Is the horned frog extinct in Texas, and if so, what caused its extinction?

No. But as you can read in the quote below, their not really frogs/toads, but are in fact lizards. I've included the following quote that answers your questions, but also gives some info on this frog/toad/lizard.

" When I was a kid, the Horny Toad as we called them, were everywhere during the summer in North Texas. I bet I have not seen on now in 30 or more years. It's not that they are extinct, I hear they can still be found on some of the ranches in West Texas. Despite low numbers in East and Central Texas, the Texas horned lizard is still locally common in portions of the Rio Grande Plains of south Texas, the Rolling and High Plains of northwest Texas and the Trans Pecos of far west Texas.

As a matter of fact, these are not "Toads" at all, they are really a type of lizard, the Phrynosoma cornutum. Texas Horned Lizards can be found from the South-Central United States to Northern Mexico. They are usually found in arid and semiarid habitats in open areas with sparse plant cover throughout much of Texas, Oklahoma, Kansas and New Mexico.

The Texas horned lizard was most recently bestowed the honor as the Texas State Reptile in 1992.

These little rascals are currently listed as a threatened species (federal category C2)." But are NOT yet extinct!

Texas Horned Frog

It is not extinct but it is in decline. The population is declining going from east towards the west. They were still found occasionally in north central Texas just 4 years ago. I have not seen one in 4 years. The reason is not clear for the decline. It seems to coincide with the advancement of the imported fire ant. It also seems to go with the decline and almost none existent bobwhite quail population. One idea put forward is a form of malaria that effects them. Bullfrogs are also in decline here. I believe the problem is the fire ants but what do I know.

Are Horned Toads Endangered

Presumably, by "horned frog" you meant the Texas horned lizard, sometimes called a "horned frog" or "horny toad." It is not extinct, although populations have declined due to land development.

Not extinct, critically endangered. Use of pesticides are doin' the little guys in.

no i dont think its extinct.