Misplaced Pages

Acanthodii

Article snapshot taken from Wikipedia with creative commons attribution-sharealike license. Give it a read and then ask your questions in the chat. We can research this topic together.

The shoulder girdle or pectoral girdle is the set of bones in the appendicular skeleton which connects to the arm on each side. In humans, it consists of the clavicle and scapula ; in those species with three bones in the shoulder, it consists of the clavicle, scapula, and coracoid . Some mammalian species (such as the dog and the horse ) have only the scapula.

#832167

45-482: Acanthodii or acanthodians is an extinct class of gnathostomes (jawed fishes ). They are currently considered to represent a paraphyletic grade of various fish lineages basal to extant Chondrichthyes , which includes living sharks , rays , and chimaeras . Acanthodians possess a mosaic of features shared with both osteichthyans (bony fish) and chondrichthyans (cartilaginous fish). In general body shape, they were similar to modern sharks, but their epidermis

90-564: A cartilaginous skeleton , but their fins had a wide, bony base and were reinforced on their anterior margin with a dentine spine. As a result, fossilized spines and scales are often all that remains of these fishes in ancient sedimentary rocks . The earliest acanthodians were marine, but during the Devonian , freshwater species became predominant. Acanthodians have been divided into four orders: Acanthodiformes , Climatiiformes , Diplacanthiformes , and Ischnacanthiformes . "Climatiiformes"

135-628: A branch of Placoderms was most likely the ancestor of present-day gnathostomes. A 419-million-year-old fossil of a placoderm named Entelognathus had a bony skeleton and anatomical details associated with cartilaginous and bony fish, demonstrating that the absence of a bony skeleton in Chondrichthyes is a derived trait. The fossil findings of primitive bony fishes such as Guiyu oneiros and Psarolepis , which lived contemporaneously with Entelognathus and had pelvic girdles more in common with placoderms than with other bony fish, show that it

180-458: A full terrestrial life), both among extant species and along evolutionary lines, and determining homologies for individual pectoral elements is difficult. Except for the sternum, these elements (along with the pelvic girdle ) were, however, present in early bony fishes before there were even limbs, arising from their ancestral external armor plates. In digitless choanates , the cleithrum , clavicle, and interclavicle are dermal and linked to

225-418: A neck, and a flat or slightly curved diamond-shaped crown. Despite being called "spiny sharks", acanthodians predate sharks. Scales that have been tentatively identified as belonging to acanthodians, or "shark-like fishes" have been found in various Ordovician strata, though, they are ambiguous, and may actually belong to jawless fishes such as thelodonts . The earliest unequivocal acanthodian fossils date from

270-457: A number of causes. Inflammation or injury of associated tendons , bone , muscles , nerves , ligaments , and cartilage can all cause pain. Also, past injury compensation, and stress can result in complicated shoulder pain. In humans, winged scapula is a condition in which the shoulder blade protrudes from a person's back in an abnormal position. The pectoral girdle demonstrates an enormous variation in amniotes (vertebrates adapted to

315-1215: A paraphyletic assemblage leading to cartilaginous fish, while bony fish evolved from placoderm ancestors. Burrow et al. 2016 provides vindication by finding chondrichthyans to be nested among Acanthodii, most closely related to Doliodus and Tamiobatis . A 2017 study of Doliodus morphology points out that it appears to display a mosaic of shark and acanthodian features, making it a transitional fossil and further reinforcing this idea. Phylogeny after Galeaspida Osteostraci " Placodermi " Osteichthyes Tetanopsyrus Nerepisacanthus Ischnacanthus Poracanthodes Culmacanthus Uraniacanthus Diplacanthus Rhadinacanthus Cassidiceps Mesacanthus Lodeacanthus Triazeugacanthus Promesacanthus Acanthodes Cheiracanthus Homalacanthus Euthacanthus Ptomacanthus Brachyacanthus Climatius Parexus Vernicomacanthus Lupopsyrus Obtusacanthus Kathemacanthus Brochoadmones Gyracanthides Chondrichthyes (conventionally defined) The oldest remains attributed acanthodian-grade chondrichthyans are Fanjingshania and Qianodus from

