This would have coincided with the mass extinction of other
mega-fauna that occurred in North America at the end of the
Pleistocene; a period of biodiversity loss which has been blamed in
part on humans and their novel spear technologies at the time.
But analysis of fossil bones found in the Sante Fe River,
Florida, which are thought to represent the last known T walleri,
suggests the terror bird had disappeared long before this.
"The last occurrence of Titanis, as far as we know it, dates to
about two million years ago. It didn't persist into the last ice
age," Professor MacFadden said.
Hitch a ride?
Dating of another fossil in Texas - the earliest known example of
a terror bird in North America - also yielded a surprising result
for the team.
Most researchers thought the big bird had migrated from South
America to North America after the two continents had become
connected by the Panamanian land bridge about 3.5 million years ago,
explained Professor MacFadden.
"But based on the new chemical dates that we have established,
that previous hypothesis is no longer correct," he added.
"What we now believe, based on the age of the Titanis from Texas,
is that Titanis dispersed from South America into North America
about five million years ago, significantly earlier than the land
He said the researchers did not yet know how the flightless beast
could have crossed unconnected continents.
"Did it swim across? Or did it raft across on a float? There were
a series of closely spaced volcanic islands, which now forms Panama,
so maybe it swam from one to the other - but we really don't know,"