is being investigated. Another line of research is artificial insemination, either in vitro or by inserting spermatophores into the cloacae of females. The results of this research may be used in captive-breeding programmes for endangered species. Taxonomy Disagreement exists among different authorities as to the definition of the terms Caudata and Urodela. Some maintain that the Urodela should be restricted to the crown group, with the Caudata being used for the total group. Others restrict the name Caudata to the crown group and use Urodela for the total group. The former approach seems to be most widely adopted and is used in this article. The ten families belonging to Urodela are divided into three suborders. The clade Neocaudata is often used to separate the Cryptobranchoidea and Salamandroidea from the Sirenoidea. Phylogeny and evolution The origins and evolutionary relationships between the three main groups of amphibians (gymnophionans, urodeles and anurans) is a matter of debate. A 2005 molecular phylogeny, based on rDNA analysis, suggested that the first divergence between these three groups took place soon after they had branched from the lobe-finned fish in the Devonian (around 360 million years ago), and before the breakup of the supercontinent Pangaea. The briefness of this period, and the speed at which radiation took place, may help to account for the relative scarcity of amphibian fossils that appear to be closely related to lissamphibians. However, more recent studies have generally found more recent (Late Carboniferous to Permian) age for the basalmost divergence among lissamphibians. The earliest known salamander-line lissamphibian is Triassurus from the Middle-Late Triassic of Kyrgyzstan. Other fossil salamanders are known from the Middle-Late Jurassic of Eurasia, including Kokartus honorarius from the Middle Jurassic of Kyrgyzstan, two species of the apparently neotenic, aquatic Marmorerpeton from the Middle Jurassic of England and Scotland, and Karaurus from the Middle-Late Jurassic of Kazakhstan, resembled modern mole salamanders in morphology and probably had a similar burrowing lifestyle. They looked like robust modern salamanders but lacked a number of anatomical features that characterise all modern salamanders. The two groups of extant salamanders are the Cryptobranchoidea (which includes asiatic and giant salamanders) and the Salamandroidea (which includes all other living salamanders), also known as Diadectosalamandroidei. Both groups are known from the Middle-Late Jurassic of China. the former being exemplified by Chunerpeton tianyiensis, Pangerpeton sinensis, Jeholotriton paradoxus, Regalerpeton weichangensis, Liaoxitriton daohugouensis and Iridotriton hechti, and the latter by Beiyanerpeton jianpingensis.