360-472: A plane joint. The sternoclavicular joint accommodates a wide range of scapula movements and can be raised to a 60° angle. The scapulocostal joint (also known as the scapulothoracic joint) is a physiological joint formed by an articulation of the anterior scapula and the posterior thoracic rib cage . It is musculotendinous in nature and is formed predominantly by the trapezius , rhomboids and serratus anterior muscles. The pectoralis minor also plays

405-404: A role in its movements. The gliding movements at the scapulocostal joint are elevation , depression , retraction , protraction and superior and inferior rotation of the scapula. Disorders of the scapulocostal joint are not very common and usually restricted to snapping scapula . The suprahumeral joint (also known as the subacromial joint) is a physiological joint formed by an articulation of

450-454: A single dorsal fin, toothless jaws, and long gill rakers . They were the last and most specialized off the traditional acanthodians, as they survived up until the Permian period. The scales of Acanthodii have distinctive ornamentation peculiar to each order. Because of this, the scales are often used in determining relative age of sedimentary rock. The scales are tiny, with a bulbous base,

495-622: A study of early jawed vertebrate relationships, Davis et al. (2012) found acanthodians to be split among the two major clades Osteichthyes (bony fish) and Chondrichthyes (cartilaginous fish). The well-known acanthodian Acanthodes was placed within Osteichthyes, despite the presence of many chondrichthyan characteristics in its braincase. However, a newly described Silurian placoderm , Entelognathus , which has jaw anatomy shared with bony fish and tetrapods , has led to revisions of this phylogeny: acanthodians were then considered to be

SECTION 10

#1732772611833

540-452: A ventral coracoid. As for the sternum, it also came from the fusion of the inner ends of the pectoral girdles in tetrapods , subsequently growing between the ribs . In dinosaurs , the main bones of the pectoral girdle were the scapula (shoulder blade) and the coracoid , both of which directly articulated with the clavicle . The clavicle was present in saurischian dinosaurs but largely absent in ornithischian dinosaurs. The place on

585-434: Is a complex of 5 joints that can be divided into two groups. 3 of these joints are true anatomical joints, while 2 are physiological ("false") joints. Within each group, the joints are mechanically linked so that both groups simultaneously contribute to the different movements of the shoulder to variable degrees. In the first group, the scapulohumeral or glenohumeral joint is the anatomical joint mechanically linked to

630-474: Is a paraphyletic assemblage of early acanthodians such as climatiids , gyracanthids , and diplacanthids ; they had robust bony shoulder girdles and many small sharp spines ("intermediate" or "prepelvic" spines) between the pectoral and pelvic fins. The climatiiform subgroup Diplacanthida has subsequently been elevated to its own order, Diplacanthiformes. Ischnacanthiforms were predators with tooth plates fused to their jaws. Acanthodiforms were filter feeders with

675-406: Is that jaws are homologous to the gill arches . In jawless fishes a series of gills opened behind the mouth, and these gills became supported by cartilaginous elements. The first set of these elements surrounded the mouth to form the jaw. The upper portion of the second embryonic arch supporting the gill became the hyomandibular bone of jawed fish, which supports the skull and therefore links

720-437: Is the articulation between the acromion process of the scapula and the lateral end of the clavicle . It is a plane type of synovial joint. The acromion of the scapula rotates on the acromial end of the clavicle. The sternoclavicular joint is the articulation of the manubrium of the sternum and the first costal cartilage with the medial end of the clavicle . It is a saddle type of synovial joint but functions as

765-472: The clavicle and scapula and allow for the motion of the sternoclavicular joint (connection between sternum and clavicle) and acromioclavicular joint (connection between clavicle and scapula). The five muscles that comprise the function of the shoulder girdle are the trapezius muscle (upper, middle, and lower), levator scapulae muscle , rhomboid muscles (major and minor), serratus anterior muscle , and pectoralis minor muscle . The shoulder girdle

