Tsuga seed cones from the late paleogene of southwestern china and their evolutionary and paleoenvironmental implications
The Geological Society of America
The fossil record of Tsuga (Pinaceae) can be traced back to the Late Cretaceous in North America and Eurasia. However, in southwestern China, a critical region that experienced rapid Cenozoic uplifting and climate changes due to the formation of the Himalayas and the Qinghai–Tibetan Plateau, fossil record of this genus has been sparse and confined in deposits of late Miocene or younger ages. Recently, six well-preserved Tsuga ovuliferous/seed cone impression fossils were discovered in late Paleogene lacustrine beds in two localities in southeastern China: Three specimens were from the late Eocene (34.64 ± 0.8 Ma) Lawula Formation at Kajun Village, Mangkang County, eastern Tibet and the other three were from the early Oligocene (32 ± 1 Ma) mudstone at the Lühe Basin, Lühe Town, Nanhua County, Yunnan Province. These two sites are both located at the southeastern edge of the Qinghai–Tibetan Plateau, ~800km apart from each other. Based upon comparisons with seed cones of all living and fossil species of Tsuga, we established T. asiatica M. X. Wu et Z. K. Zhou sp. nov. to accommodate five specimens (two from the Kajun site and three from the Lühe site), leaving one from the Lühe site to be assigned to T. cf. dumosa (D. Don) Eichler. Both qualitative and quantitative (nonmetric multidimensional scaling) comparisons suggested that T. asiatica shares more similarities with the basal species of the genus. The establishment of late Paleogene fossil records of Tsuga in southeastern China enriched our understanding of the evolutionary history of this coniferous genus. Along with information provided by associated plants from these fossil floras, these fossil cones from deposits at the current elevations of 3,910 m above sea level (a.s.l) (the Kajun site) and 1,882 m a.s.l (the Lühe site) offer invaluable information regarding paleoenvironment and paleoclimate in this critical area. The age and location of these fossils bear strong implications to the interpretation of the uplifting of the Himalayas and the Qinghai–Tibetan Plateau and monsoonal climate system that it controls.