Evolution and Ecological Associations in Herbivorous Theropods Albert Chen 4/25/2016 Advisor: Dr. Thomas Holtz GEOL 394 1 Abstract Theropod dinosaurs are inferred to have been ancestrally carnivorous and include numerous lineages specialized for hypercarnivory. However, evidence from fossil gut contents, anatomical characteristics, and phylogenetic bracketing suggests that several theropod clades convergently transitioned away from a carnivorous lifestyle to become herbivores or omnivores. The evolutionary drivers of these trophic shifts are unknown. Methods involving the use of the Paleobiology Database (PBDB) were used to test for the potential impact of ecological factors that may have affected the diversification of non-hypercarnivorous theropods, such as the diversity of other herbivorous vertebrates, the diversity of plants, and change in global sea level. After demonstrating feasibility of the proposed methods by using restricted parameters (solely considering oviraptorosaurian theropods from the Cretaceous of Asia and contemporaneous herbivores), said methods were applied to an expanded dataset including more than 500 taxa from 51 geologic formations. No statistically significant correlations were found between non- hypercarnivorous theropod diversity and that of plants, but overall diversity of non- hypercarnivorous theropods was found to positively correlate through space and time with the diversity of other herbivores. These results suggest that non-hypercarnivorous theropods did not strongly compete with contemporaneous herbivores. Instead, their diversity may have been promoted by the presence of other herbivores or by extrinsic environmental factors that favored herbivorous species as a whole. Table of Contents Abstract ...........................................................................................................................................2 Table of Contents ...........................................................................................................................2 Introduction and Background ......................................................................................................3 Method of Analysis ........................................................................................................................6 Presentation of Data and Analysis of Uncertainty ......................................................................8 Case study ...........................................................................................................................8 Expanded dataset of herbivorous taxa ...........................................................................18 Testing for correlation with plant diversity ...................................................................26 Testing for correlation with average global sea level ...................................................27 Discussion of uncertainty ................................................................................................27 Discussion......................................................................................................................................28 Suggestions for Future Work ......................................................................................................29 Conclusions ...................................................................................................................................30 Acknowledgements ......................................................................................................................30 Bibliography .................................................................................................................................30 Appendix A: Taxon Occurrence Data Used in Case Study .....................................................35 Appendix B: Additional Herbivore Occurrence Data Used in Expanded Dataset ................46 Appendix C: Plant Occurrence Data .........................................................................................71 2 Appendix D: Average Global Sea Level of Examined Geologic Stages ..................................75 University of Maryland Honor Pledge .......................................................................................76 Figure 1: Schematic of theropod skull morphology....................................................................4 Figure 2: Phylogenetic tree of theropods .....................................................................................5 Table 1: Genus counts of oviraptorosaurs and potential competitors ......................................9 Figure 3: Oviraptorosaur diversity plotted against diversity of potential competitors ........11 Figure 4: Oviraptorosaur diversity plotted against diversity of other non-hypercarnivorous theropods ..........................................................................................................................12 Figure 5: Measures of diversity plotted against geologic stages ..............................................13 Table 2: Calculated correlation coefficients for case study .....................................................14 Figure 6: Residual diversity of oviraptorosaurs over time ......................................................15 Figure 7: Residual diversity of other non-hypercarnivorous theropods over time ...............16 Figure 8: Residual diversity of all potential competitors over time ........................................17 Table 3: Calculated correlation coefficients after correction of biases ...................................18 Figure 9: Expanded dataset of diversity plotted over time ......................................................19 Figure 10: Residual diversity of all non-hypercarnivorous theropods over time (by DBCs) ............................................................................................................................................20 Figure 11: Residual diversity of all non-hypercarnivorous theropods over time (by DBFs) 20 Figure 12: Residual diversity of all potential competitors over time (by DBCs) ...................21 Figure 13: Residual diversity of all potential competitors over time (by DBFs) ....................21 Table 4: Calculated correlation coefficients using expanded herbivore dataset....................22 Table 5: Calculated correlation coefficients relating theropod and plant diversity ..............27 Table 6: Calculated correlation coefficients relating theropod diversity and average global sea level .............................................................................................................................27 Introduction and Background Theropods are a diverse group of dinosaurs, comprising numerous disparate species both extant (in the form of birds) and extinct. Theropods are ancestrally carnivorous and encompass all dinosaurs known to be specialized for carnivory (Hendrickx et al., 2015). However, some Mesozoic theropods preserve fossil evidence of departure from a hypercarnivorous lifestyle, including plant material found as gut contents (Zhou and Zhang, 2002; Zheng et al., 2011; Ji et al., 2012) and gastroliths suggestive of a gastric mill similar to modern herbivorous birds (Ji et al., 1998; Kobayashi et al., 1999; Ji et al., 2003; Zhou and Zhang, 2006; Xu et al., 2009; Lee et al., 2014; Wang et al., 2016). In 2011, Zanno and Makovicky identified 21 morphological characters strongly correlated with herbivory in Mesozoic theropods: a downturned dentary symphyseal region (1); a rostrally projecting dentary symphysis (2); a ventrally concave cranioventral margin of the dentary (3); rostral (4), caudal (5), or total (6) tooth loss in the 3 dentary; conical dentary (7) or premaxillary (8) teeth, particularly the rostralmost dentition (9); symmetrical teeth (10); loss of ziphodonty (blade-shaped teeth) (11); elongate (12), procumbent (13), or unserrated (14) premaxillary teeth; tooth loss in the premaxilla (15); lack of pronounced replacement waves of teeth (16); lanceolate (lance-shaped) cheek teeth (17); heterodont dentition (teeth varied in shape) (18); densely-packed dentition (19); a ventrally displaced mandibular joint (20); and the presence of more than 10 cervical (neck) vertebrae (21) (see Fig. 1 for a pictorial orientation of anatomical terms). Figure 1. Schematic of the skull of the therizinosaur Erlikosaurus, in left lateral view of the upper jaw (A), left lateral view of the lower jaw (B), and dorsal view of the lower jaw (C), with anatomical terms used in this paper labeled. Based on a digital reconstruction of specimen IGM 100/111, provided in Lautenschlager et al., 2014. 4 By documenting the distribution of these characters among theropods, Zanno and Makovicky inferred herbivory as the predominant diet in the ceratosaur Limusaurus and many clades within Maniraptoriformes (Ornithomimosauria, Therizinosauria, Alvarezsauria, Oviraptorosauria, Scansoriopterygidae, Avialae, and the troodontid Jinfengopteryx) (Zanno and Makovicky, 2011). Subsequently, the theropod Chilesaurus was described by Novas et al. in 2015 as a basal tetanuran that had adapted to a non-hypercarnivorous diet independently of the aforementioned groups (Fig. 2). Additionally, though modern birds have diversified to become specialized for a vast variety of feeding habits, herbivory has evolved several times in their history (Olsen, 2015). Because carnivory is the likely ancestral condition for theropods, herbivorous theropods almost certainly went through a