810-416: The clavicle . The glenohumeral joint is the articulation between the head of the humerus and the glenoid cavity of the scapula . It is a ball and socket type of synovial joint with three rotatory and three translatory degrees of freedom. The glenohumeral joint allows for adduction , abduction , medial and lateral rotation , flexion and extension of the arm. The acromioclavicular joint

855-425: The coracoacromial ligament and the head of the humerus . It is formed by the gap between the humerus and the acromion process of the scapula. This space is filled mostly by the subacromial bursa and the tendon of supraspinatus . This joint plays a role during complex movements while the arm is fully flexed at the glenohumeral joint, such as changing a lightbulb, or painting a ceiling. From its neutral position,

900-624: The jawed vertebrates . Gnathostome diversity comprises roughly 60,000 species, which accounts for 99% of all living vertebrates, including humans. Most gnathostomes have retained ancestral traits like true teeth , a stomach , and paired appendages (pectoral and pelvic fins, arms, legs, wings, etc.). Other traits are elastin , a horizontal semicircular canal of the inner ear, myelin sheaths of neurons , and an adaptive immune system which has discrete lymphoid organs ( spleen and thymus ), and uses V(D)J recombination to create antigen recognition sites, rather than using genetic recombination in

945-399: The operculum in later bony fishes. However, most of these characteristics are considered homologous characteristics derived from common placoderm ancestors, and present also in basal cartilaginous fish . Overall, the acanthodians' jaws are presumed to have evolved from the first gill arch of some ancestral jawless fishes that had a gill skeleton made of pieces of jointed cartilage. In

SECTION 20

#1732772611833

990-408: The sister taxon of Gnathostomata. Jaw development in vertebrates is likely a product of the supporting gill arches. This development would help push water into the mouth by the movement of the jaw, so that it would pass over the gills for gas exchange. The repetitive use of the newly formed jaw bones would eventually lead to the ability to bite in some gnathostomes. Newer research suggests that

1035-601: The variable lymphocyte receptor gene. It is now assumed that Gnathostomata evolved from ancestors that already possessed a pair of both pectoral and pelvic fins . Until recently these ancestors, known as antiarchs , were thought to have lacked pectoral or pelvic fins. In addition to this, some placoderms (extinct fish with bony plates) were shown to have a third pair of paired appendages, that had been modified to claspers in males and basal plates in females—a pattern not seen in any other vertebrate group. The Osteostraci (bony armored jawless fish) are generally considered

1080-724: The Early Silurian of China, dating to around 439 million years ago. Compared to other contemporary groups of fish, acanthodians were relatively morphologically and ecologically conservative. Acanthodians rose in diversity during the Late Silurian, reaching their apex of diversity during the Lochkovian stage of the Early Devonian, declining during the Pragian but rising again during the following Emsian , which

1125-420: The acanthodians close to the ancestors of the bony fishes. Although their interior skeletons were made of cartilage , a bonelike material had developed in the skins of these fishes, in the form of closely fitting scales (see above). Some scales were greatly enlarged and formed a bony covering on top of the head and over the lower shoulder girdle . Others developed a bony flap over the gill openings analogous to

1170-590: The beginning of the Silurian Period, some 50 million years before the first sharks appeared. Later, the acanthodians colonized fresh waters, and thrived in the rivers and lakes during the Devonian and in the coal swamps of Carboniferous . By this time bony fishes were already showing their potential to dominate the waters of the world, and their competition proved too much for the spiny sharks, which died out in Permian times (approximately 250 million years ago). Many palaeontologists originally considered

1215-401: The caudal part of the head while the humerus articulates with a small scapulocoracoid bone. As the first digits appeared, the pectoral structure lost its direct connection to the head skeleton while the scapulocoracoid grew more prominent and started to face laterally. In true tetrapods, the dermal part of the girdle was gradually reduced and the scapulocoracoid split into a dorsal scapula and

