450 FOSSIL PLANTS/Gymnosperms resemble cones, and they were borne at the tips of leafy branches The major difference between the cones of true conifers lies in the nature of the structure that bore the ovules The ovule-bearing scales are attached to a short shoot rather than directly to the bract as in conifers This condition is interpreted as intermediate between the fructifications of Cordaitales and the cones of Coniferales, to which Voltziales are clearly closely related Coniferales (Triassic to Recent) This major group of gymnosperms contains some 537 living species classified into 69 genera and families (Pinaceae, Podocarpaceae, Araucariaceae, Phyllocladaceae, Sciadopityaceae, Cephalotaxaceae, Cupressaceae, Taxaceae, Taxodiaceae) Most living members are medium to large evergreen trees, but the group contains shrubs and one rare parasitic species (Parasitaxus, Podocarpaceae) Several extinct family level units are recognized, of which the best known and most diverse is the Mesozoic Cheirolepidiaceae The leaves of conifers are on the whole simple, needle-shaped or flattened and strap-shaped and more rarely ovate-lanceolate-elliptical Pollen and ovules are produced in cones, except for Taxales in which single ovules terminate branches Araucariaceae ($32 living species) have a tropical– subtropical Old World distribution, but they are absent from Africa This is an ancient family that probably originated during the Late Permian Araucariaceae had a much wider geographic distribution during the Mesozoic in both southern and northern hemispheres (Figure 11) Cephalotaxaceae ($12 living species) are plants of temperate to subtropical south-east Asia They have a fossil record that extends possibly as far back as the Triassic Cupressaceae ($125 living species) is a cosmopolitan group Leaf shoots assignable to this family have been described from the Early Jurassic The extinct Cheirolepidiaceae range from Triassic to Mid-Cretaceous These were probably mostly trees with scale-like foliage of the Cupressaceae type (Figure 12) They produced a distinctive type of pollen called Classopollis Pinaceae ($200 living species) are almost exclusively northern hemisphere This is the largest living family of Coniferales The fossil record of Pinaceae might extend back into the Triassic, but it seems likely that the crown group began to diversify comparatively late during the Cretaceous period Podocarpaceae ($125 living species) are tropical–subtropical mostly montane conifers of the southern hemisphere This ancient family is first documented in the Late Triassic The monotypic Sciadopityaceae is confined to temperate south-east Asia A Late Cretaceous or Palaeocene origin of this group seems likely Taxaceae ($20 living species) occur mainly in the northern hemisphere The earliest fossils are Early Jurassic Taxodiaceae ($16 living species) are mainly northern temperate—subtropical This family is known from the Jurassic (Figure 13) Fossils leaves in the form genus Elatides are most like living Cunninghamia Much fossil wood of Mesozoic age is assignable to the Coniferales Glossopteridales (Permian to Triassic) This is an extinct group of Gondwanan gymnosperms Over 50 species have been described based on leaf morphology Many of these are probably variants of Figure 11 Silicified cones of Araucaria mirabilis (Upper Jurassic, Cerro Alto, Santa Cruz, Argentina) Specimen on right cut and polished to reveal inner structure