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 "".
Animals
Stapes
Stapes | Animals
It is one of three ossicles in mammals, in non-mammalian four-legged animals its homologous form is called the columella Yes, in mammals, non-mammalian four-legged animals and fishes. 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. Yes, in reptiles, fish and amphibians.
what are the 3 smallest bones in the human body
user
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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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
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 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
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
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
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
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
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
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 many amphibians, there is also a second auditory ossicle, the "operculum" (not to be confused with the structure of the same name in fishes). This is a flat, plate-like bone, overlying the fenestra ovalis, and connecting it either to the stapes or, via a special muscle, to the scapula. It is not found in any other vertebrates.
Middle ear | Other animals
This system had evolved independently within several different amphibian lineages. The impedance matching ear had to meet certain conditions to work. The stapes had to be perpendicular to the tympanum, small and light enough to reduce its inertia, and suspended in an air-filled cavity. In modern species that are sensitive to over 1 kHz frequencies, the footplate of the stapes is 1/20th the area of the tympanum. However, in early amphibians the stapes was too large, making the footplate area oversized, preventing the hearing of high frequencies. So it appears they could only hear high intensity, low frequency sounds—and the stapes more probably just supported the brain case against the cheek.
Tetrapod | Hearing
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
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
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
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
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
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 reptiles and amphibians, the bone is instead referred to as the "ulnare", since (at least in the most primitive fossils) it articulates with the ulna.
Triquetral bone | In animals
herschelensis". Assuming that only a few vertebrae are missing from the skeleton, the animal is estimated to be about 2.5 to 3 metres in length. The snout is long and thin, with numerous tooth sockets. However, very few of the thin, sharp teeth remain.
Ancient Echoes Interpretive Centre | "Dolichorhynchops herschelensis"
They have a broad, rounded pro-ostracum (the section of the guard (the hard internal skeleton commonly fossilised) closest to the head of the living animal). This characteristically lacks longitudinal alveolar canals and the associated splitting surfaces or open fissures. Commonly there are one or more longitudinal furrows in the apical region of the guard, similar furrows may be found in the alveolar region, these would not be accompanied by splitting surfaces or open fissures.
Belemnitina | Morphology
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
This species is likely now extinct.
Theliderma stapes | Conservation
The stapes is commonly described as having been discovered by the professor Giovanni Filippo Ingrassia in 1546 at the University of Naples, although this remains the nature of some controversy, as Ingrassia's description was published posthumously in his 1603 anatomical commentary '. Spanish anatomist Pedro Jimeno is first to have been credited with a published description, in ' (1549). The bone is so-named because of its resemblance to a stirrup (), an example of a late Latin word, probably created in mediaeval times from "to stand" (), as stirrups did not exist in the early Latin-speaking world.
Stapes | History
The cephalopharyngeal skeleton is 0.57–0.61 mm long. Mandibular sclerites (hardened portions of the exoskeletons) exist as long, narrow, mouth-hooks that appear triangular from a side-view. Dentary sclerites located next to the mandible are pointed down, and are lightly pigmented towards the back of the fly. Small sclerites are present between the mandibular ones, and an additional sclerite is found on the posterior end near the hypostome (a structure found near the mouth which allows an animal to anchor itself firmly on another to suck, as in the tick's hypostome). The third instar stage is 4.10–9.42 mm long and 0.76–2.13 mm wide.
Dryomyza anilis | Larva
The bones come from the back, tail and fin, with the upper fin bone providing strong evidence of the creature being a new species. It possesses a large triangular projection and a deep pit where muscles and ligaments were probably attached.
Dearcmhara | Description
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 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
The body of the animal is limaciform, subcylindrical and tapering behind; inferior tentacles wanting. Mantle is anterior, small, triangular, lateral, adherent, enclosing the shell-plate. There are no longitudinal furrows above the margin of the foot, and no caudal mucous pit. There is no distinct locomotive disk. External respiratory and anal orifices are on the right central margin of the mantle. Orifice of the combined genital system is behind and below the right eye-peduncle. The shell-plate is internal, flat, calcareous, oblong and sometimes in separate grains. Jaw is smooth, with median projection and quadrate accessory plate.
