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Cranial exostoses (areas of periosteal ornamentation) are present on the external surfaces of the skull and mandible of Scelidosaurus harrisonii. True osteoderms have also been identified on the skull, forming a ‘brow-ridge’ of three supraorbital bones, dished plates that are attached to the lateral surface of the postorbitals and a pair of larger, horn-shaped structures that project from the posterodorsal surface of the occiput. Postcranial osteoderms form an extensive series of oval-based, ridged osteoderms that extend backward across the dorsal and lateral surfaces of the neck and torso. Smaller, narrow-based ridged osteoderms are also found on the lateral surfaces of the limbs. The tail is surrounded by four longitudinal rows of large, narrow-based, ridged or keeled osteoderms.The neck, unlike the rest of the body, is encased dorsolaterally by a variety of osteoderms. These can be differentiated into two fundamental types: base-plate osteoderms that develop deep within the compact layers of the dermis and, superficial to each base-plate, tall, ridged or cap-like osteoderms. These latter, project outward from the skin surface and were covered by an epidermal scale or a rigid keratinous sheath. The base-plates are true osteodermal components, but to differentiate them from the more familiar superficial osteoderms, they will be called here simply ‘base-plates’. Lying on the dorsal midline between and beneath the occipital horns is a single, ridged, nuchal osteoderm comprising a base-plate and osteoderm cap. The nuchal plate is flanked by a pair of prominent ‘tricorn’ osteoderm arrays mounted on shallowly arched blocks of fused base-plate osteoderms. Behind the tricorn arrays is a succession of four partial collar-like arrays of osteoderms formed (at least in ontogenetically mature specimens) by coalesced base-plates that anchor tall and either carinate or more plate-like osteoderms. The largest of these are always positioned on the ventrolateral margin of each collar. The osteoderms become progressively smaller toward the midline. It is at present unclear whether the base-plate supported collar arrays on either side fuse together along the midline to form cervical half-rings, as is often reported in more derived ankylosaurian thyreophorans. Individual collar arrays do not imbricate with each other, but are likely to have been interconnected by sheets of tough connective tissue.On the ventrolateral flanks of the pectoral region are found the largest, bladed osteoderms. In two partly articulated skeletons an osteoderm is preserved on the posterodistal surface of the scapular blade. Although this position is reminiscent of the parascapular spines found in some stegosaurs, these bones are not regarded as homologues; their placement is a coincidence of positioning an osteoderm row adjacent to the scapular blade.The torso preserves three principal rows of large, ridged osteoderms that show no evidence of accompanying base-plates. The ventrolateral row has the largest osteoderms and these are succeeded in size by the lateral row and dorsolateral row, respectively. There is no evidence to support the existence of a midline dorsal row of osteoderms. The principal rows extend backward across the dorsal and lateral flanks of the body as far as the pelvic area. Smaller cap-shaped osteoderms are scattered between the principal rows, but whether they were organized into subsidiary rows or were more randomly distributed cannot be ascertained. Smaller, narrow-based, ridged osteoderms are found in oblique rows across the anterior chest; they also flank the proximal half of the forelimb (as far as the elbow) and extend to the ankle region in the hind limb.The tail is surrounded by large, narrow-based, high-ridged osteoderms. Unlike the neck and torso, there is a row of dorsal midline osteoderms that are flanked by large, lateral osteoderms, and beneath these there is a midline ventral row. The latter are close-set and particularly deeply keeled in the area nearest to the pelvis.Osteoderms vary considerably both in structure and texture. Base-plates have a rough, porous external texture as a consequence of the abundant vascular canals that penetrate these bones. Internally, their surface is arched and has a woven-textured fabric comprising bundles of mineralized fibres interspersed with large vascular foramina. Accompanying osteoderms are generally a little denser than their base-plates and have a smoother cortex, although abundant small foramina and shallow vascular channels pit and groove this external surface. The pair of occipital osteoderms closely resemble bovid (ungulate mammal) horn-cores and are likely to have been sheathed by keratin (as preserved exceptionally in the ankylosaurians Zuul and Borealopelta). Farther posteriorly, the principal osteoderms in the major rows along the torso and tail are generally thin-walled, cap-shaped and ridged. They have a rough and porous external surface, which suggests that the bone surface was covered by keratinous scales. The generally porous fabric of these osteoderms has been remarked upon and it is probable that these were flushed with blood. Interspersed between the visually dominant parasagittal rows of osteoderms is a scattering of smaller cap-shaped osteoderms and polygonal or rounded, flat ossicles. Scattered populations of these ossicles were probably lost because they were, in effect, ‘invisible’ during excavation and skeletal preparation, being of millimetric dimensions. These smaller osteodermal ossicles formed a mosaic-like pattern on the skin surface and toughened the flexible portions of the skin of the animal. Skin impressions and epidermal peels, probably deriving from the ventral surface of the body, reveal a closely packed mosaic of smaller flat osteoderms that underlie similarly shaped keratinous scales.The discovery of smaller, partly articulated skeletons has revealed aspects of the growth and development of the cervical osteoderm arrays. Individual base-plates begin to form deep in the dermis through mineralization of the woven connective tissue fibres in the stratum compactum and, as these thicken, they also involve the looser and more irregular fibres of the stratum superficiale. Individual base-plates expand peripherally, deepen and form shallowly convex pads externally upon which primordial osteoderms developed. The latter form initially as narrow, elongate, pup-tent-shaped structures with a posteriorly off-set apex and arched, slightly hollow bases. Differential patterns of mineral deposition progressively modify these ‘templates’ into the range of osteoderm morphologies seen in ontogenetically mature skeletons: from subconical curved horns, through tall, carinate blades, to extremely tall, plate-shaped structures, as well as to the simpler oval-based, ridged, pup-tent-shaped osteoderms. As the skeleton approaches full size, in the neck region the base-plates and their osteodermal caps fuse together, and adjacent base-plates interlock before finally fusing together to form partial collars that anchor and support transverse arrays of prominent osteoderms. Osteoderms had the potential to contribute to a number of biological roles in the life of these animals, including protection (defence-retaliation), thermoregulation and more subtle aspects of their behaviour.

