A New Oofamily of Dinosaur Egg from the Upper Cretaceous of Tiantai Basin, Zhejiang Province, and Its Mechanism of Eggshell Formation
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Article Progress of Projects Supported by NSFC doi: 10.1007/s11434-012-5353-2 Geology SPECIAL TOPICS: A new oofamily of dinosaur egg from the Upper Cretaceous of Tiantai Basin, Zhejiang Province, and its mechanism of eggshell formation WANG Qiang1, WANG XiaoLin1*, ZHAO ZiKui1 & JIANG YanGen2 1 Key Laboratory of Evolutionary Systematics of Vertebrates, Institute of Vertebrate Paleontology and Paleoanthropology, Chinese Academy of Sciences, Beijing 100044, China; 2 Tiantai Bureau of Land and Resources of Zhejiang Province, Tiantai 317200, China Received April 13, 2012; accepted June 18, 2012 Here we describe new types of dinosaur eggs found from the Late Cretaceous Chichengshan Formation in the Tiantai Basin, Zhejiang Province. On the basis of such characters as small spheroid or near-spheroid, columnar layer composed of three zones, the outer zone consisted of stalagmite-like or coralliform secondary shell units, we established two new oogenera, one new and one combination oospecies: Stalicoolithus shifengensis oogen. et oosp. nov. and Coralloidoolithus shizuiwanensis oogen. et comb. nov. In addition, re-examination of the holotype of Shixingoolithus erbeni from the Upper Cretaceous Pingling Formation, Guangdong Province reveals that it was erroneously attributed to Spheroolithidae, and should be transferred to stalicoolithid. Consequently, we established a new oofamily: Stalicoolithidae oofam. nov. Stalicoolthids represents a new model of dinosaur eggshell and thus sheds new light on the formation and evolution of amniotic eggshells. dinosaur egg, stalicoolthids, Upper Cretaceous, Chichengshan Formation, Tiantai Basin Citation: Wang Q, Wang X L, Zhao Z K, et al. A new oofamily of dinosaur egg from the Upper Cretaceous of Tiantai Basin, Zhejiang Province, and its mecha- nism of eggshell formation. Chin Sci Bull, doi: 10.1007/s11434-012-5353-2 The Tiantai Basin in Zhejiang Province is a very important jia and Chichengshan formations indicated an age of 98–91 locality for dinosaur eggs research. Since the dinosaur eggs Ma (to be published elsewhere), corresponding to the early were first found in 1958, a large number and verity of dino- Late Cretaceous (Cenomanian-Turonian). saur eggs [1–9], turtle eggs [10], and dinosaur bones [11] Since 2008, we have reported a large number of new have been found. The Upper Cretaceous strata of the Tiantai types of dinosaur egg from the Tiantai Basin [6–9], and Basin consist of the Laijia Formation and the overlying have undertaken some taxonomic revisions of dinosaur eggs Chichengshan Formation. The Laijia Formation is com- described by other researchers [2–4]. Recently, we found posed of lacustrine sediments such as red silty mudstones more than a dozen eggs from the lower member of the and granule conglomerates, with many layers of interbedded Chichengshan Formation in Shuangtang, Qiaoxia and laminated tuffs. The Chichengshan Formation can be subdi- Brewery in the Tiantai Basin (Figure 1). These eggs have a vided into two members. The lower member, which has distinctive eggshell microstructure not seen in other types of yielded a large number of dinosaur eggs and bones, is com- dinosaur egg. Based on both egg macrostructure and egg- posed of red conglomerates, sandstones, and silty mud- shell microstructure characteristics, we established in this stones with interbedded tuffs; whereas the upper member is paper one new oofamily, two new oogenera, one new oo- composed of red conglomerates and sandstones interbedded species, and one new binomial combination oospecies. The with muddy siltstones. SIMS U-Pb zircon dating of the Lai- newly discovered dinosaur eggs are very important for un- derstand the composition of the Tiantai dinosaur eggs oo- *Corresponding author (email: [email protected]) fauna and providing new materials to study the eggshell © The Author(s) 2012. This article is published with open access at Springerlink.com csb.scichina.com www.springer.com/scp 2 Wang Q, et al. Chin Sci Bull January (2012) Vol.57 No.1 Figure 1 Dinosaur eggs localities and geological units of the Tiantai Basin, Zhejiang Province (modified from Wang et al. [1]). 