In anatomy , the atlas (C1) is the most superior (first) cervical vertebra of the spine and is located in the neck .
152-511: Odobenocetops ( / ˌ oʊ d ə b iː ˈ n ɒ s ɪ t ɒ p s / ) is an extinct genus of small toothed whale known from Chile and Peru . Its fossils are found in Miocene -aged marine strata of the Bahía Inglesa Formation and Pisco Formation . Two species of Odobenocetops are currently recognized, O. peruvianus and the slightly younger O. leptodon . Odobenocetops
304-426: A broad range of sounds using nasal airsacs located just below the blowhole. Clicks are directional and are used for echolocation, often occurring in a short series called a click train. The click rate increases when approaching an object of interest. Toothed whale biosonar clicks are amongst the loudest sounds made by marine animals . The cetacean ear has specific adaptations to the marine environment. In humans,
456-444: A burst of air into the water and allowing it to rise to the surface, forming a ring, or swimming repeatedly in a circle and then stopping to inject air into the helical vortex currents thus formed. They also appear to enjoy biting the vortex rings, so that they burst into many separate bubbles and then rise quickly to the surface. Dolphins are known to use this method during hunting. Dolphins are also known to use tools. In Shark Bay ,
608-400: A delicate bony spiculum which arches backward from the posterior end of the superior articular process. This anatomical variant is known as an arcuate foramen . This groove transmits the vertebral artery , which, after ascending through the foramen in the transverse process, winds around the lateral mass in a direction backward and medially to enter the vertebrobasilar circulation through
760-625: A derived trait.. This suggests that they are two different branches of the same genus, rather than one species having evolved from the other. Despite their very limited range, no transitional form between Odobenocetops and other whales is known, leaving their precise origin a mystery. Lipotidae " Pontoporiidae " Iniidae Hadrodelphis " Kentriodontidae "† Albireonidae † Odobenocetops Denebola † Delphinapterus leucas (Beluga whale) Monodon monoceros (Narwhal) Phocoenidae (Porpoises) Delphinidae (Dolphines) The melon, an important fatty sensory organ present towards
912-439: A few, like the orca , feed on mammals, such as pinnipeds . Males typically mate with multiple females every year, making them polygynous . Females mate every two to three years. Calves are typically born in the spring and summer, and females bear the responsibility for raising them, but more sociable species rely on the family group to care for calves. Many species, mainly dolphins, are highly sociable, with some pods reaching over
1064-454: A lesser extent in Amazon river dolphins . Odobenocetops is among the cetaceans with the greatest range of head motion, exceeding even the values of the beluga whale . This may have helped while foraging, extending the neck in a way that keeps their tusks roughly parallel to the rest of the body. Due to the anatomy of the palate and other similarities to the walrus, it is thought that this whale
1216-425: A male bottlenose dolphin tends to be similar to that of his mother, while the signature whistle of a female bottlenose dolphin tends to be more identifying. Bottlenose dolphins have a strong memory when it comes to these signature whistles, as they are able to relate to a signature whistle of an individual they have not encountered for over twenty years. Research done on signature whistle usage by other dolphin species
1368-432: A mirror; then whether the animal shows signs of self-recognition is determined. In 1995, Marten and Psarakos used television to test dolphin self-awareness. They showed dolphins real-time footage of themselves, recorded footage, and another dolphin. They concluded that their evidence suggested self-awareness rather than social behavior. While this particular study has not been repeated since then, dolphins have since "passed"
1520-460: A more limited capacity for colour vision than most mammals. Most toothed whales have slightly flattened eyeballs, enlarged pupils (which shrink as they surface to prevent damage), slightly flattened corneas, and a tapetum lucidum ; these adaptations allow for large amounts of light to pass through the eye, and, therefore, a very clear image of the surrounding area. In water, a whale can see around 10.7 m (35 ft) ahead of itself, but they have
1672-449: A non-violent social way may explain why female individuals lacked these enlarged tusks. One way the tusks could have been used in such a fashion would to establish hierarchy without actually having to fight. However they might have still served some unknown role in feeding that wouldn't require the tusk to be endangered by breakage. Studies conducted on the second species shows that in O. leptodon , both tusks have noticeable wear facets. In
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#17331066458121824-410: A population of Indo-Pacific bottlenose dolphins put sponges on their beak to protect them from abrasions and sting ray barbs while foraging in the seafloor. This behaviour is passed on from mother to daughter, and it is only observed in 54 female individuals. Self-awareness is seen, by some, to be a sign of highly developed, abstract thinking. Self-awareness, though not well-defined scientifically,
1976-411: A preference for feeding using their right side. All this combined indicates that Odobenocetops was a bottomfeeding molluscivore , detecting various bivalves or crustaceans either through, depending on the species, the use of echolocation or exceptional vision and possibly with the assistance of tactile hair. While foraging the animal would keep its head down and the tusks parallel to the sediment while
2128-438: A small bulge sitting on top of its skull, whereas a sperm whale's head is filled mainly with the melon. Directional asymmetry in the skull has been seen amongst many generations, used for echolocation. This asymmetry is useful in focusing the use of bio sonar effectively when deep diving for prey. Odontocetes are well adapted to hear sounds at ultrasonic frequencies, as opposed to mysticetes who generally hear sounds within
2280-570: A smaller range above water. They also have glands on the eyelids and outer corneal layer that act as protection for the cornea. The olfactory lobes are absent in toothed whales, and unlike baleen whales, they lack the vomeronasal organ , suggesting they have no sense of smell. Toothed whales are not thought to have a good sense of taste, as their taste buds are atrophied or missing altogether. However, some dolphins have preferences between different kinds of fish, indicating some sort of attachment to taste. Toothed whales are capable of making
2432-426: A social function appears to have been the most likely function even though the exact details of how they would be used remains mysterious. Muizon and colleagues argue that although the tusks were positioned in a way that would allow them to slash at the flanks of other individuals after approaching head on, their fragile nature seems to preclude the use in actual combat. Purely visual display would be more consistent with
2584-541: A specific individual. These whistles are used in order for dolphins to communicate with one another by identifying an individual. It can be seen as the dolphin equivalent of a name for humans. These signature whistles are developed during a dolphin's first year; it continues to maintain the same sound throughout its lifetime. An auditory experience influences the whistle development of each dolphin. Dolphins are able to communicate to one another by addressing another dolphin through mimicking their whistle. The signature whistle of
2736-560: A thousand individuals. Once hunted for their products, cetaceans are now protected by international law. Some species are very intelligent . At the 2012 meeting of the American Association for the Advancement of Science , support was reiterated for a cetacean bill of rights, listing cetaceans as nonhuman persons . Besides whaling and drive hunting , they also face threats from bycatch and marine pollution. The baiji , for example,
2888-416: A vacuum pump. Such a feeding mechanism is further supported by the musculature connecting the upper and lower jaw. The glenoid fossa allows for forward and backward movement of the mandible while the temporalis muscle, masseter , tongue and throat musculature may have all contributed to moving the lower jaw back. The pterygoid muscles would have been responsible for forward movement. After having sucked out
