Situated between the incus and the inner ear, the stapes transmits sound vibrations from the incus to the oval window, a membrane-covered opening to the inner ear. The stapes is also stabilized by the stapedius muscle, which is innervated by the facial nerve.
Function
Stapes
Stapes | Function
It transmits sound vibrations from the incus to the oval window, a membrane-covered opening to the inner ear. Transport sound vibrations from the incus to the oval window. It transmits sound vibrations from the incus to the oval window, a membrane-covered opening to the inner ear, it also stabilized by the stapedius muscle, which is innervated by the facial nerve It transmits sound vibrations from the incus to the oval window.
what are the 3 smallest bones in the human body
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Strapes is one of them
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what is the size of this above bone?
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Roughly 3 x 2.5mm
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which part of the body is this located?
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Middle ear of humans
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besides the human, is this bony structure present in other living species in the animal kingdom?
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It is one of three ossicles in mammals, in non-mammalian four-legged animals its homologous form is called the columella
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what are the functions this bony structure serves?
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The stapes is one of three ossicles in mammals. In non-mammalian four-legged animals, the bone homologous to the stapes is usually called the columella; however, in reptiles, either term may be used. In fish, the homologous bone is called the "hyomandibular", and is part of the gill arch supporting either the spiracle or the jaw, depending on the species. The equivalent term in amphibians is the "".
Stapes | Animals
For example, the lower branch of the squamosal bone is shortened to offset the tall dorsal process of quadratojugal which connects to it. On the other hand, the rear branch jugal bone lengthens to fill some of the space left by the shortening of the anterior process of the quadratojugal. In archosauriforms, the jugal even re-encloses the lower temporal fenestra. The stapes are long, thin, and solid, without a perforating hole (stapedial foramen) present in the more robust stapes of other reptiles.
Archosauromorpha | Skull
Within mammals and other synapsids the columella has evolved into the stapes, a homologous bone within the newly evolved inner ear. As the tympanic cavity evolved to reduce in size, the columella shortened in length. The stirrup-shaped articular processes of the columella inspired a new name for this auditory ossicle, the stapes. The auditory ossicles continue to function in conducting transmitting sound through the auditory pathway; however, they have lost their function in conducting low frequency ground vibrations. Later-arising reptiles with columella likely evolved stronger limbs and a more crawling posture, which removed the body from the ground and prevented the transmission of ground-conducted sounds.
Columella (auditory system) | Homology in mammals
In mammals, the articular and quadrate bones have migrated to the middle ear and are known as the malleus and incus. Along with the stapes, these are known as the ossicles and are a defining characteristic of mammals.
Quadrate bone | Function in mammals
In the auditory system, the columella contributes to hearing in amphibians, reptiles and birds. The columella form thin, bony structures in the interior of the skull and serve the purpose of an eardrum. It is an evolutionary homolog of the stapes, one of the auditory ossicles in mammals. In many species, the extracolumella is a cartilagenous structure that grows in association with the columella. During development, the columella is derived from the dorsal end of the hyoid arch.
Columella (auditory system) | Introduction
The morphology of the stapes suggests that the animal was capable of hearing high-frequency sound. "B. woodi" does not possess lateral line sulci or an ossified branchial system. The principal method of respiration was probably buccal (gulping air through mouth) rather than costal (expanding chest volume to take in air), indicated by the small straight ribs.
Balanerpeton | Introduction
The stapes remained in contact with the quadrate bone, but functioned as auditory ossicles rather than supports for the brain case. As a result, the quadrate bones of therapsids likely had a dual function in both the jaw joint and auditory system.
Evolution of mammalian auditory ossicles | Early therapsid jaws and ears
Situated between the incus and the inner ear, the stapes transmits sound vibrations from the incus to the oval window, a membrane-covered opening to the inner ear. The stapes is also stabilized by the stapedius muscle, which is innervated by the facial nerve.
Stapes | Function
In advanced cynodonts, including the mammaliaforms, have lost the quadratojugal, with the diminutive quadrate connecting to the stapes to function as a hearing structure. In modern mammals, the quadrate bone evolves to become the incus, one of the ossicles of the middle ear. This is an apomorphy of the mammalian clade, and is used to identify the fossil transition to mammals.
Quadratojugal bone | In mammals
As evolution later attached the cranium of terrestrial vertebrates to the rest of the skull, the hyomandibula lost its supportive function and became an interior organ, the stapes, and thus its secondary function had become its primary function.
Hyomandibula | Evolutionary context
The configuration of the stapes is intermediate between non-amniote tetrapods and amniotes. On the one hand, its connection to the otic notch is unusual, since true reptiles and other amniotes have lost an otic notch, forcing the tympanum and stapes to shift downwards towards the quadrate bone of the jaw joint. On the other hand, the thin, sensitive structure of "Seymouria"'s stapes is a specialization over most non-amniote tetrapods, which have a thick stapes useless for hearing yet useful for reinforcing the skull. The inner ear of "Seymouria baylorensis" retains a cochlear recess located behind (rather than below) the vestibule, and its anterior semicircular canal was likely encompassed by a cartilaginous (rather than bony) supraoccipital.
Seymouria | Skull
The stapes is the third bone of the three ossicles in the middle ear. The stapes is a stirrup-shaped bone, and the smallest in the human body. It rests on the oval window, to which it is connected by an annular ligament. The stapes is described as having a base, resting on the oval window, as well as a head that articulates with the incus. These are connected by anterior and posterior limbs (). The stapes articulates with the incus through the incudostapedial joint. The stapes is the smallest bone in the human body, and measures roughly 3 x 2.5mm, greater along the head-base span.