1260-486: The deep remodelling of the vertebrate skull that must have taken place as early jaws evolved. The ancestor of all jawed vertebrates have gone through two rounds of whole genome duplication. The first happened before the gnathostome and cyclostome split, and appears to have been an autopolyploidy event (happened within the same species). The second occurred after the split, and was an allopolyploidy event (the result of hybridization between two lineages). The customary view

1305-481: The early vertebrate jaw has been described as "a crucial innovation" and "perhaps the most profound and radical evolutionary step in the vertebrate history". Fish without jaws had more difficulty surviving than fish with jaws, and most jawless fish became extinct during the Triassic period. However studies of the cyclostomes , the jawless hagfishes and lampreys that did survive, have yielded little insight into

1350-676: The jaw to the cranium. The hyomandibula is a set of bones found in the hyoid region in most fishes. It usually plays a role in suspending the jaws or the operculum in the case of teleosts . While potentially older Ordovician records are known, the oldest unambigious evidence of jawed vertebrates are Qianodus and Fanjingshania from the early Silurian ( Aeronian ) of Guizhou , China around 439 million years ago, which are placed as acanthodian -grade stem -chondrichthyans. [REDACTED] [REDACTED] [REDACTED] [REDACTED] [REDACTED] [REDACTED] [REDACTED] Shoulder girdle The pectoral girdles are to

1395-419: The jawless craniates Agnatha .   † Placodermi    [REDACTED]    Acanthodians , incl. Chondrichthyes (cartilaginous fishes) [REDACTED]    Actinopterygii    [REDACTED]    Amphibia    [REDACTED]    Sauria    [REDACTED]    Mammalia    [REDACTED] The appearance of

Acanthodii - Misplaced Pages Continue

1440-412: The lateral end of the clavicle is rotated posteriorly so that the angle at the acromioclavicular joint opens up slightly. When the scapula is moved laterally it lies in a sagittal plane with the glenoid cavity facing anteriorly. At this position, the lateral end of the clavicle is rotated anteriorly so that the clavicle lies in a frontal plane. While this slightly closes the angle between the clavicle and

1485-405: The origin of teeth along with, or soon after, the evolution of jaws. Late Ordovician -aged microfossils of what have been identified as scales of either acanthodians or "shark-like fishes", may mark Gnathostomata's first appearance in the fossil record. Undeniably unambiguous gnathostome fossils, mostly of primitive acanthodians, begin appearing by the early Silurian , and become abundant by

1530-434: The physiological subdeltoid or suprahumeral joint (the "second shoulder joint") so that movements in the suprahumeral joint results in movements in the glenohumeral joint. In the second group, the scapulocostal or scapulothoracic joint is the important physiological joint that can not function without the two anatomical joints in the group, the acromioclavicular and sternoclavicular joints , i.e. they join both ends of

1575-460: The scapula where it articulated with the humerus (upper bone of the forelimb) is the called the glenoid . The scapula served as the attachment site for a dinosaur's back and forelimb muscles. Chimpanzees are far better at brachiation than humans. Their clavicles possess a cranially oriented twist on the acromial end, conducive to better force transfer through it - a very important function in arboreal locomotion. Chimpanzee scapulas also possess

1620-422: The scapula, it also widens the shoulder. The scapula can be elevated and depressed from the neutral position to a total range of 10 to 12 centimetres (3.9 to 4.7 in); at its most elevated position the scapula is always tilted so that the glenoid cavity is facing superiorly. During this tilting, the scapula rotates to a maximum angle of 60° about an axis passing perpendicularly through the bone slightly below

