question: Prey animals have eyes on their sides, right? If so, why do Hammerhead Sharks have eyes so far apart?
comment: Hammerhead sharks apparently have significant overlap in their field of vision which makes their ability to track prey with binocular vision adequate. However it may also come down to the idea that the hammerhead shark doesn't use its eyes primarily to track prey it is trying to bite, rather the sensitive electro receptors called Ampullae of Lorenzini sense electrical signals from their prey.
passages: Section::::Stages of eye evolution.:Other developments.:Location.
  
  Prey generally have eyes on the sides of their head so to have a larger field of view, from which to avoid predators. Predators, however, have eyes in front of their head in order to have better depth perception. Flatfish are predators which lie on their side on the bottom, and have eyes placed asymmetrically on the same side of the head. A transitional fossil from the common symmetric position is Amphistium.
  
  Section::::See also.
  
  BULLET::::- Ocelloid
  
  Section::::Further reading.
  
  BULLET::::- Illustration. Review
   The eyes of pinnipeds are relatively large for their size and are positioned near the front of the head. One exception is the walrus, whose smaller eyes are located on the sides of its head. This is because it feeds on immobile bottom dwelling mollusks and hence does not need acute vision. A seal's eye is adapted for seeing both underwater and in air. The lens is mostly spherical, and much of the retina is equidistant from the lens center. The cornea has a flattened center where refraction is nearly equal in both water and air. Pinnipeds also have very muscular and vascularized irises. The well-developed dilator muscle gives the animals a great range in pupil dilation. When contracted, the pupil is typically pear-shaped, although the bearded seal's is more diagonal. In species that live in shallow water, such as harbor seals and California sea lions, dilation varies little, while the deep-diving elephant seals have much greater variation.
   The Australian magpie ("Gymnorhina tibicen") uses both left-eye and right-eye laterality when performing anti-predator responses, which include mobbing. Prior to withdrawing from a potential predator, Australian magpies view the animal with the left eye (85%), but prior to approaching, the right eye is used (72%). The left eye is used prior to jumping (73%) and prior to circling (65%) the predator, as well as during circling (58%) and for high alert inspection of the predator (72%). The researchers commented that "mobbing and perhaps circling are agonistic responses controlled by the LE[left eye]/right hemisphere, as also seen in other species. Alert inspection involves detailed examination of the predator and likely high levels of fear, known to be right hemisphere function."
   Some predator animals, particularly large ones such as sperm whales and killer whales, have their two eyes positioned on opposite sides of their heads, although it is possible they have some binocular visual field.
  
  Other animals that are not necessarily predators, such as fruit bats and a number of primates also have forward-facing eyes. These are usually animals that need fine depth discrimination/perception; for instance, binocular vision improves the ability to pick a chosen fruit or to find and grasp a particular branch.
   One of the best-known examples of convergent evolution is the camera eye of cephalopods (such as squid and octopus), vertebrates (including mammals) and cnidaria (such as jellyfish). Their last common ancestor had at most a simple photoreceptive spot, but a range of processes led to the progressive refinement of camera eyes — with one sharp difference: the cephalopod eye is "wired" in the opposite direction, with blood and nerve vessels entering from the back of the retina, rather than the front as in vertebrates. As a result, cephalopods lack a blind spot.
  
  Section::::In animal morphology.:Flight.
   In most species, a wide mouth extends all around the anterior circumference of the head, and bands of inwardly inclined teeth line both jaws. The teeth can be depressed so as to offer no impediment to an object gliding towards the stomach, but prevent its escape from the mouth. The anglerfish is able to distend both its jaw and its stomach, since its bones are thin and flexible, to enormous size, allowing it to swallow prey up to twice as large as its entire body.
  
  Section::::Behaviour.
  
  Section::::Behaviour.:Swimming and energy conservation.
   The number of lenses in the compound eyes of "Erettopterus" is comparable to the number in "Pterygotus" and "Jaekelopterus" which suggests that while undoubtedly predatory, "Erettopterus" was not as active, nor as specialized, as these genera.
   BULLET::::- In Trian Aspect (a rare, later 16th and 17th century heraldry term) is when the animal's head is facing at a 3/4 view to give the appearance of depth. The head will be viewed at an angle somewhere between profile and straight-on.
  
