Whole-plant reconstruction of a Triassic voltzialean conifer from Antarctica

BOMFLEUR, BENJAMIN; DECOMBEIX, ANNE-LAURE; ESCAPA, IGNACIO; SCHWENDEMANN, ANDREW; AXSMITH, BRIAN

Tokyo

Congreso; International Organization of Palaeobotany Conference; 2012

Chuo University

We present a whole-plant reconstruction of a Triassic voltzialean conifer from Gondwana, based on a wealth of well-preserved material from Triassic deposits of the Transantarctic Mountains. Plant parts in compression/impression preservation include Heidiphyllum foliage, Telemachus seed cones, and Switzianthus pollen cones. Anatomically preserved taxa from permineralized peat deposits comprise Notophytum (stems, roots, and leaves) and Parasciadopitys seed cones. Associated pollen is of the Alisporites type. Evidence for the affiliation of these individual organs is comprehensive, and consists of a combination of organic connections, structural analogies, similarities in cuticles and epidermal morphologies, association/disassociation data, and palynology. The great amount of anatomical and morphological information on the individual organs enables a detailed habit reconstruction. The architecture of the plant corresponds to Rauh’s model (essentially orthotropic branching and rhythmic growth) with a modification of long- and short-shoot growth. The largest axes known exceed 20 cm in diameter. By analogy with architecturally similar extant trees (e.g., Larix), we reconstruct this Gondwanan voltzialean conifer as a 15‒ 20 m tall forest tree. The occurrence in polar latitudes during the Triassic makes is highly likely that the crown shape was predominantly vertical and narrow-conical, as this shape is known to enable a much more efficient interception of the high amount of low-angle irradiation at such high latitudes. Leaves were up to 25 cm long, strap-shaped to narrow elliptical with about 8‒ 12 parallel veins, and borne in dense clusters on short shoots. Taphonomic and anatomical data indicate that these conifers were seasonally deciduous. Of special interest is the remarkably diverse set of evidence for biotic interactions, which include odonatan oviposition on leaves, two distinct types of mycorrhizal associations, and other endophytic as well as epiphyllous fungi. Altogether, we conclude that this conceptual whole-plant genus, referred to as ‘a Telemachus conifer’, probably represents one of the most completely known fossil conifers.