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Evaluating deformation in Spheroolithus dinosaur eggs from Zhejiang, China

Article in Historical Biology · July 2013 DOI: 10.1080/08912963.2013.807252

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Historical Biology: An International Journal of Paleobiology Publication details, including instructions for authors and subscription information: http://www.tandfonline.com/loi/ghbi20 Evaluating deformation in Spheroolithus dinosaur eggs from Zhejiang, China Hannah M. Wilson a , Christian T. Heck b , David J. Varricchio c , Frankie D. Jackson c & Xingsheng Jin d a Department of Economics and Department of History , Montana State University , Bozeman , MT , 59717 , USA b Department of Cell Biology and Neuroscience , Montana State University , Bozeman , MT , 59717 , USA c Department of Earth Sciences , Montana State University , Bozeman , MT , 59717 , USA d Zhejiang Museum of Natural History , No. 6 in the Westlake Cultural Plaza, Hangzhou , Zhejiang , P.R. China Published online: 01 Jul 2013.

To cite this article: Historical Biology (2013): Evaluating deformation in Spheroolithus dinosaur eggs from Zhejiang, China, Historical Biology: An International Journal of Paleobiology, DOI: 10.1080/08912963.2013.807252 To link to this article: http://dx.doi.org/10.1080/08912963.2013.807252

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Evaluating deformation in Spheroolithus dinosaur eggs from Zhejiang, China Hannah M. Wilsona1, Christian T. Heckb1*, David J. Varricchioc, Frankie D. Jacksonc and Xingsheng Jind aDepartment of Economics and Department of History, Montana State University, Bozeman, MT 59717, USA; bDepartment of Cell Biology and Neuroscience, Montana State University, Bozeman, MT 59717, USA; cDepartment of Earth Sciences, Montana State University, Bozeman, MT 59717, USA; dZhejiang Museum of Natural History, No. 6 in the Westlake Cultural Plaza, Hangzhou, Zhejiang, P.R. China (Received 31 January 2013; final version received 18 April 2013)

Lack of stratigraphic context for dinosaur eggs inhibits understanding of dinosaur reproductive biology and the taphonomic processes of egg preservation. Past taphonomic work suggests two features, compression ridges (sharp edge of broken eggshell around egg circumference) and deformation asymmetry (proportion of crushed to rounded sides of the egg), as geopetal structures. We examined these features across a large sample of Spheroolithus eggs from the of Zhejiang, China, to test their utility. On 103 isolated eggs, we determined asymmetry ratios (crushed side egg height divided by rounded side egg height) and observed an average asymmetry ratio of 0.71. Additional observations of in situ eggs demonstrate the stratigraphic downside as more rounded and less fractured, the stratigraphic upside as flatter with heavier fracturing and compression ridges as parallel to original bedding plane. Burial-caused fractures on the upper side of the egg allowed sediment to partially fill, subsequently supporting the bottom portion. Examining these features within 16 clutches allowed differentiation of biotic versus taphonomically altered arrangements. Three common clutch arrangements include planar (minimal egg overlap), offset (extreme overlap) and agglomerate (randomly arranged, closely packed). Analysis of egg strike and dip across clutches favours planar clutches as the principal configuration for Spheroolithus clutches. Keywords: Spheroolithus; compression; orientation; Zhejiang; asymmetry; deformation

Introduction high levels of fracturing and a unique crease-like fracture Research on dinosaur eggs provides insight into dinosaur about the equator. After extensive observations on the reproductive biology, biodiversity, climatic conditions, preservation of spherical Cretaceous eggs, including climate change and dinosaur extinction (Thaler 1965; Faveoolithus and Dictyoolithus, Mueller-Towe et al. Folinsbee et al. 1970; Erben et al. 1979; Williams 1981; (2002) concluded that an egg’s original shape was better Hirsch et al. 1989; Zhao et al. 1991; Zelenitsky and Hills preserved after infilling with sediment. Through the use of 1997; Chiappe et al. 2000; Yang et al. 2001; Zhao et al. computed tomography, they observed that some eggs 2002; Varricchio and Jackson 2004). However, taphonomic exhibited a sediment-filled bottom overlain by a hollow processes such as lithostatic compaction and solifluction space or, alternatively, crystals that precipitated and filled have the potential to alter egg clutch arrangement and the previously open space. More recently, Soja (2008) original egg morphology (Hayward et al. 1989; Hayward performed burial experiments on intact modern eggs of et al. 2000; Jackson et al. 2004; Jackson and Schmitt 2008; alligators, chickens, emus and ostriches. Her experiments Downloaded by [David J. Varricchio] at 05:33 05 July 2013 Hayward et al. 2011). The altered features can potentially showed that fractures appeared on eggs during burial and lead to misidentification of eggs and misinterpretations of that sediment sifted through the fractures into the eggs, nest construction, incubation and hatching behaviours. filling their interior and preventing further collapse. In Thus, understanding the effects of mechanical alteration of addition, shell membrane that lined the inside of eggs acted fossilised eggs is essential for accurate interpretation of egg as an adhesive, ‘gluing’shell pieces together after the initial clutch arrangement and egg morphology. Despite the phases of burial and fracturing. importance of understanding taphonomic effects, there has The Zhejiang Museum of Natural History (ZMNH) in been a limited number of research on mechanical alteration Hangzhou, China, houses a large collection of dinosaur of eggs and eggshell (e.g. Hayward et al. 1989; Hayward eggs and egg clusters from Upper Cretaceous formations et al. 2000; Mueller-Towe et al. 2002; Soja 2008). of the Tiantai basin of Zhejiang Province. We consider egg Hayward et al. (2000) used a hydraulic press to clusters to consist of multiple eggs adjacent to one another simulate the effects of triaxial loading with a greater within the same matrix block. The majority of ZMNH vertical than horizontal force on complete chicken eggs. eggs exhibit a distinctly crushed side and a more rounded After the simulated loading, the compressed eggs displayed side presumably reflecting lithostatic compaction.

