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.
Tens of thousands of undocumented migrants, mostly Haitians, have arrived in recent months in southern Mexico, heading north in search of a new life in the United States.
In Nicaragua, governed with an iron fist by Daniel Ortega, official coronavirus figures do not reflect the reality of a population scrambling to find oxygen tanks for stricken loved ones.
Mexican authorities have arrested more than 147,000 undocumented migrants already this year -- three times more than in the same period of 2020, according to the National Migration Institute.
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.
Nicaragua accused Colombia of openly defying judges at the UN's top court in a bitter decades-long legal battle over maritime borders.
U.S. Americans not fully vaccinated will still be able to enter but only on testing negative within a day of travel.
Maduro showed up at the last minute at a one-day meeting of the 33-member Community of Latin American and Caribbean States, or CELAC.