The nostrils were placed further back than in most other theropods. The premaxillae were in close articulation with each other, and while the premaxilla only connected to the maxilla (the following bone of the upper jaw) at the middle of the palate, with no connection at the side, they formed a strong joint through the robust, interlocking articulation between the hindwards and forwards directed processes of these bones. Hindwards and below, the premaxilla formed a wall for a gap between itself and the maxilla called the subnarial gap (also termed a "kink"). Such a gap is also present in coelophysoids, as well as other dinosaurs.
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At the front, the nasal formed the boundary at the lower back of the narial opening. The nasal sloped downwards at the front, whereas it flattened hindwards. The frontal bones were long, and were not fused. Each frontal was triangular when viewed from above, and as in other troodontids, the frontals were widest at the point where they contacted the (bone behind the eye socket).
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The ilium of the pelvis had a convex upper border, a low postacetabular blade (behind the acetabulum), and a narrow brevis-shelf (a projection where tail muscles attached). The pubic foot was pronounced and shorter at the front than behind. The ischium was straight and expanded hindwards, ending in a lobe-shape. The femur was sigmoid-shaped, and had a very robust, upwards pointing head, with a deep sulcus (groove).
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The dentary had three processes that extended backwards into other bones placed further back in the mandible. The articular bone at the back of the mandible was completely fused with the surangular and prearticular bones. The mandible extended hindwards beyond the cotyla (which connected with the condyle of the upper jaw), and this part was therefore similar to a retroarticular process as seen in other taxa. The surangular enclosed two mandibular fenestrae.
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Kosmoceratops had an estimated length of and a weight of . As a ceratopsid, it would have been quadrupedal with a heavily constructed skeleton. It had a triangular beak with a pointed tip and a blade-like nasal horn with a flattened upper portion. While the horns above the eyes were oriented forwards or hindwards in most of its relatives, the horns of Kosmoceratops pointed up and to the sides, then downwards, ending in pointed tips.
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The maxilla was kept from being part of the margin of the narial opening by the maxillary process. The maxillary process of the premaxilla extended hindwards to the same level as the nasal process. Due to not being fused together, the premaxillae had a fissure along their lower midline. There were two small openings (connected to each other by a shallow groove) near the base of the third and fourth premaxillary teeth, but none near the first and second.
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Segnosaurus was distinct from both Nothronychus and Enigmosaurus in having a deep (a groove where the caudofemoralis brevis muscle of the tail originated) and because its pubic boot lacked a well developed hindwards projection. The femur was straight with an oval cross-section and was in length. The head of the femur was placed on a long "neck" and the lower condyles were well-defined. The tibia was straight, slightly shorter than the femur, and twisted along its axis.
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Casts of Giganotosaurus and the contemporary sauropod Limaysaurus, Hungarian Natural History Museum In 2002, Coria and Currie found that various features of the rear part of the skull (such as the frontwards slope of the occiput and low and wide occipital condyle) indicate that Giganotosaurus would have had a good capability of moving the skull sideways in relation to the front neck vertebrae. These features may also have been related to the increased mass and length of the jaw muscles; the jaw articulation of Giganotosaurus and other carcharodontosaurids was moved hindwards to increase the length of the jaw musculature, enabling faster closure of the jaws, whereas tyrannosaurs increased the mass of the lower jaw musculature, to increase the power of their bite. In 2005 Therrien and colleagues estimated the relative bite force of theropods (estimates in absolute values like newtons were impossible) and found that Giganotosaurus and related taxa had adaptations for capturing and bringing down prey by delivering powerful bites, whereas tyrannosaurs had adaptations for resisting torsional stress and crushing bones. The bite force of Giganotosaurus was weaker than that of Tyrannosaurus, and the force decreased hindwards along the tooth row.
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The external naris was large and located in a hindwards position, similar to tetanuran theropods. The orbit was large, while the lateral temporal fenestra was not as large as would be expected from more derived (or "advanced") members of the Ceratosauria. Uniquely to Limusaurus, the inner bottom edge of the premaxilla, the frontmost bone of the upper jaw, was convex. The nasal bone was distinct in having a "shelf" on its side, was short, wide, less than one third of the length of the , and twice as long as it was wide.
