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87-496: Stegouros ( / ˌ s t ɛ ɡ ə ˈ jʊər ɒ s / , meaning "roofed tail") is a genus of ankylosaurian dinosaur from the Late Cretaceous Dorotea Formation of southern Chile . The genus contains a single species, Stegouros elengassen , known from a semi-articulated, near-complete skeleton. In February 2018, the skeleton of a small ankylosaur was recovered by a team of Texan researchers near

174-432: A minimally-invasive endoscopic procedure called Tessys method . A laminectomy is a surgical operation to remove the laminae in order to access the spinal canal. The removal of just part of a lamina is called a laminotomy . A pinched nerve caused by pressure from a disc, vertebra or scar tissue might be remedied by a foraminotomy to broaden the intervertebral foramina and relieve pressure. It can also be caused by

261-518: A "strongly curved" back (an error based on the alleged similarity to stegosaurs and glyptodonts , as ankylosaurs have flat backs). Therefore, "rigid lizard" and "curved lizard" could be additional meanings applied to the name of ankylosaurs. Ankylosauria and Stegosauria together form the two major subgroups of Thyreophora , a group of armoured dinosaurs distinct from ornithopods and marginocephalians . Historically used for forms lacking large vertical plates, Kenneth Carpenter proposed in 1997

348-453: A facet on each side of the vertebral body, which articulates with the head of a rib . There is also a facet on each of the transverse processes which articulates with the tubercle of a rib . The number of thoracic vertebrae varies considerably across the species. Most marsupials have thirteen, but koalas only have eleven. The usual number is twelve to fifteen in mammals , (twelve in the human ), though there are from eighteen to twenty in

435-441: A foramina stenosis , a narrowing of the nerve opening, as a result of arthritis . Another condition is spondylolisthesis when one vertebra slips forward onto another. The reverse of this condition is retrolisthesis where one vertebra slips backward onto another. The vertebral pedicle is often used as a radiographic marker and entry point in vertebroplasty , kyphoplasty , and spinal fusion procedures. The arcuate foramen

522-489: A length of four to five centimeters. Some other ankylosaurians are known to have such osteoderms to protect the flanks. These eight scutes were not in apparent association with any skeletal element except one that was directly adjacent to a neural arch of a vertebra. The small number of such scutes may indicate that the rump was not very heavily armored. Near the left hand was a cluster of four smaller osteoderms, fifteen to twenty millimeters in diameter, with more pointed keels. On

609-404: A natural lumbar lordosis (a spinal curvature that is concave posteriorly). This is due to the difference in thickness between the front and back parts of the intervertebral discs. The lumbar vertebrae are located between the ribcage and the pelvis and are the largest of the vertebrae. The pedicles are strong, as are the laminae, and the spinous process is thick and broad. The vertebral foramen

696-472: A posterior vertebral arch , also called a neural arch . The body is composed of cancellous bone , which is the spongy type of osseous tissue , whose microanatomy has been specifically studied within the pedicle bones. This cancellous bone is in turn, covered by a thin coating of cortical bone (or compact bone), the hard and dense type of osseous tissue. The vertebral arch and processes have thicker coverings of cortical bone. The upper and lower surfaces of

783-1045: A same-definition junior synonym of Ankylosauria. The clade Euankylosauria was named by Soto-Acuña and colleagues in 2021 in their description of a unique basal ankylosaur Stegouros to represent the grouping uniting ankylosaurids and nodosaurids, to the exclusion of their newly discovered clade Parankylosauria . This clade is formally defined in the PhyloCode as "the largest clade containing Ankylosaurus magniventris and Nodosaurus textilis , but not Stegouros elengassen ". Scelidosaurus Stegosauria Kunbarrasaurus Antarctopelta Stegouros Cedarpelta Dongyangopelta Gargoyleosaurus Gastonia Hylaeosaurus Mymoorapelta Panoplosaurus Peloroplites Polacanthus Hoplitosaurus Sauroplites Taohelong Nodosaurinae Aletopelta Chuanqilong Liaoningosaurus Gobisaurus Shamosaurus Ankylosaurinae A 2023 review of Thyreophora rejects