Scelidosaurus fossils were first discovered during the commercial quarrying of the Liassic sea-cliffs between Charmouth and Lyme Regis in Dorset during the late 1850s. The original specimens included a well-preserved skull embedded in a block of argillaceous limestone (marlstone). Shortly after this skull was retrieved, a series of more-or-less contiguous marlstone slabs were recovered, containing most of the skeleton of the same animal (NHMUK R1111). After rudimentary (hammer and chisel) mechanical preparation, Owen published descriptions of this material (Owen, 1861, 1863). These two monographs have been the sole references pertaining to the anatomy of Scelidosaurus for >150 years. The skeleton of the lectotype of Scelidosaurus harrisonii (NHMUK R1111) has since been extracted from the surrounding matrix using an acid-immersion technique. Some additional specimens held in the collections of the Natural History Museum London, the Bristol City Museum and the Sedgwick Museum in Cambridge provide anatomical material that allows detailed description of this taxon, for which we have had, until now, a surprisingly poor understanding.Axial skeleton: The axial skeleton of Scelidosaurus comprises eight cervical, 16 dorsal, four sacral and > 40 caudal vertebrae. During ontogeny, the posterior centrum articular surface of the 16th dorsal vertebra develops a firm, ligament-bonded junction with the succeeding sacral centrum. Apart from the atlas rib, which is single headed, double-headed ribs are present throughout the presacral vertebral series, and none shows any indication of fusion to its associated vertebra. However, those ribs attached to cervical vertebrae 2–4 were evidently bound firmly by connective tissue to rugose diapophyses. The last two (presacral) dorsal ribs show merger of the capitulum and tuberculum, meaning that they are separated by only a step. The angulation and arching of the dorsal ribs suggest that these animals had a broad (barrel-like) torso. Intercostal uncinate plates were present, attached to the posterior margins of some of the largest dorsal ribs. Their attachment sites are clearly marked, and these plates might have been composed of calcified cartilage in larger individuals. The sacral vertebrae fuse progressively during ontogeny, in an anterior-to-posterior sequence. The sacral ribs are long and robust, and tilt the iliac blade outward dorsally. A sacricostal ‘yoke’ (created by the fusion of the distal ends of adjacent sacral ribs) never forms. The base of the tail has a unique ball-and-socket-style joint between the centra of caudal vertebrae 1 and 2 in only one skeleton. This might have permitted powerful, but controlled, movements of the tail as a defensive weapon (or increased flexibility at the base of the tail, which might have been necessary for reproduction). Caudal ribs are initially long, blade-shaped projections that gradually decrease in size and become stub-like remnants that persist as far back as the midtail (approximately caudal vertebra 25). Haemal arches (chevrons) disappear nearer to the distal end of the tail (approximately caudal vertebra 35). Ossified tendons are preserved as epaxial bundles that are clustered in the ‘axillary’ trough (between the neural spine and transverse processes on either side of the midline). Ossified tendons are restricted to the dorsal and sacral region. Flattened ossified tendons are fused to the sides of sacral neural spines. In life, the ossified tendons might have formed a low-angled trellis-like arrangement.Appendicular skeleton: The pectoral girdle comprises a long scapula, with a distally expanded blade. The proximal portion is expanded and supports an oblique promontory, forming an acromial process anteriorly and a thick, collar-like structure posteriorly above the glenoid. Between these two features is a shallow basin, bordered ventrally by a sutural edge for the coracoid. The scapula–coracoid suture remains unfused in large (5-m-long) individuals. The coracoid bears a discrete foramen and forms a subcircular dished plate, with the shallowest of embayments along its posterior edge. Clavicles are present as small fusiform bones attached to the acromial process of the scapulae and leading edge of each coracoid. A sternum was reported as ‘some partially ossified element of the endoskeleton’ Owen (1863: 13), but subsequent preparation of the skeleton has removed all trace of this material. The humerus is relatively long and has a prominent rectangular and proximally positioned deltopectoral crest. The ulna is robust and tapers distally, but there is no evidence of an olecranon process. The radius is more rod-like and terminates distally in an enlarged, subcircular and convex articular surface for the carpus. The carpus is represented by an array of five discoid carpals. The manus is pentadactyl and asymmetrical, with short, divergent metacarpals and digits that terminate in small, arched and pointed unguals on digits 1–3 (only). The phalangeal formula of the manus is 2-3-4-3-2. The pelvis is dominated by a long ilium; the preacetabular process is arched, transversely broad, and curves laterally. In juveniles, this process is short and horizontal, but during ontogeny it increases considerably in length and becomes arched. The iliac blade is tilted laterally, meaning that its dorsal blade partly overhangs the femur. The acetabulum forms a partial cupola, and there is a curtain-like medial wall that reduces the acetabular fenestra to a comparatively low, triangular opening between the pubis and ischium. The postacetabular portion of the ilium is long and supports a brevis shelf. The ischium has a long, laterally compressed shaft that hangs almost vertically beneath the ilium, and there is no obturator process. The pubis has a long, narrow shaft and a relatively short, deep, laterally compressed prepubic process that twists laterally (its distal end lies almost perpendicular to the long axis of the ilium). The articular pad on the pubis for the femoral head faces posteriorly. The obturator foramen is not fully enclosed within the pubis, but its foramen is closed off posteriorly by the pubic peduncle of the ischium. The femur is stout and has a slightly medially offset femoral head, and the greater trochanter forms a sloping shoulder continuous with, and lateral to, the femoral head. The anterior (lesser) trochanter is prominent and forms a thick, thumb-shaped projection on the anterolateral corner of the femoral shaft. The fourth trochanter is pendent and positioned at midshaft. In larger individuals, it appears to become thickened and reinforced by becoming coated with metaplastic bone derived from the tendons attached to its surface. The distal end of the femoral shaft is slightly curved and expands to form condyles. There is a deep and broad posterior intercondylar groove, but the anterior intercondylar groove is barely discernible in juveniles and not much better developed in subadults. The tibia and fibula are shorter than the femur. The tibia is structurally dominant, and the shorter fibula is comparatively slender and bowed. The proximal tarsals are firmly bound by connective tissue to the distal ends of the tibia and fibula. The distal end of the tibia is stepped, which aids the firm interlock between the crus and proximal tarsals. There appear to be two roughly discoid tarsals (distal tarsals 3 and 4), and a rudiment of distal tarsal 5 appears to be sutured to the lateral margin of distal tarsal 4. Five metatarsals are preserved, but the fifth is a splint of bone attached to the proximal end of metatarsal 4. Metatarsals 2–4 are dominant, long and are syndesmotically interlocked proximally, but their shafts splay apart distally. Metatarsal 1 is much shorter than the other three, but it retains two functional phalanges (including a short, pointed ungual). The foot is anatomically tetradactyl but functionally tridactyl. The pedal digit formula is 2-3-4-5-0. The digits diverge, but each appears to curve medially along its length, creating the impression of asymmetry. This asymmetry is emphasized, because the three principal unguals are also twisted medially. The ungual of digit 2 is the largest and most robust of the three, whereas that of digit 4 is the smallest and least robust.The general girth of the torso and the displacement of the abdomen posteriorly (a consequence of the opisthopubic pelvic construction in this dinosaur) constrained the excursion of the hindlimb during the protraction phase of the locomotor cycle. The anterolateral displacement of the hindlimb during protraction is in accord with the freedom of motion that is evident at the acetabulum, the susceptibility of the hindlimb to torsion between and within its component parts, and the asymmetry of the foot. It is probable that thyreophorans (notably, ankylosaurs) used a similar oblique-parasagittal hindlimb excursion to accommodate their equally large and wide abdomens. This surmise accords with the structure of the pelves and hindlimbs of ankylosaurs. Derived stegosaurs might have obviated this ‘problem’, in part, because their hindlimbs were longer and their torsos and abdomens narrower and capable of being ‘stretched’ vertically to a greater extent. Nevertheless, the structure of their acetabula and hindlimbs indicates that the oblique-parasagittal style of hindlimb excursion remained a possibility and might be an evolutionary remnant of the locomotor style of basal, shorter-limbed stegosaurs.A reconstruction of the endoskeleton of Scelidosaurus is presented on the basis of this updated description. Although quadrupedal, this animal was only facultatively so, judged by its forelimb-to-hindlimb proportions and structure; it therefore betrays bipedality in its ancestry.

A layer of keratinous scutes encased the skull of Scelidosaurus. The neurocranium and the associated principal sensory systems of this dinosaur are described. The cranial musculature is reconstructed and a subsequent functional analysis suggests that jaw motion was orthal, allowing pulping of vegetation and some high-angle shearing between opposing teeth. Wishboning of the lower jaw was enabled by transverse displacement of the quadrates, and the long-axis mandibular torsion that occurred during the chewing cycle was permitted by flexibility at the dentary symphysis. Limb proportions and pectoral and pelvic musculature reconstructions suggest that Scelidosaurus was a facultative quadruped of ‘average’ locomotor ability. It retained some anatomical features indicative of a bipedal-cursorial ancestry. Hindlimb motion was oblique-to-parasagittal to accommodate the girth of the abdomen. Scelidosaurus used a combination of costal and abdominally driven aspiration. The hypothesis that respiration was an ‘evolutionary driver’ of opisthopuby in all dinosaurs is overly simplistic. A critical assessment of datasets used to analyse the systematics of ornithischians (and thyreophoran subclades) has led to a revised dataset that positions Scelidosaurus as a stem ankylosaur, rather than a stem thyreophoran. The value of phylogenetic definitions is reconsidered in the light of the new thyreophoran cladogram.