Stapes | Structure
The stapes or stirrup is a bone in the middle ear of humans and other mammals which is involved in the conduction of sound vibrations to the inner ear. This stirrup-shaped bone is connected to the oval window by its annular ligament, which allows the footplate to transmit sound energy through the oval window into the inner ear. The stapes is the smallest and lightest bone in the human body, and is so-called because of its resemblance to a stirrup ().
Stapes | Introduction
In such animals, the scapula is usually a relatively simple plate, lacking the projections and spine that it possesses in mammals. However, the detailed structure of these bones varies considerably in living groups. For example, in frogs, the procoracoid bones may be braced together at the animal's underside to absorb the shock of landing, while in turtles, the combined structure forms a Y-shape in order to allow the scapula to retain a connection to the clavicle (which is part of the shell). In birds, the procoracoids help to brace the wing against the top of the sternum. In the fossil therapsids, a third bone, the true coracoid, formed just behind the procoracoid.
Scapula | In other animals
The other set is more dorsal and consists of sub-linear arrays. This set of pores may have housed bristles, which may have been used for touching the animal's surroundings and related functions, including temporary attachment. There is no evident anus, which means that the animal must have consumed its food and excreted it from the same orifice, though the body cones may have served this function as well in addition to expelling water. However, the strong folding found in the fossils makes this conclusion tentative, with Simon Conway Morris, one of the British scientists involved in its discovery, admitting the possibility that the team simply has not spotted it.
Saccorhytus | Description
As a homologous structure in lemuriforms, the toothcomb serves variable biological roles, despite its superficially stereotypic shape and appearance. It is primarily used as a toiletry device or grooming comb. Additionally, some species use their toothcomb for food procurement or to gouge tree bark.
Toothcomb | Functions
Like the stapes bone to which it attaches, the stapedius muscle shares evolutionary history with other vertebrate structures. The mammalian stapedius evolved from a muscle called the depressor mandibulae in other tetrapods, the function of which was to open the jaws (this function was taken over by the digastric muscle in mammals). The depressor mandibulae arose from the levator operculi in bony fish, and is equivalent to the epihyoidean in sharks. Like the stapedius, all of these muscles derive from the hyoid arch and are innervated by cranial nerve VII.
Stapedius muscle | Other animals
However, they were too incompletely preserved to estimate the light sensitivity of the eyes. The footplates of the bony stapes are large, associated with hearing low-frequency sounds underground, although its inner-ear is not as specialised as "Kawingasaurus".
Kembawacela | Burrowing
Evolution of the columella is closely related to the evolution of the jaw joint. It is an ancestral homolog of the stapes, and is derived from the hyomandibular bone of fishes. As the columella is derived from the hyomandibula, many of its functional relationships remain the same. The columella resides in the air-filled tympanic cavity of the middle ear. The footplate, or proximal end of the columella, rests in the oval window. Sound is conducted through the oval window to the interior of the otic capsule. This motion ultimately stimulates sensory cells in the inner ear. In the transition of tetrapods from sea to land, the earliest appearance of functional columella appeared in temnospondyls.
Columella (auditory system) | Evolution
The human skeleton performs six major functions; support, movement, protection, production of blood cells, storage of minerals, and endocrine regulation. The human skeleton is not as sexually dimorphic as that of many other primate species, but subtle differences between sexes in the morphology of the skull, dentition, long bones, and pelvis exist. In general, female skeletal elements tend to be smaller and less robust than corresponding male elements within a given population. The human female pelvis is also different from that of males in order to facilitate childbirth. Unlike most primates, human males do not have penile bones.
Human skeleton | Introduction
Over the course of the evolution of mammals, one bone from the lower and one from the upper jaw (the articular and quadrate bones) lost their purpose in the jaw joint and migrated to the middle ear. The shortened columella connected to these bones within the middle ear to form a chain of three bones, the ossicles, which serve to effectively transmit air-based vibrations and facilitate more acute hearing.
Evolution of mammalian auditory ossicles | Introduction
In monotremes, the coracoid is a separate bone. Reptiles, birds, and frogs (but not salamanders) also possess a bone by this name, but is not homologous with the coracoid process of mammals. Analyses of the size and shape of the coracoid process in "Australopithecus africanus" (STS 7) have shown that in this species it displayed a prominent dorsolateral tubercle placed more laterally than in modern humans. This reflect, according to one interpretation, a scapula positioned high on a funnel-shaped thorax and a clavicle positioned obliquely as in extant great apes.
Coracoid process | Other animals
The bony palate is short, with its posterior end often located between the third molars. The alisphenoid strut, an extension of the alisphenoid bone of the skull that separates two foramina (openings) in the skull, is present in some individuals. The mastoid bone usually contains some openings. In the holotype, the head and body length is 130 mm, the tail length is 160 mm, the hindfoot length (without claws) is 31 mm, the ear length is 27 mm, and the skull length is 35.7 mm.
Nephelomys levipes | Introduction
The stapes bone transmits movement to the oval window. As the stapes footplate moves into the oval window, the round window membrane moves out, and this allows movement of the fluid within the cochlea, leading to movement of the cochlear inner hair cells and thus hearing. If the round window were to be absent or rigidly fixed (as can happen in some congenital abnormalities), the stapes footplate would be pushing incompressible fluid against the unyielding walls of the cochlea. It would therefore not move to any useful degree leading to a hearing loss of about 60dB. This is, unsurprisingly, the same as for conditions where the stapes itself is fixed, such as otosclerosis.
Round window | Function
However, according to Ibrahim and colleagues, the vertebra (which probably belonged to the same species) appeared to come from a larger individual, measuring about 6 meters (20 ft) in wingspan. A rostrum fragment was described in 2015 and referred to cf. "Alanqa" based on provenance. This fragment has two bony protuberances where the jaw occludes, coinciding with an eminence on one of the mandibles originally referred to "Alanqa". These imply an unusual functional specialization in this pterosaur; possible functions include visual display, anchoring of soft tissue, and crushing hard-shelled food.