3040-406: A vestigial structure in the group, only found in adult Amazon river dolphins , some mysticetes and the calves of a few other toothed whales. If they were present, they and the strong upper lip may have formed a structure similar to the rostral disc of the modern dugong . Generally its length and slenderness both make it rather fragile, which is supported by the fact that the tooth of the holotype
3192-403: A walrus. The skull of O. leptodon differs from that of O. peruvianus in several ways. The palate is much deeper, longer and wider and the anterior border is curved more gently, giving it a U-shape rather than a V-shape as in O. peruvianus . The palate itself is also asymmetrical and was likely positioned parallel to the seafloor, but not at a right angle with the sagittal plane . The apex of
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#17331066458123344-452: A way that the animal's body shape is restored, and infection of such large wounds are rare. Toothed whales are fully aquatic creatures, which means their birth and courtship behaviours are very different from terrestrial and semiaquatic creatures. Since they are unable to go onto land to calve, they deliver their young with the fetus positioned for tail-first delivery. This prevents the calf from drowning either upon or during delivery. To feed
3496-450: A year, dependency until one to two years, and maturity around seven to 10 years, all varying between the species. This mode of reproduction produces few offspring, but increases the survival probability of each one. Females, referred to as "cows", carry the responsibility of childcare, as males, referred to as "bulls", play no part in raising calves. In orcas, false killer whales , short-finned pilot whales , narwhals , and belugas, there
3648-469: Is a nearly complete skull with the associated atlas , the topmost of the neck vertebrae. The other specimen of O. leptodon is a much less complete skull, badly weathered and missing the right tusk, but preserving an assortment of postcranial elements such as ribs, vertebrae and a partial forelimb. While the referred O. peruvianus skull was found in the SAS horizon like the type specimen, the new species stems from
3800-404: Is an unusually long post-reproductive lifespan ( menopause ) in females. Older females, though unable to have their own children, play a key role in the rearing of other calves in the pod, and in this sense, given the costs of pregnancy especially at an advanced age, extended menopause is advantageous. Atlas (anatomy) The bone is named for Atlas of Greek mythology , just as Atlas bore
3952-408: Is arched, large and deep like in walruses and besides the two tusks in the premaxilla, Odobenocetops was toothless. The tip of the snout, specifically the premaxilla , is covered in important insertion points for facial musculature while also housing a great number of neurovascular foramina. This has been interpreted as supporting a strong upper lip and potentially even vibrissae similar to those in
4104-408: Is believed to be the precursor to more advanced processes like metacognitive reasoning (thinking about thinking) that are typical of humans. Research in this field has suggested that cetaceans, among others, possess self-awareness. The most widely used test for self-awareness in animals is the mirror test , in which a temporary dye is placed on an animal's body, and the animal is then presented with
4256-467: Is considered functionally extinct by IUCN , with the last sighting in 2004, due to heavy pollution to the Yangtze River . Whales sometimes feature in literature and film, as in the great white sperm whale of Herman Melville 's Moby-Dick . Small odontocetes, mainly dolphins, are kept in captivity and trained to perform tricks. Whale watching has become a form of tourism around the world. The tube in
4408-418: Is convex, and presents at its center the anterior tubercle for the attachment of the longus colli muscles and the anterior longitudinal ligament ; posteriorly it is concave, and marked by a smooth, oval or circular facet ( fovea dentis ), for articulation with the odontoid process (dens) of the axis. The upper and lower borders respectively give attachment to the anterior atlantooccipital membrane and
4560-440: Is herding, where a pod squeezes a school of fish into a small volume, known as a bait ball . Individual members then take turns plowing through the ball, feeding on the stunned fish. Coralling is a method where dolphins chase fish into shallow water to catch them more easily. Orcas and bottlenose dolphins have also been known to drive their prey onto a beach to feed on it, a behaviour known as beach or strand feeding. The shape of
4712-440: Is mostly known for its large asymmetric tusks , which emerge from pronounced processes formed by the premaxillae , known as the alveolar sheaths. These tusks are thought to be sexually dimorphic and are only strongly pronounced in male individuals, while females appear to possess two similarly sized tusks. In the holotype of O. peruvianus the elongated right tusk is broken, leaving its precise length ambiguous. O. leptodon on
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4864-412: Is one of the most accessible species for early cetologists , because it could be seen very close to land, inhabiting shallow coastal areas of Europe. Many of the findings that apply to all cetaceans were therefore first discovered in the porpoises. One of the first anatomical descriptions of the airways of the whales on the basis of a harbor porpoise dates from 1671 by John Ray. It nevertheless referred to
5016-449: Is only a single set of functional teeth (monophyodont dentition). Except for the sperm whale, most toothed whales are smaller than the baleen whales. The teeth differ considerably among the species. They may be numerous, with some dolphins bearing over 100 teeth in their jaws. At the other extreme are the narwhals with their single long tusks and the almost toothless beaked whales with tusk-like teeth only in males. In most beaked whales
5168-407: Is only slightly concave, whereas it is deeply notched in O. peruvianus which suggests that the binocular vision of O. leptodon wasn't as well-developed as in the older form. Although no mandibles are known for either species, it has been inferred that it was short and toothless based on the well developed pterygoid and temporalis muscles. Like the rest of the skull, the periotic bone surrounding
5320-413: Is quickly dismissed due to how such behavior would be out of place for anything but the basalmost cetaceans, while any use that would involve sea ice (such as creating breathing holes) is dismissed due to the climate of the region, which is much too warm. The possibility that they are simply an evolutionary leftover is also discarded due to how such a trait would quickly be lost if it served no purpose. Again
5472-405: Is relatively limited. The research on other species done so far has yielded varied outcomes and inconclusive results. Sperm whales can produce three specific vocalisations: creaks, codas, and slow clicks. A creak is a rapid series of high-frequency clicks that sounds somewhat like a creaky door hinge. It is typically used when homing in on prey. A coda is a short pattern of 3 to 20 clicks that
5624-490: Is required for the accommodation of the spinal cord. The transverse processes are large; they project laterally and downward from the lateral masses, and serve for the attachment of muscles which assist in rotating the head. They are long, and their anterior and posterior tubercles are fused into one mass; the foramen transversarium is directed from below, upward and backward. The atlas is usually ossified from three centers. Of these, one appears in each lateral mass about
5776-479: Is that they served a non-violent social role, as they are too fragile for combat. The alveolar sheaths on the other hand may have been used as orientation guides during foraging. Besides the two tusks in the upper jaw, Odobenocetops is thought to have been toothless. Another difference between this genus and other whales is that the melon , an organ important for echolocation , is reduced in O. leptodon and vestigial or entirely absent in O. peruvianus . At least
5928-428: Is the presence of a strong upper lip, further supporting what was already inferred for O. peruvianus . The premaxillary foramina are missing in O. leptodon and a dorsal fossa (shallow depression) is present on the premaxilla. This fossa suggests the presence of a melon in O. leptodon , an organ either absent or strongly reduced in O. peruvianus . On the other hand, the orbit in O. leptodon has an anterior edge that