*Corresponding author. Email: [email protected]

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Figure 1. (A) Crushed Spheroolithus from ZMNH with visible compression ridge (arrows) around circumference of egg separating crushed side and rounded side. (B) Crushed side of egg displaying flatter surface and high eggshell fracturing. (C) Rounded side of egg has convex shape and minimal eggshell fracturing (scale bar ¼ 3 cm).

A ‘compression ridge’ defined here as an irregular band of sufficient stratigraphic data. For example, most Zhejiang broken and protruding eggshell, extends around the specimens were acquired from construction sites and circumference of the egg and separates the two sides. independent fossil collectors, and thus, the majority lack This feature is most visible on isolated eggs (Figure 1). We detailed stratigraphic and taphonomic data. This type of consider this compression ridge analogous with the fossil acquisition and absence of data is true for many ‘horizontal crease-like fracture’ of Hayward et al. (2000). museum specimens in China (Dalton 2000; Stone 2010; These observations, along with the taphonomic pers. obs. CTH, HMW, DJV 2012). Developing a method to research described above, suggest potential methods for determine the stratigraphic orientation of eggs and egg recognising both the stratigraphic upside and the compac- clusters will provide important taphonomic data and thus tion direction of crushed eggs. We propose that lithostatic facilitate better paleobiological interpretations of dinosaur compaction early in an egg’s taphonomic history should reproductive biology. Furthermore, the methods presented produce a ‘compression ridge’, thereby providing an for analysing the consistency of compaction across a cluster indicator of the original bedding plane or, minimally, the of eggs can aid in understanding the timing and mechanism

Downloaded by [David J. Varricchio] at 05:33 05 July 2013 compression direction. The studies of Soja (2008) and of compression. Mueller-Towe et al. (2002) also suggest that post-burial infilling of unhatched eggs could result in asymmetric preservation, and that this deformation asymmetry could be Materials and methods used as a geopetal structure, indicative of stratigraphic up All eggs in this study come from Upper Cretaceous strata orientation. Thus, we propose that compression ridges and exposed in the Tiantai and Jinqu basins, Zhejiang Province, compaction asymmetry in fossil eggs can be used to southeastern China (Jin 2009). The Tiantai basin includes determine stratigraphic orientation and undertake this study the Tangshang, Liangtoutang and Chichengshan For- to determine if these compaction features are consistent mations, the latter two being early in age across a large sample of eggs. and producing the greatest number and diversity of This research introduces new methods for (1) dinosaur eggs (Fang et al. 2000, 2003; Jin et al. 2007; He determining the stratigraphic position of isolated eggs et al. 2013). Similarly, the Jinqu basin includes the Jinhua using a quantitative analysis of egg compaction features and Quixian Formations that are likely stratigraphically and (2) better understanding the taphonomic history of egg equivalent to the Liangtoutang and Chichengshan For- clusters by quantifying the effects of compaction on egg mations (Jin 2009). The sample of eggs consists of 16 egg morphology throughout the contained eggs. Determining clusters and 327 intact isolated eggs. All eggs used in this the original stratigraphic orientation of a fossil egg is an study are referable to Spheroolithus cf. zhangtoucaoensis important first step in studying fossil eggs that lack on the basis of macrostructural measurements and Historical Biology 3

Figure 2. Location of Tiantai city (star) and Dongyang city (triangle) in Zhejiang Province, China.

