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

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1985, Bryant and Seymour 1990). If a fossil taxon does not have a morphologically similar modem relative, or if it possesses a novel osteological feature not seen in extant vertebrates, inference of an unpreserved organ is still viable through the ahistorical extrapolatory approach (Bryant and Russell 1992). Extrapolatory inference draws from biological generalizations of gross anatomy, histology, and constnictional morphology. These universalities include the marks soft tissues leave on bone, such as scaning at the origins of tendons and ligaments, or the foramina through which blood vessels and nerves pass as bone grows around them. Examples of the extrapolatory approach include vascuiar evidence for nasal mucosal elaboration in herbivorous dinosaurs (Witmer and Sampson 1999), reconstruction of pelvic respiratory systems in omithischians (Carrier and Farmer 2000), and histological inference of ligaments associated with the platelike armor of Stegosaurus (Buffrenil et al. 19s). Thus unpreserved organs in fossil vertebrates are interpreted most reliably through consideration of homology, surface aratomy, and fine histology when possible. Osteological anatomy reveals marks of soft tissues that have developmental precedenœ over the skeleton (Witmer 1995), but that act in conjunction with bones. One example of a functionally integrated system of soft and hard tissues is the metatarsus of Mesozoic theropod dinosaurs, wtiich incorporated bones, ligaments, and their associated vasculature and nervous supplies.
The arctometatarsus as an example of ligament-bone integration During the Cretaceous, an unusual morphology of the metatarsus evolved in several taxa of the Theropoda, a predominateiy camivorous clade of bipedal dinosaurs. Termed the arctometatanus (Holtz 1994a), this structure displays a striking third metatarsal that is wmparatively gracile towards the ankle and robust towards the toes. Figure 1.1 shows an example. The word "arctometatarsus" refers to the entire pedal metapodium of these theropods; arctometatarsalian describes the structure, or designates a taxon whose members possess an ardometatarsus. There are four elements to the osteological definition of the arctometatarsus (Holtz 1994a). The third (central) metatarsal (designated herein as MT III) is constricted proximally relative to the condition in other theropods. MT III is also triangular in distal cross section, and thus constricted towards the plantar surface (flat of the foot). The outer weight bearing metatarsals, the second and fourth (MT II and MT IV), encroach towards the midsagittal plane of MT III where it wnstricts, and maintain contact with MT III distally and proximally. All three metatarsals therefore forrn a wedge-and-buttress morphology, in which buttressing surfaces of the outer metatarsals overhang and contact surfaces of the wedgelike third metatarsal (Holtz 1994a). In addition to these osteological characteristics, severai authors have commented on the likely presence of ligaments that bound the arctometatarsus together. <strong>Snively</strong> (1 994) reported extensive rugosities on the metatarsal articular
Page 1 and 2: THE UNIVERSITY OF CALGARY Functiona
Page 3: Many figures in this thesis use col
Page 6 and 7: ACKNOWLEûGEM ENTS Many friends and
Page 8 and 9: Approval page Acknowledgements Tabi
Page 10 and 11: CONCLUDING COMMENTS Figures for Cha
Page 12 and 13: CHAPTER 5: Mechanical and phylogene
Page 14 and 15: LIST OF FIGURES Figure 1 .l. Phylog
Page 16 and 17: Figure 3.6. Osteological correlates
Page 18 and 19: AMNH GI HMN IVPP MOR NMC OMNH PIN P
Page 20 and 21: and constructional morphology revea
Page 24 and 25: surfaces of a Tyrannosaurus rex spe
Page 26 and 27: 3. Troodontidae (Figure 1.2): Trwdo
Page 29 and 30: Hypothesized functions of the tyran
Page 31 and 32: 1. Atomization (Chapters 2 and 3).
Page 33 and 34: Figure 1.1. P hylogenetic diagram o
Page 35 and 36: Figure 1.2. Phylogenetic diagram of
Page 41: Figure 1 .S. Skeletal restorations
Page 44 and 45: did not quantify the degree of prox
Page 46 and 47: qualitative debate over arctometata
Page 48 and 49: This hypothesis focuses on tyrannos
Page 50 and 51: Table 2.1. Theropod and Plafeosauru
Page 52 and 53: specimens in the figures reflects a
Page 54 and 55: were not attempted. While this limi
Page 56 and 57: Chapter 3). 1 now address variation
Page 58 and 59: - Ç6'P 1 68'€tr 1 L'OC 99'66 L'9
Page 60 and 61: Table 2.3: Log-transformed values f
Page 62 and 63: experiences a sharp laterally indin
Page 64 and 65: ecause it can be cursorily dassifie
Page 66 and 67: arctometatarsalian specimens, the l
Page 68 and 69: ) Shaf€ and region of proximal ar
Page 70 and 71: 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 3.7. Osteological correlates
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Figure 3.9. Osteological correlates
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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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. - 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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