Facultative bipedality is regarded as an enigmatic middle ground in the evolution of obligate bipedality and is associated with high mechanical demands in extant lepidosaurs. Traits linked with this phenomenon are largely associated with the caudal end of the animal: hindlimbs and tail. The articulation of the pelvis with both of these structures suggests a morphofunctional role in the use of a facultative locomotor mode. Using a three-dimensional geometric morphometric approach, we examine the pelvic osteology and associated functional implications for 34 species of extant lepidosaur. Anatomical trends associated with the use of a bipedal locomotor mode and substrate preferences are correlated and functionally interpreted based on musculoskeletal descriptions. Changes in pelvic osteology associated with a facultatively bipedal locomotor mode are similar to those observed in species preferring arboreal substrates, indicating shared functionality between these ecologies.

Scelidosaurus fossils were first discovered during the commercial quarrying of the Liassic sea-cliffs between Charmouth and Lyme Regis in Dorset during the late 1850s. The original specimens included a well-preserved skull embedded in a block of argillaceous limestone (marlstone). Shortly after this skull was retrieved, a series of more-or-less contiguous marlstone slabs were recovered, containing most of the skeleton of the same animal (NHMUK R1111). After rudimentary (hammer and chisel) mechanical preparation, Owen published descriptions of this material (Owen, 1861, 1863). These two monographs have been the sole references pertaining to the anatomy of Scelidosaurus for >150 years. The skeleton of the lectotype of Scelidosaurus harrisonii (NHMUK R1111) has since been extracted from the surrounding matrix using an acid-immersion technique. Some additional specimens held in the collections of the Natural History Museum London, the Bristol City Museum and the Sedgwick Museum in Cambridge provide anatomical material that allows detailed description of this taxon, for which we have had, until now, a surprisingly poor understanding.Axial skeleton: The axial skeleton of Scelidosaurus comprises eight cervical, 16 dorsal, four sacral and > 40 caudal vertebrae. During ontogeny, the posterior centrum articular surface of the 16th dorsal vertebra develops a firm, ligament-bonded junction with the succeeding sacral centrum. Apart from the atlas rib, which is single headed, double-headed ribs are present throughout the presacral vertebral series, and none shows any indication of fusion to its associated vertebra. However, those ribs attached to cervical vertebrae 2–4 were evidently bound firmly by connective tissue to rugose diapophyses. The last two (presacral) dorsal ribs show merger of the capitulum and tuberculum, meaning that they are separated by only a step. The angulation and arching of the dorsal ribs suggest that these animals had a broad (barrel-like) torso. Intercostal uncinate plates were present, attached to the posterior margins of some of the largest dorsal ribs. Their attachment sites are clearly marked, and these plates might have been composed of calcified cartilage in larger individuals. The sacral vertebrae fuse progressively during ontogeny, in an anterior-to-posterior sequence. The sacral ribs are long and robust, and tilt the iliac blade outward dorsally. A sacricostal ‘yoke’ (created by the fusion of the distal ends of adjacent sacral ribs) never forms. The base of the tail has a unique ball-and-socket-style joint between the centra of caudal vertebrae 1 and 2 in only one skeleton. This might have permitted powerful, but controlled, movements of the tail as a defensive weapon (or increased flexibility at the base of the tail, which might have been necessary for reproduction). Caudal ribs are initially long, blade-shaped projections that gradually decrease in size and become stub-like remnants that persist as far back as the midtail (approximately caudal vertebra 25). Haemal arches (chevrons) disappear nearer to the distal end of the tail (approximately caudal vertebra 35). Ossified tendons are preserved as epaxial bundles that are clustered in the ‘axillary’ trough (between the neural spine and transverse processes on either side of the midline). Ossified tendons are restricted to the dorsal and sacral region. Flattened ossified tendons are fused to the sides of sacral neural spines. In life, the ossified tendons might have formed a low-angled trellis-like arrangement.Appendicular skeleton: The pectoral girdle comprises a long scapula, with a distally expanded blade. The proximal portion is expanded and supports an oblique promontory, forming an acromial process anteriorly and a thick, collar-like structure posteriorly above the glenoid. Between these two features is a shallow basin, bordered ventrally by a sutural edge for the coracoid. The scapula–coracoid suture remains unfused in large (5-m-long) individuals. The coracoid bears a discrete foramen and forms a subcircular dished plate, with the shallowest of embayments along its posterior edge. Clavicles are present as small fusiform bones attached to the acromial process of the scapulae and leading edge of each coracoid. A sternum was reported as ‘some partially ossified element of the endoskeleton’ Owen (1863: 13), but subsequent preparation of the skeleton has removed all trace of this material. The humerus is relatively long and has a prominent rectangular and proximally positioned deltopectoral crest. The ulna is robust and tapers distally, but there is no evidence of an olecranon process. The radius is more rod-like and terminates distally in an enlarged, subcircular and convex articular surface for the carpus. The carpus is represented by an array of five discoid carpals. The manus is pentadactyl and asymmetrical, with short, divergent metacarpals and digits that terminate in small, arched and pointed unguals on digits 1–3 (only). The phalangeal formula of the manus is 2-3-4-3-2. The pelvis is dominated by a long ilium; the preacetabular process is arched, transversely broad, and curves laterally. In juveniles, this process is short and horizontal, but during ontogeny it increases considerably in length and becomes arched. The iliac blade is tilted laterally, meaning that its dorsal blade partly overhangs the femur. The acetabulum forms a partial cupola, and there is a curtain-like medial wall that reduces the acetabular fenestra to a comparatively low, triangular opening between the pubis and ischium. The postacetabular portion of the ilium is long and supports a brevis shelf. The ischium has a long, laterally compressed shaft that hangs almost vertically beneath the ilium, and there is no obturator process. The pubis has a long, narrow shaft and a relatively short, deep, laterally compressed prepubic process that twists laterally (its distal end lies almost perpendicular to the long axis of the ilium). The articular pad on the pubis for the femoral head faces posteriorly. The obturator foramen is not fully enclosed within the pubis, but its foramen is closed off posteriorly by the pubic peduncle of the ischium. The femur is stout and has a slightly medially offset femoral head, and the greater trochanter forms a sloping shoulder continuous with, and lateral to, the femoral head. The anterior (lesser) trochanter is prominent and forms a thick, thumb-shaped projection on the anterolateral corner of the femoral shaft. The fourth trochanter is pendent and positioned at midshaft. In larger individuals, it appears to become thickened and reinforced by becoming coated with metaplastic bone derived from the tendons attached to its surface. The distal end of the femoral shaft is slightly curved and expands to form condyles. There is a deep and broad posterior intercondylar groove, but the anterior intercondylar groove is barely discernible in juveniles and not much better developed in subadults. The tibia and fibula are shorter than the femur. The tibia is structurally dominant, and the shorter fibula is comparatively slender and bowed. The proximal tarsals are firmly bound by connective tissue to the distal ends of the tibia and fibula. The distal end of the tibia is stepped, which aids the firm interlock between the crus and proximal tarsals. There appear to be two roughly discoid tarsals (distal tarsals 3 and 4), and a rudiment of distal tarsal 5 appears to be sutured to the lateral margin of distal tarsal 4. Five metatarsals are preserved, but the fifth is a splint of bone attached to the proximal end of metatarsal 4. Metatarsals 2–4 are dominant, long and are syndesmotically interlocked proximally, but their shafts splay apart distally. Metatarsal 1 is much shorter than the other three, but it retains two functional phalanges (including a short, pointed ungual). The foot is anatomically tetradactyl but functionally tridactyl. The pedal digit formula is 2-3-4-5-0. The digits diverge, but each appears to curve medially along its length, creating the impression of asymmetry. This asymmetry is emphasized, because the three principal unguals are also twisted medially. The ungual of digit 2 is the largest and most robust of the three, whereas that of digit 4 is the smallest and least robust.The general girth of the torso and the displacement of the abdomen posteriorly (a consequence of the opisthopubic pelvic construction in this dinosaur) constrained the excursion of the hindlimb during the protraction phase of the locomotor cycle. The anterolateral displacement of the hindlimb during protraction is in accord with the freedom of motion that is evident at the acetabulum, the susceptibility of the hindlimb to torsion between and within its component parts, and the asymmetry of the foot. It is probable that thyreophorans (notably, ankylosaurs) used a similar oblique-parasagittal hindlimb excursion to accommodate their equally large and wide abdomens. This surmise accords with the structure of the pelves and hindlimbs of ankylosaurs. Derived stegosaurs might have obviated this ‘problem’, in part, because their hindlimbs were longer and their torsos and abdomens narrower and capable of being ‘stretched’ vertically to a greater extent. Nevertheless, the structure of their acetabula and hindlimbs indicates that the oblique-parasagittal style of hindlimb excursion remained a possibility and might be an evolutionary remnant of the locomotor style of basal, shorter-limbed stegosaurs.A reconstruction of the endoskeleton of Scelidosaurus is presented on the basis of this updated description. Although quadrupedal, this animal was only facultatively so, judged by its forelimb-to-hindlimb proportions and structure; it therefore betrays bipedality in its ancestry.