microstructural analysis (Barta et al. In press). In addition, all eggs included in the quantitative analysis exhibit clear compression ridges, and range from 6.2 to 12 cm in greatest diameter, with most ranging between 7 and 11 cm. These specimens are housed in the ZMNH in Hangzhou, China, and lack taphonomic data and stratigraphic orientation. However, for comparative purposes, the study includes additional three eggs with known stratigraphic orientations: an egg from cluster M8898 housed in the ZMNH, originally from the Jinhua Formation exposed near Dongyang city, and two in situ eggs observed in the cross section from the Chichengshan Formation in Tiantai basin near Tiantai (Figure 2). Figure 3. To calculate asymmetry in crushed Spheroolithus eggs: (A) total thickness was measured of crushed eggs. C-side thickness determined by distance from compression ridge to C-side pole. R-side thickness determined by subtracting C-side Method 1: Deformational asymmetry in egg morphology thickness from total egg thickness. (B) Eight measurements (dark lines) of C-side thickness taken at equal intervals around egg. To document egg asymmetry, we measured 103 individual Marked cardboard circle was used to stabilise egg during eggs (of the sample of 327) from the ZMNH collections measurements. that lacked taphonomic context and an egg from cluster M8898 excavated near Dongyang city. Measurements for the in situ egg from the Tiantai basin were made from fragments. The compression ridge forms the greatest photographs using the software program ImageJ. maximum circumference and includes the plane within

Downloaded by [David J. Varricchio] at 05:33 05 July 2013 Selection of isolated egg specimens was based on their which the long axis of the egg sits. This distinct ridge completeness, presence of a compression ridge, clear top partitions the egg into two distinguishable hemispheres and bottom and sub-spherical shape. An absence of major (Figure 1). openings enabled us to interpret the eggs chosen as being The eggs typically exhibit a compressed side of unhatched. The 224 eggs not included consist of those that irregularly displaced shell, and an opposite side that were incomplete (109 eggs), had obstructive matrix retains the original round shape. For this study, we identify covering more than 50% of the compression ridge (75 the compressed side of the egg as ‘C’ and the rounded side eggs) and eggs that failed to exhibit a clear compression as ‘R’ (Figure 3(A)). The compression ridge defines the ridge (40 eggs). Incomplete eggs were considered not to plane separating the R and C sides. The height of the C exhibit a true height because either their top or bottom was side was measured at eight equally spaced locations along missing, impeding accurate measurements of each side of the compression ridge, using Exploit digital callipers. The the egg. In addition, eggs had to allow measurements of eight measurements were averaged to ensure an accurate both the crushed and rounded sides. estimate of the distance from the two poles of the egg to We define the ‘compression ridge’ as the outermost the compression ridge. The C-value was then subtracted visible circumference of the egg delineated by irregular from the total height of the egg to obtain the R-side height. and protruding eggshell. Here, compaction has displaced A cardboard circle was used to stabilise the callipers and to pieces into a jutting-out ‘V’ formation of closely appressed provide consistent measurement locations on the egg shell, often forming a sharp angle between the jutted-out (Figure 3(B)). A ratio was derived for each egg by taking 4 H.M. Wilson et al.

the average C-value divided by the average R-value. The C-to-R ratio defines the degree of compression observed for each egg.

Method 2: Compression ridge plane(s) within egg clusters We examined 16 egg clusters in order to compare the orientations of compression ridges among eggs comprising a cluster. Each egg was labelled alphabetically for identification purposes. We measured strike and dip angles for the planes defined by the compression ridges for each complete egg using a Brunton compass and followed the right-hand rule convention (Figure 4(A)). Incomplete eggs and eggs whose compression ridges were covered by matrix were not used in this study. To facilitate the measurements of strike and dip, we marked the dip direction on opposite ends of the egg with clay and string (Figure 4(B)). These points provided an imaginary line from which the angle of the dip was measured. To facilitate comparison between the strikes and dips of eggs within and between clusters, for each cluster the egg with the lowest value for dip was used as a reference point and the noted values were converted to 08 dip and 08 strike through rotation of the plane to the horizontal. Similarly, the values for each egg in the cluster were subjected to the same rotation as on the reference egg. These converted strike and dip measurements were then plotted on a rose diagram and stereonet for each individual egg cluster (Figure 4(C)).