Athoracophorus | Description
Barremitinae is a subfamily belonging to the Ammonoidea subclass. Whorl section in this group ranges from more or less circular through rectangular to oxyconic. Ribbing, if present, is weak. Suture is relatively simple, without markedly retracted suspensive lobe. This animal lived during the Lower Cretaceous, from Upper Valanginian to Upper Barremian.
Barremitinae | Introduction
The largest bone in the body is the femur or thigh-bone, and the smallest is the stapes in the middle ear.
Bone | Introduction
Living mammal species can be identified by the presence in females of mammary glands which produce milk. Other features are required when classifying fossils, since mammary glands and other soft-tissue features are not visible in fossils. Paleontologists therefore use the ossicles as distinguishing bony features shared by all living mammals (including monotremes), but is not present in any of the early Triassic therapsids ("mammal-like reptiles"). Early amniotes had a jaw joint composed of the articular (a small bone at the back of the lower jaw) and the quadrate (a small bone at the back of the upper jaw). All non-mammalian amniotes use this system including lizards, crocodilians, dinosaurs (and their descendants the birds) and therapsids; so the only ossicle in their middle ears is the stapes.
Evolution of mammalian auditory ossicles | Defining characteristic of mammals
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
The tympanic cavity and eustachian tube are derived from the first pharyngeal pouch (a cavity lined by endoderm). The distal part of the cleft, the tubotympanic recess, widens to create the tympanic cavity. The proximal part of the cleft remains narrow and creates the eustachian tube. The bones of the middle ear, the ossicles, derive from the cartilages of the pharyngeal arches. The malleus and incus derive from the cartilage of the first pharyngeal arch, whereas the stapes derives from the cartilage of the second pharyngeal arch.
Human embryonic development | Middle ear
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 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
The middle ear of tetrapods is analogous with the spiracle of fishes, an opening from the pharynx to the side of the head in front of the main gill slits. In fish embryos, the spiracle forms as a pouch in the pharynx, which grows outward and breaches the skin to form an opening; in most tetrapods, this breach is never quite completed, and the final vestige of tissue separating it from the outside world becomes the eardrum. The inner part of the spiracle, still connected to the pharynx, forms the eustachian tube. In reptiles, birds, and early fossil tetrapods, there is a single auditory ossicle, the columella (that is homologous with the stapes, or "stirrup" of mammals).
Middle ear | Other animals
The holotype of "E. primordialis" is the uncrushed and mostly intact anterior half of an individual with the articulating head and trunk armor preserved in three dimensions. The holotype is about long, and the live animal is estimated to have been over long. In overall form, the animal resembles primitive arthrodires, but the anatomy of the jaws strongly suggests the anatomies of bony fish and tetrapods. Specifically, this is the first stem gnathostome with dermal marginal jaw bones. These bones are the premaxilla, maxilla, and dentary. Most known placoderms had simple beak-like jaws made of bone plates. The researchers' cladistic diagram suggests that "E.
Entelognathus | Specimen and taxonomy
A peculiar characteristic of this group were the auditory bulla, protective structures of the bones of the ear : they were very large, like those that are found today in small mammals that live in open and dry environments. This evolved cranial anatomy was in stark contrast to the rest of the skeleton, rather primitive: the cainotherids still possessed four non-reduced toes (an ancestral condition of the artiodactyls), even if the lateral fingers were shorter; they ended in long claws, as in modern rabbits. The hind legs were much longer than the front ones, and indicate a remarkable adaptation to running and jumping.
Cainotheriidae | Introduction
From the Emsian of New South Wales, it is known from several scrappy remains. It had a narrow skull, and the dermal surfaces of the bony armor were covered in a pattern of fine, granular tubercles.
