Reconstruction of the Jurassic conifer Sewardiodendron laxum (Taxodiaceae)

Abstract

Compressed seed cones and pollen cones of Sewardiodendron laxum are described from the Middle Jurassic of Yima, Henan, central China. They are either organically attached to or associated with leafy shoots. Seed cones are terminally borne. Each cone is ovate to elongated, up to 6.5 cm long and 3.5 cm wide, and consists of a stout axis and numerous helically arranged bract-scale complexes. The bract protrudes beyond and is partially fused with the reduced ovuliferous scale. The ovuliferous scale bears approximately six inverted, small, and flattened seeds. Pollen cones are borne in terminal clusters. Microsporophylls are helically arranged, each bearing three abaxial, basally fused pollen sacs. Pollen is assaccate, rounded, and with an inconspicuous pore. Morphological, structural, and cuticular features of seed cones, pollen cones, and leafy shoots of S. laxum are compared with those of fossil and extant conifers. S. laxum is included in Taxodiaceae and believed to have its closest affinities with a Mesozoic conifer Elatides and a group of Cunninghamia-like conifers. It is reconstructed as a half-evergreen tree that lived in a humid, warm-temperate climate.

Distribution of living Cupressaceae reflects the breakup of Pangea

“…The divergence of Cupressaceae from their sister lineage occurred >200 Ma (node 1 in Fig. 1 and Table 1; 209-282 Ma), while Pangea was still intact, matching fossil evidence of Cupressaceae in the Jurassic of Europe (Hughmillerites juddii) (35), Asia (Sewardiodendron laxum and Austrohamia acanthobractea) (32,36), and South America (Austrohamia minuta) (34). Cupressaceae diversified into seven major lineages (subfamilies) during the Triassic and Jurassic (nodes 2-7 in Fig.…”

“…The family has a well-studied fossil record going back to the Jurassic (32)(33)(34)(35)(36). Using ancient fossils to calibrate genetic distances in molecular phylogenies can be problematic, because the older a fossil is, the more likely it is to represent an extinct lineage that diverged somewhere along the line leading to the extant taxon with which it is being compared (37).…”

Voltziales y Pinales (= Coniferales) de la Formación Cortaderita (Triásico Medio), Argentina, y su implicancia en la reconstrucción de las coníferas triásicas

“…pers.). Para el Jurásico Medio a Tardío, han sido descriptos Elatides williamsonii (Lindley & Hutton) Nathorst basado en órganos reproductivos de la fl ora de Yorkshire (Harris, 1943(Harris, , 1979; Sewardiodendron laxum de China, que incluye conos megasporangiados en conexión orgánica con ramas foliosas (Yao et al, 1989); y Hughmillerites Rothwell, Stockey, Mapes & Hilton, 2011, de Escocia, representado por conos megasporangiados permineralizados.…”

The in situ Glyptostroboxylon forest of Hoegaarden (Belgium) at the Initial Eocene Thermal Maximum (55 Ma)

“…Evidence for Cunninghamia-type fossils occurs as early as the Middle Jurassic with several genera of permineralised seed cones, some wood pieces and compressed vegetative and fertile remains (Yao et al, 1998, and references therein). The earliest fossil identi¢ed as Cunninghamia dates back to the Hauterivian^Barremian (middle Early Cretaceous) of Inner Mongolia (Kester, 2000) but fossil cones most similar to those of Cunninghamia are known to occur in the Lower Cretaceous beds of California (Miller, 1974).…”