Amphibians transport water, oxygen, carbon dioxide and various ions (e.g. sodium and potassium) across their skin. This cutaneous permeability is thought to affect their ability to respond to environmental change and to play a role in global population declines. Sexual dimorphism of skin anatomy has been accepted in some species, but rejected in others. The species in which such dimorphism has been detected have all been sexually dimorphic in body size, with males that are smaller and have thinner skin. It is unclear whether this difference in skin thickness manifests a functional difference or if it is related to body size alone. Skin thickness (epidermis, spongy dermis, compact dermis and total thickness) was examined in males and females of the white-lipped treefrog (Litoria infrafrenata). Although the skin of males is absolutely thinner than that of females, this difference is explained by body size differences between the sexes. Overall, we conclude that skin thickness in male and female L. infrafrenata correlates with body size dimorphism and suggest that future studies on amphibian skin anatomy include measures of body size, test the ecological significance of sexually dimorphic skin anatomy and better document the prevalence of sexually dimorphic amphibian skin anatomy.

The history of discovery and interpretation of several dinosaurs collected from quarries near the town of Hastings during the latter half of the 19th century is more complicated than it should be. Samuel Husbands Beckles and Charles Dawson collected several large ornithopod skeletons from this area, but just a few bones from these skeletons were subsequently described and interpreted (principally) by Richard Owen and Richard Lydekker. All these specimens merited recognition because they had the potential to contribute to an on-going debate about the anatomical structure and relationships of the iconic Wealden dinosaur Iguanodon. Unfortunately, no detailed description of these important skeletons was published in later years. Furthermore, previously known associations of bones and even provenance information, linked to the specimens that were gradually acquired by the Natural History Museum, are unclear. Confusion may have arisen because Richard Lydekker used the private collector Charles Dawson as a voluntary curatorial assistant. This account documents the past work on the osteology of material that can be attributed to Hypselospinus fittoni. Nearly all such material is described here for the first time, and every effort has been made to re-establish associations between bones as well as provenance information. A skeletal reconstruction of Hypselospinus is attempted on the basis of the hypodigm. Most of the on-going confusion concerning the affinity of this material with either Hy. fittoni or its sympatric contemporary Barilium dawsoni has been resolved. Hypselospinus fittoni (Lydekker, 1889) is rediagnosed on the basis of this new and relatively comprehensive anatomical description, and this animal is compared with known contemporary and closely related taxa. Some recently published accounts claiming to be revisions of the taxonomy of Wealden ‘iguanodonts’, including material belonging to the hypodigm of Hy. fittoni, have failed to adhere to basic taxonomic principles and have caused more confusion than was strictly necessary. The systematic position of Hypselospinus is reassessed cladistically. The cladistic analysis forms the basis for a revised hierarchical classification of derived ornithopods. The consensus topology generated by the systematic analysis has been used to explore the phylogenetic history of these dinosaurs and create an internally consistent classificatory hierarchy (phylogenetic definitions and Linnaean diagnoses are given for critical positions in the topology). This analysis suggests that there is a fundamental split amongst the more derived (clypeodontan) ornithopod ornithischians into the clades Hypsilophodontia and Iguanodontia. There is evidence for anatomical parallelism and convergence (homoplasy) particularly between large-bodied representatives of both clades. Hypselospinus is one of the earliest known styracosternan iguanodontians and displays anatomical characteristics that presage the evolution of the extraordinarily abundant and diverse hadrosaurs of the latest Cretaceous (Campanian−Maastrichtian). These observations cast fresh light on the phylogeny, classification, diversity, and biology of derived ornithopods. There is little doubt that Hy. fittoni could have been understood far better more than a century ago. That this statement is undoubtedly true is reflected in the century of doubt and confusion that has surrounded this taxon and its original incarnation as Iguanodon fittoni.

For nearly 130 years dinosaurs have been divided into two distinct clades – Ornithischia and \ud Saurischia. Here, we present a radical new hypothesis for the phylogenetic relationships of the \ud major dinosaurian groups, one that challenges the current consensus concerning early dinosaur \ud evolution and highlights problematic aspects of current cladistic definitions. Our study recovers, \ud for the first time, a sister-group relationship between Ornithischia and Theropoda \ud (Ornithoscelida), with Sauropodomorpha + Herrerasauridae forming its monophyletic outgroup. \ud This new tree topology requires redefinition and rediagnosis of Dinosauria and the subsidiary \ud dinosaurian clades. In addition, it forces re-evaluations of early dinosaur cladogenesis and \ud character evolution, suggests the independent acquisition of hypercarnivory in herrerasaurids and \ud theropods, and offers an explanation for many of the anatomical features previously regarded as \ud striking convergences between theropods and early ornithischians.

It has become accepted in recent years that the fossil record can preserve labile tissues. We report here the highly detailed mineralization of soft tissues associated with a naturally occurring brain endocast of an iguanodontian dinosaur found in c. 133 Ma fluvial sediments of the Wealden at Bexhill, Sussex, UK. Moulding of the braincase wall and the mineral replacement of the adjacent brain tissues by phosphates and carbonates allowed the direct examination of petrified brain tissues. Scanning electron microscopy (SEM) imaging and computed tomography (CT) scanning revealed preservation of the tough membranes (meninges) that enveloped and supported the brain proper. Collagen strands of the meningeal layers were preserved in collophane. The blood vessels, also preserved in collophane, were either lined by, or infilled with, microcrystalline siderite. The meninges were preserved in the hindbrain region and exhibit structural similarities with those of living archosaurs. Greater definition of the forebrain (cerebrum) than the hindbrain (cerebellar and medullary regions) is consistent with the anatomical and implied behavioural complexity previously described in iguanodontian-grade ornithopods. However, we caution that the observed proximity of probable cortical layers to the braincase walls probably resulted from the settling of brain tissues against the roof of the braincase after inversion of the skull during decay and burial.

