Conifers can be traced back 350 million years (to the Carboniferous). While swamps were dominated by horsetails and seed ferns, drier uplands were host to conifer trees. Early conifers were probably only 2-3 m (about 10 feet) in height. Leaves of these early conifers were needle-like but their cones were not as compact as modern cones. By the Permian, conifers had diversified into many forms, including large, woody trees much like modern conifers. At the end of the Permian, an enormous extinction event caused a major change in land ecosystems. Many of the primitive conifers went extinct, but survivors gradually spread during the Triassic until they became dominant forest trees. The early and middle Mesozoic (about 250-130 million years ago) became the age of conifers. Like modern forms, Mesozoic conifers were large, woody plants that made seeds. With the exception of one group that went extinct (the Cheirolepidiaceae), families of Mesozoic conifers are still on Earth today.