Abstract
Previously, the identification of fossil Pseudolarix at the species level has been based on the morphology of the bract-scale complex of the seed cone. The morphological consistence of fossils through most of the Cenozoic with extant P. amabilis has led them to be considered conspecific, suggesting that P. amabilis is an extraordinary example of morphological stasis. However, the lack of cuticular evidence, especially for the leaf-homologous bract, reduces the accuracy of fossil identification based on morphology, thus weakening the evidence for morphological stasis in P. amabilis. For the first time, we provide cuticular evidence of the bract-scale of fossil P. amabilis based on the bract-scale complex from the late Miocene Shengxian Formation, Zhejiang, East China, which improves the identification accuracy and reinforces the concept of morphological stasis in this species. Second, we preliminarily reveal the niche stability of P. amabilis, which corresponds to its morphological stasis. Finally, we infer that the late Miocene forest containing P. amabilis in Zhejiang was an evergreen sclerophyllous broad-leaved or mixed mesophytic forest, which combined with the evergreen broad-leaved forest suggested by previous megafossil studies, indicates the occurrence of vertical vegetation zonation.
Highlights
Today, Pseudolarix Gordon (Pinaceae) is a monotypic genus represented by the single species P. amabilis (Nelson) Rehder [1]
The described fossil bract-scale complexes were collected from the Shengxian Formation outcrop near Jiahua village, Tiantai County, Zhejiang, East China (29.2 ̊N, 121.2 ̊E; Fig 2). 40Ar-39Ar dating indicates the age of the Shengxian Formation to be 10.5±0.5 Ma [18]
The bract-scale complexes of conifers are persistent or deciduous after seed cone maturity [19], and the fossil bract-scale complexes studied here appear individually and integrally, which implies that the complexes are originally deciduous
Summary
Pseudolarix Gordon (Pinaceae) is a monotypic genus represented by the single species P. amabilis (Nelson) Rehder [1]. The unique biological features of Pseudolarix that distinguish it from other members of the Pinaceae are its combination of deciduous bract-scale complexes and needles and branch dimorphism. The dimorphic branching system is characterized by needles borne helically in long shoots (leading shoots) and fascicularly in short shoots (brachioblasts) [1]. As an endemic genus to China, Pseudolarix is highly restricted to the lower Yangtze River valley in Southeast China [1, 2], whereas the geographical distribution of fossil Pseudolarix is much wider (Fig 1). Pseudolarix fossils are preserved as seed cones, seeds, needles, wood, brachioblasts and pollen and have been widely reported geographically from Eurasia and North America and stratigraphically from the late Jurassic to the Pleistocene (Fig 1). The earliest Pseudolarix (Pseudolarix sp.) fossil was found in the upper Jurassic (ca. 156 Ma)
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