Lesothosaurus diagnosticus from the upper Elliot Formation of South Africa and Lesotho (?Hettangian–Sinemurian) is an important early representative of Ornithischia. In previous studies it has been recovered in several positions on the ornithischian tree including as the earliest known member of Thyreophora, the earliest known member of Neornithischia and as a member of an even a more basal ornithischian lineage, one that diverged before these major groups appeared. Given this taxon's important position as one of the few well-known early ornithischians, it is surprising that details of much of its anatomy remain unpublished. A second non-heterodontosaurid ornithischian taxon, also from the upper Elliot Formation, Stormbergia dangershoeki, has also been recovered as the earliest known member of Neornithischia; however, the validity of this taxon has been challenged. Hence, a reassessment of the taxonomic statuses and systematic positions of L. diagnosticus and S. dangershoeki within Ornithischia is required as an important step in the investigation of the early evolution of this group. A comprehensive redescription of the post-cranial material of L. diagnosticus and a re-evaluation of other ‘fabrosaur’ material (including the hypodigm of S. dangershoeki) was carried out to provide new information on the anatomy of these taxa and to better resolve the relationships at the base of the ornithischian tree. This study has found that the material of L. diagnosticus and S. dangershoeki almost certainly represents the same taxon and that the apparent differences between these genera is probably a product of ontogentic (rather than taxonomic) differences. A revision of the phylogenetic relationships of L. diagnosticus (when synonymized with S. dangershoeki) recovers it as the basal most member of Neornithischia.

The predominantly unknown nature and magnitude of the total taphonomic biasing that affects fossil assemblages commonly limits the testing of paleoecological hypotheses by the quantitative comparison of fossil assemblages. Multiple regression analyses of a suite of taphonomic characteristics against a measure of the total taphonomic biasing of a fossil assemblage can be used to generate a taphonomic model that identifies and quantifies many of those taphonomic processes that are important in biasing fossil assemblages. By examining the parameters of regression-based quantitative taphonomic models, key elements of the taphonomic history of a fossil assemblage can be reconstructed and such histories compared between fossil assemblages. We discuss the methodology pertinent to the building of quantitative taphonomic models and illustrate the effectiveness of such an approach using a case study considering two samples (857 specimens) of an Oligocene mammalian fossil assemblage from the Scenic Member of the Brule Formation, South Dakota. It is possible to quantify all of the taphonomic biasing affecting bone abundances in each of the two sampled assemblages using a small number of taphonomic characteristics. The most important of these characteristics is bulk density. The control of biasing by density is attributed to a combination of the increased resistance to physical damage of dense bones as well as the decreased probability of transport. Element shape and surface area to volume ratio are shown to have a significant but lesser control on assemblage biasing. Comparison of the taphonomic models for each sampled assemblage using currently viable methods demonstrates that the two assemblages are not statistically isotaphonomic. This interpretation may change with the gathering of additional data.

In 1835 Charles Darwin's geological observations on Isla Santiago (James Island) in the Galápagos Islands led him to important insights as to the process by which different varieties of igneous rock might be produced from the same volcanic vent. His work figured in a tradition of interpretation that began with the work of George Poulett Scrope and would end in the twentieth century with the theory of magmatic differentiation of igneous rocks through the process of crystal fractionation. This article reports on the findings of an expedition to Isla Santiago in July 2007 during which we were able to locate samples of igneous rocks similar to those collected by Darwin. We have used these, together with Darwin's original specimens and transcriptions of his field notes, to examine how his understanding of the separation of the trachytic and basaltic series of magmas developed from his initial field observations through to publication of Volcanic Islands in 1844.

Heterodontosaurids are an enigmatic group of primitive ornithischian dinosaurs best known from the Early Jurassic of southern Africa. Because fossil material is rare and often poorly preserved, the taxonomy, systematics, and palaeobiology of this clade are controversial. Here we describe a new partial skull of a juvenile Heterodontosaurus tucki from the 'Stormberg' of South Africa. This skull provides new information on the cranial anatomy of this taxon as well as insights into cranial ontogeny, sexual dimorphism and tooth replacement in heterodontosaurids. Few ontogenetic changes in dental morphology occur in Heterodontosaurus, supporting previous suggestions that tooth characters are informative for species-level taxonomy in heterodontosaurids. Furthermore, the presence of well-developed caniniform teeth in the juvenile specimen does not support the hypothesis that these represent secondary sexual characteristics in heterodontosaurids. Computed tomography reveals that replacement teeth are absent in both juvenile and adult specimens of Heterodontosaurus; however, the difference in the absolute size of the teeth between the juvenile and adult specimens demonstrates that replacement must have occurred during ontogeny.

The lectotype of the Middle Jurassic theropod dinosaur Megalosaurus bucklandii, a right dentary, can be diagnosed on the basis of two unique characters: a longitudinal groove on the ventral part of the lateral surface of the dentary and a slit-like anterior Meckelian foramen. This taxon, the first dinosaur to be scientifically described, is therefore valid. Currently, however, no further material can be referred to this species with any certainty. Megalosaurus bucklandii occupies an uncertain systematic position but is not an abelisaurid or coelophysoid. Additionally, it does not possess the diagnostic dentary characters that are present in all known spinosauroids. Owing to this uncertainty, use of the family Megalosauridae should be discontinued until such time as its systematic position becomes clearer.

Synopsis Stegosauria is a clade of ornithischian dinosaurs characterised by a bizarre array of dermal armour extending, in two parasagittal rows, from the cervical region to the end of the tail. Although Stegosaurus is one of the most familiar of all dinosaurs, little is known regarding the evolutionary history of this clade. Alpha‐level taxonomic revision of all proposed stegosaur taxa shows that 11 species of stego‐saur can be regarded as valid on the basis of autapomorphies. These are: Dacentrurus armatus and Loricatosaurus priscus (gen. nov.) from Europe; Kentrosaurus aethiopicus and Paranthodon afric‐anus from Africa; Tuojiangosaurus multispinus, Chungkingosaurus jiangbeiensis, Huayangosaurus taibaii, Gigantspinosaurus sichuanensis and Stegosaurus homheni (comb. nov.) from China; and Stegosaurus mjosi (comb. nov.) and Stegosaurus armatus from North America. A cladistic analysis of Stegosauria (the first to be based upon direct observation of all relevant specimens) is presented, which indicates that ...

The relative abundances of taxa or skeletal elements in a fossil assemblage can provide important information concerning the palaeoecology and taphonomy of the assemblage. However, these relative abundances must be estimated from samples of the assemblage, rather than measured directly. The sampling error this produces decreases the accuracy with which relative abundances can be estimated from the fossil record. Using the multinomial distribution it is possible to place constraints on the accuracy of estimation of relative abundance, provided that two out of three key parameters (sample size, required degree of similarity and confidence level) are known. Applying this methodology to the fossil record it can be shown that in order to be 95% confident the taxon relative abundances of a fossil assemblage lie within 5% of those found in a sample, 534 individuals must be collected. This methodology enables the assessment of published relative abundance estimates and the development of sampling protocols for future studies.

