider tail base. A characteristic feature of this species is the two central but separate occipital horns that generally project straight back and are noticeably longer than the other spikes on their head. Along their back, several isolated, pointed scales project up and a single row of enlarged, pointed scales line their sides. A row of enlarged, pointed scales also project from each side of the throat (Brennan 2008).
Their unusual appearance is due to unique and integrated set of adaptations. Their camouflaging colors, flat-body form, and sedentary nature make them difficult to see. Their horns and spiny scales make them difficult to swallow. In addition, their pancake shape provides them with a large, flat surface for rapid solar heating, capturing raindrops, or warding off predators. A capacious body provides room for development of numerous eggs and for a large stomach. However, at the same time, their awkward shape limits their speed, which affects their ability to hunt and escape predators. Walking through dense strands of ground-level herbs and grasses make walking difficult for them. Despite these unorthodox strategies with the benefits outweighing the costs, the Desert Horned Lizard continues to survive and reproduce successfully over a broad range (Sherbrooke, 2003).
Native Range: The Desert Horned Lizard has a broad range across the western United States from southeastern Oregon and southwest Idaho down into nearly the entire state of Nevada, northern Utah, southwest California, down into western Arizona and northern Mexico (Cossel, 1997). They have been found in Arizona up to 6,500 feet above sea level (Brennan, 2008).
Habitat and Ecological Associations: Desert Horned Lizards are found in arid regions that have some loose substrate for burrowing such as sand flats with limited vegetation, generally small shrubs such as sagebrush, shadscale, saltbush, or big greasewood with large clear areas separating them. They been found in places with hardpan and gravelly soils, dune systems, dry washes and hillsides with loose soil as well (Cossel, 1997).
Trophic Strategy: Desert Horned Lizards feed predominately on larger ants, making up about 90 percent of their diet. This dietary preference is easily verified by examination of the contents of one of their large and distinctive looking fecal pellets, or scats which contain numerous undigested exoskeletons of ants (Sherbrooke, 2003). They also feed on spiders and insects such as beetles, moth/butterfly larvae (Brennan, 2008).
Behavior/Life cycle: These lizards are diurnal with most of their activity occurring during the morning and evening, taking shelter during the high mid-day temperatures (Brennan, 2008). Once above ground, the horned lizard usually begins to bask by tilting its body and turning its back toward the sun while standing high on extended forelegs or orient a lowered side toward the eastern horizon while elevating its opposite side by extending the legs on that side. The Desert Horned Lizard will also elevate itself on small rises or objects or sits on steep, east-facing slopes or rocks. This directed exposure increases the horned lizard’s body temperature more rapidly because a surface held perpendicular to incoming rays absorb more radiant heat (Sherbrooke, 2003).
Desert Horned Lizards have a seasonal inactivity period, but it varies with local climate. In southern Nevada, they will emerge in March with little adult activity after mid-July. In more southern ranges, they may be active during warm nights, whereas in the north, they bury in substrate (Cossel, 1997). The Desert Horned Lizard is known to have lived at least 8 years in the wild (Sherbrooke, 2003).
Reproduction: Desert Horned Lizards are oviparous (Hallermann). They generally lay one or two clutches of eggs in spring and summer and range from 2-16 eggs (Brennan, 2008). Mating season is from April to June with eggs laid from April to July. Females have 1-2 clutches per year. Incubation period is 50 to 60 days. Individuals reach maturity around 22 months (Cossel, 1997).
Predators: Predators include prairie falcons, loggerhead shrikes, longnose leopard lizards, and striped whipsnakes (Cossel, 1997). Other snake varieties that prey on horned lizards include sidewinders and kestrels.
Functional Adaptations: When threatened, the Desert Horned Lizard immediately flatten their bodies against the soil, hold still, and wait until danger has passed. If the danger is a hawk circling above in the sky, the lizard may tilt its head to keep the enemy in sight and when safe, quickly slip under a shrub for increased protection (Sherbrooke, 2003).
The Desert Horned lizard is more likely to run than other horned lizard species, but often stops under the nearest bush (Brennan, 2008). When frightened into running, horned lizards run a short distance and then stop abruptly. The brief run and sudden stop has reestablished the horned lizard’s first line of defense: invisibility. The predator loses the lizard as it abruptly runs a short distance and then freezes into immobility, and it may never relocate the horned lizard again (Sherbrooke, 2003). Horned lizards can lose their tails, but not easily when grabbed by it, nor do they regenerate a new one if the tip is lost (Sherbrooke, 2003).
Conservation status/management: The Desert Horned Lizard’s status is considered an unprotected nongame species (Cossel, 1997).
The desert horned lizard (Phrynosoma platyrhinos) is a species of phrynosomatid lizard native to western North America. They are often referred to as "horny toads", although they are not toads, but lizards.