870-438: A secondary palate. The row of teeth starts slightly in front of the lacrimal bone and continues below the eye socket. The entire top of the eye socket is formed by fused supraoccipitalia that form a continuous thickened canopy. Similar to Kunbarrasaurus the posterior parts of the skull are not fused so that the sutures remain visible. These parts are rough with pits so that raised bone pates or horn plates were probably present. In

957-422: A small bump at the upper end, in the same position in which Stegosauria have a tubercule for the attachment of the musculus triceps brachii . The radius is slender but the ulna is robust and broadened at the top with a well-developed olecranon , an upper projection to bend the elbow. An ulnare was presumably present in the wrist; this is indicated by the discovery in the left wrist of a small U-shaped element that

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1044-407: A small surface. It lacks the skull roof, the rear lower jaws, the shoulder blades, the right humerus and the pubic bones. Some osteoderms were recovered. It represents an adult individual. Stegouros is a very small ankylosaur. It was estimated at to be about 1.8–2 metres (5.9–6.6 ft) long. Only the tail was considered to be strictly distinctive. Unlike all other known Ankylosauria, the tail

1131-442: A thick stratum corneum. On the undersides there are perpendicular intersecting notches for the attachment of fibers that presumably connect the plates to the skin. Those notches are typical for Parankylosauria. Thus, a flexible armor was formed. Thirteen "free" vertebrae have been preserved in the tail base. Five additional vertebrae are enclosed in a structure made of osteoderms that has been compared to an Aztec macuahuitl . After

1218-467: A typical ankylosaur feature, but they have hollow sides like Stegosauria. Towards the rear of the vertebral column, the transverse processes rise steeper, up to 60° on the posterior back. The vertebrae have high neural arches with both the pedicles and the neural spines reaching a considerable length. The anterior joint processes are U-shaped in top view. The sacrum has four true sacral vertebrae and an anterior sacral rod of two captured dorsosacrals that touch

1305-424: A vertebra varies; the bone is the body, and the central part of the body is the centrum. The upper and lower surfaces of the vertebra body give attachment to the intervertebral discs . The posterior part of a vertebra forms a vertebral arch , in eleven parts, consisting of two pedicles ( pedicle of vertebral arch ), two laminae, and seven processes . The laminae give attachment to the ligamenta flava (ligaments of

1392-416: Is a common anatomical variation more frequently seen in females. It is a bony bridge found on the first cervical vertebra, the atlas where it covers the groove for the vertebral artery . Degenerative disc disease is a condition usually associated with ageing in which one or more discs degenerate. This can often be a painfree condition but can also be very painful. In other animals, the vertebrae take

1479-415: Is a facet for articulation with the dens of the axis. Specific to the cervical vertebra is the transverse foramen (also known as foramen transversarium ). This is an opening on each of the transverse processes which gives passage to the vertebral artery and vein and a sympathetic nerve plexus . On the cervical vertebrae other than the atlas, the anterior and posterior tubercles are on either side of

1566-408: Is a facet on each of the transverse processes of thoracic vertebrae which articulates with the tubercle of the rib . A facet on each side of the thoracic vertebral body articulates with the head of the rib . The transverse process of a lumbar vertebra is also sometimes called the costal or costiform process because it corresponds to a rudimentary rib ( costa ) which, as opposed to the thorax,

1653-674: Is a group of herbivorous dinosaurs of the clade Ornithischia . It includes the great majority of dinosaurs with armor in the form of bony osteoderms, similar to turtles . Ankylosaurs were bulky quadrupeds , with short, powerful limbs. They are known to have first appeared in North Africa during the Middle Jurassic , and persisted until the end of the Late Cretaceous . The two main families of ankylosaurians, Nodosauridae and Ankylosauridae are primarily known from

1740-479: Is connected to the proximal surface of the fifth metacarpal bone. The hand claws are hoof-shaped, not pointed. The second finger is reduced to two phalanges as in the Stegosauria. The second finger ends in a flat disc-shaped phalanx that is blunt and probably no longer had a claw at all. More such phalanges have been found around both hands, suggesting the same was true for the third, fourth and fifth fingers. In

1827-412: Is correspondingly flattened. At the fifteenth to eighteenth vertebrae, which are in the weapon, a CAT scan shows that the anterior joint processes, the prezygapophyses, are short while the posterior joint processes extend over the posterior vertebra, fused together on their inner sides to form a wedge-shaped structure in top view, filling a corresponding V-shaped space between the anterior joint processes of

