How does fossil evidence of forests and freshwater organisms in antarctica show that the climate there was warmer in the past

The fossil record of Antarctica shows the presence of tropical plants, such as one particular species related to the present day breadfruit. Most plants cannot survive in prolonged temperatures of less than 6 degrees Celsius. Antarctica is freezing all year round and could only have supported tropical and sub tropical plants if it was once much closer to the equator.
The presence of fresh water species also suggest that the continent was closer to the equator. Antarctica is frozen solid with a thick ice sheetrivers would be frozen solid all year round or would be limited to water movement under glaciers that melt as a result of pressure and friction. This environment is not suitable to support large fresh water organisms.