6080-413: Is the topmost vertebra and the axis (the vertebra below it) forms the joint connecting the skull and spine. The atlas and axis are specialized to allow a greater range of motion than normal vertebrae. They are responsible for the nodding and rotation movements of the head. The atlanto-occipital joint allows the head to nod up and down on the vertebral column . The dens acts as a pivot that allows
6232-476: Is thought to be merely a compromise necessitated by the enlarged tusk. Regardless, the fact that they are of generally similar size indicates that they have a function beyond housing the tusks and were likely subject to their own selective pressure. Their possible functions were explored in greater detail in the same publication as the tusks, again exploring different ideas and assessing the advantages and disadvantages. For instance, although their function to support
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6384-400: Is used in social situations to identify one another (like a signature whistle), but it is still unknown whether sperm whales possess individually specific coda repertoires or whether individuals make codas at different rates. Slow clicks are heard only in the presence of males (it is not certain whether females occasionally make them). Males make a lot of slow clicks in breeding grounds (74% of
6536-464: Is well adapted for both air and water, so much so that some can survive even if they are blind. Some species are well adapted for diving to great depths. Almost all have a layer of fat, or blubber , under the skin to keep warm in the cold water, with the exception of river dolphins . Toothed whales consist of some of the most widespread mammals, but some, as with the vaquita, are restricted to certain areas. Odontocetes feed largely on fish and squid, but
6688-519: Is well-adapted for hunting Arctic whales and calves. Bears are known to use sit-and-wait tactics, as well as active stalking and pursuit of prey on ice or water. Whales lessen the chance of predation by gathering in groups. This, however, means less room around the breathing hole as the ice slowly closes the gap. When out at sea, whales dive out of the reach of surface-hunting orca. Polar bear attacks on belugas and narwhals are usually successful in winter, but rarely inflict any damage in summer. For most of
6840-407: Is what is commonly referred to as "telescoping", a term that generally describes the fact that bones typically far apart are very closely spaced in cetaceans and largely overlap. However, Odobenocetops is unique due to how its skull appears to reverse the telescoped condition of the cetacean skull. This is achieved through the maxilla and frontal bones regressing towards the tip of the snout and
6992-551: The Pisco Formation in Peru . Although initially thought to correlate with the earliest Pliocene , later studies have found that these sediments were deposited during the Miocene . This skull , designated USNM 460306 initially and later USNM 488252, was described by Christian de Muizon in 1993, establishing the genus Odobenocetops with O. peruvianus serving as the type species . Due to this genus' strange anatomy Muizon also coined
7144-453: The anterior atlantoaxial ligament ; the former connects it with the occipital bone above, and the latter with the axis below. The posterior arch forms about two-fifths of the circumference of the ring: it ends behind in the posterior tubercle, which is the rudiment of a spinous process and gives origin to the recti capitis posteriores minores and the ligamentum nuchae . The diminutive size of this process prevents any interference with
7296-401: The artiodactyl order (even-toed ungulates). They are closely related to the hippopotamus , sharing a common ancestor that lived around 54 million years ago (mya). The primitive cetaceans, or archaeocetes , first took to the sea approximately 49 mya and became fully aquatic by 5–10 million years later. The ancestors of toothed whales and baleen whales diverged in the early Oligocene. This
7448-573: The blowholes of whales and dolphins located on the top of the skull. In other odontocetes, parts of the frontal and maxillae cover the temporal fossae . In Odobenocetops , these bones are reduced and narrowed so that the temporal fossae are open dorsally. Additionally the parietal bones are well exposed dorsally, which corresponds with a well developed temporalis muscle . The periotic and tympanic bones are similar to those in other dolphins. The eye-sockets are oriented upwards and sideways, and not fully laterally like in other dolphins. The palate
7600-417: The bony nares being moved forward. Subsequently, this gives the rostrum its characteristic short and round appearance, in contrast to the elongated skulls found in other cetaceans. Related to this the type species O. peruvianus is thought to have lacked a melon (an important sensory organ), or at the least only had a vestigial melon. The bony nares are now located near the tip of the skull, in contrast to
7752-608: The colossal squid , octopuses , and fish like demersal rays , but their diet is mainly medium-sized squid . Some prey may be taken accidentally while eating other items. A study in the Galápagos found that squid from the genera Histioteuthis (62%), Ancistrocheirus (16%), and Octopoteuthis (7%) weighing between 12 and 650 grams (0.026 and 1.433 lb) were the most commonly taken. Battles between sperm whales and giant squid or colossal squid have never been observed by humans; however, white scars are believed to be caused by
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#17331066458127904-426: The foramen magnum ; it also transmits the suboccipital nerve (first spinal nerve). On the under surface of the posterior arch, behind the inferior articular facets, are two shallow grooves, the inferior vertebral notches. The lower border gives attachment to the posterior atlantoaxial ligament , which connects it with the axis. The lateral masses are the most bulky and solid parts of the atlas, in order to support
8056-430: The inner ear is highly derived and does not closely resemble the typical anatomy expected from a cetacean. Still, the cochlear canal follows the general anatomy also present in its closest relatives the beluga and narwhal. The inner ear also has large semicircular canals, vestibular aqueduct and a large count of facial and vestibular nerve fibres. Other toothed whales have semicircular canals that are notably smaller than
8208-413: The middle ear works as an impedance equalizer between the outside air's low impedance and the cochlear fluid's high impedance. In whales, and other marine mammals, no great difference exists between the outer and inner environments. Instead of sound passing through the outer ear to the middle ear, whales receive sound through the throat, from which it passes through a low-impedance, fat-filled cavity to
8360-416: The pontoporiid Pliopontos , the beaked whale Ninoziphius as well as the porpoise Piscolithax and multiple sperm whales including the giant Livyatan . Other marine animals include the marine sloth Thalassocnus , the giant shark Megalodon , two species of marine gharials , and various seals and penguins. Bivalves that could have served as prey to Odobenocetops have also been found in
8512-846: The sperm whales . 73 species of toothed whales are described. They are one of two living groups of cetaceans, the other being the baleen whales (Mysticeti), which have baleen instead of teeth. The two groups are thought to have diverged around 34 million years ago (mya). Toothed whales range in size from the 1.4 m (4 ft 7 in) and 54 kg (119 lb) vaquita to the 20 m (66 ft) and 100 t (98 long tons; 110 short tons) sperm whale . Several species of odontocetes exhibit sexual dimorphism , in that there are size or other morphological differences between females and males. They have streamlined bodies and two limbs that are modified into flippers. Some can travel at up to 20 knots. Odontocetes have conical teeth designed for catching fish or squid. They have well-developed hearing that
8664-566: The Pacific Ocean in the Langhian (15–13 ma) and diversified from there during the Serravallian and Tortonian (13–7 ma). The relation between the two species may be that of sister taxa rather than successive species. Muizon points out that Odobenocetops leptodon clearly has a more derived palate than its older relative, yet retains the basal melon which is heavily reduced in O. peruvianus as
