Sprecher
Beschreibung
Leaf-wax n-alkane concentrations and average chain lengths (ACL) significantly vary among extant gymnosperm groups. When investigating deep-time archives, further plant groups need to be considered that since went extinct. Also, entirely aquatic plants, as known in the angiosperm clade, are not known to be amongst any fossil or extant gymnosperm group. The Middle to Late Jurassic macroplant assemblage preserved in the volcanic lake deposits of the Haifanggou Formation in Inner Mongolia, China, and attributed to the Yanliao Fossillagerstätte, reflects such a gymnosperm-dominated environment, amongst which the extinct Bennettitales constituted the dominant seed-plant component, with ginkgophytes and cupressoid conifers as additional major components. This fossil environment existed c. 40 million years prior to the rise of the angiosperms. The current study examines the relative n-alkane concentrations preserved in 33 samples from two excavations in the Haifanggou Formation. Despite the high age of the sampled strata, n-alkane preservation is excellent. In addition, the two excavations yield mean ACL25–37 values of 28.2 and 27.8, respectively, and the n-alkane distributions are dominated by n-C27 alkanes and, in some samples, by n-C25 alkanes. Thus, given that Bennettitales were the dominant plant group in the assemblage, we hypothesize that bennettitalean cuticles were composed of n-alkanes with shorter chain lengths than that of extant gymnosperm groups. To test this hypothesis, further verification is required involving the direct analysis of well-preserved fossil bennettitalean cuticles.