Alanqa | Description
In non-avian dinosaurs, the jugal bone functioned as passive structural support during biting, and not as a site of jaw muscle attachment. In extant reptiles, the jugal bone continues to form the orbit of the eye and provide passive structural support.
Jugal bone | In reptiles
The carpal bones function as a unit to provide a bony superstructure for the hand.
Trapezoid bone | Function
The resulting three-boned structure is still seen in modern monotremes, but in all other living mammals, the procoracoid has disappeared, and the coracoid bone has fused with the scapula, to become the coracoid process. These changes are associated with the upright gait of mammals, compared with the more sprawling limb arrangement of reptiles and amphibians; the muscles formerly attached to the procoracoid are no longer required. The altered musculature is also responsible for the alteration in the shape of the rest of the scapula; the forward margin of the original bone became the spine and acromion, from which the main shelf of the shoulder blade arises as a new structure.
Scapula | In other animals
If used for display, the horn likely would have been brightly colored. A display function was also proposed for the row of osteoderms running down the body midline.
Ceratosaurus | Function of the nasal horn and osteoderms
The skeleton serves six major functions: support, movement, protection, production of blood cells, storage of minerals and endocrine regulation.
Human skeleton | Functions
In the tetrapod and higher clades from the lower-middle Famennian there are several defining changes on the basis of anatomy of "Ichthyostega", "Tulerpeton", and "Acanthostega". In the cranium, there is a stapes derived from the hyomandibular of fishes; a single bilateral pair of nasal bones, and a fenestra ovalis in the otic capsule of the braincase. The opening of the otic wall of the braincase can be considered a paedomorphic feature for tetrapods and is linked to the stapes functionally. The stapes was thought to be just a structural support between the palate and the stapedial plate of the braincase.
Skeletal changes of organisms transitioning from water to land | Head changes in aquatic tetrapods
In the two other "Histioteuthis" species with tuberculate ridges—"H. meleagroteuthis" and "H. miranda"—these structures likely have the same function.
Cephalopod dermal structures | Pseudoskeletal support
Air vibrations could not set up pulsations through the skull as in a proper auditory organ. The spiracle was retained as the otic notch, eventually closed in by the tympanum, a thin, tight membrane. The hyomandibula of fish migrated upwards from its jaw supporting position, and was reduced in size to form the stapes. Situated between the tympanum and braincase in an air-filled cavity, the stapes was now capable of transmitting vibrations from the exterior of the head to the interior. Thus the stapes became an important element in an impedance matching system, coupling airborne sound waves to the receptor system of the inner ear.
Tetrapod | Hearing
The mantle of "Cranchia scabra" is covered in multi-pointed cartilaginous tubercles. An anti-predator function has been proposed in the past, but this is thought unlikely given the small size and transparent nature of the tubercles. The tubercles of this species are covered by a thin, epidermal sheath that is often lost during capture. It has been speculated that in the live animal the interstitial space is filled with a buoyant fluid (likely an ammonium chloride solution) and acts as a "buoyancy vest". The hard tubercles may serve to maintain the shape of this structure. It has been estimated that in a "C.
Cephalopod dermal structures | Buoyancy vest
The skeleton consists of both fused and individual bones supported and supplemented by ligaments, tendons, muscles and cartilage. It serves as a scaffold which supports organs, anchors muscles, and protects organs such as the brain, lungs, heart and spinal cord. Although the teeth do not consist of tissue commonly found in bones, the teeth are usually considered as members of the skeletal system. The biggest bone in the body is the femur in the upper leg, and the smallest is the stapes bone in the middle ear. In an adult, the skeleton comprises around 14% of the total body weight, and half of this weight is water.
Skeleton | Humans
Different cephalopod dermal structures are hypothesised to play roles in buoyancy, locomotion, and even pseudoskeletal support.
Cephalopod dermal structures | Function
The stapes, the bone transmitting sound waves from the eardrum to the middle ear, is elongated and not pierced by a foramen. Pterygoid teeth are typically lacking.
Ichthyosaur | Skull
In bony fish, dermal bone is found in the fin rays and scales. A special example of dermal bone is the clavicle. Some of the dermal bone functions regard biomechanical aspects such as protection against predators . The dermal bones are also argued to be involved in ecophysiological implications such as the heat transfers between the body and the surrounding environment when basking (evidenced in crocodilians) as well as in bone respiratory acidosis buffering during prolonged apnea (evidenced in both crocodilians and turtles) . These ecophysiological functions rely on the set-up of a blood vessel network within and straight above the dermal bones.
Dermal bone | Introduction
The bone flap represents the first and second epiparietal pairs, the "P1s" and "P2s", as is evidenced by the osteoderm points still being visible, those of the first pair pointing to the front near the midline, those of the second pair forming the corners of the flap. The third epiparietals, pointing to behind, together form a pincer-like construction around the notch. At each rear corner of the frill a very large osteoderm is present. As it spans the suture between the squamosal and the parietal, this has been called an epiparietosquamosal or "EPS".
Spiclypeus | Skeleton
In reptiles, the quadrate and articular bones of the skull articulate to form the jaw joint. The squamosal bone lies anterior to the quadrate bone.
Squamosal bone | Function in reptiles
Milner (2018) further refined this based on his restudy of "Mordex", including only characters 1, 3, and 5 from Schoch & Milner (2014), noting that some typical trematopid features are either not known or are not present in the primitive "Mattauschia" and "Mordex". The function of the naris remains largely unresolved. Olson (1941) suggested that the anterior half served the typical function of smell detection and that the posterior half housed some kind of gland. Bolt (1974) conjectured that the well-developed nasal flange was probably for distribution of stresses throughout the skull and might be a hallmark of terrestrial dissorophoids.
