Researchers in China reported on Wednesday that they have created two cloned monkeys, the first time that primates have been cloned with the technique that produced Dolly the sheep more than 20 years ago.

The long-tailed macaques, named Zhong Zhong and Hua Hua, were made from fetal cells grown in a petri dish. The clones are identical twins and carry the DNA of the monkey fetus that originally provided the cells, according to a study published in the journal Cell. They were born at the Chinese Academy of Sciences in Shanghai.

Dolly the sheep was produced from udder cells that had been frozen for six years. Until that feat, many researchers had thought that type of cloning was impossible, because it required taking adult cells and bringing them back to their original state, when sperm first fertilized egg.

The cell would then have to start to grow in a surrogate’s womb and to differentiate into an entire animal, genetically identical to the one that provided the initial cell.