Jurassic Plants of Sardinia: an overview witn new data

The Jurassic flora of Sardinia is the largest Middle Jurassic Flora of Italy. Fossil plants coming from various levels of the Genna Selole Formation and from the lower part of the Dorgali Formation (Dieni et al., 1983; Costamagna and Barca, 2004; Scanu et al., 2012), and the better-preserved series are located in the Tacchi Area (central-eastern Sardinia). These fossiliferous levels contain the most abundant Jurassic species of Sardinia (Scanu et al., 2012) and are distributed over a wide area, representing lacustrine-fluvial to coastal transitional environments. The updated list of the Bajocian-Bathonian flora consists of 18 genera belonging to seven divisions. The flora is dominated by well-preserved cycadophytes. Conifers, ginkgophytes and ferns are abundant, while seed ferns and horsetails are rare. The horsetails are represented only by some fragmentary stem impressions with distinct vascular bundles and nodes. The ferns belong to five genera. Some frond fragments with a basal dichotomy belong to the genus Phlebopteris, and particularly to the species P. polypoidioides. The pinnules are narrow and totally or broadly attached to the rachis. Todites cf. williamsonii shows bipinnate frond fragments with grooved midribs. The Cladophlebis sp. fronds are bipinnate with smooth-edged pinnules. In Hausmannia sp. a wedge-shaped structure with marked midribs are present. From the midrib, secondary veins arise and form rectangular or square meshes. Two species of Coniopteris have been identified in the flora: C. simplex shows elongated, narrow pinnules whilst in C. hymenophylloides the pinnules are broad and with a rounded apex. Two different genera of seed ferns have been identified as well, Sagenopteris and perhaps Ptilozamites. Sagenopteris sp. has leaflets with a marked midrib, while Ptilozamites show rhombic to slightly falcate segments inserted laterally to the rachis. In particular, Ptilozamites has thick cuticle with isodiametric cells. Cycadophytes are the most represented plants in the Middle Jurassic of Sardinia and at least seven genera are present. Fragments of Nilssonia have parallel and undivided secondary veins. The leaves are hypostomatic and epidermal cells are sub-rectangular to polygonal with straight anticlinal walls. Another cycads, Pterophyllum cf. thomasi, shows elongated segments with parallel veins and slightly expanded bases. The genus Ptilophyllum is present perhaps with two species and a detailed cuticular analysis, in progress, will confirm the presence of P. pectinoides and of another new species. Taeniopteris sp. shows leaves with a typical taeniopterid venation arising from the thick midrib. Impression fossils with a round-oval shape and a scale-like structure belong to the genus Cycadeospermum. Lastly, Williamsonia hildae includes bennettitalean female fructifications with a gynoecium showing a minutely reticulated surface surrounded by interseminal scales; Weltrichia sp., the male fructification, has cup-like structures with extensive lobes. Czekanowskiales count the only species Czekanowskia cf. furcula whereas conifers are well-represented in the flora with 3 genera: Brachyphyllum (with at least 2 species), Geinitzia sp. and Elatocladus sp. Furthermore, seeds of Carpolithes sp. have also been found. In summing up the flora shows a high biodiversity. Additionally, the Jurassic of Sardinia shows analogies with the other European floras of the same age, particularly with the Yorkshire Middle Jurassic flora wherewith shares 14 genera of plant fossils.