  Section::::Attitudes of beasts.
   Distinguishing features of the teleosts are mobile premaxilla, elongated neural arches at the end of the caudal fin and unpaired basibranchial toothplates. The premaxilla is unattached to the neurocranium (braincase); it plays a role in protruding the mouth and creating a circular opening. This lowers the pressure inside the mouth, sucking the prey inside. The lower jaw and maxilla are then pulled back to close the mouth, and the fish is able to grasp the prey. By contrast, mere closure of the jaws would risk pushing food out of the mouth. In more advanced teleosts, the premaxilla is enlarged and has teeth, while the maxilla is toothless. The maxilla functions to push both the premaxilla and the lower jaw forward. To open the mouth, an adductor muscle pulls back the top of the maxilla, pushing the lower jaw forward. In addition, the maxilla rotates slightly, which pushes forward a bony process that interlocks with the premaxilla.
   extremely little light is available; the view from below is like the sky at twilight. The sabertooth fish use their telescopic, upward-pointing eyes—which are thus adapted for improved terminal vision at the expense of lateral vision—to pick out squid, cuttlefish, and smaller fish silhouetted against the gloom above them.
   Section::::Description.:Eyes.
  
  In pelagic trilobites, such as the species in the proetid family Telephinidae, and in Cyclopygidae, as in many extant pelagic crustaceans, the eyes are particularly large and have very wide angles of view, both horizontal and vertical. This is in stark contrast to contemporary benthic trilobites, that may have an extensive horizontal angle of view, but always have a limited vertical angle of view.
   Most cephalopods rely on vision to detect predators and prey, and to communicate with one another. Consequently, cephalopod vision is acute: training experiments have shown that the common octopus can distinguish the brightness, size, shape, and horizontal or vertical orientation of objects. The morphological construction gives cephalopod eyes the same performance as sharks'; however, their construction differs, as cephalopods lack a cornea, and have an everted retina. Cephalopods' eyes are also sensitive to the plane of polarization of light. 
   Birds that fish by stealth from above the water have to correct for refraction particularly when the fish are observed at an angle. Reef herons and little egrets appear to be able to make the corrections needed when capturing fish and are more successful in catching fish when strikes are made at an acute angle and this higher success may be due to the inability of the fish to detect their predators. Other studies indicate that egrets work within a preferred angle of strike and that the probability of misses increase when the angle becomes too far from the vertical leading to an increased difference between the apparent and real depth of prey.
   The collected specimen of "Laurentaeglyphea" was observed to be very active and aggressive, using its semichelate first pereiopods to attack.
  
  Section::::Taxonomy.
   BULLET::::- En Arrière is said of a creature positioned with its back to the viewer. It is most common used of birds and insects, where the understanding is of an overhead view of the animal with its wings spread.
  
  BULLET::::- Guardant or In Full Aspect indicates an animal with a body positioned sideways but with its head turned to face the viewer.
  
  BULLET::::- Regardant indicates an animal with its head turned backward, as if looking over its shoulder. Unless other instructions are given, the body will face "to dexter", making the head's direction "to sinister".
   Towards the centre of the retina is the fovea (or the less specialised, area centralis) which has a greater density of receptors and is the area of greatest forward visual acuity, i.e. sharpest, clearest detection of objects. In 54% of birds, including birds of prey, kingfishers, hummingbirds and swallows, there is second fovea for enhanced sideways viewing. The optic nerve is a bundle of nerve fibres which carry messages from the eye to the relevant parts of the brain. Like mammals, birds have a small blind spot without photoreceptors at the optic disc, under which the optic nerve and blood vessels join the eye.
   Some other animals - usually, but not always, predatory animals - have their two eyes positioned on the front of their heads, thereby allowing for binocular vision and reducing their field of view in favor of stereopsis. However, eyes on the front is a highly evolved trait in vertebrates, and there are only three extant groups of vertebrates with truly forward-facing eyes: primates, carnivorous mammals, and birds of prey.
   Most cephalopods possess complex extraocular muscle systems that allow for very fine control over the gross positioning of the eyes. Octopuses possess an autonomic response that maintains the orientation of their pupils such that they are always horizontal.
  