8816-619: The SAO horizon, which is slightly younger. The generic name Odobenocetops comes from the Greek odon for "tooth", baino which means "walk", the Latin word cetus for "whale" and ops , "like". In combination the name means "cetacean that seems to walk on its teeth", a name chosen both to reflect the animal's potential feeding position as well as referring to the similarity with the extant walrus ( Odobenus ). The species name of O. peruvianus refers to Peru ,
8968-507: The alveolar sheaths, formed by the premaxilla, which are directed back- and downwards at a 60° angle from the horizontal plane of the skull. Such a tusk is only known in a single other cetacean, the extant narwhal, in which they are also asymmetric. However, in narwhals the tusk is implanted in the left maxilla, whereas the tusk in Odobenocetops originates in the right premaxilla. The tusks in these two genera are therefore not homologous , and
9120-402: The alveolar sheaths, most are thought to have been secondary and not the reason for their evolution. Instead, Muizon suggests that it was primarily the function as hydrofoils that caused Odobenocetops to develop these elongated structures. Research conducted on the atlas of Odobenocetops suggests that the head, when held in its neutral position, would be positioned at a 133° angle relative to
9272-402: The animal tried to feed and their stiff attachment to the skull makes them less effective than flippers. The sheaths are not dense enough to serve as ballast and are not angled correctly to form an effective plough during foraging (which would further clash with the interpretation that they might have been covered in tactile hair). They may not have been points for muscle attachment, as the back of
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#17331066458129424-560: The animals surroundings, it is not nearly as complex as the biosonar seen in other toothed whales. However, Muizon suggests that this may not have been a hindrance to the animal and that if positioned oblique to the seafloor, the enlarged and dorsally located eyes of the whale may have provided good binocular vision . This would mean that while losing its biosonar, O. peruvianus instead developed much better vision to compensate for this. Odobenocetops leptodon differed significantly in this regard. The eyes were still oriented more dorsally, but
9576-532: The area, including the genera Anadara , Trachycardium , Hybolophus , Panopea and Miltha . Odobenocetops is also known from the Late Miocene -aged Cerro Ballena locality of the Bahía Inglesa Formation of Chile. It is composed of silty sandstones and sands that were deposited in a supratidal flat (flattened beach or berm zone). Contemporaneous vertebrates from this locality include
9728-429: The atlas and attached head to rotate on the axis, side to side. The atlas's chief peculiarity is that it has no body, which has fused with the next vertebra . It is ring-like and consists of an anterior and a posterior arch and two lateral masses. The atlas and axis are important neurologically because the brainstem extends down to the axis. The anterior arch forms about one-fifth of the ring: its anterior surface
9880-434: The average human brain which averages 1,450 cm (88 in ) in mature males. The brain to body mass ratio in some odontocetes, such as belugas and narwhals, is second only to humans. Dolphins are known to engage in complex play behaviour , which includes such things as producing stable underwater toroidal air-core vortex rings or " bubble rings ". Two main methods of bubble ring production are: rapid puffing of
10032-455: The axis of the body. This means that the tusk, which is angled downward relative to the skull, would be held in a raised position at a 13° angle relative to the torso. Due to the flexibility of the neck, Odobenocetops could have easily changed the angle at which it held its head, allowing it to change the position of the tusk as needed. Muizon and colleagues suggest that it may have angled its head down while swimming, which would effectively bring
10184-419: The base of his neck, on C7. Sometime around 1522, anatomists decided to call the first cervical vertebra the atlas. Scholars believe that by switching the designation atlas from the seventh to the first cervical vertebra Renaissance anatomists were commenting that the point of man’s burden had shifted from his shoulders to his head--that man’s true burden was not a physical load, but rather, his mind. The atlas
10336-451: The brain homologous to where they are found in humans, suggesting they perform a similar function. Brain size was previously considered a major indicator of the intelligence of an animal. Since most of the brain is used for maintaining bodily functions, greater ratios of brain to body mass may increase the amount of brain mass available for more complex cognitive tasks. Allometric analysis indicates that mammalian brain size scales around
10488-438: The case of the enlarged right tusk, this facet runs parallel to the crest of the palate and the seafloor, indicating that the wear of the tooth may have been caused by it being dragged along the bottom of the ocean during foraging. Muizon and colleagues suggest that the tusks could have been held parallel to the seafloor, serving as a sort of orientation guide for the animal during foraging. In 2002 Muizon and colleagues considered
10640-409: The cochlear canal. Again Odobenocetops most closely resembles the related beluga. It is possible that this correlates with increased mobility of the neck and head. In addition to the unique shape of the skull, Odobenocetops is most easily distinguished from other cetacean by the presence of a pair of asymmetric tusks composed entirely of dentine . These tusks are housed by large processes, known as
10792-399: The concentration of myoglobin than haemoglobin. Before going on long dives, many toothed whales exhibit a behaviour known as sounding; they stay close to the surface for a series of short, shallow dives while building their oxygen reserves, and then make a sounding dive. Toothed whale eyes are relatively small for their size, yet they do retain a good degree of eyesight. Also, the eyes are on
10944-429: The country it was found in. The body length has been estimated to range from 3–4 metres (9.8–13.1 ft). It is possible that Odobenocetops reached a mass similar to that of modern narwhals, between 800–1,000 kg (1,800–2,200 lb). The skull of O. peruvianus is large, measuring 46 cm (18 in) throughout its preserved length. The skull has a characteristic profile, appearing strongly concave between
11096-436: The diverticula in the nasal passage. Furthermore, the extremely derived skull of Odobenocetops likely means that many of the nasolabialis muscles were reduced or entirely absent. Overall this suggests that Odobenocetops peruvianus was most likely incapable of producing the beamed, gated signals that define echolocation and could only passively listen to ultrasonic sound. While this could still provide valuable information about
11248-441: The dolphin to the sperm whale's spermaceti organ . These send out high-frequency clicks through the sound-modifying organs of the extramandibular fat body, intramandibular fat body and the melon . The melon consists of fat, and the skull of any such creature containing a melon will have a large depression. The melon size varies between species, the bigger it is, the more dependent they are on it. A beaked whale, for example, has
11400-423: The early evolution, before the length of the sheaths reached the size seen in the known fossils of Odobenocetops . It is possible that they could have also served social functions in display or combat, making the animal appear larger or serving as a shield against attacks. The idea that they are a retained primitive feature on the other hand is questioned as it does not explain what caused them to attain their size in
11552-461: The elevated snout and skullroof. When viewed from above, it is also clearly separated into two large portions. The anterior most portion, which includes the premaxillae, tusks and nares is separated from the back of the head by a strong constriction, giving the skull somewhat of an hourglass-shape. The skulls of modern whales show a great variety of adaptations towards aquatic life, clearly setting them apart from all other mammals. Among these adaptations