Trematopidae | Anatomy
They have also developed a muscle that allows the pharyngeal jaws to have a role in grinding food in addition to transporting it. The caudal fin is homocercal, meaning the upper and lower lobes are about equal in size. The spine ends at the caudal peduncle, the base of the caudal fin, distinguishing this group from those in which the spine extends into the upper lobe of the caudal fin, such as most fish from the Paleozoic (541 to 252 million years ago). The neural arches are elongated to form uroneurals which provide support for this upper lobe. In addition, the hypurals, bones that form a flattened plate at the posterior end of the vertebral column, are enlarged providing further support for the caudal fin.
Teleost | Anatomy
The vertebrae of lobe-finned fishes consist of three discrete bony elements. The vertebral arch surrounds the spinal cord, and is of broadly similar form to that found in most other vertebrates. Just beneath the arch lies a small plate-like pleurocentrum, which protects the upper surface of the notochord, and below that, a larger arch-shaped intercentrum to protect the lower border. Both of these structures are embedded within a single cylindrical mass of cartilage. A similar arrangement was found in the primitive Labyrinthodonts, but in the evolutionary line that led to reptiles (and hence, also to mammals and birds), the intercentrum became partially or wholly replaced by an enlarged pleurocentrum, which in turn became the bony vertebral body.
Vertebral column | Fish and amphibians
The quadrate is also smooth, and it encloses a circular hole (only visible from behind) along its contact with the quadratojugal. Part of the nasal cavity was filled in by sediment, showing that the olfactory bulbs were separated at the midline. The braincase is incomplete, only preserving the parabasisphenoid (the bone which forms the base of the braincase). As with other archosaurs, the rear lower part of the braincase possessed two different pairs of large, rounded plates: The basipterygoid processes (which are positioned at the base of the braincase and contact the roof of the mouth) and the basitubera (which are positioned further up and do not contact any bone, acting as levers for the "musculi recti capitis anteriores" that make the head nod).
Venaticosuchus | Description
However, only males possessed the "armoured" first dorsal fin and spine, and this suggests that the function was merely sexual display.
Stethacanthidae | Function
"Ambulocetus" had a pubic symphysis connecting the two pubic bones at the base of the pelvis together, which indicates the animal could support its own weight on land. The modern cetacean pubis bone lacks this and functions to anchor abdominal and urogenital muscles. The leg proportions of "Ambulocetus" are similar to otters and seals, and American mammalogist Alfred Brazier Howell predicted similar proportions for a transitional cetacean in 1930. The femur measures , which is similar to the presumably cursorial mesonychid "Pachyaena". Archaeocete femurs are generally much shorter. The femoral head is spherical and, at maximum, has a width of , similar to "Indocetus" but much larger than mesonychids and "Rodhocetus".
Ambulocetus | Limbs
Projecting upward from the middle line of this plate is a thick, smooth, triangular process, the crista galli, so called from its resemblance to a rooster's comb. The long thin posterior border of the crista galli serves for the attachment of the falx cerebri. Its anterior border, short and thick, articulates with the frontal bone, and presents two small projecting "alae" (wings), which are received into corresponding depressions in the frontal bone and complete the foramen cecum.
Cribriform plate | Structure
While the structure may have been used for moving food and nest materials, the likelihood of that being the only function is low, as the trigger hairs would not be needed then. The most likely use for the horn and mandibles would have been trapping large prey with the setae providing sensory information on the prey position and creating friction to prevent movement. The size of the horn and mandibles makes the capture of small prey unlikely, as the prey would have time to move before the mandibles were fully shut.
Ceratomyrmex | Biology
In reptiles, the columella function to transduce sound through the middle ear as part of the auditory pathway. The columella is relatively straight and moves in a piston-like motion in response to vibration. Due to the rigid bony structure, the columella primarily respond to low-frequency vibrations transmitted through the ground.
Columella (auditory system) | Anatomy in reptiles
The selective pressure that shaped the original lemuriform toothcomb has been a topic of considerable debate since the 1970s. Evidence can be seen as supporting a grooming function, food procurement function, or both. In the early 1900s, there was less debate. Grooming was seen as the primary function since primates lack the claws needed to adequately comb the fur, although prosimian primates (strepsirrhines and tarsiers) possess at least one grooming claw on each foot to compensate. Grooming—in the form of fur-combing—is generally considered the primary function and original role of the lemuriform toothcomb, and subsequent changes in morphology across multiple lineages have altered its function and obscured its original function.
Toothcomb | Original function of the lemuriform toothcomb
Like other "Thelenota," "T. rubralineata" contains calcareous spicules in the form of granules and branched rods. Located throughout the body wall, these structures serve as both structural support and defense from predators. Two Polian vesicles provide the basis for locomotion. 5 longitudinal muscles are broad, V-shaped, and attached to the body wall. A short digestive tract, two narrow respiratory trees, and a small circulatory system running parallel to the intestines is also present. When in motion, the lateral protuberances play a role in walking. When disturbed, "T. rubralineata" bends its body in a helical fashion, arranging its mouth close to the anus, and assumes this position for up to 10 minutes or longer, then moves again.
Thelenota rubralineata | Biology
They also pointed out that a lack of sexual dimorphism does not preclude the use of horns in mate competition; male bovines use their horns for this purpose while females use them primarily for defense and secondarily for sexual selection. In 2013, paleontologists David E. Hone and Darren Naish criticized the "species recognition hypothesis", arguing that no extant animals use such structures primarily for species recognition and that Padian and Horner had ignored the possibility of mutual sexual selection (where both sexes are ornamented). They noted that if the primary purpose of the structures was species recognition, they would have differed in the shape of a single structure because additional structures would have been redundant at additional cost.
