The world's growing extinction threats are typically worst for the largest and smallest creatures, a finding that should temper conservation efforts, new research has found.

The study, published on Tuesday in the Proceedings of the National Academy of Sciences, examined 27,647 vertebrate species based on body mass as assessed by the Union for Conservation of Nature's Red List. About 17 per cent of all species, for which size data is available, are threatened with extinction.

The Leadbeater's possum, one of Australia's threatened small species. Credit:Justin McManus

The threat to larger animals has been relatively well known, not least because creatures, such as blue whales, elephants and tigers, are often highlighted by conservation groups.

For many species, the risks are often from growing populations of humans hunting or fishing wild meat, or the purported medicinal value of animal parts.