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Osteology of a Near-Complete Skeleton of Tenontosaurus tilletti (Dinosauria: Ornithopoda) from the Cloverly Formation, Montana, USA

The character diagnosis of Tenontosaurus tilletti has been revised and redefined into a more robust and quantifiable state. Significant emphasis is placed on constructing phylogenetic definition in such a method, as it prevents occlusion of true character states by alleviating potential individual interpretational bias. Previous placement within the Iguanodontia is refuted based on the lack of character affinity with the defining synapomorphies of the clade. The clade Hypsilophodontidae (=Hypsilophodontia), along with Iguanodontia, however is deemed to be in critical need of refinement to account for recent discoveries and re-classifications of certain euornithopods. Several of the synapomorphies are out-dated and deemed redundant in favour of a more quantifiable approach. Re- definition of these clades is critical if the current state of basal euornithopodan relationships is to be resolved. Phylogenetic studies must be approached from a multidisciplinary perspective; integration of tectonostratigraphical, ontogenetic, palaeoecological, and biomechanical data with sets of well-defined primary homologies are essential in increasing phylogenetic resolution and generating stratigraphically feasible ancestor-descendant relationships. Material attributed to Tenontosaurus tilletti is in need of strict re-analysis; the significant quantity of specimens attributed to this species is potentially the result of poor stratigraphic constraints and the vast spatiotemporal span occupied. Future revision of this material is expected to reveal temporal variations on the species -level inherently linked to environmental evolution, as well as possibly provide clues to sexual dimorphism in contemporaneous, yet morphologically distinct tenontosaurs.


Abstract
The character diagnosis of Tenontosaurus tilletti has been revised and redefined into a more robust and quantifiable state. Significant emphasis is placed on constructing phylogenetic definition in such a method, as it prevents occlusion of true character states by alleviating potential individual interpretational bias.
Previous placement within the Iguanodontia is refuted based on the lack of character affinity with the defining synapomorphies of the clade. The clade Hypsilophodontidae (=Hypsilophodontia), along with Iguanodontia, however is deemed to be in critical need of refinement to account for recent discoveries and re-classifications of certain euornithopods. Several of the synapomorphies are outdated and deemed redundant in favour of a more quantifiable approach. Redefinition of these clades is critical if the current state of basal euornithopodan relationships is to be resolved. Phylogenetic studies must be approached from a multidisciplinary perspective; integration of tectonostratigraphical, ontogenetic, palaeoecological, and biomechanical data with sets of well-defined primary homologies are essential in increasing phylogenetic resolution and generating stratigraphically feasible ancestor-descendant relationships. Material attributed to Tenontosaurus tilletti is in need of strict re-analysis; the significant quantity of specimens attributed to this species is potentially the result of poor stratigraphic constraints and the vast spatiotemporal span occupied. Future revision of this material is expected to reveal temporal variations on the species -level inherently linked to environmental evolution, as well as possibly provide clues to sexual dimorphism in contemporaneous, yet morphologically distinct tenontosaurs.

Introduction
Tenontosaurus tilletti is a moderately-sized graviportal ornithopod from the Lower

Aims and Objectives
The aim of this study is to provide a full inexplicably had their restored portions removed, and many of the more slender elements have become broken and damaged beyond repair. Despite this, the entire skeleton (estimated to be 85-90% complete) retains an incredible degree of preservation, with most significant structures largely intact rendering it a critical specimen for study. The intention is to compare this specimen with the holotype (AMNH 3040; paratypes YPM-PU 16338 and YPM 3456) and other previously described specimens by Ostrom (1970) and Forster (1990), to detect specific variations to ascertain true identity and test the reliability of these previous studies in terms of the completeness of the material described. The variable degree of restoration is taken into account, as in some areas this largely occludes detail (e.g. in the skull). The condition of the vertebral column is also problematic as many elements have been largely fragmented, distorted and disordered, and the assignment to any particular genus or species thus challenging.
A significant feature of this specimen is that it represents a sub-adult stage (assuming the given classification to Tenontosaurus tilletti to be unequivocal), so variations to the adult holotype will only be subtle if present. The description of this specimen will allow for more robust phylogenetic analyses rather than using a combination of several different specimens that could potentially represent multiple stages of tenontosaur growth, or even entirely new species. A complete comparison with Hypsilophodon foxii (and minor additional material) is also undertaken to elucidate the nature of the relationship between Tenontosaurus and the clade 'Hypsilophodontidae'. A full phylogenetic analysis unfortunately is beyond the scope of this study, but hopefully this will provide a firm basis for future revision. Understanding ontogeny to reconstruct phylogeny is also intended to be highlighted, as currently character matrices used in phylogenetic studies provide no account for ontogenetic variations, thus potentially occluding true primary homology identification and leading to phylogenetic instability.  Fauna include T. tilletti, ankylosaurs (e.g. Sauropelta edwardsi), sauropods, a small theropod, ornithomimids, a hypsilophodont (Zephyrosaurus), dromaeosaurids (e.g.