Results Deformational asymmetry in egg morphology From the observations of our entire sample of measured eggs (n ¼ 327), we found that those eggs showing a clear

Downloaded by [David J. Varricchio] at 05:33 05 July 2013 compression ridge also exhibited distinct crushed and rounded sides. The latter typically exhibits a smooth surface, fewer fractures and larger eggshell fragments with minimal overlap (Figure 1(C)). In contrast, a greater degree of eggshell fracturing and displacement occurred on the Figure 4. (A) Brunton compass and ruler used to determine strike and dip of plane defined by egg’s compression ridge to the compressed side, resulting in a more irregular exterior horizontal. (B) Clutch M8643 with dip direction of compression with eggshell fragments forming ridges and valleys ridge marked with string and clay. (C) Resulting stereonet and (Figure 1(B)). These fragments typically occur in 1–3- rose diagram showing strike and dip of planes defined by cm pieces and despite eggshell displacement and overlap, individual eggs’ compression ridges. Note egg F (arrow) rests on a plane 2–4 cm away from principal egg layer and strike, and dip the fragments generally conform to their original of egg F differs greatly from rest of clutch (scale bar ¼ 10 cm). orientation on the egg. However, some eggshell is present within the sediment infill. Some sections of the egg surface lack eggshell due to excavation and/or erosion damage, but asymmetry of the sampled Spheroolithus eggs lies between matrix typically maintains the internal wall and shape of 0.62 and 0.80 (with a 95% confidence interval). the crushed egg. Compared with the data of the 103 eggs given above, The degree of asymmetry varied from 0.36 to 0.98 the asymmetrical ratios for the excavated Dongyang egg (Figure 5). A mean asymmetry ratio of 0.71 was calculated and the in situ Tiantai egg are 0.83 and 0.34, respectively to have a standard deviation of 0.17. The true mean (Figures 5 and 6). The degree of asymmetry of the Historical Biology 5

Figure 5. Asymmetrical ratios for 103 isolated Spheroolithus eggs housed in ZMNH, Dongyang road cut egg (DRE), also housed in ZMNH and the measured in situ Tiantai egg (TE). The mean asymmetry ratio of top-to-bottom distances from the compression ridge for the sample was 0.71, with a standard deviation of 0.17.

Dongyang egg appears as a representative of many eggs in flat top (Figure 6(C),(D)). Furthermore, both the Dongyang our study because 21% of measured eggs fall between 0.80 egg and the measured Tiantai egg show minimal and 0.89. However, the Tiantai egg’s asymmetry ratio of compression on the rounded, and stratigraphic down, side 0.34 does not appear as a representative because only 4.9% of the egg. of measured eggs exhibit a ratio between 0.30 and 0.39. The true height of the in situ Tiantai egg remains unknown because the egg was not collected and the visible cross Compression ridge planes within clusters section may not include the true centre of the egg. The The 16 egg clusters are composed of 2–11 eggs exhibiting second in situ egg from Tiantai lacks a visible compression a greater degree of fracturing on the compressed sides. ridge, but exhibits a distinct round bottom and relatively Typically the clusters were prepared by exposing either the Downloaded by [David J. Varricchio] at 05:33 05 July 2013

Figure 6. Two eggs in situ from Tiantai basin area of Zhejiang, China. (A, B) The Tiantai basin egg exhibits a clear compression ridge as well as a round bottom and crushed top. The dashed lines indicate the estimated compression ridge. (C, D) The Tiantai road cut egg, although lacking a clear compression ridge, still exhibits a distinctly round bottom and crushed top (scale bar ¼ 10 cm). 6 H.M. Wilson et al.

