Adapid

These belong either to the lemurlike adapids, the tarsierlike omomyids, or the early simians, forerunners of monkeys, apes, and humans.

Only adapids and omomyids have turned up at North American and European sites of comparable age; several African simians dating to about 40 million years ago have been discovered since 1988.

The proposed Chinese simian, dubbed Eosimias sinensis, displays several jaw and tooth features that distinguish it from adapids and omomyids, Beard argues.

In particular, Ciochon's group stresses the similarities between Amphipithecus, and hence anthropoids, and a family of lower primates called adapids, which led to modern-day lemurs and lorises.

"But [even] if it is, I don't think it shows that adapids are related to anthropoids," he says.

Scientists divide forest-dwelling primates living 55 million to 36 million years ago into two families: the adapids, including many species resembling modern lemurs; and the omomyids, comprising several animals with anatomical ties to modern tarsiers.

Dissenters, such as Simons, view the adapids as more likely simian ancestors.