The Wet Tropics contains one of the most complete and diverse living records of the major stages in the evolution of land plants, from the very first land plants to higher plants (gymnosperms and angiosperms), as well as one of the most important living records of the history of marsupials and songbirds.
The Wet Tropics contains a unique record of a mixing of two continental floras and faunas, following the collision of the Australian and Asian continental plates about 15 million years ago. Two different evolutionary linages of flora and fauna mixed while some of these linages had been largely separated for at least 80 million years after coming from a common origin.
Components of Wet Tropics rainforests are surviving fragments of the primordial Gondwana forests and are among the oldest tropical rainforests on Earth. The earliest known terrestrial plant forms were from the Silurian period more than 400 million years ago. These were spore-producing plants which reached their greatest development 100 million years later during the Carboniferous period. The range of ancient evolutionary groups of ferns and fern allies such as fork ferns and tassel ferns occurring in the Wet Tropics is equalled only in the more extensive New Guinea rainforests that were once linked with those of the Wet Tropics.
The origin of seed plants over 320 million years ago was one of the most significant events in the evolution of terrestrial vegetation - an adaptive breakthrough that allowed colonisation of habitats that were inhospitable to spore-producing plants. The cone-bearing cycads and southern conifers (gymnosperms) are amongst the most ancient of living seed plants, little changed from ancestors that flourished in the Jurassic period between 136 and 195 million years ago. The closest modern counterpart of these Jurassic forests, such as the archaic Australian endemic Araucarians, occur in the Wet Tropics. For example, the World Heritage Area retains three species of Agathis, the kauri pines, two of which are endemic to the Wet Tropics.
The emergence of the flowering plants (angiosperms) some 200 million years after the first appearance of the gymnosperms marked the beginning of one of the most fundamental changes in biological diversity on this planet. By the late Cretaceous period, gymnosperms had largely been replaced by angiosperms. Catastrophic events around the Cretaceous–Tertiary boundary (70 million years ago) led to major biological extinctions, with the loss of an estimated 75 percent of all living species. This mass extinction was most pronounced in the northern hemisphere. However, East Gondwana (Australia, New Zealand and New Guinea) in the southern hemisphere was relatively unaffected and, consequently, the highest concentrations of Cretaceous angiosperm families survived in that region, many of which were still present on the Australian landmass when it finally broke away from Antarctica. Today, the highest concentration of primitive, archaic and relict taxa relating back to the origins of flowering plants survive in the Wet Tropics.
The Wet Tropics contains 16 of the 28 primitive angiosperm lineages. One of these 16 primitive dicot plant families is only found here in the Wet Tropics (Austrobaileyaceae). Five of the plant genera within these 16 dicot families are endemic and each is represented by one species only (is monotypic):
See A Re-evaluation of Queensland's Wet Tropics based on Primitive Plants for details.
Please note that the Queensland Herbarium still recognises Idiospermaceae as a family in it own right (instead of Calycanthaceae), which means that sometimes people may say that Wet Tropics has two endemic families. The two herbariums agree on the five endemic primitive (near-basal) genera with the five endemic species.
You can read all about the evolution of plants and animals in the updated World Heritage nomination (2002).
You can read all about ancient, threatened and endemic flora of the Wet Tropics in the State of Wet Tropics Report 2013-2014.