Buchanosteidae | "Arenipiscis"
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
Scattered hairs cover the body. Just in front of the anus there is in Chaetosorna a double, and in Tristicochaeta a triple row of about fifteen stout cylindrical projections upon which the animals creep. The females are a little larger than the males; in Ch. claparedii the former attain a length of 1.5 mm., the latter of 1.12 mm. The mouth opens into an oesophagus which passes into an intestine; this opens by a ventral anus situated a little in front of the posterior end. The testis is single, and its duct opens with the anus, and is provided with a couple of spicules.
Chaetosomatida | Introduction
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
The tail is dark and hardly furred, except for a pencil of long hairs at the end; some animals have a white tail tip. Females have six mammae. In thirty-six specimens, head and body length is , averaging ; tail length is , averaging ; hindfoot length is , averaging ; ear length is , averaging ; and weight is , averaging . The front (rostral) part of the skull is short—shorter and broader than in "T. hylophilus"—and flat and the notches in the zygomatic plates at the sides are poorly developed. The plates themselves are broad. The zygomatic arches (cheekbones) spread broadly and are rounded in shape.
Thomasomys ucucha | Description
Remains of the soft parts have been preserved, including partial wing membranes, a membrane attached to the tibia, a "mane" on the neck and webbing of the feet. It had a wingspan of , and the animal itself had a length of about , however, this is only if the skull had the same length as the remainder of the body: for the neck, ten centimetres for the rump and for the tail. In the wing finger the fourth, normally most extreme, phalanx was absent; according to Lü this was not an artifact of preservation but the normal condition of the animal, one also known from "Nyctosaurus".
Beipiaopterus | Introduction
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
Though it existed far earlier than "Archaeopteryx", its skeletal structure is allegedly more bird-like. "Protoavis" has been reconstructed as a carnivorous bird that had teeth on the tip of its jaws and eyes located at the front of the skull, suggesting a nocturnal or crepuscular lifestyle. Reconstructions usually depict it with feathers, as Chatterjee originally interpreted structures on the arm to be quill knobs, the attachment point for flight feathers found in some modern birds and non-avian dinosaurs. However, re-evaluation of the fossil material by subsequent authors such as Lawrence Witmer have been inconclusive regarding whether or not these structures are actual quill knobs.
Protoavis | Introduction
The living animal would have been fairly large, as the head shield is estimated to be at least 40 centimeters long.
Angarichthys | Introduction
The frontal bones, which occupy the part of the skull roof between the eyes, are rectangular and form most of the upper edge of the orbits. The parietals, which are situated behind the frontals and between the upper temporal fenestrae, are smaller than the frontals and have lateral (outward) extensions which project downwards to form the rear edge of the upper temporal fenestrae. The front part of the parietals taper inwards above the orbits, and in some specimens (such as ZAR 07), a small pineal foramen can be seen, completely enclosed by that part of the parietals. The pineal foramen is a hole in the middle of the skull which in some modern reptiles houses a sensory organ sometimes referred to as a "third eye".
Jesairosaurus | Skull roof and braincase
However, an otic notch can now be considered a feature of this taxa. Also present are interpterygoid , and a pair of palatal tusks within the vomer which lay medially to the internal naris. Palatal tusk pairs can also be found the ectopterygoid and the palatine. As for the lower jaw, if the animal catches prey it is able to get it to the denticulate palate because compression of the mandibles is not lateral along their length. The dentary of the lower jaw was found to be the biggest of all the mandibular parts. There also looked to be approximately 40–50 teeth found on each mandible (both the premaxilla and maxilla), producing marginal teeth.
Dendrerpeton | Skull and Skeleton
The middle ear contains three tiny bones known as the ossicles: "malleus", "incus", and "stapes". The ossicles were given their Latin names for their distinctive shapes; they are also referred to as the "hammer", "anvil", and "stirrup", respectively. The ossicles directly couple sound energy from the eardrum to the oval window of the cochlea. While the stapes is present in all tetrapods, the malleus and incus evolved from lower and upper jaw bones present in reptiles. The ossicles are classically supposed to mechanically convert the vibrations of the eardrum into amplified pressure waves in the fluid of the cochlea (or inner ear), with a lever arm factor of 1.3.