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1914-574: Is derived from an armoured creature in the mythology of the Aónik’enk , the indigenous inhabitants of the region where the holotype was discovered. The holotype , CPAP-3165 , was found in a layer of the Dorotea Formation dating from the upper Campanian . It consists of a relatively complete skeleton with skull and lower jaws. The rear part, the hindlimbs, sacrum, pelvis and tail, was preserved articulated. The front parts were scattered over

2001-404: Is large and triangular. The transverse processes are long and narrow and three tubercles can be seen on them. These are a lateral costiform process , a mammillary process and an accessory process . The superior, or upper tubercle is the mammillary process which connects with the superior articular process. The multifidus muscle attaches to the mammillary process and this muscle extends through

2088-454: Is long and lacks an obturator projection on the anterior margin. The ischia are not fused together at their distal ends. The ischium tapers downwards with a slight bend forward halfway through. Nothing of the pubic bones has been found. The thighbones are only slightly longer than the shinbones. In this, Stegouros is closer to running ancestors who had a noticeably shorter femur. Later Ankylosauria typically have very short lower legs. The femur

2175-408: Is not bifurcated, and is substantially longer than that of the other cervical spinous processes). The atlas differs from the other vertebrae in that it has no body and no spinous process. It has instead a ring-like form, having an anterior and a posterior arch and two lateral masses. At the outside centre points of both arches there is a tubercle, an anterior tubercle and a posterior tubercle , for

2262-419: Is not developed in the lumbar region. There are superior and inferior articular facet joints on each side of the vertebra, which serve to restrict the range of movement possible. These facets are joined by a thin portion of the vertebral arch called the pars interarticularis . Vertebrae take their names from the regions of the vertebral column that they occupy. There are usually thirty-three vertebrae in

2349-455: Is not made up of fused ossicles. Two pairs of small cone-shaped osteoderms with pointed keels and concave lower surfaces are present at the base of the tail. Very distinctive is the so-called "tail weapon". Ankylosaurids typically have a tail club but the Stegouros weapon has a very distinct build, representing a type not yet known from Ankylosauria. It has been compared by the describers to

2436-418: Is often used to refer to the cervical and thoracic vertebrae together, and sometimes also their surrounding areas. The twelve thoracic vertebrae and their transverse processes have surfaces that articulate with the ribs . Some rotation can occur between the thoracic vertebrae, but their connection with the rib cage prevents much flexion or other movement. They may also be known as "dorsal vertebrae" in

2523-432: Is probably proportionally large, though it is difficult to precisely gauge the proportions due to limited preservation. The praemaxillae of the front snout are toothless, short, high and narrow, and completely fused at the midline. The front palate to which they contribute is high. The maxillary bones merge seamlessly into the plate-shaped lacrimal bones that slope backwards. The maxillary bones have internal branches that form

2610-404: Is short with no more than twenty-six caudal vertebrae, the last twelve of which are covered by seven pairs of large osteoderms, the last five of which again are fused together to form a flat connected structure. Stegouros differs from its close relative Antarctopelta in its smaller body size, relatively larger neural canal, longer dorsosacral vertebrae, higher and narrower vertebral bodies of

2697-415: Is straight and not bent as in running forms. The fourth trochanter, the protrusion on the posterior femoral shaft that served to attach the tail retractor muscle, is small and shaped like a vertical ridge. The lesser trochanter is fused with the greater trochanter. As with running forms, the feet are quite narrow. The third and fourth metatarsal bones have long contact surfaces at the top. This indicates that

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2784-593: The Northern Hemisphere ( North America , Europe and Asia ), but the more basal Parankylosauria are known from southern Gondwana ( South America , Australia and Antarctica ) during the Cretaceous. Ankylosauria was first named by Henry Fairfield Osborn in 1923. In the Linnaean classification system, the group is usually considered either a suborder or an infraorder. It is contained within

2871-555: The PhyloCode . Phylogenetic and morphological studies have differed on the inclusion of certain early taxa into Ankylosauria, especially the armoured Early Jurassic form Scelidosaurus . As some analyses, like that of Carpenter from 2001 or David B. Norman in 2021 find Scelidosaurus and possibly other early forms like Emausaurus and Scutellosaurus to fall closer to Ankylosaurus than Stegosaurus , Carpenter and later Norman suggested redefining Ankylosauria to limit it to

