A new landmark memorial - designed to increase awareness of "lost species" of animals and plants - will be created on Portland after the plans were backed by Dorset County Council (DCC).

The council's cabinet agreed to provide a one-off £30,000 grant from its special projects budget towards the £150,000 development stage of the Mass Extinction Memorial Observatory (MEMO) scheme. Two further pledges from private benefactors will also help to finance the development stage of the project, which will cost between £3-5m and is due to be completed in 2012.

DCC will provide no further funding towards the MEMO development, with the remaining funding expected to come from private donations, corporate sponsorship and charitable grants. The MEMO project is being led by former Weymouth College student Sebastian Brooke, with the support of organisations including WWF UK, Eden Project co-founder Tim Smit and the Royal Society.

Two sites are currently being considered - New Ground, overlooking Fortuneswell, and Chesil Beach. The memorial will comprise stone blocks carved to depict the 850 species made extinct since 1662. DCC cabinet member for environment Robert Gould said: "This is an imaginative and ambitious project which has attracted national and international support.

"We have agreed strictly limited funding from our existing special projects budget and it is right that at this difficult time for public finances we focus our efforts on projects that will bring in significant private and charitable investment to benefit our local community."