DIVERSITY OF ANCIENT CONIFERS: THE JURASSIC SEED CONE BANCROFTIASTROBUS D1G1TATA GEN. ET SP. NOV. (CONIFERALES)

摘要

Premise of research. A third genus of anatomically preserved conifer seed cones has been recognized from a Late Jurassic deposit in northeastern Scotland. This cone is described as Bancroftiastrobus digitata Rothwell, Mapes, Stockey et Hilton. Methodology. The cone was sectioned with the classic coal ball peel technique and studied and photographed with transmission light. Pivotal results. Bancroftiastrobus digitata is a cylindrical cone with large, helically arranged ovuliferous scales subtended by short bracts, each bract/scale complex bearing two unwinged inverted seeds on the adaxial surface of the ovuliferous scale. Ovuliferous scales have abaxial plications in the midregion and divide distally, forming up to nine free distal lobes that are vascularized and covered by a dense ramentum of trichomes. The cone axis forms a continuous woody cylinder that surrounds a parenchymatous pith. There are numerous resin canals in the cortex of the cone axis that extend into each bract/scale complex, both abaxial and adaxial to the vascular traces. Vascular tissue to the bract diverges as a prominent terete bundle that separates from the stele immediately below a large inverted-U-shaped scale trace. More distally, the scale trace flattens and divides into a single row of C-shaped woody bundles. Conclusions. This new genus provides additional evidence for the diversity of stem group conifers that lived during the interval when most crown group conifer families originated. The new species is reminiscent of both Sciadopityaceae and Pinaceae. However, like the three anatomically preserved species of Pararaucaria Wieland (Cheirolepidiaceae), this cone does not clearly conform to any family with living species. Rather, these taxa have novel combinations of characters that make fossils vital for resolving deep internal nodes of the seed plant tree and that help to resolve the overall pattern of phylogeny.