THE UNIVERSITY OF CALGARY Eric Snively A ... - Ohio University

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Proximal intermetatarsal ligaments were probably a prerequisite to the developmental cascade responsible for the arctometatarsus (including the appearance of extensive distal ligaments). The arctometatarsus is a homoplasious (convergent) complex that evolved several times in caelurosaurs. The developmentat potential for the arctometataisus was present within coeiurosaurs, but apparentiy not in other theropod taxa. An arctometatarsus discovered in a noncoelurosaurian theropod will falsify this conclusion. Finite element results suggest that distal ligaments were mechanically necessary in the arctometatarsus, to prevent breakage of the proximal splint of MT III during vigorous activity. If tensile keystone dynamics abetted agility, the probable selective regime under which the arctometatarsus became established was predation performance in carnivorous taxa. These conclusions, and the mapped distribution of characters in Figures 5.1 through 5.6, suggest possible scenarios for the evolution of the arctometatarsus. The parsimonious distribution on Holtz's phylogeny (Holtz 2000) predicates the scenario outlined below. A scenario serves as an expanded evolutionary hypothesis inwrporating a number of Iines of evidence, and is most valid when based on simpler hypotheses of relationship (Taffersall and Eldredge 1977). While scenario building was more the rubric in evolutionary systernatics, the following narrative phylogeny is faisfiable in whde or in part, and integrates the
available evidence without proprietaiy didacticism, Thus the scenario is presented as a tentative hypothesis of arctometatarsus evolution. lnterrnetatarsal ligaments were present in early camivorous coelurosaurs. At some point the clade acquired the phylogenetic and developmental propensity for plantar angulation of the metatarsals. When this potential was triggered (along with the development of a lengthened metapodium), the third metatarsal became canstricted plantarly and proximally, and interrnetatarsal ligaments developed distally on the artictular surfaces. The arctometatarsus developed convergently in the Arctometatarsalia, Elmisaufldae (induding Umisaurus), and in the alvarezsaurid Mononychus. The arctometatarsus may have imparted functional and selective benefits to predation andior escape behavior. Within the Arctometatarsalia, predation performance was the likely selective benefit to adult tyrannosaurids and troodontids, and was possibly of benefit to omithomimosaurs and elmisaurids as well (omnivory has been suggested for these foms and for troodontids; Cume 1997, Holtz et al. 2000; although see Ryan et al. 2000). The scenario is consistent with the evidence presented in this thesis, but is speculative given the lack of observational data. The remoteness of fossil organisms, their temporal span, and taphonomic limitations to sample sire curtail more extensive investigation into the evolution of the arctometatarsus. However, while evolutionary scenarios are difficult to corroborate (Gee 2000), they are easy to falsify with phylogenetic evidence (Lauder et al. 1989). By this criterion, evolutionary hypotheses are as scientifically credible as hypotheses
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THE UNIVERSITY OF CALGARY Functiona
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Many figures in this thesis use col
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ACKNOWLEûGEM ENTS Many friends and
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Approval page Acknowledgements Tabi
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CONCLUDING COMMENTS Figures for Cha
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CHAPTER 5: Mechanical and phylogene
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LIST OF FIGURES Figure 1 .l. Phylog
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Figure 3.6. Osteological correlates
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AMNH GI HMN IVPP MOR NMC OMNH PIN P
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and constructional morphology revea
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1985, Bryant and Seymour 1990). If
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surfaces of a Tyrannosaurus rex spe
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3. Troodontidae (Figure 1.2): Trwdo
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Hypothesized functions of the tyran
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1. Atomization (Chapters 2 and 3).
