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|Orca vs Dunkleosteus|
|Topic Started: Jan 21 2012, 12:31 AM (38 Views)|
|LeopJag||Jan 21 2012, 12:31 AM Post #1|
Orca (Killer Whale) - Orcinus orca
The killer whale (Orcinus orca), commonly referred to as the orca whale or orca, and less commonly as the blackfish, is a toothed whale belonging to the oceanic dolphin family. Killer whales are found in all oceans, from the frigid Arctic and Antarctic regions to tropical seas. Killer whales as a species have a diverse diet, although individual populations often specialize in particular types of prey. Some feed exclusively on fish, while others hunt marine mammals such as sea lions, seals, walruses and even large whales. Killer whales are regarded as apex predators, lacking natural predators. Killer whales are highly social; some populations are composed of matrilineal family groups which are the most stable of any animal species. Their sophisticated hunting techniques and vocal behaviors, which are often specific to a particular group and passed across generations, have been described as manifestations of culture. Orcinus orca is the only recognized extant species in the genus Orcinus, one of many animal species originally described by Linnaeus in 1758 in Systema Naturae. Konrad Gessner wrote the first scientific description of a killer whale in his "Fish book" of 1558, based on examination of a dead stranded animal in the Bay of Greifswald that had attracted a great deal of local interest. The killer whale is one of 35 species in the oceanic dolphin family, which first appeared about 11 million years ago. The killer whale lineage probably branched off shortly thereafter. Although it has morphological similarities with the pygmy killer whale, the false killer whale and the pilot whales, a study of cytochrome b gene sequences by Richard LeDuc indicated that its closest extant relatives are the snubfin dolphins of the genus Orcaella. Killer whales distinctively bear a black back, white chest and sides, and a white patch above and behind the eye. Calves are born with a yellowish or orange tint, which fades to white. Killer whales have a heavy and robust body with a large dorsal fin up to 2 metres (6.6 ft) tall. Behind the fin, they have a dark grey "saddle patch" across the back. Antarctic killer whales may have pale grey to nearly white backs. Adult killer whales are very distinctive and are not usually confused with any other sea creature. When seen from a distance, juveniles can be confused with other cetacean species such as the false killer whale or Risso's dolphin. The killer whale's teeth are very strong and covered in enamel. Its jaws are a powerful gripping apparatus, as the upper teeth fall into the gaps between the lower teeth when the mouth is closed. The front teeth are inclined slightly forward and outward, thus allowing the killer whale to withstand powerful jerking movements from its prey while the middle and back teeth hold it firmly in place. Killer whales are the largest extant members of the dolphin family. Males typically range from 6 to 8 metres (20–26 ft) long and weigh in excess of 6 tonnes (5.9 long tons; 6.6 short tons). Females are smaller, generally ranging from 5 to 7 metres (16–23 ft) and weighing about 3 to 4 tonnes (3.0 to 3.9 long tons; 3.3 to 4.4 short tons). The largest male killer whale on record was 9.8 metres (32 ft), weighing over 10 tonnes (9.8 long tons; 11 short tons), while the largest female was 8.5 metres (28 ft), weighing 7.5 tonnes (7.4 long tons; 8.3 short tons). Calves at birth weigh about 180 kilograms (400 lb) and are about 2.4 metres (7.9 ft) long. The killer whale's large size and strength make it among the fastest marine mammals, able to reach speeds in excess of 30 knots (56 km/h). The skeleton of the killer whale is of the typical delphinid structure but is more robust in all respects. The killer whale's integument, unlike that of most other dolphin species, is characterised by a well-developed dermal layer with a dense network of fascicles of collagen fibers.
Dunkleosteus - Dunkleosteus terrelli
Dunkleosteus (From "(David) Dunkle" + osteus (ïóôåïò, Greek: bone)) is a genus of prehistoric fish, one of the largest arthrodire placoderms ever to have lived, existing during the Late Devonian period, about 380-360 million years ago. This hunter, measuring up to 10 metres (33 ft) and weighing 3.6 tonnes (4.0 short tons), was a hypercarnivorous apex predator. Few other placoderms, save, perhaps, its contemporary, Titanichthys, rivaled Dunkleosteus in size. Dunkleosteus is a member of the pachyosteomorph arthrodires, and is more specifically usually placed in the family Dinichthyidae, a family composed mostly of large, carnivorous arthrodires like Gorgonichthys. Placodermi first appeared in the Silurian, and the group became extinct during the transition from the Devonian to the Carboniferous, leaving no descendants. The class lasted barely 50 million years, in comparison to the 400 million year long history of sharks. Due to its heavily armoured nature, Dunkleosteus was likely a relatively slow, but powerful, swimmer. It is thought to have dwelled in diverse zones of inshore waters. Fossilization tends to have preserved only the especially armoured frontal sections of specimens, and thus it is uncertain what exactly the hind sections of this ancient fish were like. As such, the reconstructions of the hindquarters are often based on smaller arthrodires, such as Coccosteus, that had hind sections preserved. Instead of teeth, Dunkleosteus possessed two pairs of sharp bony plates which formed a beak-like structure. Morphological studies done on the "jaw bones" (inferognathals) of juvenile and adult Dunkleosteus suggest that Dunkleosteus went through a change in jaw morphology and diet as it aged. Juveniles had stiffer jaws more similar to Coccosteus, and appear to have fed on various soft-bodied aquatic animals. The jaws of adults were more flexible to hold struggling prey, and were well equipped to bite through the bony armor of hard-bodied animals like other placoderms.
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