11704-406: The elongated tusk was 23 cm (9.1 in) long, indicating that it grew continuously. The short tusk also appeared to still be growing, even if at a much slower speed. The holotype of the younger species O. leptodon was found with both tusks in situ , the right one was needle-like and 1.35 metres (4 ft 5 in) long, 1.07 metres (3 ft 6 in) of which being located outside of
11856-409: The exception sperm whales), and eyes placed on the sides of their heads. Toothed whales range in size from the 4.5 ft (1.4 m) and 120 lb (54 kg) vaquita to the 20 m (66 ft) and 55 t (61-short-ton) sperm whale. Overall, they tend to be dwarfed by their relatives, the baleen whales (Mysticeti). Several species have sexual dimorphism, with the females being larger than
12008-413: The family Odobenocetopsidae. Several additional fragmentary fossils, namely periotic and tympanic bones, were later referred to the genus as well. More substantial material was found in the form of three additional specimens, one of which is thought to represent a female O. peruvianus while the other two were described as a second, younger species named O. leptodon . The holotype specimen of O. leptodon
12160-468: The first place, as they likely didn't serve to support the tusks. Two of the hypotheses regarding the function of the sheaths were however found to lack any direct evidence to the contrary. Skin attached to the sheaths could have been an adaptation for feeding, protected the eyes from mud and sediment, while the use as orientation guides is an idea Muizon had already suggested in previous publications. Although there may have been several possible advantages to
12312-403: The first year after birth, and joins the lateral masses from the sixth to the eighth year. The lines of union extend across the anterior portions of the superior articular facets. Occasionally there is no separate center, the anterior arch being formed by the forward extension and ultimate junction of the two lateral masses; sometimes this arch is ossified from two centers, one on either side of
12464-433: The front of the head and associated with echolocation in toothed whales, appears to be either heavily reduced or entirely absent in Odobenocetops due to the highly specialised skull shape of the animal. The anatomy of the inner ear as seen in O. peruvianus indicates that Odobenocetops was capable of ultrasonic hearing . Specifically, the cochlear anatomy resembles that of belugas and narwhals, which generally allows for
12616-475: The front, and a tail fin. These flippers contain four digits. Although toothed whales do not possess fully developed hind limbs, some, such as the sperm whale, possess discrete rudimentary appendages, which may contain feet and digits. Toothed whales are fast swimmers in comparison to seals, which typically cruise at 5–15 knots, or 9–28 km/h (5.6–17.4 mph); the sperm whale, in comparison, can travel at speeds of up to 35 km/h (22 mph). The fusing of
12768-410: The function of the tusks in greater detail, writing on the pros and cons of various potential uses. Many of these proposed functions were however quickly dismissed due to their strange nature. The use as ballast or as a forceful feeding adaptation is considered unlikely due to their asymmetrical nature, nor would such a use be supported by modern relatives or analogues. Using the tusks for climbing on land
12920-463: The greatest range of motion still living today. Further support for this can be found in the anatomy of the atlantooccipital joint. In accordance with this, Odobenocetops had a range of motion at least 29% greater than belugas. While the hyperextension of the neck would be used in feeding, the precise purpose of the great possible range of flexion is not known. Regardless of purpose, such a position would have effectively allowed Odobenocetops to bring
13072-484: The harsh climate. Calves are born with only a thin layer of blubber, but some species compensate for this with thick lanugos . Toothed whales have also evolved the ability to store large amounts of wax esters in their adipose tissue as an addition to or in complete replacement of other fats in their blubber. They can produce isovaleric acid from branched chain fatty acids (BCFA). These adaptations are unique, are only in more recent, derived lineages and were likely part of
13224-450: The head being whipped back on the shoulders, causing whiplash. In minor cases, the anterior longitudinal ligament of the spine is damaged which is acutely painful for the patient. In more severe cases, fractures can occur to any of the cervical vertebrae as they are suddenly compressed by rapid deceleration. Again, since the vertebral foramen is large there is less chance of spinal cord involvement. The worst-case scenario for these injuries
13376-405: The head to the seafloor while the buoyant body would be held oblique to the ground. In this position the neck would be hyperextended and the tusks may have been held at a 45° angle relative to the torso. Here too Odobenocetops shows clear convergence with the walrus. Muizon and colleagues contrast this to the position taken on by sirenians like the dugong, which are capable of swimming parallel to
13528-483: The head, through which this kind fish takes its breath and spitting water, located in front of the brain and ends outwardly in a simple hole, but inside it is divided by a downward bony septum, as if it were two nostrils; but underneath it opens up again in the mouth in a void. In Aristotle 's time, the fourth century BC, whales were regarded as fish due to their superficial similarity. Aristotle, however, could already see many physiological and anatomical similarities with
13680-406: The inner ear. The ear is acoustically isolated from the skull by air-filled sinus pockets, which allow for greater directional hearing underwater. Odontocetes generate sounds independently of respiration using recycled air that passes through air sacs and phonic (alternatively monkey) lips. Integral to the lips are oil-filled organs called dorsal bursae that have been suggested to be homologous in
13832-507: The invertebrate in place before utilizing a complex suctionfeeding mechanism created by the palate and tongue to suck out the soft parts. Once these were out, the shell could be easily discarded. Odobenocetops is mainly known from the Miocene Pisco Formation of Peru, which is thought to represent a coastal environment with calm, shallow waters. The rock units preserve a great cetacean diversity, including cetotheriids , rorquals ,
13984-900: The large squid. A 2010 study suggests that female sperm whales may collaborate when hunting Humboldt squid . The orca is known to prey on numerous other toothed whale species. One example is the false killer whale . To subdue and kill whales, orcas continually ram them with their heads; this can sometimes kill bowhead whales , or severely injure them. Other times, they corral their prey before striking. They are typically hunted by groups of 10 or fewer orca, but they are seldom attacked by an individual. Calves are more commonly taken by orca, but adults can be targeted, as well. Groups even attack larger cetaceans such as minke whales , gray whales , and rarely sperm whales or blue whales . Other marine mammal prey species include nearly 20 species of seal , sea lion and fur seal . These cetaceans are targeted by terrestrial and pagophilic predators. The polar bear
14136-434: The lateral mass Type 5: Bilateral burst fracture (AKA Jefferson Fracture) A break in the first vertebra is referred to as a Jefferson fracture . Craniocervical junction misalignment is also suspected as a factor in neurodegenerative diseases where altered CSF flow plays a part in the pathological process. Hyperextension (Whiplash) Injury A rear-end traffic collision or a poorly performed rugby tackle can both result in
14288-440: The left and right tusk of the type specimen, the tusks of the second specimen were both mostly symmetrical and short. Rather than taking this as evidence for an additional species, Muizon suggests that this skull may have belonged to a female individual displaying sexual dimorphism . This is supported by the dimorphism seen in modern narwhals, in which only males possess the iconic tusk while most females lack them. The pulp cavity of
14440-456: The lower jaw was likely toothless, similar to the upper jaw, the strong musculature could not have functioned to allow for chewing and grinding. Instead the musculature is thought to have enabled Odobenocetops to suctionfeed. Like the walrus, Odobenocetops might have used its upper lip to grab various marine bivalves and sucked out the foot and siphon with the help of a large piston-like tongue. The entire mouth would essentially function like