Institutional Abbreviations
Deinonychus antirrhopus), turtles, frogs, crocodiles, and triconodont mammals (e.g. Ostrom, 1969;Forster, 1984Forster, , 1990Cifelli et al., 1998). This represents a large, diverse parautochthonous taxa, the palaeoecology of which has been preliminarily studied by Oreska et al. (2007) based on vertebrate microfossil assemblages presumably from members of the above taxa, and is the first palaeoecological study of the Cloverly Formation since Forster (1984). Unfortunately, this is published only in abstract form, so a recent palaeoecological study is currently unavailable for integrative review.

Geological Setting
A sedimentological overview is fundamentally tied to palaeontology in its use to interpret palaeoecology; that is to say using palaeontology (e.g. functional morphology, morphometrics, and diet) to interpret behaviour is directly coupled with palaeoenvironmental data inferre d from sedimentology to reconstruct the lifestyle and ecological behaviour of an organism -essentially the central aim for a palaeontologist. A stratigraphic summary is also critical in placing dinosaur-bearing units into an intraformational temporal and spatial context and for correlation with extraformational fossiliferous units. A synopsis is presented here for such a purpose.

Palaeoecology
Tenontosaurus is frequently cited as being found associated with remains of the dromaeosaur Deinonychus antirrhopus, such as the presence of shed teeth at multiple dig sites along with other more-complete skeletal material (Forster, 1984(Forster, , 1990Cifelli et al., 1997;Ostrom, 1969Ostrom, , 1970Maxwell and Ostrom, 1995). As it is rarely found with other prey taxa, it is apparent that the food of choice for D.
antirrhopus was T. tilletti -it is unlikely that this association is due to a taphonomic or collecting bias. LL.12275 was also found with two Deinonychus teeth embedded in its neck (J. Nudds, pers. comm.) Roach and Brinkman (2007)  Tenontosaurus was clearly herbivorous based primarily on tooth morphology.
Norman and Weishampel (1985) studied ornithopod feeding mechanisms as during the latter half of the Mesozoic era, ornithopods diversified from an originally simple bauplan, becoming increasingly abundant with a range of body sizes, and thus dietary requirements. The authors conclude that a range of alternative modes of transverse food grinding were utilised by ornithopods achieved by a combination of an "isognathic" jaw frame and relatively simple adductor muscles with complex tooth batteries and either maxillary or mandibular rotation. Such motions are indicated by median-angle tooth wear on many ornithopods (Weishampel and Jianu, 2000). This ultimately led to a more efficient method of grinding plant fibres analogous to modern mammals, and may have been one of the critical factors contributing to the ascent and diversification of the Ornithopoda. Norman (1998) emphasizes similarly that functional improvements in cranial complexity are contiguous with increased proficiency in the gathering and processing of food. This is suggested to be related to niche partitioning of individual species (hence the substantial interspecific variation in cranial and tooth morphologies), or as a direct response to progressively arid ("xeric") adapted vegetation throughout the latter half of the Mesozoic.
Further evidence on the dietary habits of Tenontosaurus is provided in Stokes, is that the erection of some species, or genera, may be erroneous in that they simply represent the alternative gender to another organism. Whether such an incongruity has ever been recorded is presently unknown; however determining such potential fundamental flaws would be extremely difficult to discern, and requires careful consideration in future phylogenetic studies.

Biomechanics
The structure and morphology of the appendicular and axial skeleton of   This would need to be tested rigorously with a wide sample range (destructive analysis) of all known hypsilophodonts; it may be that the clade Hypsilophodontidae is dissolved, as has been suggested previously but never fully enforced, with all taxa being assigned as younger ontogenetic stages of known iguanodontian genera. If this becomes the case, then the term "hypsilophodont" will not become redundant -instead of providing a specimen with a phylogenetic status, it will merely be a ancestor-descendant relationships are coupled to tectonic processes is an essential prerequisite; that is to say that to draw a link between two taxa requires an 'event' (e.g. tectonics creating a dispersal or vicariant signal; co-evolution and adaptation; palaeoclimatic variation) to force an evolutionary response in an organism or group of organisms. If no such event is recorded, then phylogenetic relationships become unfeasible. Therefore great care must be taken to ensure that when generating cladograms one forges taxa associations that are consistent with tectonostratigraphic records. Thus palaeontology becomes a multidisciplinary study, combining knowledge of not only biological processes, but also an understanding of large-scale and local geological interactions which are inherently, but often subtly, linked to a palaeoecosystem.
One point that requires emphasis may be something that has been broadly overlooked in the past: does a relatively complex morphology necessarily represent a 'derived' state within a clade? The question arises, as within a given ecosystem, the organisms will often be in steady-state equilibrium for the ecological duration, as each species will be specifically adapted to its individual partitioned niche within the system. If the ecosystem were to change, and suddenly there is a more

