Abstract

Premise of research. Exceptionally well-preserved lignified fossils from the Early Cretaceous of Mongolia include abundant conifer leafy shoots with attached pollen cones and seed cones. A whole-plant reconstruction based on these fossils enables a critical evaluation of the relationship of this extinct plant with extant conifers.

Methodology. Bulk lignite samples collected from the Tugrug lignite mine were disaggregated in water, cleaned with hydrochloric and hydrofluoric acids, washed, and dried in air. Fossils were then examined using light and scanning electron microscopy.

Pivotal results. Elatides zhoui sp. nov. has helically arranged leaves with two narrow lateral stomatal bands, predominantly on the adaxial leaf surface. Pollen cones are usually borne laterally on shoots in tight spirals; each microsporophyll bears three pollen sacs that produce nonsaccate pollen with a small circular aperture. Seed cones have numerous bract-scale complexes, each with a small membranous ovuliferous scale and four to six seeds. Elatides zhoui is the most completely understood of all described Elatides species, and major features of seed cone and pollen cone morphology indicate that it is most closely related to extant Cunninghamia, which today has two species restricted to East Asia. Morphological cladistic analyses using parsimony resolved an expanded Cunninghamioideae clade, which includes extant Cunninghamia, E. zhoui, and other Cunninghamia-like fossils, as the sister group to all other extant Cupressaceae sensu lato.

Conclusions. Elatides zhoui provides further evidence for the diversity of Cupressaceae sensu lato during the Cretaceous and supports the hypothesis that cunninghamioid conifers in particular were diverse and widespread during the early evolution of the Cupressaceae.