They look like snakes, but don't be fooled: Legless, slithering amphisbaenians are more closely related to lizards than to boa constrictors.

Now, the first complete skull of the ancestor of today's bizarre "worm lizards" reveals that these strange reptiles have been largely unchanged for at least 11 million years. The fossil skull, discovered in Spain, is only 0.44 inches (11.2 millimeters long), but represents a new species, Blanus mendezi.

This family, known as blanids, includes the only worm lizards found on land in Europe, said study researcher Arnau Bolet, a doctoral student at the Institut Catal de Paleontologia Miquel Crusafont in Barcelona.

"Their fossil record was until now limited to isolated and usually fragmented bones," Bolet told Live Science in an email. "Thus, the study of a complete fossil skull more than 11 million years old was an unprecedented opportunity." [The 12 Weirdest Animal Discoveries]

Lizards without legs

Worm lizards are found around the world today, though most of the 180 or so extant species live in the Arabian Peninsula, Africa and South America. Some have rudimentary legs, but most have no limbs at all, and resemble large earthworms.

Today, there are three groups of worm lizards in the Mediterranean region: one group is eastern, one is Iberian and one is northwest African. The Iberian and northwest African groups probably arose from one western Mediterranean group that only later subdivided, Bolet and his colleagues explain today (June 4) in the journal PLOS ONE.

The new skull was found in sediments excavated in 2011 in the Valls-Peneds Basin in Spain's Catalonia region. Manel Mndez, a technician at the Institut Catal de Paleontologia Miquel Crusafont, was sifting through the dirt for fossils using a screen when he found a lumpy, pinkish rock that he knew was something more.

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11-Million-Year-Old Weird Worm Lizard Discovered