1665-498: The shoulder and adjacent features can fluctuate in severity depending on the person's age, sport, position, recurring shoulder dysfunction, and many other factors. Some other common shoulder injuries are fractures to any shoulder girdle bones i.e. clavicle , ligamentous sprains such as AC joint or GH ligaments, rotator cuff injuries, different labral tears, and other acute or chronic conditions related to shoulder anatomy. Shoulder girdle pain can be acute or chronic and be due to

1710-460: The shoulder girdle can be rotated about an imaginary vertical axis at the medial end of the clavicle (the sternoclavicular joint). Throughout this movement the scapula is rotated around the chest wall so that it moves 15 centimetres (5.9 in) laterally and the glenoid cavity is rotated 40–45° in the horizontal plane. When the scapula is moved medially it lies in a frontal plane with the glenoid cavity facing directly laterally. At this position,

1755-512: The spine; this causes the inferior angle to move 10 to 12 centimetres (3.9 to 4.7 in) and the lateral angle 5 to 6 centimetres (2.0 to 2.4 in). Shoulders are a common place for tissue injuries, especially if the person plays overhead sports such as tennis , volleyball , baseball , swimming , etc. According to Bahr's major injury related statistics, shoulder dislocations or subluxations account for 4% of injuries in adults ages 20–30 and 20% of shoulder injuries are fractures. Damage to

1800-415: The start of the Devonian . Gnathostomata is traditionally a infraphylum , broken into three top-level groupings: Chondrichthyes , or the cartilaginous fish; Placodermi , an extinct grade of armored fish; and Teleostomi , which includes the familiar classes of bony fish , birds , mammals , reptiles , and amphibians . Some classification systems have used the term Amphirhina . It is a sister group of

1845-543: The two permits great mobility of the shoulder girdle compared to the compact pelvic girdle ; because the upper limb is not usually involved in weight bearing, its stability has been sacrificed in exchange for greater mobility. In those species having only the scapula, no joint exists between the forelimb and the thorax , the only attachment being muscular. The shoulder girdle is the anatomical mechanism that allows for all upper arm and shoulder movement in humans. The shoulder girdle consists of five muscles that attach to

Acanthodii - Misplaced Pages Continue

1890-448: The upper limbs as the pelvic girdle is to the lower limbs; the girdles are the part of the appendicular skeleton that anchor the appendages to the axial skeleton. In humans, the only true anatomical joints between the shoulder girdle and the axial skeleton are the sternoclavicular joints on each side. No anatomical joint exists between each scapula and the rib cage ; instead the muscular connection or physiological joint between

1935-458: Was a relative rather than a direct ancestor of the extant gnathostomes. It also indicates that spiny sharks and Chondrichthyes represent a single sister group to the bony fishes. Fossil findings of juvenile placoderms, which had true teeth that grew on the surface of the jawbone and had no roots, making them impossible to replace or regrow as they broke or wore down as they grew older, proves the common ancestor of all gnathostomes had teeth and place

1980-507: Was covered with tiny rhomboid platelets like the scales of holosteians ( gars , bowfins ). The popular name " spiny sharks " is because they were superficially shark-shaped, with a streamlined body, paired fins , a strongly upturned tail, and stout, largely immovable bony spines supporting all the fins except the tail—hence, "spiny sharks". However, acanthodians are not true sharks; their close relation to modern cartilaginous fish can lead them to be considered " stem -sharks". Acanthodians had

2025-885: Was followed by a decline in diversity during middle-Late Devonian. The diversity of the group was consistently low but stable during the Carboniferous, slightly decreasing going into the Permian. The youngest records of the group are isolated scales and fin spines from Middle-Late Permian strata in the Paraná Basin of Brazil. [REDACTED] [REDACTED] [REDACTED] [REDACTED] [REDACTED] [REDACTED] [REDACTED] [REDACTED] [REDACTED] [REDACTED] [REDACTED] Gnathostomata Gnathostomata ( / ˌ n æ θ oʊ ˈ s t ɒ m ə t ə / ; from Ancient Greek : γνάθος ( gnathos ) 'jaw' + στόμα ( stoma ) 'mouth') are

#832167