Deserts and semi-deserts are vast open spaces, with sandy, pebbly, or clay soil. The main distinguishing features of these corners of the Earth are the extremely low amount of average annual precipitation (rain) and high temperatures. Within a single day, the temperature can vary dramatically. In deserts, unbearable heat can prevail during the day (above +50°C), and frosts may occur at night (temperature drops below 0°C). There can also be significant temperature variations throughout the year. In semi-deserts, the temperature fluctuations are not so drastic, and the level of precipitation is higher.

Extreme conditions significantly affect the local flora and fauna. Vegetation in semi-deserts is typically sparse, and in deserts, it may almost completely be absent. It is difficult to definitively say which plants existed in the Paleogene desert. After all, in deserts, plant remains have virtually no chance of preservation. Perhaps for this reason, no reliable fossil remains of such t...