OLDEST KNOWN AMPHISBAENIAN FROM THE UPPER CRETACEOUS OF CHINESE INNER-MONGOLIA

THE amphisbaenians, lizards and snakes constitute a monophyletic group , the Squamata. Although amphisbaenians are known to have occurred in the Mesozoic1,2, their remains are rare and fragmentary. The oldest an d most primitive known skull of an amphisbaenian is from the Eocene of North America3 and differs little from that of modern taxa4-9. A subs tantial structural map exists between this skull and that of the sever al possible sister groups8,10. No derived features uniquely linking am phisbaenians to any other group of the Squamata have been recognized, so the relationship of amphisbaenians is uncertain11,12. We report her e on the late Cretaceous lizard-like amphisbaenian represented by well -preserved cranial and postcranial material from the Bayan Mandahu red beds of the Gobi Desert, Inner Mongolia, China. This material document s the oldest and most primitive amphisbaenian yet known, and permits a re-evaluation of the relationship between the amphisbaenians and othe r squamates.