ON THE MOPHOLOGY,MEASUREMENT AND DESCRIPTION OF TRIPROJECTACITES

Triprojectacites Mtchedlishvili, 1961 emend. Stanley, 1970 is a group of angiosperm pollen with great significance in the Late Cretaceous and Paleocene stratigraphy and palynofloristic biogeography in the Northern Hemisphere. Their extreme complexity in morphology makes it very difficult in measuring and describing these pollen. There is no clear and uniform standard so far, which as a result hampers the progress on the classification of Triprojectacites.Triprojectacites is diagnosed by three or occasionally four to five projections with colpate apertures, which excludes tricolporate types from this group. The equatorial zone, where projections grow from body, divides the body into two parts, which determine the polarity of the pollen grain(Fig. 1). The initiation area of projections from the body is called the base of projection while the distal part at the opposite direction is called the terminal of projection.Based on the observation of a large number of specimens from the Cretaceous strata in the Songliao Basin, northeastern China, a standard of measuring methodology of Triprojectacites is here proposed. Base Point(B) of projection is defined as the beginning of the endexinous thickening along the projection, which marks the border between projection and body. Similarly, Distal Point(D) of the endexinous thickening represents the base of terminal of a projection. These referring points, together with Tip Point(T) of projection and two poles(P), provide the basis for an accurate implementation of the following measurements(Fig. 7), i. e. length(h) and width(w_b) of body, length of distal(h₁)and proximal(h₂) body, length(l_p) and width(w₁) of projection, terminal width of projection(w₂) and length of endexinous thickening(w_t).Based on these measurements, six mathematical indices are designated for evaluating the morphology of body and projection. Length-width ratios of body(R_b) and projection(R_p) can describe the shape of body and projection. Width Index of projection(WI=w₁/h) and Length Index of projection(LI=l_p/w_b) can tell if the projection is robust or not as compared to body. Reduction Rate of projection(R_r) reveals the narrowing gradient from the base towards the terminal of a projection. Polarity Index(PI=h₁/h₂ shows how much projection is deviated away from the center of the body. The last index has an advantage in avoiding the interference of the angle and width of projection.With the assistance of the indices above, body can be divided into different types of shapes as cylindrical, ellipsoidal, biconical, or diamond-shaped and projection can be described as slat-like, lingulate, ear-like, or lanceolate. Also, specimens preserved at different position, e.g. in polar view and equatorial view, can be well compared.These description terms and indices and their measurement methodology will provide a significant contribution to the establishment of a scientific and reasonable classification system for Triprojectacites.

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