Trends during teleostean phylogeny page192-197in our book —— 王波

Trends in five areas can be readily linked to functional improvements that contributed to teleostean success reduction in bony elements repositioning and elaboration of the dorsal fin change in placement and function of paired fins structural modifications to and interaction between the caudal fin and gas bladder jaw improvements

Reduction in bony elements This reduction occurred through fusion or actual loss of bones. For example, higher teleosts have the following features. There are few，more ossified vertebrae ——allow for attachment of stronger trunk musculature, thus enhancing locomotion. tuna catfish

2 .There are fewer intermuscular bones肌间骨 3. There are fewer bones in the skull

4.There is a reoganization and reduction in the number of bones of the tail,including fusion of the supporting bones and a reduction of the number of fin rays in the tail (most lower teleosts have 18 or 19 principal fin rays,never more than 17 in perciforms). 5 .There is a reduction of the number of biting bones in the upper jaw from two to one.

6. There is a reduction in the number of fin rays in paired fins 7 6 .There is a reduction in the number of fin rays in paired fins 7. There is a reduction in the amount of bone in the scales most lower teleosts  most paracanthopterygian 副鳍类 Most acanthopterygians 棘鳍类 six or more soft pelvic rays six or fewer  one spine with five or fewer rays

Repositioning and elaboration of the dorsal fin The dorsal fin in primintive In higher teleosts a simple, spineless fixed single midbody，keel that prevents rolling serves as a pivot point for fish that typically swim in open water situations dorsal fin become elongate and diversifed manifested as two fins, the anteriorp ortion spinous and the posterior portion soft-rayed. diversity

More functions of dorsal fin Stability is still provided when the fin is erect Provide protection from predators  Fold the spinous dorsal against the body enhances streamlining Serves as a social signal in many fishes(Rapid raising and lowering of the do rsal ) function as a rudder Serves in locomotion Serve as lures …………………………

Change in placement and function of paired fins In basal teleosts During teleostean phylogeny pectoral fins are located in the thoracic position below the edge of the gill cover pelvic fins occur at mid- body in an abdominal location pectoral fins move up onto the sides of the body and their base ass umes a vertical orientation; pelvic fins move into thoracic or even jugular (throat) position.  both fins  help stabilize movement up and down or from side to side , as well as providing some braking force  Pectorals on the side can be sculled for fine movement and positioning such as slow swimming, and hovering and backing in midwater.  Placement of the pelvics forward   helps in braking and reduces pitching; their location under the spinous dorsal, in combination with spinous armament,increases the effective body depth of a fish at the point at which it is most likely to be attacked by a predator

Structural modifications to and interaction between the caudal fin and gas bladder Primitive teleosteans have a physostomous gas bladder, in which a pneumatic duct connects the gas  bladder with the gut and ultimately the mouth.  More advanced teleosts have lost the pneumatic duct and the link to atmospheric air.They stead rely more on internally generated and aborbed  gases to fill and empty the gas bladder and  are capable of buoyancy.  Tail fins become externally and functionally homocercal fairly early in the group’s history.     By focusing muscle contraction on the t ail and its supporting structures,  advanced teleosts could swim faster and more efficiently than  more primitive teleosts.

Jaw improvements(Wikipedia） Teleosts have a movable premaxilla and corresponding modifications in the jaw musculature which make it possible for them to protrude their jaws outwards from the mouth.which enabling them to grab prey and draw it into the mouth. the enlarged premaxilla is the main tooth-bearing bone, and the maxilla, which is attached to the lower jaw, acts as a lever, pushing and pulling the premaxilla as the mouth is opened and closed. Other bones further back in the mouth serve to grind and swallow food. 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. The pharyngeal jaws of teleosts, a second set of jaws contained within the throat In the more basal teleosts the pharyngeal jaws consist of well-separated thin parts that attach to the neurocranium神经颅, pectoral girdle, and hyoid bar. Their function is limited to merely transporting food, and they rely mostly on lower pharyngeal jaw activity. In more derived teleosts the jaws are more powerful, with left and right ceratobranchials fusing to become one lower jaw; the pharyngobranchials fuse to create a large upper jaw that articulates with the neurocranium. They have also developed a muscle that allows the pharyngeal jaws to have a role in grinding food in addition to transporting it.

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