The footprints were left in mud on the banks of a long-since dried up lake, which is now part of a New Mexico desert.
Many migrants have died trying to cross the area linking South and Central America. Conditions are difficult.
U.S. Americans not fully vaccinated will still be able to enter but only on testing negative within a day of travel.
Reduced agricultural production, water scarcity, rising sea levels and other adverse effects of climate change could cause up to 216 million people to migrate within their own countries by 2050.
Weather-related disasters have skyrocketed over the past half-century, causing far more damage even as better warning systems have meant fewer deaths, the UN said.
The European Union on Monday recommended that its member states reimpose travel restrictions on US tourists over rising covid infections in the country.
The seven Cocle Parita- and Cocle Conte-style pottery vessels claimed by the country are among more than 300 pre-Hispanic objects from Mexico, Guatemala, Costa Rica, Panama, Bolivia and Peru.
The first space tourism mission by Elon Musk's SpaceX blasted off from Florida on Wednesday and the four crew members -- a billionaire and...