In Eastern Antarctica, seed ferns or pteridosperms became abundant and large amounts of sandstone and shale were laid down at this time. Synapsids, commonly known as “mammal-like reptiles”, were common in Antarctica during the Early Triassic and included forms such as Lystrosaurus. The Antarctic Peninsula began to form during the Jurassic period (206–146 Ma), and islands gradually rose out of the ocean. Ginkgo trees, conifers, bennettites, horsetails, ferns and cycads were plentiful during this period. In West Antarctica, coniferous forests dominated through the entire Cretaceous period (146–66 Ma), though southern beech became more prominent towards the end of this period. Ammonites were common in the seas around Antarctica, and dinosaurs were also present, though only three Antarctic dinosaur genera (Cryolophosaurus and Glacialisaurus, from the Hanson Formation,[63] and Antarctopelta) have been described to date.[64] It was during this era that Gondwana began to break up.
Source: Antarctica – Wikipedia
Tim B.
https://oceanwide-expeditions.com/blog/the-ancient-fossil-forests-of-antarctica
“Antarctic coniferous trees
In a small part of Alexander Island, on the west coast of the Antarctic Peninsula, ancient fossil trees that date back 100 million years can be found, with logs up to seven metres high (23 feet) still found standing upright. The roots of these coniferous trees are still attached to the carbonaceous soil deposits today. Their root systems indicate that these trees thrived on the rich plains alongside large meandering rivers. However, the coarse sand that buries the trunks shows the power of floods in the area that eventually covered the whole plain in thick sediment. Fossilised leaves found in the area show that there was a large diversity of plants that once lived there. In fact, the area was dominated by evergreen species and had a temperate rainforest at about 75°S, while today this latitude is cold and frozen. 100 million years ago, despite a winter that witnessed around 70 days of darkness, the forests were thriving in much warmer conditions. The warmth came from the size of the landmass, with Gondwanaland keeping away the cold currents that today encircle Antarctica. Researchers have found that the floodplains in the area were covered with ferns, small podocarps, and conifers. On the coastal plain, the open canopy forests were thick with conifers and ferns.”