1, Brewery; 2, Shuangtang; 3, Qiaoxia. formation and evolution of the dinosaur eggs in the Creta- Zhejiang Province; the first member of the Chichengshan ceous. Formation, Upper Cretaceous. Diagnosis. Small spheroid egg with the polar axis about 9.54 cm and shape index 93.19. Eggshell thickness 1 Systematic paleontology 3.90–4.00 mm. Cone layer is thin, about 1/20 of eggshell thickness. Columnar layer consists of the inner, medial, Stalicoolithidae oofam. nov. and outer zone. The medial zone is thick, with a thickness Etymology. From Stalicoolithus. of 1.60–1.70 mm. There are some parallel light-colored Known oogenera. Stalicoolithus, Coralloidoolithus, Shi- streaks in the lower part of the medial zone. The outer zone xingoolithus. is consisted of the loosely arranged stalagmite-like second- Diagnosis. Small spheroid or nearly spheroid eggs, ir- ary eggshell units. There are 80–100 second eggshell units regularly arranged in the nest. Eggshell thickness, 2.4–4.0 per square millimeter. mm. Outer surface of the eggshell is coarsely decorated. Description. A complete spheroid egg (Figure 2). The Cone layer is thin with 0.18–0.25 mm thick, about 1/20–1/4 polar axis is 9.54 cm, and the equatorial diameter is 8.89 cm, of eggshell thickness. Three distinct zones of the columnar layer: (1) Horizontal growth lines develop in the inner zone. (2) Light and dark bands with varying thickness and lengths develop in the medial zone. (3) Secondary eggshell units are loosely arranged in the outer zone. The pore cannel is irreg- ular. Stalicoolithus oogen. nov. Etymology stalic-, Greek, “stalagmite-like”, in reference to stalagmite-like arrangement of the second eggshell units in the outer layer of the eggshell columnar layer. Diagnosis. Same as the type and only known oospecies. Stalicoolithus shifengensis oogen. et oosp. nov. Etymology shifeng, from the ancient name of Tiantai County. Holotype. A complete egg (TTM29) (Figure 2), housed in Tiantai Museum, Zhejiang Province. Figure 2 Stalicoolithus shifengensis oogen. et oosp. nov. holotype Locality and horizon. Shuangtang, Tiantai County, (TTM29). Wang Q, et al. Chin Sci Bull January (2012) Vol.57 No.1 3 with shape index 93.19. Outer surface of the eggshell is Coralloidoolithus shizuiwanensis oogen. et comb. nov. coarsely decorated. The eggshell thickness is 3.90–4.00 Paraspheroolithus shizuiwanensis Fang et al., 1998 mm. Paraspheroolithus cf. shizuiwanensis Fang et al., 2000 There is no obvious boundary between the cone layer and Referred specimens. An incomplete nest composed of the columnar layer (Figure 3a). Cone layer is 0.18–0.20 mm six nearly complete and three broken dinosaur eggs (TTM2) in thickness, about 1/20 of the eggshell thickness. Cones are (Figure 4a), an incomplete nest composed of five nearly round, oval or irregular in shape, and tightly packed in the complete and one broken dinosaur eggs (IVPP V16966.1) tangential section through the middle part of the cone layer (Figure 4e), one nearly complete and two broken dinosaur (Figure 3b). There are 24–28 cones per square millimeter. eggs (IVPP V16966.2) (Figure 4c), one nearly complete Thickness of the columnar layer is 3.70–3.80 mm. The dinosaur eggs (IVPP V16966.3) (Figure 4b), one nearly columnar layer can be divided into three zones: inner, me- complete and two broken dinosaur eggs (IVPP V16966.4) dial, and outer zone (Figure 3a). (Figure 4d). these specimens save in the Institute of Verte- Thickness of the inner zone is 1.00–1.10 mm, with dis- brate Paleontology and Paleoanthropology, Chinese Acad- tinct horizontal growth lines (Figure 3a). Columns with emy of Sciences and Tiantai County Museum, respectively. wedge-like and boundaries between each other are visible Locality and horizon. Qiaoxia (TTM2), (IVPP V16966.1– under crossed nicols. Pore cannels are irregular; there is 4), Tiantai County, Zhejiang Province; the first member of little second eggshell unit development in some pores (Fig- Chichengshan Formation, Upper Cretaceous. ure 3c, d). Diagnosis. Eggs nearly spheroid. The average polar axis Thickness of the medial zone is 1.60–1.70 mm. Columns is 9.36 cm, average shape index is 87.50. Thickness of egg- are tightly packed and interlocking, thus forming a contin- shell is 2.60 mm. Thickness of the cone layer is 0.20–0.25 uous zone. The lower part of medial zone has some gray mm, about 1/10 of the eggshell thickness. There are 20–24 streaks of various widths, in which filled with secondary cones per square millimeter. The columnar layer is divided calcite particles (Figure 3e). This may be similar to those into the inner, medial and outer zone. There are brown found in eggshell of extant birds, such as Casuarius. There bands with varying thickness in the medial zone. The outer are numerous irregular pore canals in the upper part of the zone is composed of coralline-like secondary eggshell units. medial zone (Figure 3a). In the tangential section through Description. Eggs are nearly spheroid. The average polar the lower part of the medial zone, pores are round or oval, axis is 9.54 cm, the average equatorial diameter is 8.89 cm, about 0.10–0.41 mm wide (Figure 3f). In the tangential sec- and average shape index is 87.5 (Table 1). Outer surface of tion through the upper part of the medial zone, the diameter the eggshell is coarsely decorated. Thickness of eggshell is of pores varies 0.06–0.30 mm，and the number of pores 1.80–2.60 mm. increases upward to the eggshell surface. Some secondary There is no visible boundary between the cone layer and eggshell units within pore canals can be observed in radial the columnar layer (Figure 5a). The cone layer is thin, section or the tangential section (Figure 3a, g, h).