"And geoscience consultant Allen West added: "If the particles had gone through the skin, they may not have made it through to vital organs; but this material could certainly have blinded the animals and severely injured them."

The mammoth and bison remains all display small (about 2-3mm in size) perforations.

Raised, burnt surface rings trace the point of entry of high-velocity projectiles; and the punctures are on only one side, consistent with a blast coming from a single direction.

Viewed under an electron microscope, the embedded fragments appear to have exploded inside the tusk and bone, say the researchers. Shards have cut little channels.

The sunken pieces are also magnetic, and tests show them to have a high iron-nickel content, but to be depleted in titanium.

The ratios of different types of atoms in the fragments meant it was most unlikely they had originated on Earth, the team told the AGU meeting. "