Phylogeny
Ornithischians are defined by having a bird-hipped configuration of the pelvic girdle, which is to say the pubes have been rotated posteriorly to lie alongside the ischia (e.g. Sereno (1986, 1999a) which is perhaps the best option until conclusive systematic relationships of 'hypsilophodonts' can be elucidated with confidence. Iguanodontia represents a paraphyletic assemblage of increasingly derived taxa (e.g. Galton, 2009), yet appears to remain problematic despite the robust cladistic analysis of Butler et al. conclude with the remark that the "instability of basal ornithopod phylogeny" currently restricts any unambiguous phylogenetic definition regarding the Iguanodontia. Whereas this is somewhat challenging towards this study, it provides a direct target for future cladistic analyses to be aimed.   Within the phylogenetic analysis undertaken by Weishampel and Heinrich (1992), missing data comprises 28% of character matrix, and character absence is variably distributed. The use of incomplete data sets is therefore potentially the cause of disparity within incongruent analyses (and the source of polytomies); however, at any given time of analysis, the most-complete data sets are compiled based on what is currently known, and therefore subject to change as gaps are filled over time. Nonetheless, caution is emphasized when utilising partial data sets, as the relationships drawn will often appear conclusive when in fact are occluded to an undeterminable degree. This problematic approach is also discussed by Sereno "a fundamental requirement for including more than one species within a genus is a reasonably consistent standard of skeletal material variation within a given genus".
Based upon this, and assuming precision in the descriptions of Forster (1990) and Winkler et al. (1997), the dissection of the Tenontosaurus genus into two separate species appears authentic. Given the vast amount of material assigned to T. tilletti from the Cloverly Formation, and the associated large temporal range, it would not be unexpected that if upon careful examination of all specimens that more than one species would be present.
Forster (1990) provides the following diagnosis for T. tilletti: The clade Hypsilophodontidae has previously been defined by the following characters (from Forster 1990, sensu Sereno 1986): 1. Ossified hypaxial tendons in the tail 2. Rod-shaped pre-pubic process 3. Partially ossified sternal segments of the cranial dorsal ribs with corresponding flattening of the caudal edges of the sternal plates 4. Length of humerus either greater to or equal the length of the scapula Compared to the well-defined Iguanodontia, this set of synapomorphies poorly represents the Hypsilophodontidae clade, and if it genuinely still exists requires thorough re-analysis to determine a broad suite of defining characters. Many of the above require revision: the first is widely synapomorphic amongst ornithischians; the third may relate to ontogeny; and the fourth may relate more to functional variability (e.g. changing stance through ontogenetic growth) than taxonomic status.
Sereno (1986) defines the following synapomorphies of the Iguanodontia clade: 1. Premaxillary teeth absent 2. Ventral premaxillary margin everted 3. Maxilla with paired ventral processes: primitive rostromedial process and new rostroventral process which laps the premaxilla palate ventrally 4. Dentary with parallel dorsal and ventral borders 5. Denticulate predentary bill margin 6. Leaf-shaped denticles on teeth 7. External opening of antorbital fossa small or absent 8. Manus digit III reduced to three phalanges 9. Femur with shallow cranial intercondylar groove and deep caudal intercondylar groove 10. Premaxilla contacts the lachrymal 11. Rostral edge of quadrate notched into a "quadrate foramen" 12. Space separating the ventral margin of the quadratojugal from the jaw articulation 13. Quadratojugal reduced in size relative to the quadrate 14. Diamond-shaped maxillary and dentary crowns 15. Enamel absent from the medial side of maxillary teeth and lateral side of dentary teeth 16. Maxillary crowns narrower axially than opposing dentary crowns 17. Primary ridge on maxillary teeth stronger than primary ridge on dentary teeth 18. Low postacetabular blade and well-developed brevis shelf 19. Proximally placed obturator process on ischium 20. Ischial shaft round in cross-section, decurved and footed Comparison with this character suite is essential in defining the position of Tenontosaurus relative to the Iguanodontia clade. One would assume that a majority of character states must be present for inclusion within a clade.
The degree of preservation and restoration is highly variable: several bones are entirely restored, and are not described here; others are partially restored, and only characters that are fully visible are described, with inferences to concealed morphology. Unfortunately, most vertebrae are in poor condition, variably warped and most do not articulate; whether this status is the result of taphonomy and preservation or due to restoration is unknown, and are thus largely omitted from this study. The significance of this is low, as it is unlikely that any new autapomorphies or synapomorphies would be found and study of such damaged bones is not deemed profitable. The ribs and chevrons are also dismissed from study, partially due to their simple structures that are described elsewhere and also that on dismounting the specimen by the museum in 2004, apparently it was deemed necessary to break them into multiple disassociated pieces.
A full morphological description can be found in appendix I; only the most significant variations from previous studies are provided here. Other slight variations are encountered; however, these subtleties are likely attributed to minor intraspecific or individual distinction or ontogeny as oppose to true interspecific variation and are outlined in appendix 1. It is worth noting that there is currently no distinction between the masculine and feminine tenontosaur states.
Material from the NHM was also examined in the hope of discerning morphological variations between Tenontosaurus and other species. Material studied includes

Hypsilophodon foxii, Thescelosaurus neglectus, Valdosaurus canaliculatus and
Lesothosaurus diagnosticus. Descriptions of the various elements studied for comparative material can be found in appendices II-V.
The most striking variation between Hypsilophodon and Tenontosaurus is of course, the size variation. The specimen R2477 contains a magnificently preserved cranium, and although mostly disarticulated now, was fully articulated and restored during the production of the Hypsilophodon monograph by Galton (1974a). The skull formed an extremely brittle assemblage of complex structures; however, most of the internal structure of Tenontosaurus is missing or impossible to view in the specimen analysed, thus they are largely disregarded here too. Sutural relationships between several elements are difficult to ascertain, and thus reference to Galton (1974a) is strongly recommended for an accurate reconstruction.