There are several important characteristics that can be used to identify desert horned lizards from other horned lizards. Horned lizards can be distinguished from other lizards by the large pointed scales that protrude from the back of their heads, giving them the appearance of having horns, as well as the flat and broad shape of their bodies. [3]
This species of lizard has a distinctive flat body with one row of fringe scales down the sides. They are a medium sized lizard and can grow up to approximately 3.75 inches or 95mm in size.[3] They have one row of slightly enlarged scales on each side of the throat. Colours can vary and generally blend in with the color of the surrounding soil, but they usually have a beige, tan, or reddish dorsum with contrasting, wavy blotches of darker color. They have two dark blotches on the neck that are very prominent and are bordered posteriorly by a light white or grey color. They also have scattered pointed scales and other irregular dark blotches along the dorsum of their body. Unlike other horned lizards, Phrynosoma platyrhinos individuals do not have a prominent dorsal stripe. Their dorsal stripe can appear faintly or be entirely absent depending on the individual.[3] They also have pointed scales on the dorsum (back) of the body. Juveniles are similar to adults, but have shorter and less-pronounced cranial spines. Desert horned lizards have horns that are wide at the base, which isn't true for their congener, the short-horned lizard. Pictured to the left is Blainville's Horned Lizard (Phrynosoma blainvillii), note the colored horns and double row of fringed scales alongside the body. The desert horned lizards' horns also do not come into contact with one another at the base.[3]
Desert horned lizards prey primarily on invertebrates, such as ants (including red harvester ants,) crickets, grasshoppers, beetles, worms, flies, ladybugs, meal worms and some plant material. They can often be found in the vicinity of ant hills, where they sit and wait for ants to pass by. Ants contain a large amount of chitin, an indigestible compound, this makes them not as nutrient rich, so larger amounts must be consumed to sustain Phrynosoma platyrhinos. As an evolutionary advantage desert horned lizards developed larger stomachs to allow them to consume larger concentrations of ants.[4] When they find an area of soft sand, they usually shake themselves vigorously, throwing sand over their backs and leaving only their head exposed. This allows them to hide from predators and await their unsuspecting prey.
Found in extremely diverse habitats. The flat-tailed horned lizard occurs in areas of fine sand, while the short-horned lizard (P. douglasii) is found in shortgrass prairie all the way up into spruce-fir forest. The most common species in the Arizona Upland subdivision is the regal horned lizard (P. solare), which frequents rocky or gravelly habitats of arid to semiarid plains, hills and lower mountain slopes. The desert horned lizard (P. platyrhinos) is found mostly in the Sonoran and Mojave deserts. It can be found in southeastern Oregon, California, western Arizona Utah, Idaho and Nevada. Outside of the United States it is found in Mexico, northwestern Sonora, and northeastern Baja California.[5] They have a preference for places that they can find shrub covering with an understory.[6] Phrynosoma platyrhinos will often bury themselves in sand soil, if possible, or they will live in burrows that were constructed by other animals.[3]
They typically range from southern Idaho in the north to northern Mexico in the south. These lizards can generally be found in areas with desert climates throughout western North America.
Changes in the environment due to climate change can trigger shifts in the geographic ranges of animals. Phrynosoma platyrhinos has experienced some changes after the Last Glacial Maximum (LGM) which ended approximately 21,000 years ago. The end of the LGM resulted in the expansion of deserts throughout western North America, and with that expansion Phrynsoma platyrhinos had more areas suitable for them to live in. At the end of the LGM P. platyrhinos was able to expand north into the Great Basin, which is now part of their current geographical range.[7]
There are two subspecies which are found in a different geographic ranges: the northern desert horned lizard (Phrynosoma platyrhinos platyrhinos) ranging in Idaho, Wyoming, Utah, Nevada, the Colorado front range, and parts of southeastern Oregon; and the southern desert horned lizard (Phrynosoma platyrhinos calidiarum) ranging in southern Utah and Nevada to southeast California, western Arizona, and northern Baja California.
They are generally a gentle species, but have been known to try to push their cranial spines into the hand while held. When excited, they puff themselves up with air, similar to the way a Chuckwalla does, making themselves look bigger. If spotted near a bush, they will dash into it in an attempt to find cover from any threat. Unlike most other species of horned lizard, Phrynosoma platyrhinos is most likely to run when startled, though they will often only run for a short period of time before stopping again.[3] Like several other horned lizard species, desert horned lizards are able to squirt blood from their eyes.[8]
The desert horned lizard has also been observed to exhibit rain-harvesting behavior in the wild, a behavior previously only attributed to a handful of other species. When rain-harvesting the lizard adopts specific posture in order to get its mouth closer to the ground.[9]
Like other iguanids P. platyrhinos performs a number of displays. Iguanid displays are usually used to assert a social structure or for aggression and courtship, and can present in a variety of different behaviors such as: push ups, bobbing of the head, tail movements, along with changes in posture. In P. platyrhinos these displays are less aggressive and appear to be most concerned with sex and species recognition.[10]
These behaviors include various tail positions such as curled, between the legs, or arched down with scratching behaviors, push ups, and a three-legged stance where one of the hind legs is held off the ground and the back is presented to predators.
The desert horned lizard (Phrynosoma platyrhinos) is a species of phrynosomatid lizard native to western North America. They are often referred to as "horny toads", although they are not toads, but lizards.