14592-465: The lungs meets cold air, so it does not form in warmer climates, as with river dolphins. Almost all cetaceans have a thick layer of blubber , except for river dolphins. In species that live near the poles, the blubber can be as thick as 11 in (28 cm). This blubber can help with buoyancy, protection to some extent as predators would have a hard time getting through a thick layer of fat, energy for fasting during leaner times, and insulation from
14744-423: The males. One exception is with the sperm whale, which has males larger than the females. Odontocetes possess teeth with cementum cells overlying dentine cells. Unlike human teeth, which are composed mostly of enamel on the portion of the tooth outside of the gum, whale teeth have cementum outside the gum. Only in larger whales, where the cementum is worn away on the tip of the tooth, does enamel show. There
14896-420: The melon is absent in the type species, it was at least somewhat developed in O. leptodon . Such a small melon would further be supported by the width of the apex of the rostrum. In O. peruvianus the rostrum is simply too narrow and tapering to have room for a melon. Regardless, even with a melon present in O. leptodon , this organ would still be reduced relative to other toothed whales. All this suggests that
15048-431: The melon-shaped forehead, reflected off objects, and retrieved through the lower jaw. Skulls of Squalodon show evidence for the first hypothesized appearance of echolocation. Squalodon lived from the early to middle Oligocene to the middle Miocene , around 33-14 mya. Squalodon featured several commonalities with modern Odontocetes. The cranium was well compressed, the rostrum telescoped outward (a characteristic of
15200-409: The middle line. Accessory transverse foramen of the atlas is present in 1.4–12.5% across the population. Foramen arcuale or a bony bridge above the vertebral artery on the posterior arch of the atlas may be present. This foramen has an overall prevalence of 9.1%. Arch defects refer to the condition where a gap or cleft exists at the anterior arch or posterior arch of the atlas. The prevalence of
15352-403: The mirror test. Dolphins make a broad range of sounds using nasal airsacs located just below the blowhole. Roughly three categories of sounds can be identified: frequency modulated whistles, burst-pulsed sounds and clicks. Dolphins communicate with whistle-like sounds produced by vibrating connective tissue, similar to the way human vocal cords function, and through burst-pulsed sounds, though
15504-462: The modern parvorder Odontoceti ), giving Squalodon an appearance similar to that of modern toothed whales. However, it is thought unlikely that squalodontids are direct ancestors of living dolphins. Toothed whales have torpedo-shaped bodies with usually inflexible necks, limbs modified into flippers, no outer ears, a large tail fin, and bulbous heads (with the exception of the sperm whale family ). Their skulls have small eye orbits, long beaks (with
15656-400: The modern walrus. Due to this it is believed that the two animals, although unrelated, likely shared a very similar lifestyle. The deep palate, rounded snout supporting a strong upper lip, tusks and reduced dentition are all traits shared between this cetacean and walruses, both extant and extinct. The powerful musculature associated with the movement of the lower jaw in particular stands out. As
15808-428: The mouth and the speculative set of vibrissae. Muizon compares this to the use of sled runners, especially relative to underwater photography, which keep the camera stable and pointed in the right direction. Their function is no less disputed than that of the tusks, even though the fact that they are nearly symmetrical and found in both sexes suggests that it was unrelated to sexually dimorphic behavior. The minor asymmetry
15960-436: The movements between the atlas and the skull. The posterior part of the arch presents above and behind a rounded edge for the attachment of the posterior atlantooccipital membrane , while immediately behind each superior articular process is the superior vertebral notch ( sulcus arteriae vertebralis ). This is a groove that is sometimes converted into a foramen by ossification of the posterior atlantooccipital membrane to create
16112-403: The nature and extent of that ability is not known. The clicks are directional and are for echolocation, often occurring in a short series called a click train. The click rate increases when approaching an object of interest. Dolphin echolocation clicks are amongst the loudest sounds made by marine animals. Bottlenose dolphins have been found to have signature whistles, a whistle that is unique to
16264-536: The neck vertebrae, while increasing stability when swimming at high speeds, decreases flexibility, rendering them incapable of turning their heads; river dolphins, however, have unfused neck vertebrae and can turn their heads. When swimming, toothed whales rely on their tail fins to propel them through the water. Flipper movement is continuous. They swim by moving their tail fin and lower body up and down, propelling themselves through vertical movement, while their flippers are mainly used for steering. Some species log out of
16416-408: The neck. Whichever the case, Odobenocetops shows pronounced points for muscle attachment on the basioccipital bone, which corroborates the presence of strong neck musculature that would be needed to compensate for the weight of the large tusks. While the neck would flex to bring the tusks up while swimming, during foraging the densely built skull and tusk would keep the head down, essentially pulling
16568-416: The newborn, toothed whales, being aquatic, must squirt the milk into the mouth of the calf. Being mammals, they have mammary glands used for nursing calves; they are weaned around 11 months of age. This milk contains high amounts of fat which is meant to hasten the development of blubber; it contains so much fat, it has the consistency of toothpaste. Females deliver a single calf, with gestation lasting about
16720-415: The occurrence of tusks in Odobenocetops is a convergence with narwhals. In the holotype of Odobenocetops peruvianus both tusks are incomplete. Based on the preserved elements it is estimated that the longer, right tusk measured between 45–55 cm (18–22 in) in length. The left tusk was notably smaller, being estimated at no more than 20 cm (7.9 in) long and possibly entirely contained in
16872-431: The older species compensated for this by having large, dorsally located eyes giving it binocular vision . The fact that only the older species lost its melon has been taken as evidence that they were sister taxa , rather than one species evolving directly from the other. In addition to their vision or echolocation, Christian de Muizon argues that they may have possessed tactile hair , which are also found in walrus and to
17024-536: The original sound. In larger groups, individual whistle sounds are less prominent. Dolphins tend to travel in pods, sometimes of up to 600 members. Cetaceans are known to communicate and therefore are able to teach, learn, cooperate, scheme, and grieve. The neocortex of many species of dolphins is home to elongated spindle neurons that, prior to 2007, were known only in hominids. In humans, these cells are involved in social conduct, emotions, judgement, and theory of mind. Dolphin spindle neurons are found in areas of
17176-428: The other hand preserves complete tusks, showing that at least in this species the longer tusk reached a total length of 1.35 metres (4 ft 5 in) long, 1.07 metres (3 ft 6 in) of which is located outside of the alveolar sheath. While these tusks are reminiscent of the tusk seen in the closely related narwhals , they evolved independently . Their purpose remains unknown, but the most common interpretation
17328-439: The peak perception of sounds below 80 kHz. The anatomy points towards Odobenocetops being at the lower end of this range, its peak sensitivity likely ranging from 35 to 50 kHz. Despite this, O. peruvianus displays a series of characters suggesting that it was generally less capable at producing sounds itself. This includes not just the absent melon, but also the lack or the reduction of premaxillary sacs, nasal plugs and