Skull
Currently the only skull of T. tilletti described is that of the paratype, YPM 5456, by Ostrom (1970). The following is a comparison of a mostly-complete cranium with this specimen, taking into account ontogenetic variability and also the fact that

Vertebral Column
The vertebral column appears 100% complete, with every bone present (table 4; fig. 14). Unfortunately, the status of these bones is substandard; multiple elements are missing on nearly every vertebra, and the associated chevrons and ribs are completely disassembled and disassociated. There is no trace of hypaxial or epaxial ossified tendons, which essentially originally defined this genus. Many of the vertebrae are so incomplete and disassembled, that even a generic assignment is problematic, and it is suspected that many are sourced from different specimens.
The vertebral formula here is defined as 12-15-6-61(+), which is slightly different to Of the caudal series, all but the most proximal three are missing the neural spines, although on the most distal third it is likely that they only occur as largely inconspicuous expansions or are morphologically absent. Where preserved, the neural spines are strongly curved with parallel sides. They are very narrow transversely and anteroposteriorly expanded.    Table 4 for summary). Revealed is the lack of smooth congruity between adjacent vertebrae, either as the result of taphonomy, mishandling, or genuine variation.
The assignment of these vertebrae to a particular organism is non-specific, as Winkler et al. (1997) note that in the entire vertebral series, there are no variations between T. tilletti and T. dossi; therefore classification based on vertebral morphology is not attempted here.
As has been mentioned previously, the chevrons and ribs do not warrant description, and such a task would be futile considering the status of current preservation. Ossified tendons are not currently present, and even if they were it would be highly unlikely they would yield any significant features than those this could however represent a taphonomic, preservation or mortality process.

Pectoral Girdle
The pectoral girdle constitutes two scapulae, two coracoids and two sternal plates; the pairs exhibit near-perfect symmetry, with minor differences occurring as a direct result of either morphological contrast or preservation.
Sternum: not as broad or thick as those imaged in figure 9 of Forster (1990) ( fig. 15) -inconsistency may be function of ontogeny; it is logical that these elements become progressively structurally solid (ossified) and integrated with increasing age and growth.

Forelimb
Humerus: no noticeable variation to Forster (1990) (figs. 17, 18,19).    Proximal dorsal surfaces of phalanges articulate smoothly with associated distal surfaces of adjacent metacarpals, extending onto dorsal surfaces as far as onequarter metacarpal length. This feature is the "hyperextension" mentioned by Forster (1990), and is possible with all elements in at least the medial digits.
Hyperflexion does not appear to have been possible. This function possibly served to aid grasping during feeding, social activities, or perhaps even provided aid as a defence mechanism, giving the ability to clasp predators. Another possibility is that it could enhance locomotion over irregular terrain compared to a planar surface. It could serve to reduce tension during quadrupedal locomotion, by providing a more 'springy step' rather than a 'gallop' by allowing manual flexure.  Actually occurs proximal to obturator process (i.e. cranially, not caudally) so both proximal ischial processes are variably oblique to the long-axis of the shaft.
Sinistral ischium with gently sinuous long-axis (to higher degree than linear dextral ischium) -this characteristic possibly the "pronounced ventral bend" of Forster

Hindlimb
Femur: tip of fourth trochanter does not appear to be pointed, scarred or caudoventrally hooked as Forster (1990) expresses. Medial condyle also not "more transversely expanded" than the lateral condyle ( fig. 29). Tibia: cnemial crest not as "narrow" as Forster (1990) -approximately twice the size depicted in Fig. 20B (fig. 30). Proximal gentle cranial concavity propagates into small scar mark -succeeded by deeper perforation on sinistral tibia (not mentioned in Forster (1990)). Caudolateral surface reflects this at same distance from distal end (same arcuate, listric scar form) on both tibiae; shaft here resumes transverse expansion, developing broad, sub-triangular distal end. Long axis oblique to proximal end (slightly less than 60° as quoted by Forster (1990)) -degree of twisting either variable within individuals or function of ontogeny.

Discussion
Ontogeny is essential in understanding fossil taxa and their systematic placement in cladistic studies, and the ontogenetic fit of specimens should always be considered, especially when defining primary homologies in data matrices. Bennet Unfortunately, a phylogenetic analysis of basal euornithopods is beyond the scope of this study, but this degree of differentiation between two apparently identical species emphasizes that either, the matrix requires re-definition of synapomorphies to a greater detail, that ontogeny is occluding phylogeny to some degree, or simply that significant intraspecific variation occurs within tenontosaurs; it is perhaps a little implausible that this specimen represents a new species based on the general resemblance to previously described specimens. Given that Forster (1990) removed all previous defining cranial characters (they appear to be too universal or synapomorphic amongst ornithopods), it is impossible for the features observed here different to Ostrom (1970) to be considered diagnostic, as no robust underlying set is currently in place. One can postulate that the majority of these features relate to ontogeny, in that they vary in degrees of fusion and suture strength and placement. However, others, such as posteroventral extent of the external nares appear to be genuine morphological variations, possibly attributed to intraspecific variation. Given the tentative nature of these variations, they cannot be conclusively assigned to a separate species other than T.
tilletti for the present, or assigned autapomorphic status, until comparative morphological differences can be elucidated with increased confidence (i.e. personal observation of the paratype skull, and others exhibiting similar degrees of completion). Revision of cranial material is required; the numerous depictions of T.
Tilletti skulls in the literature convey that no unequivocal consensus on the cranial morphology currently exists, and it will take more than one semi-complete skull to resolve this.
Tenontosaurus tilletti appears to have been a facultative biped based on strong hindlimb characters, but possibly utilised a quadrupedal stance for more rapid locomotion based on manual and humeral features. A biomechanical analysis of the forelimb is essential in constraining the ability of the forelimb a weight-bearing role.

