Two extant and six extinct species are recognised. Systematic classifications dealing with both extant and extinct taxa vary more widely. Phylogeny is based on a combination of studies of extinct and extant species. Marsupials represent the clade originating from the last common ancestor of extant metatherians. Four extant species within one extant genus are widely recognised. There are two phylogenetic hypotheses on the relationships among extant and fossil bear species. Women are found in philosophical discussions across numerous other Puranas and extant era texts. The Vedas are some of the oldest extant texts in India. The early embryological stages are reminiscent of ancestral gastropods and extant Monoplacophora. They represent several independent phylogenetic branches of fishes leading to the still extant Chondrichthyes. Sandhill cranes have one of the longest fossil histories of any extant bird. Estimates of the total number of extant species are subject to even greater variation. Listed below are extant species of shark. The number of extant penguin species is debated. About 35 species of extant canids are currently recognized.