2958-569: The Río de las Chinas valley of Ultima Esperanza province in the Magallanes y la Antártica Chilena region of southern Chile. In 2021, the type species Stegouros elengassen was named and described by Sergio Soto-Acuña et al . The generic name combines the Greek stegos , meaning "roof" and oura , meaning "tail", referring to the roof-like covering of the tail end. The specific name elengassen

3045-497: The cervical vertebrae bear ribs. In many groups, such as lizards and saurischian dinosaurs, the cervical ribs are large; in birds, they are small and completely fused to the vertebrae. The transverse processes of mammals are homologous to the cervical ribs of other amniotes . In the whale, the cervical vertebrae are typically fused, an adaptation trading flexibility for stability during swimming. All mammals except manatees and sloths have seven cervical vertebrae, whatever

3132-588: The horse , tapir , rhinoceros and elephant . In certain sloths, there is an extreme number of twenty-five and at the other end only nine in the cetacean . There are fewer lumbar vertebrae in chimpanzees and gorillas , which have three in contrast to the five in the genus Homo . This reduction in number gives an inability of the lumbar spine to lordose but gives an anatomy that favours vertical climbing, and hanging ability more suited to feeding locations in high-canopied regions. The bonobo differs by having four lumbar vertebrae. Caudal vertebrae are

3219-566: The maquahuitl , the Aztec mace. The weapon consists of seven pairs of flattened osteoderms that form an elongated structure that covers the tip of the tail. The first pair has sharp keels, the tips of which point towards the rear and sides. Their upper surfaces are, apart from that, more flattened while the lower sides are more conically curved. The inner sides, facing the tail vertebra, are strongly hollowed out. On their undersides are two pairs of smaller cone-shaped osteoderms fused, resembling those on

3306-418: The sacrum , with no intervertebral discs . The sacrum with the ilium forms a sacroiliac joint on each side of the pelvis , which articulates with the hips . The last three to five coccygeal vertebrae (but usually four) (Co1–Co5) make up the tailbone or coccyx . There are no intervertebral discs . Somites form in the early embryo and some of these develop into sclerotomes. The sclerotomes form

3393-463: The superior , transverse and inferior costal facets . As the vertebrae progress down the spine they increase in size to match up with the adjoining lumbar section. The five lumbar vertebrae are the largest of the vertebrae, their robust construction being necessary for supporting greater weight than the other vertebrae. They allow significant flexion , extension and moderate lateral flexion (side-bending). The discs between these vertebrae create

3480-697: The Cretaceous of southern Gondwana, also including Kunbarrasaurus from Australia and Antarctopelta from the Antarctic Peninsula . diverging before Ankylosauridae and Nodosauridae together, which was named Parankylosauria . The results of this phylogenetic analysis are shown below: Lesothosaurus Scutellosaurus Emausaurus Scelidosaurus Huayangosaurus Stegosauridae Kunbarrasaurus Antarctopelta Stegouros Nodosauridae Liaoningosaurus Gobisaurus Shamosaurus Ankylosaurinae The discovery of Stegouros has an important implication for

3567-401: The applied loads, and to provide anchorage for the collagen fibers of the disc. They also act as a semi-permeable interface for the exchange of water and solutes. The vertebral arch is formed by pedicles and laminae. Two pedicles extend from the sides of the vertebral body to join the body to the arch. The pedicles are short thick processes that extend, one from each side, posteriorly, from

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3654-401: The attachment of muscles. The front surface of the anterior arch is convex and its anterior tubercle gives attachment to the longus colli muscle . The posterior tubercle is a rudimentary spinous process and gives attachment to the rectus capitis posterior minor muscle . The spinous process is small so as not to interfere with the movement between the atlas and the skull . On the under surface

3741-489: The back that project caudolaterally. Osteoderms of the head were not found. It may be that those in Stegouros did not ossify or that the individual of the holotype was not old enough to have completed ossification. At the second cervical vertebra, the axis, a flat bone plate with a length of nineteen millimeters was found. Apart from this, no large elements of the neck, such as cervical halfrings, were recovered. Eight medium-sized scutes have been found, oval and keeled with