Middle ear | Ossicles
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
In most vertebrates, the frontal bone is paired, rather than presenting the single, fused structure found in humans (see frontal suture). It typically lies on the upper part of the head, between the eyes, but in many non-mammalian animals it does not form part of the orbital cavity. Instead, in reptiles, bony fish and amphibians it is often separated from the orbits by one or two additional bones not found in mammals. These bones, the prefrontals and postfrontals, together form the upper margin of the eye sockets, and lie to either side of the frontal bones.
Frontal bone | Other animals
Animals within this family have elongated bodies with numerous branching cerata on their dorsal sides. The cerata contain extensions from the digestive gland which vary in extent between species. The head has an oral veil having branching extensions. The lamellate rhinophores are surrounded by a sheath and branched extensions.
Dendronotidae | Description
The earliest mammals were generally small animals, and were likely nocturnal insectivores. This suggests a plausible source of evolutionary pressure: with these small bones in the middle ear, a mammal has extended its range of hearing for higher-pitched sounds which would improve the detection of insects in the dark. The evidence that the malleus and incus are homologous to the reptilian articular and quadrate was originally embryological, and since this discovery an abundance of transitional fossils has both supported the conclusion and given a detailed history of the transition. The evolution of the stapes (from the columella) was an earlier and distinct event.
Evolution of mammalian auditory ossicles | Early mammals
Adults have a body length of approximately 9 mm. The animal's head includes two pairs of tentacles, one set of labial tentacles and another set of rhinophores, both sets of which are cylindrical, solid, and taper at their tips. The eyes are located just behind the rhinophores. The animal's creeping foot is three times the width of its head and tapers to a point at the posterior of the animal. The anterior end of the foot also has a pair of propodial tentacles. The animal's head is brown, and the tentacles and foot are semi-translucent. A distinct black stripe extends from the dorsal part of the cephalic tentacles and proceeds to the end of the animal's foot.
Bathyhedyle boucheti | Physical description
The clypeus is setose, meaning that it bears bristles or setae, except on the middle part. The mandibles are small and only contain two teeth. The antennae are moderately long, the scapes are very short but the pedicel is even shorter. The mesosoma measures and is setose. Several setae are seen around the metanotum (the dorsal sclerite) and propodeum. The coxae, the proximal segment and functional base of the leg, are setose (bearing bristle or setae), inflated and large. The metapleural gland opening is small and noticeable, located away from the propodeum and above the metacoxa (the hind of the coxa).
Sphecomyrma | "S. mesaki"
The hindmost part of the surangular had a small foramen placed in the same position as similar openings in the mandibles of non-bird theropods and modern birds. The splenial bone was three-pronged (as in some modern birds, but unlike the simple splenial of "Archaeopteryx"), and its lower margin followed the lower margin of the mandible. There was a large rostral mandibular fenestra and a small, rounded caudal fenestra behind it. Though only five specimens preserve parts of the beak's keratinous covering, these show that there would have been differences between species not seen in the skeleton. The holotype of "C.
Confuciusornis | Skull
In all three species the broad abdomen rests against the thorax with a single node petiole connecting. The eyes are sometimes not present on worker caste individuals, but in all castes where they are present they are placed just behind the mid length of the head capsule. In the known gynes the antennae are twelve segments and geniculate in structure, while the mandibles are triangular.
Casaleia | Description
These are the most unusual of the braincase bones, and were previously misidentified as stapes. While they are not stapes, it is difficult to be certain what they are. As mentioned, they are sutured to the tubera basioccipitalia, and so could not have moved freely, meaning that they were not bones for the transmission of sound in this manner. Medially, they are sutured to the posterodorsal margins of the tubera basioccipitalia by a strongly serrate and partially intergrown suture. The posterior surface of this forms a steeply inclined trough running from the suture to the distal extremity of the paraoccipital process.
