Overview
- Researchers published the study in Science, reported Thursday, July 30, 2026, after nearly doubling the known Mexican mammal fossil record by adding Spanish‑language papers, small journals, and museum samples.
- The team found that between about 10 million and 7 million years ago many North American mammals moved into lowland southern North America and Central America and diversified in place before traveling farther south.
- Regional climate change toward drier, more seasonal conditions in that interval favored traits such as larger body size and aridity tolerance that later helped those mammals establish in South America.
- When the Isthmus of Panama formed around 2.8 million years ago, pulses of exchange followed and more than half of the 217 mammal genera now in South America trace their origins to the north, the study reports.
- By showing how better sampling and inclusion of non‑English sources change the record, the work revises the long‑held view that adaptation mainly ran south to north and highlights how language and collection gaps can skew big evolutionary stories.