Kosmoceratops | Function of skull ornamentation
However, other researchers have claimed that the morphology of the hyoid is not indicative of the larynx's position. It is necessary to take into consideration the skull base, the mandible and the cervical vertebrae and a cranial reference plane.
Hyoid bone | Function
The mantle of "Asperoteuthis acanthoderma" is covered in minute, widely spaced tubercles of hyaline-like cartilage. In a 1990 study of dermal structures in squid, Clyde F. E. Roper and C. C. Lu wrote that they were "unable to suggest a function" for the tubercles of this species, but that due to their small size and spacing they were unlikely to be involved in buoyancy or locomotion.
Cephalopod dermal structures | Unknown function
A fontanelle pierces the upper layer. In "Einiosaurus", this cavity runs sideways, continuing to below into the brow horn. With "Centrosaurus" and "Styracosaurus" these passages are more narrow and do not reach the horns but "Pachyrhinosaurus" shows a comparable extension. Sampson in 1995 also expounded his general views on such skull roofs, which are not easy to interpret due to fusion. According to him, the frontal bones always extended to the parietals, so that the paired postorbitals never contacted. The parietal bone made only a small contribution to the fontanelle. The floor of the cavity is, at the frontal-parietal suture, pierced by a large foramen into the braincase, the function of this "pineal opening" being unknown.
Einiosaurus | Skeleton
The part of the skeleton that is ‘tucked under’ (the doublure) has no sutures crossing it to form a rostral plate.The thorax has 11 (rarely 10) segments, the side lobes (or pleurae) are furrowed, and the articulating facets distinct.
Phacopina | Description
The splanchnocranium (or visceral skeleton) is the portion of the cranium that is derived from pharyngeal arches. The splanchnocranium consists of cartilage and endochondral bone. In mammals, the splanchnocranium comprises the three ear ossicles (i.e., incus, malleus, and stapes), as well as the alisphenoid, the styloid process, the hyoid apparatus, and the thyroid cartilage. In other tetrapods, such as amphibians and reptiles, homologous bones to those of mammals, such as the quadrate, articular, columella, and entoglossus are part of the splanchnocranium.
Splanchnocranium | Introduction
The meshing of many spicules serves as the sponge’s skeleton. It provides structural support and defense against predators.
Sponge spicule | Function
There is a large amount of evidence that "Greererpeton" and other colosteids were completely aquatic animals. Grooves on the side of the skull indicate that "Greererpeton" had lateral lines, sensory organs commonly found only in fish and aquatic stem-tetrapods. The stapes bone at the rear of the skull is massive, probably used as a support for the skull. This contrasts with the stapes of terrestrial animals such as frogs, mammals, and lizards. In these groups the bone is thin and sensitive to vibration, so it is used for sensitive hearing. The thick stapes of "Greererpeton" is an indication that did not have good hearing like terrestrial animals.
Greererpeton | Paleobiology
Plated ribs are present in arboreal (tree-dwelling) and fossorial (burrowing) xenarthrans (sloths, anteaters, armadillos and relatives). The tail vertebrae are flattened dorsoventrally (shortened vertically and widened more horizontally); and each centrum has two pairs of transverse processes (which jut out diagonally from the centrum) on the headward side and another on the tailward side, making the centrum appear somewhat like the letter H from the top-view looking down. This tail anatomy is similar to beavers and otters, which use their tails for paddling and propulsion. Fur was preserved on the holotype, and it is the earliest known pelt; this showed that fur, with its many uses including heat retention and as a tactile sense, was an ancestral trait of mammals.
Castorocauda | Description
The stapes develops from the second pharyngeal arch during the sixth to eighth week of embryological life. The central cavity of the stapes, the obturator foramen, is due to the presence embryologically of the stapedial artery, which usually regresses in humans during normal development.
Stapes | Development
Both limbs of the loop of Henle are lined with the simple squamous epithelium. Their main function is to regulate the levels of water and solutes in the primary urine. The basement membrane of the thin limb in humans has very uniform nodular thickenings that form a network that surrounds the tubule and acts as a support structure that is homologous to the collenchyma in plants. Smith, RA et al. (Arch Pathol Lab Med Vol 108, May 1984) have designated these nodules "Belliveau Bodies" after Robert Belliveau the pathologist who originally described these structures.
Thin segment of loop of Henle | Histology
The external mandibular fenestra is large. The dentary, lower jaw, teeth are quite pointed and have no front edge denticles; their rear edge is very straight. The holotype preserves a furcula and a basket of fifteen pairs of gastralia. The arms are weakly developed, with a slender humerus and ulna. The front top of the third metatarsal is not fully overgrown by the second and fourth metatarsals. The sickle claw of the second toe is relatively large and long for a troodontid.
Sinornithoides | Description
This is connected indirectly with the eardrum via a mostly cartilaginous extracolumella and medially to the inner-ear spaces via a widened footplate in the fenestra ovalis. The columella is an evolutionary derivative of the bone known as the hyomandibula in fish ancestors, a bone that supported the skull and braincase. The structure of the middle ear in living amphibians varies considerably and is often degenerate. In most frogs and toads, it is similar to that of reptiles, but in other amphibians, the middle ear cavity is often absent. In these cases, the stapes either is also missing or, in the absence of an eardrum, connects to the quadrate bone in the skull, although, it is presumed, it still has some ability to transmit vibrations to the inner ear.
Middle ear | Other animals
In ungulates (hoofed mammals) the forelimb is optimized for speed and endurance by a combination of length of stride and rapid step; the proximal forelimb segments are short with large muscles, while the distal segments are elongated with less musculature. In two of the major groups of ungulates, odd-toed and even-toed ungulates, what remain of the "hands" — the metacarpal and phalangeal bones — are elongated to the extent that they serve little use beyond locomotion. The giraffe, the largest even-toed ungulate, has large terminal phalanges and fused metacarpal bones able to absorb the stress from running. The sloth spends its life hanging upside-down from branches, and has highly specialized third and fourth digits for the purpose.