Phantomosaurus | Opisthotic bones
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
The bony part (1/3) nearest to the middle ear is made of bone and is about 12 mm in length. It begins in the anterior wall of the tympanic cavity, below the septum canalis musculotubarii, and, gradually narrowing, ends at the angle of junction of the squamous and the petrous parts of the temporal bone, its extremity presenting a jagged margin which serves for the attachment of the cartilaginous part.
Eustachian tube | Bony part
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
333-106 lack evidence of this feature. The neck vertebrae of KDS-VP-1/1 indicate that the nuchal ligament, which stabilises the head while distance running in humans and other cursorial creatures, was either not well developed or absent. KSD-VP-1/1, preserving (among other skeletal elements) 6 rib fragments, indicates that "A. afarensis" had a bell-shaped ribcage instead of the barrel shaped ribcage exhibited in modern humans. Nonetheless, the constriction at the upper ribcage was not so marked as exhibited in non-human great apes and was quite similar to humans. Originally, the vertebral centra preserved in Lucy were interpreted as being the T6, T8, T10, T11, and L3, but a 2015 study instead interpreted them as being T6, T7, T9, T10, and L3.
Australopithecus afarensis | Torso
The three small bones in the middle ear of mammals including humans, the malleus, incus, and stapes, are today used to transmit sound from the eardrum to the inner ear. The malleus and incus develop in the embryo from structures that form jaw bones (the quadrate and the articular) in lizards, and in fossils of lizard-like ancestors of mammals. Both lines of evidence show that these bones are homologous, sharing a common ancestor. Among the many homologies in mammal reproductive systems, ovaries and testicles are homologous. Rudimentary organs such as the human tailbone, now much reduced from their functional state, are readily understood as signs of evolution, the explanation being that they were cut down by natural selection from functioning organs when their functions were no longer needed, but make no sense at all if species are considered to be fixed.
Homology (biology) | In mammals
The middle ear of "Megaconus" is more primitive than that of modern mammals. The three bones that make up the middle ear in modern mammals — the malleus, incus, and stapes — originated from the lower jaw in the ancestors of mammals. In "Megaconus", these bones are still associated with the lower jaw, placed within a groove behind the dentary bone of the lower jaw. "Megaconus" is estimated to have weighed about . It probably had an outwardly similar appearance to multituberculates, a major group of Mesozoic mammals. However, its body is longer than those of multituberculates and most other Mesozoic mammaliaforms, having more back vertebrae (24) than other early mammals.
Megaconus | Description
These occur on the remainder of the body—although some feathers did not fossilize and others were obliterated during preparation, leaving bare patches on specimens—and the lower neck.
Archaeopteryx | Plumage
In mammals, including humans, the talus forms a hinge joint with the tibia, a feature especially well developed in the artiodactyls. The calcaneus is also modified, forming a heel for the attachment of the Achilles tendon. Neither of these adaptations is found in reptiles, which have a relatively simple structure to both bones. The fifth distal tarsal disappears relatively early in evolution, with the remainder becoming the cuneiform and cuboid bones. Reptiles usually retain two centralia, while mammals typically have only one (the navicular).
Tarsus (skeleton) | Other animals
"Leonardo" also indicates that the base of the neck was heavily muscled and that the soft tissue upper neck profile was placed in an elevated position, running much higher than was usually reconstructed in drawings which tended to follow the curvature of the vertebral column, and filling much of the bend between the front back and the head. On the snout, the remains of a broad keratinous beak are visible. The skin impressions show many folds and a structure of small polygonal scales. On the back a midline frill formed by triangular or hatchet-shaped projections is present. These seem to be individually separated and are placed as extensions of each neural spine of the vertebral column.
Brachylophosaurus | Soft tissues
In some rodents, the alisphenoid strut is an extension of the alisphenoid bone that separates two foramina in the skull, the masticatory–buccinator foramen and the foramen ovale accessorium. The presence or absence of this strut is variable between species, but also within them; some Oryzomyini even have a strut on one side of the skull but lack it on the other side.