3828-427: The body of the vertebra are flattened and rough in order to give attachment to the intervertebral discs . These surfaces are the vertebral endplates which are in direct contact with the intervertebral discs and form the joint. The endplates are formed from a thickened layer of the cancellous bone of the vertebral body, the top layer being more dense. The endplates function to contain the adjacent discs, to evenly spread

3915-469: The convex articular feature of an anterior vertebra acts as the ball to the socket of a caudal vertebra. This type of connection permits a wide range of motion in most directions, while still protecting the underlying nerve cord. The central point of rotation is located at the midline of each centrum, and therefore flexion of the muscle surrounding the vertebral column does not lead to an opening between vertebrae. In many species, though not in mammals,

4002-479: The developing spinal cord , forming the vertebral arch . Other cells move distally to the costal processes of thoracic vertebrae to form the ribs. Functions of vertebrae include: There are a number of congenital vertebral anomalies , mostly involving variations in the shape or number of vertebrae, and many of which are unproblematic. Others though can cause compression of the spinal cord. Wedge-shaped vertebrae, called hemivertebrae can cause an angle to form in

4089-778: The early history of ankylosaurians ; it revealed that a novelly discovered, distinct lineage of ankylosaurs , the Parankylosauria , exist, diverging from Euankylosauria (the combined clade of Ankylosauridae and Nodosauridae ) very early in the Cretaceous and surviving until the Maastrichtian , distinguished by a unique tail weapon, dubbed ' macuahuitl ', evolved convergently to ankylosaurid tail clubs. It also suggests, through phylogenetic bracketing , that two genera found to be related by analyses by Soto-Acuña et al. ( Antarctopelta and Kunbarrasaurus ) possessed

4176-515: The eighteenth vertebra, all the vertebrae are missing: only the cavity within the macuahuitl gives an indication of how many were present. The authors estimate the maximum number of these to be eight, which would imply that there were only twenty-six tail vertebrae; the lowest number in all of Thyreophora was thirty-five until 2021, in Scelidosaurus . The vertebrae of the tail are amphiplatyan to platycoel: flat on both ends or slightly concave at

4263-409: The exception of C2 and C7, which have palpable spinous processes). C1 is also called the atlas , and C2 is also called the axis . The structure of these vertebrae is the reason why the neck and head have a large range of motion. The atlanto-occipital joint allows the skull to move up and down, while the atlanto-axial joint allows the upper neck to twist left and right. The axis also sits upon

4350-407: The first informal definition of the group, as all ornithischians closer to Ankylosaurus than Stegosaurus . This definition was further refined by Paul Sereno in 2005 to specify Ankylosaurus magniventris and Stegosaurus stenops , the type species of both genera, a definition that was followed by Madzia and colleagues in 2021 when the group name and definition was formalized following

4437-402: The first intervertebral disc of the spinal column. Cervical vertebrae possess transverse foramina to allow for the vertebral arteries to pass through on their way to the foramen magnum to end in the circle of Willis . These are the smallest, lightest vertebrae and the vertebral foramina are triangular in shape. The spinous processes are short and often bifurcated (the spinous process of C7

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4524-438: The fossil preserves. The dentary teeth are leaf-shaped and high. The teeth are asymmetrical in external view. They have a convex cingulum that extends upwards into fluted ridges ending in serrations. The cingulum is asymmetrical: horizontal when seen from the outside but an arc seen viewed the inside, that is slightly oblique towards the front. The cervical vertebrae are short. The vertebral centra are wider than they are long,

4611-409: The group Thyreophora , which also includes the stegosaurs , armored dinosaurs known for their combination of plates and spikes. The name of this group of dinosaurs is associated with a number of anatomical features in which small and large bony shields fused together, completely covering their back and sides. On the skull these shields fused with the underlying bones, and the dorsal ribs fit snugly to

4698-544: The human context. The vertebral bodies are roughly heart-shaped and are about as wide anterio-posteriorly as they are in the transverse dimension. Vertebral foramina are roughly circular in shape. The top surface of the first thoracic vertebra has a hook-shaped uncinate process, just like the cervical vertebrae. The thoracolumbar division refers to the thoracic and lumbar vertebrae together, and sometimes also their surrounding areas. The thoracic vertebrae attach to ribs and so have articular facets specific to them; these are

