I saw this cool fossil at the Museum of Natural History in the city of Prague in the Czech Republic. The large fossil (left panel) is that of a plant whose scientific name is Cordaites borassifolius. The plant was part of a tropical forest that was covered by ash during the eruption of a volcano 309 million years ago in what is now the Ore Mountains in Central Europe. What is remarkable about the fossil is the well-preserved impression of a spider (white arrow in left panel, and right panel) that was on one of the leafs of the plant when they both perished during the eruption. The spider was identified as a species of Palaranea borassifoliae. Both the plant and the spider are now extinct and only found as fossils.
The pictures belong to the author and can be used with permission.