17480-662: The porpoise as a fish. Sperm whales (Physeteridae) [REDACTED] Dwarf sperm whales (Kogiidae) [REDACTED] South Asian river dolphins (Platanistidae) [REDACTED] Beaked whales (Ziphiidae) [REDACTED] Yangtze river dolphin (Lipotidae) [REDACTED] Pontoporiidae [REDACTED] Iniidae [REDACTED] Oceanic dolphins (Delphinidae) [REDACTED] Porpoises (Phocoenidae) [REDACTED] Belugas , narwhals (Monodontidae) [REDACTED] Toothed whales, as well as baleen whales, are descendants of land-dwelling mammals of
17632-664: The posterior arch defect and anterior arch defect was 0.95% and 0.087%, respectively. The anterior arch defect may be presented along with posterior arch defect, a condition known as combined arch defect or bipartite atlas. Upper surface: Interior and dorsal part: Lower surface: Upper surface: Lower surface: There are 5 types of C1 fractures referred to as the Levine Classification of Atlas Fractures Type 1: Isolated bony apophysis (transverse process fracture Type 2: Isolated posterior arch fractures Type 3: Isolated anterior arch fracture Type 4: Comminuted fracture of
17784-408: The premaxillary process, the left tusk was only 25 cm (9.8 in) long, similar in length to the small tusk of O. perivianus . Despite the small tusk only being slightly longer than that of the type species, the wear facet of it indicates that it was erupted and not confined within the bony process of the premaxilla. The larger tusk also preserves a clear wear facet at its tip, giving the apex of
17936-408: The premaxillary process. Following the discovery of O. leptodon , Muizon speculated that both tusks could have obtained larger sizes in other individuals. This however would require additional specimens to corroborate the hypothesis. The second skull, described by Muizon in 1999, differs significantly from the 1993 skull despite being found in the same horizon. Unlike the drastic size difference between
18088-438: The range of infrasonic frequencies. Bottlenose dolphins have been found to have signature whistles unique to each individual. Dolphins use these whistles to communicate with one another by identifying an individual. It can be seen as the dolphin equivalent of a name for humans. Because dolphins generally live in groups, communication is necessary. Signal masking is when other similar sounds (conspecific sounds) interfere with
18240-478: The rest of the body would be held oblique due to its greater density. The tail fluke would help keep this position while also providing propulsion, whereas the forelimbs may have been used as stabilizers. Once a suitable prey item was detected, Odobenocetops could have created a powerful jet of water using its mouth (an ability also seen in belugas and orcas), excavating the target from the sediment. It would then have likely used its powerful upper lip to grasp and hold
18392-406: The seafloor thanks to their denser bonestructure relative to ceteaceans and pinnipeds. The hyperextension performed during feeding is the result of the incredibly mobile neck, which allows for a range of motion of up to 83°. This includes the hyperextension of 7° during feeding and hyperflexion of up to 90°. This far exceeds the 50° range of motion seen in the beluga whale, which is the odontocete with
18544-457: The seal Acrophoca , balaenopterid and sperm whales, billfish , the shark Carcharodon , and the marine sloth Thalassocnus . Other faunal components include a variety of trace fossils left by invertebrates. Toothed whale The toothed whales (also called odontocetes , systematic name Odontoceti ) are a clade of cetaceans that includes dolphins , porpoises , and all other whales with teeth , such as beaked whales and
18696-409: The seventh week of fetal life, and extends backward; at birth, these portions of bone are separated from one another behind by a narrow interval filled with cartilage . Between the third and fourth years they unite either directly or through the medium of a separate center developed in the cartilage. At birth, the anterior arch consists of cartilage; in this a separate center appears about the end of
18848-452: The shape of the orbits does not support the idea that this species also had well developed binocular vision. The precise state of this species' vision is uncertain, but it may have ranged from only having reduced binocular vision to no binocular vision at all. Unlike the older species though, O. leptodon preserves small depressions on the premaxillae that indicate that the animal was equipped with premaxillary sacs. This would mean that although
19000-418: The sides of the head, so their vision consists of two fields, rather than a binocular view as humans have. When a beluga surfaces, its lenses and corneas correct the nearsightedness that results from the refraction of light; they contain both rod and cone cells, meaning they can see in both dim and bright light. They do, however, lack short wavelength-sensitive visual pigments in their cone cells, indicating
19152-513: The skull already serves this purpose, and they appear to have been overdeveloped for simply restricting the area affected by their suction force. They could have expanded the surface area for tactile hair, however only parts of the entire sheath contain the foramina used to infer these hair, whose presence is not confirmed to begin with. Although Muizon and colleagues find flaws with these last two hypothetical functions, they cannot rule them out entirely and suggest that they may even have been factors in
19304-475: The smaller species of dolphins, only a few of the larger sharks, such as the bull shark , dusky shark , tiger shark , and great white shark , are a potential risk, especially for calves. Dolphins can tolerate and recover from extreme injuries (including shark bites) although the exact methods used to achieve this are not known. The healing process is rapid and even very deep wounds do not cause dolphins to hemorrhage to death. Even gaping wounds restore in such
19456-408: The snout in general is more massive than in the type species and at the tip of the rostrum, between the premaxillae, there is a unique pair of supplementary bones not present in the older species at all. These bones, which may have been the rostral or prenasal bones, are similar to what is seen in mammals such as elephant shrews , moles , tapirs , saigas and pigs . A unifying factor of these groups
19608-423: The snout may correlate with tooth number and thus feeding mechanisms. The narwhal, with its blunt snout and reduced dentition, relies on suction feeding . Sperm whales usually dive between 300 and 800 metres (980 and 2,620 ft), and sometimes 1 to 2 kilometres (3,300 to 6,600 ft), in search of food. Such dives can last more than an hour. They feed on several species, notably the giant squid , but also
19760-429: The soft parts of the bivalves it fed on, Odobenocetops could have simply ejected the remains of the shell. The same is also applicable to O. leptodon , although the modified and more pronounced anatomy of the palate may indicate that its ability to suck out molluscs was even greater than that of the older species. Regardless, both species are considered to be bottomfeeders like the modern walrus. The asymmetrical palate
19912-551: The strength of the structure, but is not favored by the orientation of the tusk and how it's only visible on one side. The very limited sample size only serves to deepen the mystery. Regardless of their function, Muizon and colleagues propose that they were a secondary sexual character that was subject of rapid sexual selection in a very narrow timeframe. The sheathes of the tusks themselves may have been an important feature in their own right. Muizon and colleagues speculate that they may have served as orientation guides and stabilizers to
20064-501: The teeth are seen to erupt in the lower jaw, and primarily occurs at the males sexual maturity. Not all species are believed to use their teeth for feeding. For instance, the sperm whale likely uses its teeth for aggression and showmanship. Breathing involves expelling stale air from their one blowhole , forming an upward, steamy spout, followed by inhaling fresh air into the lungs. Spout shapes differ among species, which facilitates identification. The spout only forms when warm air from
20216-515: The terrestrial vertebrates, such as blood (circulation), lungs, uterus, and fin anatomy. His detailed descriptions were assimilated by the Romans, but mixed with a more accurate knowledge of the dolphins, as mentioned by Pliny the Elder in his Natural history . In the art of this and subsequent periods, dolphins are portrayed with a high-arched head (typical of porpoises) and a long snout. The harbor porpoise