top or bottom sides, but rarely both. The exposed sides of and M8858) show high variability of dip magnitude with eggs within a cluster show uniform eggshell fracture and ranges of 248,258,118 and 118, respectively. displacement. Ten clusters consist of eggs arranged on a The range of strikes within an egg cluster had a mean single horizontal plane, whereas the other six are arranged range of 88.68 and a standard deviation of 62.78. The large on multiple planes. Cluster M8643 includes a single egg range of strike must be placed within the context of dip on a separate plane from the rest of the cluster, sitting 2– magnitudes. With very low dip angles, even wide 4 cm away from the principal egg layer (Figure 4(B),(C)). divergences of strike result in planes with minimal offset. Among the latter, cluster M8656 consists of two eggs This is best appreciated visually in the stereonet offset from one another. Three clusters (M8517-D1, projections (Figure 8, Supplemental Figures 1–3). M8538 and M8647) show eggs overlapping one another, with neighbouring eggs appearing to influence the position of one another. Egg F of M8517-D1 is overlapped slightly Discussion by eggs E and D, possibly resulting in a steeper dip for egg A large number of eggs were excluded from the study due F. Specimens M8538 and M8647 each consist of two eggs to incompleteness and obscuring matrix. Of the nearly 150 that display substantial overlap and the eggs show a higher eggs that permit thorough observation, over 72% exhibit a degree of deformation (Figure 7). Four clusters (M8102- distinct compression ridge with compaction asymmetry. D1, M8545, M8530, M8858) exhibit an irregular Many of the excluded eggs, although lacking a clear arrangement of eggs that occur at different levels rather compression ridge, still exhibit clearly visible crushed and than a single plane (Figures 8 and 9). Supplemental Table 1 rounded sides. lists eggs measured within each cluster and the rotated As detailed below, we propose that the compression values for strike and dip measurements. ridge and compaction asymmetry are best explained by an 8 The mean dip for eggs within a cluster was 11.3 , with a initial compaction at shallow depths, allowing sediment to standard deviation of 6.68. Fourteen of the clusters show a infill the egg bottom, maintaining its structural integrity. dip range of 08–158, with six ,108 (Table 1). For example, As Soja (2008) suggests, initial fracturing on the upper egg M8823 includes 10 eggs with dip magnitudes within 98 of surface may have permitted sediments to enter and fill the one another. Greater variation occurred in clusters bottom of the egg, strengthening and supporting the comprised of more irregularly arranged eggs. For example, bottom. Eventually this would have helped to maintain a a greater magnitude of dip characterises the egg that more rounded shape of the bottom of the egg, compared to occurred at a different level in specimen M8643, compared the upper portion, resulting in the distinct C and R sides of to the rest of the egg cluster. Egg overlap also appears to the eggs in this study. The observed variability in influence dip magnitude, as the contacted egg F of M8517- compaction asymmetry likely reflects the degree and D1 has the steepest dip within its clutch. However, egg timing of sediment infilling and compaction. The eggs overlap does not appear to influence the dip in a third studied by Mueller-Towe et al. (2002), like those from cluster, namely M8538 (Figure 7). The overlapping egg appears to displace only a portion of the underlying egg, Zhejiang, appear to have sediment-filled bottoms but differ resulting in a break and offset of the compression ridge in having permineralised upper portions. between the two portions. The four clusters with the most Alternate taphonomic scenarios fail to conform to our Downloaded by [David J. Varricchio] at 05:33 05 July 2013 irregular egg arrangements (M8102-D1, M8545, M8530 observations. For example, the intact preservation of the eggs eliminates hatching or predation as a mechanism for compromising the structural integrity of the eggs’ upper surface. In addition, compaction at greater burial depth with higher pressures and temperatures could potentially result in more symmetric plastic deformation and overprint previous compressional effects (Sharpe 1847; Lake 1943; Cooper 1990; Vila et al. 2010). The results of Soja’s (2008) crushing experiments occurred at shallow depth within soils and therefore may imply sediment loading or solifluction as the main compressive forces on the eggs. Furthermore, it eliminates the possibility of deformation due to tectonic forces acting on alternate planes as a cause of compression. Therefore, we interpret the rounded surface of the egg as Figure 7. Overlapping eggs in the offset clutch M8538 cause egg displacement without altering compression ridge plane (scale stratigraphic down, and the compression ridge as parallel to bar ¼ 5 cm). the bedding plane. Historical Biology 7

Figure 8. Stereonets and rose diagrams of four clutches. (A) Clutch M8545 has an agglomerate composition as evidenced by high variability between strikes and dips of eggs within the clutch. (B) Four eggs that comprise planar clutch M8633 differ moderately in strike measurements, but minimally in dip angles. (C) Overlap between the two eggs in offset clutch M8647 potentially causes the difference of strike and dip between the two eggs. (D) Egg J of planar clutch M8824 has a dip similar to other eggs in clutch but large difference in strike resulting in minimal offset. This difference is possibly due to two adjacent eggs slightly overlapping egg J.

Observations of the eggs of known orientation from rounded versus compressed egg surfaces. Clusters M8102- Tiantai and the excavated Dongyang clutch (M8898) D1, M8517-D1, M8522, M8530, M8633, M8655, M8669 concur with this interpretation. Two of the eggs from and M8823 revealed the rounded surface of the eggs after