Alisphenoid strut | Introduction
The frontal portion of the body contains the main part of the centralized nervous system, the feeding organs, defensive glands, and the legs. The upper side is covered by a sclerotized carapace, which is formed by the fused tergites of the six appendage-bearing somites. The feeding apparatus is called the "stomotheca". It is formed by extensions from the pedipalps and the first leg pair. The "ocularium", an elevated mound placed in the middle of the carapace, usually contains two simple eyes. Some species lack eyes. The prosoma can be smooth or armed with spines. In some members of the suborder Dyspnoi, the eyes are located on projections that form a hood covering the mouthparts.
Opiliones anatomy | Prosoma
Such structures include a shelf at the rear of the surangular and a thick articular bone which has a tall retroarticular process with an inner prong pierced by a "chorda tympani" foramen.
Prestosuchus | Skull
"Opabinia" looked so strange that the audience at the first presentation of Whittington's analysis laughed. The length of "Opabinia regalis" from head to tail ranged between and . The animal also had a hollow proboscis, whose total length was about one-third of the body's and projected down from under the head and then curved forwards and upwards. The proboscis was striated like a vacuum cleaner's hose and probably flexible, and it ended with a claw-like structure whose inner edges bore spines that projected inwards and forwards. The head bore five eyes: two on stalks near the front and fairly close to the middle of the head, pointing upwards and forwards; two larger eyes, also stalked, near the rear and outer edges of the head, pointing upwards and sideways; and a single eye with a shorter stalk between the larger pair of stalked eyes, pointing upwards.
Opabinia | Description
Though invertebrate chordates – such as the tunicate larvae or the lancelets – have heads, there has been a question of how the vertebrate head, characterized by a bony skull clearly separated from the main body, might have evolved from the head structures of these animals. According to Hyman (1979), the evolution of the head in the vertebrates has occurred by the fusion of a fixed number of anterior segments, in the same manner as in other "heteronomously segmented animals". In some cases, segments or a portion of the segments disappear. The head segments also lose most of its systems except for the nervous system.
Head | Vertebrates and the "new head hypothesis"
The jaw transition is a good classification tool, as most other fossilized features that make a chronological progression from a reptile-like to a mammalian condition follow the progression of the jaw transition. The mandible, or lower jaw, consists of a single, tooth-bearing bone in mammals (the dentary), whereas the lower jaw of modern and prehistoric reptiles consists of a conglomeration of smaller bones (including the dentary, articular, and others). As they evolved in synapsids, these jaw bones were reduced in size and either lost or, in the case of the articular, gradually moved into the ear, forming one of the middle ear bones: while modern mammals possess the malleus, incus and stapes, basal synapsids (like all other tetrapods) possess only a stapes.
Synapsid | Jaw
Thus, the discovery of a slender stapes in "Cacops aspidephorus" suggested that "Cacops" had an ability to hear airborne sound. The presence of a tympanum in contemporary amniotes is a difference between these terrestrial vertebrates that suggests these two groups had very different abilities to hear airborne sound.
Cacops | Predation
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
Frogs and all other living tetrapods have a rod-like bone called the stapes that aids in hearing by transferring vibrations from the ear drum —or homologous tympanum— to the inner ear. Temnospondyls also have a stapes, which projects into the otic cavity. The stapes likely evolved from the hyomandibula of lobe-finned fishes. The positioning of the stapes and the shape of the otic region suggests that the tympani of temnospondyls and frogs are homologous, but the tympani of these amphibians are no longer considered homologous with the hearing systems of reptiles, birds, and mammals. Therefore, ear structures in temnospondyls were not ancestral to those of all other tetrapods.
Temnospondyli | Hearing
The tympanum is hidden, and the body is more or less laterally compressed, and covered with unequal scales. No dorsal crest is present; and a nuchal crest can be present or absent. No gular sac or gular fold is present. A large rostral appendage occurs, at least in the males. No femoral or preanal pores are found.