Conclusions
The diagnosis of Tenontosaurus tilletti has been revised; instead of designated autapomorphies being based on multiple non-contemporaneous, partially incomplete, and possibly multi-growth stage specimens, one mostly complete, wellpreserved specimen has been utilised to create a more robust definition. The diagnostic characters have been revised as follows: 1. Vertebral count 12-15-6-61(+) 2. Tail comprising at least 57% total animal length 3. Scapula with straight but with slight proximally and distally expanded caudal margin to approximately 110-120% depth 4. Coracoid with strong, subtriangular sternal process, and coracoid foramen completely closed off from articulation (40% coracoidal width) 5. Forelimb 68% hindlimb length, with equally robust humerus and ulna 6. Humerus dominated by strong, rounded, proximally confined deltopectoral crest; expansion approximately equal to humeral shaft thickness 7. Carpus comprising unfused intermedium, radiale and ulnare 8. Manus short and broad, with phalangeal formula 2-3-3-2?-2? 9. Ilium with gently ventrally dipping preacetabular process; approximately 60% iliac body length 10. Ilium with dorsoventrally expanded postacetabular blade and rugose caudal margin, and concave ventral border 11. Ilium brevis shelf less than 1.5 times mediolateral width of postacetabular ventral margin 12. Pubis with straight postpubic rod comprising 1.5x pubic body length, and projecting at 100° to prepubic blade 13. Obturator foramen closed off from articulation 14. Prepubic blade laterally compressed, depth non-linear and approximately 75% maximum ischium depth, with distal tip variably expanded 15. Shaft of ischium non-linear, proximal half dominated by lateral ridge, with crescentic obturator process one-third length of shaft 16. Femur with hemicylindrical lesser trochanter extending one-fifth femoral length longitudinally, one-third greater trochanter width and separated by thin fissure 17. Pes with phalangeal formula 2-3-4-5-(0) This suite of characters is by no means irrefutable, and subject to variation as complete adult specimens are utilised to refine the values presented here. A single specimen exhibiting the observed degree of completion (relative to the holotype) is however deemed qualified in re-assessing the character state. The quantifiable manner in which each character is expressed greatly aids interpretation of features, in that they no longer source an independent bias based on an individual's interpretation of a statistically unbound term. Autapomorphy '3' designated by

Acknowledgements
Initial thanks go to D. Gelsthorpe (UoMM) and M. Edwards (UoM) for entrusting the specimen into my care and providing storage, and to the former for generously providing photographs of when the specimen was assembled. Many thanks to P.
Falkingham, J. Jepson, and K. Bates (UoM) for their ever-present support and direction. The expert guidance of D. Norman (UoC) directed the study and provided invaluable comments on specific topics to focus on, and is much appreciated.
Gratification also is extended to L. Steel, S. Maidment, S. Chapman, and P. Barrett (NHM) for allowing access to specimens in their care, and especially to the former two for helpful discussion and assistance. A special thanks to J. Nudds (UoM) for his patient, friendly, and first-class supervision, for without which this project would not have ensued. Thanks John.  Posteriorly (adjacent to penultimate tooth), surface smoothly curves ventrally into a gracile, somewhat rectangular "coronoid process" (lateral aspect). Ventral border deflects and expands ventrally (two-thirds length anteriorly from predentary contact) into thin sheet, expanding anteriorly and ventrolaterally into angularforms 'flattened-S' shape in dextral ventral aspect.

References
Horizontal dorsal margin deflects orthogonally (ventrally) into straight posterior margin, curving posteriorly into small notch (directed dorsolaterally) before tapering into "coronoid process" of surangular (Ostrom, 1970). Sinistral surangular partially obscured and restored (mostly ventral portion); suture between dentary and surangular runs anteroventrally in smooth curve prior to small medial deflection, becoming more complex and ultimately tapering to terminate approximately half lower jaw length -at point of deflection, angular suture appears, running sub-parallel to lower jaw ventral border, terminating adjacent to point of beginning of coronoid process.
Dorsal border of surangular broadly expands ventromedially before twisting slightly into gracile posterior process -posterior-most tip absent, therefore extent unknown; process deflects dorsally and thins posteriorly. caudal border obtuse to caudoventral-facing glenoid fossa surface curving gently into slightly thickened sternal process; mid-way down cranial border becomes mediolaterally expanded and laterally canted, which Forster (1990) defines as a "rugose muscle scar"; caudal border deeply but non-uniformly concave -more linear adjacent to intersection with ventral border at sternal process.
Cranioventral curvature deflects gently medially in medial aspect; slight depression in cranial third of body reflected in lateral expansion -maintains uniform thickness; only heterogeneity being slight cranial thickening.
Coracoid foramen circular with inwardly-sloping walls; centre is 25mm from articular surface with 12mm diameter concordant with Forster (1990) and dissimilar to Camptosaurus where it is more proximally placed; develops most prominently, but still shallow, on lateral surface centred relative to articulation as in Forster (1990); on medial surface (both coracoids) foramen completely obscured -only poorly preserved vestige remains as channel directed ventrally and orthogonal to articular surface.