4785-416: The human vertebral column — seven cervical vertebrae , twelve thoracic vertebrae , five lumbar vertebrae , five fused sacral vertebrae forming the sacrum and four coccygeal vertebrae , forming the coccyx . Excluding rare deviations, the total number of vertebrae ranges from 32 to 35. In about 10% of people, both the total number of pre-sacral vertebrae and the number of vertebrae in individual parts of

4872-434: The ilium with short ribs but are not fused to it. At the rear, the sacrum lacks caudosacrals, a basal feature shared with Antarctopelta . The humerus has a slender shaft, a basal feature. However, the ends are strongly transversely broadened, especially in the epiphyses, and there is a well-developed deltopectoral crest projecting anteriorly. On the outer posterior margin of the humerus, a conspicuous ridge runs downwards with

4959-424: The junctions of the posteriolateral surfaces of the centrum, on its upper surface. From each pedicle a broad plate, a lamina , projects backward and medially to join and complete the vertebral arch and form the posterior border of the vertebral foramen, which completes the triangle of the vertebral foramen. The upper surfaces of the laminae are rough to give attachment to the ligamenta flava . These ligaments connect

5046-407: The laminae of adjacent vertebra along the length of the spine from the level of the second cervical vertebra . Above and below the pedicles are shallow depressions called vertebral notches ( superior and inferior ). When the vertebrae articulate the notches align with those on adjacent vertebrae and these form the openings of the intervertebral foramina . The foramina allow the entry and exit of

5133-405: The laminae. The spinous process serves to attach muscles and ligaments . The two transverse processes, one on each side of the vertebral body, project laterally from either side at the point where the lamina joins the pedicle , between the superior and inferior articular processes. They also serve for the attachment of muscles and ligaments, in particular the intertransverse ligaments . There

5220-541: The larger animals since they attach to the muscles and ligaments of the body. In the elephant , the vertebrae are connected by tight joints, which limit the backbone's flexibility. Spinous processes are exaggerated in some animals, such as the extinct Dimetrodon and Spinosaurus , where they form a sailback or finback. Vertebrae with saddle-shaped articular surfaces on their bodies, called "heterocoelous", allow vertebrae to flex both vertically and horizontally while preventing twisting motions. Such vertebrae are found in

5307-509: The lateral braincase, the basisphenoid is short, shorter than the basioccipital of the lower occiput. In the lower jaws, the central predentary, the bony core of the lower bill, is short and high with thin upper branches that are longer than the lower branches. The dentarium or os dentale is undulating in side view. The row of teeth is curved inwards, so that the rows of teeth of the lower jaws combined show an hourglass shape when viewed from above. The dentarium bears fourteen teeth, some of which

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5394-420: The length of the neck. This includes seemingly unlikely animals such as the giraffe, the camel, and the blue whale, for example. Birds usually have more cervical vertebrae with most having a highly flexible neck consisting of 13–25 vertebrae. In all mammals, the thoracic vertebrae are connected to ribs and their bodies differ from the other regional vertebrae due to the presence of facets. Each vertebra has

5481-416: The length of the vertebral column, giving support. The inferior, or lower tubercle is the accessory process and this is found at the back part of the base of the transverse process. The term lumbosacral is often used to refer to the lumbar and sacral vertebrae together, and sometimes includes their surrounding areas. There are five sacral vertebrae (S1–S5) which are fused in maturity, into one large bone,

5568-406: The lowest of the lumbar vertebrae (L5), but may also occur in the other lumbar vertebrae, as well as in the thoracic vertebrae. Spinal disc herniation , more commonly called a slipped disc , is the result of a tear in the outer ring ( anulus fibrosus ) of the intervertebral disc , which lets some of the soft gel-like material, the nucleus pulposus , bulge out in a hernia . This may be treated by

5655-485: The midfoot was not spread out to support the weight, as is the case with most Ankylosauria and Stegosauria. The number of phalanges has not been reduced. At the third and fourth toes, however, the extreme phalanx is not in the shape of a claw but is a flat disc. Those claws present are shaped like hooves. The shoulder blades (scapulae) were not found. The coracoids are not fused with the shoulder blades. The sternal plates are unfused, and have long lateral tubular processes at