Phalanx bone | Other mammals
The reason for this evolutionary change is still unknown; however, it may be to assist in grasping small objects and thin branches.
Sesamoid bone | Other animals
Cassowaries use their claws to defend themselves, to attack threatening animals, and in agonistic displays such as the Bowed Threat Display. The seriema also has an enlarged second toe claw, and uses it to tear apart small prey items for swallowing. Phillip Manning and colleagues (2009) attempted to test the function of the sickle claw and similarly shaped claws on the forelimbs. They analyzed the bio-mechanics of how stresses and strains would be distributed along the claws and into the limbs, using X-ray imaging to create a three-dimensional contour map of a forelimb claw from "Velociraptor". For comparison, they analyzed the construction of a claw from a modern predatory bird, the eagle owl.
Dromaeosauridae | Claw function
The carpal bones function as a unit to provide a bony superstructure for the hand.
Hamate bone | Function
The posterior displays a series of hooks, which likely acted as anchors during burrowing. Muscles support the animal and retract the bursa and proboscis. A gut leading from the anus in the bursa to the mouth in the proboscis runs through the trunk's spacious body cavity, and a concentration of gut muscles serve the function of a gizzard. A nerve chord runs down the organism's length. In addition to the other organs, it is possible "Ottoia" contained urogenital organs in its trunk. There is no evidence of a respiratory organ, though the bursa may have served this purpose. The everted proboscis of "Ottoia" bears an armature of teeth and hooks.
Ottoia | Morphology
The nasal cavity was large, situated directly below the snout roof. It was divided into a left and right side by a thick vertical bone wall. It was also horizontally divided in two by high internal wings of the praemaxillae and the upper side of a "crista maxilloturbinalis". This latter was a scroll-like structure, a turbinate bone serving with warm-blooded animals to condense and preserve exhaled moisture. Normally, in dinosaurs these turbinates are not ossified. Together with a "crista nasoturbinalis", the "crista maxilloturbinalis" filled the lower half of the nasal cavity. Maryańska presumed it was connected with the underlying premaxillary sinus, allowing the animal to exhale air through the lower hole of the nasal vestibule.
Saichania | Skeleton
In addition, the proteins of the desmotubule help to provide structural support to the plasmodesmata.
Desmotubule | Function
The stapedius is the smallest skeletal muscle in the human body. At just over one millimeter in length, its purpose is to stabilize the smallest bone in the body, the stapes.
Stapedius muscle | Introduction
The mammalian jaw joint is composed of different skull bones, including the dentary (the lower jaw bone which carries the teeth) and the squamosal (another small skull bone). In mammals, the quadrate and articular bones have evolved into the incus and malleus bones in the middle ear. The mammalian middle ear contains three tiny bones known as the ossicles: malleus, incus, and stapes. The ossicles are a complex system of levers whose functions include: reducing the amplitude of the vibrations; increasing the mechanical force of vibrations; and thus improving the efficient transmission of sound energy from the eardrum to the inner ear structures.
Evolution of mammalian auditory ossicles | Defining characteristic of mammals
Approximately in the middle of the parietal bones was a small hole known as a pineal foramen, which may have held a sensory organ known as a parietal eye. The pineal foramen is smaller in "Seymouria" than in other seymouriamorphs. The stapes, a rod-like bone which lies between the braincase and the wall of the skull, was tapered. It connected the braincase to the upper edge of the otic notch, and likely served as a conduit of vibrations received by a tympanum (eardrum) which presumably lay within the otic notch. In this way it could transmit sound from the outside world to the brain.
Seymouria | Skull
(2012) examined their structure and function through juveniles to old adults. They found that throughout the ontogeny, the dorsal osteoderms are composed of dense ossified collagen fibres in both the cortical and cancellous sections of the bone, suggesting that plates and spikes are formed from the direct mineralization of already existing fibrous networks in the skin. However, the many structural features, seen in the spikes and plates of old adults specimens, are acquired at different stages of development. Extensive vascular networks form in the plates during the change from juveniles to young adults and persist in old adults but spikes acquire a thick cortex with a large axial vascular channel only in old adults.
Stegosauridae | Plates and spikes
The entepicondylar foramen is absent, as in all members of the Sigmodontinae; if present, as in some other rodents, this foramen (opening) perforates the distal (far) end of the humerus (upper arm bone). The pelvis and the bones of the hindlimbs are heavily built. The femoral tubercle of the acetabulum (part of the pelvis), which anchors the rectum femoris muscle, is reduced relative to "Holochilus" and "Lundomys".
Noronhomys | Postcranial skeleton
He also noted that the rigidity of the back would have been useful when using the head for this purpose. In 1978, Sues agreed with Galton that the anatomy of pachycephalosaurs was consistent with transmitting dome-to-dome impact stress, based on tests with plexi-glass models. The impact would be absorbed through the neck and body, and neck ligaments and muscles would prevent injuries by glancing blows (as in modern bighorn sheep). Sues also suggested that the animals could have butted each other's flanks. In 1997, the American palaeontologist Kenneth Carpenter pointed out that the dorsal vertebrae from the back of the pachycephalosaur "Homalocephale" show that the back curved downwards just before the neck (which was not preserved), and unless the neck curved upwards, the head would point to the ground.