Forelimb and Manus
Humerus: comprises transversely constricted shaft, massively expanded proximal head, robust pair of distal condyles, and well-developed strong deltopectoral crest, Cranial surface post-deltopectoral crest distally becomes gently and broadly concave longitudinally as intercondylar groove develops; intersects medially skewed intercondylar groove on distal articular plane; caudal surface comprises gently concave shaft running distally into more proximally extensive, transversely narrower, but distally deeper caudal intercondylar groove. Shaft bowed slightly cranially in lateral aspect (more so distally); compensated by increased expansion of radial and ulnar condyles caudally which envelop deeper and well-confined groove; intercondylar grooves termed "coronoid fossa" and "olecranon fossa" by Forster Ulna: moderately robust elements; rugose proximal articular surface dominated by massive and rounded olecranon process, cranial and lateral coronoid processes (CCP and LCP respectively) -latter two form an orthogonal association.
Olecranon process pervades onto articular surface of LCP with slight circumferential ridge tapering caudomedially into thin and shallow furrow; olecranon process flattened into cranially-directed planar slope extending onto laterally canted articular surface of CCP.
LCP has sub-triangular profile with well-rounded laterally projecting apex tapering rapidly into lateral surface; separated from CCP on surface by well-developed depression pervading no further than LCP; function of depression to accept associated radial head -also acts to inhibit distal continuation of CCP by creating mediolateral constriction. LCP expands proximally into ulnar head and distally into cranial surface of transversely narrow shaft. It is likely that this strengthened the carpus significantly, for the purpose of quadrupedal locomotion. This is somewhat dissimilar to the carpal and manual structure of Camptosaurus aphanoecetes, which retained a primarily quadrupedal stance aided by extensive manual modification with limited interphalangeal and carpal motion (Carpenter and Wilson, 2008).
Ungual phalanges: Longitudinally arcuate; variably rugose/striated surfaces; develop 'typical claw' profile with well-defined distal tips (perhaps sharp initially, but quite worn); distal surface becomes progressively convex and broader proximally -mirrored in rugose ventral surface; prominent medial and lateral ridges converge distally -narrow, rounded and moderately rugose; separated from phalangeal body by deep, well-defined groove extending for two-thirds length proximally (variable).

Pelvic Girdle
Ischium: dominated by long, moderately straight, gracile shaft; terminates distally in thickened, convex, rugose tip; proximally diverges into two heads orientated equally approximately 40° to longitudinal axis of shaft -dorsal attachment for ilium, cranioventral attachment for pubis; together encircle cranial acetabular portion; separated by smooth, concave, arcuate border with sharp caudoventral acetabular margin; develops progressive concavity proximally from shaft. Not 'footed' as higher iguanodontians.
Pubic process with gently caudocranially convex lateral surface; equally concave medial surface leading to gently curving pubic articulate -rugose, ventrally canted, Pubic peduncle with damaged distal end, therefore structure indiscernible -clearly more slender than ischiac peduncle though; lateral surface smoothly curves inwards forming concave cranial border -extends caudally to form well-defined rounded ridge extending for length of peduncle; separates from flat caudoventral surface of acetabulum; medial surface dominated by broad askew channel separated from convergent caudoventral and craniodorsal borders; cross-sectional profile subtriangular; initial 60° angle between pubic peduncle and cranial process.
Main body laterally flattened and medial surface dorsoventrally convex; medial body variably depressed for attachment of sacral ribs (Forster, 1990). Unity terminated abruptly by distal cranial intercondylar groove; caudally shaft gently convex due to terminal expansions.
Fourth trochanter develops from distally thickened ridge beginning approximately one-quarter femoral length; twists to project caudoventrally into lobate form; axis curved, slightly thickened distally and continuously thins towards apex. Overall strong development to increase leverage for vertical backswing (Bakker and Galton, 1974).
Shaft twists slightly post-fourth trochanter distally so two condyles are set slightly obliquely to femoral head; shaft begins to expand mediolaterally approximately two-thirds length -coincident with caudocranial constriction. If interpretation of Forster (1990)'s "epicondyles" are correct, the medial is as equally gently convex as the lateral one, albeit narrower caudocranially.
Medial condyle with gently convex articulate; slightly thickened periphery; flat medial surface; develops from well-developed ridge extending from one-third shaft length, parallel to fourth trochanter; greatly expanded caudocranially into massive tip, slightly oblique to shaft. Lateral condyle more rounded and rugose -greatly mediolaterally expanded; craniocaudal expansion approximately two-thirds medial condylar.
On the cranial surface, distally expanding and deepening intercondylar groove develops, similar to Dryosaurus. On caudal surface, longer rapidly diminishing "condylid" separates deep, medially broad groove from more lateral shallow concavity -all three pervade same distance proximally. Deeper groove interpreted to be "popliteal surface" of Forster (1990). Medial condyle expands gently into this groove laterally. "Flexor groove" is thus interpreted as more distal expansion of "popliteal surface". Metatarsal IV slightly shorter than metatarsal II; proximally mediolaterally expanded into triangular head; distally mediolaterally compressed, extending slightly ventrally; twists and diverges from metatarsal III distally (more so than metatarsal II).
No major differences to Forster (1990) except for the absence of the vestigial metatarsal V; Forster (1990) admits this is not always developed in Tenontosaurus, and the absence is not stratigraphically controlled. This may be a function of ontogeny, with the metatarsal reducing with age, or perhaps developing with age, although what function this would potentially provide is currently unknown.

