|Frenelopsis teixierae. from Mendes et al 2010. Note similarity to pickleweed at end of post|
In visualizing what the equatorial arid belt looked like during the Mesozoic one can not ignore perhaps the most significant aspect of the flora- the extinct conifer family Cheirolepidiaceae. Now when you visualize what these plants were like, don't be limited by what your idea of conifers is in modern ecosystems. The Cheirolepidiaceae were up to some pretty wild stuff for their time.
|Paraucaria patagonika cone x-section.|
For starters they evolved a mutualistic coevolutionary pollination partnership with extinct scorpionflies (Mecoptera), thus preceding angiosperm insect pollination by over 20 million years. They also developed a wide repertoire of lifestyles including brackish water halophytic specialists, desert specialists, and probably ranged in size from small groundcover types to large trees. They were also one of the few families of conifers to thrive in both the northern and southern hemisphere but were especially dominant in the arid equator. Indeed the presence of their unique pollen, referred to as Classopolis, is often used as a proxy for arid conditions.
It is unfortunate that we do not have today any surviving species of this unique Mesozoic conifer family. But during the Mesozoic we can imagine that members of this family filled many of the niches that modern angiosperms do today- from water plants to xeric dry adapted plants. Indeed the Cheirolepidiaceae, given their insect pollination and diversity of forms, were probably the gymnosperms most like angiosperms. And this congruence ultimately is why this family may have started losing ground to angiosperms and eventually went extinct by the end of the Cretaceous.
Gomez, Bernard et al. Frenelopsis (Coniferales: Cheirolepidiaceae) and related male organ genera from the lower Cretaceous of Spain. Paleontology 2002.
Mesozoic Floras. Omnilogos. James F Basinger. Encyclopedia of Dinosaurs. Amsterdam: Academic Press, 1997.