Morphological diversity among basal Cupressaceae: a new Austrohamia species from the Early Jurassic of Patagonia, Argentina.

CONTRERAS, DORI; ESCAPA, IGNACIO; CÚNEO, RUBÉN

Edmonton

Congreso; BOTANY 2015; 2015

The cypress family (Cupressaceae sensu lato) is well known for its high morphological and ecological diversity, as well as its rich fossil record. Recent contributions have greatly expanded our understanding of fossil taxa associated with basal extant Cupressaceae lineages, however much work remains in order to understand patterns of character evolution and basal optimization of characters for the family. Austrohamia is the earliest unambiguous representative of the Cupressaceae, known from the Early Jurassic of Patagonia and Late Jurassic in China. Here, we provide a whole plant reconstruction of a new Austrohamia species from the Early Jurassic Cañadón Asfalto Formation in Patagonia, Argentina. The specimens are preserved as impressions and charcoalified compressions in finely laminated fine-grained facies of lacustrine deposits. Vegetative specimens preserve up to two orders of branching, with ultimate shoots borne alternately and in one plane. Shoots bear univeined leaves that are dorsiventrally flattened, with decurrent bases and free distal portions that spread at angles up to 90°. The free leaf blades are lanceolate to oblong with entire margins and rounded apices. Leaves are borne helically, and on most shoots are curved at their bases so that the leaf blades are disposed approximately in one plane. Pollen cones are borne laterally in the axils of non-modified leaves, and are aggregated towards the apex of shoots to form terminal clusters of up to five cones. Pollen cones are elliptic in shape and consist of a central axis surrounded by helically arranged microsporophylls. Ovuliferous cones are terminal on ultimate and penultimate shoots, ovate-oblong in shape, and consist of a central axis surrounded by helically arranged, imbricate ovuliferous complexes. There is no evidence of structures representing discrete ovuliferous scales. Ovuliferous complexes are coriaceous, with a narrow basal portion that expands to a broadly ovate distal face with prominent abaxial keel and long acuminate apex. Each complex bears two adaxial seeds. The new taxon exhibits a novel combination of characters, differing from other known Austrohamia species most notably by having significantly larger ovuliferous cones and in lacking distinct bracts subtending the pollen cones. The new taxon shares various characteristics with other basal Cupressaceae, in particular representatives of Elatides, Cunninghamia, and Taiwania, further emphasizing the mosaic evolution of characters within the family. Using pre-existing phylogenetic hypotheses, we explore its broader implications for character evolution and relationships within the family, with emphasis on characteristics of ovuliferous cones and pollen cones.