Stegoceras | Dome function
The skeletal material, called coenenchyme, is composed of living tissue secreted by numerous wandering amoebocytes. Although it is generally soft, in many species it is reinforced with calcareous or horny material. The polyp is largely embedded within the colonial skeleton, with only the uppermost surface, including the tentacles and mouth, projecting about the surface. The mouth is slit-like, with a single ciliated groove, or "siphonoglyph", at one side to help control water flow. It opens into a tubular pharynx that projects down into a gastrovascular cavity that occupies the hollow interior. The pharynx is surrounded by eight radial partitions, or mesenteries, that divide the upper part of the gastrovascular cavity into chambers, one of which connects to the hollow space inside each tentacle.
Octocorallia | Biology
The length of the skull can range from 84mm to 104mm for midline length. to Through the analysis of the middle ear region of "Dendrerpeton acadianum", it could be determined that this taxa has a tympanic ear that is not there as a means of support for the palatoquadrate, but rather the positioning of the stapes indicates that it is used for the movement of sound. This morphology demonstrates "Dendrerpeton" having a hearing system that mimics that of anurans. This was contrary to what was previously thought, which was that it had a "squamosal embayment" rather than an otic notch.
Dendrerpeton | Skull and Skeleton
A scapula (shoulder blade), only tentatively assigned to "Plesiorycteropus", has the acromion, a process, present, but the structure is probably not as large as in aardvarks or armadillos. Six humeri have been found; the bone is robust and an entepicondylar foramen is present in the distal (far) end. There are three examples of the radius, a compact and massive bone in "Plesiorycteropus" which resembles the pangolin radius. The three known ulnae show that the olecranon process at the proximal (near) end is well-developed, but the distal end is narrow; the morphology of the bone suggests that the animal was capable of producing much force with its arms.
Plesiorycteropus | Postcranium
These considerations particularly impact hypotheses based on increasing the capabilities of systems already present in the animal, such as the salt gland and olfaction hypotheses, and indicate that these were not primary functions of the crest. Additionally, work on the nasal cavity of lambeosaurines shows that olfactory nerves and corresponding sensory tissue were largely outside the portion of the nasal passages in the crest, so the expansion of the crest had little to do with the sense of smell.
Parasaurolophus | Rejected function hypotheses
In modern amniotes (including mammals), the middle ear collects airborne sounds through an eardrum and transmits vibrations to the inner ear via thin cartilaginous and ossified structures. These structures usually include the stapes (a stirrup-shaped auditory ossicle). Early tetrapods likely did not possess eardrums. Eardrums appear to have evolved independently three to six times. In basal members of the 3 major clades of amniotes (synapsids, eureptiles, and parareptiles) the stapes bones are relatively massive props that support the braincase, and this function prevents them from being used as part of the hearing system. However, there is increasing evidence that synapsids, eureptiles and parareptiles developed eardrums connected to the inner ear by stapes during the Permian.
Evolution of mammalian auditory ossicles | Early tetrapod and amniote ears
In addition, a structure composed of fused neural spines form the dorsalmost part of the Weberian apparatus. Together, the structure interacts anteriorly with the lagenar otolith set within the skull and posteriorly with the swim bladder via the pleural rib. Postero-ventrally, it is the tripus, the os suspensorium and the third rib that interact directly with the anterior chamber of the swim bladder. The Weberian apparatus functions by transmitting auditory signals straight from the gas bladder, through the Weberian ossicles and then straight into the labyrinth structures of the inner ear. The structure essentially acts as an amplifier of sound waves that would otherwise be only slightly perceivable by the inner ear structure alone.
Weberian apparatus | Structural anatomy and function
The hyoid bone is derived from the lower half of the second gill arch in fish, which separates the first gill slit from the spiracle, and is often called the "hyoid arch". In many animals, it also incorporates elements of other gill arches, and has a correspondingly greater number of cornua. Amphibians and reptiles may have many cornua, while mammals (including humans) have two pairs, and birds only one. In birds, and some reptiles, the body of the hyoid is greatly extended forward, creating a solid bony support for the tongue. The howler monkey "Alouatta" has a pneumatized hyoid bone, one of the few cases of postcranial pneumatization of bones outside Saurischia.
Hyoid bone | Other animals
In non-avian archosaurs, including crocodiles, the capitellum and the trochlea are no longer bordered by distinct etc.- and entepicondyles respectively, and the distal humerus consists two gently expanded condyles, one lateral and one medial, separated by a shallow groove and a supinator process. Romer (1976) homologizes the capitellum in Archosauromorphs with the groove separating the medial and lateral condyles. In birds, where forelimb anatomy has an adaptation for flight, its functional if not ontogenetic equivalent is the dorsal condyle of the humerus.
Capitulum of the humerus | Archosauromorpha
The bony structure of the nose is provided by the maxilla, frontal bone, and a number of smaller bones. The topmost bony part of the nose is formed by the nasal part of the frontal bone, which lies between the brow ridges, and ends in a serrated nasal notch. A left and a right nasal bone join with the nasal part of the frontal bone at either side; and these at the side with the small lacrimal bones and the frontal process of each maxilla. The internal roof of the nasal cavity is composed of the horizontal, perforated cribriform plate of the ethmoid bone through which pass sensory fibres of the olfactory nerve.
Human nose | Bones
The appendicular skeleton (126 bones) is formed by the pectoral girdles, the upper limbs, the pelvic girdle or pelvis, and the lower limbs. Their functions are to make locomotion possible and to protect the major organs of digestion, excretion and reproduction.
Human skeleton | Appendicular skeleton
It lived in forested and riverbank environments before the evolution of grasslands. Like all entelodonts, the genus had typical artiodactyl legs but lacked specializations for fast running; though it supported its weight on cloven hooves, the foot bones remained unfused, and the toes could spread as camelid feet do. This structure, unique to entelodonts, may have helped the living animal move on soft ground. The head was unusually large, and the high spines on the vertebrae above the shoulders supported strong neck muscles and tendons to handle the weight of the head. The brain was tiny, but had relatively large olfactory lobes, suggesting that the animal had a keen sense of smell.