Skull
R2477 preserves a near-complete skull; predominantly disarticulated therefore sutural/contact relationships between elements difficult to discern (see Galton (1974a) for complete reconstruction).
Lateral surface not listric -instead ascends into ventral anterior process oriented at Galton (1974a) states the "more dorsal part of the medial sheet is overlapped by the thin sheet of the lachrymal"; this is only apparent in medial aspect -if viewed from lateral aspect, the opposite is apparent, thus this comment is slightly ambiguous. The author also mentions that "there is a large fenestra anteriorly in the medial sheet of the maxilla"; this implies the fenestra is entirely within maxilla, which is misleading, as the maxilla only forms the ventral and posterior margins.  Dorsal surface arcuate, thickened along blade width, tapering cranially; lateral surface extends as broad concavity smoothly expanding dorsoventrally -cut by "clavicular facet" (Galton, 1974a), and ventrally by glenoid; intersected ventrally by lesser depression adjacent to glenoid.
Ventral surface deeply concave and rounded -does not contribute to glenoid fossa; proximal-most surficial curvature deflects reflexively cranially and medially expanding into scapular surface of fossa; surface medially canted, depressed with thickened periphery.
Ventral border deeply concave -proximal end develops into massively thickened glenoid surface (less broad than associated scapular surface); distal end retains average coracoid thickness, curving cranioventrally into rounded, sub-triangular sternal process.  anterior border completely gently concave.

Pelvic Girdle
Specimen R193 contains a near-complete disarticulated pelvic girdle. At half ischial length blade transforms into progressively proximal thickening shaft with oval cross-section; becomes medially thickened in axis at 90° to length; shaft thins slightly caudodorsally and cranioventrally to greater extent; lateral surface twists post-obturator process forming ventral border; obturator process develops approximately half length of ischium -width equal to width of adjacent section of shaft; forms medially convex, thin lamina with somewhat quadrilateral form -this may be product of absent fragments; curved proximal border orthogonal to shaft.
Distal border slightly damaged with shard missing, therefore exact form undeterminable.
Proximal 40% craniocaudally expanding concave surface resulting from adjacent shaft twisting; distal (upper) divergence develops into massive, rounded ischiac head; caudal edge forms from remnants of proximally tapering shaft -circular cross-section; dorsal border equates to smoothly concave acetabular borde r.
Proximal border of obturator process diverges into lateral surface -dorsal border creating the twisted shaft, propagating craniodorsally to intersect dorsal border immediately pre-expansion of ischiac head in tightly acute angle.
Width of ischiac head less than height of cranial expansion of lateral surfacedevelops cranial half of acetabular shelf; cranial expansion thins greatly ventrally as Anterior process develops smooth arc (lateral aspect), with bladed 'scimitar' form; uniform thickness except for slight distal tapering; distal third bends gently ventrally; distally thins in dorsal aspect; deflects laterally from otherwise linear dorsal border; lateral surface revealed as process twists. Medial surface initially thickens medially (dorsal half) into elongated wedge -abruptly ceases sloping laterally into ventral half of process; remaining ventral surface gradually develops into medially expanded shelf/ledge -develops moderately convex form. Overall sinuous profile in cross-section (for proximal two-thirds); shelf gradually tapers to continue as flattened ventral border -where process begins to deflect ventrally, small subsidiary oblique ridges develop horizontally to cleave intersecting channel (between shelf and dorsal expansion) -had otherwise diverged forming flattened, vertical process tip.
Pubic peduncle set 30° to cranial process; much more robust structure, although partially deformed; ventral edge greatly flattened before strongly curving into ischiac peduncle developing dorsal acetabular margin; lateral edge forms sharp ridge; medial edge heavily damaged. Pubis: comprises robust main body, rod-like prepubic process, slender post-pubic rod approximately twice length of prepubic process (most distal part absent).
Prepubic process smooth forming depressed oval cross-sectional profile; transversely broadened; ceases abruptly cranially; flattened medial surfaceexpands before immediately dipping caudally and flaring into broad depression dominating medial surface of body -ventral surface exhibits associated constriction; mimicked to lesser degree on lateral surface.
Smoother ventral border of main body much less concave than associated s trong convexity of rough dorsal border -develops as gently obtuse refraction between two processes. Pubic/obturator foramen completely enclosed; lesser robust caudal wall; develops caudally to depressions; articular surface rough, thinning caudally where curvature strongest. Contact between postpubic process and body longitudinally orthogonal; slightly expanded before progressively thinning into medially concave blade; slight dorsal expansion immediately post-mediolateral thickening ("dorsal sheet" of Galton (1974a)).
In medial aspect posterior border anteriorly concave; anterior border convex creating longitudinal gently curving arc; both proximal and distal ends expand caudocranially -proximal expansion of greater extent; shaft mostly uniform thickness (excluding fourth trochanter); lateral surface pinches into longitudinallyorientated ridge; medial surface fairly even, diverging at extremities covering lesser trochanter and femoral head, and outer and inner condyles distally; surface also punctuated by broad, shallow groove immediately anterior to fourth trochanter.
Lesser trochanter canted cranially, developing as a cranial expansion orthogonal to femoral head; separated from head by shallow linear channel adjacent to lesser trochanter and part of lateral surface; significant fragment of femoral head is absent.
Greater trochanter separated from femoral head by depression for ischiac head of ilium (Galton, 1974a) forming an acute angle between both -depression forms rough convex strip terminating proximally in slight expansion separating femoral head and both proximal trochanters; lesser trochanter axis perfectly splits midline between femoral head and greater trochanter axes.
Fourth trochanter terminates 45% of femoral length distally -caudally directed and lobate form; distally thickens laterally; medial surface perpendicular to shaft axis; lateral surface forms from continuation of lateral surface of shaft, developing gentle concavity.
No development of cranial intercondylar groove due to gently convex and flattened cranial surface; inner condyle missing distal tip -appears same size as outer condyle, but with slightly different orientation and sectional profile; caudal intercondylar groove begins at 75% femoral length distally diverging mediolaterally to be cradled by two condyles; outer condyle provides more prominent bounding margin to groove than inner condyle; outer condyle with cranially canted proximal surface, oval cross-section; slightly more expanded caudocranially than inner condyle by approximately 20%; slightly convex in lateral aspect with borders gently converging into shaft proximally.
R195 femur distal quarter missing; displays several slight variations to R192a femur: fourth trochanter more 'fin-shaped' with sharper craniodorsal edge orientated 45° to longitudinal axis; femoral head more massive, smooth cranial surface -displays oblique concavity on medial surface, possible signs of strain directly distal to head. Fibula (R5830): distal end absent; proximal end missing fragments. Forms gracile element; gently concave longitudinally (medial surface); expands slightly proximally -coincides with caudocranial concavity; shaft twisted slightly at mid-sectionlateral surface rotates developing cranial surface.