  Section::::Polarized light.
   In the past, spinosaurids have often been considered piscivores (fish-eaters) in the main, based on comparisons of their jaws with those of modern crocodilians. British paleontologist Emily J. Rayfield and colleagues, in 2007, conducted biomechanical studies on the skull of "Baryonyx", which had a long, laterally compressed skull, comparing it to gharial (long, narrow, tubular) and alligator (flat and wide) skulls. They found that the structure of baryonychine jaws converged on that of gharials, in that the two taxa showed similar response patterns to stress from simulated feeding loads, and did so with and without the presence of a (simulated) secondary palate. The gharial, exemplar of a long, narrow, and tubular snout, is a fish specialist. However, this snout anatomy does not preclude other options for the spinosaurids. The gharial is the most extreme example and a fish specialist; Australian freshwater crocodiles ("Crocodylus johnstoni"), which have similarly shaped skulls to gharials, also specialize more on fish than sympatric, broad snouted crocodiles and are opportunistic feeders which eat all manner of small aquatic prey, including insects and crustaceans. Thus, spinosaurids' snouts correlate with piscivory; this is consistent with hypotheses of this diet for spinosaurids, in particular baryonychines, but it does not indicate that they were solely piscivorous.
   "Anguanax" possesses two unique traits among other plesiosaurians including a projection on the palpebral placed at midheight of the front-facing margin of the eye socket; and a posteroventral process of coracoid developed as a distinct trapezoid that does not reach the glenoid level from the side, and with a straight margin directed back and to the side from its back facing position. Additionally, other traits are relatively rare in pliosaurids and thus their combination in "Anguanax" distinguishes it from other pliosaurids. These include narrow axial neural spines, a back-directed retroarticular projection on the vertebrae, a hill on the coronoid depression, a stepped posteroventral corner of the back margin of the eye socket, rib facets that are placed dorsally on caudal vertebrae but does not extended to the neural arches, and front cervical centra that bear a low and broad midline ridge on their bottom surface.
   Although stalked eyes on peduncles occur in some species of crustaceans and some insects, only some of the Crustacea, such as crabs, bear their eyes on articulated peduncles that permit the eyes to be folded out of the way of trouble.
  
  Section::::Evolution.:Myriapods.
   As is the case in all scallops, "Spondylus" spp. have multiple eyes around the edges of their mantle, and they have relatively well-developed nervous systems. Their nervous ganglia are concentrated in the visceral region, with recognisable optic lobes connected to the eyes.
  
  Section::::Evolutionary history.
  
  The genus "Spondylus" appeared in the Mesozoic era, and is known in the fossil records from the Triassic Cassian beds in Italy (235 to 232 million years ago) onwards. About 40 extinct species are known. 
   Some animals - usually, but not always, prey animals - have their two eyes positioned on opposite sides of their heads to give the widest possible field of view. Examples include rabbits, buffaloes, and antelopes. In such animals, the eyes often move independently to increase the field of view. Even without moving their eyes, some birds have a 360-degree field of view.
   When searching for prey, each eye moves independently from the other. However, when a prey enters the visual field of one of the eyes, they lock into place focused on the prey.
  
  Section::::Behavior.
   Cephalopods, as active marine predators, possess sensory organs specialized for use in aquatic conditions. They have a camera-type eye which consists of an iris, a circular lens, vitreous cavity (eye gel), pigment cells, and photoreceptor cells that translate light from the light-sensitive retina into nerve signals which travel along the optic nerve to the brain. For the past 140 years, the camera-type cephalopod eye has been compared with the vertebrate eye as an example of convergent evolution, where both types of organisms have independently evolved the camera-eye trait and both share similar functionality. Contention exists on whether this is truly convergent evolution or parallel evolution. Unlike the vertebrate camera eye, the cephalopods' form as invaginations of the body surface (rather than outgrowths of the brain), and consequently they lack a cornea. Unlike the vertebrate eye, a cephalopod eye is focused through movement, much like the lens of a camera or telescope, rather than changing shape as the lens in the human eye does. The eye is approximately spherical, as is the lens, which is fully internal.
  
presuppositions: Because prey animals normally have eyes on the sides of their head, hammerhead sharks should not have their eyes on the side of their heads.
corrections: Hammerhead sharks have eyes on the sides of their heads to enhance their abilities to track prey, not because they are prey themselves. 
raw_presuppositions: Because prey animals normally have eyes on the sides of their head, hammerhead sharks should not have their eyes on the side of their heads. Hammerhead sharks primarily use their eyes to locate prey.
raw_corrections: Hammerhead sharks have eyes on the sides of their heads to enhance their abilities to track prey, not because they are prey themselves.  Hammerhead sharks use sensitive electro receptors called Ampullae of Lorenzini to locate prey.