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

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Tensionat keystone dynarnics may explain the benefit of retention of multiple elements in the tyrannosaurid arctometatarsus, which contrasts with fused metapodia in ratites and in horses, bovids, cervids, camelids, giraffids, and other ungulates. A system of three bones and elastic ligaments may have imparted resilience and enhanced collective strength, properties diminished in a single metapodial element. The retention of multiple metapodial elements as a stay against torsion may be paralleled the Patagonian cavy, an agile cursorial rodent whose mesaxonic metapodia subtend an arch (personal observation). However, the rnetatarsals of the cavy lack the extremity of plantar angulation seen in the arctometatarsus, so the analogy is superficial and remains to be tested biornechanically. A dynamically robust metatarsus is perhaps selectively Iogical in tyrannosaurids, which are much larger than most classically cursorial ratites and ungulates. Giraffes are potentially problematic to this view, because they are cioser in mass to tyrannosaurids and have fused metapodia. As quadrupeds, giraffes have the advantage of lower loadings on the metapodia when trotting because the load is shared by two limbs, although forces on each metapodium when galloping would be higher because the duty factor is low (Alexander et al. 1977). Giraffes are also not as fast as might be expected from the extrerne elongation of their limbs. The energy-absorbing metapodium of adult tyrannosaurids conceivably enabled them to outmatch giraffes in certain maneuvers or in linear speed, but such speculative transtemporal cornparisons are unprodudive.
The preceding discussion derives from an adaptationist perspective. In contrast, phylogenetic and developmental wntingency, rather than seledive canalization, c m also explain the persistence of separate elements in the tyrannosaurid metatarsus. Giraffids, including the modem giraffe and okapi, inherited their metatarsal morphology from less specialized artiodactyls. Ratite birds inherited fused metapodial elements from their avian ancestors, and selective pressures for cursoriality need not be invoked to explain their ankylosed morphology. With this caveat in mind, I now explore arctometatarsus function in the context of performance and phylogeny. Comparative phylogenetic and functional implications The tensional keystone model diers from kinematics likely evident in the foot of Allosaurus or other theropods with three largely autonomous metatarsals. As with humans (Kerr et al. 1987), footfall loadings wolild cause their outer metatarsals to splay beyond their resting orientation, essentially spreading the foot apart. During deviations from linear locomotion, metatarsals would experience increased bending Ioads individually, rather than as part of a single structure as predicted for the arctometatarsus (Figure 3.12). Results from Chapter 2 show that broad-footed theropods are not uniforrn in metatarsus morphology. None of these animals, however, displays plantar constriction of MT III consistent with distal unification of the metatarsals, which would occur in the arctometatarsalian pes under the tensional keystone model.
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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
Page 105 and 106: Figure 2.7. Left MT III of Tyrannos
Page 107 and 108: Figure 2.8. Left MT III of Gorgosau
Page 109 and 110: Figure 2.9. Left MT III of an omith
Page 111 and 112: Figure 2.10. Left metatarsus of Tmd
Page 113 and 114: Figure 2.1 1. Left MT III of Elmisa
Page 115 and 116: Figure 2.12. Right MT III of Deinon
Page 117 and 118: Figure 2.13. Left MT III of Allosau
Page 119 and 120: Figure 2.14. Left metatarsus of Sin
Page 121 and 122: Figure 2.15. Plots of MT Ill specir
Page 123: Figure 2.16. Plot of third metatars
Page 126 and 127: tv . ... . Ri. . . .
Page 129 and 130: Figure 2.19. Plot of third metatars
Page 131 and 132: CHAPTER 3: Tensile keystone model o
Page 133 and 134: dynamically transmitted Iommotor fo
Page 135 and 136: Table 3.1 . Metatarsi examined in t
Page 137 and 138: interrnetatarsal dynamics in these
Page 139 and 140: compelled analysis of movement evid
Page 141 and 142: Once prepared, TMP 94.1 2.602 and i
Page 143 and 144: Daspletosaurus tomsus (MOR 590), an
Page 145 and 146: 2. Freedom of movement inferred fro
Page 147 and 148: Table 3.2. Surface areas of intemet
Page 149 and 150: phylogenetic bracketing Wtmer 1995)
Page 151 and 152: 4) Forces from anterior displacerne
Page 153: e expected for tyrannosaurid interm
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Page 159: Figure 3.1. Schematic representatio
Page 163: Figure 3.3. CT reconstruction of ri
Page 167: Figure 3.5. MT II (left element) an
Page 171: Figure 3.7. Osteological correlates
Page 175: Figure 3.9. Osteological correlates
Page 179: Figure 3.1 1 ae. The metatarsal rec
Page 187: Figure 3.13. Ligament contribution
Page 191 and 192: Figure 3.15. Anatorny of the equid
Page 193: Figure 3.16. Cornparison of loading
Page 196 and 197: (nodes), and solving stresslstrain
Page 198 and 199: The practicality of the finite elem
Page 200 and 201: collective density of trabeculae (K
Page 202 and 203: 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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. - Elastic modulus (GP4 Ex EY Ez P
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conversion. Volume-to-nuages facili
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maintained. An angle of 2 degrees p
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of MT III (Figure 4.4, pinpointed b
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anterodorsal rotation of the distal
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allowed to stretch slightly under t
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Figure 4.1. Initial loads and bound
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Figure 4.3. Finite element mesh of
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Figure 4.5. Strain distribution in
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CHAPTER 5: Mechanical and evolution
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y distal intermetatarsal ligaments,
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Probable fundion of the tyrannosaur
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Ornitholestes, and camosaurs) incre
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morphology matches in degree the co
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discussion elucidates the evolution
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face of the skull met part of the m
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Alternately, a morphological novelt
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outgroup to ail theropods, and the
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convincingly evident in figures of
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parsimonious scenarios are outlined
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dromaeosaurids], and a dade compris
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arctometatarsalian forrns. The conv
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Proximal intermetatarsal ligaments
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witti a surfeit of potentially supp
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Figure 5.2. Phylogeny of the Therop
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Bock W.J. and von Wahlert G. Evolut
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Cume P.J. 1997. Theropoda. In: Fari
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Grenard S. 1991. Handbook of Alliga
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Liem K.F. and Osse J.W.M. 1975. Bio
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Richtsmeier J.T. and Cheverud J.M.
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Woo S., Maynard J., Butler O. 1987.
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Different variables in a PCA will h
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THE UNIVERSITY OF CALGARY Eric Snively A ... - Ohio University

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