Appendix 3: Comparative Morphology II -Thescelosaurus neglectus
Femur ( fig. 38): head projects medially and slightly dorsally as massive, bulbous structure on dorsal articular surface; caudal surface cut by U-shaped ventrolateral groove beginning at proximal tip -merges with caudal surface immediately distal to head; head exhibits distinct signs of pervasive arthritis -extends entirely over articulate and down caudal surface of shaft ('gritty' appearance). Greater  flanked by convex-inwards subsidiary/secondary ridge (both sides) extending for tooth length; tertiary ridges occur between these and primary ridge parallel to secondary ridges -mimic gentle curvature pre-termination approximately one-third up tooth; tooth narrows ventrally to approximately half the distal/dorsal width.
Ventral border slightly concave laterally, converging at terminus of primary ridge; margins strongly denticulate (approximately 16 denticles per half tooth) -become less prominent and more acicular medially; ventral denticles more tabulate (leaf-  shaft greatly more bowed than Hypsilophodon foxii and Tenontosaurus, with less twisting. Femoral head massive, elongate medially; separated from greater trochanter by smooth, shallow depression on caudal surface; concave caudal surface relating to expansion of subsidiary, moderately rugose trochanter/process -sub-triangular profile, separated from femoral head tip by oblique depression (for ischiac head of ilium); caudal surface gently convex -develops thin ridge transversely on distal surface, extending fully around thickened ridge connecting head to shaft. Greater trochanter elongate perpendicular to femoral head medial-axis; forms abrupt, rounded edge with slightly inclined lateral surface; curves gently into caudal depression; constricts caudocranially into depression; oval cross-section; proximal surface broadly convex (caudocranially). Thin neck unites greater and lesser trochanters -orientated 45° to caudocranial axis on lateral border; two grooves facing craniomedially and caudolaterally also separate trochanters -former greater longitudinal extent but slightly shallower, latter deepens distally terminating abruptly with listric 'head'. Lesser trochanter semi-lunate (proximal aspect); forms thin rod constricting slightly before contacting convex shaft (craniolateral surface); moderately rugose proximal surface; proximal quarter of lateral surface gently striated longitudinally.

Appendix 5: Comparative Morphology IV -Lesothosaurus diagnosticus
Lesothosaurus is a basal ornithischian from the Early Jurassic of Stormberg, South Africa; its phylogenetic position is currently disparate, but its basal position with the Ornithischia is commonly acknowledged, grouped with other primitive ornithischians such as Eocursor parvus and Pisanosaurus mertii (e.g. Butler et al.,  intercondylar groove similar to H. foxii -more prominent than cranial surface (groove absent); cranial surface flattened with virtually no cranial expansion of rugose condyles; inner condyle projects further caudally than massive outer condyle -forms thick, rounded ridge extending half femoral length; long axis parallel to twisted axis of fourth trochanter.