Holcosus quadrilineatus Four-lined Ameiva
Some other names for this species:
Four-lined Whiptail
This species was recently moved into the genus Holcosus; it was formerly known as Ameiva quadrilineata.
San Josecito, Osa Peninsula, Puntarenas province, Costa RicaApril 15, 2001
Four-lined Ameiva (Holcosus quadrilineatus) Four-lined Ameiva (Holcosus quadrilineatus)
Like most lizards in this family, these guys spend almost all of their waking hours poking nervously about for insects and skittering away at the slightest disturbance. I photographed these two shortly after a mid-day rain shower, so they were somewhat more inclined than usual to bask in sunny patches of ground.

Our guides identified these as Ameiva festiva, but I'm sure they were wrong. Ameiva festiva has a broad stripe down the center of the back, whereas these guys have four stripes, none of which go down the center of the back. Also, the same guides called them skinks, so they were not exactly lizard experts (Ameivas are in the family Teiidae; skinks are in the family Scincidae).

Esquinas Rainforest Lodge, Golfito region, Puntarenas province, Costa RicaSeptember 27, 2001
Four-lined Ameiva (Holcosus quadrilineatus) Four-lined Ameiva (Holcosus quadrilineatus)
These lizards are sun worshippers, and on sunny mornings would skitter along the lodge area trails, daring you to take their pictures. As soon as the sky clouded over they were nowhere to be seen. The first one here, an adult, is basking on a rock in front of my room. The second one, a juvenile, was captured and made to pose against its will on a table. Making an ameiva sit still is not a job for the impatient.

Here is a complete list of the species we found on this GreenTracks trip.

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