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The largest tooth of the maxilla was either in or near the fourth alveolus, and the height of the tooth crowns decreased hindwards. The first tooth of the maxilla pointed slightly forwards from its alveolus because the lower border of the prexamilla process (which projected backwards towards the maxilla) was upturned. The teeth of the dentary were much smaller than those of the maxilla. The third or fourth tooth in the dentary of Dilophosaurus and some coelophysoids was the largest there, and seems to have fit into the subnarial gap of the upper jaw.
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The crest extended hindwards and down, forming a round arch at the highest point. The diameter of the orbit (eye opening) was 52 mm (2 in); the eyes looked large due to the shortness of the skull. The antorbital cavity in front of the eye consisted of two fenestrae (openings); a large antorbital fenestra at the back, and a small maxillary fenestra at the front. Nemegtomaia was distinct from other oviraptorids in that the frontal bone on the midline of the skull was about 25% the length of the parietal bone from front to back.
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The opisthotics, which sat at both sides of the basioccipital, had extensions pointing backwards and upwards, the paroccipital processes. These processes were elongated and slender in Acamptonectes and Ophthalmosaurus icenicus, but short and stout in other ophthalmosaurids. The dentary, the tooth-bearing bone of the lower jaw, was elongated, straight, and had a blunt front tip, contrasting with the downturned and beak-like tips of some platypterygiines. The splenial bones expanded hindwards in depth to form the lower border of the mandible and much of its midline surface.
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The skull of Xixiasaurus was long, similar to that of Byronosaurus overall, and the snout was distinctly long and low. The premaxillae were not fused to each other, and bore a few small pits on their side surfaces. When viewed from below, the front margin of the upper jaw formed a tapering U-shape, distinct from the shape in other troodontids; the U-shape tapered less in Byronosaurus and was very elongated in Sinornithoides, for example. Viewed from above, the nasal processes that extended hindwards from the premaxillae were wedged between the premaxillary processes of the nasal bones, which extended forwards.
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The skull was rather robust, with deep jaws, especially the mandible. The tomial crest of the upper jaw (a bony support for the jaw's cutting edge) was straight for its entire length. The premaxillae (front bones of the upper jaw) were fused together for most of the front half of the snout, but were separated at the tip by a V-shaped notch. The frontal processes that projected hindwards from the premaxillae were thin and extended above the orbits (eye openings) like in modern birds, but unlike Archaeopteryx and other primitive birds without pygostyles, where these processes end in front of the orbits.
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By comparison, the teeth of Erlikosaurus were smaller, symmetrical, and simpler. The bases of the crowns increased slightly in size hindwards across the tooth row, which reflected a decrease in sideways compression. The front surfaces of the crowns and outward-facing sides were convex while the inward-facing sides were concave. A thickened ridge ran along the longitude of the inward-facing side near the upper half of the crown, which was flanked by weak grooves near the front and back edges of the teeth, reaching almost to the cervix (neck; the transition between the crown and root) of the teeth.
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In general, the 18 front-most teeth were relatively homodont (of the same type), though the crown of the second tooth was relatively shorter and more tapered; this may also have been true for the first tooth, but it was not preserved. The teeth further back in the row also decreased in relative height hindwards. By comparison, the front four to five dentary teeth of Erlikosaurus were conidont (cone-shaped) with a gradual transition to foliodont teeth. The dentary teeth were tightly packed, but not pressed closely together, with the tooth crowns approaching each other at mid-length.
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It differed from other troodontids in that the front end of the dentary of the lower jaw was downturned, similar to what is seen in therizinosaurian theropods. The (the area where the two halves of the mandible connected at the front) was short, and this region was slightly curved towards the middle. Two rows of foramina ran along the outer side of the dentary, just below the first seven dentary teeth (only one of the rows continued hindwards past the seventh of these teeth). The foramina lay in a groove, which is a distinct feature of troodontids, while the inner surface of the dentary was smooth.