Downloaded by [David J. Varricchio] at 05:33 05 July 2013 Dongyang and Tiantai exhibit round bottoms and bedding preparation and, thus, the stratigraphic downside of the parallel compression ridges, whereas the third egg, also egg. In contrast, the exposed egg surfaces in M8503, from Tiantai, lacks the latter feature but still exhibits a M8519, M8538, M8545 and M8643 are flattened and/or round bottom (Figure 6). These specimens provide fragmented, indicating the stratigraphic up orientation of evidence that the bottom of the egg maintains its rounded these clusters. The two remaining clusters (M8647, shape while its stratigraphic up portion appears crushed. M8656) lack sufficient exposure to permit identification Quantitative measurements of deformation asymmetry of crushed and rounded sides. Although most ZMNH could not be done on egg clusters due to impeding matrix clusters are only partially exposed, the eggs display either that prohibits measurements of both C and R sides. exclusively compressed or rounded egg surfaces on one However, the stratigraphic orientation could be tentatively face. This consistency of orientation of egg deformation determined by qualitative analysis of exposed eggs. within the majority of these clusters provides qualitative Fourteen clusters (M8102-D1, M8503, M8517-D1, support for our proposed interpretation of deformation M8519, M8522, M8530, M8538, M8545, M8633, asymmetry. M8643, M8655, M8669, M8823 and M8858) consisted We characterised egg clusters into three distinct of eggs that included portions above and below the arrangements: planar, offset and agglomerate (Figure 9). compression ridge. Comparisons of these areas allowed Due to similar orientations and similar degrees of tentative assessment of egg cluster orientation using deformation across planar and offset arrangements, we criteria derived from this study, namely the use of the interpret these two egg cluster types as partial egg 8 H.M. Wilson et al.

Figure 9. Egg clutches are categorised into three arrangements: planar, offset and agglomerate. (A) Planar clutch M8824 has 11 eggs comprising a single plane and minimal overlap (scale bar ¼ 10 cm). Offset arrangements (B, C) include clutches with moderate overlap and clutches with a single egg resting on a separate plane. (B) Moderate egg overlap displayed visually on offset clutch M8647 (scale bar ¼ 7 cm). (C) Egg F (arrow) within offset clutch M8643 exists 2–4 cm away from primary egg layer (scale bar ¼ 10 cm). (D) Agglomerate clutches, such as M8102-D1, show random arrangement and close packing while failing to define a single plane (scale bar ¼ 6 cm).

clutches. Planar clutches (M8503, M8517-D1, M8519, prior to, or after compaction. The two eggs of clutch M8633, M8522, M8655, M8669 and M8823) consist of M8538 have similar dips despite overlap, which provides eggs with minimal overlap and compression ridges that evidence for displacement prior to compaction. Clutch

Downloaded by [David J. Varricchio] at 05:33 05 July 2013 show little variation in orientation. The eggs comprise a Table 1. Strike and dip variation within egg clusters. single plane. Presumably, if these eggs are interpreted as incubated within substrates (Deeming 2006), this plane Specimen no. Strike variation Dip variation defines the initial nest orientation. Furthermore, we M8102-D1 1228 248 hypothesise that the plane defined by the clutch parallels M8503 538 108 the original bedding plane with minimal displacement by M8517-D1 358 178 M8519 188 98 post-burial compaction. Dip variation in these clutches M8522 718 108 ranges from 08 to 178, with a mean of 98. We attribute this M8530 828 118 low dip variation within these partial clutches to M8538 1118 58 irregularities in the fracturing, infilling and compaction M8545 1658 258 M8633 1118 118 of the eggs. M8643 1478 138 Offset clutches (M8538, M8643, M8647 and M8656) M8647 688 158 include those with extreme overlap of eggs or a single egg M8655 618 58 on a lower level. These clutches show a dip variation M8656 178 68 M8669 128 08 between 58 and 158, with a mean of 108, similar to that of M8823 1418 98 clutches that occur on a single plane. Offsetting and M8858 158 118 overlapping could potentially result from displacement Historical Biology 9

M8647 has a dip range of 158 due to the overlap and is additional in situ specimens with known field orientation. interpreted as post-compaction displacement. Bioturba- Furthermore, we examined only Spheroolithus eggs from tion, sediment heterogeneity, solifluction and other soil Zhejiang Province of China; therefore, results may processes could account for post-burial displacement. As potentially differ when applied to other ootaxa and some of these partial clutches consist of only two eggs geographic regions. Nevertheless, Mueller-Towe et al. (M8538, M8647 and M8656), they could alternatively (2002) document similar compaction and infilling patterns represent the results of hydraulic transport. in Faveoolithus and Dictyoolithus eggs from other regions Agglomerate clusters (M8102-D1, M8530, M8545 and in China. Our methods should be applicable to eggs of M8858) are randomly arranged, closely appressed egg similar shape and microstructure, provided they display a masses that do not clearly define a single plane. Each of clear compression ridge and are unobstructed by matrix on these clusters consists of three to four eggs. The dip both C and R sides. variation ranges from 118 to 258, with a mean of 188. Possible scenarios that could result in these arrangements include (1) reworking followed by hydraulic transport and Acknowledgements deposition, (2) more intense post-burial displacement as We thank D. Barta, D. Simon, S. Oser, D. Lawver and A. Moore- discussed above of a planar clutch and (3) a more massive, Nall, with the other members of the 2012 IRES (International non-planar clutch configuration representing a different Research Experience for Students) Dinosaur Eggs and Education trip for early reviews of this manuscript, discussion and insight. nesting behaviour, perhaps similar to that of sea turtles We would also like to thank the Zhejiang Museum of Natural (Bishop et al. 2011). In scenario 3, with no compaction History staff Zheng Wenjie, Li Xiuti and Gu Shengxiao for their displacement, we would expect values of dip variation to assistance and congeniality. Funding for this study was provided be similar to those of planar and offset clutches. Thus, by National Science Foundation IRES grant # 0854412 to F. Jackson and D. Varricchio, National Geographic Grant # 8752- based upon the increased variation of dip, we favour more 10 to D. Varricchio, X. Jin and F. Jackson, and the Montana State intense post-burial displacement for these four clusters as University Vice President for Research Internship and a MSU in scenarios 1 and 2. Undergraduate Scholars Programme travel grant to H. Wilson.

