The conifer family Cheirolepidiaceae (sometimes called Hirmeriellaceae) was one of the most important and widespread groups of the Mesozoic, despite being entirely extinct today. These conifers first appeared in the Triassic and survived into the Paleocene in some regions. They are united by their distinctive pollen type, Classopollis, which is so common in fossil deposits that it’s used to identify ancient warm-climate environments. Members of this family were highly variable in form. Some were small, shrubby plants, while others grew into large trees with broad, spreading crowns. Many had cypress-like branching and bore tiny, scale-like leaves, an adaptation likely tied to water conservation in dry environments. Although they occurred in a wide range of habitats, including lowland swamps and floodplains, Cheirolepidiaceae seem to have had a particular affinity for warm, arid climates. Around the Tethys Sea, they were dominant components of coastal ecosystems, giving rise to the term “Classopollis belt” to describe this distinctive dry-climate biome. In many Jurassic and Cretaceous floras, these conifers were among the most common trees, often forming the backbone of semi-arid plant communities long before the rise of modern flowering plants.