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The nasal process of the premaxilla ended at the level of the hind margin of the external (bony nostril), and was quadrangular in cross-section rather than triangular, as in Byronosaurus. The nasal process of the premaxilla formed the upper hind corner of the narial opening, and Xixiasaurus was distinct in having an opening on the side surface at the base of the nasal process. The suture between the premaxilla and maxilla curved upwards from the front of the snout, and straightened out under the narial opening when seen from the side. The maxillary process of the premaxilla tapered hindwards and wedged between a small forwards-extended process of the maxilla and the main part of that bone.
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According to Carpenter, the shape of the nasal chambers of Ankylosaurus indicate that airflow was unidirectional (looping through the lungs during inhalation and exhalation), although it may also have been bidirectional in the posterior nasal chamber, with air directed past the olfactory lobes. The enlarged olfactory region of ankylosaurids indicates a well-developed sense of smell. Though hindwards retraction of the nostrils is seen in aquatic animals and animals with a proboscis, it is unlikely either possibility applies to Ankylosaurus, as the nostrils tend to be reduced or the premaxilla extended. In addition, though the widely separated nostrils may have allowed for stereo-olfaction (where each nostril senses smells from different directions), as has been proposed for the moose, little is known about this feature.
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A 2005 beam- theory study by the palaeontologist François Therrien and colleagues found that the bite force in the mandible of Dilophosaurus decreased rapidly hindwards in the tooth-throw. This indicates that the front of the mandible, with its upturned chin, "rosette" of teeth, and strengthened symphysal region (similar to spinosaurids), was used to capture and manipulate prey, probably of relatively smaller size. The properties of its mandibular symphysis was similar to those of felids and crocodilians that use the front of their jaws to deliver a powerful bite when subduing prey. The loads exerted on the mandibles were consistent with struggle of small prey, which may have been hunted by delivering slashing bites to wound it, and then captured with the front of the jaws after being too weakened to resist.
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The scapulae were held very horizontally, the resting orientation of the elbow would have been close to a right angle, and the orientation of the hand would not have deviated much from that of the lower arm. The first three-dimensional standing skeleton of Dilophosaurus, Museum of Northern Arizona. The hand posture is outdated; since the wrists were unable to pronate, the palms would have faced each other rather than hindwards In 2018, Senter and Corwin Sullivan examined the range of motion in the fore limb joints of Dilophosaurus by manipulating the bones, to test hypothesized functions of the fore limbs. They also took into account that experiments with alligator carcasses show that the range of motion is greater in elbows covered in soft tissue (such as cartilage, ligaments, and muscles) than what would be indicated by manipulation of bare bones.
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The pelvis was distinct from those of other therizinosaurs in that the upper margin of the ilium had a pronounced overhang on the lower side and that the hindwards projecting process of the ischium was extensive, almost 50 percent of the front-to-back length of the . Some features of the pelvis were similar to that of Nothronychus, particularly the ischia, but it is uncertain whether these similarities were due to them having a common ancestor to the exclusion of other derived therizinosaurids, or because they retained basal features since lost in other relatives. The ischium of Segnosaurus was distinct from that of Nothronychus in that it had an almost-rectangular obturator process and an almost-circular obturator foramen. The pelvis was distinct from that of Enigmosaurus by its deep obturator process not fusing with its counterpart at the middle, by its unfused pubic boot, and because the lower part of the pubic shaft was wide from front to back.
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Arbour and the Canadian paleontologist Philip J. Currie disagreed with Carpenter's interpretation in 2015 and pointed out that the cervical half-ring fragments of specimen AMNH 5895 did not fit together in the way proposed by Carpenter (though this could be due to breakage). They instead suggested that the fragments represented the remains of two cervical half-rings, which formed two semi-circular plates of armor around the upper part of the neck, as in the closely related Anodontosaurus and Euoplocephalus. Arbour and Mallon elaborated on this idea, describing the shape of these half-rings as "continuous U-shaped yokes" over the upper part of the neck, and suggested that Ankylosaurus had six keeled osteoderms with oval bases on each half-ring. The first osteoderms behind the second cervical half-ring would have been similar in shape to those in the first half-ring, and the osteoderms on the back probably decreased in diameter hindwards.
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