Conclusions Note Crushed Spheroolithus eggs from Zhejiang Province 1. Both of these authors have contributed equally to this work. exhibit a crushed-to-rounded side ratio of 0.71. Two compaction features assist in determining the orientation of eggs. First, we interpret the rounded side of isolated References eggs displaying deformation asymmetry, as representing Barta DE, Brunbridge KM, Croghan JA, Jackson FD, Varricchio DJ, Jin X, Poust AW. In press. Eggs and clutches of the Spheroolithidae the stratigraphic down orientation. Second, the plane of the from the Cretaceous Tiantai basin, Zhejiang Province, China. compression ridge separating the crushed and rounded Historical Biol. sides occurs parallel to the original bedding. Furthermore, Bishop GA, Pirkle FL, Meyer BK, Pirkle WA. 2011. The foundations for sea turtle geoarchaeology and zooarchaeology: morphology of recent the preservation quality and characteristics observed in and ancient sea turtle nests, St. Catherines Island, Georgia, and these eggs likely resulted from initial fracture and partial Cretaceous Fox Hills Sandstone, Elbert County, Colorado. Anthro- Downloaded by [David J. Varricchio] at 05:33 05 July 2013 infill followed by compaction at relatively shallow depths. pol Paper Am Mus Nat Hist. 94:247–269. Chiappe LM, Dingus L, Jackson FD, Grellet-Tinner G, Aspinall R, Clarke Analysis of strike and dip levels of eggs within clutches J, Coria R, Garrido A, Loope D. 2000. Sauropod eggs and embryos can identify the original bedding plane. In addition, from the Late Cretaceous of Patagonia. 2000. First International analysis of egg strike and dip across clutches favours planar Symposium on Dinosaur Eggs and Babies: Extended Abstracts. p. 23–29. clutches as the principal configuration for Spheroolithus Cooper RA. 1990. Interpretation of tectonically deformed fossils. clutches. Other configurations are observed, but these New Zeal J Geol Geop. 33(2):321–332. likely resulted from post-burial taphonomic modification. Dalton R. 2000. Chasing the dragons. Nature. 406(6799):930–932. Deeming DC. 2006. Ultrastuctural and functional morphology of We propose that compression ridges and deformation eggshells supports the idea that dinosaur eggs were incubated buried asymmetry can be used as geopetal structures, orientating in a substrate. Palaeontology. 49(1):171–185. Erben HK, Hoefs J, Wedepohl KH. 1979. Paleobiological and isotopic both eggs and clutches lacking field context. Our studies of eggshells from a declining dinosaur species. Paleobiology. interpretation could be further tested by gathering 5(4):380–414. quantitative data on the variation in deformation asym- Fang X, Lu L, Jiang Y, Yang L. 2003. Cretaceous fossil eggs from the Tiantai basin of Zhejiang, with a discussion on the extinction of metry of eggs throughout a fully exposed clutch. Matrix dinosaurs. Geol Bull China. 22(7):512–520. currently prohibits measurement of deformation asymme- Fang X, Wang Y, Jiang Y. 2000. On the Late Cretaceous fossil eggs of try in ZMNH specimens. Further analysis would require Tiantai, Zhejiang. Geol Rev. 46(1):105–112. Folinsbee RE, Fritz P, Krouse HR, Robblee AR. 1970. Carbon-13 and more extensive clutch preparation. Our orientation oxygen-18 in dinosaur, crocodile, and bird eggshells indicate hypotheses would also benefit from the examination of environmental conditions. Science. 168(3937):1353–1356. 10 H.M. Wilson et al.

