The earliest evidence for conifer biology reveals specializations for water stressed environments, but otherwise suggests that conifer reproduction was essentially comparable to contemporaneous primitive seed plants of wetland communities. Microgametophytes were monosaccate, and germinated from a proximal suture. As a result, microgametophytes are thought to be similar to those of living heterosporous free-sporing pteridophytes. From a close conifer relative, there is evidence that a pollination mechanism like that of several genera of the Pinaceae was present in Pennsylvanian age conifers. The micropyle of the ovule apparently did not close after pollination. Rather, seeds had a large pollen chamber that may have functioned as the post-pollination sealing mechanism. Embryos were polycotyledonary and at least one species displays postzygotic quiescence, an early form of seed dormancy. By the Permian the pollen of some species was bisaccate, and in other species no inflated saccus was produced. Many Triassic species were characterized by pollen germination from a proximal suture, and this may signal the origin of modern microgametophyte development. As is common in living conifers, seeds from Mesozoic strata show evidence for post-pollination sealing of the micropyle. The earliest evidence for pollen tubes is known from Jurassic Araucariaceae, but occurrence of this character in a Pennsylvanian age gymnosperm suggests that some Paleozoic conifers could have produced either haustorial or simphonogamous pollen tubes. Pollen cones, germinating pollen grains, seed cones, seeds and embryos from Jurassic deposits reveal that essentially modern forms of conifer reproduction were present in some living families by the mid-Mesozoic.

Key words: embryology, evolution, fossil, pollination, reproduction