20368-542: The time), both near the surface and at depth, which suggests they are primarily mating signals. Outside breeding grounds, slow clicks are rarely heard, and usually near the surface. All whales are carnivorous and predatory . Odontocetes, as a whole, mostly feed on fish and cephalopods , and then followed by crustaceans and bivalves . All species are generalist and opportunistic feeders. Some may forage with other kinds of animals, such as other species of whales or certain species of pinnipeds . One common feeding method
20520-434: The tips of the tusks in a position above their origin without hindering the movement of the flippers due to the angle at which the tusks protrude outwards. The great range of motion estimated from the articulation of the bones is further supported by the numerous strongly developed muscle attachments seen on the skull of Odobenocetops . In the morphology of the skull, Odobenocetops peruvianus shares many characteristics with
20672-425: The toothed whale lineage. Modern toothed whales do not rely on their sense of sight, but rather on their sonar to hunt prey. Echolocation also allowed toothed whales to dive deeper in search of food, with light no longer necessary for navigation, which opened up new food sources. Toothed whales (Odontocetes) echolocate by creating a series of clicks emitted at various frequencies. Sound pulses are emitted through
20824-449: The transition for species to become deeper divers as the families of toothed whales (Physeteridae, Kogiidae, and Ziphiidae) that have the highest quantities of wax esters and BCFAs in their blubber are also the species that dive the deepest and for the longest amount of time. Toothed whales have a two-chambered stomach similar in structure to terrestrial carnivores. They have fundic and pyloric chambers. Cetaceans have two flippers on
20976-430: The tusk a strongly oblique shape due to how the tusk was used. Given the tusks length and slenderness, it was likely very fragile, which is considered to be an argument against it being held at a 45° angle from the body. This is corroborated by the anatomy of the neck. The way the atlas and the occipital condyle articulate suggests that in neutral position, the neck would have been angled slightly downward, which inclines
21128-416: The tusk into a position roughly parallel with the rest of the body and reduce drag. When looking the anatomy of the occipital condyle these values change however. Here the tusk would diverge from the body at an angle of only 6°, running effectively parallel to the rest of the body. This difference may be caused by the difficulty in determining the neutral position between maximum flexion and maximum extension of
21280-407: The tusk slightly upward into a position parallel to the rest of the body. Due to the fact that the tusk additionally projects slightly towards the side, Odobenocetops could lower its head even further than that without having its tooth get in the way of its front flippers. The atlas itself, like the skull, is asymmetrical, with a stronger left side to compensate for the enlarged tusk. Odobenocetops
21432-480: The tusks seems natural, this would not explain why the sheaths are much more symmetrical despite only one of the two tusks being enlarged. Although Odobenocetops may have profited from the presence of hydrofoils , the sheaths are considered to be too small to serve this function effectively. Furthermore, hydrofoils might not have been very useful for the slow-swimming Odobenocetops , the sheaths would have generated little lift and if anything been counterproductive when
21584-440: The two species varied in their approach to foraging. O. peruvianus with its vestigial or non-existent melon relied on its vision, which was exceptionally well developed compared to that of other cetaceans. O. leptodon on the other hand appears to have had much poorer binocular vision if at all and instead possessed a small melon, likely hunting primarily through the use of echolocation. Another sense Odobenocetops may have used
21736-439: The two-thirds or three-quarters exponent of the body mass. Comparison of a particular animal's brain size with the expected brain size based on such allometric analysis provides an encephalization quotient that can be used as another indication of animal intelligence. Sperm whales have the largest brain mass of any animal on earth, averaging 8,000 cm (490 in ) and 7.8 kg (17 lb) in mature males, in comparison to
21888-504: The water, which may allow them to travel faster. Their skeletal anatomy allows them to be fast swimmers. Most species have a dorsal fin . Most toothed whales are adapted for diving to great depths, porpoises are one exception. In addition to their streamlined bodies, they can slow their heart rate to conserve oxygen; blood is rerouted from tissue tolerant of water pressure to the heart and brain among other organs; haemoglobin and myoglobin store oxygen in body tissue; and they have twice
22040-403: The weight of the head. Each carries two articular facets, a superior and an inferior. Just below the medial margin of each superior facet is a small tubercle, for the attachment of the transverse atlantal ligament which stretches across the ring of the atlas and divides the vertebral foramen into two unequal parts: This part of the vertebral canal is of considerable size, much greater than
22192-413: The weight of the heavens, the first cervical vertebra supports the head . However, the term atlas was first used by the ancient Romans for the seventh cervical vertebra (C7) due to its suitability for supporting burdens. In Greek mythology, Atlas was condemned to bear the weight of the heavens as punishment for rebelling against Zeus . Ancient depictions of Atlas show the globe of the heavens resting at
22344-469: Was a suctionfeeding molluscivore , searching for bivalves on the ocean floor, uncovering them with precise jets of water, grasping the uncovered molluscs with a powerful upper lip and using its tongue like a piston to suck out the soft parts of their prey, leaving the shell intact. The first fossil material, a single skull missing much of its left side, was recovered in 1990 from the Sud Sadaco horizon of
22496-543: Was an early member of the dolphin superfamily , more closely related to narwhals than dolphins but with tusks projecting towards the rear of its body. Muizon placed Odobenocetopsidae as a sister group to the Monodontidae (the family including the narwhal and beluga whale ). Murakami and colleagues placed Odobenocetopsidae in a large clade together with Phocoenidae (porpoises), Monodontidae, and Albireonidae (an extinct group similar to porpoises). This clade originated in
22648-442: Was broken while the animal was still alive. The function of the tusks themselves is not entirely clear. Initially, Muizon proposed that they were merely a social instrument and not used in foraging, a hypothesis favored by later discoveries. The fragile nature of the enlarged tusks indicates that they were not used in any ways that would require it to apply force, for instance digging or fighting. The idea that they were possibly used in
22800-614: Was due to a change in the climate of the southern oceans that affected where the environment of the plankton that these whales ate. The adaptation of echolocation and enhanced fat synthesis in blubber occurred when toothed whales split apart from baleen whales, and distinguishes modern toothed whales from fully aquatic archaeocetes. This happened around 34 mya. Unlike toothed whales, baleen whales do not have wax ester deposits nor branched fatty chain acids in their blubber. Thus, more recent evolution of these complex blubber traits occurred after baleen whales and toothed whales split, and only in
22952-491: Was inclined more towards the left to compensate for the massive right tusk. Muizon and colleagues also mention the possibility that it was the other way around, and that the asymmetry wasn't responsible for the preference of the left side, but rather that this already established preference was responsible for the development of the tusk. A preference for one particular side is not unheard of in modern cetaceans, as bottlenose dolphins occasionally and gray whales consistently show
23104-402: Was touch through the presence of vibrissae, sensitive hair as seen in the modern walrus and other seals, which Muizon speculates may have been present. The later discovery of small foramina along the sheaths of the tusks may correspond with this idea. However, the presence of fully formed vibrissae is not confirmed and would be a unique adaptation among toothed whales, as tactile hair are typically
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