Systematic progress has been made in the study of trichoid pollen in the Late Cretaceous

Trichophyllum pollen is a unique, complex form of angiosperm pollen characterized by protrusions at three equatorial positions. It flourished mainly in the Late Cretaceous and is now completely extinct. The pollen flora of the Northern Hemisphere of the Late Cretaceous can be divided into a normal powder area and an eagle powder area represented by a trifoliosis. The northeast region of China belongs to the eagle powder area, and there are a large number of tri-protruding pollen fossils. This type of pollen has obvious morphological characteristics, high degree of differentiation, short geological delay and rapid evolution, and has important research and application significance in the division and comparison of Cretaceous on the continental facies, paleoecology and paleoclimate.

However, the complex morphological characteristics of trichoid pollen make observation difficult, and morphological description and measurement are highly confusing. Therefore, it has systematically caused a chaotic situation of classification confusion and unclear classification of genera and species, which has seriously affected its application in stratigraphy, paleoecology and paleogeography.

Recently, Wu Yixiao, a doctoral candidate at the Nanjing Institute of Geology and Paleontology of the Chinese Academy of Sciences, and Li Jianguo, a supervisor, have carried out detailed research on trifoliate pollen based on the fossil pollen material of Songke 1 in the Songliao Basin, and made a series of new progress in morphology, systematic classification, evolution and distribution. The results have been published in the famous journal Ofgrana, a well-known journal for the study of the international systematic classification of plants, and Cretaceous Research, a journal of comprehensive geological research.

The scientific drilling of Pine 1 well in the Songliao Basin is highly studied, and a high-precision chronopatric stratigraphic framework has been established, which provides superior conditions for studying the classification and evolution of trilodon pollen. Using single-particle pollen microscopic imaging technology, the researchers observed and counted the tri-erection pollen fossils of a total of 101 samples from Pine family 1 well through optical microscopy, scanning electron microscopy and transmission electron microscopy, and clarified the morphological characteristics of tri-erection class shape, polarity, germination device, ornamentation, wall layer and so on.

In view of the confusion in the morphological description of the three protrusions in the past, unclear meaning of terms, and unclear measurement methods, a set of clear morphological academic terms and measurement specifications is proposed. On this basis, 39 fossil pollen genera associated with trichotics were evaluated globally, and a total of 31 genera with late allogeneic synonyms and those that did not belong to trichophyllum were excluded. After the necessary revisions, 8 genera were finally retained under the trichoctor class, and a taxonomic identification system was established for these genera.

The researchers also studied in detail the species composition of the trichoid genus and the geological history development of each genus in the Pine family 1 well, and identified the five evolutionary stages of trichophyllum occurrence, radiation, steady development, extreme prosperity and gradual extinction in the Songliao Basin. Its morphological evolutionary tendencies are manifested in the enlargement of individuals, the thicker and more complex ornamentation, and the emergence of special structures.

These advances can lay a good foundation for further study of the taxonomy, evolution and stratigraphy of trichoids, and will also greatly promote the classification and comparison of this pollen taxon in the global continental Cretaceous and its application in paleoecology, paleogeography and other fields.

Fig. 1 SEM and TEM photos of representative ornaments of the three protrusions

Figure 2 Species diversity of trichoticoids in the Songliao Basin

Figure 3 Species evolution path of trichophyllum in the Songliao Basin

The related research has been jointly funded by the Strategic Pilot Science and Technology Project of the Chinese Academy of Sciences and the National Natural Science Foundation of China. (Source: Nanjing Institute of Geology and Palaeontology, Chinese Academy of Sciences)

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