30 - 60 % of species per taxonomic order
||Ceballos G, Ehrlich PR, Dirzo R. Biological annihilation via the ongoing sixth mass extinction signaled by vertebrate population losses and declines. Proc Natl Acad Sci U S A. 2017 Jul 25 114(30):E6089-E6096. doi: 10.1073/pnas.1704949114 p.E6094 right column 4th paragraphPubMed ID28696295
|| Régnier C et al., Mass extinction in poorly known taxa. Proc Natl Acad Sci U S A. 2015 Jun 23 112(25):7761-6. doi: 10.1073/pnas.1502350112PubMed ID26056308
||Primary source abstract: "Here [investigators] show, based on extrapolation from a random sample of land snail species via two independent approaches, that we may already have lost 7% (130,000 extinctions) of the species on Earth."
||P.E6094 right column 4th paragraph: "Recent reviews indicate that species extinctions, population decreases, and range contraction (implying population extinctions) among terrestrial invertebrates and plants are as severe as among vertebrates (e.g., refs. 35, 37, 38, primary source 36). For example, long-term monitoring of insect populations in the United Kingdom shows that 30–60% of species per taxonomic order have contracting ranges (primary source). "