Hayward JL, Amlaner CJ, Young KA. 1989. Turning eggs into fossils: a Sharpe D. 1847. On slaty cleavage. Q J Geol Soc Lond. 3:74–105. natural experiment in taphonomy. J Vertebr Paleontol. Soja C. 2008. Unscrambling dinosaur eggs. Am Paleontol. 16(2):21–25. 9(2):196–200. Stone Richard. 2010. Altering the past: China’s faked fossils problem. Hayward JL, Dickson KM, Gamble SR, Owen AW, Owen KC. 2011. Science. 330(6012):1740–1741. Eggshell taphonomy: environmental effects on fragment orientation. Thaler L. 1965. Les oeufs des dinosaurs de Midi de la France livrent le Historical Biol. 23(1):5–13. secret de leur extinction. Paris Sci. Progres-La Nature. 45:41–48. Hayward JL, Zelenitsky DK, Smith DL, Zaft DM, Clayburn JK. 2000. Varricchio DJ, Jackson FD. 2004. Two eggs sunny-side up: reproductive Eggshell taphonomy at modern gull colonies and a dinosaur clutch physiology in the dinosaur Troodon formosus. In: Currie PJ, site. Palaios. 15(4):343–355. Koppelhus EB, Shugar MA, Wright JL, editors. Feathered dragons: He H, Wang X, Wang Q, Jiang S, Cheng X, Zhang J, Zhou Z, Zhao Z, studies on the transition from dinosaurs to birds. Bloomington, IN: Jiang Y, Yu F, Deng C, Yang J, Zhu R. 2013. SIMS zircon U-Pb Indiana University Press. p. 215–233. dating of the Late Cretaceous dinosaur egg-bearing red deposits in Vila B, Jackson FD, Fortuny J, Selles AG, Galobart A. 2010. 3-D the Tiantai Basin, southeastern China. J Asian Earth Sci. modelling of Megaloolithid clutches: insights about nest construc- 62(2013):654–661. tion and dinosaur behavior. PLoSONE. 5(5):e10362. Hirsch KF, Stadtman KL, Miller WE, Madsen JH. 1989. Upper doi:10.1371/journal.pone.0010362 dinosaur egg from Utah. Science. 243(4899):1711–1713. Williams DLG. 1981. Genyornis eggshell (Dromornithidae; Aves) from Jackson FD, Garrido A, Schmitt JG, Chiappe LM, Dingus L, Loope DB. the late Pleistocene of South Australia. Alcheringa. 5(2):133–140. 2004. Abnormal, multilayered titanosaur (Dinosauria: Sauropoda) Yang G, Mao Z, Yang J, Lu Y, Ouyang H, Zhang Z, Chai Z. 2001. A eggs from in situ clutches at the Auca Mahuevo locality, Nuequen study on the relationship between iridium concentration in hen Province, Argentina. J Vertebr Paleontol. 24(4):913–922. Jackson FD, Schmitt JG. 2008. Recognition of vertebrate egg eggshell and iridium-enriched feed by NAA. J Radioanal Nucl Ch. abnormalities in the Upper Cretaceous fossil record. Cret Res. 247(3):567–570. 29(1):27–39. Zelenitsky DK, Hills LV. 1997. Normal and pathological eggshells of Jin X. 2009. The paleontological study of dinosaur and turtle fossil eggs Spheroolithus albertensis, oosp. nov. from the from Zhejiang Province, China [Dissertation]. Toyama, Japan: (Judith river group, late Campanian), southern Alberta. J Vertebr University of Toyama. Paleontol. 17(1):167–171. Jin X, Azuma Y, Jackson FD, Varricchio DJ. 2007. Giant dinosaur eggs Zhao ZK, Mao XY, Chai ZF, Yang GC, Kong P, Ebihara M, Zhao ZH. from the Tiantai basin, Zhejiang Province, China. Can J Earth Sci. 2002. A possible causal relationship between the extinction of 44(1):81–88. dinosaurs and K.T iridium enrichment in the Nanxiong Basin, South Lake P. 1943. Restoration of the original form of distorted specimens. China: evidence from dinosaur eggshells. Palaeogeogr Palaeoclima- Geol Mag. 80(4):139–147. tol Palaeoecol. 178(1):1–17. Mueller-Towe IJ, Sander PM, Schuller H, Thies D. 2002. Hatching and Zhao ZK, Ye J, Li H, Zhao Z, Yan Z. 1991. Extinction of the dinosaurs infilling of dinosaur eggs as revealed by computer tomography. across the Cretaceous-Tertiary boundary in Nanxiong basin, Paleontographica. 267:119–168. Guangdong Province. Vert PalAsia. 29:1–20. Downloaded by [David J. Varricchio] at 05:33 05 July 2013

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