The early Mesozoic fossil fauna collected from the Lower Lufeng Formation of Yunnan Province, China, has attracted considerable interest and attention since its discovery in the late 1930s. Its importance reflected a combination of its comparatively remote geographical position and, more particularly, the similarities of its fauna compared with approximately contemporary discoveries from Europe, North and South America, and southern Africa. The fragmentary and poorly preserved Lufeng ornithischian dinosaur Tatisaurus oehleri was described in 1965 and proved taxonomically and systematically enigmatic from the start. Originally assigned, with some noted ambivalence, to the basal ('primitive') group of ornithischians known as hypsilophodontids, since 1965 Tatisaurus has been variously ignored, assigned to a more rigorously defined Hypsilophodontidae, referred to both of the armoured (thyreophoran) ornithischian dinosaur clades (Stegosauria and Ankylosauria), or referred to a more basal position within the thyreophoran lineage. In 1996 the holotype of Tatisaurus was renamed Scelidosaurus oehleri, and the genus Scelidosaurus was proposed as an index fossil of the 'Scelidosaurus biochron' with the potential to be used for the global stratigraphic correlation of Early Jurassic (early Sinemurian) rocks. Because of this chequered history Tatisaurus oehleriSimmons, 1965 has been re-examined and is redescribed so that its taxonomic status and systematic position could be reassessed. Tatisaurus is identified as a basal thyreophoran (armoured ornithischian dinosaur); there is no basis for amalgamating it in synonymy with the genus Scelidosaurus, and the proposed creation of a 'Scelidosaurus biochron' for the purposes of biostratigraphic correlation of Lower Jurassic outcrops has no utility whatever. © 2007 The Linnean Society of London, Zoological Journal of the Linnean Society, 2007, 150, 865–874.

Previous descriptions of the postcranial skeleton of the primitive stegosaur Huayangosaurus taibaii (Middle Jurassic: People's Republic of China) are insufficient for character determinations in cladistic analysis. Reexamination of the postcranium has revealed several important characters, most of which are retained plesiomorphies that have not been identified previously. For example, Huayangosaurus retains ossified tendons, the loss of which has been used as a synapomorphy of Stegosauria. These purported stegosaurian synapomorphies now serve to unite the monophyletic clade Stegosauridae, defined as all stegosaurs more closely related to Stegosaurus than to Huayangosaurus. In addition, some anatomical characters previously used as ‘ankylosauromorph’ synapomorphies have now been identified in Huayangosaurus: this suggests that these characters occur more basally within Thyreophora. The plesiomorphic status of Huayangosaurus suggests that substantial convergence between ankylosaurs and stegosaurs o...

The Middle Jurassic (Bathonian) Ardley trackway site in Oxfordshire, UK is described in detail. The track site is extensive, containing over 40 more-or-less continuous theropod and sauropod trackways preserved together on a single bedding plane with some trackways up to 180 m in length. The trackways display reasonable preservation, with claw marks discernible. Sauropod trackways are by far the most abundant and are representative of taxa that exhibit both narrow and wide-gauge styles of locomotion. Theropod trackways are represented by large tridactyl prints and claw impressions that display exceptionally low pace angulation values during their walking phase. One theropod trackway is unique in that it reveals a gait transition associated with a temporary increase of speed. These dinosaurs were walking over a lime-mud firmground to hardground that was emergent, or locally very shallowly submerged. GPS (Global Positioning Satellite) data reveal that the tracks, preserved during a short time interval, trend in a north-easterly direction. Multi-herding behaviour is suggested for the sauropods of differing size. The discovery of this site adds significantly to our knowledge of the taxonomic composition of Middle Jurassic ecosystems. Evidence concerning locomotor styles employed by saurischian dinosaurs, footprint identification, potential trackmaker, social interactions and observations concerning estimates of Middle Jurassic faunal diversity, as well as aspects of dinosaur locomotor evolution are discussed.

Synopsis The dinosaurs of the Hateg Basin of Transylvania (late Maastrichtian; western Romania) include Theropoda, Sauropoda, Ornithopoda and Ankylosauria. Of these, one of the most enigmatic taxa is the ornithopod that Franz Baron Nopcsa originally described as Mochlodon suessi and M. robustus in 1902. These two species have come to be regarded as a single species of Rhabdodon, R. robustus, which is distinct from R. priscus from the Late Cretaceous of southern France and northern Spain. This study provides a detailed anatomical revision of the Rhabdodon material that was described originally by Nopcsa during the early decades of the 20th century. It also adds information on material discovered in the Hateg area of Romania since the 1930s. A phylogenetic analysis of basal euornithopods indicates that the non‐hadrosaurid material from Hateg comprises two distinct, but congeneric, species. These two species can be distinguished unambiguously from R. priscus. A new genus Zalmoxes is established for the Roman...

The genus Probactrosaurus was first established for material discovered by a joint Russian/Chinese expedition to the Chinese autonomous region of Neimongol (Inner Mongolia). Fossils were collected at a site named Maorty (= Maortu). Material attributable to ornithopod dinosaurs was considered sufficiently distinct to permit the definition of two species of the new genus: Probactrosaurus gobiensis and P. alashanicus. The former species was based on a considerable quantity of skeletal material, much of which is still to be found in the collections of the Palaeontological Institute (PIN), Moscow. The latter was based on far less well-preserved specimens, including a holotype (a posterior skull roof) that can no longer be found in the collections of the PIN and which, along with other materials, was reportedly returned to the Institute of Vertebrate Palaeontology and Palaeoanthropology, Beijing. Some remnants of the original material attributed to P. alashanicus have been located in the PIN collections. Both taxa, established by A. K. Rozhdestvensky, are re-described using all of the available material collected during the early Sino-Soviet expeditions. Probactrosaurus alashanicus is considered to be a junior subjective synonym of P. gobiensis. Further comparisons are made with the recently described species Probactrosaurus mazongshanensis Lu, 1997. The latter does not appear to be referable to the genus Probactrosaurus. Probactrosaurus is a gracile ornithopod (ranging between 4 and 6 m in length). The skull is unadorned by any form of cranial crest; however, the premaxillary beak is deflected ventrally and the dentition is similar to that seen in more derived hadrosaurid ornithopods. The postcranial skeleton is notable for its gracility, in particular the elongate forearm and manus, and the retention of a small, conical pollex spine. Systematic analysis suggests that P. gobiensis is a derived non-hadrosaurid iguanodontian ornithopod and the basal sister-taxon to the clade Hadrosauridae. The phylogeny of currently known iguanodontians is reviewed. © 2002 The Linnean Society of London, Zoological Journal of the Linnean Society, 2002, 136, 113–144.

This weighty pocket-book provides a general survey of the dinosaurs (and pterosaurs) collected from the Wealden Group (Lower Cretaceous) of the Isle of Wight. This island, because of the combination of poorly consolidated Mesozoic ‘continental’ sediments and high levels of erosion, is by far and away the richest and most productive area for dinosaur fossils in the British Isles and, for this reason alone, merits its own guidebook. However this is clearly also a very timely production in the sense that it appears during the year of the opening of the new ‘Dinosaur Isle’ visitor centre (which will formally replace the older Museum of Isle of Wight Geology that for many years shared its cramped living space with the local town library). The book has been compiled by a number of workers who have been, for many years, involved directly with the geology and palaeontology of this part …

From my rather limited perspective as a vertebrate palaeontologist (albeit one that is informed by some of my current work on the Cretaceous vertebrates of Asia), any prospect of being able to improve my understanding of the general regional geology and stratigraphy of ‘Central Asia’ (particularly Mongolia and northern China) is to be welcomed. This whole area has a distinctly ‘will-o-the-wisp’ quality particularly when it comes to stratigraphic correlation. Much (dare I say the majority?) of the published information appears to rely upon heavily circular argument. Therefore the prospect of learning a little more about the stratigraphy, general geology and …