5742-423: The necks of birds and some turtles. "Procoelous" vertebrae feature a spherical protrusion extending from the caudal end of the centrum of one vertebra that fits into a concave socket on the cranial end of the centrum of an adjacent vertebra. These vertebrae are most often found in reptiles , but are found in some amphibians such as frogs. The vertebrae fit together in a ball-and-socket articulation, in which

5829-423: The pelvis, the horizontal ilium has a very long and low anterior blade. It curves strongly forwards and to the sides, apparently to support a wide abdominal cavity. The rest of the ilium is very similar to that of the Stegosauria. The position and shape of the horizontal lateral ridge above the hip joint, i.e. semicircular, and the shape of the rear blade suggest that the latter turned inward during growth. The ischium

5916-546: The posterior vertebra. This system must have stiffened the tail tip. However, no ossified tendons are used for this as with the Ankylosauridae, because they are completely lacking. Flattened vertebrae have also been found in Antarctopelta , suggesting that a similar tail weapon was present in that species. Stegouros was found by Soto-Acuña et al. to belong to a distinct lineage of small ankylosaurs known from

6003-411: The rear. The lateral processes are long, twice longer than the neural spines, and are still present as far as the tail weapon. In the seventh through twelfth vertebrae, the neural spines are somewhat thickened at the top and shorter than the neural arches. Behind the twelfth vertebra, the undersides have a longitudinal groove and are as long as they are wide but very low. The inner cavity of the tail weapon

6090-423: The sacral vertebrae, absence of ossified tendons on the tail, teeth with six serrations on the anterior margin instead of seven or eight, and cingula , thickened tooth crown bases, without vertical grooves. Stegouros differs from Kunbarrasaurus by having a curved instead of straight ulna and radius and a process from the maxilla running towards the lacrimal bone that is narrower and sloping backwards. The head

6177-477: The same regional names except for the coccygeal – in animals with tails, the separate vertebrae are usually called the caudal vertebrae . Because of the different types of locomotion and support needed between the aquatic and other vertebrates, the vertebrae between them show the most variation, though basic features are shared. The spinous processes which are backward extending are directed upward in animals without an erect stance. These processes can be very large in

6264-463: The same tail weapon. Stegouros was discovered in layers of the Dorotea Formation . The Dorotea Formation dates to the late Campanian - Maastrichtian , between 71.7 ± 1.2 and 74.9 ± 2.1 million years ago. Fossils belonging to amphibians, mammals, fish, reptiles, and several invertebrates have also been discovered there, along with material belonging to indeterminate sauropod, theropod, and ornithischian dinosaurs. Ankylosauria Ankylosauria

6351-405: The spinal column, and the shape at their back and front aspects determines the range of movement. Structurally, vertebrae are essentially alike across the vertebrate species, with the greatest difference seen between an aquatic animal and other vertebrate animals. As such, vertebrates take their name from the vertebrae that compose the vertebral column. In the human vertebral column , the size of

6438-410: The spinal nerves from each vertebra, together with associated blood vessels. The articulating vertebrae provide a strong pillar of support for the body. There are seven processes projecting from the vertebra: A major part of a vertebra is a backward extending spinous process (sometimes called the neural spine) which projects centrally. This process points dorsally and caudally from the junction of

6525-483: The spine can vary. The most frequent deviations are eleven (rarely thirteen) thoracic vertebrae, four or six lumbar vertebrae and three or five coccygeal vertebrae (rarely up to seven). The regional vertebrae increase in size as they progress downward but become smaller in the coccyx. There are seven cervical vertebrae (but eight cervical spinal nerves ), designated C1 through C7. These bones are, in general, small and delicate. Their spinous processes are short (with

6612-419: The spine which can result in the spinal curvature diseases of kyphosis , scoliosis and lordosis . Severe cases can cause spinal cord compression. Block vertebrae where some vertebrae have become fused can cause problems. Spina bifida can result from the incomplete formation of the vertebral arch. Spondylolysis is a defect in the pars interarticularis of the vertebral arch. In most cases this occurs in