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Figure 1.1. P hylogenetic diagram o
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Figure 1.2. Phylogenetic diagram of
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Figure 1 .S. Skeletal restorations
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did not quantify the degree of prox
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qualitative debate over arctometata
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This hypothesis focuses on tyrannos
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Table 2.1. Theropod and Plafeosauru
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specimens in the figures reflects a
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were not attempted. While this limi
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Chapter 3). 1 now address variation
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- Ç6'P 1 68'€tr 1 L'OC 99'66 L'9
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Table 2.3: Log-transformed values f
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experiences a sharp laterally indin
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ecause it can be cursorily dassifie
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arctometatarsalian specimens, the l
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) Shaf€ and region of proximal ar
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a) Ginglymus. Figure 2.14 shows the
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) Shaft and region of proximal arti
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measurements of width pV2S%TU-DE an
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Table 2.4b Variancelmeasurement eac
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the largest sum of linear measureme
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Table 2.5: Specimen statistics Herr
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and Sinraptor dongi specimens. With
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In addition, a hook like proximal a
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oth physical narrowing and elongati
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1s the MT 111 shape segregation fun
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tyrannosaurids, ornithomimid, and t
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proximal constriction, white EImisa
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Figure 2.2. Tyrannosaurid, trwdonti
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Figure 2.4. Dromaeosaurid and carno
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- Anterior (flexor) surface medial
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Figure 2.7. Left MT III of Tyrannos
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Figure 2.8. Left MT III of Gorgosau
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Figure 2.9. Left MT III of an omith
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Figure 2.10. Left metatarsus of Tmd
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Figure 2.1 1. Left MT III of Elmisa
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Figure 2.12. Right MT III of Deinon
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Figure 2.13. Left MT III of Allosau
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Figure 2.14. Left metatarsus of Sin
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Figure 2.15. Plots of MT Ill specir
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Figure 2.16. Plot of third metatars
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tv . ... . Ri. . . .
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Figure 2.19. Plot of third metatars
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CHAPTER 3: Tensile keystone model o
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dynamically transmitted Iommotor fo
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Table 3.1 . Metatarsi examined in t
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interrnetatarsal dynamics in these
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compelled analysis of movement evid
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Once prepared, TMP 94.1 2.602 and i
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Daspletosaurus tomsus (MOR 590), an
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2. Freedom of movement inferred fro
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Table 3.2. Surface areas of intemet
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phylogenetic bracketing Wtmer 1995)
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4) Forces from anterior displacerne
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e expected for tyrannosaurid interm
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The preceding discussion derives fr
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weapons sparring), and the arctomet
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Figure 3.1. Schematic representatio
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Figure 3.3. CT reconstruction of ri
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Figure 3.5. MT II (left element) an
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Figure 3.1 1 ae. The metatarsal rec
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Figure 3.13. Ligament contribution
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Figure 3.15. Anatorny of the equid
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Figure 3.16. Cornparison of loading
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(nodes), and solving stresslstrain
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The practicality of the finite elem
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collective density of trabeculae (K
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A FORCE INPUTS AND MATERIAL PROPERT
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Alexander et al. (1 979) rewrded a
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The preceding loading regime entait
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detemined by using the photographic
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2. Preparation of data for contour
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Page 224: Figure 4.1. Initial loads and bound
Page 228: Figure 4.3. Finite element mesh of
Page 232: Figure 4.5. Strain distribution in
Page 236 and 237: CHAPTER 5: Mechanical and evolution
Page 238 and 239: y distal intermetatarsal ligaments,
Page 240 and 241: Probable fundion of the tyrannosaur
Page 242 and 243: Ornitholestes, and camosaurs) incre
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Page 248 and 249: face of the skull met part of the m
Page 250 and 251: Alternately, a morphological novelt
Page 252 and 253: outgroup to ail theropods, and the
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Page 258 and 259: dromaeosaurids], and a dade compris
Page 260 and 261: arctometatarsalian forrns. The conv
Page 264 and 265: witti a surfeit of potentially supp
Page 267: Figure 5.2. Phylogeny of the Therop
Page 278 and 279: Bock W.J. and von Wahlert G. Evolut
Page 280 and 281: Cume P.J. 1997. Theropoda. In: Fari
Page 282 and 283: Grenard S. 1991. Handbook of Alliga
Page 284 and 285: Liem K.F. and Osse J.W.M. 1975. Bio
Page 286 and 287: Richtsmeier J.T. and Cheverud J.M.
Page 288 and 289: Woo S., Maynard J., Butler O. 1987.
Page 290 and 291: Different variables in a PCA will h
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