Archaeotherium | Paleobiology
"Stegosaurus" plates are so large that it has been suggested that they were not arranged in paired but alternated rows or even formed a single overlapping midline row. With "Stegosaurus" fossils also ossicles have been found in the throat region, bony skin discs that protected the lower neck. Apart from protection, suggested functions of the osteoderms include display, species recognition and thermoregulation.
Stegosauria | Osteoderms
As the dentary bone of the lower jaw continued to enlarge during the Triassic, the older quadrate-articular joint fell out of use. Some of the bones were lost, but the quadrate, the articular, and the angular bones became free-floating and associated with the stapes. This occurred at least twice in the mammaliformes. The multituberculates had jaw joints that consisted of only the dentary and squamosal bones, and the quadrate and articular bones were part of the middle ear. Other features of their teeth, jaws and skulls are significantly different from those of mammals.
Evolution of mammalian auditory ossicles | Fossil evidence for mammal-like jaws and ears
Ironically, the diminutive "Liaoceratops" may also help scientists understand the roles of horns and frills in ceratopsian dinosaurs. First thought of as offensive or defensive organs, these structures are seen by many paleontologists today as display devices used in species recognition and to attract mates. "Liaoceratops" has a small jugal horn facing sideways under and behind each of its eyes. As this structure is relatively small and light, Makovicky believed that it was a display organ and had no purpose in defense.
Liaoceratops | Function of the horns and frill
At least five posterior caudal vertebrae are fused into a structure that resembles a pygostyle. The function of this structure is unclear, but it may have been involved in the support of a dermal caudal fin.
Umoonasaurus | Description
The strongly drooping snout is blunt, wide and high, and filled with very complex air passages and sinuses, the form and function of which are not yet completely understood. Each side has two external nostrils. The lower jaw has a very concave upper rim with twenty-one teeth. At its front a short low extension is present, to provide contact with the wide predentary, the bony core of the lower horny beak, that fitted within the upper beak of the snout. As in most quadrupedal ornithischians, its neck is moderately short. The scapula is massive and robust, and the very robust forelimbs are shorter than the hindlimbs.
Euoplocephalus | Skeleton
The skeleton morphologically reflects its evolutionary history as well as its daily activities. At the caudal end, the sloth’s head connects to its neck with a class one lever. The skull is two to three orders of magnitude larger than that of living species of sloth, but the muzzle itself shows highly positive allometry to the size of the skull in comparison to modern sloths and even other megafauna of the same order Pilosa. "L. armatus" had a large, blunt, and square mandible well adapted for foliage consumption. Its muzzle and dentition show a significant adaptation to this diet. The shape of the muzzle aided the ground sloth in the grazing necessary to sustain the metabolic activity of its large body; square, flat muzzles are associated with bulk feeders while pointed snouts are adaptive features of precision eaters, like the long sloping snout of modern anteaters, which are also in the same class Xenarthra (Bargo "et al.", 2006).
Lestodon | Cranial
Morphological comparisons with modern ungulates practicing head butting have found similar dome shaped structures used in combat. The cancellous region found in head striking artiodactyls have been considered to be covering the domes of pachycephalosaur to aid in protection against head impacts. In addition, tubular struts in the dome of the related taxa, Stegoceras, were comparable to pneumatized frontal sinuses found in some head-stricking mammals. Modern archosaurs such as Ostriches and crocodiles exhibit similar ranges of pathologies due to intra-species combat.
Acrotholus | Behavior
The cranium of the dromedary consists of a postorbital bar, a tympanic bulla filled with spongiosa, a well-defined sagittal crest, a long facial part and an indented nasal bone. Typically, there are eight sternal and four non-sternal pairs of ribs. The spinal cord is nearly long; it terminates in the second and third sacral vertebra. The fibula is reduced to a malleolar bone. The dromedary is a digitigrade animal; it walks on its toes, which are known as digits. It lacks the second and fifth digits. The front feet are wide and long; they are larger than the hind feet, which measure wide and long.
Dromedary | Anatomy
This forms the rear of the hard palate, separating the oral and nasal cavities, and making it easier to breathe while eating. A parallel development has occurred to varying degrees in many living reptiles, reaching its greatest extent in crocodilians. In birds, the palatine bones remain separate, long the sides of the rear part of the upper jaw, and typically have a mobile articulation with the cranium. There are numerous variations amongst mammals, amphibians and other species. For example, the palatine bone in many amphibians such as the rough-skinned newt manifests as a distinct V-shaped structure. In the case of cat species, the horizontal and a vertical elements join at a forty five degree angle.
Palatine bone | Other animals
The generalized structure of the Weberian apparatus is akin to a skeletal complex of bones and ossicles that are physically connected to the labyrinth auditory complex anteriorly and the anteriormost region of the swim bladder posteriorly. The entire structure is derived from skeletal elements of the first four vertebrae. The involved elements include: the supraneural bones of the skull; modified neural arch bones, specifically the paired claustra and the scaphia; the intercalarium and the lateral processes; the tripus; the os suspensorium from the fourth vertebra; the parapophysis of vertebra number five including the vertebra itself, plus the vertebra's corresponding pleural rib.
Weberian apparatus | Structural anatomy and function
In many bony fish and amphibians, the supraoccipital is never ossified, and remains as cartilage throughout life. In primitive forms the basioccipital and exoccipitals somewhat resemble the centrum and neural arches of a vertebra, and form in a similar manner in the embryo. Together, these latter bones usually form a single concave circular condyle for the articulation of the first vertebra.
Occipital bone | Other animals
The carpal bones function as a unit to provide a bony superstructure for the hand.
Triquetral bone | Function