This compilation of articles takes its name from an original review by Michael Novacek Mammal phylogeny: shaking the tree , which itself was published by Nature almost a decade ago (1992). In fact looking through the list of reviews re-published here, what jumps out at the reader is that the vast majority of papers hail from the first half of the decade (only 3 of the total of 19 were published in the second half of the decade). While this does not make it an antique, it is nevertheless creaking a little given the pace of research in evolutionary biology and systematics – the primary subjects of this volume. To compensate for this Gee offers a …

Interest in the nature of the interaction between plants and animals has a history, based largely on anecdotal natural history, that can be traced back to Aristotle. However, it was not until George Cuvier (at the beginning of the 19th century), and his more canalized functional interpretation of vertebrate form, that comparative studies took on the implications of, for example, the evidence for feeding preference exhibited in the structure of teeth and jaws in vertebrates. Among those involved in herbivory among vertebrates, by far the most instructive research lines follow from the examination of living forms, their mechanical and behavioural adaptations as well as those linked to biochemistry and physiology; this can in turn be linked directly to equivalent studies in the botanical realm where the ‘prey’ adaptations can be examined and the two fields linked into a satisfyingly multi-disciplinary branch of co-evolution – applied natural history. However, while the most detailed work can be done on living taxa, the Earth has a tangible history, and the fossil remains of vertebrate herbivores and their plant prey are known and, despite the Darwinian caveat about the imperfections of the fossil record, comparative functional morphology can reveal aspects relevant to the early evolution and diversification of …

Finite element analysis (FEA) is used by industrial designers and biomechanicists to estimate the performance of engineered structures or human skeletal and soft tissues subjected to varying regimes of stress and strain. FEA is rarely applied to problems of biomechanical design in animals, despite its potential to inform structure-function analysis. Non-invasive techniques such as computed tomography scans can be used to generate accurate three-dimensional images of structures, such as skulls, which can form the basis of an accurate finite element model. Here we have applied this technique to the long skull of the large carnivorous theropod dinosaur Allosaurus fragilis. We have generated the most geometrically complete and complex FEA model of the skull of any extinct or extant organism and used this to test its mechanical properties and examine, in a quantitative way, long-held hypotheses concerning overall shape and function. The combination of a weak muscle-driven bite force, a very 'light' and 'open' skull architecture and unusually high cranial strength, suggests a very specific feeding behaviour for this animal. These results demonstrate simply the inherent potential of FEA for testing mechanical behaviour in fossils in ways that, until now, have been impossible.

A few years ago it could be claimed, with some justification, that records of dinosaur footprints and their study was at best a Cinderella subject. Fossilized footprints of this general type had been considered to be of some considerable importance during the early decades of the 19th century –notably through the work of Edward Hitchcock in the (Early Jurassic) Connecticut Valley of the USA. Such work documented the presence of very large, three-toed animals that were presumed to have offered evidence of the apocryphal ‘Noah’s Raven’. While such fossils were recognized as generally ‘interesting’, they were long considered to be of little scientific value; the identity of the actual footprint maker could not be established from the osteological evidence in the fossil record with any real confidence, and they seemed to have little other geological or palaeontological utility. However such materials have undergone significant renaissance during the last two decades – very much paralleling the large-scale renaissance of interest in palaeontology as a whole. Martin Lockley has been at the forefront …

Scelidosaurus was discovered in the Liassic cliffs of Charmouth, Dorset in 1858. It was the first essentially complete dinosaur to be discovered and subjected to proper scientific scrutiny. It was also very early, geologically, coming from the Early Jurassic (Sinemurian), thus quite close in time to the dawn of the dinosaurian era. On these grounds, hindsight leads us to expect that Scelidosaurus would occupy a seminal position in dinosaurian studies—but it does not. The year 1858 is instead widely recognised as being important on account of the announcement of Joseph Leidy's work on Hadrosaurus foulkii. Leidy's (1859) key paper cast Richard Owen's (1842) vision of dinosaurs as giant, scaly, quadrupeds in doubt. However, by 1863 Owen had completed his description of Scelidosaurus. It was quite clear that this large, scaly, quadrupedal creature entirely vindicated his own inductive reasoning of 1842. Richard Owen's work on Scelidosaurus is shown to be curiously narrow‐minded and somewhat muddled. He singul...

The holotype of the Mongolian species of ornithopod dinosaurIguanodon orientalisfrom the Early Cretaceous (Barremian-Aptian of Khamarin Khural) has been shown to have been established on holotype material that is non-diagnostic, but appears to be closely similar osteologically to the Western European speciesI. bernissartensis. Additional material collected from the locality known as Khuren Dukh (Dornogov′, Mongolia), which had previously been referred toI. orientalishas been re-examined and shown to represent a new genus and species (Altirhinus kurzanovigen.etsp. nov) of ornithopod dinosaur from the Early Cretaceous (Late Aptian/Early Albian). The anatomy of this new ornithopod is described; it shows a number of similarities to the known species ofIguanodon, but also demonstrates features which are in some instances unique to this taxon, while others seem to be either convergent upon, or transformational with respect to, the more derived hadrosaurid ornithopods of the Late Cretaceous. Palaeogeographic evidence is corroborative in that it suggests contemporaneous, albeit episodic, links between the Northern Hemisphere landmasses during the Barremian-Albian interval; these explain the appearance of very ‘European’ large ornithopods (Iguanodon) in Asia in Barremian/Aptian times as a consequence of land-based dispersal. Subsequent isolation of Asia from the European ‘domain’ during the late Early Cretaceous (Albian) may be responsible for the appearance of derived forms such asAltirhinus, and is suggestive of an Asian centre of origin for the family Hadrosauridae in middle Cretaceous times; this contradicts an earlier vicariance-biogeographic model of ornithopod evolution. The cranial anatomical modifications seen in this new taxon: vertical expansion of the dorsal nasal cavity, lateral expansion and lowering of the cropping beak relative to the jaw line, increase in the number of replacement teeth (but no significant miniaturization of the crowns) and the trend toward formation of a more integrated battery of cheek teeth, seen to varying degrees in several mid-Cretaceous ornithopods are commented upon; they can be interpreted within the context of an evolutionary trend culminating in the cranial complexity seen in the terminal lineage of ornithopods represented by the Late Cretaceous Hadrosauridae. Functionally, some of these changes can be correlated with what can be interpreted as ‘improvements’ to the efficiency of food gathering and processing which might represent increased niche partitioning and/or responses to increasingly tough and abrasive (xeric adapted) foliage; others, notably the modifications to the nasal cavity (perhaps associated with providing space for a counter-current moisture conserving turbinal system), are suggestive of a biological response to increasingly seasonal/xeric conditions in the middle of the Cretaceous Period or changes in the floral composition of these times.

The hadrosaurid dinosaur Arstanosaurus akkurganensis was described on the basis of the posterior end of a left maxilla, an associated distal end of a femur and an unreported isolated tooth, all of which were collected from the Akkurgan locality. East of the Aral Sea in central Kazakhstan. Redescription of the type material reveals that the material was inaccurately described, appears to lack specifically diagnostic characters and, although it can be assigned tentatively to the hadrosaurid subfamily Lambeosaurinae on the basis of the form of the caudodorsal margin of the maxilla, should for taxonomic purposes be regarded as a nomen dubium . Arstanosaurus cannot be assigned to any known hadrosaurid taxon from Kazakhstan with any confidence at present partly because of a lack of comparative material, and difficulties of comparative dating across what appear to be very similar localities (e.g. Shakh-Shakh). Broad anatomical similarities can be drawn with the Chinese genus Bactrosaurus . Additional hadrosaurid material collected from Baynshin Tsav, Mongolia, previously attributed to the genus Arstanosaurus , represents two new ornithopod taxa assignable to the subfamilies Hadrosaurinae and Lambeosaurinae. General comparison between the forms collected from Akkurgan, Iren Nor (China) and Baynshin Tsav supports the contention that all three localities may be dated as Early Senonian (Coniacian-Santonian) in age.