6699-489: The spine). There are vertebral notches formed from the shape of the pedicles, which form the intervertebral foramina when the vertebrae articulate . These foramina are the entry and exit conduits for the spinal nerves . The body of the vertebra and the vertebral arch form the vertebral foramen, the larger, central opening that accommodates the spinal canal , which encloses and protects the spinal cord . Vertebrae articulate with each other to give strength and flexibility to

6786-442: The tail base, one pair pointing obliquely to the rear and the other obliquely sideways and downwards. The next pair is larger and covers two entire vertebrae. It is flatter and lacks the small osteoderms on the underside. The construction of the next five pairs is similar, but they have grown together with their leading and trailing edges to form one whole. They are still separately recognizable as pentagonal plates with pointed ends. At

6873-595: The traditional Ankylosauridae-Nodosauridae split, instead finding "nodosaurids" to be referrable to three separate families: Panoplosauridae , Polacanthidae , and Struthiosauridae . Sarcolestes Paw Paw juvenile Animantarx Cedarpelta Gargoyleosaurus Hoplitosaurus Niobrarasaurus Polacanthus Texasetes Patagopelta Hylaeosaurus Gastonia burgei Gastonia lorriemcwhinneyae Peloroplites Sauropelta Tatankacephalus Invictarx Silvisaurus Vertebral centra The basic configuration of

6960-399: The transverse foramen on each transverse process. The anterior tubercle on the sixth cervical vertebra is called the carotid tubercle because it separates the carotid artery from the vertebral artery . There is a hook-shaped uncinate process on the side edges of the top surface of the bodies of the third to the seventh cervical vertebrae and of the first thoracic vertebra. Together with

7047-416: The two subclades Nodosauridae and Ankylosauridae , creating the new clade Ankylosauromorpha for all taxa closer to Ankylosaurus than Stegosaurus . However, as historically even these primitive forms were considered ankylosaurs if they were more derived than Stegosaurus , Madzia and colleagues considered a redefinition of Ankylosauria to be undesirable, instead preferring to abandon Ankylosauromorpha as

7134-542: The upper right ulna is a small round bone plate, keeled with a concave inner surface, next to a flat triangular osteoderm. Keeled osteoderms were found on the outside of the feet, three on the left foot and two on the right foot. Between the ilium and the neural spines of the sacrum is a continuous thin layer of ossified skin armor covered with vein grooves and pits. This indicates the presence of some kind of sacral shield as in Nodosauridae. However, it differs in that it

7221-450: The vertebrae as well as the rib cartilage and part of the occipital bone . From their initial location within the somite, the sclerotome cells migrate medially toward the notochord . These cells meet the sclerotome cells from the other side of the paraxial mesoderm . The lower half of one sclerotome fuses with the upper half of the adjacent one to form each vertebral body. From this vertebral body, sclerotome cells move dorsally and surround

7308-429: The vertebrae varies according to placement in the vertebral column, spinal loading, posture and pathology. Along the length of the spine , the vertebrae change to accommodate different needs related to stress and mobility. Each vertebra is an irregular bone. A typical vertebra has a body ( vertebral body ), which consists of a large anterior middle portion called the centrum ( vertebral centrum , plural centra ) and

7395-401: The vertebrae. The Latin name Ankylosauria is derived from the Greek ἀγκύλος [ankylos] — "curved", "bent" with the anatomical meaning "hard" or "fused" and σαῦρος [sauros] — "lizard". In the 1908 description of the genus Ankylosaurus , Barnum Brown described the family Ankylosauridae as a group of representatives with a "rigid spine", but noted the wide, curved shape of the ribs, suggesting

7482-421: The vertebral disc, this uncinate process prevents a vertebra from sliding backward off the vertebra below it and limits lateral flexion (side-bending). Luschka's joints involve the vertebral uncinate processes. The spinous process on C7 is distinctively long and gives the name vertebra prominens to this vertebra. Also a cervical rib can develop from C7 as an anatomical variation . The term cervicothoracic

7569-411: The very end, this structure also covers the undersides of the vertebrae. At the extreme tail tip is an eighth pair of small knob-shaped osteoderms. Numerous ossicles in the form of circular disks, four to five millimeters in diameter, were found around all skeletal elements. They are flattened into an oblate spheroid with an almost square profile. The outer sides are covered with numerous pits, indicating

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