Ceratophora | Description
this animals represents structure of the ancestral coelenterate.
Tubularia | Introduction
Numerous mammal bone remains appear very fragmented and a big proportion of them also shows clear evidences of exposure to fire (about 88% of the total amount). Most of these bone remains belong to ("Equus ferus") followed in quantity by bovines. Also, remains belonging to other species are present, among which the most relevant are "Cervus elaphus" and "Dama dama" and, in a lesser amount "Sus scrofa", "Stephanorhinus hemitoechus", "Palaeloxodon antiquus", "Ursus arctos", "Lynx pardinus", "Oryctolagus cuniculus" and "Capra pyrenaica". Equine bones are mainly adult skull bones and long bone diaphysis form front and rear legs. They display defleshing and disarticulation cutting marks.
Cave of the Angel | Mammals
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 all extant and extinct primates, including humans, the auditory bulla is formed by the petrosal bone (the petrous part of the temporal bone). This is a diagnostic trait that can be used to distinguish primates, including anthropoids, tarsiers, lemurs, and lorises, from all other mammals.
Tympanic part of the temporal bone | Other animals
"S. lamperti" has an elongated, opaque body with several dark-coloured, longitudinal stripes. There are no tube feet on the body but a few have been modified into a tuft of pinnate feeding tentacles which are constantly in motion. The skeletal system consists of small calcareous plates which are embedded in the cuticle. These ossicles consist of little hooks that protrude through the skin and make the animal seem sticky. It moves around rapidly and efficiently using the hooks at one end of its body for adhesion while muscular contractions and hydrostatic pressure changes alter the position of the other end.
Synaptula lamperti | Description
The head is incapable of rotating laterally. Two pairs of antennae are set at the front of the head. The eyes are usually well developed and the mouthparts do not form a suctorial cone or proboscis. The thorax or pereon is smooth or slightly sculptured and sometimes spinose or rugose. A flexion occurs between it and the abdomen or pleon, so from a lateral view, the front part of the animal is arched up. The pereiopods are held close to the head, while the pleopods are attached to the pleon, making it appear no appendages on the pereon.
Arcturidae | Description
"Estemmenosuchus" could reach a body length of more than . Its skull was long and massive, up to in length, and possessed several sets of large horns, somewhat similar to the antlers of a moose, growing upward and outward from the sides and top of the head. The animal had a sprawling posture as indicated by analysing its shoulder joints. The skull superficially resembles that of "Styracocephalus", but the "horns" are formed from different bones; in "Estemmenosuchus" the horns are located on the frontals and protrude upward, whereas in Styracocephalus the horns are formed by the tabular and extend aft.
Estemmenosuchus | Description
The animal is bluish-black, with the foot-sole perhaps a shade lighter in colour. On the head and neck are a few regular rows of rugae, somewhat quadrate in outline; on other parts of the body the rugae appear to be oval-shaped, irregular in size, and not forming continuous rows. The mantle has a sharp even margin, and a deeply incised line or groove rather less than 2 mm from the edge. On the underside of the mantle is the usual prominent lappet which conceals the respiratory and anal pores, and in addition to this is a long narrow fold on the left side.
Paryphanta busbyi | Anatomy
"Dendronotus" has an elongated, broad body, with 4 to 8 pairs of branched cerata on the notum. Animals in this genus have an obvious oral veil with 2 to 5 extensions. These extensions may be branched. Smaller unbranched extensions are found around the mouth. The rhinophores are surrounded by a sheath and the sheath itself has branched extensions. A large extension is found on the side at the base of each rhinophore. The anal opening occurs between the first and second set of dorsal cerata on the right side of the body.
Dendronotus | Description
All vertebrates are built along the basic chordate body plan: a stiff rod running through the length of the animal (vertebral column and/or notochord), with a hollow tube of nervous tissue (the spinal cord) above it and the gastrointestinal tract below. In all vertebrates, the mouth is found at, or right below, the anterior end of the animal, while the anus opens to the exterior before the end of the body. The remaining part of the body continuing after the anus forms a tail with vertebrae and spinal cord, but no gut.