The specimen is identified as the partial cranium of a nodosaurid ankylosaur (Ornithischia: Thyreophora) on the basis of the presence of bone which is fused to the dorsal surface of the skull and has secondarily closed the upper temporal fenestrae. The only unequivocally nodosaurid material recovered from the Isle of Wight to date comes from Wealden facies, and has been referred to the genus Polacanthus; it is considered highly probable that this new skull is referable to the same genus. Despite having undergone abrasion, through post-emergence water-rolling, the skull and cranial walls have proved to be relatively informative of the general anatomy of the braincase and the neural and vascular anatomy of this part of the head. The anatomy of the braincase of most ankylosaurs (with the notable exception of the juvenile specimens of the ankylosaurid Pinacosaurus) is surprisingly poorly known, despite the relative abundance of cranial material in North American and Asian collections.The cranial neural and vascular anatomy is well shown in this specimen and enables the first detailed description of nodosaurid endocranial structures. The general form of the brain can be outlined from the structure of the endocast and the principal lobes can be identified; the majority of the cranial nerves have been identified, and a significant component of the associated vascular system is also visible. In most respects the endocast shows a neural anatomy which is common to that known in most dinosaurs. When compared to their nearest relatives, the ankylosaurid ankylosaurs (Euoplocephalus), the nodosaurid endocranial cast shows a more pronounced cerebral flexure, a forebrain which is broader and more expanded dorsally, and a more prominent cerebellum (although there is no evidence for a floccular lobe); there are minor differences in the arrangement of the cranial nerves, and the dorsal portions of the vascular system are better shown.Because of erosion, the olfactory lobes of this specimen of cf. Polacanthus are not preserved, and cannot be compared to those of ankylosaurid ankylosaurs; the latter are unusual in the strong separation of the lobes (reflected in the divergent olfactory stalks); this feature may be associated with the very complex passages within the nasal region of the skull, which are lacking in the nodosaurids described to date.

The type material of the Cretaceous ornithopod Iguanodon orientalis Rozhdestvensky, 1952 is redescribed. The characters which were originally used to establish a new species are shown to be either incorrect or indistinguishable from Iguanodon bernissartensis Boulenger, 1881. Additional material, previously unrecognized, further confirms the similarity of I. orientalis to I. bernissartensis . It is proposed that I. orientalis should be relegated in synonymy as a junior subjective synonym of I. bernissartensis Boulenger, 1881. The identification of the Barremian species I. bernissartensis in Asia indicates an unusually wide geographic spread for this species, and provides a potential biostratigraphic indicator for beds in Mongolia which had been previously dated variously between the Cenomanian and Maastrichtian stages.

Sabre-like canines clearly have the potential to inflict grievous wounds leading to massive blood loss and rapid death. Hypotheses concerning sabretooth killing modes include attack to soft parts such as the belly or throat, where biting deep is essential to generate strikes reaching major blood vessels. Sabretoothed carnivorans are widely interpreted as hunters of larger and more powerful prey than that of their present-day nonsabretoothed relatives. However, the precise functional advantage of the sabretooth bite, particularly in relation to prey size, is unknown. Here, we present a new point-to-point bite model and show that, for sabretooths, depth of the killing bite decreases dramatically with increasing prey size. The extended gape of sabretooths only results in considerable increase in bite depth when biting into prey with a radius of less than ~10 cm. For sabretooths, this size-reversed functional advantage suggests predation on species within a similar size range to those attacked by present-day carnivorans, rather than “megaherbivores” as previously believed. The development of the sabretooth condition appears to represent a shift in function and killing behaviour, rather than one in predator-prey relations. Furthermore, our results demonstrate how sabretoothed carnivorans are likely to have evolved along a functionally continuous trajectory: beginning as an extension of a jaw-powered killing bite, as adopted by present-day pantherine cats, followed by neck-powered biting and thereafter shifting to neck-powered shear-biting. We anticipate this new insight to be a starting point for detailed study of the evolution of pathways that encompass extreme specialisation, for example, understanding how neck-powered biting shifts into shear-biting and its significance for predator-prey interactions. We also expect that our model for point-to-point biting and bite depth estimations will yield new insights into the behaviours of a broad range of extinct predators including therocephalians (gorgonopsian + cynodont, sabretoothed mammal-like reptiles), sauropterygians (marine reptiles) and theropod dinosaurs.

The cranial anatomy of the Lower Jurassic ornithischian dinosaur Heterodontosaurus tucki Crompton & Charig, 1962 is described in detail for the first time on the basis of two principal specimens: the holotype (SAM-PK-K337) and referred skull (SAM-PK-K1332). In addition several other specimens that have a bearing on the interpretation of the anatomy and biology of Heterodontosaurus are described. The skull and lower jaw of Heterodontosaurus are compact and robust but perhaps most notable for the heterodont dentition that merited the generic name. Details of the cranial anatomy are revealed and show that the skull is unexpectedly specialized in such an early representative of the Ornithischia, including: the closely packed, hypsodont crowns and ‘warping’ of the occlusal surfaces (created by progressive variation in the angulation of wear on successive crowns) seen in the cheek dentition; the unusual sutural relationships between the bones along the dorsal edge of the lower jaw; the very narrow, deeply vaulted palate and associated structures on the side wall of the braincase; and the indications of cranial pneumatism (more commonly seen in basal archosaurs and saurischian dinosaurs). Evidence for tooth replacement (which has long been recognized, despite frequent statements to the contrary) is suggestive of an episodic, rather than continuous, style of tooth replacement that is, yet again, unusual in diapsids generally and particularly so amongst ornithischian dinosaurs. Cranial musculature has been reconstructed and seems to conform to that typically seen in diapsids, with the exception of the encroachment of M. adductor mandibulae externus superficialis across the lateral surface of the temporal region and external surface of the lower jaw. Indications, taken from the unusual shape of the occlusal surfaces of the cheek dentition and jaw musculature, are suggestive of a novel form of jaw action in this dinosaur. The taxonomy of currently known late Karoo-aged heterodontosaurids from southern Africa is reviewed. Although complicated by the inadequate nature of much of the known material, it is concluded that two taxa may be readily recognized: H. tucki and Abrictosaurus consors. At least one additional taxon is recognized within the taxa presently named Lanasaurus and Lycorhinus; however, both remain taxonomically problematic and their status needs to be further tested and may only be resolved by future discoveries. The only other named taxon, Geranosaurus atavus, represents an invalid name. The recognition of at least four distinct taxa indicates that the heterodontosaurids were speciose within the late Karoo ecosystem. The systematics of Heterodontosaurus and its congeners has been analysed, using a restricted sample of taxa. A basal (nongenasaurian) position within Ornithischia is re-affirmed. There are at least four competing hypotheses concerning the phylogenetic placement of the Heterodontosauridae, so the evidence in support of the various hypotheses is reviewed in some detail. At present the best-supported hypothesis is the one which places Heterodontosauridae in a basal (non-genasaurian) position; however, the evidence is not fully conclusive and further information is still needed in respect of the anatomy of proximate outgroups, as well as more complete anatomical details for other heterodontosaurids. Heterodontosaurids were not such rare components of the late Karoo ecosystem as previously thought; evidence also suggests that from a phylogenetic perspective they occupied a potentially crucial position during the earliest phases of ornithischian dinosaur evolution.