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THE FIRST IN SITU TURTLE CLUTCH FROM THE CRETACEOUS TIANTAI BASIN, ZHEJIANG PROVINCE, CHINA
The first in situ turtle egg clutch reported from China comes from the Lower Cretaceous (Albian) Liangtoutang Formation in the Tiantai Basin, Zhejiang Province. This clutch originally contained a minimum of 27 eggs, but four eggs separated from the clutch during excavation. The spherical eggs vary from 34 to 52 mm in diameter. The eggshell is 0.7–1.0 mm thick and has straight, narrow shell units with parallel margins and a height-to-width ratio of 2.5–3:1. Two eggs from this clutch previously were used to establish the new oogenus and oospecies Tiantaioolithus jiangi Fang et al., 2003, within the oofamily Testudoolithidae Fang et al., 2003. Based on our examination of all available eggs from this clutch, we propose the following: (1) Testudoolithidae Fang et al., 2003, is a junior homonym for Testudoolithidae Hirsch, 1996; (2) Tiantaioolithus Fang et al., 2003, is a junior subjective synonym of Testudoolithus Hirsch, 1996; and (3) the eggs pertain to a distinct oospecies, namely Testudoolithus jiangi (new combination). A previously unreported, isolated egg from the Upper Cretaceous (stage unknown) Chichengshan Formation in the Tiantai Basin is also referred to Testudoolithus jiangi based on its similar size, shell thickness, and shell unit height-to-width ratio; this specimen thus extends the fossil record of this oospecies into the Late Cretaceous. Taphonomic assessment of the egg block suggests that the egg clutch was buried in the substrate in a manner similar to modern turtles. The large, spherical eggs and large number of eggs in the clutch indicate the eggs were laid by a turtle taxon of large body size. The thick eggshell and sparse pores penetrating the shell indicate adaptation for a relatively arid, terrestrial environment.
Testudoolithus jiangi eggs from the Tiantai Basin, China. A, sandstone block containing ZMNH M8713, a partial clutch with 23 turtle eggs from the Lower Cretaceous (Albian) Liangtoutang Formation; scale bar equals 10 cm. B, close up of part of ZMNH M8713 showing three layers of superimposed eggs; scale bar equals 1 cm. C, SEM of eggshell ES137, sampled from one egg in clutch ZMNH M8713 (see Fig. 2A); scale bar equals 400 m. Sediment overlies the outer surface of the eggshell near the top of the image. White triangles indicate parallel shell unit margins and the black arrow indicates dissolution of the inner eggshell surface. D, isolated egg TM 006, from the Upper Cretaceous (stage unknown) Chichengshan Formation; scale bar equals 5 cm. E, thin section of eggshell from TM 006 under crossed polars; scale bar equals 100 m. A calcite-filled pore (P) is visible near the lower right edge of the image and evidence of diagenetic alteration along adjacent shell unit margins is visible near the left side of the image. Triangles and arrow as in Figure 2C.