Australia: The Land Where Time Began

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Sauropod Rib with a Theropod Tooth Embedded in it – Direct Evidence of Feeding Behaviour in the Jehol Group, China

Direct evidence of feeding behaviour of an unidentified theropod has been found in a fragmentary rib from the Yixian Formation dating to the Lower Cretaceous (Barremian) in northeastern China. A broken theropod tooth was preserved embedded in the rib from the holotype of Dongbetitan. It is suggested by comparison of the tooth with the teeth from all the theropods known from the Yixian Formation that it was from a new taxon of medium-sized theropod. The bite is believed likely to have occurred post-mortem during scavenging as there was a large difference in size between the sauropod and the theropod. The diversity that is known of the taxa from the Yixian Formation is increased by the recognition of a new theropod, of medium size, and it helps fill the gap in the palaeoecology of theropods known from the Yixian Formation which had previously consisted of only small forms less than 2 m.

Tooth gouges, punctures and serration marks on bone can be used to interpret the feeding behaviour of dinosaurs (Tanke & Currie, 2000). Understanding of dinosaur feeding behaviour have been added to significantly by supplementary anatomical descriptions, which includes probable gut contents, wear rates of teeth and their replacement rates, finite element analysis and mathematical approaches (Erickson, 1996; Erickson & Olson, 1996; Varricchio, 2001; Snively & Russell, 2007; Bell et al., 2009; Tanoue et al., 2009; Bell & Currie, 2010).

It is rare to encounter broken teeth embedded in bone, in spite of the bite mark frequency that is reported from isolated elements, skeletons and bone beds (Jacobsen, 1998, 2001; Farlow & Holtz, 2002; Eberth & Getty, 2005). Direct evidence of predation or scavenging is provided by broken teeth embedded in bone (type 5 bite marks of Tanke & Currie, 2000), though they require pathological information to identify whether they were incurred prior to or after death of an animal (Buffetaut et al., 2004). It is rare to find such examples of embedded teeth, though there are several occurrences that have been described that involved pterosaur (Currie & Jacobsen, 1995; Buffetaut et al., 2004), hadrosaur (Farlow & Holtz, 2002), and tyrannosaur (Bell & Currie, 2010) bones. In most of these there is clear evidence of predator-prey interaction. It has been suggested that a fatal agonistic encounter, scavenging, or both may be represented by a broken tyrannosaurid tooth that was found embedded in the jaw of another tyrannosaurid (Currie & Bell, 2010).

In this paper Xing et al. describe a theropod tooth that was found embedded in a fragmentary rib of a sauropod (LDRCv2) from the Liaoning site, China that dated to Early Cretaceous. This is the first sauropod bone that has been reported to have had a theropod tooth embedded in it and provides new information of the palaeoecology of the Yixian Formation.

Geological setting

LDRCv2 was recovered from the Jianshangou Bed, Yixian Formation, Jehol Group, from the Lower Cretaceous (Barremian) near Beipiao City, western Liaoning, China. The rock types comprising the Jehol Group are shale, sandy conglomerates, tuffaceous sandstones, siltstones and andesites (Chen et al, 2005). Together with the underlying Lujiatun Bed, the Jianshangou Bed, comprises the lower part of the Yixian Formation, preserves the earliest portion of the Jehol Biota. It has been interpreted that the Jianshangou Bed was deposited in a landscape that was predominantly volcanoclastic (Liu et al., 2002) that was punctuated by lakes of various sizes (Fürsich et al., 2007). Sediments from catastrophic floods and air fall volcanic ash were deposited in these lakes (Fürsich et al., 2007) that were responsible for the remarkable quality of preservation of many of the fossils that have been recovered from the lower Yixian Formation. A diverse assemblage of primitive mammals and birds, feathered dinosaurs and other reptiles, as well as abundant invertebrates and angiosperms comprise the Jehol Biota (Chen et al., 2005; Fürsich et al., 2007) that flourished between 125 and 120 Ma (Swisher et al., 1999, 2002; He et al., 2004, 2006).

Conclusions

LDRCv2 is the first sauropod that has preserved an embedded theropod tooth, thus providing the best evidence of feeding interaction between these 2 groups. It is suggested by the comparison of the embedded tooth with the teeth of all theropods that are known from the Jianshangou Bed that it is from a new taxon of theropod that was of medium size. This new theropod adds to the diversity of fauna from the Yixian Formation as well as substantially contributing to theropod palaeoecology from that formation, which was dominated by coelurosaurs of small body size, less than 2 m. It is indicated that the bite occurred during scavenging by the lack of healing and the disparity in size between the theropod and Dongbetitan. A preliminary assessment of the bite force that would be required to embed the tooth gave a value of 8,880 N, which is similar to that of the upper bite force that has been estimated for Deinonychus.

Sources & Further reading

1. Xing, L., P. R. Bell, P. J. Currie, M. Shibata, K. Tseng and Z. Dong (2012). "A sauropod rib with an embedded theropod tooth: direct evidence for feeding behaviour in the Jehol group, China." Lethaia 45(4): 500-506.