Vertebrate | Anatomy and morphology
The pterygoids and palatines were seemingly toothless, although this observance may be due to poor preservation. The tip of each ectopterygoid expands into a fan-shaped structure, and the suborbital fenestra is very short.
Prolacertoides | Description
Larsson found that "Sebecus" and "Allosaurus fragilis" had similar ratios to "C. saharicus", falling within the 95% confidence range characterizing living reptile species. The Eustachian tubes, passages that connect the middle ear with the pharynx, are very complex in crocodilians. Unlike those of other vertebrates, the tubes are made of several interconnected branches. This branching is fully developed in "Sebecus", and probably appeared much earlier in crocodylomorphs.
Sebecus | Description
Compared to other prehistoric agnathan groups, such as the Heterostraci and Osteostraci, anaspids did not possess a bony shield or armor, hence their name. The anaspid head and body are instead covered in an array of small, weakly mineralized scales, with a row of massive scutes running down the back, and, at least confirmed among the birkeniids, the body was covered in rows of tile-like scales made of aspidine, an acellular bony tissue. Anaspids all had prominent, laterally placed eyes with no sclerotic ring, with the gills opened as a row of holes along either side of the animal, typically numbering anywhere from 6-15 pairs.
Anaspida | Anatomy
An forward-directed extension of the supratemporal formed the inner-rear edge of the supratemporal fenestra, an opening through the skull roof behind the eyes. The parietal, which would have formed the inner margin of the supratemporal fenestra, had a complex front margin that was interdigitating with either the frontal or postfrontal bones, which are not preserved in the known specimens. The quadrate bone, which connected to the lower jaw to form the jaw joint, was C-shaped in side view. Two probable hyoid bones (tongue bones) are preserved with specimen SNHM1284-R; these bones were rod-like, with one end spatula-shaped. The stapes (bone in the ear region that is used for hearing) had a shaft that was more slender than in any other ichthyosaur, and its head was large and square—these features are regarded an autapomorphy (unique feature) and serve to distinguish the genus from related genera.
Acamptonectes | Skull
The absence of a hard part in the fossil implies that the animal did not possess organs composed of bone, chitin or calcium carbonate. There is evidence of serially repeated internal structures. Its head is poorly differentiated. A transverse bar-shaped structure, which was either dorsal or ventral, terminates in two round organs which are associated with dark material which have been identified as melanosomes (containing the pigment melanin). Their form and structure is suggestive of a camera-type eye. "Tullimonstrum" possessed structures which have been interpreted as gills, and a possible notochord or rudimentary spinal cord.
Tullimonstrum | Description
In other great apes, the foramen spinosum is found not in the sphenoid bone but in parts of the temporal bone such as the squamous part, found at the sphenosquamosal suture, or absent.
Foramen spinosum | Animals
The stapedius emerges from a pinpoint foramen in the apex of the pyramidal eminence (a hollow, cone-shaped prominence in the posterior wall of the tympanic cavity), and inserts into the neck of the stapes.
Stapedius muscle | Structure
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
The pair of relatively short antennas are implanted behind the horns of the hypostome and stick out to the sides. There appear to be three pairs of limbs under the cephalon, carrying side branches with bristle-like gills (or setae).
Emucarididae | Description
The first three digits of both manus (fore foot) and pes (hind foot) are armed with horny claws, which also belong to the epidermal part of the exoskeleton. The dermal exoskeleton consists of bony scutes that underlie the epidermal scales of the dorsal surface of the trunk and anterior part of the tail. The overlying scales, except in very young animals, are always rubbed off, so that the bony scales are exposed. The ventral or inner surface of the scutes is flat, while the outer surface is strongly keeled and in old animals is often rough and pitted. The plates are nearly square in outline and are closely joined together in most places.
Crocodilian armor | Structure and anatomy